In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire （0001） substrate with double A1N buffer layers. The buffer layer consists of a low-temperature （LT）...In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire （0001） substrate with double A1N buffer layers. The buffer layer consists of a low-temperature （LT） A1N layer and a high-temperature （HT） A1N layer that are grown at 600 ℃ and 1000 ℃, respectively. It is observed that the thickness of the LT-A1N layer drastically influences the quality of GaN thin film, and that the optimized 4.25-min-LT-A1N layer minimizes the dislocation density of GaN thin film. The reason for the improved properties is discussed in this paper.展开更多
The anisotropic strain of a nonpolar （1120） a-plane GaN epilayer on an r-plane （1102） sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-tempe...The anisotropic strain of a nonpolar （1120） a-plane GaN epilayer on an r-plane （1102） sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.展开更多
Laterally enlarged single crystal diamond is grown on （001） diamond substrates by microwave plasma chemical vapor deposition. Based on the largest side-to-side width of the seed of 7.5 mm, we achieve the as-grown ep...Laterally enlarged single crystal diamond is grown on （001） diamond substrates by microwave plasma chemical vapor deposition. Based on the largest side-to-side width of the seed of 7.5 mm, we achieve the as-grown epilayer with the width of about 10mm between the same two sides. The luminescence difference between the broadened part of the single crystal diamond and the vertically epitaxial part is investigated by characterizing the vertical cross section of the sample, and the possible growth mechanism is suggested. Vertical epitaxy on the top （001） surface and lateral growth on the side surfaces occur simultaneously, and thus the growth fronts along the two directions adjoin and form a coalescence zone extending from the edge of the substrate towards the edge of the expanded single crystal diamond top surface. The luminescence intensity of the nitrogen-vacancy center is relatively high in the coalescence zone and a laterally grown part right below, which are attributed mainly to the higher growth rate. However, stress change and crystal quality change are negligible near the coalescence zone.展开更多
Epitaxial growth of InA1GaN/GaN structures are performed on the c-plane sapphire by pulsed metal organic chemical vapor deposition with different triethylgallium （TEGa） flows in the growth process of InA1GaN qua- te...Epitaxial growth of InA1GaN/GaN structures are performed on the c-plane sapphire by pulsed metal organic chemical vapor deposition with different triethylgallium （TEGa） flows in the growth process of InA1GaN qua- ternary alloys. X-ray photoelectron spectroscopy results show that the A1/In ratio of the samples increases as the TEGa flows increase in the InAIGaN quaternary growth process. High-resolution x-ray diffraction results show that the crystal quality is improved with increasing TEGa flows. Morphology of the InA1GaN/GaN het- erostructures is characterized by an atomic force microscopy, and the growth mode of the InA1GaN quaternary shows a 21） island growth mode. The minimum surface roughness is 0.2Ohm with the TEGa flows equaling to 3.6 μool/rain in rms. Hall effect measurement results show that the highest electron mobilityμ is 1005.49 cm2/Vs and the maximal two-dimensional electron gas is 1.63 × 1013 em-2.展开更多
CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are dete...CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostruetures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlCaN quaternary layer is nearly lattice-matched to the CaN channel. Capacitance-voltage results show that there is no parasitic channel formed between the InAIGaN layer and the AlCaN layer. Compared with the InAl- CaN/CaN heterostructure, the electrical properties of the InAlCaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V.s, 1.44 × 10^13 cm-2 and as low as 201.1 Ω/sq, respectively.展开更多
We investigate the phonon limited electron mobility in germanium(Ge) fin field-effect transistors(FinFETs)with fin rotating within(001),(110),and(111)-oriented wafers. The coupled Schrodinger-Poisson equations are sol...We investigate the phonon limited electron mobility in germanium(Ge) fin field-effect transistors(FinFETs)with fin rotating within(001),(110),and(111)-oriented wafers. The coupled Schrodinger-Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas, and Fermi's golden rule is used to calculate the phonon scattering rate. It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge FinFETs. The phonon limited electron motilities are influenced by wafer orientation, channel direction, in thickness Wfin, and inversion charge density Ninv. With the fixed Wfin, fin directions of(110),(112) and(110) within(001),(110), and(111)-oriented wafers provide the maximum values of electron mobility. The optimized for mobility is also dependent on wafer orientation and channel direction. As Ninv, increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as Ninv increases.展开更多
Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostruct...Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.展开更多
The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-r...The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.展开更多
C-implantation N-polar CaN films are grown on c-plane sapphire substrates by metal organic chemical vapor deposition. C-implantation induces a large number of defects and causes disorder of the lattice structure in th...C-implantation N-polar CaN films are grown on c-plane sapphire substrates by metal organic chemical vapor deposition. C-implantation induces a large number of defects and causes disorder of the lattice structure in the N-polar GaN film. Raman measurements performed on the N-polar GaN film before C-implantation after C-implantation and subsequent annealing at 1050℃ for 5 rain indicate that after annealing the disordered GaN lattice is almost recovered. High resolution x-ray diffraction shows that after implantation there is an obvious increase of screw-dislocation densities, and the densities of edge dislocation show slight change. Carbon implantation can induce deep acceptors in GaN, thus the background carriers induced by the high oxygen incorporation in the N-polar GaN film will be partially compensated for, resulting in 25 times the resistivity, which is demonstrated by the temperature-dependent Hall-effect measurement.展开更多
A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor（GTCE-HEMT）with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshol...A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor（GTCE-HEMT）with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 m S/mm, and subthreshold slope of 85 m V/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage（VB） is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode（D-mode） polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits.展开更多
We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope...We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.展开更多
In this paper, the effect of alumina thickness on Al2O3/InP interface with post deposition annealing （PDA） in the oxygen ambient is studied. Atomic layer deposited （ALD） Al2O3 films with four different thickness v...In this paper, the effect of alumina thickness on Al2O3/InP interface with post deposition annealing （PDA） in the oxygen ambient is studied. Atomic layer deposited （ALD） Al2O3 films with four different thickness values （5 nm, 7 nm, 9 nm, 11 rim） are deposited on InP substrates. The capacitance-voltage （C-V） measurement shows a negative correlation between the alumina thickness and the frequency dispersion. The X-ray photoelectronspectroscopy （XPS） data present significant growth of indium-phosphorus oxide near the Al2O3/InP interface, which indicates serious oxidation of InP during the oxygen annealing. The hysteresis curve shows an optimum thickness of 7 nm after PDA in an oxygen ambient at 500 ℃ for 10 min. It is demonstrated that both sides of the interface are impacted by oxygen during post deposition annealing. It is suggested that the final state of the interface is of reduced positively charged defects on Al2O3 side and oxidized InP, which degrades the interface.展开更多
We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask. Transmission electron microscopy, scanning electron microscopy...We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask. Transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy are used to reveal the effect of SiN on the overgrown a-plane GaN growth. The SiN layer effectively terminates the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN regrowth through the interlayer, resulting in the window region shrinking from a rectangle to a ＂black hole＂. Furthermore, strong yellow luminescence （YL） in the nonpolar plane and very weak YL in the semipolar plane on the GaN grain is revealed by cathodoluminescence, suggesting that C-involved defects are responsible for the YL.展开更多
A GaN-based high electron mobility transistor(HEMT)with p-GaN islands buried layer(PIBL)for terahertz applications is proposed.The introduction of a p-GaN island redistributes the electric field in the gate–drain cha...A GaN-based high electron mobility transistor(HEMT)with p-GaN islands buried layer(PIBL)for terahertz applications is proposed.The introduction of a p-GaN island redistributes the electric field in the gate–drain channel region,thereby promoting the formation of electronic domains in the two-dimensional electron gas(2DEG)channel.The formation and regulation mechanism of the electronic domains in the device are investigated using Silvaco-TCAD software.Simulation results show that the 0.2µm gate HEMT with a PIBL structure having a p-GaN island doping concentration(Np)of 2.5×10^(18)cm^(−3)–3×10^(18)cm^(−3)can generate stable oscillations up to 344 GHz–400 GHz under the gate–source voltage(V_(gs))of 0.6 V.As the distance(D_(p))between the p-GaN island and the heterojunction interface increases from 5 nm to 15 nm,the fundamental frequency decreases from 377 GHz to 344 GHz,as well as the ratio of oscillation current amplitude of the fundamental component to the average component I_(f1)/I_(avg) ranging from 2.4%to 3.84%.展开更多
First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range bet...First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes （Al （LO） and E2 （high）） are obtained. We focus our attention on the temperature dependence of E2 （high） mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.展开更多
The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in Al...The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.展开更多
The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate...The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate-source voltage on the contact length （source and drain electrodes＇ length） related contact resistance of bottom-contact OTFTs are performed with a modified transmission line model. It is found that the contact resistance increases dramatically when the contact length is scaled down to 20O nm. With the help of the contact length related contact resistance, contact-size-dependent fT Of bottom-contact OTFTs is studied and it is found that fr increases with the decrease of the contact length in bottom-contact OTFTs.展开更多
High indium semipolar（1122） and polar（0001） In Ga N layers each with a thickness of about 100 nm are realized simultaneously on sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The m...High indium semipolar（1122） and polar（0001） In Ga N layers each with a thickness of about 100 nm are realized simultaneously on sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The morphology evolution, structural and optical characteristics are also studied. The indium content in the layer of the surface（1122）is larger than that of the surface（0001）, which is confirmed by reciprocal space map, photoluminescence spectrum and secondary ion mass spectrometer. Additionally, the（0001） surface with island-like morphology shows inhomogeneous indium incorporation, while the（1122） surface with a spiral-like morphology shows a better homogeneous In composition.This feature is also demonstrated by the monochromatic cathodoluminescence map.展开更多
TiO2deposited at extremely low temperature of 120°C by atomic layer deposition is inserted between metal and n-Ge to relieve the Fermi level pinning. X-ray photoelectron spectroscopy and cross-sectional transmiss...TiO2deposited at extremely low temperature of 120°C by atomic layer deposition is inserted between metal and n-Ge to relieve the Fermi level pinning. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy indicate that the lower deposition temperature tends to effectively eliminate the formation of GeOxto reduce the tunneling resistance. Compared with TiO2deposited at higher temperature of 250°C,there are more oxygen vacancies in lower-temperature-deposited TiO2, which will dope TiO2contributing to the lower tunneling resistance. Al/TiO2/n-Ge metal-insulator-semiconductor diodes with 2 nm 120°C deposited TiO2achieves 2496 times of current density at-0.1 V compared with the device without the TiO2interface layer case, and is 8.85 times larger than that with 250°C deposited TiO2. Thus inserting extremely low temperature deposited TiO2to depin the Fermi level for n-Ge may be a better choice.展开更多
A new small-signal model for anisomerous AlGaN/GaN high electron mobility transistors（HEMTs） is proposed for accurate prediction of HEMT behavior up to 20 GHz.The parasitic elements are extracted from both cold-FET ...A new small-signal model for anisomerous AlGaN/GaN high electron mobility transistors（HEMTs） is proposed for accurate prediction of HEMT behavior up to 20 GHz.The parasitic elements are extracted from both cold-FET and pinch-off bias to obtain more precise results and the intrinsic part is directly extracted.All the parameters needed in this process are determined by the device structure rather than optimization methods.This guarantees consistency between the parameter values and the component＇s physical meaning.展开更多
基金Project supported by the National Key Science & Technology Special Project,China(Grant No.2008ZX01002-002)the Fundamental Research Funds for the Central Universities,China(Grant No.JY10000904009)the Major Program and State Key Program of the National Natural Science Foundation of China(Grant Nos.60890191 and 60736033)
文摘In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire （0001） substrate with double A1N buffer layers. The buffer layer consists of a low-temperature （LT） A1N layer and a high-temperature （HT） A1N layer that are grown at 600 ℃ and 1000 ℃, respectively. It is observed that the thickness of the LT-A1N layer drastically influences the quality of GaN thin film, and that the optimized 4.25-min-LT-A1N layer minimizes the dislocation density of GaN thin film. The reason for the improved properties is discussed in this paper.
基金supported by the National Key Science and Technology Special Project, China (Grant No. 2008ZX01002-002)the Major Program and State Key Program of National Natural Science Foundation of China (Grant Nos. 60890191 and 60736033)the Fundamental Research Funds for the Central Universities, China (Grant No. JY10000904009)
文摘The anisotropic strain of a nonpolar （1120） a-plane GaN epilayer on an r-plane （1102） sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.
文摘Laterally enlarged single crystal diamond is grown on （001） diamond substrates by microwave plasma chemical vapor deposition. Based on the largest side-to-side width of the seed of 7.5 mm, we achieve the as-grown epilayer with the width of about 10mm between the same two sides. The luminescence difference between the broadened part of the single crystal diamond and the vertically epitaxial part is investigated by characterizing the vertical cross section of the sample, and the possible growth mechanism is suggested. Vertical epitaxy on the top （001） surface and lateral growth on the side surfaces occur simultaneously, and thus the growth fronts along the two directions adjoin and form a coalescence zone extending from the edge of the substrate towards the edge of the expanded single crystal diamond top surface. The luminescence intensity of the nitrogen-vacancy center is relatively high in the coalescence zone and a laterally grown part right below, which are attributed mainly to the higher growth rate. However, stress change and crystal quality change are negligible near the coalescence zone.
基金Supported by the National Science and Technology Major Project of China under Grant No 2013ZX02308-002the National Natural Science Foundation of China under Grant Nos 11435010,61474086 and 61334002
文摘Epitaxial growth of InA1GaN/GaN structures are performed on the c-plane sapphire by pulsed metal organic chemical vapor deposition with different triethylgallium （TEGa） flows in the growth process of InA1GaN qua- ternary alloys. X-ray photoelectron spectroscopy results show that the A1/In ratio of the samples increases as the TEGa flows increase in the InAIGaN quaternary growth process. High-resolution x-ray diffraction results show that the crystal quality is improved with increasing TEGa flows. Morphology of the InA1GaN/GaN het- erostructures is characterized by an atomic force microscopy, and the growth mode of the InA1GaN quaternary shows a 21） island growth mode. The minimum surface roughness is 0.2Ohm with the TEGa flows equaling to 3.6 μool/rain in rms. Hall effect measurement results show that the highest electron mobilityμ is 1005.49 cm2/Vs and the maximal two-dimensional electron gas is 1.63 × 1013 em-2.
基金Supported by the National Science and Technology Major Project under Grant No 2013ZX02308-002the National Natural Science Foundation of China under Grant Nos 11435010,61474086 and 61334002
文摘CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostruetures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlCaN quaternary layer is nearly lattice-matched to the CaN channel. Capacitance-voltage results show that there is no parasitic channel formed between the InAIGaN layer and the AlCaN layer. Compared with the InAl- CaN/CaN heterostructure, the electrical properties of the InAlCaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V.s, 1.44 × 10^13 cm-2 and as low as 201.1 Ω/sq, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61534004,61604112 and 61622405
文摘We investigate the phonon limited electron mobility in germanium(Ge) fin field-effect transistors(FinFETs)with fin rotating within(001),(110),and(111)-oriented wafers. The coupled Schrodinger-Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas, and Fermi's golden rule is used to calculate the phonon scattering rate. It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge FinFETs. The phonon limited electron motilities are influenced by wafer orientation, channel direction, in thickness Wfin, and inversion charge density Ninv. With the fixed Wfin, fin directions of(110),(112) and(110) within(001),(110), and(111)-oriented wafers provide the maximum values of electron mobility. The optimized for mobility is also dependent on wafer orientation and channel direction. As Ninv, increases, phonon limited mobility degrades, which is attributed to electron repopulation from a higher mobility valley to a lower mobility valley as Ninv increases.
基金Supported by the National Science and Technology Major Project of China under Grant No 2013ZX02308-002the National Natural Sciences Foundation of China under Grant Nos 61574108,61334002,61474086 and 61306017
文摘Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204006 and 61574108the Fundamental Research Funds for the Central Universities under Grant No JB141101the Foundation of Key Laboratory of Nanodevices and Applications of Suzhou Institute of Nano-Tech and Nano-Bionics of Chinese Academy of Sciences under Grant No 15CS01
文摘The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204006,61574108,61334002,61474086 and 51302306
文摘C-implantation N-polar CaN films are grown on c-plane sapphire substrates by metal organic chemical vapor deposition. C-implantation induces a large number of defects and causes disorder of the lattice structure in the N-polar GaN film. Raman measurements performed on the N-polar GaN film before C-implantation after C-implantation and subsequent annealing at 1050℃ for 5 rain indicate that after annealing the disordered GaN lattice is almost recovered. High resolution x-ray diffraction shows that after implantation there is an obvious increase of screw-dislocation densities, and the densities of edge dislocation show slight change. Carbon implantation can induce deep acceptors in GaN, thus the background carriers induced by the high oxygen incorporation in the N-polar GaN film will be partially compensated for, resulting in 25 times the resistivity, which is demonstrated by the temperature-dependent Hall-effect measurement.
基金supported by the National Science and Technology Major Project,China(Grant No.2013ZX02308-002)the National Natural Science Foundation of China(Grant Nos.11435010,61474086,and 61404099)
文摘A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor（GTCE-HEMT）with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 m S/mm, and subthreshold slope of 85 m V/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage（VB） is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode（D-mode） polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFB0406504 and 2016YFB0400105)the National Postdoctoral Program for Innovative Talents,China(Grant No.BX20190263)
文摘We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.
基金supported by the National Natural Science Foundation of China(Grant No.61204006)the Fundamental Research Funds for the Central Universities,China(Grant No.K50511250002)the National Key Science and Technology Special Project,China(Grant No.2008ZX01002-002)
文摘In this paper, the effect of alumina thickness on Al2O3/InP interface with post deposition annealing （PDA） in the oxygen ambient is studied. Atomic layer deposited （ALD） Al2O3 films with four different thickness values （5 nm, 7 nm, 9 nm, 11 rim） are deposited on InP substrates. The capacitance-voltage （C-V） measurement shows a negative correlation between the alumina thickness and the frequency dispersion. The X-ray photoelectronspectroscopy （XPS） data present significant growth of indium-phosphorus oxide near the Al2O3/InP interface, which indicates serious oxidation of InP during the oxygen annealing. The hysteresis curve shows an optimum thickness of 7 nm after PDA in an oxygen ambient at 500 ℃ for 10 min. It is demonstrated that both sides of the interface are impacted by oxygen during post deposition annealing. It is suggested that the final state of the interface is of reduced positively charged defects on Al2O3 side and oxidized InP, which degrades the interface.
基金Project supported by the Fundamental Research Funds for the Central Universities,China (Grant No. K50511250002)the National Key Science and Technology Special Project,China (Grant No. 2008ZX01002-002)the National Natural Science Foundation of China (Grant Nos. 60736033,60976068,and 61076097)
文摘We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask. Transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy are used to reveal the effect of SiN on the overgrown a-plane GaN growth. The SiN layer effectively terminates the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN regrowth through the interlayer, resulting in the window region shrinking from a rectangle to a ＂black hole＂. Furthermore, strong yellow luminescence （YL） in the nonpolar plane and very weak YL in the semipolar plane on the GaN grain is revealed by cathodoluminescence, suggesting that C-involved defects are responsible for the YL.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61974108 and 61674117)the National Natural Science Foundation for Young Scholars of China(Grants No.61804119)the Postdoctoral Science Foundation of China(Grants No.2018M643576)。
文摘A GaN-based high electron mobility transistor(HEMT)with p-GaN islands buried layer(PIBL)for terahertz applications is proposed.The introduction of a p-GaN island redistributes the electric field in the gate–drain channel region,thereby promoting the formation of electronic domains in the two-dimensional electron gas(2DEG)channel.The formation and regulation mechanism of the electronic domains in the device are investigated using Silvaco-TCAD software.Simulation results show that the 0.2µm gate HEMT with a PIBL structure having a p-GaN island doping concentration(Np)of 2.5×10^(18)cm^(−3)–3×10^(18)cm^(−3)can generate stable oscillations up to 344 GHz–400 GHz under the gate–source voltage(V_(gs))of 0.6 V.As the distance(D_(p))between the p-GaN island and the heterojunction interface increases from 5 nm to 15 nm,the fundamental frequency decreases from 377 GHz to 344 GHz,as well as the ratio of oscillation current amplitude of the fundamental component to the average component I_(f1)/I_(avg) ranging from 2.4%to 3.84%.
基金supported by the National Key Science & Technology Special Project (Grant No.2008ZX01002-002)the Fundamental Research Funds for the Central Universities (Grant No.JY10000904009)the Major Program and State Key Program of National Natural Science Foundation of China (Grant Nos.60890191 and 60736033)
文摘First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes （Al （LO） and E2 （high）） are obtained. We focus our attention on the temperature dependence of E2 （high） mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.
基金the National Key Research and Development Program of China(Grant No.2018YFB1802100)the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2020JM-191 and 2018HJCG-20)+2 种基金the National Natural Science Foundation of China(Grant Nos.61904135,61704124,and 61534007)the China Postdoctoral Science Foundation(Grant Nos.2018M640957 and 2019M663930XB)the Wuhu and Xidian University Special Fund for Industry-University-Research Cooperation,China(Grant No.XWYCXY-012019007).
文摘The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.
基金Supported by the State Key Fundamental Research Project of China under Grant No 2011CBA00606the National Natural Science Foundation of China under Grant Nos 51503167 and 61574107
文摘The contact-size-dependent characteristic of cutoff frequency fT in bottom-contact organic thin film transistors （OTFTs） is studied. The effects of electrode thickness, field-effect mobility, channel length and gate-source voltage on the contact length （source and drain electrodes＇ length） related contact resistance of bottom-contact OTFTs are performed with a modified transmission line model. It is found that the contact resistance increases dramatically when the contact length is scaled down to 20O nm. With the help of the contact length related contact resistance, contact-size-dependent fT Of bottom-contact OTFTs is studied and it is found that fr increases with the decrease of the contact length in bottom-contact OTFTs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61204006 and 61574108)the Fundamental Research Funds for the Central Universities,China(Grant No.7214570101)
文摘High indium semipolar（1122） and polar（0001） In Ga N layers each with a thickness of about 100 nm are realized simultaneously on sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The morphology evolution, structural and optical characteristics are also studied. The indium content in the layer of the surface（1122）is larger than that of the surface（0001）, which is confirmed by reciprocal space map, photoluminescence spectrum and secondary ion mass spectrometer. Additionally, the（0001） surface with island-like morphology shows inhomogeneous indium incorporation, while the（1122） surface with a spiral-like morphology shows a better homogeneous In composition.This feature is also demonstrated by the monochromatic cathodoluminescence map.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61534004,61604112 and 61622405
文摘TiO2deposited at extremely low temperature of 120°C by atomic layer deposition is inserted between metal and n-Ge to relieve the Fermi level pinning. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy indicate that the lower deposition temperature tends to effectively eliminate the formation of GeOxto reduce the tunneling resistance. Compared with TiO2deposited at higher temperature of 250°C,there are more oxygen vacancies in lower-temperature-deposited TiO2, which will dope TiO2contributing to the lower tunneling resistance. Al/TiO2/n-Ge metal-insulator-semiconductor diodes with 2 nm 120°C deposited TiO2achieves 2496 times of current density at-0.1 V compared with the device without the TiO2interface layer case, and is 8.85 times larger than that with 250°C deposited TiO2. Thus inserting extremely low temperature deposited TiO2to depin the Fermi level for n-Ge may be a better choice.
文摘A new small-signal model for anisomerous AlGaN/GaN high electron mobility transistors（HEMTs） is proposed for accurate prediction of HEMT behavior up to 20 GHz.The parasitic elements are extracted from both cold-FET and pinch-off bias to obtain more precise results and the intrinsic part is directly extracted.All the parameters needed in this process are determined by the device structure rather than optimization methods.This guarantees consistency between the parameter values and the component＇s physical meaning.
