The conventional AlGaN/GaN high electron mobility transistor(HEMT),the AlGaN/GaN/AlGaN HEMT,and the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N HEMT are fabricated on sapphire substrates to study the drain-induced barrier-lowerin...The conventional AlGaN/GaN high electron mobility transistor(HEMT),the AlGaN/GaN/AlGaN HEMT,and the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N HEMT are fabricated on sapphire substrates to study the drain-induced barrier-lowering(DIBL)effect.It is found that the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N HEMT with AlGaN channel has the lowest DIBL coefficient of 6.7 mV/V compared with the other two HEMTs.This is attributed to the best two-dimensional electron gas confinement of the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N structure.This opinion is further confirmed by the conduction band diagrams and electron distribution calculated from the one-dimensional Poisson–Schrödinger equation.展开更多
The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-t...The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/(V.s) and a sheet resistance of 890Ω/口 under room temperature. The crystalline quality and the electrical properties of the A1GaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance-voltage (C-V) measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.展开更多
Nonpolar (1120) GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of th...Nonpolar (1120) GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 (high) phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 (high) peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 (high) peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.展开更多
An approach based on depth-sensitive skew-angle x-ray diffraction (SAXRD) is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that (...An approach based on depth-sensitive skew-angle x-ray diffraction (SAXRD) is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that (103) plane and (101) plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive (103)/(101) ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.展开更多
基金Supported by the National S&T Project of China under Grant Nos 2011ZX01002-002 and 2013ZX02308-002the National Natural Science Foundation of China under Grant Nos 61204006 and 61106063.
文摘The conventional AlGaN/GaN high electron mobility transistor(HEMT),the AlGaN/GaN/AlGaN HEMT,and the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N HEMT are fabricated on sapphire substrates to study the drain-induced barrier-lowering(DIBL)effect.It is found that the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N HEMT with AlGaN channel has the lowest DIBL coefficient of 6.7 mV/V compared with the other two HEMTs.This is attributed to the best two-dimensional electron gas confinement of the Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N structure.This opinion is further confirmed by the conduction band diagrams and electron distribution calculated from the one-dimensional Poisson–Schrödinger equation.
基金Project supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant Nos.2011ZX01002-002 and 2013ZX02308-002)the Fundamental Research Funds for the Central Universities of Ministry of Education of Chinathe National Natural Science Foundation of China(Grant Nos.61204006 and 61106063)
文摘The quality of an A1GaN channel heterojunction on a sapphire substrate is massively improved by using an A1- GaN/GaN composite buffer layer. We demonstrate an A10.4Gao.6N/AI0.18Ga0.82N heterojunction with a state-of-the-art mobility of 815 cm2/(V.s) and a sheet resistance of 890Ω/口 under room temperature. The crystalline quality and the electrical properties of the A1GaN heterojunction material are analyzed by atomic force microscopy, high-resolution X-ray diffraction, and van der Pauw Hall and capacitance-voltage (C-V) measurements. The results indicate that the improved electrical properties should derive from the reduced surface roughness and low dislocation density.
基金Project 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 & Technology Special Project,China(Grant No.2008ZX01002-002)
文摘Nonpolar (1120) GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 (high) phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 (high) peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 (high) peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant Nos.61306017 and 61204006)the Key Program of the National Natural Science Foundation of China(Grant No.61334002)the Fundamental Research Funds for the Central Universities of China(Grant Nos.K5051225016 and K5051325020)
文摘An approach based on depth-sensitive skew-angle x-ray diffraction (SAXRD) is presented for approximately evalu- ating the depth-dependent mosaic tilt and twist in wurtzite c-plane GaN epilayers. It is found that (103) plane and (101) plane, among the lattice planes not perpendicular to the sample surface, are the best choices to measure the depth profiles of tilt and twist for a GaN epilayer with a thickness of less than 2 μm according to the diffraction geometry of SAXRD. As an illustration, the depth-sensitive (103)/(101) ω-scans of a 1.4-μm GaN film grown by metal-organic chemical vapor deposition on sapphire substrate are measured and analyzed to show the feasibility of this approach.