AlGaN/AlN/GaN high electron mobility transistor （HEMT） structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas （2DEG） mobility of 1944cm^2/（V·s） at room temperature and 11588cm^2/（V ·s） at 80K with almost equal 2DEG concentrations of about 1.03 × 10^13 cm^-2. High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0.27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.
AlGaN/GaN high electron mobility transistor (HEMT) materials are grown by RF plasma-assisted molecular beam epitaxy (RF-MBE) and HEMT devices are fabricated and characterized.The HEMT materials have a mobility of 1035cm2/(V·s) at sheet electron concentration of 1.0×10 13cm -2at room temperature.For the devices fabricated using the materials,a maximum saturation drain-current density of 925mA/mm and a peak extrinsic transconductance of 186mS/mm are obtained on devices with gate length and width of 1μm and 80μm respectively.The f t,unit-current-gain frequency of the devices,is about 18.8GHz.
Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask. Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers. The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process. Cl2/Ar and Cl2/He were employed as etching gas. Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions. Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.
A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer. A sample without interlayer was also grown at the same time for comparison. Significant reductions of dislocation density in W-GaN film is confirmed by the result of high-resolution X-ray diffraction and transmission electron microscope (TEM) observation. The improvement of optical properties of the W-GaN is confirmed by photoluminescence (PL) result. A shift of PL peak suggests that the strain is lower in the W-GaN than the film without W interlayer. This technique offers a potential path to obtain high-quality GaN film as free-standing substrate.
Magnetotransport properties of two-dimensional electron gases （2DEG） in AlxGa1-x N/GaN heterostructures with different Al compositions are investigated by magnetotransport measurements at low temperatures and in high magnetic fields. It is found that heterostructures with a lower Al composition in the barrier have lower 2DEG concentration and higher 2DEG mobility.
