MOCVD Growth Of GaN Based Materials On SiC Substrates And HEMT Fabrication

GaN material is considered as one of the most ideal materials to make high temperature, high frequency, and high power microwave electronic circuits with, due to its characters of large band-gap, high saturation electron velocity, ability of enduring high voltage and radiation, and the unique polarization effect. GaN based devices, particularl the AlGaN/GaN HEMT device have wide application prospects for phased-array radar, electronic countermeasure, satellite communication, aerospace, et al. Because of its low crystal lattice mismatch and coefficients of thermal expansion mismatch between GaN epilayer and SiC substrate, SiC is the best alternative substrate for GaN hetero-epitaxy. Meanwhile, SiC substrate’s good thermal conductivity made it best suited for making AlGaN/GaN HEMT device. However, there is certain crystal lattice mismatch between GaN epilayer and SiC substrate, and SiC substrate induces high density of cracks and defects, which can easily cause sepitaxial layers cracking. Thus, more research is needed on the growth of GaN HEMT on SiC substrate.This paper focused on the main problems and difficulties in the growth of GaN film on SiC substrate. We researched into the design of the perfect buffer layer for the GaN growth on SiC, the design of insert layers, the characterization of the material, SiC based AlGaN/GaN heterostructure growth and characterization, the fabrication and measurement of AlGaN/GaN HEMT device on SiC substrate. The main achievements in this work are summarized as follows:1. Effect of AlN buffer layer on SiC based GaN epitaxial layer growth was researched. The temperature, thickness of and growth Ⅴ/Ⅲ of A1N buffer layer were optimized. The optimized A1N buffer layer was found decrease cracking of GaN layer and can improve the GaN quality.2. Influence of the AlGaN superlattice interlayer on SiC based GaN epitaxial layer growth was researched, and AlGaN growth conditions were optimized.1.8μm high quality crack-free GaN film was successfully grown on 2-inch SiC substrates with HT AIN/graded-AlGaN multibuffer and AIN/GaN superlattice interlayer. Overall mirror-like and specular surface was presented in the crack-free GaN epilayer. Smooth surface mophology with a root mean square roughness (RMS) of 0.150nm was exhibited by AFM. The full width at half maximum (FWHM) of symitric GaN(002) ω scan rocking curve peak was 192.2arcsec, and was 176.8 arcsec of symitric GaN(102) ω scan rocking curve peak.3. With the above-mentioned method, we developed entirely crack-free AlGaN/GaN heterostructre on 2-inch SiC substrate for the first time in China. The sheet carrier density was steadily about 3×1012cm-2, while the electron mobility of the two-dimension elecron gas (2DEG) was 2029cm2/V·s.4. Fabrication of the AlGaN/GaN HEMT device was carried out and the AlGaN/GaN HEMT power devives on SiC substrate was tested...