中文摘要：

采用一个AlN缓冲层和两个Al组分阶变的A1GaN过渡层作为中间层，在76．2mmSi衬底上外延生长出1．7μm厚无裂纹AlGaN／GaN异质结材料，利用原子力显微镜、X射线衍射、Hall效应测量和CV测量等手段对材料的结构特性和电学性能进行了表征。材料表面平整光滑，晶体质量和电学性能良好，2DEG面密度为1．12×10^13cm^-2，迁移率为1208cmz／（v·s）。由该材料研制的栅长为1bcm的AlGaN／GaNHEMT器件，电流增益截止频率fT达到10．4GHz，这些结果表明组分阶变AlGaN过渡层技术可用于实现高性能Si基GaNHEMT。

英文摘要：

A 1.7 μm thick, crack-free AlGaN/GaN heterostructure had been grown on 76.2 mm diameter Si substrate by using an AlN buffer layer and two Al-content step-graded AlGaN transition layers （TL）. The structural and electrical properties of the AlGaN/GaN heterostructure were characterized by atomic force microscopy, X-ray diffractometer, Hall and capacitancevoltage measuring instruments. The AlGaN/GaN heterostructure containing the step-graded AlGaN TL exhibited flat surface morphology and good crystalline quality. An electron mobility of 1 208 cm2/（V·s） with sheet carrier density of 1.12 × 10^13cm-2 was measured on the heterostructure. High electron mobility transistors （HEMTs） with 1 μm gate lengths were fabricated by this heterostructure. A current gain cutoff frequencies （fa-） of 10. 4 GHz was obtained on the AlGaN/ GaN HEMTs. These results show that Al-content step-graded AlGaN transition layers could be used to achieve GaN HEMTs on Si substrate with high performance.