Investigation of buffer structures for the growth of a high quality AlGaN/GaN hetero-structure with a high power operation FET on Si substrate using MOCVD

摘要

In order to obtain a high quality thick GaN layer on a 2-inch Si substrate without any crack, we investigated three kinds of buffer layer (AlGaN graded structure, AlN/GaN super lattice (SL) structure, and AlN/thick GaN/AlN structure) using a metal-organic chemical vapor deposition (MOCVD). As a result, we obtained a crack-free AlGaN/GaN hetero-structure with a smooth surface using three kinds of buffer structure. We also observed the cross-sectional TEM image of three kinds of buffer structures. In the case of using an AlGaN graded buffer on the AlN buffer, the number of surface defect with the size of 10000 nm was comparatively larger compared with the other buffer structures. In the case of using an AlN (18 nm)/ GaN (5 nm) super-lattice (SL) buffer, a 1000 nm-thick GaN was grown without crack. In the case of using three AlN (50 nm)/two thick GaN (200 nm) buffer structure, the threading dislocation using this buffer was 1.5 x 10~9 cm~(-2) and the value was smaller compared with the other buffer structures. This reduction effect of dislocation was larger than the other buffer structures. We also fabricated a HFET using the AlGaN/GaN heterostructure using three AlN/two thick GaN buffer. It was confirmed that the breakdown voltage of FET was over 400 V.