Investigation Of Defects In GaN Grown On Silicon

In this paper, GaN with different thickness were grown on Si(111) using metalorganic chemical vapor deposition, the buffer layers were composed of high-temperature A1N (1060℃, 20nm) and low-temperature GaN (525℃, 30nm), then the epilayers were deposited at 1040℃ for 600s, 800s, 1000s, and 1200s, respectively. The surface topography of GaN was investigated by scanning electronic microscopy and atomic force microscopy, it can be seen that GaN grew as the model of Volmer-Weber, i.e., nuclear growth model. Double-crystal X ray diffraction showed that the (0001) GaN epilayers had high crystal quality, and little impurities were detected in GaN epilayer, which was conformed by Fourier-transformed infrared absorption.We carried out the transmission electronic microscopy investigation for the top layer of GaN, there were many kinds of dislocations, such as screw dislocations, edge dislocations and mixed dislocations, their density was about 10⁸cm^-2, besides that dislocation-interactions were also found in GaN epilayer that grew for 800s. Furthermore, V defects appeared on the surface of GaN with growth time of 800s, their density was the same to that of dislocations, and theirshapes were inverted hexagonal cones formed by six{1101} facets. EDS was carried out at theepilayer, a higher carbon (C) peak appeared at the zone of dislocation, and the Ga:N excessed 1:1. The same results were found in V defects, while those zones without dislocations or V defects, no C atoms were detected. We analyzed the influence of C atoms on the formation of V defects.Then dislocations were investigated by wet chemical etching. After etching in KOH solution, hexagonal etch pits appeared at the zone of dislocations, they were also formed by six{1101} facets. Some experiments were carried out to conform the effect of etch condition,especially light on etch topography. In our experiment, tungsten lamp was taken as the light souce, superior etch topography realized without making ohmic contact, and it's a greatachievement to GaN etching. Furthermore, we found etch pits with different shape appeared at the zones of lonely dislocation, vicinal dislocation and dislocation interaction, and a model has been built to interpret the phenomenon.