Molecular beam epitaxy of gallium nitride on silicon carbide
Abstract
We have studied the molecular beam epitaxy (MBE) growth of GaN on 6HSiC(0001). In order to achieve high quality growth, we have prepared atomically-flat polish-damage-free 6H-SiC(0001) substrate surfaces using ex situ hydrogen etching. Our studies on the etching process throw more light on the etching mechanism. In ultra high vacuum, we have further processed the substrates using a Si pre-deposition followed by an anneal in order to remove the native oxide layer. The substrate thus prepared shows a 3x3 -R30° reconstruction. We have studied the electronic structure of this surface for both p- and n-type material using scanning tunneling spectroscopy (STS) and microscopy (STM). Our results support a silicon adatom model which predicts a Mott-Hubbard type density of surface states. The heteroepitaxial growth of GaN on 6H-SiC(0001) 3x3 has been studied at a number of substrate temperatures and the films are characterized at both low an high thickness. The films are found to be of high quality and to exhibit different temperature-dependent morphologies. Below the critical thickness, low temperature growth is two-dimensional; at high temperatures the growth is in the form of 3-D columnar islands. The width of X-ray diffraction peaks from the films is seen to decrease with increasing substrate temperature. We have also investigated the surfactant effect of magnesium in GaN MBE. Mg incorporation in small quantities during growth in the nitrogen rich regime, where MBE growth is known to be rough, improves growth. Exposure to larger amounts of Mg is seen to lead to crystal inversion of the Ga-polar GaN crystal, simultaneously introducing a large defect density.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- October 1999
- Bibcode:
- 1999PhDT.......156R