Effects of Carrier Gas and Substrate on the Electrical Properties of Epitaxial GaAs Grown by the Single Flat Temperature Zone Chloride VPE Method

The doping profiles and trap levels in the epitaxial layers, and the effect of the carrier gas on the growth were studied for Ga-AsCl3-He-H2 GaAs vapor-phase epitaxy (VPE) with the single flat temperature zone (SFT) method. When inexpensive N2 carrier gas was used instead of He, the growth was more diffusion limited and the mobilities were worse because of contamination from the N2. An anomalous carrier density dip at the epi-substrate interface was observed even in the epitaxial layers grown by the new SFT method, but it was smaller when the growth was kinetically limited, smaller for a liquid-encapsulated Czochrolski (LEC) substrate than for a horizontal Bridgeman (HB) substrate, and could be reduced by gas etching. Many Cu and Fe levels were found at the interface, explaining the dip in the carrier density. Point defects induced at the beginning of the growth are thought to cause these impurities to accumulate at the interface.