Effect of carrier gas in hydride vapor phase epitaxy on optical and structural properties of GaN

Abstract

Variation of the H 2 fraction in the carrier gas affects partial pressures and homogeneity of the species at the growth front. Changing the H 2 :N 2 ratio thus requires readjustment of the flows of the reacting species to keep the V/III ratio at the growth front constant. In this paper the complex effect of the carrier gas composition, i.e., the H 2 þ N 2 mixture on optical and structural properties of GaN films grown by hydride vapor phase epitaxy (HVPE) is studied. With constant input flows of the main reactants but different H 2 fractions in each experiment, good morphology was observed only in a small parameter window. Partial pressures at the growth front were calculated using a commercial virtual reactor simulation tool. After readjustment of the growth species partial pressures to those which previously provided good morphology, it became possible to achieve higher growth rates, comparable morphologies, and widths of the rocking curves (FWHM) for a wide range of hydrogen fractions (0-70%). Further flow pattern correction enabled growth of 1 mm thick layers for 40-75% H 2 in the carrier gas. The results of the study allow to find optimal conditions for HVPE growth of thick GaN layers when scaling up from 2 to 3 in. substrate diameter.