Elimination of nonuniformities in thick GaN films using metalorganic chemical vapor deposited GaN templates

Thick hydride vapor phase epitaxial GaN layers are grown on metalorganic ch emical vapor deposited GaN template layers as well as directly on sapphire, with the aim of investigating the effect of the template on the strain rel axation and spatial distribution of free carriers in the overgrown GaN film s. Spatially resolved cross-sectional micro-Raman spectroscopy, cathodolumi nescence, and transmission electron microscopy show improved crystalline qu ality for growth on metalorganic chemical vapor deposited GaN templates. Th e highly doped and highly defective near-substrate layer composed of column ar domains, typically present in hydride vapor phase epitaxial GaN films gr own directly on sapphire, is absent in the layers grown on templates. Conse quently, this results in elimination of the nonuniformities of free electro n distribution, a lower residual free carrier concentration (<10(17) cm(-3) ), and improved strain relaxation. (C) 2001 American Institute of Physics.