Metal–Organic Chemical Vapor Deposition of ZnGeGa₂N₄

Abstract

An alloy of ZnGeN2 and GaN in equal proportions can form the octet-rule-preserving quaternary heterovalent nitride semiconductor ZnGeGa2N4. Single-crystal films of the alloy targeting this composition were deposited on (11̅02) Al2O3 (r-plane sapphire), (0001) Al2O3 (c-plane sapphire), and (0001) GaN/Al2O3 by metal–organic chemical vapor deposition using the precursors diethylzinc, germane, trimethylgallium, and ammonia. The growth directions were along the c-axis for films grown on the c-plane sapphire and GaN templates, as well as along the orthorhombic [010] axis for films grown on r-plane sapphire. The effects of varying the growth temperature from 550 to 700 °C, choice of substrate, and trimethylgallium and germane flow rates on film composition and morphology were examined by X-ray diffraction, field-emission scanning electron microscopy, and atomic force microscopy. The Zn/Ge atomic ratios were observed to decrease with growth temperature but increase with trimethylgallium flow rate. Growth rates, which varied with growth temperature from approximately 1 to 3.5 μm/h, were observed to increase with growth temperature up to 670 °C, then decrease abruptly with further increase in temperature. The growth rates were similar for growth on r- and c-plane sapphire substrates at the lower growth temperatures. However, above 650 °C the growth rates on c- and r-plane sapphire differed by as much as 70%. A broad photoluminescence double peak was observed only for samples grown on r-plane sapphire at the highest growth temperature. Hall measurements show n-type carrier concentrations in the mid-1018/cm–3 range and mobilities of a few cm2/V-s for material grown on r-sapphire substrates at 670 °C and above.