Metal-Organic Chemical Vapor Deposition of ZnGeGa2N4

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 (1 (1) over bar 02) 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 degrees 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 mu m/h, were observed to increase with growth temperature up to 670 degrees 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 degrees 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-10(18)/cm(-3) range and mobilities of a few cm(2)/V-s for material grown on r-sapphire substrates at 670 degrees C and above.