BASIC STUDIES OF GALLIUM NITRIDE GROWTH ON SAPPHIRE BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION AND OPTICAL-PROPERTIES OF DEPOSITED LAYERS

We have studied the growth of gallium nitride on c-plane sapphire subs trates. The layers were grown in a horizontal metalorganic chemical va por deposition reactor at atmospheric pressure using trimethylgallium (TMG) and ammonia (NH3). Variation of the V/III ratio (150-2500) shows a distinct effect on the growth rate. With decreasing V/III ratio, we find an increasing growth rate. Variation of the growth temperature ( 700-1000 degrees C) shows a weak increase in growth rate with temperat ure. Furthermore, we performed secondary ion mass spectroscopy measure ments and find an increasing carbon incorporation in the GaN films wit h decreasing ammonia partial, pressure and a growing accumulation of c arbon at the substrate interface. Photoluminescence measurements show that samples with high carbon content show a strong yellow luminescenc e peaking at 2.2 eV and a near band gap emission at 3.31 eV. With incr easing carbon content, the intensity of the 3.31 eV line increases sug gesting that a carbon related center is involved.