GROWTH OF GAN FILMS BY COMBINED LASER AND MICROWAVE PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

GaN films have been grown on quartz and (01 (1) over bar 2) sapphire substrates using combined ultraviolet excimer laser and microwave plasma enhanced metalorganic chemical vapour deposition (MOCVD) at a substrate temperature of 500 degrees C. Film compositions were analysed by X-ray photoelectron spectroscopy (XPS) and less than 5% residual impurity, principally carbon and oxygen was found. Films grown on quartz were polycrystalline wurtzite with a preferential (0002) orientation, while (0002) and (2<(11)over bar>0) orientations were both found on (01 (1) over bar 2) sapphire. Electron carrier concentration was found to be controllable between 10(17) and 10(14) cm(-3) via control of ammonia plasma injection rate, whilst electron mobility also increased proportionally with the flow rate of the plasma. A room-temperature mobility of 95 cm(2) V-1 s(-1) was obtained for films on (01 (1) over bar 2) sapphire, saturating at a plasma flow rate of 100 ml/min. The results are interpreted as showing a reduction of nitrogen vacancies by an increase in the reacting species liberated in the plasma.