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 s ubstrates using combined ultraviolet excimer laser and microwave plasm a enhanced metalorganic chemical vapour deposition (MOCVD) at a substr ate temperature of 500 degrees C. Film compositions were analysed by X -ray photoelectron spectroscopy (XPS) and less than 5% residual impuri ty, principally carbon and oxygen was found. Films grown on quartz wer e polycrystalline wurtzite with a preferential (0002) orientation, whi le (0002) and (2<(11)over bar>0) orientations were both found on (01 ( 1) over bar 2) sapphire. Electron carrier concentration was found to b e controllable between 10(17) and 10(14) cm(-3) via control of ammonia plasma injection rate, whilst electron mobility also increased propor tionally 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) s apphire, saturating at a plasma flow rate of 100 ml/min. The results a re interpreted as showing a reduction of nitrogen vacancies by an incr ease in the reacting species liberated in the plasma.