Growth of GaN films by combined laser and microwave plasma enhanced chemical vapour deposition

GaN films have been grown on quartz and (011̄2) sapphire substrates using combined ultraviolet excimer laser and microwave plasma enhanced metalorganic chemical vapour deposition (MOCVD) at a substrate temperature of 500°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 (21̄1̄0) orientations were both found on (011̄2) sapphire. Electron carrier concentration was found to be controllable between 10¹⁷ and 10¹⁴ 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 cm² V^-1 s^-1 was obtained for films on (011̄2) 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.