GaN thin films deposited by pulsed laser ablation in nitrogen and ammonia reactive atmospheres

Well-oriented, crystalline GaN films were grown on (112̄0) sapphire substrates in reactive atmospheres of N2 and NH3 by pulsed laser deposition. GaN targets were ablated at 2.8 J cm−2 and the substrate temperature was varied from 500 to 700°C. The background gas pressure was varied from 0.04 to 0.3 mbar. All the films had a wurtzite structure. The crystal quality and preferential orientation depended on the substrate temperature, laser fluence and the presence of the nitriding atmosphere. For both N2 and NH3, the most resistive films were preferentially orientated in the [000l] direction. For 700°C the film resistivity was found to increase from 10−3 Ω cm when deposited in NH3 to 102 Ω cm when deposited in N2. The band-gap, obtained from optical transmission measurements shifted from 3.1 to 3.4 eV. Violet photoluminescence was found in all samples and was centered at 3.2 eV with a full width at half maximum of 0.2 eV. A broad peak in the yellow, centered at 2.1 eV, was detected for films grown in vacuum and ammonia.