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

Well-oriented, crystalline GaN films were grown on (11 (2) over bar 0) sapphire substrates in reactive atmospheres of N-2 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 degrees 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 N-2 and NH3, the most resistive films were preferentially orientated in the [0001] direction. For 700 degrees C the film resistivity was found to increase from 10(-3) Omega cm when deposited in NH3 to 10(2) Omega cm when deposited in N-2. 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. (C) 1997 Elsevier Science S.A.