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Electrical properties and deep traps spectra of a-plane GaN films grown on r-plane sapphire
Polyakov, A.Y.,Smirnov, N.B.,Govorkov, A.V.,Markov, A.V.,Sun, Q.,Zhang, Y.,Yerino, C.D.,Ko, T.S.,Lee, I.H.,Han, J. Elsevier 2010 Materials science & engineering. B, Advanced funct Vol.166 No.3
Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample A and 1.7x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near E<SUB>c</SUB> -0.6eV, with other prominent traps having the activation energy of 0.25eV. The Fermi level was pinned by the E<SUB>c</SUB> -0.6eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25eV traps for sample B, most likely due to the reduced density of the 0.6eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed.