Disordering of InGaN/GaN Superlattices after High-Pressure Annealing
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M.D. McCluskey*, L.T. Romano**, B.S. Krusor**, D. Hofstetter**, D.P. Bour**, M. Kneissl**, N.M. Johnson**, T. Suski***, J. Jun*** *Department of Physics, Washington State University, Pullman, WA 99164-2814 **Xerox PARC, 3333 Coyote Hill Rd., Palo Alto, CA 94304 *** Unipress, Ul. Sokolowska 29, 01-142 Warsaw, Poland Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G3.42 (1999) ABSTRACT Interdiffusion of In and Ga is observed in InGaN multiple-quantum-well superlattices for annealing temperatures of 1250 to 1400°C. Hydrostatic pressures of up to 15 kbar were applied during the annealing treatments to prevent decomposition of the InGaN and GaN. In as-grown material, x-ray diffraction spectra show InGaN superlattice peaks up to the fourth order. After annealing at 1400°C for 15 min, only the zero-order InGaN peak is observed, a result of compositional disordering of the superlattice. Composition profiles from secondary ion mass spectrometry indicate significant diffusion of Mg from the p-type GaN layer into the quantum well region. This Mg diffusion may lead to an enhancement of superlattice disordering. For annealing temperatures between 1250 and 1300°C, a blue shift of the InGaN spontaneous emission peak is observed, consistent with interdiffusion of In and Ga in the quantum-well region. INTRODUCTION The development of blue light-emitting diodes (LEDs) [1] and laser diodes (LDs) [2] has focused a great deal of research activity on GaN-based III-V nitrides. The band gaps of InxGa1-xN alloys cover a wide spectral range, from red (InN) to UV (GaN), making this alloy system ideal for optoelectronic applications [3]. The diffusion characteristics of host and impurity atoms in InxGa1-xN alloys are of considerable interest [4]. In this paper, results from structural and optical studies of In-Ga interdiffusion in InGaN/GaN multiple quantum wells (MQWs) are presented. While compositional disordering of superlattices within the InAlGaAs materials system has been extensively studied [5,6], superlattice disordering in III-nitrides has only recently been observed [4]. The interdiffusion of In and Ga in InxGa1-xN alloys is complicated by the immiscibility of InN and GaN [7], which can result in phase separation in thick InGaN layers [8] and MQW structures [9]. In this study, we have investigated the diffusion of In and Ga in annealed In0.18Ga0.82N/GaN MQW structures. We observe quantum-well superlattice disordering, with no phase separation, for annealing temperatures from 1250 to 1400oC.
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EXPERIMENTAL DETAILS The MQW structures were grown by metalorganic chemical vapor deposition (MOCVD). The structures consist of a 1 µm GaN:Mg layer, a 20 period superlattice of 16 Å In0.18Ga0.82N well / 64 Å GaN barrier, and a 4 µm GaN:Si layer on a sapphire substrate. The thickness of the w
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