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High electron mobility AlGaN/GaN heterostructures grown on sapphire substrates by molecular-beam epitaxy

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6 Author(s)
Li, L.K. ; Department of Electrical Engineering, Columbia University, New York, New York 10027 ; Turk, B. ; Wang, W.I. ; Syed, S.
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High-quality AlGaN/GaN heterostructures have been grown by ammonia gas-source molecular-beam epitaxy on sapphire substrates. Incorporation of a low-temperature-grown AlN interlayer during the growth of a thick GaN buffer is shown to substantially increase the mobility of the piezoelectrically induced two-dimensional electron gas (2DEG) in unintentionally doped AlGaN/GaN heterostructures. For an optimized AlN interlayer thickness of 30 nm, electron mobilities as high as 1500 cm2/V s at room temperature, 10 310 cm2/V s at 77 K, and 12 000 cm2/V s at 0.3 K were obtained with sheet densities of 9×1012cm-2 and 6×1012cm-2 at room temperature and 77 K, respectively. The 2DEG was confirmed by strong and well-resolved Shubnikov–de Haas oscillations starting at 3.0 T. Photoluminescence measurements and atomic force microscopy revealed that the densities of native donors and grain boundaries were effectively reduced in the AlGaN/GaN heterostructures incorporating low-temperature-grown AlN interlayers. © 2000 American Institute of Physics.

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Applied Physics Letters  (Volume:76 ,  Issue: 6 )