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25 September 2007 Origin of the high photoconductive gain in AlGaN films
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Abstract
In this paper we report the properties of photoconductive detectors fabricated on GaN and AlGaN films produced by plasma assisted MBE. The spectral dependence of such devices shows a sharp increase over many orders of magnitude at the gap of the semiconductor but it remains constant at shorter wavelengths consistent with absence of surface recombination. The mobility-lifetime product, which is the intrinsic figure of merit of the photoconductive gain, decreases monotonically with the resistivity of GaN films. This result is attributed to the existence of exponential tails due to potential fluctuations arising from stacking faults, point defects and impurities. In the case of AlGaN alloys similar dependence of the mobility-lifetime product on film resistivity has been observed. However, the mobility-lifetime product for films with AlN mole fraction close to 50% is about two orders of magnitude higher than that of GaN films with comparable resistivity. This result was accounted for by the longer lifetime of the photogenerated carriers due to the partial atomic ordering in these alloys. The band structure of the ordered and random domains form a type-II heterostructure and thus photogenerated electrons and holes in these detectors are physically separated, leading to an increase in recombination lifetime.
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Theodore D. Moustakas and Mira Misra "Origin of the high photoconductive gain in AlGaN films", Proc. SPIE 6766, Optoelectronic Devices: Physics, Fabrication, and Application IV, 67660C (25 September 2007); https://doi.org/10.1117/12.736772
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