A. Knigge, M. Brendel, F. Brunner, S. Einfeldt, A. Knauer, V. Kueller, U. Zeimer, and M. Weyers

Published in:

phys. stat. sol. (c), vol. 11, no. 3-4, pp. 802-805 (2014).

Abstract:

Solar-blind Schottky-type metal-semiconductor-metal (MSM) photodetectors (PDs) based on Al_xGa_1-xN absorber layers with x varying between 0.4 and 1 are investigated. The impact of the epitaxial lateral overgrowth (ELO) technique on stripe patterned AlN/sapphire templates is evaluated by comparing devices on ELO as well as planar AlN/sapphire templates. Device characteristics have been found to depend on the orientation of the finger- electrodes with respect to the stripe pattern. The responsivity of ELO PDs with finger-electrodes perpendicular to the stripes is higher than that for the parallel case or for PDs on planar templates. For x ≥ 0.9 an enhancement of about 50 % and for x = 0.4 of more than two orders of magnitude due to photoconductive gain are observed. The orientation dependence is explained by a non-uniform dislocation density on the ELO template, involving channels of low dislocation density. Additionally, the Al/Ga incorporation is found to be non-uniform, particularly for low values of x. Due to the absence of photoconductive gain for x ≥ 0.9, the gain observed for x = 0.4 using ELO templates with perpendicular finger orientation is attributed to compositional modulation of the absorber layer.

Keywords:

AlN, AlGaN, epitaxial lateral overgrowth, ultraviolet, solar-blind, metal-semiconductor-metal, photodetector

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