Solar blind Al0.5Ga0.5N/AlN metal-semiconductor-metal photodetectors (MSM PDs) are characterized by means of photocurrent spectroscopy. In order to enhance the external quantum efficiency (EQE) at low bias voltages several strategies have been adopted including absorber layer thicknesses, electrode layout and metallization scheme. Analysis of experimental EQE-bias characteristics under top and bottom illumination conditions reveals (1) a correlation between EQE and electrode pair density for symmetric electrode designs and (2) a slight asymmetry of the EQE with respect to bias polarity for bottom-illuminated MSM PD consisting of electrode pairs with different electrode widths (asymmetric design) and (3) zero-bias operation for a-MSM PD consisting of electrode pairs with different metallization schemes. In addition, the combination of thin absorber layer and asymmetric electrode design leads to high EQE values under bottom illumination at very low voltages and zero-bias operation is achieved for the a-MSM detector. The zero-bias EQE of the a-MSM is further enhanced by combining the symmetric detector design with a high electrode pair density.
M. Brendel, F. Brunner, A. Knigge, and M. Weyers, "AlGaN-based metal-semiconductor-metal photodetectors with high external quantum efficiency at low operating voltage," Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 101040J (Presented at SPIE OPTO: January 31, 2017; Published: 16 February 2017); https://doi.org/10.1117/12.2250742.
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