On the EQE-bias characteristics of bottom-illuminated AlGaN-based metal-semiconductor-metal photodetectors with asymmetric electrode geometry

Abstract

The bias dependence of the external quantum efficiency (EQE) of bottom-illuminated Al0.5Ga0.5N/AlN metal-semiconductor-metal photodetectors shows certain features which are directly related to the device geometry, i.e., the electrode design and the absorber layer thickness. Asymmetric detectors of any absorber thickness between 0.5 μm and 0.1 μm show a reduced EQE in reverse saturation. Furthermore, an enhanced EQE appears below the threshold either in reverse polarity for thick (i.e., 0.5 μm, 0.3 μm) or in forward polarity for thin (0.1 μm) AlGaN absorber layers. In order to understand the underlying physics of these phenomena, measured and simulated data are compared in the framework of a recently developed model for symmetric devices, taking into account defect-related non-radiative recombination and electric polarization effects. The electron capture time for recombination in the AlGaN absorber and the (background) donor density in the AlN buffer layer are the only parameters to be adjusted to reproduce all experimental trends qualitatively.