The authors have made an attempt to investigate the effect of electron versus hole photocurrent on the optoelectric properties of structured Wurtzite-GaN (Wz-GaN) reach-through avalanche photodiodes (RAPDs). The photo responsivity and optical gain of the devices are obtained within the wavelength range of 300 to 450？nm using a novel modeling and simulation technique developed by the authors. Two optical illumination configurations of the device such as Top Mounted (TM) and Flip Chip (FC) are considered for the present study to investigate the optoelectric performance of the device separately due to electron dominated and hole dominated photocurrents, respectively, in the visible-blind ultraviolet (UV) spectrum. The results show that the peak unity gain responsivity and corresponding optical gain of the device are 555.78？mA？W？1 and , respectively, due to hole dominated photocurrent (i.e., in FC structure); while those are 480.56？mA？W？1 and , respectively, due to electron dominated photocurrent (i.e., in TM structure) at the wavelength of 365？nm and for applied reverse bias of 85？V. Thus, better optoelectric performance of Wz-GaN RAPDs can be achieved when the photocurrent is made hole dominated by allowing the UV light to be shined on the -layer instead of -layer of the device. 1. Introduction Ultraviolet detectors are of a great interest to a wide range of industrial, defense, scientific, commercial, environmental, and even biological applications. Most of these applications inherently require high sensitivity, low noise, and visible-blind detection. Photomultiplier tubes (PMTs) may be used as UV detectors due to their large internal gain (~106) which ensures high detectivity in UV range. However, the drawbacks of PMTs are as follows: they are bulky, and they require large bias voltage (~1000？V) for operation [1]. Thus, the semiconductor-based alternatives such as avalanche photodiodes (APDs) are preferred over PMTs due to their small size, high gain and also they require much lower voltage for biasing. APDs working in ultraviolet (UV) range are in immense interest of researchers nowadays for numerous applications, including bioaerosol detection, UV imaging, harsh environment gamma sensing [2] and long-range flame detection in the solar-blind window. Conventional Si APDs generally have limited deep-UV quantum efficiency and appreciable visible response [3, 4]. Thus, additional filtering is essential for them to operate in deep-UV range. Further, very low quantum efficiency of Si APDs at these range make them inefficient. APDs based on wide bandgap
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