Experimental and simulation study of power performance improvement of GaN PIN betavoltaic cell

Abstract

We have demonstrated the gallium nitride (GaN)-based betavoltaic (BV) cells with PN and PIN junction to investigate the relationship between the intrinsic GaN (i-GaN) layer and power performance of BV cells. A short-circuit current (ISC) and an open-circuit voltage (VOC) of the fabricated BV cells were evaluated by using an electron-beam (e-beam) irradiation. The cell with PIN junction exhibited an improved ISC and VOC compared to the cell with PN junction. This is because the additional 200 nm-thick i-GaN layer extends the depletion region of BV cell, resulting in improved charge collection. When a 17 kV e-beam irradiated into the fabricated GaN PIN BV cell, the device exhibited an ISC of 1.86 μA, a VOC of 2.23 V, a maximum output power (Pmax.out) of 2.74 μW, and a power conversion efficiency (PCE) of 4.5%, respectively. This PCE is the best value among GaN BV cell researches using 17 keV e-beam irradiation. To study a role of i-GaN layer in PIN BV cell, the technology computer-aided design (TCAD) simulator was implemented. The effect of layer thickness and native defects in GaN material on the power performance of BV cell was evaluated. The power performance of PIN BV cell was degraded by introducing native defects in layers due to an increase of recombination rate. The BV cell with 500 nm-thick i-GaN layer exhibited better power performance when the electrons with average energy of Ni-63 irradiated into device because the maximum absorption rate of electrons was well positioned in the depletion region. The experimental and simulated results showed that the introduction of i-GaN layer and the optimization of parameters such as thickness and crystalline quality were important to improve the power performance of BV cells.