Charge Collection Efficiency of Single GaN Core-Shell Wires Assessed by High-Precision Ion-Beam-Induced Charge Measurements

We report on the charge collection efficiency (CCE) of GaN core-shell p-n junction microwires obtained through high-precision ion-beam-induced charge (IBIC) measurements. Single wires are processed into working radiation detectors using a set of microfabrication processes and are irradiated with either 1 MeV or 750 keV Si ions. We show that we are able to accurately probe the microwires and measure structures that have dimensions below 1 mu m. CCE maps show that the detectors are efficient in collecting the charge induced by the Si ions, presenting average CCE magnitudes between 20 and 30% when applying a small reverse bias. Additionally, three-dimensional Monte Carlo simulations were carried out to gain a better understanding of the energy deposition in the depletion region of the p-n junction. Comparison between the experimental and simulated data shows good agreement despite also revealing some drawbacks associated with the microwire detectors, namely, the poor collection efficiency of charge carriers generated in the neutral n-GaN core. Nevertheless, the average CCE of the detectors is promising, especially when only considering the energy deposited in the active region of the detector. In this case, depending on the applied bias, we obtain a CCE between 45 and 80%.