A Study on the Increase of Leakage Current in AlGaN Detectors with Increasing Al Composition

The dark leakage current of Al_xGa_1-xN Schottky barrier detectors with different Al contents is investigated. It was found that the dark leakage of Al_xGa_1-xN detectors increased with increasing Al content. The XRD and SIMS results showed that there was no significant difference of the dislocation density and carbon impurity concentration in five Al_xGa_1-xN samples with different Al content. This was likely not the main reason for the difference in dark leakage current of Al_xGa_1-xN detectors. However, the results of positron annihilation showed that the vacancy defect concentration increased with increasing Al content. This was consistent with the result that the dark leakage current increased with increasing Al content. With the increase of vacancy concentration, the vacancy defect energy levels also increased, and the probability of electron tunneling through defect levels increased. In contrast, the Schottky barrier height decreased, which eventually led to the increase of dark leakage current. This discovery should be beneficial to an accurate control of the performance of Al_xGa_1-xN detectors.