Electronic and ionic conductivity in β-Ga2O3 single crystals

In this work, we quantify electronic and ionic contributions to conductivity in the bulk and depletion widths of back-to-back sputtered Pt Schottky contacts on single crystals of β-Ga2O3. We also demonstrate asymmetric changes to these contacts induced by DC bias at temperatures as low as 200 °C, which has obvious bearing on the performance and reliability of devices. Crystals, which were unintentionally doped, doped with Zr donors, and doped with Mg acceptors, were characterized from room temperature to 900 °C. Electrochemical impedance spectroscopy, current–voltage (IV), capacitance–voltage, and the Wagner DC polarization method were employed to characterize changes in conductivity, doping, and built-in potentials with temperature and bias. This work demonstrates that ionic conductivity can be on-par with electronic conductivity in multiple circumstances in bulk crystal samples and leads to changes in Schottky contacts with an applied bias. While it has not been demonstrated that these phenomena are endemic to all melt-grown β-Ga2O3 crystals and epitaxially grown layers were not investigated, these results highlight the importance of understanding and controlling ionic conductivity and defect reactions involving impurities and native defects to enable reliable and long-lived β-Ga2O3 power devices.