Defect states and their electric field-enhanced electron thermal emission in heavily Zr-doped β-Ga2O3 crystals

Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (E-c) in Czochralski-grown unintentionally doped (UID) and vertical gradient freeze-grown Zr-doped beta-Ga2O3 crystals. In UID crystals with an electron concentration of 10(17)cm(-3), we observe levels at 0.18eV and 0.46eV in addition to the previously reported 0.86 (E2) and 1.03eV (E3) levels. For 10(18)cm(-3) Zr-doped Ga2O3, signatures at 0.30eV (E15) and 0.71eV (E16) are present. For the highest Zr doping of 5x10(18)cm(-3), we observe only one signature at 0.59eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (Fe-Ga) defect. The 0.71eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59eV signature in the highest Zr-doped sample likely corresponds to the 0.71eV signature in lower-doped samples. Our analysis highlights the importance of testing for and reporting on field-enhanced emission, especially the electric field present during DLTS and other characterization experiments on beta-Ga2O3 along with the standard emission energy, cross section, and lambda-corrected trap density. This is important because of the intended use of beta-Ga2O3 in high-field devices and the many orders of magnitude of possible doping.