Unusual conduction mechanism of n-type β-Ga2O3: A shallow donor electron paramagnetic resonance analysis

Abstract

We have investigated the conduction mechanism in n-type, Si doped β-Ga2O3 bulk samples and evidenced carrier dynamics in the GHz frequency range at room temperature by electron paramagnetic resonance (EPR) spectroscopy. The Si shallow donor EPR and conduction electron spin resonance (CESR) spectra show an unusual temperature dependence of the linewidth and line shape, which reveals a variable range hopping conduction and donor clustering. The temperature dependence of the EPR signal intensity can be fitted with two thermally activated processes with energies of 4 meV and 40 meV in the below and above 40 K temperature range. The value of 40 meV is attributed to the ionization energy of the Si shallow donor, indicating that hopping proceeds via the conduction band. Above T = 130 K and up to room temperature, the conduction electron spin resonance (CESR) can be observed with a decreasing linewidth of ΔB < 1 G, which indicates negligible spin flip scattering. To illustrate the unusual behavior of the shallow donor in Ga2O3, we have analyzed the hydrogen shallow donor in ZnO, for which we observe a different “classical” behavior, characterized by donor localization below 40 K and thermal ionization in the conduction band above T = 90 K. In ZnO, the CESR can only be observed in a small temperature range at 90 K due to excessive line broadening for higher temperatures.