Temperature Dependence of Anisotropic Complex Conductivity of β-Ga2O3.

Anisotropic conductivity and its temperature dependence of unintentionally doped and Fe-doped bulk (010) β-Ga2O3 were studied by using terahertz time-domain spectroscopy (THz-TDS) with the THz polarization being parallel to the [100] and the [001] directions. The responses to the THz waves were different along the a-axis and the c-axis, where the Drude and the Drude-Smith model were applied for fitting the data of these two axes, respectively. This suggests that the carriers travel along the a-axis as free carriers while those are highly localized along the c-axis. The unintentionally doped sample showed a unique temperature dependence, in particular, a decreasing trend of the real part of the complex conductivity with increasing temperature. This is attributed to carriers being completely thermally excited from shallow impurity levels, and afterward, the scattering behavior has been enhanced, causing the conductivity to decrease. Conversely, the Fe-doped sample showed little temperature dependence, indicating this sample to be thermally stable. Moreover, the mobility along the a-axis in the Fe-doped sample was estimated to be much higher than that along the c-axis. [ABSTRACT FROM AUTHOR]