Electrical transport in undoped and carbon doped b-Ga2O3

In this paper, we focus on the electrical transport properties of undoped, and carbon doped b-Ga2O3 thin-films. For this purpose, b-Ga2O3 samples were grown on sapphire substrates by plasma assisted pulsed laser deposition. The samples were characterized by Raman scattering and temperature dependent dark conductivity measurements. Raman scattering shows that all samples are polycrystalline. The dark conductivity exhibits two distinctly different ranges in the measured temperature range. In the relaxed state the conductivity is activated with an energy of 0.68 eV for T > 250 K. For T < 250 K the conductivity approaches a constant value of 6x10-12 Scm-1. After illumination with sub band-gap light the dark conductivity increases up to 3 orders of magnitude. This is accompanied by a decrease of the activation energy to 0.36 eV. For C-doped samples the activation energy decreases. The state with the smaller activation energy is metastable . The time and temperature dependence of this relaxation reveals two process and can be described with two stretched exponential decays. From the temperature dependence of the time constants the energies of the traps are determined.