Realization of highly rectifying Schottky barrier diodes and pn heterojunctions on κ-Ga2O3 by overcoming the conductivity anisotropy

Novel devices based on orthorhombic kappa - Ga 2 O 3 could enable solar blind infrared detection or high-electron mobility transistors with large two-dimensional electron gas densities. Here, we report on the current transport parallel to the growth direction of kappa - Ga 2 O 3 layers grown by pulsed-laser deposition on highly conductive Al-doped ZnO back contact layers. Besides ohmic Ti/Al/Au contact layer stacks, vertical Pt / PtO x / kappa - Ga 2 O 3 and Pd / PdO x / kappa - Ga 2 O 3 Schottky barrier diodes and NiO / kappa - Ga 2 O 3 and ZnCo 2 O 4 / kappa - Ga 2 O 3 p n-heterodiodes are investigated by current-voltage measurements. While a lateral current transport is severely suppressed to less than 10 - 9 A cm - 2 due to rotational domains, we record a significant current flow through the ohmic contacts in the vertical direction of > 0.1 A cm - 2. The Schottky barrier diodes and the p n-heterojunctions exhibit rectification ratios of up to seven orders of magnitude. Room temperature current-voltage characteristics of diode ensembles as well as temperature-dependent measurements for selected Pt-based diodes reveal a mean barrier height of phi B m approximate to 2.1 eV and ideality factors down to eta approximate to 1.3.