Realization of highly rectifying Schottky barrier diodes and pn heterojunotions on κ-Ga_2O_3 by overcoming the conductivity anisotropy

摘要

Novel devices based on orthorhombic κ-Ga_2O_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 κ-Ga_2O_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/κ-Ga_2O_3 and Pd/PdO_x/κ-Ga_2O_3 Schottky barrier diodes and NiO/κ-Ga_2O_3 and ZnCo_2O_4/κ-Ga_2O_3 pn-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 pn-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 Φ~m_B≈ 2.1 eV and ideality factors down to η≈ 1.3.