Abstract
Novel devices based on orthorhombic κ-Ga2O3 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-Ga2O3 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/PtOx/κ-Ga2O3 and Pd/PdOx/κ-Ga2O3 Schottky barrier diodes and NiO/κ-Ga2O3 and ZnCo2O4/κ-Ga2O3 pn-heterodiodes are investigated by current–voltage measurements. While a lateral current transport is severely suppressed to less than 10−9Acm−2 due to rotational domains, we record a significant current flow through the ohmic contacts in the vertical direction of >0.1Acm−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 ϕBm≈2.1eV and ideality factors down to η≈1.3.
Highlights
The wide bandgap semiconductor Ga2O3 became one of the most intensively researched power device materials within the last two decades
We report on the current transport parallel to the growth direction of κ-Ga2O3 layers grown by pulsed-laser deposition on highly conductive Al-doped ZnO back contact layers
We used two different contact configurations similar to the ones employed for β-Ga2O3 layers in Ref. 8 that both enable the current in the κ-Ga2O3 layer to flow vertically, i.e., electrons are not forced to cross domain boundaries
Summary
The wide bandgap semiconductor Ga2O3 became one of the most intensively researched power device materials within the last two decades. This was initially triggered by its large expected electric breakdown field of about 8 MV cmÀ1 for the monoclinic β-modification.[1] Further, homoepitaxial growth of devices is possible since high-quality single crystal β-Ga2O3 wafers up to 4 in. Reports on rectifying contacts and devices are limited to the rhombohedral α-modification.[22–26] For the orthorhombic κ-phase ( referred to as ε-Ga2O3), there are no reports available on rectifying SBDs or pn heterojunctions to the best knowledge of the authors
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