Ohmic contact structures on β-Ga2O3 with n+ β-Ga2O3 pulsed laser deposition layers

Thin (40-150 nm), highly doped n+ (10(19)-10(20) cm(-3)) Ga2O3 layers deposited using pulsed laser deposition (PLD) were incorporated into Ti/Au ohmic contacts on (001) and (010) beta-Ga2O3 substrates with carrier concentrations between 2.5 and 5.1 x 10(18) cm(-3). Specific contact resistivity values were calculated for contact structures both without and with a PLD layer having different thicknesses up to 150 nm. With the exception of a 40 nm PLD layer on the (001) substrate, the specific contact resistivity values decreased with increasing PLD layer thickness: up to 8x on (001) Ga2O3 and up to 16x on (010) Ga2O3 compared with samples without a PLD layer. The lowest average specific contact resistivities were achieved with 150 nm PLD layers: 3.48 x 10(-5) Omega cm(2) on (001) Ga2O3 and 4.79 x 10(-5) Omega cm(2) on (010) Ga2O3. Cross-sectional transmission electron microscopy images revealed differences in the microstructure and morphology of the PLD layers on the different substrate orientations. This study describes a low-temperature process that could be used to reduce the contact resistance in Ga2O3 devices.