Characteristics of Native Oxides-Interfaced GaAs/Ge np Diodes

We report the fabrication and characteristics of native oxides-interfaced heterovalent GaAs/Ge np heterojunction diodes. The native oxides (GaAs)xOy and GexOy were intentionally created as a passivation layer for single crystal GaAs surface and single crystal Ge surface via exposing the p-type Ge (
${2}\times {10} ^{{19}}$
cm
$^{-{3}}\text {)}$
substrate and the released n-type GaAs (
${2}\times {10} ^{{18}}$
cm
$^{-{3}}\text {)}$
layer in air for different time lengths. X-ray photoelectron spectroscopy (XPS) confirmed the formation of these oxides and their content variations with the oxidation time lengths. The surface oxidized GaAs and Ge were then put together via chemical bonding with careful consideration of the thermal budget such that atomic inter-diffusion between Ge and GaAs do not occur. The measured current-voltage characteristics of the diodes with different oxidation times were compared showing that the 2-hour air oxidation displays the optimal diode characteristics. This work supports the semiconductor grafting concept where interface passivation is necessary to form high-performance pn abrupt heterojunctions between two single crystalline semiconductors and may provide useful guidance for future applications employing GaAs/Ge heterojunctions.