Low-voltage-operation avalanche photodiode based on n-gallium oxide/p-crystalline selenium heterojunction

In this study, we demonstrate the avalanche multiplication phenomenon in a crystalline-selenium (c-Se)-based heterojunction photodiode. The carrier injection from an external electrode, which is considered to be the major factor contributing to dark current at a high electric field, was significantly decreased by employing a thin n-type Ga2O3 layer with a high hole-injection barrier. The fabricated Ga2O3/c-Se diode exhibited extremely high external quantum efficiency of over 100% in the short-wavelength region at a relatively low reverse-bias voltage of ∼20 V. Furthermore, Sn-doping of the Ga2O3 layer increases the carrier concentration; hence, the resulting device has a lower threshold voltage for avalanche multiplication.