Investigating the effect of self-trapped holes in the current gain mechanism of β−Ga2O3 Schottky diode photodetectors

Abstract

Monoclinic gallium oxide $(\beta\mathrm{-}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}})$ has found great research interest in solar blind photodetector (SBP) applications due to its' bandgap $\mathrm{\sim}$4.85 eV and availability of high quality native crystal growth. Applications including missile guidance, flame detection, underwater/intersatellite communication and water purification systems require SBPs. $\beta\mathrm{-}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ SBPs with high responsivity values have been published indicating internal gain in these devices. The gain has been attributed to accumulation of self-trapped hole (STH) below Schottky metal which the lowers Schottky barrier in these devices based on some approximations rather than a proper device simulation. In this paper, technology computer-aided design (TCAD) simulation of $\beta\mathrm{-}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ SBPs are performed to numerically investigate the effect of low hole mobility STHs on Schottky barrier lowering (SBL). The simulations revealed that based on the theoretical hole mobility of $\mathrm{1}\mathrm{\ }\mathrm{\times }\mathrm{\ }{\mathrm{10}}^{-\mathrm{6}}\mathrm{\ }{\mathrm{cm}}^{\mathrm{2}}{\mathrm{V}}^{-\mathrm{1}}{\mathrm{s}}^{-\mathrm{1}}$, photoconductive gain in $\beta\mathrm{-}{\mathrm{Ga}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ based photodetectors cannot be attributed to STH related hole accumulation near Schottky contact. It is found that hole mobility in the range of $\mathrm{1}\mathrm{\ }\mathrm{\times }\mathrm{\ }{\mathrm{10}}^{-\mathrm{10}}\mathrm{\ }{\mathrm{cm}}^{\mathrm{2}}{\mathrm{V}}^{-\mathrm{1}}{\mathrm{s}}^{-\mathrm{1}}\mathrm{-}\mathrm{\ }\mathrm{1}\mathrm{\ }\mathrm{\times }\mathrm{\ }{\mathrm{10}}^{-\mathrm{12}}\mathrm{\ }{\mathrm{cm}}^{\mathrm{2}}{\mathrm{V}}^{-\mathrm{1}}{\mathrm{s}}^{-\mathrm{1}}$ is required to induce $\mathrm{\sim}$0.3 eV of SBL potential. Unless such low hole mobility is reported either experimentally or theoretically, it is not reasonable to attribute gain to STH formation in these devices.