Investigating the effect of self-trapped holes in the current gain mechanism of $ eta mathbf{-}{mathbf{Ga}}_{mathbf{2}}{mathbf{O}}_{mathbf{3}}$ Schottky diode photodetectors

摘要

Monoclinic gallium oxide $(etamathrm{-}{mathrm{Ga}}_{mathrm{2}}{mathrm{O}}_{mathrm{3}})$ 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. $etamathrm{-}{mathrm{Ga}}_{mathrm{2}}{mathrm{O}}_{mathrm{3}}$ 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 $etamathrm{-}{mathrm{Ga}}_{mathrm{2}}{mathrm{O}}_{mathrm{3}}$ 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 $mathrm{1}mathrm{ }mathrm{imes }mathrm{ }{mathrm{10}}^{-mathrm{6}}mathrm{ }{mathrm{cm}}^{mathrm{2}}{mathrm{V}}^{-mathrm{1}}{mathrm{s}}^{-mathrm{1}}$, photoconductive gain in $etamathrm{-}{mathrm{Ga}}_{mathrm{2}}{mathrm{O}}_{mathrm{3}}$ based photodetectors cannot be attributed to STH related hole accumulation near Schottky contact. It is found that hole mobility in the range of $mathrm{1}mathrm{ }mathrm{imes }mathrm{ }{mathrm{10}}^{-mathrm{10}}mathrm{ }{mathrm{cm}}^{mathrm{2}}{mathrm{V}}^{-mathrm{1}}{mathrm{s}}^{-mathrm{1}}mathrm{-}mathrm{ }mathrm{1}mathrm{ }mathrm{imes }mathrm{ }{mathrm{10}}^{-mathrm{12}}mathrm{ }{mathrm{cm}}^{mathrm{2}}{mathrm{V}}^{-mathrm{1}}{mathrm{s}}^{-mathrm{1}}$ 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.