Abstract
As one of the successful approaches to GaAs surface passivation, wet-chemical nitridation is applied here to relate the effect of surface passivation to carrier recombination processes in bulk GaAs. By combining time-resolved photoluminescence and optical pump—THz probe measurements, we found that surface hole trapping dominates the decay of photoluminescence, while photoconductivity dynamics is limited by surface electron trapping. Compared to untreated sample dynamics, the optimized nitridation reduces hole- and electron-trapping rate by at least 2.6 and 3 times, respectively. Our results indicate that under ambient conditions, recovery of the fast hole trapping due to the oxide regrowth at the deoxidized GaAs surface takes tens of hours, while it is effectively inhibited by surface nitridation. Our study demonstrates that surface nitridation stabilizes the GaAs surface via reduction of both electron- and hole-trapping rates, which results in chemical and electronical passivation of the bulk GaAs surface.
Highlights
Bulk GaAs crystals with their direct band gap and high electron mobility have extensive applications in electronic and optoelectronic devices.[1−4] The development of the GaAs technology has been impeded by high density of surface states on GaAs
We studied the effect of surface nitridation on carrier recombination dynamics in GaAs crystals by means of time-resolved photoinduced luminescence (TRPL) and optical pump THz probe (TRTS) techniques
From PL quantum yield (PLQY) measurements, we found that surface nitridation significantly reduces the density of nonradiative trapping centers as compared to naturally oxidized and HCl solutionprocessed GaAs surfaces
Summary
Bulk GaAs crystals with their direct band gap and high electron mobility have extensive applications in electronic and optoelectronic devices.[1−4] The development of the GaAs technology has been impeded by high density of surface states on GaAs. Sulfidation of the surface by wet chemistry improves the efficiency of solar cells.[24,25] the sulfide layer is unstable at ambient conditions, and a protective layer is needed to prevent the sulfide layer’s degradation.[26] Surface nitridation by hydrazine sulfide solution can form a GaN monolayer at the GaAs surface This monolayer can protect the crystal surface against oxidation over a period of months and significantly improve the GaAs optical and electrical properties.[17,26−28] Overall, surface nitridation is a stable and effective method for passivation of the GaAs surface. These results demonstrate that nitridation does stabilize the GaAs surface and reduce both electron- and hole-trapping rates
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