Abstract
We report on photoluminescence in the 3–7 µm mid-wave infrared (MWIR) range from sub-100 nm strained thin films of rocksalt PbSe(001) grown on GaAs(001) substrates by molecular beam epitaxy. These bare films, grown epitaxially at temperatures below 400 °C, luminesce brightly at room temperature and have minority carrier lifetimes as long as 172 ns. The relatively long lifetimes in PbSe thin films are achievable despite threading dislocation densities exceeding 109 cm−2 arising from island growth on the nearly 8% lattice- and crystal-structure-mismatched GaAs substrate. Using quasi-continuous-wave and time-resolved photoluminescence, we show that the Shockley–Read–Hall recombination is slow in our high dislocation density PbSe films at room temperature, a hallmark of defect tolerance. Power-dependent photoluminescence and high injection excess carrier lifetimes at room temperature suggest that degenerate Auger recombination limits the efficiency of our films, although the Auger recombination rates are significantly lower than equivalent III–V bulk materials and even a bit slower than expectations for bulk PbSe. Consequently, the combined effects of defect tolerance and low Auger recombination rates yield an estimated peak internal quantum efficiency of roughly 30% at room temperature, unparalleled in the MWIR for a severely lattice-mismatched thin film. We anticipate substantial opportunities for improving performance by optimizing crystal growth as well as understanding Auger processes in thin films. These results highlight the unique opportunity to harness the unusual chemical bonding in PbSe and related IV–VI semiconductors for heterogeneously integrated mid-infrared light sources constrained by tight thermal budgets in new device designs.
Highlights
Narrowband incoherent and coherent mid-infrared light sources emitting in the mid-wave infrared (3–7 μm) are increasingly in demand for a range of applications such as chemical spectroscopy, healthcare, manufacturing and environmental monitoring, and free space communication.1,2 Optoelectronic active regions in the visible and near-infrared yield devices with internal quantum efficiencies (IQE) exceeding 90%.3 In the mid-wave infrared (MWIR), bulk II–VI and III–V materials suffer from low room-temperature IQEs around 5%, and even highly engineered III–V superlattices are below 10%.4–7 Interband Cascade Lasers (ICLs) have achieved high room-temperature IQEs of 64% via recycling of carriers between active stages, but they require complex band structure engineering and device design.8,9 While higher efficiency MWIR emitters are appealing for generation devices, there is substantial interest in expanding their functionality beyond simple emission
Using quasi-continuous-wave and time-resolved photoluminescence, we show that the Shockley–Read–Hall recombination is slow in our high dislocation density PbSe films at room temperature, a hallmark of defect tolerance
Power-dependent photoluminescence and high injection excess carrier lifetimes at room temperature suggest that degenerate Auger recombination limits the efficiency of our films, the Auger recombination rates are significantly lower than equivalent III–V bulk materials and even a bit slower than expectations for bulk PbSe
Summary
Narrowband incoherent and coherent mid-infrared light sources emitting in the mid-wave infrared (3–7 μm) are increasingly in demand for a range of applications such as chemical spectroscopy, healthcare, manufacturing and environmental monitoring, and free space communication. Optoelectronic active regions in the visible and near-infrared yield devices with internal quantum efficiencies (IQE) exceeding 90%.3 In the mid-wave infrared (MWIR), bulk II–VI and III–V materials suffer from low room-temperature IQEs around 5%, and even highly engineered III–V superlattices are below 10%.4–7 Interband Cascade Lasers (ICLs) have achieved high room-temperature IQEs of 64% via recycling of carriers between active stages, but they require complex band structure engineering and device design. While higher efficiency MWIR emitters are appealing for generation devices, there is substantial interest in expanding their functionality beyond simple emission. While higher efficiency MWIR emitters are appealing for generation devices, there is substantial interest in expanding their functionality beyond simple emission These include seamless heterogeneous integration with cost-effective substrates such as Si and light manipulation through plasmonic or electronic/structural phase-change engineering.. Klann et al probed the Auger coefficient in 2 μm thick PbSe films (p-type, 1.6 × 1017 cm−3) in the high-injection regime, finding C = 1.1 × 10−28 cm s−1 at 300 K.15 Their samples have low-injection lifetimes of around 100 ns attributed to either radiative or SRH channels. We study light emission, using photoluminescence (PL), from sub-100 nm epitaxial PbSe bare thin films with dislocation density exceeding 109 cm−2, grown directly on technologically relevant GaAs(001) substrates by molecular beam epitaxy We find that these PbSe thin films emit brightly even at room temperature despite this large defect density and exhibit SRH-limited minority carrier lifetimes at low injection. The injection dependence of the carrier lifetime, suggests that the Auger recombination process is degenerate and even weaker than previously reported
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