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Tunable hot-carrier photodetection beyond the bandgap spectral limit


The spectral response of common optoelectronic photodetectors is restricted by a cutoff wavelength limit λc that is related to the activation energy (or bandgap) of the semiconductor structure (or material) (Δ) through the relationship λc = hc/Δ. This spectral rule dominates device design and intrinsically limits the long-wavelength response of a semiconductor photodetector. Here, we report a new, long-wavelength photodetection principle based on a hot–cold hole energy transfer mechanism that overcomes this spectral limit. Hot carriers injected into a semiconductor structure interact with cold carriers and excite them to higher energy states. This enables a very long-wavelength infrared response. In our experiments, we observe a response up to 55 µm, which is tunable by varying the degree of hot-hole injection, for a GaAs/AlGaAs sample with Δ = 0.32 eV (equivalent to 3.9 µm in wavelength).

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Figure 1: Sample structure and the VLWIR response at 5.3 K.
Figure 2: Spectral weight (SW) of response and differential photocurrents.
Figure 3: Photoresponse obtained using long-pass filters and an external optical excitation source.
Figure 4: Tuning the VLWIR response.


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This work was supported in part by the US Army Research Office (grant no. W911NF-12-2-0035), monitored by William W. Clark, and in part by the US National Science Foundation (grant no. ECCS-1232184, monitored by John M. Zavada). The University of Leeds acknowledges supports from the UK Engineering and Physical Sciences Research Council and E.H.L. from the European Research Council Advanced Grant ‘TOSCA’. Authors wish to dedicate this paper to the memory of Dr. H. C. Liu (H.C. as he was universally known). H.C. was an integral part of this work, and was inspirational to generations of researcher.

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A.G.U.P. conceived the split-off heterojunction concept and was involved in designing the device structure. Y.F.L. and A.G.U.P. conceived the experiments and wrote the paper. L.H.L., S.P.K. and E.H.L. grew the samples using molecular beam epitaxy. H.C.L. carried out the device processing. Y.F.L. performed electrical and optical measurements and data analysis. A.G.U.P. guided the project. All authors contributed to the content in the paper.

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Correspondence to A. G. Unil Perera.

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Lao, YF., Perera, A., Li, L. et al. Tunable hot-carrier photodetection beyond the bandgap spectral limit. Nature Photon 8, 412–418 (2014).

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