The InAs/GaSb type-II superlattices have drawn extensive research interest in the past few decades. The type-II band alignment in this material system provides a long cutoff wavelength and a wide optical tunable range in the mid-infrared regime. Photodetectors based on type-II superlattices are theoretically predicted to surpass the performance of those based on the commercialized HgCdTe II-VI system. An electronic band structure model is formulated based on the 8-band k · p method. The absorption and quantum efficiency spectra are calculated, showing good agreement with experimental data. The interfacial effect in type-II superlattices is investigated. It is shown that the interfacial layers can be employed not only to balance lattice strain and reduce detector dark current, but also to simultaneously increase the cutoff wavelength and quantum efficiency. State-of-art interface controlled samples designed for comparison study are processed into devices. The device performance is characterized electrically by dark current measurements, and optically by Fourier transform infrared spectroscopy. Significant improvement of device performance by interface control is demonstrated, which agrees with the prediction by the theoretical model.
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Theory and experiments of type-II superlattice infrared photodetectors
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