Extended Short-Wave Photodiode Based on CdSe/HgTe/Ag₂Te Stack with High Internal Efficiency

Nanocrystal integration into focal plane arrays requires the development of new photodiode designs combining an efficient charge dissociation with a low dark current. Previously reported architectures based on HgTe/Ag2Te stacks appear to be suboptimal for cutoff wavelengths below 2.5 μm. Here, we show that the introduction of a thin and strongly coupled CdSe layer acting as an electron transport layer and a unipolar barrier drastically improves the electrical performances. This diode achieves a responsivity as high as 0.8 A W–1, corresponding to an internal efficiency above 90% for a 2 μm cutoff wavelength. The specific detectivity is close to 1011 Jones at room temperature and reaches 9 × 1011 Jones at 200 K, the highest value reported for a HgTe nanocrystal-based photodiode with operation around 2 μm. The diode time response can be as short as 200 ns and appears to be limited by band bending dynamics as revealed by time-resolved photoemission measurements.