Long-Wave Infrared HgTe Quantum Dot Photoconductors with Optical Enhancement

HgTe quantum dots are studied for long-wave infrared detection using interband absorption. The optical constant, photoluminescence, mobility, carrier lifetime, and doping are measured. Simple photoconductors are made as films on interdigitated electrodes, and the best performance is obtained with intrinsic films of quasi-spherical HgTe particles that have been cast from polar inks and exposed to HgCl₂ solutions. As the temperature is lowered to 85 K, the photoresponse extends past 8 μm. The performance is limited by a low absorption coefficient near the absorption edge and by a very short exciton lifetime as determined by the photoluminescence quantum yield of 10^-5. A metal-insulator-metal structure combined with gold nanoantennas and a 100 nm thick HgTe dot film gives a ∼20-fold increase in responsivity and detectivity for a peak resonance at 8.5 μm at 85 K. The best detectivity is 1.47 × 10¹⁰ Jones at 0.8 V bias, 25 kHz frequency, and TE polarization. An external quantum efficiency (EQE) of 12.5% is also achieved at a higher bias.