In(Ga)Sb/InAs quantum dot based IR photodetectors with thermally activated photoresponse

We report on the device characterization of In(Ga)Sb/InAs quantum dots (QDs) based photodetectors for long wave IR detectors. The detection principle of these quantum-dot infrared photodetectors (QDIPs) is based on the spatially indirect transition between the In(Ga)Sb QDs and the InAs matrix, as a result of the type-II band alignment. Such photodetectors are expected to have lower dark currents and higher operating temperatures compared to the current state of the art InSb and mercury cadmium telluride (MCT) technology. The In(Ga)Sb QD structures were grown using metal-organic vapour-phase epitaxy and explored using structural, electrical and optical characterization techniques. Material development resulted in obtaining photoluminescence up to 10 μm, which is the longest wavelength reported in this material system. We have fabricated different photovoltaic IR detectors from the developed material that show absorption up to 8 μm. Photoresponse spectra, showing In(Ga)Sb QD related absorption edge, were obtained up to 200 K. Detectors with different In(Ga)Sb QDs showing different cut-off wavelengths were investigated for photoresponse. Photoresponse in these detectors is thermally activated with different activation energies for devices with different cut-off wavelengths. Devices with longer cut-off wavelength exhibit higher activation energies. We can interpret this using the energy band diagram of the dots/matrix system for different QD sizes.