Photoconductive Cells Based on Type-II Conical Quantum Dots for Thermophotovoltaic and Other Mid-infrared Applications

Thermophotovoltaic (TPV) power generation involves the conversion of solar or other thermal energy to electrical energy using diode structures or photoconductive cells (PCCs) that respond to middle-wavelength infrared radiation. The most photovoltaic devices developed for TPV applications have bandgaps ranging from 0.5 to 0.75 eV. System modeling results have indicated the advantages of lower bandgap TPV cells. Therefore, there is a need for development in both new materials used for TPVs and in processing, to produce high-performance TPV converters. It is well known that application of quantum wells, quantum dots (QDs), and other nanostructures especially with the type-II band alignments sufficiently improved the output characteristics of traditional semiconductor devices like photodiodes, light emitting diodes, photoconductive cells (PCCs), etc. In this report, we present the results of our efforts to fabricate and investigate the low bias and room temperature PCCs made of n-InAs(100) crystals with InAsSbP composition type-II conical QDs (CQDs) on the PCC surface for TPV and other special mid-infrared applications. The modified version of liquid phase epitaxy (MLPE) is applied for the growth of CQDs. High-resolution SEM and AFM techniques are used to investigate the size, shape, and distribution density of the CQDs. Based on type-II CQDs PCCs, open-circuit voltage and short-circuit current are measured at room temperature versus output radiation power density of the He–Ne continuously operated laser at different (λ = 3.39 and 1.15 μm) wavelengths. Electrophysical and optoelectronic properties of the developed PCCs are measured and investigated. We showed that the formation of the CQDs on the n-InAs(100) surface leads to the increasing of the PCC’s electrical sheet resistance up to one order, as well as results in enlargement of the photoresponse spectrum toward the long wavelength region. The CQD-based PCC’s voltage and current responsivity at room temperature are equal to 1.2 V/W and 0.8 mA/W, respectively, at zero bias and λ = 3.39 μm monochromatic radiation. Theoretical evaluation shows increasing of CQD-based PCCs efficiency up to 10% compared with the same structures without CQDs.