High-Performance Uncooled Mid-Infrared Detector Based on a Polycrystalline PbSe/CdSe Heterojunction.

Developing high-performance, uncooled mid-wavelength infrared (MWIR) detectors is a challenging task due to the inherent physical properties of materials and manufacturing technologies. In this study, we designed and manufactured an uncooled polycrystalline PbSe/CdSe heterojunction photovoltaic (PV) detector through vapor physical deposition. The resulting 10 µm × 10 µm device exhibited a peak detectivity of 7.5 × 109 and 3 × 1010 cm·Hz1/2·W-1 at 298 and 220 K, respectively, under blackbody radiation. These values are comparable to those of typical PbSe photoconductive detectors fabricated through standard chemical bath deposition. Additionally, the sensitization-free process used to create these PbSe/CdSe PV detectors allows for high replicability and yield, making them promising candidates for low-cost, high-performance, uncooled MWIR focal plane array imaging in commercial applications.

Epitaxial CdSe/PbSe Heterojunction Growth and MWIR Photovoltaic Detector.

A novel Epitaxial Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by Molecular Beam Epitaxy (MBE) growth of n-type CdSe on p-type PbSe single crystalline film. The use of Reflection High-Energy Electron Diffraction (RHEED) during the nucleation and growth of CdSe indicates high-quality single-phase cubic CdSe. This is a first-time demonstration of single crystalline and single phase CdSe growth on single crystalline PbSe, to the best of our knowledge. The current-voltage characteristic indicates a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement. A 30 µm × 30 µm pixel achieved a peak responsivity of 0.06 A/W and a specific detectivity (D*) of 6.5 × 108 Jones under a zero bias photovoltaic operation. With decreasing temperature, the optical signal increased by almost an order of magnitude as it approached 230 K (with thermoelectric cooling) while maintaining a similar level of noise, achieving a responsivity of 0.441 A/W and a D* of 4.4 × 109 Jones at 230 K.

Low-cost uncooled MWIR PbSe quantum dots photodiodes.

A mid-wave infrared (MWIR) uncooled PbSe-QDs/CdS p-n heterojunction photodiode has been fabricated using a wet-chemical synthesis route. This offers a low-cost alternative to traditional monocrystalline photodiodes relying on molecular beam epitaxy (MBE) technology. It was demonstrated that the post-annealing is critical to tailor the photoresponse wavelength and to improve the performance of photodiodes. After annealing at 673 K in air for 0.5 h, the ligand-free PbSe-QDs/CdS photodiode exhibits a MWIR spectral photoresponse with a cutoff wavelength of 4.2 µm at room temperature. Under zero-bias photovoltaic mode, the peak responsivity and specific detectivity at room temperature are 0.36 ± 0.04 A W-1 and (8.5 ± 1) ×108 cm Hz1/2 W-1, respectively. Temperature-dependent spectral response shows an abnormal intensity variation at temperatures lower than 200 K. This phenomenon is attributed to the band alignment transition from type II to type I, resulting from the positive temperature coefficient of PbSe. In addition, it was proved that In doped CdSe (CdSe:In) films could be used as a promising new candidate of infrared transparent conductive electrodes, paving the way for monolithic integration of uncooled low-cost MWIR photodiodes on Si readout circuitry.