CdSe:In Mid-infrared transparent conductive films prospering uncooled PbSe/CdSe heterojunction photovoltaic detectors

Abstract

Infrared transparent and conductive coatings (ITCCs) are in significant demand in infrared imaging applications. The combination of high optical transparency in the infrared range (1–12 μm) and high electrical conductivity, however, sets stringent requirements on ITCC materials. A high carrier concentration (> 10²⁰ cm⁻³) employed for high conductivity commonly results in a dramatic drop in the transparency and a distinguishable cutoff blueshift (<2 μm) due to the plasmon effect, which is unable to meet the requirements of infrared optoelectronic devices. To overcome this technical issue, herein, we demonstrate indium-doped cadmium selenide (CdSe:In) ITCC electrodes with high transparency in the infrared range and excellent conductive properties. After optimizing the In/CdSe beam flux ratio and substrate temperature, a champion sheet resistance of 22 Ω per sq was achieved on a BaF₂ substrate with an electron concentration of 7.6 × 10¹⁸ cm⁻³ and a mobility of 307 cm² V⁻¹ s⁻¹. The average transmittance is 75% in the 1.0–6.0 μm middle-wavelength infrared (MWIR) range, and more than 50% in the 8–10 μm long-wavelength infrared range (LWIR). By using CdSe:In as an ITCC electrode, we demonstrated an uncooled Au/PbSe/CdSe/CdSe:In/quartz heterojunction photovoltaic detector array. An uncooled PbSe/CdSe PV detector of 50 × 50 μm exhibits an MWIR spectral photo response 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 0.075 A W⁻¹ and 1.02 × 10⁹ cm Hz^1/2 W⁻¹, respectively. Therefore, a CdSe:In ITCCs and PbSe/CdSe heterojunction PV detector provides a technical solution for the manufacturing of low-cost megapixel uncooled lead salt FPA imagers.