Uncooled mid-infrared photovoltaic detector based on Pb1−xCdxSe thin films for use in non-dispersive infrared methane gas sensors

Abstract This work is focussed on sputtered lead cadmium selenide (Pb 1−x Cd x Se) thin films as the active material within high-speed room temperature mid-infrared photovoltaic (PV) detectors for use in non-dispersive infrared gas sensors. Variation of the Cd content provides a means of controlling material bandgap and hence wavelength response. Traditional methods of Pb 1−x Cd x Se deposition are thermal evaporation or chemical bath techniques which do not provide required stable deposition for accurate control of Cd content and hence wavelength response. This paper describes pulsed direct current (DC) sputter deposition of Pb 1−x Cd x Se, from a sintered pre-mixed sputter target as an alternative deposition technique. Sputtered Pb 1−x Cd x Se material characterisation is described identifying optimum Cd content as x = 0.1 for maximised response at a wavelength of 3.3 μm, matching use as a detector for methane gas detection. Work has focussed on characterising pulsed DC sputter deposition of the 3.3 μm optimised Pb 0.9 Cd 0.1 Se (n-type) and post deposition oxygen doping by thermal diffusion to create p-type Pb 0.9 Cd 0.1 Se: O thereby maximising PV detector photo-response at a specific wavelength of 3.3 μm. PV detector design, associated photolithographic mask designs/ lift-off process sequence, sputter deposition of Pb 1−x Cd x Se and Ti interdigitated electrodes for PV detector fabrication is described. The resulting 1 × 1 mm 2 PV detector device exhibited a peak detectivity D* of 1 × 10 10 , 4 × 10 9 and 3 × 10 9 cm∙Hz 1/2 ∙W −1 at 233 K, 298 K and 313 K respectively under 500 K blackbody illumination.