Optically resonant structures for the enhancement of polycrystalline PbSe photoconductors
The mid-wave infrared (MWIR) regime of the electromagnetic spectrum is attractive for long-range imaging systems due to the atmospheric window between 3 and 5 [mu]m. Due to ambient thermal background, it is often necessary to operate sensor systems below room temperature to achieve an adequate signal-to-noise ratio (SNR). This cooling requirement adds size, weight, and complexity to systems in which these parameters are at a premium. In this work I investigated two methods for optically enhancing the absorptive properties of lead selenide (PbSe) photoconductive films to increase the operating temperature up to 290 K, thereby mitigating system cooling requirements. By employing surface plasmon resonant (SPR) and embedded reflective structures, we were able to demonstrate enhanced responsivity and raise the operating temperature to room-temperature. Sensitivity was observed to increase by a factor of three for SPR enhanced detectors, and up to two-times at room temperature in detectors with an embedded Pt back reflector. Moreover, PbSe detectors with SPR discs operating at room temperature were observed to have responsivity comparable to reference detectors at 230 K. Photoconductors with the embedded Pt back reflector had a performance at room temperature that was similar to the reference detector at 250 K. Herein, I discuss my design process, as well as the fabrication of these resonant structures. Also discussed are the measurement and test results I obtained from surface plasmon and embedded reflector enhanced PbSe detectors. In this dissertation, I present results that demonstrate the viability of SPR and interference structures as mechanisms for increasing the operating temperature of PbSe MWIR photodetectors up to 290 K
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