Electrical and optical characterization of extended SWIR detectors based on thin films of nano-columnar PbSe

There is an increasing demand for detectors with extended Short Wavelength Infrared (SWIR) absorption at wavelengths between 1.6 μm and 2.8 μm. Towards that end, PbSe absorber layers were grown by the Chemical-Bath-Deposition (CBD) technique in a nano-columnar morphology on n-type (1 0 0) oriented GaAs substrate, where the nano-columns are densely packed perpendicular to the substrate. The spectral absorption edge and photoluminescence (PL) peak of these layers were blue shifted from the bulk bandgap of 4.7 μm to 2.2 μm, i.e., within the extended SWIR range, due to quantum confinement effect. Current voltage (I-V) measurements were carried out in a vertical geometry of different circular mesa sizes (250–2000 μm in diameter). The area dependent current–voltage measurements indicate a densely packed layer with no apparent pinholes. On the other hand, it was found out that surface leakage currents on the mesa perimeters are the dominant mechanism of the dark current. A photo-response to SWIR illumination was evident, confirming the feasibility of using such structures as extended SWIR photodetectors upon minimizing leakage currents using surface treatments.