The role of traps in dark current and photocurrent of chemical bath deposition grown nano-domains PbS/GaAs heterojunction layers

Lead sulfide (PbS) nano-domain (ND) thin layers were grown by a chemical bath deposition technique on a heavily doped n-type GaAs substrate forming a heterojunction. The PbS NDs' absorption was blue shifted from its original wavelength due to the quantum confinement effect (by controling their sizes below the Bohr radius) to sense short wavelength infrared (SWIR) light (ranging between 1200 and 1800 nm). In order to assess the electrical properties of the PbS ND based layers to be used as a SWIR detector, we performed electrical measurements that included current–voltage (I–V), capacitance–voltage (C–V), electron impedance spectroscopy (EIS), and transmission electron microscopy (TEM). The I–V measurements showed hysteresis behavior that was found to be imposed by the high trap concentration within the PbS NDs and at the layer interfaces. The hysteresis that was demonstrated during the electrical measurement is explained by the slow filling of the trap within the PbS ND thin layer. In order to reduce the trap density, we performed a thermal treatment at 150 ° C for 30 min prior to the electrical measurements. Using C–V measurements, we expected to find a reduction in the capacitance due to the decrease of the trap density after the thermal treatment. However, we discovered an increase in the capacitance, where temperature-dependent I–V measurements revealed an additional slow charging mechanism in series with the heterojunction. We found that this can be attributed to the generation of a thin isolation layer at the interface between the PbS-NDs layer and the GaAs substrate that also contains interface traps induced by the thermal treatment that was performed in an air atmosphere. We corroborated our assumption by performing EIS measurements and TEM analysis, which showed the generation of a thin isolation layer at the PbS/GaAs interface.