Field-effect-assisted photoconductivity in PbS films deposited on silicon dioxide

Abstract

Cataloged from PDF version of article.Lead sulfide (PbS) thin films were deposited from a chemical bath onto SiO2/Si (n-type) substrates. Pseudo-metal-oxide-semiconductor devices were obtained by evaporating source and drain gold electrodes on a PbS surface and aluminum gate electrode on a Si substrate. Field-effect-assisted photoconductivity in the PbS layer was investigated at room temperature, in the 800-2700-nm-wavelength domain for different values and polarities of the drain and gate voltages. The best results were obtained for a positive gate, when both semiconductors are in depletion. An enhancement of about 25% of the photoconductive signal is obtained compared with the case when the gate electrode is absent or is not used. A simple model is proposed that explains the behavior of the dark current and photoconductive signal in PbS film with changing the gate voltage. (C) 2002 American Institute of Physics

Investigation of metal-oxide semiconductor field-effect transistor-like Si/SiO2/(nano)crystalline PbS heterostructures

“…First observation is that contrary to results reported in [14] on macroscopic PbS, the dark I-V S-D characteristics is not symmetric with respect to 0 bias and the current does not show a linear variation with bias, i.e. the source-drain contact does not behave as a simple resistance, even for zero gate bias.…”

“…The larger dark resistance is also associated with a better photoconduction, which makes these layers promising candidates for applications. It is shown later in this paper that this increased dark resistance is also associated with a field-effect mechanism of the Si-gate on the source-drain photocurrent, different from the one reported for a similar heterostructure but with a macrocrystalline PbS channel [14,15] instead of a nano-crystalline PbS layer as in the present case.…”

“…4 suggests that the photo-generated electron-hole pairs are created in Si for wavelengths in the range 500-1180 nm. The photo-signal for longer wavelengths is given by the carriers generated in the PbS layer, similar to the results reported in [14,15] for similar pseudo-MOS (n-Si)/SiO 2 /(macroscopic PbS) heterostructures. This signal increases with increasing the positive gate bias.…”

“…The dielectric constant is expected to be much larger in this case. Further on, we will consider a value of ε PbS = 175 for the static dielectric constant of our nano-crystalline PbS layers [14,17]. Assuming a complete depletion in the PbS layer, the condition of continuity for the electric displacement at the interface between PbS and SiO 2 gives V PbS cV G e SiO 2 e PbS , which means that the majority of the gate voltage drops on the SiO 2 layer.…”

“…the source-drain contact does not behave as a simple resistance, even for zero gate bias. When the source-drain I-V dependence is linear and symmetric a simple model can be developed considering that the PbS film can be divided into two regions [14]: a space charge region free of carriers near the PbS/SiO 2 interface and a neutral region. No current flows through the space charge region and the dielectric is a perfect insulator.…”