Polycrystalline PbSe on a polyimide substrate

In addition to the films of lead salts used in the photoconductive IR detectors, we quest for the polycrystalline films appropriate to the photovoltaic detectors. This work focues on PbSe, for it exhibits Auger coefficient much lower than HgCdTe and still lower compared to PbTe. To provide thermal and mechanical stability, we chose a pseudo-crystalline polyimide for being the films deposition substrate. Various regimes regarding the substrate temperature at the deposition process, and its duration managing the film thickness, were probed. The films were characterized structurally and morphologically. To determine the type of carriers, their concentration and mobility, effect of Hall and electrical conductivity were measured in the range 77–300K. To infer on the optical quality of the films, the IR reflectance and transmittance spectra at 300K were measured in the range 1–5.3μm. These diverse characterizations allowed us to find a regime optimal for growing the films with good grain crystallinity and relatively small surface roughness. Using optical bi-layer model, we showed that the measured IR spectra of these films are compatible with some effective-medium complex refractive index, the extracted effective band gap energy being about the same as that for bulk PbSe.