Study Of Lead Selenide Thin Films Deposited By Magnetron Sputtering

The lead selenide (PbSe) thin films are widely used as the mid-infrared detectors due to the excellent photoelectric sensitivity and responsivity even at room temperature. However, the detectivity and responsivity of the domestic PbSe infrared dectetors are much lower than the foreign products, which is attributed to the lack of advanced preparation techniques and fundamental researches. Within this research, the PbSe thin films were successfully deposited on the monocrystalline silicon substrates by the mid-frequency magnetron sputtering method. The effects of the sputtering parameters, sensitizing treatment and doping treatment on the film composition, growth mechanism, crystal structure, optical and photoelectric properties were theoretically and experimentally studied. The main results are as follows:(1) The thermodynamic modeling results based on the first principles showed that the growth mechanism of the PbSe thin films is mainly affected by the interface and strain energy variation. Specially, when the interface energy variation dominates the growth mechanism, the PbSe[200] preferred growth orientation is obtained due to its lower interface energy density compared with the PbSe[220] orientation. On the contrary, when the strain energy variation dominates the growth mechanism, the PbSe[220] preferred growth orientation is obtained due to its lower strain energy density compared with the PbSe[200] orientation. Moreover, the different growth orientations of the PbSe thin films lead to different optical properties, specifically, the band gap of the [220] orientated PbSe thin films is narrower than the [200] orientated PbSe thin films, which is confirmed by the theoretical and experimental results.(2) The effects of two sputtering parameters (deposition time and temperature) were studied within this research, and the results showed that the micro-structure instead of the composition of the sputtered PbSe thin films is affected by these two parameters. Moreover, the average crystal size, lattice constant and micro-strain of the sputtered PbSe thin films decrease when the deposition time increases from 60 min to 240 min. which consequently leads to the photoelectric sensitivity of the thin films increases with the deposition time. A texture transition ([220] to [220]) was obtained at 188℃ due to growth mechanism of the sputtered PbSe thin films is dominated by the strain and interface energy variation in 50-188℃ and 188-250℃ temperature range, respectively. Besides, the photoelectric sensitivity of the sputtered PbSe thin films decreases with the deposition temperature due to the structure change.(3) An oxidation layer containing lead oxide (PbO) and selenium dioxide (SeO2) was created on the surface of the sensitized PbSe thin films, which can act as a passivation layer and inhibit the combination of the charge carriers, and consequently enhances the photoelectric sensitivity of the PbSe thin films. Moreover, the film structure transformation during the recovery (<200℃) and recrystallization (>200℃) process proceeded in the PbSe thin films leads to the equilibrium charge carriers concentration decreases linearly with the sensitizing temperature, which consequently results in the photoelectric sensitivity of the PbSe thin films increases linearly with the sensitizing temperature.(4) The doping effects of indium (In) and tellurium (Te) on the properties of the sputtered PbSe thin films were studied, and the results showed that the In atoms prefer to substitute the Pb atoms, while the Te atoms prefer to substitute the Se atoms due to the similar atomic properties. Interestingly, the deep impurity levels were created in the band gap of the PbSe thin films by the In doping element, which can act as the trap centers for the charge carries and inhibit the combination of the charge carriers, and consequently increase the photoelectric sensitivity of the In-doped PbSe thin films. Conversely, the Te-doped PbSe thin films showed similar photoelectric sensitivity to the pure PbSe thin films due to the negligible doping effects of the Te element on the band structure of the PbSe thin films.(5) The PbSe thin film infrared detector was assembled and the photoelectric sensitivity testing results showed that the peak response wavelength and responsivity is 5.43μm and 2417 V·W-1. repectively, which are smilar to the existing products. The peak detectivity of the PbSe infreared detector is 2.92×109 cm·Hz1/2W-1. which is better than the domestic products and some foreign products.