(GexSi1-x:H) films are of much interest for many device applications because of narrow band gap and compatibility with films deposited by plasma. However, electronic properties of GexSi1-x:H films for high Ge content x > 0.5 have been studied less than those of Si films. In this work, we present a study of sub-gap photoconductivity (σpc) in GexSi1-x:H films for x = 1 and x = 0.97 deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) with both various H-dilution (RH) during growth (non-doped films) and boron (B) incorporation in the films. Spectra of sub-gap photoconductivity σpc(hν) were measured in the photon energy range of hν = 0.6 to 1.8 eV. σpc(hν) spectra were normalized to constant intensity. For hν < Eg two regions in σpc(hν) can be distinguished: “A”, where σpc is related to transitions between tail and extended states, and “B”, where photoconductivity is due to defect states. σpc(hν) in ”A” region showed exponential behavior that could be described by some characteristic energy EUPC similar to Urbach energy EU in spectral dependence of optical absorption. EUPC > EU was observed in all the films studied. This together with higher relative values (i.e. normalized by the maximum value at hν = Eg) for photoconductivity comparing with those for α means that mobility-lifetime product (μτ) depends on photon energy μτ = f(hν) that was determined from α(hν)and σpc(hν). μτ(hν) increases by factor of 20 to 40 depending on the sample with reducing hν from 1.1 to 0.7 eV. In some samples, this dependence was monotonous, while in others demonstrated maxima related to both interference and density of states. Effects of both RH and boron incorporation have been found and are discussed.

Variable frequency microwaves (VFM) and rapid thermal annealing (RTA) were used to activate ion implanted dopants and re-grow implant-damaged silicon. Four-point-probe measurements were used to determine the extent of dopant activation and revealed comparable resistivities for 30 seconds of RTA annealing at 900 °C and 6-9 minutes of VFM annealing at 540 °C. Ion channeling analysis spectra revealed that microwave heating removes the Si damage that results from arsenic ion implantation to an extent comparable to RTA. Cross-section transmission electron microscopy demonstrates that the silicon lattice regains nearly all of its crystallinity after microwave processing of arsenic implanted silicon. Secondary ion mass spectroscopy reveals limited diffusion of dopants in VFM processed samples when compared to rapid thermal annealing. Our results establish that VFM is an effective means of low-temperature dopant activation in ion-implanted Si.

We investigate the effect of hydrogenation of grain boundaries on the performance of solar cells for hydrogenated nanocrystalline silicon (nc-Si:H) thin films. Using hydrogen effusion, we found that the amplitude of the lower temperature peak in the H-effusion spectra is strongly correlated to the open-circuit voltage in solar cells. This is attributed to the hydrogenation of grain boundaries in the nc-Si:H films.

Purified Si film is prepared directly from metallurgical-grade Si (MG-Si) by chemical transport using subatmospheric-pressure H2 plasma. The purification mechanism is based on the selective etching of Si by atomic H. Since most metals are not etched by H, this process is efficient to reduce metal impurities in Si films. It is demonstrated that the concentrations of most metal impurities (Fe, Mn, Ti, Co, Cr, Ni, etc.) in the prepared Si film are in the acceptable range for applying it to solar-grade Si (SOG-Si) material, or below the determination limit of the present measurements. On the other hand B and P atoms, which make volatile hydrogen compounds such as B2H6 and PH3, are difficult to eliminate by the present principle. From the infrared absorption measurements of the etching product produced by the reaction between H2 plasma and MG-Si, it is found that the main etching product is SiH4. Therefore, a remote-type chemical transport process is possible to produce SiH4 gas directly from MG-Si. Combining other purifying principle (such as a pyrolysis filter), this process may have an advantage to eliminate B2H6 and PH3 from the produced SiH4 gas.