Y.N. Guo

Dilution effect of Ar/H2 on the microstructures and photovoltaic properties of nc-Si:H deposited in low frequency inductively coupled plasma

This work reports upon the dilution effect of Ar + H2 on the microstructures, optical, and photovoltaic properties of the hydrogenated nanocrystalline silicon (nc-Si:H) thin films. High crystallinity (up to 82.6%) nc-Si:H thin films were fabricated from silane diluted by Ar + H2 in a low-frequency inductively coupled plasma (LFICP) facility at a low temperature of 300 °C. The substitution of H2 by Ar in the diluent gas leads to an increase of the deposition rate, grain size, and crystallinity, and a decrease of the optical bandgap. Varying the Ar content caused a fluctuation of the H concentration and a change of the preferential orientation from (111) to (220) in the synthesized thin films. These effects physically originated from changes of the Ar + H2 + SiH4 plasma environment in the LFICP system. The enhancement of the dissociation of SiH4/H2 molecules by ion Ar+ and the metastable state Ar* were discussed in terms of related chemical reactions between the diluent gases and silane. Furthermore, it was...

Crystalline silicon surface passivation by intrinsic silicon thin films deposited by low-frequency inductively coupled plasma

Amorphous and microcrystal hydrogenated intrinsic silicon (a-Si:H/μc-Si:H) thin films with good silicon surface passivation effect were deposited using a precursor gases of silane and hydrogen, which were discharged by low frequency inductively coupled high density plasma source. With regard to silicon surface passivation, the effect of discharge power on thin films properties, including the optical band gap, the crystal fraction, and bond configuration, as well as the deposition rate were thoroughly investigated. It was found that the best passivation effect was obtained at the region near the transition regime from a-Si:H to μc-Si:H with a minimized incubation layer between the passivation layer and substrate. Cz-silicon wafer passivated by as-deposited μc-Si:H thin films without any post-deposition thermal annealing possesses minority carrier lifetime of about 234 μs. This is attributed to the chemical annealing from the high-density hydrogen plasma during the deposition process. Subsequent thermal ann...

Low-temperature deposition of µc-Si : H thin films by a low-frequency inductively coupled plasma for photovoltaic applications

Low-temperature depositions of Si films from hydrogenated amorphous silicon (a-Si : H) to highly crystallized hydrogenated microcrystalline silicon (µc-Si : H) were realized by the low-frequency inductively coupled plasma (LF-ICP) technique, with low hydrogen dilution (50%) and without any intentional substrate heating. µc-Si : H films with a thin incubation layer ( 0.8). Low-temperature growth of µc-Si : H is attributed to high atomic H flux and suppression of high-energy ion bombardment due to the high density of low-temperature electrons in the plasma. A µc-Si : H solar cell with a less dense intrinsic layer (on a SnO2 : F glass substrate) exhibits a high Voc (584 mV), showing great potential for photovoltaic applications.

Effect of silane/hydrogen ratio on microcrystalline silicon thin films by remote inductively coupled plasma

Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by remote low frequency inductively coupled plasma (ICP) chemical vapor deposition system, and the effect of silane/hydrogen ratio on the microstructure and electrical properties of μc-Si:H films was systematically investigated. As silane/hydrogen ratio increases, the crystalline volume fraction Fc decreases and the ratio of the intensity of (220) peak to that of (111) peak drops as silane flow rate is increased. The FTIR result indicates that the μc-Si:H films prepared by remote ICP have a high optical response with a low hydrogen content, which is in favor of reducing light-induced degradation effect. Furthermore, the processing window of the phase transition region for remote ICP is much wider than that for typical ICP. The photosensitivity of μc-Si:H films can exceed 100 at the transition region and this ensures the possibility of the fabrication of microcrystalline silicon thin film solar cells with a open-circuit voltage of abo...

Silicon homojunction solar cells via a hydrogen plasma etching process

We report on the one-step formation of an efficient Si homojunction solar cell produced by a simple exposure of p-type Si wafers to low-temperature inductively coupled hydrogen plasma. The formation of oxygen thermal donors during hydrogen plasma treatment is responsible for the conductivity type conversion and the final formation of Si homojunction. The hydrogen plasma etching with suppressed heavy ion bombardment results in a relatively flat surface, which is favourable for deposition of passivation layers such as silicon nitride. The integrated Si homojunction solar cell consisting of Al/p-c-Si/n-c-Si/SiN/Al-grid has demonstrated a maximum photovoltaic conversion efficiency of 13.6%.

Phase evolution and room-temperature photoluminescence in amorphous SiC alloy

Amorphous SiC thin films with varying phases and compositions have been synthesized using a low frequency inductively coupled high density plasma source in a hydrogen diluted methane (CH4) and silane (SiH4) mixture. The optical and electrical properties along with the microstructures of the thin films are systematically investigated. The feedstock gas ratio of CH4/SiH4 leads to the fluctuations of the optical bandgap, the carbon content, and the transition of Si–Si bonding structure from crystalline to intermediate phase and finally to amorphous phase. Room temperature photoluminescence (PL) with nearly fixed emission energy has been observed in the thin films. The underlying PL mechanism is explained in the framework of quantum confinement-luminescence center model. The photoexcitation process occurs in the nc-Si quantum dots embedded in the host SiC matrix, whereas the photoemission process occurs in the luminescence centers in the surrounding SiC or at SiC-Si interfaces. The PL evolution with the chemi...