Electrical, optical and structural investigation of plasma-enhanced chemical-vapor-deposited amorphous silicon oxynitride films for solar cell applications

Abstract

Hydrogenated amorphous silicon oxynitride (a-SiO x N y :H) films, which are deposited by the plasma decomposition of silane and nitrous oxide at low temperatures (T dep o 300 1C), are investigated in order to evaluate the potential of these films for photovoltaic applications. In this work both, intrinsic and doped a-SiO x N y :H films are investigated in terms of their electrical, optical and structural properties using Fourier-transform infra-red (FTIR) and secondary-ion mass-spectroscopy (SIMS), as well as highresolution transmission electron microscopy (HRTEM), photo-conductance decay (PCD), spectral ellipsometry and temperature-dependent conductivity measurements. The plasma deposition parameters are optimized in terms of effective minority carrier lifetime, dark conductivity and low absorbance (i.e. high optical band gap). The optical band gap of the a-SiO x N y :H films can be widened up to 2.2 eV compared to a-Si:H due to the incorporation of oxygen and nitrogen into the amorphous network. Not only the optical band gap but also the passivation quality and the dark conductivity of the films are well correlated with the oxygen and nitrogen concentration, which are monitored by means of SIMS measurements. When applying an a-SiO x N y :H film with an optical band gap of 2.0 eV, a very high effective minority carrier lifetime of 2.5 ms is measured. In case of doped films, conductivities up to s dark ¼ 4.5 Â 10 À 3 S/cm for the n-type doping and s dark ¼ 3.9 Â 10 À 4 S/cm for the p-type doping are achieved. Combining the intrinsic and doped a-SiO x N y :H films to heteroemitter stacks on a crystalline Si base, a very high implied open circuit voltage of up to 733 mV is demonstrated. FTIR and HRTEM measurements reveal a homogenous distribution of Si-Si and Si-O-Si bonds in the a-SiO x N y :H films.

Dielectric surface passivation for silicon solar cells: A review

“…Laades et al and Shwab et al corroborated previous findings on the thermal stability of SiON films, and additionally showed that H passivation played a key role in the passivation properties upon high‐temperature firing. Zhou et al systematically studied the plasma deposition parameters, while Brinkmann et al investigated the films’ electrical, optical and structural properties. They found optimal conditions for passivation with results similar to Seiffe's.…”

Effects of high-temperature treatment on the hydrogen distribution in silicon oxynitride/silicon nitride stacks for crystalline silicon surface passivation

“…Also double layer passivation systems consisting of two different silicon nitrides [6,7] or an amorphous silicon (a-Si) layer and a SiN layer [8,9] are applied. Recently, also silicon oxynitrides are investigated as passivation layer for solar cell application [10][11][12][13].…”

Investigation of optical properties of silicon oxynitride films deposited by RF PECVD method

“…From the analysis of the measured data it follows that the growth rate of the SiO x N y film is decreasing linearly with the increasing flow rate of NH 3 . The increase of the NH 3 flow rate results in the increase of the nitrogen (ammonia) to oxygen radicals ratio.…”

“…The SiO x N y films have diverse parameters, ranging from those of the silicon dioxide (SiO 2 ) to the silicon nitride (Si 3 N 4 ). The versatile properties of the films create many possibilities of application in different fields such as microelectronics [1,2], optoelectronics [3,4] or in micro-electro-mechanical systems (MEMS) technology [5].…”