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.

Thin films of nanocrystalline SiO x N y are studied in view of their application in silicon heterojunction (SHJ) solar cells. In particular, the formation of the nanocrystals and their effects on the electrical and optical properties of the films are investigated. The role of the oxygen content on the properties of the layers is clarified as well. The obtained layers show very high conductivity (44 S/cm), low activation energy (1.85 meV) and high Tauc gap (2.5 eV), promising features for their application in photovoltaics.

No abstract

a b s t r a c t a r t i c l e i n f oAmorphous silicon (a Si) is common in the production of technical devices and can be deposited by several techniques. In this study intrinsic and doped, hydrogen less amorphous silicon films are RF magnetron sputter deposited and post hydrogenated in a remote hydrogen plasma reactor at a temperature of 370°C. Secondary ion mass spectrometry of a boron doped (p) a Si layer shows that the concentration of dopants in the sputtered layer becomes the same as present in the sputter target. Improved surface passivation of phosphorous doped 5 Ω cm, FZ, (n) c Si can be achieved by post hydrogenation yielding a minority carrier lifetime of~360 μs finding an optimum for~40 nm thin films, deposited at 325°C. This relatively low minority carrier lifetime indicates high disorder of the hydrogen less sputter deposited amorphous network. Post hydrogenation leads to a decrease of the number of localized states within the band gap. Optical band gaps (Taucs gab as well as E 04 ) can be determined to~1.88 eV after post hydrogenation. High resolution transmission electron microscopy and optical Raman investigations show that the sputtered layers are amorphous and stay like this during post hydrogenation. As a consequence of the missing hydrogen during deposition, sputtered a Si forms a rough surface compared to CVD a Si. Atomic force microscopy points out that the roughness decreases by up to 25% during post hydrogenation. Nuclear resonant reaction analysis permits the investigation of hydrogen depth profiles and allows determining the diffusion coefficients of several post hydrogenated samples from of a model developed within this work. A dependency of diffusion coefficients on the duration of post hydrogenation indicates trapping diffusion as the main diffusion mechanism. Additional Fourier transform infrared spectroscopy measurements show that hardly any interstitial hydrogen exists in the post hydrogenated a Si layers. The results of this study open the way for further hydrogen diffusion experiments which require an initially unhydrogenated drain layer.

The annealing effect on the properties of silicon oxynitride (SiO x N y) thin films has been investigated. The present contribution aims to study the structural and optical properties of SiO x N y thin films deposited by plasma enhanced chemical vapor deposition in view of their application in the field of photovoltaics. Evolution of the surface morphology and increase of the optical band gap with the thermal treatment have been determined and discussed in view of the application of the film as an emitter layer in heterojunction solar cells.