Model based prediction of the trap limited diffusion of hydrogen in post-hydrogenated amorphous silicon

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Morphology and Hydrogen in Passivating Amorphous Silicon Layers

Hydrogenated intrinsic amorphous silicon ((i)°a-Si:H) can be grown by plasma-enhanced chemical vapor deposition with a non-columnar or columnar morphology. Nuclear resonant reaction analysis and corresponding effective stopping cross section analysis indicate a dependency of hydrogen effusion on the morphology of the (i)°a-Si:H layer as well as the doping type and concentration of the c-Si wafer. The doping type of the c-Si wafer also affects the growth of the amorphous network. It is found that for moderately doped p-type c-Si a non-columnar (i)°a-Si:H layer yields a significantly better and more stable passivation already during thermal anneal and illumination, while for passivating n-type c-Si a columnar layer is recommended. Passivating lowly doped c-Si by (i)°a-Si:H is not dependent on morphology. Combining different (i)°a-Si:H morphologies to a multi-layer stack improves the quality of surface passivation. Hydrogen embedded in a well passivating but hydrogen-permeable columnar layer supports good surface passivation when covered by a non-columnar layer, featuring a fast growing layer acting as a hydrogen barrier and enhancing surface passivation quality

Fundamental Studies of Hydrogen at the Silicon / Silicon Nitride Interface

The quality of the interface between silicon and a dielectric is one of the main influencing parameters for crystalline silicon surface passivation. In this work, this interface is examined by means of capacitance voltage (CV) and nuclear resonance reaction analysis (NRRA) measurements for SiNx:H as well as SiO2 capped SiNx:H passivated p-type float zone silicon samples. Due to a highly sensitive NRRA measurement setup, very small differences in hydrogen concentration at the interface could be detected for the first time and a significant correlation between hydrogen concentration, interface state trap densities Dit and passivation quality is found. The results of this study present easily implementable processes to improve the quality of SiNx:H surface passivation and process stability for solar cell and module production applications. First optimised industrial type Al-BSF p-type cells feature 2 mV and 0.5 mA/cm² gains in Voc and jsc, leading to efficiencies of up to 19.1%

Investigation of Hydrogen Dependent Long-Time Thermal Characteristics of PECV-Deposited Intrinsic Amorphous Layers of Different Morphologies

Hydrogenated intrinsic amorphous silicon ((i) a-Si:H) layers deposited on n-type crystalline silicon (c-Si) by plasma enhanced chemical vapour deposition (PECVD) are investigated during long-time thermal treatment (100 h at 200°C) with regard to the depth profile of hydrogen in the a-Si layer and its diffusion into the c-Si bulk. The morphology of the (i) a-Si:H is manipulated by the PECVD process parameters. A columnar and a non-columnar growth can be distinguished. Microscopic investigations are carried out by scanning electron microscopy (SEM). Minority carrier lifetime (eff) measurements permit an evaluation of the surface passivation and thus the saturation of defects like dangling bonds at the (i) a-Si:H/c-Si interface. A non-columnar structure leads to a high stability of the passivation during thermal treatment of up to 100 h. In contrast a columnar structure of the amorphous silicon layer results in a better but less stable passivation of the c-Si wafer surface. Microvoids in the columnar layer are the reason for this behavior. Fourier transform infrared spectroscopy (FTIR) measurements confirm the formation of microvoids, i. e. a high concentration of Si-H2 bonds. Investigating the changes in hydrogen depth profile by nuclear resonant reaction analysis (NRRA) reveals a higher loss in hydrogen concentration during thermal treatment of the (i) a-Si:H layers with columnar morphology. The hydrogen concentration profiles as measured by NRRA illustrate the dependency of passivation quality with time on the specific morphology of different amorphous layers

About Nuclear Resonant Reaction Analysis for Hydrogen Investigations in Amorphous Silicon

Nuclear Resonant Reaction Analysis (NRRA) is a common method detecting the nearsurface hydrogen distribution of a sample in a depth of up to a few microns. The mass density and related stopping power of a hydrogenated amorphous silicon (a-Si:H) layer depends on the hydrogen content. Correct hydrogen depth profiles are calculated considering the effective ion beam stopping crosssection as well as the related stopping power of the investigated film. The consideration of the local hydrogen concentration is important to avoid misinterpretations of the hydrogen distribution regarding profile depth. Therefore, stopping powers have to be considered carefully when interpreting hydrogen depth profiles especially of films that exhibit variations in hydrogen concentration. Moreover, further investigations like morphology dependent changes of the effective stoppingcross section are not possible without correctly calculated hydrogen depth profiles. Here the correct way is presented how to consider the embedded hydrogen of an a-Si:H layer when calculating absolute depth information of a NRRA measured hydrogen depth profile.publishe