In situ study of hydrogen diffusion in a-Si: H based junctions exposed to hydrogen plasma

Just after their deposition by plasma enhanced chemical vapor deposition (PECVD) process, we have exposed Cr/I/N, Cr/I/P, Cr/N/I and Cr/P/I a-Si:H based junctions to H ₂ plasma and followed in situ, by ellipsometry, the modifications induced by hydrogen diffusion. In the case of Cr/N/I and Cr/P/I junctions, no significant effects of the junction on the hydrogen diffusion were observed since the time-evolution of the thickness of the H-modified layer is similar to that of a single intrinsic layer. However, Cr/I/N, Cr/I/P structures present an attenuated thickness of the H-modified layer in the first few minutes of hydrogen plasma exposure. This effect should be attributed to the charges in the field regions of I/N or I/P junctions which increase the hydrogen trap concentration and restrain the hydrogen diffusion.