Effective hydrogen diffusivity in n- and p-type crystalline silicon from 300 to 450 °C

Abstract

We study hydrogen diffusion in silicon by annealing wafers with hydrogen-rich aluminum oxide layers on one surface and intrinsic PECVD silicon films acting as a hydrogen capture sink on the other surface. The hydrogen concentration in the silicon film is monitored via spectrally resolved sub-bandgap photoluminescence, calibrated by comparison with time-of-flight secondary ion mass spectrometry measurements. This provides a convenient and rapid method for hydrogen concentration measurements. Modeling the kinetics of the increasing hydrogen concentration in the silicon film as hydrogen diffuses through the wafer allows the effective hydrogen diffusivity to be extracted at annealing temperatures of 300–450 °C, a range that is relevant for silicon solar cell technology, but has not often been directly measured. The extracted hydrogen diffusivities in undoped silicon and both moderately and heavily doped n- and p-type silicon are compared with the existing literature reports. The results match very well with the model of Herring et al. for moderately doped n-type and undoped silicon. For heavily doped n-type and p-type silicon with different dopant concentrations, however, we report significantly reduced effective hydrogen diffusivity values. Finally, we present the modeling of hydrogen charge states in differently doped silicon and consider possible explanations for the reduction in effective hydrogen diffusivity.