External Gettering of Metallic Impurities by Black Silicon Layer

Black silicon (b-Si) has many attractive properties and is currently being adopted in various fields of semiconductor technology. It is shown here that b-Si during thermal activation may serve as an external gettering layer to remove metallic impurities and associated defects from bulk Si. The gettering efficiency by b-Si is estimated according to the results of studying the resistivity, defect density, interstitial iron concentration, and effective minority carrier lifetime on gettered test and ungettered reference Si samples. It is shown that in the thermal oxidation process, the b-Si layer serves as an effective drain for excess iron atoms and other fast-diffusing impurities, thereby significantly reducing the density of oxidation-induced stacking faults in Si. In addition, the resistivity of the substrates decreases, and the bulk carrier lifetime increases significantly. Finally, gettering by b-Si is introduced into the solar cells fabrication process and its effect on solar cell current-voltage characteristics is investigated. It has been shown that all electronic parameters of the solar cells are improved. The conversion efficiency of ungettered solar cells is 16.8%, and for gettered solar cells, depending on the oxidation temperature, it increases by 1.36-1.96%.