Impacts of phosphorus and aluminum gettering with porous silicon damage for p-type Czochralski silicon used in solar cells technology

Abstract

In this paper, porous silicon damage (PSD) is introduced like a simple sequence for efficient extrinsic gettering schemes. The technique consists to create a sacrificial porous silicon layer on both sides of the silicon substrates with randomly hemispherical voids. Then, two main sample types are processed. In the first group, thin aluminium layers (≥ 1 μm) are thermally evaporated followed by photo-thermal annealing at 700 and 800 °C, under N 2 atmosphere. In the second group, phosphorous is continually diffused during heating at one of several temperatures ranging between 750 and 950 ° C for 1 h in a solid phase from POCl 3 solution, in N 2/O 2 ambient. Hall Effect and Van Der Pauw methods prove the existence of an optimum temperature in the case of phosphorus gettering equal to 900 °C yielding a hall mobility of about 982 cm 2 V − 1 s − 1 . FTIR investigations show an increase of interstitial oxygen enhancing the precipitation phenomena and proving that extrinsic and intrinsic gettering are in work at the same time. However, in the case of aluminum gettering, there isn't a gettering limit in the as mentioned temperature range. Moreover, silicon solar cells are processed to clarify this effect.