Application of Stain Etched Porous Silicon in Solar Cells and Light Emitting Diodes

Abstract

Nano-porous silicon/c-Si heterostructures have been formed by stain etching (SE). The properties of solar cells (SC) and light emitting diodes (LED) have been studied. In the earlier applications of porous Si (PS) to SC, it was used as an emitter [1,2]. The high values of the PS resistivity, however, require use of a thin PS layer and optimization of the contact grid, to obtain higher values of the short circuit current. Another approach is to apply PS as an anti-reflection coating, because of the good reported properties [3]. The method of SE proposed by us [3] offers the advantage of a very simple technology, which could be integrated with the SC fabrication process. In this method, an Al film is evaporated onto the surface of the n+-diffusion layer in c-Si. A thin a-SiC:H film is then deposited by magnetron sputtering through a grid mask over the Al film, before the SE. It is used to protect the Al contact below it during the SE process. As the prepared structure is subjected to SE, PS is formed only between the Al grid lines. Application of PS in SC results in an increase in the short circuit current, and in the efficiency of the cells, of about 30%. The transport mechanism in the LED structures has been investigated from the I-V characteristics measured at different temperatures. A model based on the multi-step tunnelling of carriers at reverse and low forward bias ( 1.5V), is proposed for the LEDs. [1] D.Dimova-Malinovska, M.Tzolov. N.Tzenov, D.Nesheva, Thin Solid Films, 297 (1997) 285. [2] S.Bastide, S.Strehlke, M.Cuniot, A.Bourty-Forveille, Q.N.Le. D.Sarti, C. Levy-Clement, Proc.13th EPVECE, (H.S. Skephew and Ass. Publ., Bedford, UK, 1995) p.1280. [3] D.Dimova-Malinovska, M.Sendova-Vassileva, N.Tzenov, M.Kamenova, Thin Solid Films, 297 (1997) 9.