Evaluation of the influence of an embedded porous silicon layer on the bulk lifetime of epitaxial layers and the interface recombination at the epitaxial layer/porous silicon interface

Abstract

Porous silicon plays an important role in the concept of wafer-equivalent epitaxial thin-film solar cells. Although porous silicon is beneficial in terms of long-wavelength optical confinement and gettering of metals, it could adversely affect the quality of the epitaxial silicon layer grown on top of it by introducing additional crystal defects such as stacking faults and dislocations. Furthermore, the epitaxial layer/porous silicon interface is highly recombinative because it has a large internal surface area that is not accessible for passivation. In this work, photoluminescence is used to extract the bulk lifetime of boron-doped (1016/cm3) epitaxial layers grown on reorganised porous silicon as well as on pristine mono-crystalline, Czochralski, p+ silicon. Surprisingly, the bulk lifetime of epitaxial layers on top of reorganised porous silicon is found to be higher (~100-115s) than that of layers on top of bare p+ substrate (32-50s). It is believed that proper surfa ce closure prior to epitaxial growth and metal gettering effects of porous silicon play a role in ensuring a higher lifetime. Furthermore, the epitaxial layer/porous silicon interface was found to be ~250 times more recombinative than an epitaxial layer/p+ substrate interface (S103cm/s). However, the inclusion of an epitaxially grown back surface field on top of the porous silicon effectively shields minority carriers from this highly recombinative interface

Filling of porous silicon with magnetic materials

“…Nanostructuring of silicon leads to unique properties, different from the bulk material, such as light emission in the visible range [16][17][18], high surface area [19,20], tunable morphology [21,22], and biocompatibility [23], to name a few. Due to the porous structure it is distinguished as a template for the incorporation of various materials [24][25][26]. Molecules can be attached size-selectively due to different pore diameters [20,27], which allows the use of the system as a sensor, where the detection is mainly performed by determining the reflective index [28].…”

Effective lifetimes exceeding 300 μs in gettered p-type epitaxial kerfless silicon for photovoltaics

“…Structural defects are one possibility and are believed to originate in single-crystal epi wafers from incomplete pore closure during porous silicon annealing. 15,46 Stacking faults and dislocations are revealed in portions of Gen I (1 cm 2 ) and Gen II (4 cm 2 ) samples after gettering 47 and analyzed with an optical microscope and counting software. 48 The wafer surface area covered by regions of high (>10 5 cm…”

Manufacturing metrology for c-Si photovoltaic module reliability and durability, Part I: Feedstock, crystallization and wafering

“…High defect density may play a role in breakage and shunts. Recently, it has been shown that porosity can be completely extracted from the epi-layer if high quality material and engineered macropores with large aspect ratios are used [135]. It turns out an epi-layer is not even needed since the carefully engineered macropores can be manipulated to exfoliate a high quality thin wafer from the thick substrate [136][137][138].…”