Characterization of Epitaxial Heavily Doped Silicon Regions Formed by Hot-Wire Chemical Vapor Deposition Using Micro-Raman and Microphotoluminescence Spectroscopy

Tasmiat Rahman,Hieu T Nguyen,Stuart A Boden,Daniel Macdonald,Antulio Tarazona,Young-Joon Han,Jingxing Shi,Evan Franklin

doi:10.1109/jphotov.2018.2818284

Abstract

We report on the characterization of heavily boron doped epitaxial silicon regions grown in a hot-wire chemical vapor deposition tool, using micro-Raman and photoluminescence spectroscopy. In particular, the use of this approach for emitter fabrication in an interdigitated back contact silicon solar cell is studied, by analyzing its suitability concerning selective growth, uniformity, anneal time, and luminescent defects. We show that by reducing the silane flow rate, both the required postanneal time and intensity of defect luminescence are reduced. Furthermore, we show that selective area growth does not affect either the quality of the films or the sharpness of the resulting lateral doping profile. The uniformity of the doping is shown to be better than that achieved using laser doping.

Highlights

I NTERDIGITATED back contact (IBC) architectures are amongst the highest efficiency silicon solar technologies
A c-Si substrate gives a sharp Stoke-shift Raman peak at ∼520.7 cm−1, whereas amorphous silicon (a-Si) gives a broad peak located around ∼480 cm−1 [37]
The intermediate peak is attributed to microcrystalline silicon, and its position and width are dependent on the grain size of the crystal [37], [38]

Summary

INTRODUCTION

I NTERDIGITATED back contact (IBC) architectures are amongst the highest efficiency silicon solar technologies. Various approaches exist for forming the p- and n- type selective contact regions in an IBC solar cell, including high temperature diffusions with gaseous dopant sources of BBr3 and POCl3 [4], [5], as well as ion implantation [6]. We have undertaken a study to understand the influence of reduced silane rates, annealing times, and selective area growth on doping quality and luminescent defects. To characterize these parameters effectively, photoluminescence (PL) imaging, micro-PL spectroscopy and micro-Raman spectroscopy are used. Micro-PL spectroscopy is used to compare doping uniformity in selective area growth regions with that of doped regions formed by scanning, pulsed nanosecond laser doping

Process

Characterization

RESULTS

Reducing Silane Flow Rate

Selective Area Width

CONCLUSION