High Quality GaAs Epilayers Grown on Si Substrate Using 100 nm Ge Buffer Layer

Wei-Cheng Kuo,Chien-Chieh Lee,Huang Wen-Hsiang,Hung-Chi Hsieh,Wu Chih-Hung,Jenq-Yang Chang

doi:10.1155/2016/7218310

Wei-Cheng Kuo, Chien-Chieh Lee + Show 4 more

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https://doi.org/10.1155/2016/7218310

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Abstract

We present high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers. The thin Ge buffer layers were modulated by hydrogen flow rate from 60 to 90 sccm to improve crystal quality by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at low growth temperature (180°C). The GaAs and Ge epilayers quality was verified by X-ray diffraction (XRD) and spectroscopy ellipsometry (SE). The full width at half maximum (FWHM) of the Ge and GaAs epilayers in XRD is 406 arcsec and 220 arcsec, respectively. In addition, the GaAs/Ge/Si interface is observed by transmission electron microscopy (TEM) to demonstrate the epitaxial growth. The defects at GaAs/Ge interface are localized within a few nanometers. It is clearly showed that the dislocation is well suppressed. The quality of the Ge buffer layer is the key of III–V/Si tandem cell. Therefore, the high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers is suitable to develop the low cost and high efficiency III–V/Si tandem solar cells.

Highlights

Photovoltaics is widely recognized as one of the most desirable options yet suggested for future sustainable energy supply, with on-going cost reduction key to fulfilling this potential
GaAs epilayers grow on Ge/Si by metal organic chemical vapor deposition (MOCVD)
Crystallization rate of Ge films is the highest at H2 flow rate 80 sccm,which is consistent with the Ge quality measurement result of X-ray diffraction (XRD)

Summary

Introduction

Photovoltaics is widely recognized as one of the most desirable options yet suggested for future sustainable energy supply, with on-going cost reduction key to fulfilling this potential. III–V solar cell has the highest conversion efficiency in the world [2] This device has high cost, making it diffcult to command the solar cell market. Two different process technologies were investigated for the fabrication of III–V/Si tandem cells: direct epitaxial growth and wafer bonding. Ichikawa et al [8] proposed a four-junction III–V/Si tandem solar cell which uses thin Ge buffer layers. In this structure, Ge absorption is dependent on Ge layer thickness and Ge absorption is significantly affecting the bottom Si cell efficiency. GaAs epilayers grow on Ge/Si by metal organic chemical vapor deposition (MOCVD)

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