硅上多晶磷化铟的生长和表征

Abstract

IIl-V thin film solar cells attract large interest among the scientific community as ahighly efficient solar energy source. High cost of the Ill-V materials, however, is thefundamental limitation for using these materials as a household energy sourceIntegrating these materials on low cost and large area Si wafer both for photovoltaicand photonics application is a field of research that draw intense attention of thescientific community. The fundamental challenge to fabricate Ill-V materials directlyon silicon wafers arises from the disparity in polarity, large lattice and thermalmismatch between the II-V semiconductors and Si.

In this work, we introduce a method to synthesize polycrystalline InP directly onsilicon wafer by using InO; or In as intermediate material. The crystal quality andconversion degree of the intermediate material and the final poly-InP were analyzedby Powder X-ray Diffraction. Depending on the type of the intermediate material andsubstrate orientation (Si (100) or Si(111)), the crystallite size was found to be varyingfrom 739 to 887 nm. The surface morphology of poly-ln was studied by usingAtomic Force Microscopy. The root mean square surface roughness of the InP thin film was found to be varying from 314 to 1944 nm. Structural and optical qualities ofintrinsic and sulfur doped InP layers were compared at different growth conditionsgrowth time, growth temperature, PH; source flow), intermediate material type(InO and In) and substrate type (Si (100) and Si (111)). Within the investigatedexperimental parameter range, the higher PH; source flow at longer growth time improved the structural quality of InP layer grown on InO; coated on silicon substrate,which also result in good optical quality.

Comparison of structural and optical qualities of lnP grown from In and indium oxideprecoated substrates show that the former gave better quality InP. These achievementswill be helpful in the realization of the high efficiency Ill-V solar cell on silicon substrate as a low cost option.

Introduction

1.1 Why Polycrystalline InP on Silicon Substrate?

IIl-V semiconductor solar cells have demonstrated the highest power conversionefficiencies to date (1]. Specifically, InP and GaAs have the most ideal band gaps andhighest theoretical efficiencies for single-junction cells. InP solar cells have shownsuperior radiation resistance when compared to GaAs and silicon solar cells, whichmakes them ideal for space applications.

However, the cost of Ill-V semiconductor solar cells is too high for household or touse as a common energy source. This is mainly due to the insufficient availability ofthe elements that make up the Ill-V compound semiconductors in nature. In addition.the Ill-V semiconductors are very fragile and the size of the wafers is limited. On theother hand, silicon is mechanically strong, largely abundant and large wafers can be produced.

Integrating the Ill-V materials with silicon can give the combined advantages of largesize and low-cost Ill-V solar cells. Therefore, this thesis mainly focuses on a methodof synthesizing polycrystalline InP on Si by combining both chemical and epitaxialtechniques, a generic approach to achieve low cost and high efficiency solar cells.