Integration of GaAsP alloys on Si for high-efficiency Ill-V/Si PV

Abstract

Introduction: The motivation of this work is to create a platform that leverages the large area and low cost of Silicon wafers with the high performance of Ill-V materials. Ill-V semiconductor materials have enabled a host of electronic devices from record setting solar cells, high efficiency light emitting diodes, power amplifiers and high-mobility electron transistors. The last 60 years of research and development by the Si microelectronics industry has made the use of Si for microelectronics, power electronics and photovoltaics (PV) ubiquitous and low cost. The low cost of silicon technology is due to a mature and well developed supply chain infrastructure built from the microelectronics industry. While there has also been decades of research into III-V materials and electronic devices, widespread utilization has been limited due to the high cost of Ill-V substrates. Consequently Ill-V technologies have been limited to applications of high value added devices. Integration of high quality Ill-V materials on Si would open new dimensions of design space for electronic devices with high performance and at low cost. Potential applications could be the integration of light emitters, power amplifiers, RF radios and CMOS all on one large area low cost substrate. However, integration of these materials in non-trivial. Considerable challenges related to lattice mismatch, coefficient of thermal expansion mismatch, polarity mismatch and chemical incompatibility can degrade material quality and negate the potential benefits of Ill-V integration. This research specifically focuses on how to overcome these integration challenges to enable a high-efficiency, low-cost Ill-V/Si tandem solar cell. While the project motivation is solar, integration of Ill-V on Si in amenable for many semiconductor applications and the processes developed here can be generalized for other device structures. This research investigates the effect of growth processing parameters on the microstructure, electronic and optical properties of GaAsxP1 x alloys grown on Si substrates. From the knowledge gained in those studies, we demonstrate world class GaAsxP1 x single junction solar cells grown on Si substrates. This body of work serves as a demonstration of the potential of GaAsxP1 x solar cells integrated with Si solar cells and provides a tool kit for further optimization of cell design, processing and implementation.