MBE growth of 1.7eV Al0.2Ga0.8As and 1.42eV GaAs solar cells on Si using dislocations filters: an alternative pathway toward III-V/ Si solar cells architectures

Metamorphic epitaxial growth of III-V solar cells on Si has attracted significant interest for the development of III-V/Si photovoltaic architectures. In this work, we present an alternative pathway - using MBE growth techniques - based on the direct nucleation of Al_xGa_1-xAs materials on Si, followed by the growth of a 1.7eV Al_0.2Ga_0.8As or a 1.42eV GaAs solar cell. Dislocation Filter Layers (DFLs), in conjunction with Thermal Cycle Annealing (TCA), have been used to reduce the Threading Dislocation Density (TDD) below 10⁷ cm^-2 in the base of the cell; close to the best results demonstrated with metamorphic buffers.

I. Introduction

Silicon-based hybrid photovoltaic devices have gained substantial academic interest in the recent years, with a wide range of absorber materials and fabrication techniques being investigated in order to overcome the efficiency limitations of crystalline silicon (c-Si) single junction photovoltaic technologies [1]–[2]. Among these approaches, epitaxial growth of III-V cells on a c-Si substrate, the latter potentially acting as a bottom cell, represents an elegant pathway. This technique-on top of taking advantage of the robust supply chain and low cost associated with market-dominant c-Si photovoltaic technologies-potentially enables the formation of the different p-n junctions of a multijunction solar cell in a single growth reactor and the use of a 2-terminal contacting architecture, leading to a possibly straightforward deposition and fabrication process.