Multijunction Solar Cell Mesa Isolation: A Comparative Study

International audienceAt the end of the fabrication process, multijunction solar cells must be electrically isolated from one to another; a step commonly known as mesa isolation. In this paper, three different techniques are assessed to perform this step: sawdicing, wet etching and plasma etching. Triple junction solar cells were fabricated with each process and the open-circuit voltages were measured in order to compare the impact of each technique on the device performance. An optional wet treatment is also proposed to clean the sidewalls after the mesa isolation process. The process throughput and the wafer area yield are also assessed for all techniques in order to determine which one is the most suitable from the industrial standpoint. This study indicates that a plasma etching process followed by a wet clean is the process that maximizes the solar cell performance, the process throughput and the wafer area yield. EXPERIMENTS Multijunction solar cells were fabricated using the process presented in fig 1. The starting epiwafers (fig 1a) are quantum dot-enhanced III-V/Ge triple junction heterostructure with an InGaP top cell, an (In)GaAs middle and a G