Thickness reduction and doping profile optimization for enhanced radiation tolerance of GaAs multi-junction laser photovoltaic converters

High-efficiency GaAs multijunction laser photovoltaic converters (MJLPCs) show considerable potential for space laser wireless power transmission (LWPT), but their power conversion efficiency can degrade under charged-particle irradiation during in-orbit operation. In this work, a structural optimization strategy for improving the radiation tolerance of a GaAs four-junction laser photovoltaic converter is proposed. Compared with the conventional structure, the optimized device incorporates a thinned bottom cell, a 20-pair Al_0.9Ga_0.1As/Al_0.1Ga_0.9As distributed Bragg reflector (DBR) beneath the bottom cell, and a specifically designed step-doped profile in the bottom-cell base region. These modifications significantly suppress Shockley-Read-Hall (SRH) recombination caused by radiation-induced displacement defects while maintaining favorable initial optical absorption. The structural parameters are determined through device simulations based on the established irradiation degradation model and then verified experimentally. Relative to the original structure, the maximum output power ( P _max) is improved by 10.5%, while the P _max remaining factor after 1 MeV electron irradiation at a fluence of 1 × 10¹⁵ cm⁻²and 500 keV proton irradiation at a fluence of 1 × 10¹¹ cm⁻² is increased by 26.8% and 27.1%, respectively. These findings demonstrate the effectiveness of the proposed structural optimization strategy and provide guidance for the radiation-hardening design of GaAs MJLPCs for space LWPT applications.