Gallium nitride: a strong candidate to replace GaAs as base material for optical photovoltaic converters in space exploration

Abstract

High power laser transmission technology is expected to play an important role in spatial exploration. To increase the amount of power delivered, some issues must be addressed. Currently, optical photovoltaic converters are based on GaAs, a material with a bandgap energy of 1.42 eV. In this work we propose gallium nitride (GaN) as base material for optical photovoltaic converters due to its high bandgap (3.39 eV), which reduces both ohmic and intrinsic entropic losses, and its high thermal conductivity and resistance to radiation damage, making it suitable for space applications. We have optimized several GaN optical photovoltaic converter devices under a wide range of laser power densities and temperatures. The resilience to variations in the design parameters is also tested. Results show that, due to their large bandgap energy, GaN devices could suffer from fewer performance losses with the temperature when compared to other materials with lower bandgaps. The devices show great tolerance to variations in the P layer (bottom layer), while the N layer thickness and doping concentration must be carefully manufactured. When compared to GaAs-based devices, GaN shows higher efficiency across the entire laser power density range, achieving efficiencies near 80 % and surpassing the current state-of-the-art power converter by 10 % at 10 . The proposed GaN devices show a peak of performance at a laser power density as high as 100 . Although manufacturing issues could degrade the efficiency of GaN power converters, this results position GaN as a promising material for a new generation of ultra-high efficient optical photovoltaic converters.