Incomplete Dopant Ionization Effects in GaN Optical Photovoltaic Converters Over 4–400 K for Space Solar Energy Applications

We present a comprehensive numerical study of temperature- and concentration-dependent dopant ionization in GaN optical photovoltaic converters (OPCs), covering 4–400 K and doping levels from 1×10¹⁴ to 1×10¹⁸ cm⁻³. Acceptor dopants (Mg, Zn, Be) exhibit incomplete ionization at room temperature, with Mg achieving PA≈0.60 at 300 K and severe freeze-out PA < 1 below 50 K. Donor dopants (Si, O, S) are nearly fully ionized at 300 K PD > 0.95 and maintain high electron density even at cryogenic temperatures. Increasing dopant concentration mitigates acceptor freeze-out but cannot overcome intrinsic activation limits at low temperatures. These results highlight the asymmetry between p- and n-type GaN, emphasize the importance of co-doping strategies, and provide quantitative guidance for predicting carrier densities, resistivity, and device performance in high-power, space-based GaN OPCs.

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