Doping control of GaAsPN alloys by molecular beam epitaxy for monolithic III-V/Si tandem solar cells

This paper presents intentional doping of n- and p-type GaAs0.19P0.76N0.05 alloys by molecular beam epitaxy, followed by rapid thermal annealing (RTA). Sulfur and magnesium were respectively used as n- and p-type dopants. The carrier concentrations were controllable between 1017 and 1019 cm−3 by adjusting the dopant cell temperature. It was revealed that Hall mobility of the n-type GaAsPN alloys was increased by the RTA process compared to as-grown ones, whereas no significant difference was apparent in the p-type alloys. It is believed that improvement of the conduction band spatial uniformity was mainly responsible for the Hall mobility increase of the n-type GaAsPN alloys by RTA. Finally, a p-i-n GaAsPN diode structure was grown on n-type GaP substrates. A current-voltage characteristic showed a typical rectifying curve with a built-in voltage of 1.8 V and an ideality factor of 1.45. The reverse saturation current was estimated to be less than 10 nA/cm2.