Effect of thermal annealing on the photovoltaic properties of GaP/Si heterostructures fabricated by plasma-enhanced atomic layer deposition

The effect of thermal annealing on the photovoltaic properties of a GaP/Si heterostructures obtained by plasma-enhanced atomic layer deposition under different conditions is examined. It is shown that in the structures containing amorphous GaP, annealing at 550$^{\circ}$C leads to a sharp decrease in the quantum efficiency and open-circuit voltage, while in the structures with microcrystalline GaP on an epitaxial sublayer, the photovoltaic characteristics are improved. Annealing at a temperature of 750$^{\circ}$C improves the photovoltaic characteristics in all the structures due to the diffusion of phosphorus atoms from GaP to Si and leads to the formation of a layer with $n$-type conductivity in the substrate. As the annealing temperature is increased to 900$^{\circ}$C, the carrier lifetime in the silicon substrate decreases. It is shown that the atomic-layer-deposition technique is promising for the formation of a GaP nucleation layer on the surface of silicon before subsequent epitaxial growth.