Charge transport study and spectral response of GaSb/GaAs heterojunctions prepared by MOVPE

The purpose of our work was the evaluation of GaSb/GaAs heterostructures grown on GaAs substrates for thermophotovoltaics (TPV). Heterojunctions p-GaSb/n-GaAs with p-layer prepared by metal organic vapour phase epitaxy (MOVPE) method at growth temperatures ranging from 500°C to 560°C were investigated. We have studied the charge transport in these structures and its influence on photovoltage spectral response of the cells. Measurement of I–V characteristics in the temperature range from 200 to 350 K show that the charge transport can be described by a combination of emission and diffusion processes. There is a spike and hence a discontinuity in the band diagram of the junction. The discontinuity increases with increasing GaSb growth temperature. Photovoltage spectral response shows higher signal from GaAs than that from GaSb. The experimental curves were compared with theoretically calculated ones accounting for the reduction of electron current crossing the barrier. The discontinuity is very probably connected with the lattice mismatch between both materials rather than with the affinity difference. Our results show that p-GaSb/n-GaAs heterojunctions prepared by this MOVPE method are not suitable enough for use in TPV.