Influence of temperature on bandgap shifts, optical properties and photovoltaic parameters of GaAs/AlAs and GaAs/AlSb p–n heterojunctions: insights from ab-initio DFT + NEGF studies

Abstract

The III-V group semiconductors are highly promising absorbers for heterojunctions based solar cell devices due to their high conversion efficiency. In this work, we explore the solar cell properties and the role of electron-phonon coupling on the solar cell parameters of GaAs/AlSb and GaAs/AlAs p-n heterojunctions using non-equilibrium Green function method (NEGF) in combination of ab-initio density functional theory (DFT). In addition, the band offsets at the heterointerfaces, optical absorption and bandgap shifts due to temperature are estimated using DFT+NEGF approach. The interface band gaps in heterostructures are found to be lower than bulk band gaps leading to a shift in optical absorption coefficient towards lower energy side that results in stronger photocurrent. The temperature dependent electronic band gap shift is significantly influenced by the phonon density and phonon energy via electron phonon coupling. The phonon influenced band gap shift is found to change the optical absorption, photocurrent density and open-circuit voltage. In case of GaAs/AlSb junction, the interface phonons are found to have significantly higher energies as compared to bulk phonons and thereby may have important implications for photovoltaic properties. Overall, the present study reveals the influence of electron-phonon coupling on the optical absorption and photovoltaic properties of GaAs/AlSb and GaAs/AlSb p-n heterojunctions. Furthermore, the study shows that the DFT+NEGF method can be successfully used to obtain the reasonable quantitative estimates of temperature dependent bandgap shifts, optical absorption and photovoltaic properties of p-n heterojunctions.