Electrical field dependence of emission rate of deep levels in InAsxP1−x/InP multiquantum well solar cell structure

The addition of multiquantum well structures was found to improve the quantum efficiency of InP based solar cells as the absorption region of the cell extends into the infrared region of the spectral response of the multiquantum structure. However, the open circuit voltages of the solar cells that are under investigation was not up to the expected levels. In order to understand the reason behind this observation, an investigation of electron/hole emission from chemical beam epitaxy grown InAs_xP_1-x/InP multiquantum solar cell structures has been carried out. Deep level transient spectroscopy (DLTS) was used to investigate the defects in the samples, their location and their possible role in reduced efficiency. DLTS measurements have revealed that the thermal emission of electrons from the deep level E3 is dependent on the electric field. Emission rate versus field data have been obtained over a wide range of temperature and field values. This data has been successfully fitted with the Poole-Frenkel model in the entire range of the temperature over which the data has been taken.