Non-radiative carrier recombination mechanism in the InGaAs/GaAsP strain-balanced quantum well solar cells with different number of stacks by using a piezoelectric photothermal method

Abstract

To optimize the multiple quantum well (QW) structure of the strain-balanced InGaAs/GaAsP inserted into GaAs p-i-n solar cell, carrier escaping process from QW, carrier radiative and non-radiative recombination processes in QW were investigated by using surface photovoltage (SPV), photoluminescence (PL) and piezoelectric photothermal (PPT) spectroscopies, respectively. Distinctive peaks at 1.19 eV were observed for all spectra below the bandgap of GaAs substrate (1.42 eV) and concluded that the peak was arisen from the excitonic transitions associated between the 1st order subbband in QWs. Although the optical absorption intensity of this transition was proportional to the number of QW stacks, SPV and PPT signals showed saturation above the QW stacks of 20. Band diagram calculation showed that an entire region of 10-stacked QWs was located in the flat band potential area, whereas a part of 20-stacked QWs was placed in an internal electric field. It was then suggested that the potential barrier height of 20-stacked QWs is small than that of 10-stacked QW.