No abstract

The effects of doping InAs quantum dots (QDs) with Si on charge carrier dynamics and recombination in the InAs/GaAs quantum dot solar cells with AlAs cap layers was investigated. Non-radiative and radiative recombination paths in the doped cells were identified by changes in emission intensity, longwavelength photovoltage (PV) as well as time-resolved PV and photoluminescence (PL) measurements.We find that the reduction of long-wavelength PV and PL with n-doping is due to the electron population of the QD ground states and shrinkage of the depletion layer. The time constants, derived from the timeresolved PV, grow non-monotonically with increasing of the doping density in the QDs due to redistribution of electrostatic potential in the intrinsic region of p-i-n diode and electron population of EL2 defect states of GaAs barriers. We also find that the ground state emission from the InAs QDs decreases with n-doping. The results show that PL traces depends on carrier dynamic in the top QD layers populated partially with electrons from ionized impurities, whereas PV transients were found to be strongly dependent on recombination via QD and defect states located outside the depletion layer. We conclude that the non-radiative recombination of photogenerated electrons and holes via defects is suppressed due to the spatial separation by the local electric fields in and around doped AlAs/InAs QDs, as the potential profile of the intrinsic region is modulated spatially by built-in charges. The interpretation of experimental data suggests limiting mechanisms in the InAs/GaAs quantum dot solar cells operation and sheds light on possible approaches for their further improvement.

The effects of direct, delta, and modulation Si QD doping on InAs/GaAs QDSCs are studied. The PL, EQE, and J-V characterisation results show a clear relationship between the doping methods and the non-radiative recombination. All doped QDSCs exhibited increase in the VOC due to reduced thermal coupling from QD Si doping. Delta and modulation-doped QDSCs exhibit further improvements in VOC due to reduced nonradiative recombination. Moreover, the modulation-doped QDSC shows improvements in both the current density and the voltage compared with the directly doped QDSC. Index Terms -Quantum dots, intermediate band, Si doping, molecular beam epitaxy.

No abstract