Carrier Transport Characteristics In InAs/GaAs Quantum Dots And Their Applications In Optoelectronic Devices

Owing to its quantum confinement effect,InAs/GaAs self-assembled quantum dots have great importance in microelectronics and optoelectronic devices applications.Nowadays,InAs/GaAs quantum dots are widely used in lasers,solar cells and quantum dots infrared detectors.The carrier transport process in InAs quantum dots has a critical influence on the performance of the device.Photoluminescence spectroscopy is a non-invasive and efficient method for the study of carrier recombination and transport properties in semiconductor materials.In this paper,we analyzed the carrier transport characteristics in InAs/GaAs quantum dots by testing its photoluminescence characteristics and electrical characteristics and proposed a new physical model.By adjusting the growth parameters of InAs quantum dots,quantum dots' absorption wavelength has been expend and has great potential in multijunction solar cell application.Firstly,the photoluminescence spectroscopy of 3 ML InAs quantum dots with bimodal size distribution in the resonant excitation and nonresonance excitation modes were measured.It was found that the temperature-dependent photoluminescence spectroscopy showing single peak and its intensity is monotonically decreased.While under resonance excitation,the PL shows double peak and the PL of large dot quenched fast and small dots quenched slow with the increasement of temperature.It is speculated that carriers in InAs quantum dots cannot transport between different dots but relaxed to ground state for radiation recombination.The resonant PL spectra of 10-layer quantum dots with p-n junction were measured at 150 K under open-and short-circuit conditions.The integrated PL intensity in the short-circuit condition was reduced to approximately 12% of the intensity in the open-circuit.Furthermore,the resonant PL spectra of 10-layer quantum dots with n-n junction were measured at 150 K under open-and 0.7 V bias conditions.The PL intensity under the 0.7 V bias is reduced by 7.3% compared with that under the open-circuit condition,which is result from quantum–confined Stark effect.These results indicate that the final state of carriers is a free excited state in the QDs within a p-n junction under the short condition.The changes of the physical nature increase the absorption coefficient when the QDs within a p-n junction under the short condition.the incorporation of quantum well and quantum dots in well result in extend solar spectrum absorption which contribute to the sub-band gap current gains for GaAs solar cell.Especially,2.2 ML InAs quantum dots in In0.15Ga0.85 As quantum well inserted in intrinsic region can extend the solar spectrum to 1300 nm,and bring about 37.8% increase in short-circuit current over the GaAs solar cell current,which shows great potential in multiple junction solar cell and resolved the current limiting GaAs middle junction.Further,the new design of multiple junction become possible.