Influence of low-defective buffer on photoelectric properties of InAs/InGaAs and InAs/GaAs quantum dot structures

Photoluminescent and photoelectric properties of the InAs/In0.15Ga0.85As and InAs/GaAs quantum dot (QD) structures with thick metamorphic buffers (MBs) grown on GaAs substrates were studied. Bottom contacts on both the types of vertical structures were made on both the substrates and the bottom buffer layers. The last configuration allowed to avoid the flow of electrical current through the n-InGaAs/n-GaAs and n-GaAs/substrate interfaces. The structures showed an effective photoluminescence form QDs close to 1.3 ?m telecommunication spectral window. Luminescence spectra showed only the bands related to QDs and wetting layers (WL), whereas also the features from other layers was observed in the photovoltage (PV) and photocurrent spectra of the structures with the bottom contacts on MBs. In addition, there was an essential contribution of EL2 defects to the photoelectric spectra in the case of the substrate bottom contacts. It was shown that the EL2 defects and a thin intermediate n+-GaAs layer between the MB and substrate had a negative impact on the total PV signal from another layers of the structures which is related to features of the band structure slops at the interfaces between the layers. The PV of the structures with bottom contacts on MB for different wavelengths showed a predominantly linear dependence of charge carrier density on intensity at higher power densities that transformed to superlinear for low ones which evidences that weak Shockley-Read recombination apparently occurs through the defects. The obtained results allow to conclude a positive role of the thick MBs in the charge carrier collection to the QDs rather than their capture and subsequent recombination through the defects.