Kinetics peculiarities of photovoltage in vertical metamorphic InAs/InGaAs quantum dot structures

Metamorphic InAs/InGaAs quantum dot (QD) structures have been successfully used in optoelectronics as light-emitting and sensing devices. Previous optical and photoelectrical studies showed many benefits such as the shift of the operating range in the infrared and the possibility of engineering their properties via the control of strain. However, photovoltage (PV) kinetic properties of metamorphic QD structures have not been studied yet. PV kinetics in the vertical metamorphic InAs/In0.15Ga0.85As QD and wetting layer (WL) structures compared with conventional pseudomorphic InAs/GaAs QD ones are investigated. A red-shift of the photoresponse from metamorphic QDs in comparison with pseudomorphic QDs was observed, while the PV magnitudes remain similar. Moreover, time-dependent PV measurements reveal faster increase and decay rates in both the metamorphic samples. At the same time, all the structures reveal a non-monotonous kinetics. This kinetics is explained by an unwanted PV component generated in the interface of n+-GaAs buffer to the semi-insulating GaAs substrate, causing a signal opposite to the main PV generated at the top layers of structure. We believe the findings on faster carrier kinetics in metamorphic QDs can be helpful for the development of novel efficient optoelectronic devices. Specifically, the design of metamorphic QD structure is proposed to be improved by: (i) minimizing strain-related defects, (ii) keeping such interface defects far from QDs, (iii) utilizing n+-GaAs substrates.