Abstract
The surface photovoltage (SPV) spectra of a series of vertically stacked self-organized InAs/GaAs quantum dot (QD)-based laser structures with different spacer layer (SL) thickness were obtained as a function of temperature (77 K </= T </= 300 K). A decrease of the compressive stress for thinner SL samples arising from coherent relaxation enables us to designate the effect of material intermixing as the most probable mechanism of the energetic blueshift of the observed structures. The turnaround characteristic of the temperature-dependent spectral intensity shows that the reduced SPV signal at higher temperature is limited by the carrier scattering and at lower temperature it is governed by the magnitude of built-in electric field and the escape efficiency of the photogenerated carriers. The dot states to be blueshifted by material intermixing are expected to have higher escape rate for carriers out of QDs, thus resulting in lower measurable temperature for the detected SPV signal. The relatively higher signal at low temperature for the 10 nm SL sample provides a direct evidence of the tunneling process of carriers in the stacked QD layers.
Highlights
There has been considerable interest in the implementation of semiconductor quantum dots (QDs) because of the relative ease at which they can be grown and offering substantially improved optical and electronic properties associated with three-dimensional quantum confinement of carriers [1,2,3,4,5]
The surface photovoltage (SPV) spectra of a series of vertically stacked self-organized InAs/GaAs quantum dot (QD)-based laser structures with different spacer layer (SL) thickness were obtained as a function of temperature (77 K ≤ T ≤ 300 K)
A decrease of the compressive stress for thinner SL samples arising from coherent relaxation enables us to designate the effect of material intermixing as the most probable mechanism of the energetic blueshift of the observed structures
Summary
There has been considerable interest in the implementation of semiconductor quantum dots (QDs) because of the relative ease at which they can be grown and offering substantially improved optical and electronic properties associated with three-dimensional quantum confinement of carriers [1,2,3,4,5]. The operating characteristics of lasers can be readily improved by using an array of vertically coupled QDs (VCQDs) as the active region, i.e., sequences of QD planes separated by narrow spacer layer (SL) [7,8,9]. This structural arrangement increases the total number of states in the QD ensemble and enhances the optical gain. The use of the thinner VCQD active region can improve the carrier injection efficiency via the tunneling effect
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