Impact of variation in monolayer coverage on the optical and structural properties of InAs/InGaAs dot-in-a-well heterostructures

Dot-in-a-well (DWELL) heterostructures have been widely studied for the applications in quantum dot (QD)-based infrared (IR) photodetectors and such heterostructures provide several benefits such as adjustable detection peak wavelengths, reduced dark current, and improved operating temperatures through optimized quantum well thickness and compositions. The current research investigates the effect of varying InAs monolayer coverages on the structural and optical properties of InAs DWELL heterostructures. Three samples (S1, S2, and S3) are grown with varying InAs QD coverages of 3ML, 3.2ML, and 3.4ML, respectively. Sample S1 is capped with a 6nm In_0.15Ga_0.85As layer, whereas samples S2 and S3 are additionally doped with Si for 2 seconds before being capped with the same In_0.15Ga_0.85As layer. Photoluminescence (PL) measurements are performed to analyse the optical characteristics of the heterostructures and corresponding highest activation energy is obtained for S2, which indicate more thermal stability and carrier confinement within the potential well. Power-dependent PL spectra show that there is no shift in emission wavelengths between low and high-power conditions which implies the uniformity in the size and composition of the QDs. A slight red shift in the PL emission wavelength from 1140nm to 1152nm is observed at 20K when the monolayer coverage is decreased due to the relaxation of strain. Additionally, high-resolution X-ray diffraction (HRXRD) measurements are conducted to analyse the crystalline quality and strain propagation in the heterostructures, which indicates that strain values are increased with higher monolayer coverage. Thus, current study provides a significant insight about impact of monolayer coverage variation on optical and structural properties of InAs DWELL heterostructures, which can be further useful for optimizing the performance of QD based optoelectronic devices.