Department: Metallurgical Engineering and Materials Science
Supervising professor: Prof. Subhananda Chakrabarti, Electrical Engineering Department, IIT Bombay
Numerous civilian and military applications, including night vision, missile tracking, and environmental monitoring, require high-sensitivity and low-noise infrared sensors. Quantum-dot infrared photodetectors (QDIPs) are positioned to become an essential technology in the field of infrared (IR) detection. My work mainly focuses on the InAs/GaAs quantum dots(QDs) devices, primarily investigating the influence of the dot's capping layer on the carrier confinement. We have introduced a theoretical analysis of the hybrid heterostructure consisting of submonolayer (SML) stacks grown above the SK(Stranski-Krastanov) QDs with various capping layer combinations. By simulating the hydrostatic and biaxial strain in the multiple samples, we came up with the best device structure that can give better carrier confinement. Thus the device can be operated at a higher temperature compared to conventional HgCdTe detectors leading to higher efficiency.
Abstract: Hybrid coupled quantum dot (QD) structures have a high absorption coefficient along with the minimum cumulative strain in the heterostructure compared to that in the homogeneous heterostructure of SK QDs. Here, we are introducing a theoretical analysis of the hybrid heterostructure consisting of six Submonolayer (SML) stacks above SK QDs with various capping layer combination. Sample A (InGaAs-InGaAs) has both SK and SML capping layers of InGaAs. Similarly, Sample B (InGaAs-InAlGaAs), sample C (InAlGaAs-InGaAs), and sample D (InAlGaAs-InAlGaAs) have different variations in the capping composition of SK and SML dots. Barrier thickness between SML stacks and SK dots is taken to be 7.5nm, and the capping layer The thickness of the SK dot is 3nm which has been optimized from another study. The number of SML stacks and barrier thickness has been optimized from our previous experimental work. Hydrostatic and biaxial strains of the four samples are analyzed and compared. It has been
found that Sample D shows the lowest magnitude of hydrostatic strain in both SML and SK dots, suggesting better carrier confinement in both QDs. Moreover, Sample D has the highest biaxial strain in the SK dot indicating the maximum splitting of the valence band which results in lowering the bandgap in the sample. Thus, we demonstrate that Sample D could be the potential candidate for optoelectronic device applications.