Spectroscopy of semiconductor nanostructures for mid-IR photonics

• Main Author: Lewis, Michael K
• Format: Dissertation
• Language: English
• Published: University of Surrey 2013

Quantum dot structures of InAs(Sb)/InGaAs/InP designed as easy to fabricate, low cost mid-IR emitting lasers, have been spectroscopically characterised using temperature and power dependent photoluminescence. These structures have been simulated using a truncated pyramid structure in the Nextnano software package. The results show that the observed experimental data is the result of a bimodal dot distribution in both samples. In the InAs case, the bimodal behaviour is the result of varying width dots (35nm and 38.5nm). In the InAsSb case the dot groups were calculated to contain ~10% and zero antimony, indicating difficulties during the growth process. Additionally the InAs dots were found to have a dominant radiative recombination process, while the InAsSb dots were found to be affected by a defect related recombination process. It is suggested this is a result of increased defects formed by the larger lattice mismatch. InAs/InAsSb superlattice structures have potential as mercury cadmium telluride (MCT) alternative mid-IR photo-detectors, and are predicted to not suffer from Ga-related defect recombination as other superlattice structures. High pressure techniques and modelling were used to probe the defect level in these structures. High pressure, low temperature photoluminescence experiments were performed using the sapphire ball cell to move the conduction band minima up in energy until overlap with the predicted defect level state was achieved. This resulted in a decrease in the measured integrated intensity of the sample due to carriers recombining via the defect states. Additionally power dependent measurements at high and low pressure were performed and an observed shift from radiative to defect dominated recombination was observed. This provides the first experimental evidence of a defect level positioned above the conduction band edge. This means that SRH recombination in the forbidden band gap will not be a contributing factor to the dark currents in InAs/InAsSb superlattice photo-detectors showing their promise for low dark current mid-IR detectors.