Photoluminescence spectroscopy and carrier dynamics modeling of quantum dot structures

Abstract

This thesis deals mainly with the optical investigation of strain induced quantum dots (SIDQ). SIQDs were measured by continuous wave photoluminescence spectroscopy and time resolved photoluminescence, and mathematical models were used to explain the results. Also GaAsN quantum dots on InP, surface passivation of GaAs based structures and indium nitride films were studied. The SIQDs were formed by manufacturing self assembled nanoscopic islands on top of a quantum well (QW) structure. All the studied materials were III-V compound semiconductors. The influence of the nitrogen concentration on the carrier dynamics in dilute GaInAsN SIQDs was investigated. The small scale lateral variation in the bandgap of the QW is observed. Carrier dynamics was also studied in InGaAsP/InP SIQDs and in coupled GaInAs/GaAs SIQDs. It was found, out, that surface recombination has a more significant role in the InAs islands and wetting layer on top of the InGaAsP/InP structure than in the traditional InP capped GaAs based structures. A rate-equation model was developed to take into account the effect of the surface states by introducing additional terms to the traditional quantum dot recombination and relaxation terms. Modified model agrees well with the measured results. The effect of the gaussian excitation beam distribution was also taken into account in the rate-equation model. The results agree well with the continuous wave PL results from GaInAs/GaAs SIQDs.