Electronic structure and optical properties of sb-based self-assembled quantum dots for the mid-infrared range

Quantum dots (QDs) are zero-dimensional nanostructures that confined carriers in three dimensions comparable to their de Broglie wavelengths. Therefore, carriers exhibit δ-shaped energy levels and densities of states. Due to their band structure, QD systems show significant advantages as active regions in laser cavities, both in term of lower threshold current densities and better thermal behaviour. The most studied system beingInAs/GaAs system but the antimonide-based (Sb-based) material system has been paid much attention due to their potential for optical devices in the 3-5 μm (0.25-0.40 eV) spectral regions and motivated by feasibility of active medium in high speed electronic and long wavelength photonic devices. In most cases, QDs structures had been obtained with an intrinsic elastic strain field arising from the lattice mismatch between the matrix and QD materials. The strain field plays a very significant role in the fabrication of the self-assembled QDs (SAQDs).Strain fields inside SAQD structures strongly affect the electronic band structure, which in turn, strongly affects the performance of optoelectronic devices. Therefore,knowledge and determination of the strain field in the dots and surrounding matrix is crucial in order to obtain a well ordered SAQDs structure. While knowledge and determination of the electronic structure calculation are necessary for further device modelling to improve the performance of the devices.Numerical work based on continuum-elasticity based on Finite Element Method (FEM) and standard-deformation-potential theory has been carried out to investigate the effect of strain on the band structure for InSb-based SAQD systems with type-I and type-II band alignment. The effect of elastic anisotropy on both strain distribution and band edges profile is also performed. Next, multi-band k·p method is used to model the electronic structure of InSb-based SAQD systems.The results from the modelling show that the strain-modified band profile of the zinc-blende III-V compound semiconductor SAQDs is not very sensitive to the details of the dot shape and the major governing parameter of the geometry is the aspect ratio of the dot. The modelling results also reveal that there are no appropriate material combinations for zinc-blende III-V compound semiconductors that would applicable for the MIR 3-5 μm (0.25-0.40 eV) emission range when type-I band alignment is possible. This leads to the investigation of type-II broken gap InAsxSb(1-x)/InAs SAQDs.Finally, the optical properties of the InSb-based SAQDs are investigated by means of the photoluminescence (PL) measurement using Fourier transform infrared (FT-IR) spectroscopy. The PL results are analysed and compared to the modelling results