Sanjib Kabi

Calculations for the band lineup of strained InxGa1-xN/GaN quantum wells : Effects of strain on the band offsets

Band lineup is one of the most important parameters associated with carrier confinement in heterostructures. Relations for computing the band lineups of InxGa1−xN based heterostructures have been developed. The band positions for InxGa1−xN/GaN heterointerfaces are calculated from the equations developed, which directly corelate the positions of the bands with the band gap of InN and strain at the interface. The strains are calculated from the In mole fractions and lattice constants. The parameters implicitly involved are the elastic stiffness constants (C11 and C12), the hydrostatic deformation potential of the conduction band (a′), and the hydrostatic deformation potential (a) and shear deformation potential (b) for the valence band. Computations have been carried out for different reported band gaps of InN. The effects of strain become prominent as the mole fraction of In increases, changing the band offset ratio.

Computations of the optical transitions and absorption spectra in a set of realistic, elongated InAs/GaAs quantum boxes having a Gaussian distribution

InAs/GaAs quantum dots (QDs) grown by various methods do not have the same dimensions in the three axes. This paper reports on expressions for computations of the optical transitions and absorption spectra of InAs/GaAs QDs that have a square base and the variation of the height is Gaussian. The dots were considered to be elongated quantum boxes with square bases having finite potentials at the boundaries. The results are in excellent agreement with reported experimental data of photoluminescence and absorption. The expressions could be successfully applied to short quantum wires.

Conspicuous Presence of Higher Order Transitions in the Photoluminescence of InxGa1-xN/GaN Quantum Wells

For successive annealing stages the photoluminescence (PL) peaks of InXGa1-XN/GaN quantum wells (QWs) shift initially towards red which is followed by a blue. This phenomenon contradicts the usual monotonic blueshift. We have found that the phenomena can be explained properly only if we consider recombinations from the higher sub-bands to be present in the PL of the InXGa1-XN/GaN QWs, which is not usual. When a strong piezoelectric field exists across a QW, as encountered in InXGa1-XN/GaN QWs, the probability of optical transitions from higher sub-bands of the QW become more probable. In this paper this theory has been established from experimental results.

Dependence of the photoluminescence of annealed III-V semiconductor quantum dots on their shape and dimension

Interdiffusion in III-V semiconductor quantum dots (QDs) may occur during growth and subsequent device processing steps. The photoluminescence (PL) spectra of InXGa1−XAs/GaAs and InXGa1−XN/GaN QDs change significantly on annealing. The size and shape of a QD dot are important parameters, which govern this change of the PL spectra. In this communication, we have investigated the effects of interdiffusion in realistic InXGa1−XAs/GaAs and InXGa1−XN/GaN QDs with various geometries which are of theoretical and practical interest such as pyramidal, truncated pyramidal, and lens shaped, through quantum mechanical computations.

DEPENDENCE OF THE ABSORPTION SPECTRA OF III–V SEMICONDUCTOR QUANTUM DOTS ON THE FUNDAMENTAL PARAMETERS

The absorption spectra of semiconductor quantum dots (QDs) are expected to be a series of δ-function-like discrete lines due to the nature of the density of states. In a realistic III–V QD system, the absorption spectra is the superimposition of the contribution from each individual dot and the overall behavior is modeled by considering a Gaussian size distribution. In this paper, we study and present the dependence of the Gaussian nature of the absorption spectra of InXGa1-XN/GaN QD systems on the dot size distribution and some fundamental parameters such as bowing effect of the band gap, band offset ratio, and so on. It is observed that the absorption spectra depend strongly on the dot size distribution. The results presented helps to get a better insight of the optical properties of InXGa1-XN/GaN QD systems.

Effects of size nonuniformity on the optical transitions in a set of realistic InxGa1-xN/GaN quantum dots, having a Gaussian distribution

The absorption spectra of semiconductor quantum dots (QDs) are expected to be a series of δ-function-like discrete lines due to the nature of the density of states. In a realistic III–V QD system, the absorption spectra is the superimposition of the contribution from each individual dot and the overall behavior is modeled by considering a Gaussian size distribution. In this paper, we study and present the dependence of the Gaussian nature of the absorption spectra of InXGa1−XN/GaN QD systems on the dot size distribution. The dots were approximated as elongated rectangular boxes having finite potentials at the boundaries. The optical transitions and absorption spectra of InXGa1−XN/GaN QDs that have a square base and the variation of the height is Gaussian, are computed and analyzed

Investigations on optical transitions in InAs/InP quantum dash structures

In this paper, we report the dependence of the Gaussian nature of absorption spectra of InAs/InP shallow quantum dot or quantum dash systems on the depth of the dash and also on its relative standard deviation. The dash is considered to be an elongated quantum box with a square base having finite potentials at the boundaries. Our observations reveal that the absorption spectra of the quantum dashes are strongly sensitive to the depth and also on the standard deviation of the dash depth. Predicted results help unveil a better physical insight regarding the optical properties of InAs/InP quantum dash structures. The results are in excellent agreement with reported experimental data of photoluminescence and absorption.

Effects of shape, dimension and interdiffusion on the photoluminescence of III-V semiconductor quantum dots

Interdiffusion in InxGa1-x As/GaAs QDs may occur during growth and subsequent device processing steps. As monitored through photoluminescence (PL), the experimental results on the annealing of InxGa1-x As/GaAs QDs depicts one particular phenomenon, that is, the initially observed PL spectrum is very broad. After annealing, the PL peak undergoes a blueshift and the full width at half maximum (FWHM) decreases, while there is an increase in the intensity. In this paper we have investigated the effects of interdiffusion in QDs with various shapes of theoretical and practical interest like pyramidal, truncated pyramidal and lens shaped through quantum mechanical computations.