Density of impurity states in flat quantum dots with different shapes (original) (raw)

Binding energies and density of impurity states in spherical GaAs-(Ga,Al)As quantum dots

Journal of Applied Physics, 1993

The binding energies of hydrogenic donor in both finite and infinite GaAs-(Ga,Al)As spherical quantum dots are calculated as a function of the donor position for different radii within the effective-mass approximation. It is observed an enhancement of the binding energy of donors in quantum dots when compared to results in quantum wells and quantum-well wires, which is an expected consequence of the higher geometrical electronic confinement in these systems. The density of impurity states as a function of the donor binding energy was also calculated. As a general feature it presents structures associated with special impurity positions that may be important in the understanding of the absorption and photoluminescence experiments of doped quantum dots.

Quantum box energies as a route to the ground state levels of self-assembled InAs pyramidal dots

2000

A theoretical investigation of the ground state electronic structure of InAs/GaAs quantum confined structures is presented. Energy levels of cuboids and pyramidal shaped dots are calculated using a single-band, constant-confining-potential model that in former applications has proved to reproduce well both the predictions of very sophisticated treatments and several features of many experimental photoluminescence spectra. A connection rule between their ground state energies is found which allows the calculation of the energy levels of pyramidal dots using those of cuboids of suitably chosen dimensions, whose solution requires considerably less computational effort. The purpose of this work is to provide experimentalists with a versatile and simple method to analyze their spectra. As an example, this rule is then applied to successfully reproduce the position of the ground state transition peaks of some experimental photoluminescence spectra of self-assembled pyramidal dots. Furthermore the rule is used to predict the dimensions of a pyramidal dot, starting from the knowledge of the ground state transition energy and an estimate for the aspect ratio Q.

Electronic Structure of Elongated In_{0.3}Ga_{0.7}As/GaAs Quantum Dots

Acta Physica Polonica A, 2013

In this contribution the electronic structure of large In0.3Ga0.7As/GaAs quantum dots is studied theoretically by means of 8 band k • p modeling. These quantum dots constitute unique physical system due to the low strain limit of the StranskiKrastanow growth mode resulting in relatively large physical volume and elongation of the quantum dots in [110] direction. As a result of these critical growth conditions the electronic structure is expected to be very sensitive to the nanostructure size, shape, and composition of the quantum dot as well as the accompanying wetting layer. Another peculiarity of investigated system is the conning potential which is rather shallow and weakened in comparison to standard quantum dots. It makes them very interesting in view of both fundamental study and potential applications. To reveal physical mechanisms determining the optical properties of the investigated system, the electronic structure, mainly the number of conned states, and the wave function extension as a function of both quantum dot size and geometry have been simulated numerically and the importance of electronhole Coulomb interactions has been evaluated.

Bimodal size distribution of self-assembled InxGa1-xAs quantum dots

2002

We investigate quantization of energy levels in self-assembled In x Ga 1Ϫx As quantum dots that are embedded in a GaAs matrix. We use capacitance and photoluminescence spectroscopies to analyze the evolution of the energy levels with varying amounts of deposited In x Ga 1Ϫx As. These techniques suggest that the size distribution of the quantum dots contains two well-separated peaks. Transmission electron microscopy confirms a bimodal size distribution and further shows that the big and the small quantum dots have different shapes. In addition, we use an effective-mass based method to calculate the lowest energy states of quantum dots with the physical dimensions obtained by transmission electron and atomic force microscopies. Our results allow us to construct the energy-level diagrams of the two kinds of quantum dots.

Electronic Properties of Self-Organized Quantum Dots

2007

Contents Part 1. Electronic Structure Calculations Chapter 1. Introduction Chapter 2. Method of calculation 2.1. Calculation of strain 2.2. Piezoelectricity and the reduction of lateral symmetry 2.3. Single Particle States 2.4. Many-Particle States 2.5. Optical Properties Part 2. InGaAs/GaAs Quantum Dots Chapter 3. Impact of Size, Shape and Composition on Piezoelectric Effects and Single-Particle States 3.1. The Investigated structures: Variation of size, shape and compostion 3.2. The Impact of the piezoelectric field 3.3. The vertical and lateral aspect ratio 3.4. Varying composition profiles 3.5. Conclusions Chapter 4. Few-particle Energies versus Geometry and Composition 4.1. Interrelation of QD-structure, strain and piezoelectricity, and Coulomb interaction 4.2. The Impact of QD size (series A and H) 4.3. The aspect ratio 4.4. Different composition profiles 4.5. Correlation vs. QD size, shape and particle type 4.6. Conclusions Chapter 5. Multimodal QD-size distribution: Theory and Experiment 5.1. Sample growth 5.2. Determination of QD-morphology and the spectrum of excited states 5.3. Predicted absorption spectra of truncated pyramidal InAs/GaAs QDs 5.4. Single-dot spectra obtained from cathodoluminescence spectroscopy 5.5. Results and Interpretation 5.6. Conclusion Chapter 6. Stacked quantum dots 6.1. Energetics of QD stacks 6.2. Role of strain and piezoelectricity 6.3. Strength of electronic coupling in pairs of identical QDs 6.4. Small perturbations of the size homogeneity 6.5. Asymmetric QD molecules: Coupling of different electronic shells 6.6. Tailoring the TE-TM ratio in semiconductor optical amplifiers 6.7. Conclusions 6 CONTENTS Part 3. Other Material Systems Chapter 7. Electronic and optical properties of InAs/InP quantum dots on InP(100) and InP(311)B substrates 7.1. Choice of model QDs 7.2. Absorption spectra for InAs/InP QDs 7.3. Impact of substrate orientation on the QDs optical properties 7.4. Conclusions Chapter 8. Inverted GaAs/Al x Ga 1−x As Quantum Dots 8.1. Choice of the model QDs 8.2. Influence of interface intermixing on the optical properties 8.3. External magnetic fields 8.4. Discussion 8.

Electronic structure and many-body effects in self-assembled quantum dots

Journal of Physics: Condensed Matter, 1999

A detailed model for the electronic properties of self-assembled InAs/GaAs quantum dots (SADs) is presented, with emphasis on inter-level transitions and many-body effects. The model is based on the self-consistent solution of three-dimensional Poisson and Schrödinger equations within the local (spin-) density approximation. Nonparabolicity of the band structure and a continuum model for the strain between GaAs and InAs results in position-and energydependent effective mass. The electronic spectra of SADs of various shapes have been determined with intraband level transitions and mid-infrared optical matrix elements. Shell structures obeying Hund's rule for various occupation numbers in pyramidal SADs agree well with recent capacitance measurements. It is shown that many-body interactions between orbital pairs of electrons are determined in a first approximation by classical Coulomb interaction. 0953-8984/99/315953+15$30.00

Semiconductor quantum dots: Theory and phenomenology

Bulletin of Materials Science, 1999

Research in semiconductor quantum dots (q-dots) has burgeoned in the past decade. The size (R) of these q-dots ranges from 1 to 100 nm. Based on the theoretical calculations, we propose energy and length scales which help in clarifying the physics of this mcsoscopic system. Some of these length scales are: the Bohr exciton radius (a*), the carrier de Broglie and diffusion length (~'D and ID) , the polaron radius (ap), and the reduction factor modulating the optical matrix element (M). R <a a is an individual particle confinement regime, whereas the larger ones are exciton confinement regime wherein Coulomb interaction play an important role. Similarly a size-dependent dielectric constant ~(R) should be used for R <ap <a n. An examination of M reveals that an indirect gap material q-dot behaves as a direct gap material in the limit of very small dot size. We have carried out effective mass theory (EMT) calculations to estimate the charge density on the surface of the quantum dot. We present tight binding (TB) calculation to show that the energy upshift scales as 1/R x, where x is less than 2 and the exponent depends on the orientation of the crystallite.