LINEAR AND NONLINEAR TUNABLE OPTICAL PROPERTIES OF INTERSUBBAND TRANSITIONS IN GAN/ALN QUANTUM DOTS IN PRESENCE AND ABSENCE OF WETTING LAYER (original) (raw)
Related papers
Optical properties of GaN/AlN quantum dots
Comptes Rendus Physique, 2008
We present here a review of the peculiar optical properties of GaN/AlN quantum dots. These systems show unusually large exciton binding energies and band-offsets. Moreover, when grown along the (0001) axis in the wurtzite phase, the optical properties are dominated by huge on-axis internal electric fields, leading to a very low oscillator strength and complex dynamical behavior. It is also possible to grow GaN quantum dots in the cubic phase or along nonpolar axis of the wurtzite cell. We discuss properties of ensembles of quantum dots, as well as of single quantum dots studied by micro-photoluminescence. To cite this article: P. Lefebvre, B. Gayral, C. R. Physique 9 (2008).
Self-consistent calculations of the optical properties of GaN quantum dots
2003
We present calculations of the transition energies and radiative lifetimes in GaN quantum dots embedded in AlN. The effects of elastic strains, and piezoelectric and pyroelectric fields are included. The electronic structure is described using a tight-binding method which takes into account the screening of the internal electric field by excited carriers in a fully self-consistent procedure. We show that the presence of one electronhole pair in a quantum dot increases the optical gap by a few tens of meV and decreases significantly the radiative lifetime, which could give rise to very interesting nonlinear optical effects.
Materials Science in Semiconductor Processing, 2016
The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of stacking faults inside the quantum dots, which act as zinc-blende inclusions into the wurtzite matrix, provides an additional reduction of the internal electric field.
Investigation of self-focusing effects in wurtzite InGaN/GaN quantum dots
2012
The third-order nonlinear optical properties in wurtzite InGaN/GaN pyramid and truncated-pyramid quantum dots are studied, and the oscillator strength, third-order nonlinear optical susceptibility and self-focusing effects are analyzed theoretically taken into account the strong built-in electric field effect due to the piezoelectric and spontaneous polarization in nitride materials. The numerical results clearly show that the quantum dot (QD) size of InGaN/GaN have a significant influence on the nonlinear optical properties of wurtzite InGaN/GaN quantum dots. Furthermore, the self-focusing effect increases with decrease in size of QDs.
Ground-state resonant two-photon transitions in wurtzite GaN/AlN quantum dots
Physical Review B
Two-photon transition rates are investigated in resonance to the ground state in wurtzite GaN/AlN quantum dots. The ground state transition is two-photon allowed because of the electronhole separation inherent to polar wurtzite III-nitride heterostructures. We show that this built-in parity breaking mechanism can allow deterministic triggering of single-photon emission via coherent two-photon excitation. Radiative lifetimes obtained for single-photon relaxation are in good agreement with available time-resolved micro-photoluminescence experiments, indicating the reliability of the employed computational framework based on 8-band k •p-wavefunctions. Two-photon singly-induced emission is explored in terms of possible cavity and non-degeneracy enhancement of two-photon processes.
Gan quantum dots: Physics and applications
2003
Recent works by our group on hexagonal and cubic GaN/AlN quantum dots grown by molecular beam epitaxy are reviewed. It is shown that the growth of GaN on AlN can occur either in a layerby-layer mode to form quantum wells or in the Stranski-Krastanow mode to form self-assembled quantum dots. High resolution transmission electron microscopy reveals that quantum dots are truncated pyramids (typically 3 nm high and 15 nm wide), nucleating on top of a wetting layer. The existence of internal electric fields of 7 MV/cm in hexagonal quantum dots is evidenced by observations of various physical effects related to the quantum confined Stark effect, e.g. energy redshift of the interband transition, decrease of its oscillator strength, or enhancement of the exciton interaction with LO phonons. Prospects for UV and near-IR applications, using interband and intersubband transitions of GaN/AlN quantum dots, respectively, will be discussed also in this presentation.
Optically nonlinear effects in intersubband transitions of GaN/AlN-based superlattice structures
We report optically nonlinear processes related to near-infrared intersubband transitions in short period GaN / AlN superlattices. The strong piezo-and pyroelectric effects in this material lead to intrinsic asymmetries in the electronic potential of the superlattice, and thus to strong nonlinearities of the optical susceptibility. Because of the large intersubband transition energy of nearly 1 eV and the short lifetime of excited electrons in the upper quantum state, these nonlinear effects can be exploited for the fabrication of room temperature operated high-frequency detectors in the telecommunication wavelength range. At the same time, saturation effects due to resonant two-photon absorption could be observed.
2012 15th International Workshop on Computational Electronics, 2012
Single-particle electronic structure and optical transition rates between the HOMO and LUMO states of a selforganized wurtzite GaN/AlN single quantum dot grown along the [0001] axis are calculated within an atomistic 20-band sp 3 d 5 s * tight-binding framework. The GaN/AlN quantum dot used in this computational study is realistically-sized (containing ~9 million atoms) and of truncated pyramid shape having height and base length of 4.5 nm and 23 nm, respectively. These reduced-dimensionality III-N structures are subject to competing effects of size-quantization and long-range internal fields that originate from: a) fundamental crystal atomicity and the interface discontinuity between two dissimilar materials; b) atomistically strained active region; c) strain-induced piezoelectricity; and d) spontaneous polarization (pyroelectricity). The mechano-electrical internal fields in the structure have been modeled using a combination of an atomistic valence force-field molecular mechanics (VFF MM) approach and a three-dimensional Poisson solver, and have found to strongly modulate the intrinsic single-particle electronic and optical properties of the quantum dots. In particular, in contrast to the well-studied InN/GaN systems, the effects of piezoelectric and pyroelectric fields add up (peak pyroelectric potential being larger than the piezoelectric counterpart) and result in a large redshift in the electronic bandgap near the Brillouin zone center (known as quantum confined stark effect), pronounced non-degeneracy in the excited states, strongly suppressed optical transition (increased recombination time), and anisotropic emission spectra.
Electronic structure and optical properties of zinc-blende GaN quantum dots
Chinese Physics, 2003
The ground-state and optical properties of the americium monopnictides, AmX ͑X = N, P, As, Sb, and Bi͒ are investigated theoretically on the basis of first-principles electronic structure calculations, employing the local density approximation ͑LDA͒ as well as the LDA+ U approach. The LDA predicts pseudogap-like behavior in AmN and narrow gap ͑39-78 meV͒ semiconducting behavior in AmP to AmBi at ambient conditions. The LDA+ U calculations predict semiconducting behavior with a real gap of 192 meV for AmN and a pseudogap in AmP to AmBi. The computed semiconducting or pseudogap character is in fine agreement with the first photoemission experiments performed on AmN and AmSb films by Gouder et al. ͓preceding paper, Phys. Rev. B 72, 115122 ͑2005͔͒. This property is shown to result from the strong Am spin-orbit interaction, the Coulomb repulsion, and the particular p-d-f hybridizations. The calculated equilibrium lattice constants obtained for the AmX series using the LDA+ U technique are in good agreement with available experimental data. Also, the binding energies of the 5fs computed with the LDA+ U approach correspond well to 5f binding energies deduced from the photoemission spectra measured by Gouder et al. The high, temperature-independent paramagnetic susceptibilities of the AmX are successfully explained by a Van Vleck mechanism. A pressureinduced valence transition at high pressure is predicted for AmN.
Nanoscale Research Letters, 2014
Quadratic electro-optic effects (QEOEs) and electro-absorption (EA) process in a GaN/AlGaN spherical quantum dot are theoretically investigated. It is found that the magnitude and resonant position of third-order nonlinear optical susceptibility depend on the nanostructure size and aluminum mole fraction. With increase of the well width and barrier potential, quadratic electro-optic effect and electro-absorption process nonlinear susceptibilities are decreased and blueshifted. The results show that the DC Kerr effect in this case is much larger than that in the bulk case. Finally, it is observed that QEOEs and EA susceptibilities decrease and broaden with the decrease of relaxation time.