InN Quantum Dot Research Articles

Improvement of Absorption and Emission Phenomena of 1.55µm Quantum Dot Laser using Indium Nitride

This paper presents the improvement of emission and absorption phenomena of 1.55µm quantum dot laser by enhancing the stability of oscillation frequency and minimizing absorption loss. Among the key parameters related to these absorption and emission phenomena, the effective density of state, rate of change of carrier mobility, and optical feedback level were extensively investigated to reduce the fluctuation of the oscillation frequency of the emitted light as well as the absorption loss. These phenomena were investigated through mathematical analysis and numerical simulation using AlN, GaN, and InN quantum dots as the active material of the laser structure. The numerical results were compared, confirming that the InN quantum dot in the active layer significantly improved the absorption and emission phenomena of the quantum dot laser. At the same time, InN is capable of emitting light at a wavelength of 1.55µm due to its band gap of 0.7eV. Consequently, InN has a superior potentiality to other existing materials to fabricate the quantum dot laser operating at the 1.55µm wavelength, which is the window of an optical fiber communication system that offers the lowest attenuation. Therefore, the InN quantum dot laser is expected to be a promising candidate not only in the field of semiconductor technology but also in the field of optical communication in the imminent future.

Minimization of Threshold-Current Dependence of Quantum Dot Laser Using InN

This paper focuses on the effect of threshold current density on different characteristics of quantum dot based laser. To investigate the effect, different characteristics have been analyzed using quantum dot as the active layer material of the laser structure. Performance improvement of quantum dot laser using InN has been achieved in terms of minimization of the threshold current dependence such as mirror loss, modal gain, turn-on delay and so forth. Numerical results have been analyzed considering the values of threshold current densities of GaN, AlN and InN based quantum dot lasers. Analytical results show that internal loss increases linearly with the increase of the threshold current density. However, other characteristics like mirror loss, modal gain, turn-on delay have nonlinear dependence on the threshold current density for any material used in the active layer. The threshold current density of InN quantum dot based laser is lower than that of other existing quantum dot based lasers. Analytical results ascertained that mirror loss has been increased a little bit. Conversely, internal loss and modal gain have been minimized considerably using InN based quantum dot in the active layer of the laser structure. In addition, turn-on delay time has been also minimized significantly.

Minimization of Threshold-Current Dependence of Quantum Dot Laser Using InN

This paper focuses on the effect of threshold current density on different characteristics of quantum dot based laser. To investigate the effect, different characteristics have been analyzed using quantum dot as the active layer material of the laser structure. Performance improvement of quantum dot laser using InN has been achieved in terms of minimization of the threshold current dependence such as mirror loss, modal gain, turn-on delay and so forth. Numerical results have been analyzed considering the values of threshold current densities of GaN, AlN and InN based quantum dot lasers. Analytical results show that internal loss increases linearly with the increase of the threshold current density. However, other characteristics like mirror loss, modal gain, turn-on delay have nonlinear dependence on the threshold current density for any material used in the active layer. The threshold current density of InN quantum dot based laser is lower than that of other existing quantum dot based lasers. Analytical results ascertained that mirror loss has been increased a little bit. Conversely, internal loss and modal gain have been minimized considerably using InN based quantum dot in the active layer of the laser structure. In addition, turn-on delay time has been also minimized significantly.

Infrared luminescence from N-polar InN quantum dots and thin films grown by metal organic chemical vapor deposition

N-polar InN quantum dots and thin layers grown by metal organic chemical vapor deposition were shown to exhibit tunable emission from around 1.00 μm to longer than 1.55 μm at room temperature. The emission wavelength was dependent on both the growth temperature and quantum dot size or InN layer thickness. No measurable change in InN quantum dot emission wavelength or intensity was observed after capping of the InN quantum dots with GaN, paving the way for incorporating N-polar InN quantum dots into buried regions of device structures.

InN/InGaN dot-in-a-wire nanostructures emitting at 1.55 µm

The room temperature photoluminescence emission at 1.55 µm from InN/In0.7Ga0.3N dot-in-nanowire heterostructures, which was grown on self-assembled GaN nanowires on Si (1 1 1) under N-rich condition by plasma assisted molecular beam epitaxy, has been clarified in this paper. The morphology of the nanowires was uniform along the c-axis as proved by scanning electron microscope, each of the nanowires was grown individually and homogeneously without any coalescence phenomenon respectively. The nanowires dispersed on a silicon substrate showed very clear InN dot-in-nanowire structure by high resolution transmission electron microscopy. The structural properties of the individual InGaN nanocolumn were further investigated by high-angle annular dark field image analysis and energy dispersive x-ray spectrum, which confirmed the successful growth of InN quantum dot embedded in InGaN nanowire.

Improvement of Temperature Dependence of Carrier Characteristics of Quantum Dot Solar Cell Using InN Quantum Dot

Improvements of temperature dependence of certain characteristics of quantum dot solar cell using InN as active material of the device structure has been reported in this paper. A numerical analysis of temperature dependence of different parametric characteristics related to carriers within a quantum dot solar cell has been carried out in this research work. Numerical analysis of these solar cell features have been performed using Group-III Nitride trios namely GaN, AlN and InN quantum dot as active layer material of solar cell structure. Among different parameters of quantum dot solar cell: drift length and the diffusion length have been analyzed along with the power loss of the carriers to complete the whole process. In this present research work effect of temperature on the characteristics of these parameters has been analyzed using mathematical approach. Numerical results obtained are compared for preferential outcomes. It is revealed from the comparison results that only the drift length of the carrier has been increased but the diffusion length and the power loss of the carriers have been minimized using InN quantum dot in the active layer of solar cell. Hence InN is the auspicious material to fabricate solar cell in upcoming decades.

Enhancement of Intrinsic Carrier Concentration in the Active Layer of Solar Cell Using Indium Nitride Quantum Dot

This paper presents the improvement of intrinsic carrier concentrations in the active layer of solar cell structure using Indium Nitride quantum dot as the active layer material. We have analyzed effective density of states in conduction band and valance band of the solar cell numerically using Si, Ge and InN quantum dot in the active layer of the solar cell structure in order to improve the intrinsic carrier concentration within the active layer of the solar cell. Then obtained numerical results were compared. From the comparison results it has been revealed that the application of InN quantum dot in the active layer of the device structure improves the effective density of states both in conduction band and in the valance band. Consiquently the intrinsic carrier concentration has been improved significently by using InN quantum dot in the solart cell structure.

Application of InN Based Quantum Dot in Reducing Short Circuit Current Variation of Solar Cell above Room Temperature

This paper focuses on the applicability of InN based quantum dot in the active layer of the solar cell to reduce the short circuit current variation above the room temperature. We have investigated numerically the effect of temperature on the short circuit current of the solar cell using InN based quantum dot in the active layer of the solar cell. The numerical results are compared with those obtained by using Ge based quantum dot. The comparison results revealed that the short circuit current has been increased slightly but the variation of short circuit current has been reduced significantly in the case of using InN quantum dot in the active layer of the device structure. As the results, InN can be considered as the best alternative material to fabricate solar cell with higher short circuit current in upcoming decades.

Minimization of Open Circuit Voltage Fluctuation of Quantum Dot Based Solar Cell Using InN

This paper reports the improvement of open circuit voltage stability of solar cell using InN based quantum dot in the active layer of the device structure. We have analyzed theoretically the temperature dependence of the open circuit voltage of the solar cell to investigate its fluctuation using Ge and InN based quantum dot in the active layer of the solar cell. Numerical results obtained are compared. The comparison results reveal that the open circuit voltage has been reduced a little bit but the fluctuation of terminal voltage has been reduced significantly by using InN quantum dot in the active layer of the device structure. Therefore InN is proved to be an excellent material to fabricate solar cell to provide higher stability in the open circuit voltage of the solar cell in very near future.

High In Composition InGaN for InN Quantum Dot Intermediate Band Solar Cells

We report a detailed study of the growth of InGaN by plasma assisted molecular beam epitaxy. The In composition is around 55% providing the optimum bandgap in the near-infrared spectral region of the matrix material of quantum dot (QD) intermediate band solar cells. The layer thickness is 80 nm for sufficient absorption. Optimum growth conditions are identified at elevated N flux and reduced growth temperature for minimized phase separation and smooth surface morphology. On these optimized InGaN layers, InN QDs are grown exhibiting small size and high density. Optical emission is observed from both the InGaN layer and InN QDs.

Design of Quantum Dot Based LASER with Ultra-Low Threshold Current Density

Reduction in threshold current density is the major challenge in the field of semiconductor laser design. The threshold current density can be minimized by introducing low dimensional material system with narrow band gap. InN has a narrow band gap of 0.7 eV and quantum dot provides three dimensional confinement factor. In this paper, we propose then InN quantum dot as the active layer material that will serve both the purpose of narrow band gap and three dimensional confinement. The simulation results show that the current density reduces drastically with the cavity length.

Current–voltage characteristics in III-nitride quantum dot heterostructure based high electron mobility transistors

This paper proposes an accurate model to investigate the current–voltage characteristics of AlGaN/GaN high electron mobility transistors in presence of InN quantum dots. This work has been done for different InN quantum dot size and different distance between quantum dots. The presence of InN quantum dots will approximately cause a Gaussian peak in the linear regime of the current–voltage characteristics. So, applying this model and using the I–V characteristics one can find the position or size of quantum dots in the structure.

Effect of doping and in-composition on gain of long wavelength III-nitride QDs

In this work, we calculate material gain for long wavelength III-nitride InN and AlInN quantum dot (QD) structures. Strain and QD inhomogeneity are included in the calculations. The study covers (800-2300 nm) wavelength range which is important in optical communications. While p-doping is shown to be efficient to increasing gain, changing QD size (especially QD radius) is more efficient to vary wavelength. The results predicted that n-doped QD structures are promises for broad band laser applications.

Excitation-induced energy shifts in the optical gain spectra of InN quantum dots

A microscopic theory for the optical absorption and gain spectra of InN quantum-dot systems is used to study the combined influence of material properties and interaction-induced effects. Atomistic tight-binding calculations for the single-particle properties of the self-assembled quantum-dot and wetting-layer system are used in conjunction with a many-body description of Coulomb interaction and carrier phonon interaction. We analyze the carrier-density and temperature dependence of strong excitation-induced energy shifts of the dipole-allowed quantum-dot transitions.

Electronic Structures of InN/GaN Quantum Dots

In this letter, ab-initio calculations are performed to study the electronic structures of the InN quantum dot embedded in the GaN matrix. By analyzing the site-decomposed densities of states, an anisotropic potential well in the dot region is clearly depicted. The In atom at the center of the quantum dot provides the highest densities of states for discrete peaks while the Ga atoms nearby In atoms also act as contributor due to hybridization. The partial charge densities distribution of conduction band minimum and valance band maximum illustrates that the charges are well localized in the InN dot region.

Electronic and optical properties of InGaN quantum dot based light emitters for solid state lighting

In this paper, we have made a systematic study of the electronic and optical properties of InGaN based quantum dot light emitters. The valence force field model and 6×6k⋅p method have been applied to study the band structures in InGaN or InN quantum dot devices. Piezoelectric and spontaneous polarization effects are included. A comparison with InGaN quantum wells shows that InGaN quantum dots can provide better electron-hole overlap and reduce radiative lifetime. We also find that variation in dot sizes can lead to emission spectrum that can cover the whole visible light range. For high carrier density injection conditions, a self-consistent method for solving quantum dot devices is applied for better estimation of device performance. Consequences of variations in dot sizes, shapes, and composition have been studied in this paper. The results suggest that InGaN quantum dots would have superior performance in white light emitters.

InN quantum dots grown on GaN (0001) by molecular beam epitaxy

AbstractThe growth properties of InN quantum dots on GaN (0001) surfaces by molecular beam epitaxy are being investigated. The dependence of the dimensions and density of the dots on the nucleation temperature and their evolution during growth at a constant substrate temperature are described. It is shown that both dimensions and density can be accurately controlled through nucleation temperature and deposition time. In the range from 400 °C to 450 °C, the formation of InN quantum dot structures of small dimensions and high density is feasible. InN dots with less than 3nm height, less than 22 nm diameter and with density higher than 1.7×1011 cm–2 have been obtained. Finally, vertical alignment of dots was observed for a multi‐period InN quantum dot structure in GaN matrix, grown at 430 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural characterization of InN quantum dots grown by Metalorganic Vapour Phase Epitaxy

AbstractThe effect of a low temperature GaN capping layer on the structural properties of InN quantum dots is reported. InN quantum dots grown onto sapphire using GaN buffer, with and without low temperature GaN capping layer, have been investigated by atomic force microscopy and transmission electron microscopy. The analysis revealed hexagonal shape quantum dots in both samples. Moreover, the GaN capping layer gives rise to a reduction in the dots aspect ratio. Moiré fringe patterns, obtained in planar view geometry, were used to analyse the strain relaxation of the InN quantum dots. The moiré pattern measurements demonstrated that the uncapped InN quantum dot is almost fully relaxed. These results are related to the formation of a 60° misfit dislocation network in the InN/GaN interface. However, the capping layer not only generated a change of the aspect ratio, but also a decrease in the heterostructure plastic relaxation. The reason of this effect is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Elastic and piezoelectric fields in a substrate AlN due to a buried quantum dot

Using the Green’s function solution in an anisotropic and linearly piezoelectric half space developed recently by the authors, this article studies the elastic and piezoelectric fields in substrate AlN due to a buried quantum dot (QD). Two different growth orientations are considered: One is the AlN (0001) growing along the (0001) axis, and the other is the AlN (1000) growing along the polar direction [i.e., a direction normal to (0001) axis]. For an InN QD, modeled as a concentrated source, with a volume va=4πR3/3 where R=3 nm, and the typical values of misfit strain, at a depth h=10 nm below the surface, the following features have been observed: (1): on the surface of substrate AlN (0001), the hydrostatic strain, piezoelectric potential, and vertical and horizontal electric fields are rotationally symmetric with respect to the z axis. However, these quantities are not rotationally symmetric on the surface of substrate AlN (1000); (2): a hydrostatic strain as large as 0.01 on the surface of the AlN (1000) and as large as 0.008 on the surface of AlN (0001) can be reached, both of which are larger than that on the surface of the substrate GaAs due to a QD with the same volume at the same depth; (3): the piezoelectric potential on the surface of substrate AlN (0001) is much larger than that on the surface of AlN (1000), i.e., 0.8 versus 0.3 V; and (4): large horizontal and vertical electric fields, in the order of 108 V/m, can be induced on the surface of AlN, about two orders of magnitude larger than that on the surface of the substrate GaAs due to a QD with the same volume at the same depth.

Calculations of carrier localization inInxGa1−xN

The electronic structures of cubic InGaN systems are calculated using an atomistic empirical pseudopotential method. Two extreme cases are studied. One is a pure InN quantum dot embedded in a pure GaN matrix, another is a pure ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloy without clustering. We find hole localizations in both cases. The hole wave function starts to be localized as soon as a few In atoms segregate to form a small cluster, while the electron wave function only becomes localized after the number of In atoms in the quantum dot becomes larger than 200. The hole state is also strongly localized in a pure ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloy, on top of randomly formed (110) directioned In-N-In chains. Using one proposed model, we have calculated the hole energy fluctuation, and related that to photoluminescence linewidth. The calculated linewidth is about 100 meV, close to the experimental results. Wurtzite InGaN is also studied for optical anisotropies. We find that in both quantum dot and pure alloy, the polarization is in the $\mathrm{xy}$ plane perpendicular to the c axis of the wurtzite structure.