InGaN Quantum Dots (ingan + quantum_dot)

Distribution by Scientific Domains


Selected Abstracts


Effects of composition distribution on electronic structures of self-assembled InGaN/GaN quantum dots

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010
Wei-Yi Tsai
Abstract In this study, we investigate the influences of different composition distributions on the electronic structures of truncated cone-shaped InGaN quantum dots (QDs). A varying parameter, , is defined as , in which w1 and w2 are the top and base diameter of QD, respectively. This factor is set to study the role of similar truncated cones with the same base diameter and height on electronic structures of QD. Three indium composition distributions are considered: ellipsoid, uniform, and linear. The single-band effective-mass equation and six-band kp theory are used to calculate the transition energies of electrons and holes, respectively. The numerical results reveal that the parameter plays an important role in changing the piezoelectric potential. In addition, an InGaN quantum dot with a linear distribution of indium has the maximum transition energy, whereas one with an ellipsoidal distribution has the minimum value. It is noteworthy that the binding energy greatly decreases as increases for different indium distributions. [source]


Optical properties and modal gain of InGaN quantum dot stacks

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
Joachim Kalden
Abstract We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing number of quantum dot layers while other relevant GaN related spectral features are much less intensive when compared to the photoluminescence of a single quantum dot layer. The quantum dot character of the active material is verified by microphotoluminescence experiments at different temperatures. For the possible integration within optical devices in the future the threshold power density was investigated as well as the modal gain by using the variable stripe length method. As the threshold is 670 kW/cm2 at 13 K, the modal gain maximum is at 50 cm,1. In contrast to these limited total values, the modal gain per quantum dot is as high as 10,9cm,1, being comparable to the IIVI and III-As compounds. These results are a promising first step towards bright low threshold InGaN quantum dot based light emitting devices in the near future ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Effects of composition distribution on electronic structures of self-assembled InGaN/GaN quantum dots

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2010
Wei-Yi Tsai
Abstract In this study, we investigate the influences of different composition distributions on the electronic structures of truncated cone-shaped InGaN quantum dots (QDs). A varying parameter, , is defined as , in which w1 and w2 are the top and base diameter of QD, respectively. This factor is set to study the role of similar truncated cones with the same base diameter and height on electronic structures of QD. Three indium composition distributions are considered: ellipsoid, uniform, and linear. The single-band effective-mass equation and six-band kp theory are used to calculate the transition energies of electrons and holes, respectively. The numerical results reveal that the parameter plays an important role in changing the piezoelectric potential. In addition, an InGaN quantum dot with a linear distribution of indium has the maximum transition energy, whereas one with an ellipsoidal distribution has the minimum value. It is noteworthy that the binding energy greatly decreases as increases for different indium distributions. [source]


On the way to InGaN quantum dots embedded into monolithic nitride cavities

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007
K. Sebald
Abstract We present photoluminescence measurements on single InGaN quantum dots (QDs) grown by metalorganic vapor phase epitaxy, and on monolithicly grown GaN-based quantum well airpost pillar microcavities. The observed sharp emission lines of the quantum dots are characterized by excitation density dependent measurements. The photoluminescence of individual quantum dots can easily be detected for temperatures up to 150 K. The micro-photoluminescence measurements on microcavities reveal three-dimensional confined optical modes which are not seen in the luminescence of the simply planar cavity. The realization of rather temperature stable QDs as well as of nitride based microcavity samples are promising with respect to the intended implementation of QD layers into microcavities. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Formation of InGaN quantum dots in regularly arranged GaN nanocolumns grown by rf-plasma-assisted molecular-beam epitaxy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010
Hiroto Sekiguchi
Abstract InGaN quantum dots (QDs) were successfully integrated at the apex of each pyramid-topped GaN nanocolumn. Various nanocolumn arrays with different nanocolumn diameters arranged in a triangular lattice were prepared on GaN templates by Ti-mask selective-area growth (SAG) with rf-plasma-assisted molecular-beam epitaxy (rf-MBE). The photoluminescence (PL) emission wavelength from the InGaN QDs shifted from 477 to 516 nm with increasing nanocolumn diameter from 206 to 326 nm. From the Arrhenius plot of PL integrated intensity, the PL internal quantum efficiency (IQE) was evaluated to be 48.4% for the 516-nm-wavelength sample. Threading dislocations at the bottom region of the nanocolumns were bent toward the sidewall and did not propagate to the upper active layer, which contributed to the higher PL efficiency. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Influence of piezoelectric fields on excitonic complexes in InGaN quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009
K. Sebald
Abstract We present an analysis of the optical properties of single InGaN quantum dots (QDs) grown by MOVPE. The samples were structured into mesas by focused-ion-beam etching and investigated by micro-photoluminescence measurements. The QDs are characterized by the high temperature stability of their emission up to 150 K. Furthermore, the polarization of individual QD emission lines was analyzed giving an insight into their geometrical shape. Time-resolved microphotoluminescence measurements on the excitonic and biexcitonic transition of a single quantum dot yields a radiative recombination lifetime of 2.06 ns for the exciton. The data can be fitted by a simple model for cascaded emission confirming the expected refilling of the excitonic state by biexcitonic recombination. In addition, the influence of piezoelectric fields on the exciton and biexciton emission and on their binding energy in single QDs was investigated. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Two-step growth of InGaN quantum dots and application to light emitters

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
T. Yamaguchi
Abstract A two-step growth method for creating InGaN quantum dots (QDs) was developed by using a combination of an InxGa1,xN nucleation layer (NL) without island structures and an InyGa1,yN formation layer (FL) with an indium content lower than that of the InxGa1,xN NL. The realization of QDs was confirmed by micro-photoluminescence (,-PL) measurements only for the sample with both the InxGa1,xN NL and the InyGa1,yN FL. The spectral position of the QD ensemble recombination was controlled mainly by the deposition time of the InxGa1,xN NL. Green (,520 nm) and amber (,600 nm) LEDs with the QD layers grown by the two-step growth method as the active region were also fabricated and compared with that having InGaN QW layers, reported previously. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


A novel approach for the growth of InGaN quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006
T. Yamaguchi
Abstract A novel two-step growth method for creating InGaN quantum dots (QDs) was developed by using a combination of an InxGa1,xN nucleation layer with a platelet structure and an InyGa1,yN formation layer with an indium content lower than that of the InxGa1,xN nucleation layer. The realized QDs were investigated by micro-photoluminescence measurements. We observed sharp emission lines at 4 K with a spectral width down to the spectral resolution limit of the experimental setup of 0.17 meV. This growth concept is discussed in comparison with conventional growth methods. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Growth of InGaN quantum dots on GaN by MOVPE, employing a growth temperature nitrogen anneal

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003
R. A. Oliver
Abstract We have studied the growth of InGaN epitaxial layers on GaN by MOVPE (metal-organic vapour phase epitaxy), and have discovered that nanostructures may be formed if a flat epilayer is annealed in molecular nitrogen immediately after growth. The size and density of the nanostructures are shown to be dependent on the growth/anneal temperature. We demonstrated the quantum dot nature of our nanostructures by performing spatially resolved photoluminescence on samples that had been capped with a layer of GaN, grown at the same temperature as the InGaN epilayer. This revealed narrow, delta-function-like lines in the luminescence spectrum with full width at half maximum (FWHM) limited by the resolution of the spectrometer at 4.2 K. Measurement of the FWHM as a function of temperature revealed significant broadening above 20 K. ( 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]