GaN Quantum Dots in AlxGa1-xN Confined Layer Structures

1996 ◽  
Vol 449 ◽  
Author(s):  
Satoru Tanaka ◽  
Hideki Hirayama ◽  
Sohachi Iwai ◽  
Yoshinobu Aoyagi
Keyword(s):  
Quantum Dots ◽  
Substrate Surface ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Blue Shift ◽  
Growth Conditions ◽  
Peak Position ◽  
Growth Mode ◽  
Al Content ◽  
Layer Structures

ABSTRACTNanoscale GaN quantum dots were fabricated in AlxGa1-xN confined layer structures via metalorganic chemical vapor deposition (MOCVD), by using a ‘surfactant’ which can modify the GaN growth mode on AlGaN surfaces. A two dimensional growth mode (step-flow-like) of GaN films on AlxGa1-xN (x=0∼0.2) surfaces, that is energetically commenced under the conventional growth conditions, was intentionally changed into a three dimensional mode by adding tetraethyl-silane (TESi) used as a surfactant onto the AlGaN substrate surface prior to the GaN deposition. The surfactant is believed to inhibit the GaN film from wetting the AlGaN surface due to the change in surface free energy. The resulting morphological structures of GaN dots were found to be sensitive to; the doping rate of TESi, the Al content (x) of the AlxGa1-xN layer, and the growth temperature. A very intense photoluminescence (PL) emission was observed from the GaN dots embedded in the AlGaN layers. The quantum size effect in terms of the blue-shift in a PL peak position was verified using the GaN dot samples having different dot sizes.

GaN Three Dimensional Nanostructures

1995 ◽  
Vol 395 ◽  
Author(s):  
V. Dmitriev ◽  
K. Irvine ◽  
A. Zubrilov ◽  
D. Tsvetkov ◽  
V. Nikolaev ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Blue Shift ◽  
High Energy ◽  
Peak Position ◽  
Organic Chemical ◽  
Nanoscale Structures ◽  
Dot Density ◽  
20 Nm

ABSTRACTWe report on the growth and characterization of three dimensional nanoscale structures of GaN. GaN dots were grown by metal organic chemical vapor deposition (MOCVD) on 6H-SiC substrates. The actual size of the dots measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) ranged from ∼20 nm to more than 2 μm. The average dot density ranged from 107 to 109 cm−2. The single crystal structure of the dots was verified by reflectance high energy electron diffraction (HEED) and TEM. Cathodoluminescence (CL) and photoluminescence (PL) of the dots were studied at various temperatures and excitation levels. The PL and CL edge peak for the GaN dots exhibited a blue shift as compared with edge peak position for continuous GaN layers grown on SiC.

Observations on the Growth of YBa2Cu3O7 Thin Films at Very High Laser Fluences

1995 ◽  
Vol 388 ◽  
Author(s):  
Rand R. Biggers. ◽  
M. Grant Norton ◽  
I. Maartense ◽  
T.L. Peterson ◽  
E. K. Moser ◽  
...  
Keyword(s):  
Thin Films ◽  
Substrate Surface ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
High Fluences ◽  
Laser Fluences ◽  
High Laser ◽  
High Laser Fluences ◽  
Very High

AbstractThe pulsed-laser deposition (PLD) technique utilizes one of the most energetic beams available to form thin films of the superconducting oxide YBa2Cu3O7 (YBCO). IN this study we examine the growth of YBCO at very high laser fluences (25 to 40 J/cm2); a more typical fluence for PLD would be nearer to 3 J/cm2. the use of high fluences leads to unique film microstructures which, in some cases, appear to be related to the correspondingly higher moveabilities of the adatoms. Films grown on vicinal substrates, using high laser fluences, exhibited well-defined elongated granular morphologies (with excellent transition temperature, Tc, and critical current density, Jc). Films grown on vicinal substrates using off-axis magnetron sputtering, plasma-enhanced metal organic chemical vapor deposition (PE-MOCVD), or PLD at more typical laser fluences showed some similar morphologies, but less well-defined. Under certain growth conditions, using high laser fluences with (001) oriented substrates, the YBCO films can exhibit a mixture of a- and c-axis growth where both crystallographic orientations nucleate on the substrate surface at the same time, and grow in concert. the ratio of a-axis oriented to c-axis oriented grains is strongly affected by the pulse repetition rate of the laser.

Ingan Quantum Dots Fabricated On Aigan Surfaces -Growth Mechanism And Optical Propertiesh-

1997 ◽  
Vol 482 ◽  
Author(s):  
H. Hirayama ◽  
S. Tanaka ◽  
P. Ramvall ◽  
Y. Aoyagi
Keyword(s):  
Quantum Dots ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Energy Shift ◽  
Organic Chemical ◽  
Self Assembling ◽  
Atomic Force ◽  
Peak Energy ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition

AbstractWe demonstrate photoluminescence from self- assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metal- organic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition from step- flow to three dimensional island formation by using anti-surfactant silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be ˜10nm and ˜5nm, respectively, by an atomic- force- microscope (AFM). Indium mole fraction of InxGal−x N QDs is controlled from x=˜0.22 to ˜0.52 by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, the temperature- dependent energy shift of the photoluminescence peak- energy shows a localization behavior.

Growth Evolution of (Zn,Cd)Se Quantum Dots Deduced from Spatially Resolved Structural and Optical Characterization

1999 ◽  
Vol 571 ◽  
Author(s):  
K. Leonard ◽  
D. Hommel ◽  
A. Stockmann ◽  
H. Selke ◽  
J. Seufert ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Quantum Wells ◽  
Three Dimensional ◽  
High Energy ◽  
Growth Direction ◽  
Growth Mode ◽  
Gradual Transition ◽  
Mode Transition ◽  
Spatially Resolved ◽  
Composition Fluctuations

ABSTRACTThe growth mode of CdSe layers grown by migration enhanced epitaxy between ZnSe barriers has been investigated. In situ reflection high-energy electron diffraction shows a gradual transition to a three-dimensional growth mode which, however, is not accompanied by a change of the surface lattice constant. High-resolution transmission electron micrographs reveal a strong Cd diffusion, leading to ternary ZnCdSe quantum wells. Furthermore. composition fluctuations perpendicular to the growth direction on a nanometer scale are found already prior to the beginning of the growth mode transition. In the case of heterostructures containing a CdSe layer that has undergone the growth mode transition, micrographs show Cd-rich quantum dots with diameters of around 8 nm and heights of around 1.5 nm within a ternary quantum well. By spatially resolved photoluminescence the emission from single quantum dots could be observed. The polarization dependence of the emission from single dots indicates an asymmetric shape of the dots with certain preferential orientations along the [110] and [110] directions.

Growth and Investigation of GaN/AlN Quantum Dots

2000 ◽  
Vol 639 ◽  
Author(s):  
Hadis Morkoç ◽  
Michael A. Reshchikov ◽  
Keith M. Jones ◽  
Feng Yun ◽  
Paolo Visconti ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Blue Shift ◽  
Microscopy Study ◽  
High Quantum Efficiency ◽  
Force Microscopy ◽  
Quantum Size ◽  
Atomic Force ◽  
Layer Structures ◽  
Bulk Gan ◽  
Very High

ABSTRACTWe have fabricated GaN quantum dots (QDs) in AlN confined layer structures by molecular beam epitaxy. The size distribution and density of the QDs have been estimated from an atomic force microscopy study. Very high quantum efficiency of photoluminescence (PL) has been obtained in some samples with QDs. Compared to the GaN bulk samples, it increased by orders of magnitude. In some samples the quantum size effect dominated, resulting in the blue-shift of the QD related PL peak, whereas in the samples with larger dots a red-shift up to 0.8 eV has been observed, which is related to strong polarization effects. We have observed a blue-shift of the PL peak with excitation intensity in the samples with large dots due to screening effect. The temperature-induced quenching of PL occurs at higher temperatures compared to bulk GaN due to the confinement of nonequilibrium carriers in the QDs. An excited state has been observed in some samples.

1.37 - 2.90 Micron Intersubband Transitions in GaN/AlN Superlattices

2006 ◽  
Vol 955 ◽  
Author(s):  
Eric Anthony DeCuir ◽  
Emil Fred ◽  
Omar Manasreh ◽  
Jinqiao Xie ◽  
Hadis Morkoc ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Bound States ◽  
Energy Levels ◽  
Three Dimensional ◽  
Blue Shift ◽  
Bound State ◽  
Peak Position ◽  
Multiple Quantum ◽  
Intersubband Transitions ◽  
Photovoltaic Mode

ABSTRACTIntersubband transitions in the spectral range of 1.37-2.90 °Cm is observed in molecular beam epitaxy grown Si-doped GaN/AlN multiple quantum wells using a Fourier-transform spectroscopy technique. A blue shift in the peak position of the intersubband transition is observed as the well width is decreased. A sample with a well width in the order of 2.4 nm exhibited the presence of three bound states in the GaN well. The bound state energy levels are calculated using a transfer matrix method. An electrochemical capacitance voltage technique is used to obtain the three dimensional carrier concentrations in these samples which further enable the calculation of the Fermi energy level position. Devices fabricated from these GaN/AlN quantum wells are found to operate in the photovoltaic mode.

Coherent island formation of Cu2O films grown by chemical vapor deposition on MgO(110)

2001 ◽  
Vol 16 (8) ◽  
pp. 2408-2414 ◽  
Author(s):  
P. R. Markworth ◽  
X. Liu ◽  
J. Y. Dai ◽  
W. Fan ◽  
T. J. Marks ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Strain Relaxation ◽  
Three Dimensional ◽  
High Mobility ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Growth Conditions ◽  
Island Formation ◽  
Transmission Electron

Cuprous oxide (Cu2O) films have been grown on single-crystal MgO(110) substrates by a chemical vapor deposition process in the temperature range 690–790 °C. X-ray diffraction measurements show that phase-pure, highly oriented Cu2O films form at these temperatures. The Cu2O films are observed to grow by an island-formation mechanism on this substrate. Films grown at 690 °C uniformly coat the substrate except for micropores between grains. However, at a growth temperature of 790 °C, an isolated, three-dimensional island morphology develops. Using a transmission electron microscopy and atomic force microscope, both dome- and hut-shaped islands are observed and are shown to be coherent and epitaxial. The isolated, coherent islands form under high mobility growth conditions where geometric strain relaxation occurs before misfit dislocation can be introduced. This rare observation for oxides is attributed to the relatively weak bonding of Cu2O, which also has a relatively low melting temperature.

Preparation and Spectrial Studies of Silicon Nitride Thin Films Containing Amorphous Silicon Quantum Dots

2021 ◽  
Vol 323 ◽  
pp. 48-55
Author(s):  
Jia Xin Sun ◽  
Bing Qing Zhou ◽  
Xin Gu
Keyword(s):  
Thin Films ◽  
Quantum Dots ◽  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Raman Spectra ◽  
Annealing Temperature ◽  
Chemical Vapor ◽  
Blue Shift ◽  
Silicon Quantum Dots ◽  
Plasma Chemical Vapor Deposition

Silicon-rich silicon nitride thin films are prepared on P-type monocrystalline silicon wafer (100) and glass substrate by plasma chemical vapor deposition with reaction gas sources SiH4 and NH3. The deposited samples are thermally annealed from 600°C to 1000°C in an atmosphere furnace filled with high purity nitrogen. The annealing time is 60 minutes. Fourier transform infrared spectroscopy (FTIR) is carried out to investigate the bonding configurations in the films. The results show that the Si-H bond and N-H bond decrease with the increase of annealing temperature, and completely disappear at the annealing temperature of 900°C. But the Si-N bond is enhanced with the increase of annealing temperature, and the blue shift occurs, then Si content in the film increases. The Raman Spectra show that the amorphous Si Raman peak appears at 480 cm-1 in the film at 700°C. The Raman spectra of the films annealed at 1000 °C is fitted with two peaks, and a peak at 497 cm -1 is found, which indicated that the Si phase in the films changed from amorphous to crystalline with the increase of annealing temperature. The experiment also analyses the luminescence properties of the samples through PL spectrum, and it is found that there are five luminescence peaks in each sample under different annealing temperature. Based on the analysis of Raman spectrum and FTIR spectrum, the PL peak of amorphous silicon quantum dots appears at the wavelength range of 525-555nm, and the other four PL peaks are all from the defect state luminescence in the thin films, and the amorphous silicon quantum dot size is calculated according to the formula.

Interband Transitions in GaInNAs/GaAs Single Quantum Wells

2002 ◽  
Vol 744 ◽  
Author(s):  
M. O. Manasreh ◽  
D. J. Friedman ◽  
W. Q. Ma ◽  
C. L. Workman ◽  
C. E. George ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Mole Fraction ◽  
Chemical Vapor ◽  
Blue Shift ◽  
Peak Position ◽  
Interband Transitions ◽  
Single Quantum ◽  
Pl Spectra ◽  
Vapor Deposition Technique ◽  
Pl Intensity

ABSTRACTPhotoluminescence (PL) spectra of interband transitions in GaInNAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition technique on semi-insulating GaAs substrates were measured at 77 K for several samples grown with different In composition and dimethylhydrazine (DMH)/III ratios. The results show that the PL intensity increases as the In mole fraction is increased from 0 to 25%, but the PL intensity is degraded for samples with an In mole fraction of 30% or higher. The peak position energies of the PL spectra were investigated as a function of the DMH/III ratio. Thermal annealing effect induced a blue-shift in the PL spectra peak position energy in samples grown with high DMH/III ratio.

scholarly journals HREM at orthogonal projections of GaAs islands on silicon

1989 ◽  
Vol 47 ◽  
pp. 586-587
Author(s):  
F. A. Ponce ◽  
C. J. D. Hetherington
Keyword(s):  
Three Dimensional ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Silicon Substrates ◽  
Orthogonal Projections ◽  
Nominal Thickness ◽  
Gaas Films ◽  
Metal Organic ◽  
Trimethyl Gallium

HREM studies typically examine only one projection of a structure and information in the electron beam direction is lost. In most cases, the structure in this direction is uniform and already known, but in others a second projection needs to be observed. This could involve preparing a second specimen sectioned at right angles to the first, or as described here, tilting a specimen through ±45° and observing the same volume in orthogonal projections. The specimen used here was of GaAs islands on <001> silicon, examined in the Atomic Resolution Microscope at LBL.In the effort to grow defect-free GaAs films on silicon substrates, understanding of the early stages of growth is required. For this experiment we chose a specimen of ultra-thin GaAs grown on silicon substrate by metal-organic chemical vapor deposition (MOCVD). The GaAs was grown at 550°C for a nominal thickness of20nm from trimethyl gallium and arsine sources.The growth conditions lead to three-dimensional growth of islands bound by {111}A planes, terminated on Ga layers.

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