Metalorganic vapor phase epitaxial growth of GaInN/GaN hetero structures and quantum wells

1996 ◽  
Vol 449 ◽  
Author(s):  
F. Scholz ◽  
V. HÄrle ◽  
F. Steuber ◽  
A. Sohmer ◽  
H. Bolay ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Vapor Phase ◽  
High Energy ◽  
Smooth Transition ◽  
Nucleation Layer ◽  
Time Resolved ◽  
Transmission Electron ◽  
Energy Peak ◽  
Scanning Transmission ◽  
Composition Fluctuations

ABSTRACTGaInN/GaN heterostructures and quantum wells have been grown by low pressure metalorganic vapor phase epitaxy on sapphire using an AIN nucleation layer. We found a significant In incorporation only for growth temperatures of 700°C, although still very high In/Ga ratios in the gas phase had to be adjusted. The In content could be increased by reducing the H2/N2 flow ratio in the main carrier gas. GaInN layers typically show two lines in low temperature photoluminescence which are identified as excitonic-like (high energy peak) and impurity-related-like (low energy) by time-resolved spectroscopy. Quantum wells with a thickness between 8 and 0.5 nm showed only one emission line. The peak of the thinnest wells shows excitonic-like behaviour, whereas we found a smooth transition to an impurity-related-like type with increasing thickness. By scanning transmission electron microscopy studies we found indications for composition fluctuations in these thicker quantum wells which may cause localization effects for the excitons and thus be responsible for the observed optical spectra.

scholarly journals GaInN/GaN-Heterostructures and Quantum Wells Grown by Metalorganic Vapor-Phase Epitaxy

1997 ◽  
Vol 2 ◽  
Author(s):  
A. Sohmer ◽  
J. Off ◽  
H. Bolay ◽  
V. Härle ◽  
V. Syganow ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Growth Parameters ◽  
Stokes Shift ◽  
Emission Peak ◽  
Band Edge ◽  
Time Resolved ◽  
Photothermal Deflection Spectroscopy ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Significant Line

The dependence of the In-incorporation efficiency and the optical properties of MOVPE-grown GaInN/GaN-heterostructures on various growth parameters has been investigated. A significant improvement of the In-incorporation rate could be obtained by increasing the growth rate and reducing the H2-partial pressure in the MOVPE reactor. However, GaInN layers with a high In-content typically show an additional low energy photoluminescence peak, whose distance to the band-edge increases with increasing In-content. For GaInN/GaN quantum wells with an In-content of approximately 12%, an increase of the well thickness is accompanied by a significant line broadening and a large increase of the Stokes shift between the emission peak and the band edge determined by photothermal deflection spectroscopy. With a further increase of the thickness of the GaInN layer, a second GaInN-correlated emission peak emerges. To elucidate the nature of these optical transitions, power-dependent as well as time-resolved photoluminescence measurements have been performed and compared to the results of scanning transmission electron microscopy.

Electron Correlation Microscopy: A New Technique for Studying Local Atom Dynamics Applied to a Supercooled Liquid

2015 ◽  
Vol 21 (4) ◽  
pp. 1026-1033 ◽  
Author(s):  
Li He ◽  
Pei Zhang ◽  
Matthew F. Besser ◽  
Matthew Joseph Kramer ◽  
Paul M. Voyles
Keyword(s):  
Electron Correlation ◽  
Supercooled Liquid ◽  
Scanning Transmission Electron Microscope ◽  
Correlation Spectroscopy ◽  
New Technique ◽  
Time Resolved ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
A New Technique ◽  
Correlation Microscopy

AbstractElectron correlation microscopy (ECM) is a new technique that utilizes time-resolved coherent electron nanodiffraction to study dynamic atomic rearrangements in materials. It is the electron scattering equivalent of photon correlation spectroscopy with the added advantage of nanometer-scale spatial resolution. We have applied ECM to a Pd40Ni40P20 metallic glass, heated inside a scanning transmission electron microscope into a supercooled liquid to measure the structural relaxation time τ between the glass transition temperature Tg and the crystallization temperature, Tx. τ determined from the mean diffraction intensity autocorrelation function g2(t) decreases with temperature following an Arrhenius relationship between Tg and Tg+25 K, and then increases as temperature approaches Tx. The distribution of τ determined from the g2(t) of single speckles is broad and changes significantly with temperature.

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.

High-Efficiency Three-Dimensional Visualization of Complex Microstructures via Multidimensional STEM Acquisition and Reconstruction

2020 ◽  
Vol 26 (2) ◽  
pp. 240-246 ◽  
Author(s):  
Kevin G. Field ◽  
Benjamin P. Eftink ◽  
Chad M. Parish ◽  
Stuart A. Maloy
Keyword(s):  
High Efficiency ◽  
3D Visualization ◽  
Accurate Determination ◽  
Three Dimensional ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
Chromium Steel ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractComplex material systems in which microstructure and microchemistry are nonuniformly dispersed require three-dimensional (3D) rendering(s) to provide an accurate determination of the physio-chemical nature of the system. Current scanning transmission electron microscope (STEM)-based tomography techniques enable 3D visualization but can be time-consuming, so only select systems or regions are analyzed in this manner. Here, it is presented that through high-efficiency multidimensional STEM acquisition and reconstruction, complex point cloud-like microstructural features can quickly and effectively be reconstructed in 3D. The proposed set of techniques is demonstrated, analyzed, and verified for a high-chromium steel with heterogeneously situated features induced using high-energy neutron bombardment.

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