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.

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.

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.

scholarly journals Using Pre-TMIn Treatment to Improve the Optical Properties of Green Light Emitting Diodes

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Bing Xu ◽  
Hai Tao Dai ◽  
Shu Guo Wang ◽  
Fu-Chuan Chu ◽  
Chou-Hsiung Huang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Quantum Wells ◽  
Radiative Decay ◽  
Light Emitting Diodes ◽  
Light Output ◽  
Green Light ◽  
Time Resolved ◽  
Light Emitting ◽  
Transmission Electron ◽  
Green Led

We investigated the effects of pre-TMIn treatment on the optical properties of green light emitting diodes (LEDs). Although pre-TMIn treatment did not affect the epitaxial structure of quantum wells, it significantly improved the quality of the surface morphology relative to that of the untreated sample. Indium cluster can be seen by high-resolution transmission electron microscopy (HR-TEM), which is the explanation for the red-shift of photoluminescence (PL). Time-resolved photoluminescence measurements indicated that the sample prepared with pre-TMIn treatment had a shorter radiative decay time. As a result, the light output power of the treated green LED was higher than that of the conventional untreated one. Thus, pre-TMIn treatment appears to be a simple and efficient means of improving the performance of green LEDs.

Nanoscale Features Grown by MBE on Nonplanar Patterned Si Substrates

1995 ◽  
Vol 380 ◽  
Author(s):  
Karl D. Hobart ◽  
Fritz J. Kub ◽  
Henry F. Gray ◽  
Mark E. Twigg ◽  
Doewon Park ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Growth Parameters ◽  
Multiple Quantum ◽  
Electron Microscopies ◽  
Si Substrates ◽  
Transmission Electron ◽  
Low Dimensional ◽  
20 Nm ◽  
Nanoscale Features ◽  
Qualitative Changes

ABSTRACTSi growth by molecular beam epitaxy on nonplanar patterned Si substrates is studied as a function of growth parameters. The substrates consist of a truncated pyramid template with {111} sides and (100) tops formed by anisotropic etching of Si(100). For growth temperatures ≤ 550°C no qualitative changes in the morphology of the template are observed. At growth temperatures between 650–700°C {113} facets begin to form on the (100) surface and reduce the lateral dimensions of the (100) facet to < 20 nm. At high temperatures (∼800°C) {113} facets remain stable and {111} facets no longer exist. The small (100) mesa formed at medium temperatures by facet reduction is exploited through the growth of Si/Si 1-xGex multiple quantum wells leading to low-dimensional structures. Observations are quantified by scanning electron and transmission electron microscopies.

Exciton localization behaviour in different well width undoped GaN/Al0.07Ga0.93N nanostructures

2007 ◽  
Vol 15 (3) ◽  
Author(s):  
M. Sabooni ◽  
M. Esmaeili ◽  
H. Haratizadeh ◽  
B. Monemar ◽  
P. Paskov ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Decay Time ◽  
Photo Luminescence ◽  
Peak Position ◽  
Emission Peak ◽  
Time Resolved ◽  
Exciton Localization ◽  
Decay Times ◽  
Detection Energy ◽  
Hole Transition

AbstractWe report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al0.07Ga0.93N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the “S-shape” dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.

scholarly journals Quantitative Chemical Mapping of InGaN Quantum Wells from Calibrated High-Angle Annular Dark Field Micrographs

2015 ◽  
Vol 21 (4) ◽  
pp. 994-1005 ◽  
Author(s):  
Daniel Carvalho ◽  
Francisco M. Morales ◽  
Teresa Ben ◽  
Rafael García ◽  
Andrés Redondo-Cubero ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Dark Field ◽  
Successful Implementation ◽  
Chemical Mapping ◽  
High Angle ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dark Field Micrographs ◽  
Ingan Quantum Wells

AbstractWe present a simple and robust method to acquire quantitative maps of compositional fluctuations in nanostructures from low magnification high-angle annular dark field (HAADF) micrographs calibrated by energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscopy (STEM) mode. We show that a nonuniform background in HAADF-STEM micrographs can be eliminated, to a first approximation, by use of a suitable analytic function. The uncertainty in probe position when collecting an EDX spectrum renders the calibration of HAADF-STEM micrographs indirect, and a statistical approach has been developed to determine the position with confidence. Our analysis procedure, presented in a flowchart to facilitate the successful implementation of the method by users, was applied to discontinuous InGaN/GaN quantum wells in order to obtain quantitative determinations of compositional fluctuations on the nanoscale.

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