Chemical Imaging of InGaAs/InAiAs Quantum Wells

1996 ◽  
Vol 466 ◽  
Author(s):  
G. Mountjoy ◽  
P. A. Crozier ◽  
P. L. Fejes ◽  
R. K. Tsui ◽  
G. D. Kramer
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Quantum Wells ◽  
Chemical Imaging ◽  
Double Quantum ◽  
Quantum Well Structures ◽  
Double Quantum Well ◽  
Transmission Electron ◽  
Inp Substrate ◽  
Compositional Variations

ABSTRACTWe have applied high resolution chemical imaging in a transmission electron microscope to study compositional variations across InGaAs/InAIAs double quantum well structures. The structures of interest are grown on an InP substrate and consist of two 40 Å layers of InGaAs separated by 20 Å of InAlAs. For this (InGa)x(InAl)1-xAs system, we have been able to obtain compositional information with an accuracy of about 20 % and a maximum spatial resolution of 1/2 × 1/2 unit cell. The results clearly show irregularities on a monatomic scale.

A THEORETICAL AND EXPERIMENTAL STUDY OF ELECTRONIC CONFINEMENT, COUPLING, AND TRANSLAYER INTERACTION IN NOBLE-METAL QUANTUM-WELL STRUCTURES

1994 ◽  
Vol 08 (18) ◽  
pp. 1075-1096 ◽  
Author(s):  
W. E. MCMAHON ◽  
T. MILLER ◽  
T.-C. CHIANG
Keyword(s):  
Quantum Well ◽  
Quantum Wells ◽  
Noble Metal ◽  
Experimental Studies ◽  
Surface States ◽  
Double Quantum ◽  
Multilayer Systems ◽  
Quantum Well Structures ◽  
Double Quantum Well ◽  
Bloch Electrons

Noble-metal multilayer systems have been grown and examined with angle-resolved photoemission. Surface states, and single and double quantum wells have been studied experimentally; the results can be explained with a simple theoretical model based upon Bloch electrons. In this paper, we will present our model and then give a description of some experimental studies which utilize the model. In particular, we will consider double-quantum-well systems which can be used to examine basic aspects of electronic confinement, layer–layer coupling, and translayer interaction through a barrier.

1.95 μm Compressively Strained Ingaas/Ingaasp Quantum Well DFB Laser With Low Threshold

1997 ◽  
Vol 484 ◽  
Author(s):  
Jie Dong ◽  
Akinoi Ubukata ◽  
Koh Matsumoto
Keyword(s):  
Quantum Well ◽  
Quantum Wells ◽  
Chemical Vapor ◽  
Double Quantum ◽  
Maximum Output ◽  
Quantum Well Structures ◽  
Double Quantum Well ◽  
Different Temperatures ◽  
Dfb Laser ◽  
Strained Quantum Well

AbstractIn this study, we demonstrate the growth of highly compressively strained InGaAs/JnGaAsP quantum well structures with large well thiclmess by low pressure metalorganic chemical vapor deposition for extending the emission wavelength of lasers. By comparing the photolumineswnce characteristics of quantum wells grown at different temperatures, it is clarified that a relatively high quality quantum well layer emittig at 2.0 μ, can be obtained at a growth temperature of 650°C. 1.95-μm-wavelength InGaAs/InGaAsP highly compressively strained quantum well DFB laser for laser spectroscopy monitors was also fabricated. Double quantum-well DFB laser operating at 1.95 μm exhibits threshold currents as low as 6 mA and 6.2 mW maximum output powers. 2.04-μm-wavelength DFB laser is also described.

High Resolution Electron Microscopy of InGaAs/InAIAs Interfaces

1996 ◽  
Vol 54 ◽  
pp. 120-121
Author(s):  
G. Mountjoy ◽  
P.A. Crozier ◽  
P.L. Fejes ◽  
R.K. Tsui ◽  
G.D. Kramer
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Quantum Wells ◽  
High Resolution Electron Microscopy ◽  
Frequency Component ◽  
Chemical Imaging ◽  
Inp Substrate ◽  
Resolution Electron ◽  
Compositional Changes ◽  
Lattice Matched

Recently, quantum wells (QW) have been constructed using the (In0.532Ga0.468)As/ (In0.522Al0.478)As system (hereafter InGaAs/In Al As), which is lattice matched to InP (lattice constant of 5.869Å). In order to understand the properties of such QWs, it is important to have knowledge of the structure and composition of interfaces. For III-V materials, compositional changes affect the <200> frequency component of the high resolution electron microscopy (HREM) image intensity (I200). This underlies the “chemical imaging” approach. Simulations for InGaAs/InAlAs interfaces suggest optimum conditions of microscope defocus df=-50nm and sample thickness t=14nm in the <100> orientation. A double-QW structure, consisting of InGaAs/ InAlAs/ InGaAs layers with nominal thicknesses of 4nm/ 2nm/ 4nm (respectively), and embedded in InAlAs layers, has been studied. All the layers were grown by molecular beam epitaxy at 500°C on a <100> InP substrate, with 60s growth interrupts between layers in the QW region.

MAGNETO-LUMINESCENCE OF A SINGLE LATERAL ISLAND FORMED IN A TYPE - II GaAs/AlAs QW

2004 ◽  
Vol 18 (27n29) ◽  
pp. 3807-3812 ◽  
Author(s):  
BARBARA CHWALISZ ◽  
ANDRZEJ WYSMOLEK ◽  
ROMAN STȨPNIEWSKI ◽  
ADAM BABINSKI ◽  
MAREK POTEMSKI ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Emission Lines ◽  
Luminescence Spectra ◽  
Double Quantum ◽  
Type I ◽  
Type Ii ◽  
Quantum Well Structures ◽  
Indirect Excitons ◽  
Double Quantum Well ◽  
Efficient Type

Ensembles of sharp emission lines present in the macro-luminescence of type-II GaAs / AlAs double quantum well structures were studied. Micro-luminescence experiments allowed us to conclude that the sharp emission lines originate from lateral GaAlAs islands of a few μm in diameter, formed in the structure. They serve as efficient type-I recombination centers for indirect excitons and/or carriers diffusing in the GaAs / AlAs QW structure. Magneto-luminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells. The observed emission is assigned to the recombination of neutral excitons as well as excitonic molecules.

Quantitative compositional mapping of InxGa1-XAs/GaAs quantum wells by annular dark field imaging

1995 ◽  
Vol 53 ◽  
pp. 294-295
Author(s):  
S. Hillyard ◽  
Y.-P. Chen ◽  
W.J. Schaff ◽  
L.F. Eastman ◽  
J. Silcox
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Quantum Wells ◽  
Transmission Electron Microscope ◽  
Dark Field ◽  
Thickness Variation ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Field Imaging

Annular dark field imaging in the scanning transmission electron microscope (STEM) exhibits both high resolution and Z-contrast. It is intrinsically quantitative since image data can be recorded directly from linear detectors into digital memory. Annular dark field imaging has been used, along with energy filtered imaging to correct for sample thickness variation, to map out the In concentration in InxGa1-xAs quantum wells with near atomic resolution and sensitivity. This approach is similar to “chemical lattice imaging”, which maps out composition variation using a conventional transmission electron microscope image and a vector pattern recognition algorithm.The quantum wells were grown by molecular-beam epitaxy (MBE). Figure 1 shows a typical high resolution annular dark field image of a 50 Å wide nominal In0.3Ga0.7As/GaAs quantum well. The linescan in figure 2 gives the actual numbers making up the image. Barring contaminants and lattice imperfections, the change in intensity with position is caused by two things: variation of In concentration and thickness.

MOCVD Growth and Characterization of GaInNAs/GaAs/InGaAs/GaAs Quantum Well Structures

2002 ◽  
Vol 744 ◽  
Author(s):  
Abdel-Rahman A. El-Emawy ◽  
Hongjun Cao ◽  
Noppadon Nuntawong ◽  
Chiyu Liu ◽  
Marek Osiński
Keyword(s):  
Quantum Well ◽  
Quantum Wells ◽  
Growth Parameters ◽  
Multiple Quantum Well ◽  
Double Quantum ◽  
Multiple Quantum ◽  
Quantum Well Structures ◽  
Mocvd Growth ◽  
Double Quantum Well ◽  
Wavelength Emission

ABSTRACTEffects of MOCVD growth parameters on structural and optical properties of double-quantum-well (DQW) structures containing uncoupled GaInNAs/GaAs and InGaAs/GaAs quantum wells have been investigated. By varying growth temperature, growth rate, V/III ratio, and DMHy flow rates, we have achieved a longer-wavelength emission from a GaInNAs well than from an InGaAs well grown in the same structure. GaInNAs/GaAs multiple-quantum-well structures grown under optimum conditions emitted at 1.25 μm.

GIANT INCREASE OF THE EXCITON LIFETIME IN SEMIMAGNETIC SEMICONDUCTORS WITH DOUBLE QUANTUM WELLS IN MAGNETIC FIELD

2004 ◽  
Vol 03 (04n05) ◽  
pp. 541-547
Author(s):  
I. Yu. GOLINEY ◽  
S. B. LEV ◽  
V. I. SUGAKOV ◽  
G. V. VERTSIMAKHA
Keyword(s):  
Magnetic Field ◽  
Quantum Well ◽  
Quantum Wells ◽  
Double Quantum ◽  
Quantum Well Structures ◽  
Indirect Exciton ◽  
Exciton Lifetime ◽  
Double Quantum Well ◽  
Single Well ◽  
Semimagnetic Semiconductors

Magnetic field dependence of the excitonic spectrum and the intensity of the optical transitions for excitons in the double quantum well heterostructures based on semimagnetic semiconductors of various compositions are studied. The calculations carried out for (Zn, Mn)Se -based double quantum well structures showed that in the weak magnetic fields, the lowest energy states are the single-well states (direct excitons) for which both the electron and the hole are predominantly localized in the same well. At some values of magnetic field, the crossing of the direct exciton with indirect exciton formed by an electron and a hole, situated predominantly in the different wells, occurs. In the magnetic field exceeding some critical value, the lowest energy level belongs to the indirect exciton. According to the estimates, the lifetime of the indirect exciton is by several orders of magnitude larger than that of a single-well exciton. The exciton lifetime depends significantly on the width and the material of the barrier between the wells.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

A New High Resolution Transmission Electron Microscope with Second-Zone Objective Lens

1969 ◽  
Vol 27 ◽  
pp. 176-177 ◽  
Author(s):  
H. Tochigi ◽  
H. Uchida ◽  
S. Shirai ◽  
K. Akashi ◽  
D. J. Evins ◽  
...  
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Transmission Electron Microscope ◽  
Objective Lens ◽  
High Excitation ◽  
Transmission Electron ◽  
New Instrument

A New High Excitation Objective Lens (Second-Zone Objective Lens) was discussed at Twenty-Sixth Annual EMSA Meeting. A new commercially available Transmission Electron Microscope incorporating this new lens has been completed.Major advantages of the new instrument allow an extremely small beam to be produced on the specimen plane which minimizes specimen beam damages, reduces contamination and drift.

To What Extent are Inelastically Scattered Electrons Useful in the Stem?

1973 ◽  
Vol 31 ◽  
pp. 286-287 ◽  
Author(s):  
H. Rose
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Electron Correlation ◽  
Quantum Noise ◽  
Collection Efficiency ◽  
Scanning Transmission Electron Microscope ◽  
Electron Cloud ◽  
Scanning Time ◽  
Transmission Electron ◽  
Scanning Transmission

The scanning transmission electron microscope offers the possibility of utilizing inelastically scattered electrons. Use of these electrons in addition to the elastically scattered electrons should reduce the scanning time (dose) Which is necessary to keep the quantum noise below a certain level. Hence it should lower the radiation damage. For high resolution, Where the collection efficiency of elastically scattered electrons is small, the use of Inelastically scattered electrons should become more and more favorable because they can all be detected by means of a spectrometer. Unfortunately, the Inelastic scattering Is a non-localized interaction due to the electron-electron correlation, occurring predominantly at the circumference of the atomic electron cloud.

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