Equipment for Monitoring and Controlling Rheed-Oscillations

1991 ◽  
Vol 220 ◽  
Author(s):  
M. Larsson ◽  
L. -E. Björklund ◽  
G. V. Hansson
Keyword(s):  
Crystal Growth ◽  
Growth Parameters ◽  
Substrate Surface ◽  
Control Unit ◽  
Atomic Layer ◽  
Fast Response ◽  
Growth Conditions ◽  
High Energy ◽  
Oscillation Control ◽  
Discrimination Level

ABSTRACTA Light Oscillation Control Unit System (LOCUS) has been developed for the purpose of monitoring Reflexion High Energy Electron Diffraction (RHEED) oscillations and to use the oscillations to control the crystal growth with single atomic layer resolution. The system can be used for phase-locked epitaxy, i.e., shutters controlling the growth are actuated when monolayers are completed. To reduce the usual damping of the RHEED-oscillations, the system can also use the method of synchronization of nucleation, i.e., periodically varying the surface supersaturation by changing the substrate surface temperature during each oscillation. Four shutters can be operated automatically and the superlattice composition can be chosen in a number of different ways. LOCUS gives fast response on intensity oscillation maxima and minima beyond a programmable discrimination level. Relevant crystal growth parameters can be changed during the run of the program, which implies that even quasi-periodic superlattices can be grown. There is also a possibility to switch from automatic to manual control. The shutters and substrate heater have been designed to reduce the influence of shifts of the diffraction pattern as the growth conditions are changed.

White beam X-ray Diffraction Topography (WBXDT) Studies of Bridgman Grown CdZnTe Crystals

2015 ◽  
Vol 1792 ◽  
Author(s):  
Stephen Babalola ◽  
Samuel Uba ◽  
Anwar Hossain ◽  
Giuseppe Camarda ◽  
Ralph James ◽  
...  
Keyword(s):  
Growth Parameters ◽  
Charge Trapping ◽  
Radiation Detectors ◽  
Growth Conditions ◽  
High Energy ◽  
Infrared Transmission ◽  
X Ray Diffraction ◽  
Large Area ◽  
X Ray ◽  
White Beam

ABSTRACTCZT is a semiconductor material that promises to be a good candidate for uncooled gamma radiation detectors. However, to date, we are yet to overcome the technological difficulties in production of large size, defect-free CZT crystals. The most common problem is accumulation of Tellurium precipitates as microscopic inclusions. These inclusions influence the charge collection through charge trapping and electric field distortion. We employed high energy transmission X-ray diffraction techniques to study the quality of the CdZnTe crystals grown by Bridgman Technique. Crystallinity and defects within two different growth set-ups, i.e. with and without choked seeding, were compared by imaging the crystal orientation topography with white beam X-ray diffraction topography (WBXDT). The X-ray diffraction topography results show high correlation with large-area infrared transmission images of the crystals. Grain boundaries that are highly decorated with Te inclusions are observed. Characteristic Te inclusion arrangements as a result of growth conditions are discussed. We also measured the electronic properties of the detectors fabricated from ingots grown using two Bridgman processes, and observed a reduction in electrical resistivity of choked-seeding-grown CdZnTe crystals. Our results show that although choked seeding technique holds a promise in the realization of high quality mono-crystalline CdZnTe, current growth parameters must be improved to obtain defect-free crystals. These results are helpful to attain optimal seeding process for Bridgman-growth of large single crystals of CdZnTe.

Epitaxy, microstructure, and processing-structure relationships of TiO2 thin films grown on sapphire (0001) by MOCVD

1993 ◽  
Vol 8 (10) ◽  
pp. 2634-2643 ◽  
Author(s):  
H.L.M. Chang ◽  
T.J. Zhang ◽  
H. Zhang ◽  
J. Guo ◽  
H.K. Kim ◽  
...  
Keyword(s):  
Thin Films ◽  
Single Crystal ◽  
Film Growth ◽  
Growth Parameters ◽  
Substrate Surface ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Tio2 Thin Films ◽  
Growth Plane ◽  
Deposited Films

TiO2 thin films have been deposited on sapphire (0001) substrates under various conditions by metal-organic chemical vapor deposition. The structural properties of the deposited films were characterized by x-ray diffraction and transmission electron microscopy. The important growth parameters were found to be the deposition temperature and the deposition rate. The ranges studied for the two parameters were 400 to 850 °C and 10 to 120 Å/min, respectively. Depending on the growth conditions, most of the deposited films were either single-phase anatase or rutile, or a mixture of the two. These films were all epitaxial, but none of them were single-crystal films. Three distinct epitaxial relationships were observed between the films and the substrates, and, depending on the growth conditions, a deposited film can contain one, two, or all three of them. The fact that the films we obtained, although epitaxial, were never single crystal is explained based on the consideration of the difference in the rotational symmetries of the substrate surface and the film growth plane. We believe that it should be generally true that, in heteroepitaxial growth, a true single-crystal film can never be obtained as long as the point symmetry group of the substrate surface is not a subgroup of that of the film growth plane.

Growth of Cubic AlN Films on Sapphire(0001) with Atomic Scale Surface Smoothness by Pulsed Laser Deposition

2010 ◽  
Vol 638-642 ◽  
pp. 2921-2926 ◽  
Author(s):  
Tomohiro Yoshitake ◽  
Tsuyoshi Yoshitake ◽  
Kazushi Sumitani ◽  
Ryota Ohtani ◽  
You Nakagawa ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Pulsed Laser Deposition ◽  
Film Growth ◽  
Substrate Surface ◽  
Pulsed Laser ◽  
Growth Conditions ◽  
Atomic Scale ◽  
Laser Deposition ◽  
Normal Surface ◽  
Scale Surface

We have previously reported that -AlN crystallites with diameters of 0.5–1 µm were occasionally grown on sapphire(0001) by pulsed laser deposition, which implied that the migration mobility of the species deposited on the substrate surface might be an insufficient for the film growth of -AlN. In the present study, in order to enhance the crystal growth of -AlN, sapphire(0001) substrates with an atomically smoothness (step-sapphire) were employed. The growth conditions of - and -AlN extended to higher nitrogen-pressures, as compared to those using normal surface sapphire(0001) substrates (normal-sapphire). This is due to the enhancement in the mobility of the deposited species on the substrate surface.

INVESTIGATION ON INTERMOLECULAR INTERACTION IN SUPERSATURATION STATE OF CADMIUM SULPHATE MIXED ZINC tris-THIOUREA SULPHATE SOLUTIONS

2014 ◽  
Vol 02 (03n04) ◽  
pp. 1450002 ◽  
Author(s):  
G. G. MULEY ◽  
A. B. NAIK ◽  
A. B. GAMBHIRE
Keyword(s):  
Crystal Growth ◽  
Intermolecular Interaction ◽  
Growth Parameters ◽  
Chemical Properties ◽  
Adiabatic Compressibility ◽  
Growth Conditions ◽  
Ft Ir ◽  
Solid Form ◽  
Physical And Chemical ◽  
And Chemical Properties

Zinc tris-thiourea sulphate (ZTS) is a well known nonlinear optical (NLO) crystal widely used for various NLO applications. The NLO, physical and chemical properties can be modified by adding impurities and/or modifying crystal growth conditions. The impurities present in the growth solution and growth conditions can affect the crystal growth parameters at great extent. Thus, the study on the nature of intermolecular interaction with the dopant in the solution during crystal growth process becomes important. In the present investigation, the ultrasonic velocity was measured in the aqueous solutions of pure and cadmium sulphate mixed ZTS in the supersaturation state at 313.15 K. The thermodynamic parameters such as adiabatic compressibility, inter molecular free length, acoustic impedance and relative associations have been calculated from the ultrasonic data and densities of water and solutions at 313.15 K, and the nature of intermolecular interaction has been discussed. FT-IR spectra of all mixtures in the solid form at room temperature were recorded and the shifts in the absorption peaks corresponding to the functional groups of ZTS have been reported.

Reflection High-Energy Electron Diffraction as an Intrinsic Material Property Sensor for Machine Condition Transfer Function in Molecular Beam Epitaxial Growth of III-V Compound Semiconductors

1997 ◽  
Vol 502 ◽  
Author(s):  
P. Chen ◽  
C. Wangt ◽  
A. Madhukar ◽  
T. Khant ◽  
A. Small ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Growth Parameters ◽  
Growth Conditions ◽  
High Energy ◽  
Machine Condition ◽  
Test Results ◽  
High Energy Electron ◽  
New Approach ◽  
Molecular Beam Epitaxial ◽  
Molecular Beam Epitaxial Growth

ABSTRACTA new approach is introduced for identifying a relation between the growth parameters measured in two molecular beam epitaxy systems, thereby realizing transfer of optimized growth conditions transfer. Test results show that the proposed approach is promising.

CAPABILITIES OF LEED FOR DEFECT ANALYSIS

1997 ◽  
Vol 04 (03) ◽  
pp. 489-500 ◽  
Author(s):  
M. HENZLER
Keyword(s):  
Growth Parameters ◽  
Profile Analysis ◽  
Integral Intensity ◽  
Growth Conditions ◽  
High Energy ◽  
Defect Analysis ◽  
Kinematic Approximation ◽  
Resolution Electron ◽  
Electron Energy Loss ◽  
Misfit Accommodation

A diffraction pattern using low or high energy electron diffraction may be employed via the (integral) intensity of the spots to derive the atomic positions within a unit of a periodic arrangement. Spot profile analysis (SPA) provides information on periodic and nonperiodic arrangements of units as superstructure domains, terraces or facets, strained regions and so on. The first point will be the instrumentation suited for that type of analysis (SPA-LEED, SPA-RHEED and ELS-LEED, the latter using high resolution electron energy loss spectroscopy simultaneously with SPA). It will be discussed how a simple, reliable and quantitative analysis is possible within the kinematic approximation. All deviations from simple structures via defects like strain, roughness, facets or dislocations produce characteristic modifications of the spot profile, so that a specific and quantitative evaluation is possible. Finally, examples of defect analysis of heteroepitaxial films with a thickness of one to many monolayers show that many defects are necessary and therefore unavoidable for misfit accommodation. Depending on growth conditions, many other defects may appear additionally; they, however, may be reduced or avoided by appropriate growth parameters. Examples are taken from films of metals, semiconductors and insulators on quite different substrates.

Study of MBE ZnSe Growth Using Rheed Oscillations

1989 ◽  
Vol 145 ◽  
Author(s):  
Francoise S. Turco ◽  
M.C. Tamargo
Keyword(s):  
Growth Rate ◽  
Quantitative Study ◽  
Growth Parameters ◽  
Growth Conditions ◽  
High Energy ◽  
Growth Mechanisms ◽  
Mbe Growth ◽  
Wide Range ◽  
Main Growth

AbstractReflection high energy electron diffraction (RHEED) intensity oscillations are often used to investigate in situ the growth of III-V materials by molecular beam epitaxy (MBE). In this work, we have used RHEED oscillations to perform a quantitative study of the growth mechanisms of ZnSe, a II-VI semiconductor.Our experiments illustrate that the RHEED pattern of ZnSe is far less intense than that of III-V materials grown by MBE, and no specular spot is observed over a wide range of growth conditions. We have, however, been able to record up to 25 oscillations allowing a quantitative study of the growth of ZnSe by MBE. Thus we have used RHEED oscillations to make an in situ systematic study of the influence of the three main growth parameters (substrate temperature and Zn or Se impinging fluxes) on the ZnSe growth rate. We observed that the variation of the ZnSe growth rate is due to a non unity sticking coefficient of both Zn and Se species at the interface in the standard growth conditions used. Our observations can be described using a thermodynamic model and enable us to control the desired growth conditions. Our work demonstrates the utility of RHEED oscillations to understand the MBE growth mechanisms of II-VI compounds.

EuTe/PbTe Superlattices: Mbe Growth and Optical Characterization

1993 ◽  
Vol 301 ◽  
Author(s):  
G. Springholz ◽  
Shu Yuan ◽  
G. Bauer ◽  
M. Kriechbaum ◽  
H. Krenn
Keyword(s):  
Quantum Wells ◽  
Band Gap ◽  
Growth Parameters ◽  
Energy Levels ◽  
Wide Band ◽  
Growth Conditions ◽  
High Energy ◽  
Layer By Layer ◽  
Heteroepitaxial Growth ◽  
Mbe Growth

ABSTRACTThe heteroepitaxial growth of EuTe on PbTe (111) by molecular beam epitaxy (MBE) was investigated using in situ reflection high energy electron diffraction (RHEED). As a function of substrate temperature and Te2 flux rate, the resulting EuTe (111) surfaces exhibit several different surface reconstructions corresponding to Te-stabilized or Eu-stabilized surfaces. The Eustabilized surface shows a (2√3 × 2√3)R30° surface reconstruction. Because of the strain induced tendency for 3D islanding, only in a narrow window of MBE growth parameters perfect 2D layer-by-layer heteroepitaxial growth exists. Using such optimized MBE growth conditions, we have fabricated a series of PbTe/EuTe superlattices. In such superlattices the wide band gap EuTe layers act as barriers and the narrow band gap PbTe as quantum wells. The superlattices were investigated by high resolution x-ray diffraction, showing their high structural perfection. Modulated low temperature Fourier transform infrared reflection measurements were performed in order to determine the confined energy levels in the PbTe quantum wells. The measurements indicate that mini-subbands are formed in the PbTe quantum wells with a mini-band width of 22 meV in agreement with envelope function calculations.

scholarly journals Oxide Self-Flux in Optical Floating Zone Crystal Growth of Nickel Niobate (NiNb2O6)

2017 ◽  
Author(s):  
Timothy J. S. Munsie ◽  
Anna Millington ◽  
Graeme M. Luke ◽  
Hanna A. Dabkowska
Keyword(s):  
Phase Diagram ◽  
Crystal Growth ◽  
Melting Temperature ◽  
Niobium Oxide ◽  
Growth Parameters ◽  
Growth Conditions ◽  
Floating Zone ◽  
Liquid Zone ◽  
Small Excess

Growing crystals of nickel niobate (NiNb2O6), we noticed that changing growth conditions allowed our material to enter different areas of the phase diagram. In particular, we found that excess material accumulated within and above the liquid zone. Analysis showed that this was an unincorporated constituent. Changing the ratio of the constituent oxides - an excess of ~4% of either NiO or Nb2O5 gave us the opportunity to investigate changes in zone stability, melting temperature and quality of the resulting crystal. We found that a small excess of nickel oxide decreases the melting temperature significantly, and created the best pseudo-rutile NiNb2O6 crystal studied, while higher amounts of niobium oxide allowed us to stabilize the NiNb2O6 columbite phase. This research reinforces the idea that self-flux as a travelling solvent can significantly impact crystal growth parameters and quality.

Growth and Properties of SiC On-Axis Homoepitaxial Layers

2010 ◽  
Vol 645-648 ◽  
pp. 83-88 ◽  
Author(s):  
Jawad ul Hassan ◽  
Peder Bergman ◽  
Justinas Palisaitis ◽  
Anne Henry ◽  
Patrick J. McNally ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Growth Parameters ◽  
Substrate Surface ◽  
High Surface ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
High Quality ◽  
Surface Damages ◽  
Homoepitaxial Layers

Homoepitaxial growth has been performed on 3” Si-face on-axis 4H–SiC substrates using standard gas system in a horizontal Hot-wall chemical vapor deposition system. Substrate surface damages are found to act as preferential nucleation sites for 3C inclusions also, the surface morphology after in-situ etching is found to largely influence the polytype stability in the epilayer. Different in-situ etching conditions were studied where Si-rich conditions are found to be better. Growth parameters and starting growth conditions are refined to obtain stable polytype in the epilayer. High quality homoepitaxial layers with 100% 4H–SiC are obtained on 3” substrates. Different optical and structural techniques are used to characterize the layers and to understand the growth mechanisms. The layers are found to be of high quality and no epitaxial defects typically found on off-axis epitaxial layers are observed. A high surface roughness is observed in these layers, however higher growth rate significantly lowers the surface roughness without affecting the polytype stability in the epilayer.

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