High-Resolution TEM Observation of AlN/GaN Grown on Si Substrates

2011 ◽  
Vol 110-116 ◽  
pp. 991-996
Author(s):  
Lee Siang Chuah ◽  
A. Mahyudin ◽  
Z. Hasan ◽  
C.W. Chin
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Growth Dynamics ◽  
High Energy ◽  
Ex Situ ◽  
Rf Plasma ◽  
Si Substrates ◽  
Cap Layer ◽  
High Resolution Tem ◽  
Aln Buffer

A high-quality crack-free AlN cap layer on GaN layer has been achieved using an AlN buffer layer directly grown on a silicon substrate at high temperature by radio frequency (RF) plasma-assisted molecular beam epitaxy. A two dimensional (2D) growth process guide to AlN cap layer of high grade crystal quality. The nucleation and the growth dynamics have been studied by in situ reflection high energy electron diffraction (RHEED) and ex situ by high resolution transmission electron microscopy (HR-TEM). The microstructure was investigated by energy-dispersive X-ray spectroscopy (EDX). It was disclosed that AlN is single crystalline with low defect. High densities of V-shaped pits were not detected at the interface between AlN and GaN layers. Contradictory the earlier reported V-shaped defects in nitride-based alloys; these V-shaped pits were condensed on top of the AlN layer because of H2 etching of the surface when a high temperature growth discontinuity between AlN and GaN layers.

Preparation and Characterization of La1Sr2Nb5O10−x Specimens

1990 ◽  
Vol 209 ◽  
Author(s):  
Donald H. Galvàn ◽  
M. Avalos-Borja ◽  
L. Cota-Araiza ◽  
J. Cruz-Reyes ◽  
E. A. Early
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
X Rays ◽  
High Resolution Tem ◽  
Nominal Stoichiometry

ABSTRACTRecently Ogushi et al reported a La-Sr-Nb-O compound with a superconducting temperature of about 225 K. The possibility of having superconductors with such a high temperature is certainly technologically relevant. We prepared specimens with the same nominal stoichiometry and performed characterization by SEM, high resolution TEM, Scanning Auger and X-rays.

Stresses experienced by AlN films grown on sapphire

2005 ◽  
Vol 892 ◽  
Author(s):  
Jie Bai ◽  
J. Bai ◽  
V.L. Tassev ◽  
M. Lal Nakarmi ◽  
W. Sun ◽  
...  
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Lattice Mismatch ◽  
Tem Analysis ◽  
Mocvd Growth ◽  
Compressive Stresses ◽  
Show Evidence ◽  
High Resolution Tem ◽  
Final Stress ◽  
Lower Temperature

AbstractThe evolution of stress during the MOCVD growth of AlN thin films on sapphire substrates under both low and high temperature conditions has been evaluated. The final stress state of the films is assumed to consist of the summation of stresses from three different sources: (1) the stress which arises from residual lattice mismatch between film and substrate i.e. that which persists after partial relaxation by misfit dislocation formation. The extent of relaxation is determined from High Resolution TEM analysis of the substrate/film interface; (2) the stress arising from the coalescence of the 3D islands nucleated in this high mismatch epitaxy process. This requires knowledge of the island sizes just prior to coalescence and this was provided by AFM studies of samples grown under the conditions of interest; and (3) the stress generated during post-growth cooling which arises from the differences in thermal expansion coefficient between AlN and sapphire. The final resultant stress, comprising the summation of stresses arising from these three sources, is found to be tensile in the sample grown at lower temperature and compressive in the sample grown at higher temperature. These results are in general qualitative agreement with results of TEM and High resolution X-ray diffraction (HRXRD) studies, which show evidence for tensile and compressive stresses in the low temperature and high temperature cases, respectively.

Effects of Phosphorus Exposure on Arsenic-Stabilized GaAs 2×4 Surface

1993 ◽  
Vol 312 ◽  
Author(s):  
A. H. Bensaoula ◽  
A. Freundlich ◽  
A. Bensaoula ◽  
V. Rossignol
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Growth Process ◽  
High Energy ◽  
Ex Situ ◽  
Chemical Beam Epitaxy ◽  
High Energy Electron ◽  
X Ray Diffraction ◽  
X Ray

AbstractPhosphorus exposed GaAs (100) surfaces during a Chemical Beam Epitaxy growth process are studied using in-situ Reflection High Energy Electron Diffraction and ex-situ High Resolution X-ray Diffraction. It is shown that the phosphorus exposure of a GaAs (100) surface in the 500 – 580 °C temperature range results in the formation of one GaP monolayer.

In situsynchrotron powder diffraction study of active belite clinkers

2007 ◽  
Vol 40 (6) ◽  
pp. 999-1007 ◽  
Author(s):  
Ángeles G. De la Torre ◽  
Khadija Morsli ◽  
Mohammed Zahir ◽  
Miguel A.G. Aranda
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Powder Diffraction ◽  
Polymorphic Transformation ◽  
High Energy ◽  
Dicalcium Silicate ◽  
Polymorphic Transformations ◽  
X Ray ◽  
High Temperature Reactions

The clinkerization processes to form belite clinkers, with theoretical compositions close to 60 wt% of Ca2SiO4, have been studiedin situby high-resolution high-energy (λ = 0.30 Å) synchrotron X-ray powder diffraction. In order to obtain active belite cements, different amounts of K2O, Na2O and SO3have been added. The existence range of the high-temperature phases has been established and, furthermore, Rietveld quantitative phase analyses at high temperature have been performed for all patterns. The following high-temperature reactions have been investigated: (i) polymorphic transformations of dicalcium silicate, \alpha_{\rm L}'-Ca2SiO4↔ \alpha_{\rm H}'-Ca2SiO4from 1170 to 1230 K, and \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4from 1500 to 1600 K; (ii) melting of the aluminates phases, Ca3Al2O6and Ca4(Al2Fe2)O10, above ∼1570 K; and (iii) reaction of Ca2SiO4with CaO to yield Ca3SiO5above ∼1550 K. Moreover, in all the studied compositions the temperature of the polymorphic transformation \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.

High-resolution TEM studies of mullite formation in metakaolinite

1986 ◽  
Vol 44 ◽  
pp. 466-467
Author(s):  
Mehmet Sarikaya ◽  
IInan A. Aksay
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Spinel Phase ◽  
Exothermic Reaction ◽  
High Strength ◽  
Mullite Formation ◽  
Subsequent Formation ◽  
High Resolution Tem ◽  
Mixed Systems ◽  
Microstructural Homogeneity

Studies on the compressive fracture strength (759 MPa at 15000°C) and the flexural strength (700MPaat 1300°C) of polycrystalline mullite (3Al2O3•2SiO2-2Al2O3•SiO2) illustrate its potential for high temperature applications. In the processing of these high strength mullites, molecularly mixed Al2O3-SiO2 precursors are used to enhance mullite formation rates and to achieve microstructural homogeneity in the submicrometer range. Reaction steps leading to the formation of mullite in molecularly mixed systems are not adequately understood. The prevailing problems center around (i) the composition of a spinel phase that forms at around a 980°C exothermic reaction, and (ii) the concurrent or subsequent formation and growth of mullite. Here, we report our high resolution TEM results on the formation of the spinel and mullite phases in a molecularly mixed precursor, metakaolinite (Al2O3•2SiO2).

scholarly journals An ex Situ Underground Coal Gasification Experiment with a Siderite Interlayer. Course of the Process, Production Gas, Temperatures and Energy Efficiency

2020 ◽  
Author(s):  
Marian Wiatowski ◽  
Krzysztof Kapusta ◽  
Jacek Nowak ◽  
Marcin Szyja ◽  
Wioleta Basa
Keyword(s):  
Energy Efficiency ◽  
High Temperature ◽  
Flow Rate ◽  
Coal Gasification ◽  
High Energy ◽  
Ex Situ ◽  
Hard Coal ◽  
Underground Coal Gasification ◽  
Gasification Process ◽  
Process Gas

Abstract A 72-hour ex situ hard coal gasification test in one large block of coal was carried out. The gasifying agent was oxygen with a constant flow rate of 4.5 Nm3/h. The surroundings of coal were simulated with wet sand with 11% moisture content. A 2-cm interlayer of siderite was placed in the horizontal cut of the coal block. As a result of this process, gas with an average flow rate of 12.46 Nm3/h was produced. No direct influence of siderite on the gasification process was observed; however, measurements of CO2 content in the siderite interlayer before and after the process allowed to determine the location of high-temperature zones in the reactor. The greatest influence on the efficiency of the gasification process was exerted by water contained in wet sand. At the high temperature that prevailed in the reactor, this water evaporated and reacted with the incandescent coal, producing hydrogen and carbon monoxide. This reaction contributed to the relatively high calorific value of the resulting process gas, averaging 9.41 MJ/kmol, and to the high energy efficiency of the whole gasification process, which amounted to approximately 70%.

scholarly journals Structural, Optical, and Electrical Characterization of β-Ga2O3 Thin Films Grown by Plasma-Assisted Molecular Beam Epitaxy Suitable for UV Sensing

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Abraham Arias ◽  
Nicola Nedev ◽  
Susmita Ghose ◽  
Juan Salvador Rojas-Ramirez ◽  
David Mateos ◽  
...  
Keyword(s):  
Thin Films ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Uv Light ◽  
Electrical Characterization ◽  
High Energy ◽  
Ex Situ ◽  
Rf Plasma ◽  
Light Illumination ◽  
Electrical Measurements

β-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films were grown using an elemental gallium source and oxygen supplied by an RF plasma source. Reflection high-energy electron diffraction (RHEED) was used to monitor the surface quality in real time. Both in situ RHEED and ex situ X-ray diffraction confirmed the formation of single crystal β-phase films with excellent crystallinity on c-plane sapphire. Spectroscopic ellipsometry was used to determine the film thicknesses, giving values in the 11.6–18.8 nm range and the refractive index dispersion curves. UV-Vis transmittance measurements revealed that strong absorption of β-Ga2O3 starts at ∼270 nm. Top metal contacts were deposited by thermal evaporation for I-V characterization, which has been carried out in dark, as well as under visible and UV light illumination. The optical and electrical measurements showed that the grown thin films of β-Ga2O3 are excellent candidates for deep-ultraviolet detection and sensing.

Ion Damage Production in GaAs/Al0.6Ga0.4As Heterostructures

1994 ◽  
Vol 373 ◽  
Author(s):  
B.A. Turkot ◽  
I.M. Robertson ◽  
M.A. Kirk ◽  
L.E. Rehn ◽  
P.M. Baldo ◽  
...  
Keyword(s):  
High Resolution ◽  
Point Defects ◽  
High Energy ◽  
Cross Sectional ◽  
Background Population ◽  
Ion Damage ◽  
High Resolution Tem ◽  
High Energy Ions ◽  
Extent Of Damage ◽  
Cascade Type

AbstractThe non-uniform distribution of damage with depth and the onset of amorphization produced in Al0.6Ga0.4As/GaAs heterostructures by 1.5 MeV Kr+ ion implantation at 77K have been investigated by using a combination of RBS channeling and cross-sectional high-resolution TEM techniques. The extent of damage increases with increasing depth in the Al0.6Ga0.4As layer. This depth dependence of the damage can be correlated with an increase in the number of recoil events with an energy between 30 and 50 keV. We propose that the amorphization of Al0.6Ga0.4As requires the superposition of cascade-type damage on a background population of point defects which is created by implantation with high energy ions.

High Resolution TEM of Post-Deposition Ion Implanted C-BN Films

1999 ◽  
Vol 5 (S2) ◽  
pp. 830-831
Author(s):  
T. Dolukhanyan ◽  
S. Gunasekara ◽  
E. Byon ◽  
S.W. Lee ◽  
S.R. Lee ◽  
...  
Keyword(s):  
High Resolution ◽  
Ion Implantation ◽  
Plasma Source ◽  
Si Substrates ◽  
Routine Manner ◽  
Plasma Source Ion Implantation ◽  
High Resolution Tem ◽  
Film Substrate ◽  
Post Deposition ◽  
Ion Implanted

Post-deposition ion implantation of boron nitride (BN) films is to be considered as a powerful method for improvement of adhesion between films and substrates and reduction of compressive stresses, which usually accompany the growth of cubic BN.The goal of this investigation is microcharacterization of as-deposited and ion-implanted BN films to better understand effect of ion implantation on microstructure of the films and film/substrate interface. High Resolution TEM (HF-2000 with field emission gun) has been utilized because of nanocrystalline dimensions of both cubic (c-) and hexagonal (h-) BN phases.BN films have been deposited on (100) oriented Si substrates by magnetically enhanced activated reactive evaporation2. Plasma source ion implantation has been performed to make surface modifications and to improve the adhesion of the films. X/S specimens for TEM and HRTEM have been prepared in a routine manner, using G-1 epoxy for coupling the specimens, Dimpler VCR D500I, and Gatan Precision Ion Polishing System for final thinning.

Sign in / Sign up

Export Citation Format

Share Document