Solid Phase Epitaxial Recrystallization of AlN Films on Sapphire (0001): A Novel Substrate Approach for GaN Epitaxy

1999 ◽  
Vol 587 ◽  
Author(s):  
R. D. Vispute ◽  
A. Patel ◽  
R. P. Sharma ◽  
T. Venkatesan ◽  
T. Zheleva ◽  
...  
Keyword(s):  
Thin Films ◽  
Surface Morphology ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Solid Phase ◽  
Substantial Reduction ◽  
Inert Atmosphere ◽  
Buffer Layers ◽  
Large Defect ◽  
Defect Densities

AbstractHigh quality and lattice matched buffer layers are needed for the growth of device quality GaN thin films on sapphire for optoelectronic applications. In this context, we report the fabrication of AlN thin films having low defect densities through a novel process called solid phase epitaxial recrystallization (SPER). In this process, as-grown crystalline AlN thin films, having a large defect concentration (such as threading dislocations due to a large lattice mismatch between AlN and sapphire and low angle grain boundaries), were thermally annealed in an inert atmosphere at various temperatures ranging from 1200-1600° for 30 min. The as-grown and annealed samples were characterized using x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and UV-visible spectroscopy. The ion channeling/RBS and TEM results clearly indicate a substantial reduction in the defect density for the recrystallized AlN films. The surface morphology of the SPER AlN films was smooth with a surface roughness close to the unit cell height. The optical bandgap was sharp as compared to as-grown films, with a bandgap of 6.2 eV. The recrystallized films having smooth surface morphology and low defect densities may be useful for the growth of device quality GaN films on sapphire.

Defect Reduction and Defect Engineering in Silicon-on-Sapphire Material Using Ge Implantation

1990 ◽  
Vol 201 ◽  
Author(s):  
F. Namavar ◽  
E. Cortesi ◽  
N. M. Kalkhoran ◽  
J. M. Manke ◽  
B. L. Buchanan
Keyword(s):  
Leakage Current ◽  
Defect Density ◽  
Solid Phase ◽  
Substantial Reduction ◽  
Interface Region ◽  
Radiation Environment ◽  
Solid Phase Epitaxy ◽  
Defect Reduction ◽  
Radiation Induced

AbstractSubstantial reduction of defect density in silicon-on-sapphire (SOS) material is required to broaden its range of applications to include CMOS and bipolar devices. In recent years, solid phase epitaxy and regrowth (SPEAR) and double solid phase epitaxy (DSPE) processes were applied to SOS to reduce the density of defects in the silicon. These methods result in improved carrier mobilities, but also in increased leakage current, even before irradiation. In a radiation environment, this material has a large increase in radiation induced back channel leakage current as compared to standard wafers. In other words, the radiation hardness quality of the SOS declines when the crystalline quality of the Si near the sapphire interface is improved.In this paper, we will demonstrate that Ge implantation, rather than Si implantation normally employed in DSPE and SPEAR processes, is an efficient and more effective way to reduce the density of defects near the surface silicon region without improving the Si/sapphire interface region. Ge implantation may be used to engineer defects in the Si/sapphire interface region to eliminate back channel leakage problems.

Growth of a-plane ZnO Thin Films on r-plane Sapphire by Plasma-assisted MBE

2005 ◽  
Vol 891 ◽  
Author(s):  
Junqing Q. Xie ◽  
J. W. Dong ◽  
A. Osinsky ◽  
P. P. Chow ◽  
Y. W. Heo ◽  
...  
Keyword(s):  
Thin Films ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Zno Thin Films ◽  
Rf Plasma ◽  
Misfit Dislocations ◽  
Epitaxial Relationship ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Small Lattice

ABSTRACTZnO thin films have been epitaxially grown on r-plane sapphire by RF-plasma-assisted molecular beam epitaxy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the epitaxial relationship between ZnO and r-plane sapphire is (1120)ZnO // (1102)sapphire and [0001]ZnO // [1101]sapphire. Atomic force microscopy measurements reveal islands extended along the sapphire [1101] direction. XRD omega rocking curves for the ZnO (1120) reflection measured either parallel or perpendicular to the island direction suggest the defect density anisotropy along these directions. Due to the small lattice mismatch along the ZnO [0001] direction, few misfit dislocations were observed at the ZnO/Al2O3 interface in the high-resolution cross-sectional TEM image with the zone axis along the ZnO [1100] direction.

Improved Epitaxy and Surface Morphology in YBa2Cu3Oy Thin Films Grown on Double Buffered Si Wafers

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3695-3697 ◽  
Author(s):  
J. Gao ◽  
L. Kang ◽  
H. Y. Wong ◽  
Y. L. Cheung ◽  
J. Yang
Keyword(s):  
Thin Films ◽  
Surface Morphology ◽  
Large Range ◽  
Superconducting Films ◽  
Buffer Layers ◽  
Epitaxial Thin Films ◽  
Average Surface Roughness ◽  
X Ray ◽  
Flat Interface ◽  
The Eu

Highly epitaxial thin films of YBCO have been obtained on silicon wafers using a Eu 2 CuO 4/ YSZ (yttrium-stabilized ZrO 2) double buffer. Our results showed that application of such a double buffer can significantly enhance the epitaxy of grown YBCO. It also leads to an excellent surface morphology. The average surface roughness was found less than 5 nm in a large range. The results of X-ray small angle reflection and positron spectroscpy demonstrate a very clear and flat interface between YBCO and buffer layers. The Eu 2 CuO 4/ YSZ double buffer could be promising for coating high-TC superconducting films on various reactive substrates.

scholarly journals Structural Investigation of Photocatalyst Solid Ag1−xCuxInS2 Quaternary Alloys Sprayed Thin Films Optimized within the Lattice Compatibility Theory (LCT) Scope

2014 ◽  
Vol 2014 ◽  
pp. 1-5
Author(s):  
A. Colantoni ◽  
L. Longo ◽  
K. Boubaker
Keyword(s):  
Thin Films ◽  
Lattice Mismatch ◽  
Lattice Structure ◽  
Low Cost ◽  
Buffer Layers ◽  
X Ray Diffraction ◽  
Quaternary Alloys ◽  
Solid Thin Films ◽  
Compatibility Theory ◽  
Copper Incorporation

CuxAg1−xInS2 solid thin films were fabricated through a low-cost process. Particular process-related enhanced properties lead to reaching a minimum of lattice mismatch between absorber and buffer layers within particular solar cell devices. First, copper-less samples X-ray diffraction analysis depicts the presence of AgInS2 ternary compound in chalcopyrite tetragonal phase with privileged (112) peak (d112=1.70 Å) according to JCPDS 75-0118 card. Second, when x content increases, we note a shift of the same preferential orientation (112) and its value reaches 1.63 Å corresponding to CuInS2 chalcopyrite tetragonal material according to JCPDS 89-6095 file. Finally, the formation and stability of these quaternaries have been discussed in terms of the lattice compatibility in relation with silver-copper duality within indium disulfide lattice structure. Plausible explanations for the extent and dynamics of copper incorporation inside AgInS2 elaborated ternary matrices have been proposed.

Epitaxial cerium oxide buffer layers and YBa2Cu3O7−δ thin films for microwave device applications

1999 ◽  
Vol 14 (6) ◽  
pp. 2385-2393 ◽  
Author(s):  
Sissel N. Jacobsen ◽  
Lynnette D. Madsen ◽  
Ulf Helmersson
Keyword(s):  
Thin Films ◽  
Surface Morphology ◽  
Rf Magnetron Sputtering ◽  
Sample Surface ◽  
Columnar Structure ◽  
Buffer Layers ◽  
Ex Situ ◽  
Epitaxial Relationship ◽  
Cross Sectional ◽  
Appreciable Change

CeO2 films with thicknesses ranging from 8.8 to 199 nm were grown on Al2O3 (1102) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO2 (001) planes parallel to the Al2O3 (1102) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10–90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (111)-facets. High-quality YBa2Cu3O7−δ (YBCO) thin films were deposited directly onto the CeO2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO2 layer. Postdeposition ex situ annealing was carried out on two CeO2 films and evaluated by AFM. Upon annealing samples at 930 °C, a relatively smooth morphology without facets was obtained. Annealing films at 800 °C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.

Characterization of Chemically Vapor Deposited GaN on Sic on a Simox Substrate

1997 ◽  
Vol 3 (S2) ◽  
pp. 487-488
Author(s):  
W.L. Zhou ◽  
P. Pirouz
Keyword(s):  
Lattice Mismatch ◽  
Defect Density ◽  
Silicon Layer ◽  
Large Defect ◽  
Cross Sectional ◽  
Light Emitting ◽  
Light Emitting Devices ◽  
Transmission Electron ◽  
Potential Applications ◽  
Gan Film

GaN has been intensively studied because of its potential applications for the fabrication of blue- or ultraviolet-light emitting devices. Sapphire (α-Al2O3) is generally used as the substrate for growth of GaN film. However, the large lattice mismatch between GaN and Al2O3is a possible cause of the large defect density in the GaN films. Consequently, alternative substrates are being studied with the aim of growing films of lesser defect densities and improved opto-electronic properties. In this paper, we report a transmission electron microscopy (TEM) study of a GaN film grown on cubic SiC which has been obtained by carbonization of the top silicon layer of a SIMOX substrate, i.e. the system GaN/SiC/Si/SiO2/Si.Cross-sectional TEM specimens were prepared by the conventional sandwich technique with the foil surface normal to the Si[l10] direction. The composite sample was ground and dimpled to a thickness of ∼ 10μm, and subsequently ion thinned to electron transparency.

Engineering CuInGaSSe2 Surface Properties to Enhance Device Performance

2003 ◽  
Vol 796 ◽  
Author(s):  
Shalini Menezes ◽  
Yan Li ◽  
Sharmila J. Menezes
Keyword(s):  
Surface Defects ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Dynamic Equilibrium ◽  
Spectral Response ◽  
Buffer Layers ◽  
Device Performance ◽  
Air Oxidation ◽  
Special Effect ◽  
Response Measurement

ABSTRACTThe CuInGaSSe2/CdS heterostructure interface has a special effect on the performance of an important thin film photovoltaic device. The CdS buffer layer is essential to stabilize the performance of CuInGaSSe2 based devices. It adjusts the lattice mismatch at the absorber/window interface, repairs CuInGaSSe2 surface defects and protects it from air oxidation. Unfortunately, the CdS material has many environmental issues. This paper reports an alternate chemical approach to engineer the interface defects in CuInGaSSe2 and maximize its PV output. It describes a simple processing step to manipulate the defect density. This step could potentially reduce sensitivity to the ambience, widen the surface bandgap and replace the current hazardous processes used in state-of-the-art CuInGaSSe2 modules. Photocurrent and spectral response measurement in an electrolytic medium monitor the effects of surface modification, specific metal ions and time. The CuInGaSSe2 films respond easily to a number of external stimuli with either positive or negative changes in the electro-optic properties. Strong time dependence of the photocurrent suggests a dynamic equilibrium of point defects in the CuInGaSSe2 film. The results provide new insights into the effects of stoichiometry, deposition methods and oxide formation, on the defect chemistry. They also provide directions for reconfiguring the deep defects for enhanced device performance without the need for toxic etchants or buffer layers, and the environmental hazards associated with these steps.

Effects of SrAl2O4 Homo-Buffer Layer on SrAl2O4:Eu Phosphors Film Grown on Glass by RF Sputtering

2008 ◽  
Vol 368-372 ◽  
pp. 1358-1361 ◽  
Author(s):  
Xiao Yan Fu ◽  
Hiroshi Yamada ◽  
Chao Nan Xu
Keyword(s):  
Surface Morphology ◽  
Buffer Layer ◽  
Lattice Mismatch ◽  
Rf Sputtering ◽  
Buffer Layers ◽  
Preparation Technique ◽  
X Ray Diffraction ◽  
High Quality ◽  
Crystalline Film ◽  
X Ray

The influence of pre-deposition of homo-buffer layers on film quality is studied for SrAl2O4:Eu2+ (SAO) crystalline film prepared by RF magnetron method. This preparation technique is necessary to prepare high quality films suitable for the development of SAO devices. Crystallinity and surface morphology were characterized by X-ray diffraction and scanning electron microscopy. After introducing a homo-buffer layer, not only the crystalline but also the surface morphology and adhesion of the film were obviously improved. These results imply that the buffer layer relaxes the strain due to the lattice mismatch between SAO and quartz glass, which improved the crystalline and adhesion of the film.

Epitaxial Growth and Magnetic Behavior of (Ni,Zn)Fe2O4 Thin Films on Si Substrate Using Designed Buffer Layers for Novel Memory Application

2002 ◽  
Vol 747 ◽  
Author(s):  
Naoki Wakiya ◽  
Kazuo Shinozaki ◽  
Nobuyasu Mizutani
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Remanent Magnetization ◽  
Zinc Ferrite ◽  
Lattice Mismatch ◽  
Magnetic Behavior ◽  
Buffer Layers ◽  
Si Substrate ◽  
Antiphase Boundaries ◽  
Nickel Zinc

ABSTRACTEpitaxial nickel zinc ferrite (Ni,Zn)Fe2O4 (NZF) thin films were successfully deposited on (MgO-Al2O3)/CeO2/YSZ/Si(001) substrates, where (MgO-Al2O3) is MgO doped with Al2O3. The crystallographic orientation and magnetic properties (saturation magnetization: Ms, and squareness: Mr/Ms where Mr is remanent magnetization) of NZF thin films were considerably changed with the amount of Al2O3 addition. If the amount of Al2O3 addition was less than 7 mol%, (001)-oriented epitaxial NZF thin films were obtained and the films had low squareness (around 45%). If the amount of Al2O3 addition was more than 7 mol%, (111)-oriented epitaxial NZF thin films were obtained and the films had high squareness (around 60–81%). Maximum squareness (81%) was obtained if the amount of Al2O3 addition was 26 mol%. For the sample with this Al2O3 content, the lattice mismatch between NZF and (MgO-Al2O3) buffer layer was 3.2%. The fact that high squareness was not obtained if lattice mismatch was very small (-0.3% on MgO) but obtained if lattice mismatch was 3.2% suggests that lattice mismatch to a certain content is important to avoid the formation of antiphase boundaries (APBs). This consideration was confirmed by examining other buffer layers having various lattice mismatches with NZF.

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