Bound Exciton Energies, Biaxial Strains, and Defect Microstructures in GaN/AlN/6H-SiC(0001) Heterostructures

1996 ◽  
Vol 449 ◽  
Author(s):  
W. G. Perry ◽  
T. Zheleva ◽  
K. J. Linthicum ◽  
M. D. Bremser ◽  
R. F. Davis ◽  
...  
Keyword(s):  
Defect Formation ◽  
Lattice Mismatch ◽  
Compressive Strain ◽  
Lattice Parameter ◽  
Buffer Layers ◽  
Film Stress ◽  
Thermal Expansion Coefficients ◽  
Transmission Electron ◽  
Defect Microstructures

ABSTRACTBiaxial strains resulting from mismatches in thermal expansion coefficients and lattice parameters in 22 GaN films grown on A1N buffer layers previously deposited on vicinal and on-axis 6H-SiC(0001) substrates were measured via changes in the c-axis lattice parameter (c). Six of the films were in compression, indicating the residual strain due to lattice mismatch was not relieved. A Poisson's ratio of v=0.18 was calculated. The bound exciton energy (EBx) was a linear function of these strains. The shift in EBx with film stress was 23 meV/GPa. The role of the SiC off-axis tilt was investigated for GaN films grown concurrently on the vicinal and on-axis 6H-SiC substrates. Marked variations in EBx and c were observed, with a maximum shift of ΔEBx = 15 meV and Δc = 0.0042 Å. Threading dislocations densities of ~1010/cm2 and ~108/cm2 were determined for GaN films grown on vicinal and on-axis SiC, respectively. A 0.9% residual compressive strain at the GaN/AIN interface was observed by high resolution transmission electron microscopy (HRTEM). It is proposed that the on-axis SiC substrate does not offer a sufficient density of steps for defect formation to relieve the lattice mismatch between GaN and A1N and A1N and SiC.

Transmission electron microscopy of epitaxial gallium arsenide grown on a variety of silicon substrates by metallorganic chemical vapor deposition

1987 ◽  
Vol 45 ◽  
pp. 342-343
Author(s):  
J. M. Brown ◽  
S. J. Pearton ◽  
R. Caruso ◽  
M. Stavola ◽  
K. T. Short ◽  
...  
Keyword(s):  
Integrated Circuit ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Gaas Layer ◽  
Buffer Layers ◽  
Silicon Substrates ◽  
Thermal Expansion Coefficients ◽  
Growth Regime ◽  
Transmission Electron ◽  
Strained Layer Superlattices

The growth of GaAs layers on silicon substrates is under extensive investigation with a view to achieving the integration of GaAs-based optoelectronic devices with Si integrated circuit technology. The large lattice mismatch between Si and GaAs (-4%) together with the differences in the thermal expansion coefficients between the two materials results in a highly stressed interface. Several different approaches have been undertaken in attempts to reduce the dislocation density of the GaAs layer. The inclusion of graded composition GaAsP ‘buffer’ layers, intermediate Ge layers and the inclusion of strained layer superlattices in the growth regime have been reported by many workers. Growth of GaAs directly on Si has been reported to yield GaAs heteroepitaxial films suitable for electronic applications such as FETs and low threshold AlGaAs/GaAs double heterostructure injection lasers.

Microstructures of AlN Buffer Layers for the Growth of GaN on (0001) Al2O3

1996 ◽  
Vol 449 ◽  
Author(s):  
M. Yeadon ◽  
W. Kim ◽  
A. E. Botchkarev ◽  
S. N. Mohammad ◽  
H. Morkoc ◽  
...  
Keyword(s):  
Lattice Mismatch ◽  
Wide Band ◽  
Buffer Layers ◽  
Initial Growth ◽  
Nitridation Time ◽  
Transmission Electron ◽  
Different Temperatures ◽  
Aln Buffer ◽  
Nitride Layers

ABSTRACTIll-nitride semiconductors are emerging as highly promising candidates for the fabrication of wide band-gap electronic and opto-electronic devices. Sapphire ((α-A12O3) is currently one of the primary substrates of choice for the growth of GaN despite a large lattice mismatch. Significant improvements in the quality of III-nitride layers have been demonstrated by exposure of the substrate to reactive nitrogen species followed by deposition of a low temperature AIN or GaN buffer layer. In this paper we present a study of the evolution of the surface topography and defect microstructure of nitrided α-A12O3 substrates and AIN buffer layers deposited by reactive molecular beam epitaxy (RMBE). Their influence on the morphology and properties of GaN layers is also discussed. Both nitridation time and AIN deposit thickness were varied systematically, at different temperatures and buffer growth rates. The microstructures were characterized using the atomic force microscope (AFM) and transmission electron microscope (TEM). Initial growth studies are ideally suited to in-situ experiments, and further investigations are also in progress using a unique UHV TEM with the facility for in-situ RMBE.

Defects and Interfaces in GaN Epitaxy

MRS Bulletin ◽  
1997 ◽  
Vol 22 (2) ◽  
pp. 51-57 ◽  
Author(s):  
F.A. Ponce
Keyword(s):  
Thermal Expansion ◽  
High Performance ◽  
Lattice Mismatch ◽  
Thermal Strain ◽  
Chemical Vapor ◽  
Visible Spectrum ◽  
Lattice Parameter ◽  
Buffer Layers ◽  
Semiconductor Films ◽  
Recent Developments

The recent developments in III-V-nitride thin-film technology has produced significant advances in high-performance devices operating in the blue and green range of the visible spectrum. These materials are grown by metalorganic chemical vapor deposition (MOCVD) on (0001) sapphire substrates. Highly specular surfaces are possible by use of low-temperature buffer layers following the method developed by Akasaki et al. The thin films thus grown have an interesting microstructure, quite different from other known semiconductors. In particular, epilayers with high optoelectronic performance are characterized by high dislocation densities, several orders of magnitude above those found in other optoelectronic semiconductor films. The lattice mismatch between sapphire and GaN is ∼14%, and the thermal-expansion difference is close to 80%. In spite of these large differences, little thermal strain is measurable at room temperature in epilayers grown at temperatures above 1000°C. Epitaxy on other systems, like SiC, with much better similarity in lattice parameter and thermal-expansion characteristics, has failed to produce better performance than films grown on sapphire. The origin of these puzzling properties of nitrides on sapphire rests in its microstructure. This article presents a survey of the microstructure associated with epitaxy of nitrides by MOCVD.

Preparation and Time Resolved Photoluminescence of Nanoscale InP Islands in In0.48Ga0.52P

1995 ◽  
Vol 379 ◽  
Author(s):  
K. Eberl ◽  
A. Kurtenbach ◽  
K. HÄusler ◽  
F. Noll ◽  
W.W. RÜhle
Keyword(s):  
Lattice Mismatch ◽  
Excitation Power ◽  
Buffer Layers ◽  
Time Resolved ◽  
Force Microscopy ◽  
Self Assembling ◽  
Atomic Force ◽  
Transmission Electron ◽  
Decay Times ◽  
Time Resolved Photoluminescence

ABSTRACTNanoscale InP islands are formed during InP/In0 48Ga0.52P heteroepitaxy due to the lattice mismatch of about 3.7%. The samples are prepared by solid source molecular beam epitaxy on (001) GaAs substrate. Atomic force microscopy measurements show that the size of the islands is typically 15 to 50 nm in diameter and about 5 to 10 nm high depending on the nominally deposited InP layer thickness, which is between 1 and 7.5 monolayers. Transmission electron micrographs show the coherent incorporation into the In0.48Ga0.52P matrix for InP islands with 2.5 monolayers. Resonantly excited time-resolved photoluminescence (PL) measurements of the self assembling InP dots are performed for optical characterisation. The decay times are typically 400 ps. The dependence on excitation power and temperature indicates the quantum dot nature of the InP islands. Finally a pronounced alignment of the InP islands is obtained on strained In0.61Ga0.39P buffer layers.

Epitaxial Growth and Structure of Cubic and Pseudocubic Perovskite Films on Perovskite Substrates

1995 ◽  
Vol 401 ◽  
Author(s):  
P. A. Langjahr ◽  
T. Wagner ◽  
M. RÜhle ◽  
F. F. Lange
Keyword(s):  
Electron Microscopy ◽  
Epitaxial Growth ◽  
Lattice Mismatch ◽  
High Resolution Electron Microscopy ◽  
Lattice Parameter ◽  
Ternary Oxide ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Resolution Electron

AbstractCubic and pseudocubic perovskite films on perovskite substrates are used to study the influence of the lattice mismatch on the epitaxial growth of thin films on substrates of the same structure. For the growth of the films, a metalorganic decomposition route (MOD) using 2-ethylhexanoates and neodecanoates as precursors, was developed. The decomposition of the precursors was investigated with thermogravimetric analysis (TGA) and x-ray diffraction (XRD). The films were spin-coated on (001)-oriented SrTiO3- and LaAlO3-substrates, pyrolyzed and afterwards annealed between 600°C and 1200°C. XRD-nvestigations and conventional transmission electron microscopy (CTEM) show, that epitaxial films with the orientation relationship [100](001) film ║ [100](001) substrate can be grown. With XRD, it could be shown, that not only ternary oxide films (SrZrO3, BaZrO3 and BaCeO3), but also perovskite solid solution films (SrTi0.5Zr0.5O3and BaCe0.5Zr0.5O3) can be prepared. Strong interdiffusion, detected by a shift of the film lattice parameter towards the substrate lattice parameter was found in SrZrO3- and BaZrO3-films on SrTiO3, annealed at temperatures above 1050°C. High resolution electron microscopy (HREM) studies of SrZrO3 on SrTiO3 show that a crystalline semicoherent interface with a periodical array of misfit dislocations is present.

Dependence of the Residual Strain in GaN on the AlN Buffer Layer Annealing Parameters

1997 ◽  
Vol 468 ◽  
Author(s):  
Y.-M. Le Vaillant ◽  
S. Ciur ◽  
A. Andenet ◽  
O. Briot ◽  
B. Gil ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Annealing Time ◽  
Residual Strain ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Amorphous State ◽  
Lattice Parameter ◽  
Optical Quality ◽  
Buffer Layers ◽  
Aln Buffer

ABSTRACTThe problem of residual strain in GaN epilayers is currently the attention of many studies, since it affects the optical and electrical properties of the epilayers. In order to discuss the origin of this residual strain, we have grown a series of GaN epilayers onto AlN buffer layers, sapphire (0001) being used as substrate. The buffer layer is usually deposited in an amorphous state and is recrystallized by a thermal annealing. Here we have made a systematic study of the buffer recrystallization by changing the annealing temperature and the annealing time. The surface morphology is probed using Atomic Force Microscopy (AFM). The lattice parameter c is carried out from accurate x-ray diffraction measurements. The GaN layers were studied by low temperature photoluminescence and reflectivity. The amount of residual strain is calibrated from the position of the A exciton and the optical quality of the layers is assessed from the photoluminescence linewidths. The longer the annealing time the better the strain relaxation in AlN buffer layers and the higher the lattice mismatch with GaN overlayers.

Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys

2010 ◽  
Vol 25 (6) ◽  
pp. 1149-1158 ◽  
Author(s):  
Albertus D. Setyawan ◽  
Junji Saida ◽  
Hidemi Kato ◽  
Mitsuhide Matsushita ◽  
Akihisa Inoue
Keyword(s):  
Compressive Strain ◽  
Electron Microscopic Observation ◽  
Primary Crystallization ◽  
Supercooled Liquid ◽  
Icosahedral Phase ◽  
Electron Microscopic ◽  
Glassy Alloys ◽  
Transmission Electron ◽  
Transmission Electron Microscopic Observation

Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of ˜2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr–Al–Ni–Cu–Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.

scholarly journals Growth and Characterization of High-Quality GaN Nanowires on PZnO and PGaN by Thermal Evaporation

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
L. Shekari ◽  
H. Abu Hassan ◽  
S. M. Thahab ◽  
Z. Hassan
Keyword(s):  
Gallium Nitride ◽  
Thermal Evaporation ◽  
Lattice Mismatch ◽  
Growth Direction ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gan Nanowires ◽  
Transmission Electron

In the current research, an easy and inexpensive method is used to synthesize highly crystalline gallium nitride (GaN) nanowires (NWs) on two different substrates [i.e., porous zinc oxide (PZnO) and porous gallium nitride (PGaN)] on Si (111) wafer by thermal evaporation without any catalyst. Microstructural studies by scanning electron microscopy and transmission electron microscope measurements reveal the role of the substrates in the nucleation and alignment of the GaN NWs. Further structural and optical characterizations were performed using high-resolution X-ray diffraction, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. Results indicate that the NWs have a single-crystal hexagonal GaN structure and growth direction in the (0001) plane. The quality and density of GaN NWs grown on different substrates are highly dependent on the lattice mismatch between the NWs and their substrates. Results indicate that NWs grown on PGaN have better quality and higher density compared to NWs on PZnO.

scholarly journals The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 398-404 ◽  
Author(s):  
M. Benamara ◽  
Z. Liliental-Weber ◽  
J.H. Mazur ◽  
W. Swider ◽  
J. Washburn ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layers ◽  
Structural Quality ◽  
Transmission Electron ◽  
Layer Technique ◽  
Growth Method ◽  
Microscopy Techniques ◽  
Edge Dislocations

Successive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.

Application of Electron Microscopy for the detection of point defects in MBE GaAs layers grown at low temperature

1990 ◽  
Vol 48 (4) ◽  
pp. 588-589
Author(s):  
Zuzanna Liliental-Weber
Keyword(s):  
Electron Microscopy ◽  
Low Temperature ◽  
Point Defects ◽  
Analytical Electron Microscopy ◽  
Lattice Parameter ◽  
Buffer Layers ◽  
High Resistivity ◽  
Paramagnetic Resonance ◽  
Transmission Electron ◽  
Gaas Devices

Integration of GaAs devices is a challenging problem due to the lack of stable natural oxides which could isolate devices from one another. This problem is commonly solved by ion implantation, introducing point defects which can compensate impurity-related shallow donors or acceptors to make this material highly resistive. Recently, another approach was found: growing GaAs buffer layers at low temperature (∽ 200°C) removes all sidegating effects and so achieves effective device isolation. Such layers exhibit high resistivity, which is sustained even after annealing at 600°C. Own investigations by analytical electron microscopy showed these as-grown layers to be very As rich. Electron paramagnetic resonance and optical absorption studies detected AsGa antisite defects in the low-temperature buffer layers, in concentrations up to 1020 cm-3. X-ray diffraction revealed an 0.1 % increase in the lattice parameter of the epitaxial layers. After annealing at 600°C, the lattice parameter of the layers decreases to the substrate value?Transmission electron microscopy of these layers shows that their perfection is very sensitive to growth temperature and layer thickness. The layers grown below 200°C show specific defects with noncrystalline core surrounded by dislocations, stacking faults and microtwins.

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