Thermal Expansion of GaN at Low Temperatures - a Comparison of Bulk and Homo- and Heteroepitaxial Layers

1999 ◽  
Vol 595 ◽  
Author(s):  
Verena Kirchner ◽  
Heidrun Heinke ◽  
Sven Einfeldt ◽  
Detlef Hommel ◽  
Jaroslaw Z. Domagala ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Low Temperatures ◽  
Lattice Mismatch ◽  
Thermal Strain ◽  
Chemical Vapor ◽  
Thermally Induced ◽  
Thermal Expansion Coefficients ◽  
Bulk Gan ◽  
Expansion Coefficients ◽  
Heteroepitaxial Layers

AbstractThe thermal expansion of different GaN samples is studied by high-resolution Xray diffraction within the temperature range of 10 to 600 K. GaN bulk crystals, a homoepitaxial layer and different heteroepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated. Below 100 K the thermal expansion coefficients (TEC) were found to be nearly zero which has to be taken into account when estimating the thermal strain of GaN layers in optical experiments commonly performed at low temperatures. The homoepitaxial layer and the underlying GaN substrate with a lattice mismatch of –6×10−4 showed identical thermal expansion. The comparison between the temperature behavior of lattice parameters of heteroepitaxial layers and bulk GaN points to a superposition of thermally induced biaxial strain and compressive hydrostatic strain.

scholarly journals Thermal expansion of GaN at low temperatures - a comparison of bulk and homo- and heteroepitaxial layers

2000 ◽  
Vol 5 (S1) ◽  
pp. 391-397
Author(s):  
Verena Kirchner ◽  
Heidrun Heinke ◽  
Sven Einfeldt ◽  
Detlef Hommel ◽  
Jaroslaw Z. Domagala ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Low Temperatures ◽  
Lattice Mismatch ◽  
Thermal Strain ◽  
Chemical Vapor ◽  
X Ray Diffraction ◽  
Thermally Induced ◽  
Thermal Expansion Coefficients ◽  
Bulk Gan ◽  
Heteroepitaxial Layers

The thermal expansion of different GaN samples is studied by high-resolution X-ray diffraction within the temperature range of 10 to 600 K. GaN bulk crystals, a homoepitaxial layer and different heteroepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated. Below 100 K the thermal expansion coefficients (TEC) were found to be nearly zero which has to be taken into account when estimating the thermal strain of GaN layers in optical experiments commonly performed at low temperatures. The homoepitaxial layer and the underlying GaN substrate with a lattice mismatch of −6·10−4 showed identical thermal expansion. The comparison between the temperature behavior of lattice parameters of heteroepitaxial layers and bulk GaN points to a superposition of thermally induced biaxial strain and compressive hydrostatic strain.

Defects in β-SiC thin films grown on α-SiC substrates

1988 ◽  
Vol 46 ◽  
pp. 568-569
Author(s):  
Karren L. More
Keyword(s):  
Thin Films ◽  
Semiconductor Device ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Substrate Material ◽  
Growth Interface ◽  
Si Substrates ◽  
Thermal Expansion Coefficients ◽  
Device Applications ◽  
Expansion Coefficients

Beta-SiC is an ideal candidate material for use in semiconductor device applications. Currently, monocrystalline β-SiC thin films are epitaxially grown on {100} Si substrates by chemical vapor deposition (CVD). These films, however, contain a high density of defects such as stacking faults, microtwins, and antiphase boundaries (APBs) as a result of the 20% lattice mismatch across the growth interface and an 8% difference in thermal expansion coefficients between Si and SiC. An ideal substrate material for the growth of β-SiC is α-SiC. Unfortunately, high purity, bulk α-SiC single crystals are very difficult to grow. The major source of SiC suitable for use as a substrate material is the random growth of {0001} 6H α-SiC crystals in an Acheson furnace used to make SiC grit for abrasive applications. To prepare clean, atomically smooth surfaces, the substrates are oxidized at 1473 K in flowing 02 for 1.5 h which removes ∽50 nm of the as-grown surface. The natural {0001} surface can terminate as either a Si (0001) layer or as a C (0001) layer.

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.

Parametric study on the influence of material properties and geometry on the thermally induced bistability of composite laminates

2021 ◽  
pp. 095440622110456
Author(s):  
Samir A Emam ◽  
Tarun Pherwani ◽  
Aravindh Anil ◽  
Aeman Muhammed
Keyword(s):  
Thermal Expansion ◽  
Aspect Ratio ◽  
Material Properties ◽  
Parametric Study ◽  
Composite Laminates ◽  
Thickness Ratio ◽  
Thermally Induced ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Moduli Of Elasticity

This paper presents a parametric study on the key parameters that control the thermally induced bistability of cross-ply laminates. The influence of the material properties including the moduli of elasticity and the thermal expansion coefficients and the laminate’s geometry including the aspect ratio (AR) and the width-to-thickness ratio are investigated. The unsymmetric [Formula: see text] and the antisymmetric [Formula: see text] cross-ply laminates are investigated. Five key parameters are varied: the number of plies, the width-to-thickness ratio, the laminate’s aspect ratio, the ratio of the moduli of elasticity, and the ratio of the thermal expansion coefficients of the lamina. The laminate is assumed flat at the cured temperature and a uniform temperature gradient is applied until it is reduced to the room temperature. For each set of parameters, the stable equilibrium shapes of the laminate are obtained using a Ritz model. The ABAQUS finite element package is used to validate the model and an excellent agreement is obtained. Results that show the variation of the curvatures with the width-to-thickness ratio and the onset of the bistability for a variety of parameters are presented. The ratio of the moduli of elasticity and the thermal expansion coefficients significantly affect the critical width-to-thickness ratio at which the laminates become bistable. The unsymmetric laminates show bistability at a lower width-to-thickness ratio compared with the antisymmetric laminates. The results also show that the higher the aspect ratio, the lower the critical width-to-thickness ratio for stability for both laminates.

Antiphase boundaries in β-Sic thin films

1987 ◽  
Vol 45 ◽  
pp. 282-283
Author(s):  
K. L. More ◽  
J. Bentley ◽  
R. F. Davis
Keyword(s):  
Thin Films ◽  
High Speed ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Wide Bandgap ◽  
Silicon Substrates ◽  
State University ◽  
North Carolina State University ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Beta-SiC thin films are currently being grown via chemical vapor deposition (CVD) at North Carolina State University for potential use as a semiconductor material. Silicon carbide is a wide bandgap semiconductor with a high, saturated electron drift velocity and, as such, is a primary candidate material for high-temperature, high-speed, and high-frequency electronic devices. The β-SiC thin films are epitaxially grown on {100} silicon substrates by CVD of silicon and carbon from vapors of SiH4 and C2H4 entrained in H2 at a growth temperature of 1633 K. Since there is a lattice mismatch of -20% and a difference in thermal expansion coefficients of ∼10% between the silicon substrate and β-SiC, the silicon surface is reacted with C2H4 at 1583 K. for 150 s to form a converted β-SiC surface layer, approximately 5 nm thick, which helps prevent the formation of cracks during the growth of the thin films. The films are grown at a rate of ∼2 μm/h and are grown as thick as 40 μm.

Thermal Expansion and Relaxation of W-Cu Multilayers

1992 ◽  
Vol 286 ◽  
Author(s):  
Wen-C. Chiang ◽  
Soo-Kil Kim ◽  
David V. Baxter
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Heat Treatments ◽  
Irreversible Change ◽  
Thermally Induced ◽  
Temperature Range ◽  
Thermal Expansion Coefficients ◽  
Induced Stresses ◽  
Expansion Coefficients ◽  
Bulk Behavior

ABSTRACTWe have studied the structure of W-Cu multilayers with modulation wavelengths between 65 and 110 xsÅ over the temperature range 25-400° C. Using a high temperature diffractometer stage specifically designed for low angle work, thermal expansion coefficients were measured and found to be marginally greater than would be expected from bulk behavior even when interaction with the substrate is taken into account. Upon annealing at temperature as low as 180° C, increased intensity of the low angle superlattice peaks is observed. Heat treatments above 180° C result in an irreversible change in the multilayer associated with the migration of Cu atoms to cracks produced by thermally induced stresses.

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