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.

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.

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.

Highly Mismatched Hetero-Epitaxial Growth of Cubic Sic on Si

1987 ◽  
Vol 97 ◽  
Author(s):  
Hiroyuki Matsunami
Keyword(s):  
Epitaxial Growth ◽  
Lattice Mismatch ◽  
Electronic Devices ◽  
Chemical Vapor ◽  
Buffer Layers ◽  
Optimum Conditions ◽  
Large Lattice ◽  
Impurity Doping ◽  
Large Lattice Mismatch

ABSTRACTSingle crystals of cubic SiC were hetero-epitaxially grown on Si by chemical vapor deposition (CVD) method. A carbonized buffer layer on Si is utilized to overcome the large lattice mismatch of 20 %. Optimum conditions to make the buffer layers and those structures are discussed. Crystal quality of the CVD grown cubic SiC is analyzed by using X-ray analyses and microscopic observations. Electrical properties controlled by impurity doping during epitaxial growth are described together with fundamental electronic devices.

scholarly journals Realization of III-Nitride c-Plane microLEDs Emitting from 470 to 645 nm on Semi-Relaxed Substrates Enabled by V-Defect-Free Base Layers

Crystals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1168
Author(s):  
Ryan C. White ◽  
Michel Khoury ◽  
Matthew S. Wong ◽  
Hongjian Li ◽  
Cheyenne Lynsky ◽  
...  
Keyword(s):  
Layer Structure ◽  
Emission Spectra ◽  
Chemical Vapor ◽  
Visible Spectrum ◽  
Lattice Parameter ◽  
Base Layer ◽  
Organic Chemical ◽  
Material System ◽  
Light Spectrum ◽  
Wide Range

We examine full InGaN-based microLEDs on c-plane semi-relaxed InGaN substrates grown by metal organic chemical vapor deposition (MOCVD) that operate across a wide range of emission wavelengths covering nearly the entire visible spectrum. By employing a periodic InGaN base layer structure with high temperature (HT) GaN interlayers on these semi-relaxed substrates, we demonstrate robust μLED devices. A broad range of emission wavelengths ranging from cyan to deep red are realized, leveraging the indium incorporation benefit of the relaxed InGaN substrate with an enlarged lattice parameter. Since a broad range of emission wavelengths can be realized, this base layer scheme allows the tailoring of the emission wavelength to a particular application, including the possibility for nitride LEDs to emit over the entire visible light spectrum. The range of emission possibilities from blue to red makes the relaxed substrate and periodic base layer scheme an attractive platform to unify the visible emission spectra under one singular material system using III-Nitride MOCVD.

Substrate Engineering With Plastic Buffer Layers

MRS Bulletin ◽  
1996 ◽  
Vol 21 (4) ◽  
pp. 45-49 ◽  
Author(s):  
Leo J. Schowalter
Keyword(s):  
Epitaxial Layer ◽  
Misfit Dislocation ◽  
Lattice Mismatch ◽  
Lattice Parameter ◽  
Buffer Layers ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Substrate Engineering ◽  
Two Sides ◽  
Heteroepitaxial Layers

The advantage that epitaxy offers the electronics and optoelectronics industries is that it allows the possibility of producing precisely controlled layers of very high crystal quality. Heteroepitaxy of different materials offers the promise of tailoring device layers in clever ways that nature did not intend. However unlike fruit juices, nature has made it difficult to epitaxially combine different materials. As the preceding articles have clearly pointed out, it is very difficult to obtain smooth epitaxial layers that are free both of defects and strain when there is a lattice mismatch between the layers and their substrates.As already discussed in this issue, a uniform network of dislocations at the interface between a flat, uniform epitaxial layer and its substrate can completely relieve strain in the majority of the epitaxial layer. This would be a satisfactory situation for many devices so long as the active region of the device could be kept away from the interface. The problem is how to introduce the dislocations in an appropriate way. When an epitaxial layer has a larger lattice parameter than the underlying substrate, a misfit dislocation running along the interface represents a plane of atoms that has been removed from the epitaxial layer. (One would insert a plane of atoms if the epitaxial lattice parameter was smaller. For simplicity however we will continue to assume that the epitaxial layer has a larger lattice parameter.) It is not possible for a whole half plane of atoms, bounded by the dislocation at the interface and the substrate edges along the two sides, to be removed at once. The boundary between where the extra plane of atoms has been removed and where the epitaxial layer has not relaxed yet will represent a threading dislocation. This threading dislocation would continue to move as the size of the misfit dislocation along the interface grows. Ideally it moves all the way out to the substrate edge and vanishes there while the misfit dislocation along the interface would end up extending from one side of the substrate to the other. However other dislocations and other kinds of defects can effectively pin the threading dislocation resulting in an epitaxial layer with many threading dislocations. Unfortunately these threading dislocations are generally detrimental to most kinds of devices. It is precisely this high density of threading dislocations that limits applications of many heteroepitaxial layers.

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.

Evolution of Subgrain Boundaries in Heteroepitaxial GaN/AlN/6H-SiC Grown by Metalorganic Chemical Vapor Deposition

2002 ◽  
Vol 743 ◽  
Author(s):  
H. X. Liu ◽  
G. N. Ali ◽  
K. C. Palle ◽  
M. K. Mikhov ◽  
B. J. Skromme ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Lattice Mismatch ◽  
Thick Layer ◽  
Chemical Vapor ◽  
Buffer Layers ◽  
Force Microscopy ◽  
Atomic Force ◽  
Mismatch Stress ◽  
Aln Buffer ◽  
Electron Imaging

ABSTRACTWe have characterized the surface morphology and luminescence properties of GaN/AlN/ SiC layers of various thicknesses using secondary electron imaging (SEI), panchromatic room temperature cathodoluminescence (CL), atomic force microscopy (AFM), optical Nomarski microscopy, and room and low temperature photoluminescence (PL). The nominally undoped GaN layers were grown by MOCVD on 0.1 m thick AlN buffer layers on commercial 6H-SiC(0001) substrates. The GaN layer thicknesses are 0.5, 1.0, 1.6, and 2.6 m. A second 1.0 m thick layer was grown by identical procedures on a 6H-SiC substrate that was first etched in H2 to remove scratches and damage due to mechanical polishing. Biaxial compressive lattice mismatch stress is present in all layers and decreases with increasing layer thickness, while PL linewidths decrease. The 1 m layer on the H-etched substrate is as relaxed as the 2.6 m layer on a non H-etched substrate, however. Pronounced surface structures, apparently corresponding to columnar subgrain boundaries, are observed on the samples on non H-etched SiC. Their typical sizes increase from about 3 to 10 m with increasing layer thickness. They are absent in the H-etched sample. These structures are generally nonradiative in CL images, although mottled contrast is also observed inside them. Similar layers doped with 3×1018 cm−3 Si do not show these features, suggesting a different microstructure.

Growth of Hexagonal Gallium Nitride Films On The (111) Surfaces of Silicon with Zinc Oxide Buffer Layers

1996 ◽  
Vol 449 ◽  
Author(s):  
Y. Kim ◽  
C. G. Kim ◽  
K-W. Lee ◽  
K-S. Yu ◽  
J. T. Park ◽  
...  
Keyword(s):  
Zinc Oxide ◽  
Gallium Nitride ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Photoelectron Spectroscopy ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
High Energy ◽  
Buffer Layers ◽  
X Ray

ABSTRACTThe growth of gallium nitride films on sapphire substrates has not been straightforward because of the large lattice mismatch between gallium nitride and sapphire. Zinc oxide is structurally the closest material to gallium nitride and therefore is finding use as the substrate for gallium nitride. Single crystal wafers of zinc oxide are hard to obtain and very expensive. However, a thin layer of zinc oxide on a suitable substrate might solve this problem. In this work, highly c-axis oriented zinc oxide buffer layers were grown on Si(lll) substrates at temperatures 410–540 °C by chemical vapor deposition of bis(2,2,6,6-tetramethyl–3,5-heptanedionato)zinc, Zn(tmhd)2, and the hexagonal GaN films were subsequently deposited on them at 500 °C using the single precursor tris(diethyl -μ-amido-gallium), [(C2H5)2 GaNH2]3. The compound Zn(tmhd)2 was found to require oxygen for the deposition of zinc oxide. In the case of gallium nitride, low pressure chemical vapor deposition of tris(diethyl-μ-amido-gallium) worked reasonably well with or without a carrier gas. The buffer layers and the GaN films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and reflection high energy elctron diffraction (RHEED).

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