STRAIN OF GaN LAYERS GROWN USING 6H-SiC(0001) SUBSTRATES WITH DIFFERENT BUFFER LAYERS

Gallium nitride films of increasing thickness have been grown on either AlN or AlGaN substrates. The state of stress of these biaxially stressed layers gradually changed from compression to tension with regard to both their average strain and their local strain along the [0001] growth direction. The components of both the compressive and tensile stresses are caused by the mismatch in lattice parameters between the GaN and the buffer layer and the mismatch in the coefficients of thermal expansion between GaN and SiC , respectively. The compressive stress is partially relieved within the first 20 nm in the GaN film grown on the AlN buffer layer. The relief of the remaining stress follows an exponential dependence on the thickness of the GaN layer with values for the characteristic decay length of 0.24 μm and 0.64 μm for the AlN and AlGaN buffer layer, respectively. The relaxation mechanism is discussed in terms of the formation of misfit dislocations via surface undulations.

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Effects of the Sputtering Time of AlN Buffer Layer on the Quality of ZnO Thin Films

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.881-883.1117 ◽

2014 ◽

Vol 881-883 ◽

pp. 1117-1121 ◽

Cited By ~ 1

Author(s):

Xiang Min Zhao

Keyword(s):

Thin Films ◽

Buffer Layer ◽

Rf Magnetron Sputtering ◽

Buffer Layers ◽

Zno Thin Films ◽

Zno Films ◽

Si Substrates ◽

Atomic Force ◽

Structure Morphology ◽

Aln Buffer

ZnO thin films with different thickness (the sputtering time of AlN buffer layers was 0 min, 30 min,60 min, and 90 min, respectively) were prepared on Si substrates using radio frequency (RF) magnetron sputtering system.X-ray diffraction (XRD), atomic force microscope (AFM), Hall measurements setup (Hall) were used to analyze the structure, morphology and electrical properties of ZnO films.The results show that growth are still preferred (002) orientation of ZnO thin films with different sputtering time of AlN buffer layer,and for the better growth of ZnO films, the optimal sputtering time is 60 min.

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GaN ON SILICON SUBSTRATE WITH AlN BUFFER LAYER FOR UV PHOTODIODE

Journal of Nonlinear Optical Physics & Materials ◽

10.1142/s0218863512500142 ◽

2012 ◽

Vol 21 (01) ◽

pp. 1250014 ◽

Cited By ~ 2

Author(s):

L. S. CHUAH ◽

S. M. THAHAB ◽

Z. HASSAN

Keyword(s):

Schottky Barrier ◽

Buffer Layer ◽

Barrier Height ◽

Silicon Substrate ◽

Dark Current ◽

Schottky Barrier Height ◽

Buffer Layers ◽

Current Ratio ◽

Principal Mechanism ◽

Aln Buffer

Nitrogen plasma-assisted molecular beam epitaxy (PAMBE) deposited GaN thin films on (111) n-type silicon substrate with different thickness AlN buffer layers are investigated and distinguished by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman scattering. The thickness of AlN buffer layer ranged from 200 nm to 300 nm. Besides that, the electrical characteristics of the GaN thin film for ultraviolet detecting utilizations are studied by calculating the photo current/dark current ratio on a metal-semiconductor-metal (MSM) photodiode with and without the illumination of Hg-lamp source. The devices have been tested over room temperature (RT). The photocurrent analysis, together with the study of Schottky barrier height (SBH) development, ascertain that the principal mechanism of photo transport is thermionic emission. The photocurrent value is rigorously dependent on Schottky barrier height. The GaN/AlN(200 nm)/n-Si MSM photodiode produces the highest photo/dark current ratio for the lowest strain that consists of the GaN film grown on the AlN (200 nm) buffer layer.

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Equilibrium Lattice Relaxation and Misfit Dislocations in Continuously- and Step-Graded InxGa1-xAs/GaAs (001) and GaAs1-yPy/GaAs (001) Metamorphic Buffer Layers

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156415200098 ◽

2015 ◽

Vol 24 (03n04) ◽

pp. 1520009 ◽

Cited By ~ 1

Author(s):

Tedi Kujofsa ◽

John E. Ayers

Keyword(s):

Dislocation Density ◽

Buffer Layer ◽

Minimum Energy ◽

Lattice Relaxation ◽

Structure Type ◽

Elastic Stiffness ◽

Buffer Layers ◽

Threading Dislocation ◽

Misfit Dislocations ◽

Metamorphic Buffer

The inclusion of metamorphic buffer layers (MBL) in the design of lattice-mismatched semiconductor heterostructures is important in enhancing reliability and performance of optical and electronic devices. These metamorphic buffer layers usually employ linear grading of composition, and materials including InxGa1-xAs and GaAs1-yPy have been used. Non-uniform and continuously graded profiles are beneficial for the design of partially-relaxed buffer layers because they reduce the threading dislocation density by allowing the distribution of the misfit dislocations throughout the metamorphic buffer layer, rather than concentrating them at the interface where substrate defects and tangling can pin dislocations or otherwise reduce their mobility as in the case of uniform compositional growth. In this work we considered heterostructures involving a linearly-graded (type A) or step-graded (type B) buffer layer grown on a GaAs (001) substrate. For each structure type we present minimum energy calculations and compare the cases of cation (Group III) and anion (Group V) grading. In addition, we studied the (i) average and surface in-plane strain and (ii) average misfit dislocation density for heterostructures with various thickness and compositional profile. Moreover, we show that differences in the elastic stiffness constants give rise to significantly different behavior in these two commonly-used buffer layer systems.

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Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

MRS Internet Journal of Nitride Semiconductor Research ◽

10.1557/s1092578300002829 ◽

1999 ◽

Vol 4 (S1) ◽

pp. 417-422 ◽

Cited By ~ 4

Author(s):

E. C. Piquette ◽

P. M. Bridger ◽

R. A. Beach ◽

T. C. McGill

Keyword(s):

Surface Morphology ◽

Buffer Layer ◽

Flux Ratio ◽

Plasma Source ◽

Growth Conditions ◽

Nitrogen Plasma ◽

Layer Growth ◽

Buffer Layers ◽

Flat Surfaces ◽

Aln Buffer

The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS.

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

MRS Proceedings ◽

10.1557/proc-468-173 ◽

1997 ◽

Vol 468 ◽

Cited By ~ 4

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.

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Effect of Buffer Design on AlGaN/AlN/GaN Heterostrucutres by MBE

MRS Proceedings ◽

10.1557/proc-798-y10.62 ◽

2003 ◽

Vol 798 ◽

Author(s):

Gon Namkoong ◽

W. Alan ◽

A. S. Brown ◽

M. Losurdo ◽

M. M. Giangregorio ◽

...

Keyword(s):

Electrical Properties ◽

Buffer Layer ◽

Growth Conditions ◽

Buffer Layers ◽

Structural Quality ◽

Epitaxial Layers ◽

Etch Pit Density ◽

Etch Pit ◽

Sheet Charge ◽

Aln Buffer

ABSTRACTThe effect of the buffer layers on the subsequent GaN epitaxial layers and electrical properties of AlGaN/AlN/GaN heterojunction structures nitrided at various temperatures was investigated. For AlN buffer layers, two different growth conditions of AlN buffer layers were introduced to avoid Al droplets. We found that etch pit density and structural quality of GaN epitaxial layer strongly depends on the growth conditions of AlN buffer layers. When using a double buffer layer (low temperature GaN on high temperature AlN) for 200 °C nitridation, the etch pit density was measured to high 107 cm-2 in GaN epitaxial layers. Furthermore, we observed that electrical properties of AlGaN/AlN/GaN heterostructures depend on growth conditions of buffer layers and nitridation temperatures. The mobility in Al0.33Ga0.67N/AlN/GaN structures grown on single AlN buffer layers for 200 °C nitridation were 1300 cm2/Vs at a sheet charge of 1.6×1013 cm-2. Using the double buffer layer for 200 °C nitridation, the mobility increased to 1587 cm2/Vs with a sheet charge of 1.25×1013 cm-2.

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Misfit Dislocations and Elastic Relaxation

MRS Proceedings ◽

10.1557/proc-399-313 ◽

1995 ◽

Vol 399 ◽

Cited By ~ 8

Author(s):

H.P Strunk ◽

S. Christiansen ◽

M. Albrecht

Keyword(s):

Driving Forces ◽

Maximum Shear Stress ◽

Strain Tensor ◽

Three Dimensional ◽

Local Strain ◽

Misfit Strain ◽

Relaxation Mechanism ◽

Misfit Dislocations ◽

Thermodynamical Equilibrium ◽

Three Dimensional Finite Element

ABSTRACTPrior to relaxation of misfit strain by formation of misfit dislocations, a growing heteroepitaxial layer can relax elastically by forming surface undulations called ripples. With increasing amplitude of the ripples the misfit strain and thus stress fields grow markedly inhomogeneous, and dislocation formation may thus be triggered in areas of maximum shear stress. The surface directly above such a new dislocation then represents a band of preferential growth and develops into a ridge, which in turn redistributes the strain in the growing layer. This interwoven elastic/plastic relaxation mechanism can comparably easily be deduced from transmission electron and atomic force microscopy studies of SiGe layers grown onto silicon by liquid phase epitaxy. This growth technique exerts only very small driving forces and thus operates very near thermodynamical equilibrium. The local strain tensor and strain energy density are calculated for the actual layer geometries by three dimensional finite element method and provide for quantification of the mechanism.

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Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

MRS Proceedings ◽

10.1557/proc-537-g3.77 ◽

1998 ◽

Vol 537 ◽

Cited By ~ 2

Author(s):

E. C. Piquette ◽

P. M. Bridger ◽

R. A. Beach ◽

T. C. McGill

Keyword(s):

Surface Morphology ◽

Buffer Layer ◽

Flux Ratio ◽

Plasma Source ◽

Growth Conditions ◽

Nitrogen Plasma ◽

Layer Growth ◽

Buffer Layers ◽

Flat Surfaces ◽

Aln Buffer

AbstractThe surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than l nm RMS.

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Tem Investigation of Al0.5Ga0.5As1-y Sby Buffer Layer Systems

MRS Proceedings ◽

10.1557/proc-484-31 ◽

1997 ◽

Vol 484 ◽

Cited By ~ 1

Author(s):

E. Chen ◽

J. S. Ahearn ◽

K. Nichols ◽

P. Uppal ◽

D. C. Paine

Keyword(s):

Buffer Layer ◽

Active Regions ◽

Dark Field ◽

Layer Growth ◽

Buffer Layers ◽

Growth Surface ◽

Threading Dislocation ◽

Misfit Dislocations ◽

Plan View ◽

Dark Field Imaging

AbstractWe report on a TEM study of Sb-adjusted quaternary Al0.5Ga0.5As1-y Sby buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470°C that utilize a multilayer grading scheme in which the Sb content of Al0.5Ga0.5As1-ySby is successively increased in a series of eight 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60° type and are distributed through out the interfaces of the buffer layer. Plan view studies show that the threading dislocation density in the active regions of the structure (approximately 2 μm from the GaAs substrate) is 105–6/cm2 which is comparable to equivalent InxGa1−x As buffers. Weak Sb-As compositional modulations with a period of 1.8 nm were observed that provide a marker for establishing the planarity of the growth process. These features reveal that the growth surface remains planar through out the buffer layer growth sequence.

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