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

2015 ◽  
Vol 24 (03n04) ◽  
pp. 1520009 ◽  
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.

scholarly journals Распределение дислокаций несоответствия и упругих механических напряжений в метаморфных буферных слоях InAlAs разной конструкции

2021 ◽  
Vol 63 (1) ◽  
pp. 85
Author(s):  
Д.В. Побат ◽  
В.А. Соловьев ◽  
М.Ю. Чернов ◽  
С.В. Иванов
Keyword(s):  
Dislocation Density ◽  
Buffer Layer ◽  
Composition Profile ◽  
Buffer Layers ◽  
Misfit Dislocations ◽  
Bottom Part ◽  
Metamorphic Buffer ◽  
Significant Difference ◽  
Order Of Magnitude ◽  
Total Energy Minimum

Here we report on computing of the distribution of the equilibrium misfit dislocation density ρ(z) as well as the elastic strain ε(z) along the grow direction for metamorphic buffer layer InAlAs/GaAs(001) with high In content (x ≤ 0.87) and different design of composition profile: step-, linear- and convex-graded. For the computation, an approach based on the iterative finding the system total energy minimum have been used. It was shown, that the significant difference between different types of the buffer layer is observed for the ρ(z) distribution rather than for ε(z). In contrast to traditionally used step- and linear-graded metamorphic buffer layers, which are characterized by homogenous spreading of misfit dislocations, the main part of such dislocations in the convex-graded composition profile is concentrated at the bottom part of the buffer layer near to heterointerface InAlAs/GaAs, and the dislocation density drop by more than one order of magnitude along the layer thickness reaching near the surface the minimal value among the buffer types. Despite the fact, that the significant effect of interaction between misfit dislocations is not taken into account in the computation, the results obtained allowed one to determine the main features of the ρ(z) and ε(z) distributions in the different InAlAs metamorphic buffer layers, which were previously obtained experimentally. Thus, such an approach can be effectively utilized for the development of the metamorphic heterostructure based devices.

Threading Dislocations in S-Graded ZnSxSe1-x/GaAs (001) Metamorphic Buffer Layers

2014 ◽  
Vol 23 (01n02) ◽  
pp. 1420005 ◽  
Author(s):  
Tedi Kujofsa ◽  
John E. Ayers
Keyword(s):  
Dislocation Density ◽  
Buffer Layer ◽  
Lattice Relaxation ◽  
Buffer Layers ◽  
Cumulative Distribution ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Modeling Studies ◽  
Threading Dislocation Density ◽  
Dislocation Behavior

Metamorphic semiconductor devices are commonly fabricated with linearly-graded buffer layers, but equilibrium modeling studies suggest that S-graded buffers, following a normal cumulative distribution function, may enable lower threading defect densities. The present work involves a study of threading dislocation density behavior in S-graded ZnS x Se 1-x buffer layers for metamorphic devices on mismatched GaAs (001) substrates using a kinetic model for lattice relaxation and misfit-threading dislocation interactions. The results indicate that optimization of an S-graded buffer layer to minimize the surface threading dislocation density requires adjustment of the standard deviation parameter and cannot be achieved by varying the buffer thickness alone. Furthermore, it is possible to tailor the design of the S-graded buffer layer in such a way that the density of mobile threading dislocations at the surface vanishes. Nonetheless, the threading dislocation behavior in these heterostructures is quite complex, and a full understanding of their behavior will require further experimental and modeling studies.

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

1997 ◽  
Vol 484 ◽  
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.

Optimization of Graded Buffer Layers for Metamorphic Semiconductor Devices

2018 ◽  
Vol 27 (03n04) ◽  
pp. 1840023
Author(s):  
Tedi Kujofsa ◽  
Minglei Cai ◽  
Xinkang Chen ◽  
Md Tanvirul Islam ◽  
John E. Ayers
Keyword(s):  
Semiconductor Devices ◽  
High Electron Mobility Transistors ◽  
Lattice Relaxation ◽  
Buffer Layers ◽  
Superior Performance ◽  
Threading Dislocation ◽  
Misfit Dislocations ◽  
High Electron ◽  
Threading Dislocation Density ◽  
Threading Defects

Metamorphic semiconductor devices such as high electron mobility transistors (HEMTs), light-emitting diodes (LEDs), laser diodes, and solar cells are grown on mismatched substrates and typically exhibit a high degree of lattice relaxation. In order to minimize the incorporation of threading defects it is common to use a linearly-graded buffer layer to accommodate the mismatch between the substrate and device layers. However, some work has suggested that buffer layers with non-linear grading could offer superior performance in terms of limiting the surface density of threading defects. In this work, we have compared S-graded buffer layers with different orders and thicknesses. To do so we calculated the expected surface threading dislocation density for each buffer design assuming a GaAs (001) substrate. The threading dislocation densities were calculated using the LMD model, in which the coefficient for second-order annihilation and coalescence reactions between threading dislocations is considered to be equal to the length of misfit dislocations.

Epitaxial GaN Layer Growth Using Nitrogen Enriched TiN Buffer Layers

2006 ◽  
Vol 916 ◽  
Author(s):  
Kazuhiro Ito ◽  
Yu Uchida ◽  
Sang-jin Lee ◽  
Susumu Tsukimoto ◽  
Yuhei Ikemoto ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Light Emission ◽  
Chemical Vapor ◽  
Nucleation Site ◽  
Layer Growth ◽  
Buffer Layers ◽  
Organic Chemical ◽  
Nitrogen Enrichment ◽  
Threading Dislocation ◽  
Sapphire Substrates

AbstractAbout 20 years ago, the discovery of an AlN buffer layer lead to the breakthrough in epitaxial growth of GaN layers with mirror-like surface, using a metal organic chemical vapor deposition (MOCVD) technique on sapphire substrates. Since then, extensive efforts have been continued to develop a conductive buffer layer/substrate for MOCVD-grown GaN layers to improve light emission of GaN light-emitting diodes. In the present study, we produced MOCVD-grown, continuous, flat epitaxial GaN layers on nitrogen enriched TiN buffer layers with the upper limit of the nitrogen content of TiN deposited at room temperature (RT) on sapphire substrates. It was concluded that the nitrogen enrichment would reduce significantly the TiN/GaN interfacial energy. The RT deposition of the TiN buffer layers suppresses their grain growth during the nitrogen enrichment and the grain size refining must increase nucleation site of GaN. In addition, threading dislocation density in the GaN layers grown on TiN was much lower than that in the GaN layers grown on AlN.

Effect of N/Ga Flux Ratio in GaN Buffer Layer Growth by MBE on (0001) Sapphire on Defect Formation in the GaN Main Layer

1999 ◽  
Vol 572 ◽  
Author(s):  
S. Ruvimov ◽  
Z. Liliental-Weber ◽  
J. Washburn ◽  
Y. Kim ◽  
G. S. Sudhir ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layer ◽  
Defect Formation ◽  
Flux Ratio ◽  
Growth Conditions ◽  
Buffer Layers ◽  
Simultaneous Increase ◽  
Growth Stages ◽  
Dislocation Generation ◽  
Gan Buffer Layer

ABSTRACTTransmission electron microscopy was employed to study the effect of N/Ga flux ratio in the growth of GaN buffer layers on the structure of GaN epitaxial layers grown by molecular-beamepitaxy (MBE) on sapphire. The dislocation density in GaN layers was found to increase from 1×1010 to 6×1010 cm−2 with increase of the nitrogen flux from 5 to 35 sccm during the growth of the GaN buffer layer with otherwise the same growth conditions. All GaN layers were found to contain inversion domain boundaries (IDBs) originated at the interface with sapphire and propagated up to the layer surface. Formation of IDBs was often associated with specific defects at the interface with the substrate. Dislocation generation and annihilation were shown to be mainly growth-related processes and, hence, can be controlled by the growth conditions, especially during the first growth stages. The decrease of electron Hall mobility and the simultaneous increase of the intensity of “green” luminescence with increasing dislocation density suggest that dislocation-related deep levels are created in the bandgap.

Residual Strain and Defect Analysis in as Grown and Annealed SiGe Layers

1991 ◽  
Vol 220 ◽  
Author(s):  
A. R. Powell ◽  
R. A. Kubiak ◽  
T. E. Whall ◽  
E. H. C. Parker ◽  
D. K. Bowen
Keyword(s):  
Residual Strain ◽  
Buffer Layers ◽  
Limited Area ◽  
Threading Dislocation ◽  
Misfit Dislocations ◽  
High Temperature Anneal ◽  
Dislocation Densities ◽  
Acceptable Quality ◽  
Strained Sige

ABSTRACTIn this paper we address the problem of producing SiGe buffer layers of acceptable quality for the growth of symmetrically strained SiGe structures. Initially we consider SiGe layers grown to well beyond the metastable critical thickness and examine the degree of residual strain both as - grown and post anneal. The defect levels in metastable SiGe layers following high temperature anneal were also studied. A buffer layer was grown consisting of stacked metastable SiGe layers each of which is annealed in situ prior to the growth of the next layer and terminating with a 0.45 SiGe alloy. This produces nearly fully relaxed 1.15pim thick structures with threading dislocation densities of 4 × 106cm−2. Limited area growth on Si suggests that elastically relaxed material free of both threading and misfit dislocations can be produced.

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