The Use of AlN Interlayers to Improve GaN Growth on A-Plane Sapphire

1999 ◽  
Vol 587 ◽  
Author(s):  
D.D. Koleske ◽  
M.E. Twigg ◽  
A.E. Wickenden ◽  
R.L. Henry ◽  
R.J. Gorman ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Screw Dislocation ◽  
Film Growth ◽  
Fold Increase ◽  
Large Area ◽  
Cross Sectional ◽  
Acceptor Concentration ◽  
Si Doped ◽  
Gan Film ◽  
Screw Dislocation Density

AbstractThe lack of a suitable, lattice matched substrate for the growth of the group III nitrides typically restricts GaN film growth to substrates such as sapphire or SiC, despite the large lattice and thermal mismatch. With the use of AlN or GaN nucleation layers (NL), GaN films of sufficient quality have been produced for blue LEDs. However, for laser and large-area microwave device applications, the large number of dislocations (> 108 cm−2) limit device performance, and techniques are desired to reduce dislocation density during the growth process. Here, we demonstrate how low temperature AlN interlayers (IL) sandwiched between high temperature (HT) GaN layers can be used to improve the electrical, optical, and structural properties of Si doped GaN films. A nearly two-fold increase in mobility is observed in Si doped GaN grown using 5 AlN IL compared to GaN grown on a single AlN NL. For GaN films grown on multiple AlN IL, cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density and photoluminescence spectra reveal a reduction in yellow band intensity. An analysis of the electrical data based on a single donor/single acceptor model suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film. The reduction in the calculated acceptor concentration may be associated with the reduction of the screw dislocation density.

scholarly journals Study of Edge and Screw Dislocation Density in GaN/Al2O3 Heterostructure

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4205 ◽  
Author(s):  
Vladimir Lucian Ene ◽  
Doru Dinescu ◽  
Iulia Zai ◽  
Nikolay Djourelov ◽  
Bogdan Stefan Vasile ◽  
...  
Keyword(s):  
High Resolution ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Diffusion Length ◽  
Correlation Lengths ◽  
Transmission Electron ◽  
Aln Buffer ◽  
Gan Film ◽  
Defect Densities ◽  
Screw Dislocation Density

This study assesses the characteristics (edge and screw dislocation density) of a commercially available GaN/AlN/Al2O3 wafer. The heterostructure was evaluated by means of high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), and Doppler-Broadening Spectroscopy (DBS). The results were mathematically modeled to extract defect densities and defect correlation lengths in the GaN film. The structure of the GaN film, AlN buffer, Al2O3 substrate and their growth relationships were determined through HR-TEM. DBS studies were used to determine the effective positron diffusion length of the GaN film. Within the epitaxial layers, defined by a [GaN P 63 m c (0 0 0 2) || P 63 m c AlN (0 0 0 2) || (0 0 0 2) R 3 ¯ c Al2O3] relationship, regarding the GaN film, a strong correlation between defect densities, defect correlation lengths, and positron diffusion length was assessed. The defect densities ρ d e = 6.13 × 1010 cm−2, ρ d s = 1.36 × 1010 cm−2, along with the defect correlation lengths Le = 155 nm and Ls = 229 nm found in the 289 nm layer of GaN, account for the effective positron diffusion length Leff~60 nm.

Preparation of Large Area Cross-Sectional Tem Specimen of Semiconducting Heteroepitaxial Materials

1991 ◽  
Vol 254 ◽  
Author(s):  
M. Tamura ◽  
S. Aoki
Keyword(s):  
Sample Preparation ◽  
Film Growth ◽  
General Information ◽  
One Dimension ◽  
Main Principle ◽  
Large Area ◽  
Cross Sectional ◽  
Growth Modes ◽  
Present Technique ◽  
Grinding And Polishing

AbstractThe sample preparation procedures which enable us to observe large areas over a few tens of microns in one-dimension of semiconducting heteroepitaxial materials are described. The main principle involves the careful grinding and polishing of samples. In these procedures, another side thinning of the specimen after finishing initial side polishing is carried out using a sample platform by hand throughout all of the following steps. It is shown that for some typical examples of heteroepitaxial films general information concerning the film growth modes and structures, as well as the defect morphologies and natures introduced during growth can be effectively obtained by using the present technique.

Characterization of Porous SiC Substrates and of the Epilayer Structures Grown on Them

2002 ◽  
Vol 742 ◽  
Author(s):  
Balaji Raghothamachar ◽  
Jie Bai ◽  
William M. Vetter ◽  
Perena Gouma ◽  
Michael Dudley ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Optical Microscopy ◽  
Epitaxial Growth ◽  
Screw Dislocation ◽  
Pore Morphology ◽  
Porous Substrate ◽  
X Ray ◽  
Porous Sic ◽  
Screw Dislocation Density

ABSTRACTPorous 6H-SiC and 4H-SiC wafers formed by anodization have been characterized in this study prior to and following the CVD deposition of SiC epitaxial layers, using a combination of synchrotron white beam x-ray topography (SWBXT), SEM, TEM and optical microscopy. Under the high temperatures employed during epitaxial growth, a significant change in pore morphology occurs. While no evidence of reduced screw dislocation density in the epilayers is obtained, a small tilt of the epilayers with respect to the porous substrate observed on x-ray topographs could play a role in limiting penetration of defects from the substrate.

Correlation of threading screw dislocation density to GaN 2‐DEG mobility

2014 ◽  
Vol 50 (23) ◽  
pp. 1722-1724 ◽  
Author(s):  
J.K. Hite ◽  
P. Gaddipati ◽  
D.J. Meyer ◽  
M.A. Mastro ◽  
C.R. Eddy
Keyword(s):  
Dislocation Density ◽  
Screw Dislocation ◽  
Screw Dislocation Density

scholarly journals Quantitative Analysis of the Recovery Process in Pure Iron Using X-ray Diffraction Line Profile Analysis

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 895
Author(s):  
Shota Sugiyama ◽  
Toshio Ogawa ◽  
Lei He ◽  
Zhilei Wang ◽  
Yoshitaka Adachi
Keyword(s):  
Quantitative Analysis ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Edge Dislocation ◽  
Pure Iron ◽  
Annealing Temperature ◽  
Dislocation Core ◽  
Recovery Process ◽  
Line Profile Analysis ◽  
Screw Dislocation Density

We conducted quantitative analysis of the recovery process during pure iron annealing using the modified Williamson-Hall and Warren-Averbach methods. We prepared four types of specimens with different dislocation substructures. By increasing the annealing temperature, we confirmed a decrease in dislocation density. In particular, screw-dislocation density substantially decreased in the early stage of the recovery process, while edge-dislocation density gradually decreased as annealing temperature increased. Moreover, changes in hardness during the recovery process mainly depended on edge-dislocation density. Increases in annealing temperature weakly affected the dislocation arrangement parameter and crystallite size. Recovery-process modeling demonstrated that the decrease in screw-dislocation density during the recovery process was mainly dominated by glide and/or cross-slip with dislocation core diffusion. In contrast, the decrease in edge-dislocation density during the recovery process was governed by a climbing motion with both dislocation core diffusion and lattice self-diffusion. From the above results, we succeeded in quantitatively distinguishing between edge- and screw-dislocation density during the recovery process, which are difficult to distinguish using transmission electron microscope and electron backscatter diffraction.

Correlation betweenJ c and screw dislocation density in sputtered YBa2Cu3O7-? films

1992 ◽  
Vol 86 (2) ◽  
pp. 177-181 ◽  
Author(s):  
J. Mannhart ◽  
D. Anselmetti ◽  
J. G. Bednorz ◽  
A. Catana ◽  
Ch. Gerber ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Screw Dislocation ◽  
Screw Dislocation Density

Comparison of Different Substrate Pre-Treatments on the Quality of GaN Film Growth on 6H-, 4H-, and 3C-SiC

2000 ◽  
Vol 622 ◽  
Author(s):  
K. H. Lee ◽  
M. H. Hong ◽  
K. Teker ◽  
C. Jacob ◽  
P. Pirouz
Keyword(s):  
Buffer Layer ◽  
Film Growth ◽  
Lattice Mismatch ◽  
Substrate Surface ◽  
Substrate Material ◽  
Cross Sectional ◽  
Pre Treatment ◽  
Film Substrate ◽  
Gan Film

ABSTRACTTogether with sapphire, SiC is the most common substrate material for GaN epitaxial growth. In fact, SiC has advantages over sapphire because of its better thermal conductivity and lower film substrate lattice mismatch (∼3.5%). However, nucleation of GaN on SiC is rather difficult because of the low surface energy of SiC and the sensitivity of substrate preparation. This latter point makes it essential to use a very careful cleaning step, and also to pre-treat the substrate surface by growing a thick buffer layer of AlN at a relatively high temperature. In this study, several pre-treatment steps of SiC for GaN deposition were tested including (a) nitration with NH3 for 0.5-20 minutes, (b) pre-adsorption of trimethyl gallium (TMG) or trimethyl aluminum (TMA) for 0.5-5 minutes, and (c) deposition of an AlN buffer layer at ∼1150°C. After each pre-treatment, GaN was deposited by MOCVD using dilute H2(Ar+12%H2), NH3 and TMG. All the films were characterized by XRD and cross-sectional TEM. After nitration of SiC, the deposited GaN film was found to be polycrystalline. In case of pre-adsorption of TMG, epitaxial but island-like GaN formed on the substrate. In the third case, with an ultra-thin (∼1.5nm) coverage of AlN on SiC (by pre-adsorption of TMA or by 50 seconds deposition of AlN), GaN epilayers were successfully deposited on SiC. However, when AlN was deposited for longer than 3 minutes (up to 10 minutes), only polycrystalline GaN was obtained. With this technique of covering the surface with an ultra-thin layer of AlN, epitaxial GaN has been successfully deposited on 6H-SiC (0001), on 4H-SiC(0001), and on 3C-SiC/Si(111) substrates. The effect of the different pre-treatments of SiC on the quality of the deposited GaN films will be discussed and compared, and the optimal conditions for GaN deposition for each substrate will be presented.

The Worrying Trend of Diabetes Mellitus in Saudi Arabia: An Urgent Call to Action

2020 ◽  
Vol 16 (3) ◽  
pp. 204-210 ◽  
Author(s):  
Asirvatham A. Robert ◽  
Mohamed A. Al Dawish
Keyword(s):  
Diabetes Mellitus ◽  
Saudi Arabia ◽  
Present Report ◽  
Adult Population ◽  
Current Trend ◽  
Fold Increase ◽  
Developed Countries ◽  
Evidence Base ◽  
Small Sample ◽  
Cross Sectional

From last few years, the pervasiveness of diabetes mellitus (DM), in Saudi Arabia, is growing at a frightening rate. Overall, one-fourth of the adult population is affected by DM, which is further predicted to rise to more than double by the year 2030. The most alarming is possibly the escalation propensity of diabetes, in recent years, where a nearly ten-fold increase has been witnessed over the past thirty years in Saudi Arabia. However, the number of research arbitrations on the prevalence and incidence of DM is woefully inadequate, as compared to developed countries. Apart from this, most of the existing research data carried out in Saudi Arabia is cross-sectional, with small sample sizes, which most often involve only certain parts of the country. Consequently, the present scenario demands more multidimensional and multisectoral research to strengthen the evidence base and to accumulate greater knowledge as a basis for measures and programmes to confront diabetes and its complications. Thus, the present report makes an attempt to depict the current trend of diabetes as well as intends to put forward essential measures for controlling diabetes in Saudi Arabia.

Stress, structural and electrical properties of Si-doped GaN film grown by MOCVD

2009 ◽  
Vol 30 (12) ◽  
pp. 123003 ◽  
Author(s):  
Xu Zhihao ◽  
Zhang Jincheng ◽  
Duan Huantao ◽  
Zhang Zhongfen ◽  
Zhu Qingwei ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Structural And Electrical Properties ◽  
Si Doped ◽  
Gan Film
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