Enhanced Band-Gap Luminescence in Strain-Symmetrized (Si)m(Ge)n Superlattices

1993 ◽  
Vol 298 ◽  
Author(s):  
U. Menczigar ◽  
G. Abstreiter ◽  
H. Kibbel ◽  
H. Presting ◽  
E. Kasper
Keyword(s):  
Raman Spectroscopy ◽  
Dislocation Density ◽  
Band Gap ◽  
Effective Mass ◽  
Reference Sample ◽  
Buffer Layers ◽  
Luminescence Efficiency ◽  
Short Period ◽  
Theoretical Predictions

AbstractWe report on band-gap luminescence in short period, strain symmetrized (Si)m(Ge)n superlattices grown on relaxed, step-graded Sil-xGex alloy buffer layers. The dislocation density in the superlattices, which were grown at 500°C using Sb as a surfactant, is reduced by 2-3 orders of magnitude compared with superlattices grown on thin, partly relaxed Sil-xGex buffer layers. Due to the improved quality of the superlattices, well defined band-gap luminescence could be observed which is for a (Si)6(Ge)4 superlattice strongly enhanced compared with a Si0.6Ge0.4 alloy reference sample. The measured band-gap energies compare well with theoretical predictions. To study the influence of interdiffusion of the Si- and Gelayers on the band-gap of the superlattices, the samples were annealed and studied with photoluminescence and Raman spectroscopy. An increasing band-gap and a decreasing luminescence efficiency was found with increasing intermixing of the layers. These experimental results are well described with an interdiffuision model of the layers in conjunction with an effective mass calculation.

scholarly journals The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 398-404 ◽  
Author(s):  
M. Benamara ◽  
Z. Liliental-Weber ◽  
J.H. Mazur ◽  
W. Swider ◽  
J. Washburn ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layers ◽  
Structural Quality ◽  
Transmission Electron ◽  
Layer Technique ◽  
Growth Method ◽  
Microscopy Techniques ◽  
Edge Dislocations

Successive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.

scholarly journals Analysis of GaN-based HEMTS with AlN buffer layers by using Raman spectroscopy

2021 ◽  
pp. 2141010
Author(s):  
Cheng Che Lee ◽  
Hsin Jung Lee ◽  
Hsin Che Lee ◽  
Wei Yu Lee ◽  
Wei Ching Chuang
Keyword(s):  
Raman Spectroscopy ◽  
Buffer Layer ◽  
Epitaxial Layer ◽  
Drain Current ◽  
Buffer Layers ◽  
Crystal Quality ◽  
Subthreshold Slope ◽  
Gan Hemts ◽  
Aln Buffer

In this paper, AlGaN/GaN HEMTs with an AlN buffer layer were fabricated. Analyses on the crystal quality of the GaN epitaxial layer by Raman spectroscopy have been purposed. By introducing an AlN layer on sapphire substrate, the maximum drain current of the HEMT increased from 481 mA/mm to 522 mA/mm at [Formula: see text] V. Subthreshold slope was reduced from 638.3 mV/decade to 240.9 mV/decade and the electron mobility increased from 1109 cm2 V[Formula: see text]s[Formula: see text] to 1781 cm2 V[Formula: see text]s[Formula: see text]. These results showed that using an AlN buffer layer can improve the crystal quality of the GaN epitaxial layer, thus optimize the device performances of the GaN-based HEMTs.

Alloy clustering and defect structure in the molecular beam epitaxy of In0.53Ga0.47As on silicon

1992 ◽  
Vol 7 (8) ◽  
pp. 2194-2204 ◽  
Author(s):  
Alexandros Georgakilas ◽  
Athanasios Dimoulas ◽  
Aristotelis Christou ◽  
John Stoemenos
Keyword(s):  
Dislocation Density ◽  
Spinodal Decomposition ◽  
Buffer Layers ◽  
Silicon Substrates ◽  
Threading Dislocations ◽  
Fine Scale ◽  
Double Crystal ◽  
Direction Parallel ◽  
Short Period ◽  
Antiphase Domains

The MBE growth of InxGa1−xAs (x ∼ 0.53) on silicon substrates has been investigated emphasizing the effects of substrate orientation and buffer layers between In0.53Ga0.47As and Si. It is shown that growth on silicon substrates misoriented from (001) toward a [110] direction eliminates the presence of antiphase domains. The best In0.53Ga0.47As surface morphology was obtained when a 0.9 μm epitaxial Si buffer was initially grown, followed by a pre-exposure of the silicon surface to As4 at 350 °C, followed by the growth of In0.53Ga0.47As. Threading dislocations, stacking faults, low-angle grain boundaries, and spinodal decomposition were observed by TEM in the InGaAs layers. The spinodal contrast scale was shown to depend on the buffer type and the total InGaAs thickness. Thick buffers consisted of GaAs or graded InxGa1−xAs layers, and large In0.53Ga0.47As thicknesses favor the development of a coarse-scale spinodal decomposition with periodicity around 0.1 μm. Thin GaAs buffers or direct In0.53Ga0.47As growth on Si may result in a fine-scale decomposition of periodicity ∼10 nm. The principal strain direction of the spinodal decomposition appeared along the [1$\overline 1$0] direction, parallel to the vicinal Si surface step edges. InGaAs immiscibility affects the InGaAs growth process, favoring a 3-D growth mode. X-ray diffraction measurements and photoreflectance spectra indicated that the sample quality was improved for samples exhibiting a fine-scale spinodal decomposition contrast even if they contained a higher dislocation density. Threading dislocations run almost parallel to the [001] growth axis and are not affected by strained layers and short period (InAs)3/(GaAs)3 superlattices. The lowest double crystal diffractometry FWHM for the (004) InGaAs reflection was 720 arc sec and has been obtained growing InGaAs directly on Si, while the lowest dislocation density was 3 × 109 cm−2 and was obtained using a 1.5 μm GaAs buffer before the In0.53Ga0.47As deposition.

scholarly journals The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

1999 ◽  
Vol 595 ◽  
Author(s):  
M. Benamara ◽  
Z. Liliental-Weber ◽  
J.H. Mazur ◽  
W. Swider ◽  
J. Washburn ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layers ◽  
Structural Quality ◽  
Transmission Electron ◽  
Layer Technique ◽  
Growth Method ◽  
Microscopy Techniques ◽  
Edge Dislocations

AbstractSuccessive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.

ВЛИЯНИЕ ТВЕРДОФАЗНОЙ РЕКРИСТАЛЛИЗАЦИИ С ДВОЙНОЙ ИМПЛАНТАЦИЕЙ НА ПЛОТНОСТЬ СТРУКТУРНЫХ ДЕФЕКТОВ В УЛЬТРАТОНКИХ СЛОЯХ КРЕМНИЯ НА САПФИРЕ

2020 ◽  
Vol 96 (3s) ◽  
pp. 154-159
Author(s):  
Н.Н. Егоров ◽  
С.А. Голубков ◽  
С.Д. Федотов ◽  
В.Н. Стаценко ◽  
А.А. Романов ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Solid Phase ◽  
Modern Method ◽  
Structural Defects ◽  
Structural Quality ◽  
Mos Transistors ◽  
Ultrathin Layers ◽  
Heteroepitaxial Layers ◽  
Xrd And Tem

Высокая плотность структурных дефектов является основной проблемой при изготовлении электроники на гетероструктурах «кремний на сапфире» (КНС). Современный метод получения ультратонких структур КНС с помощью твердофазной эпитаксиальной рекристаллизации позволяет значительно снизить дефектность в гетероэпитаксиальном слое КНС. В данной работе ультратонкие (100 нм) слои КНС были получены путем рекристаллизации и утонения субмикронных (300 нм) слоев кремния на сапфире, обладающих различным структурным качеством. Плотность структурных дефектов в слоях КНС оценивалась с помощью рентгеноструктурного анализа и просвечивающей электронной микроскопии. Кривые качания от дифракционного отражения Si(400), полученные в ω-геометрии, продемонстрировали максимальную ширину на полувысоте пика не более 0,19-0,20° для ультратонких слоев КНС толщиной 100 нм. Формирование структурно совершенного субмикронного слоя КНС 300 нм на этапе газофазной эпитаксии обеспечивает существенное уменьшение плотности дислокаций в ультратонком кремнии на сапфире до значений ~1 • 104 см-1. Тестовые n-канальные МОП-транзисторы на ультратонких структурах КНС характеризовались подвижностью носителей в канале 725 см2 Вс-1. The high density of structural defects is the main problem on the way to the production of electronics on silicon-on-sapphire (SOS) heteroepitaxial wafers. The modern method of obtaining ultrathin SOS wafers is solid-phase epitaxial recrystallization which can significantly reduce the density of defects in the SOS heteroepitaxial layers. In the current work, ultrathin (100 nm) SOS layers were obtained by recrystallization and thinning of submicron (300 nm) SOS layers, which have various structural quality. The density of structural defects in the layers was estimated by using XRD and TEM. Full width at half maximum of rocking curves (ω-geometry) was no more than 0.19-0.20° for 100 nm ultra-thin SOS layers. The structural quality of 300 nm submicron SOS layers, which were obtained by CVD, depends on dislocation density in 100 nm ultrathin layers. The dislocation density in ultrathin SOS layers was reduced by ~1 • 104 cm-1 due to the utilization of the submicron SOS with good crystal quality. Test n-channel MOS transistors based on ultra-thin SOS wafers were characterized by electron mobility in the channel 725 cm2 V-1 s-1.

EVALUATION OF TRIBOTECHNICAL PROPERTIES OF THE COATING OBTAINED BY ELECTRIC SPARK HARDENING

2020 ◽  
Vol 4 (141) ◽  
pp. 157-163
Author(s):  
IL’YA ROMANOV ◽  
◽  
ROMAN ZADOROZHNIY
Keyword(s):  
Wear Resistance ◽  
Reference Sample ◽  
Optical Microscope ◽  
Research Purpose ◽  
Tribotechnical Properties ◽  
Uncoated Surface ◽  
Before And After ◽  
Materials Used ◽  
Friction Track

When applying coatings using various methods on the surfaces of moving parts that work in joints, it is important to make sure that the coatings are strong and wear-resistant in order to return them to their original resource. All existing hardening technologies and materials used to perform coatings have their own characteristics, therefore, the quality of the resulting coatings can be judged only after specific tests. (Research purpose) The research purpose is in evaluating the properties of the coating obtained by the method of electric spark hardening, and its ability to resist friction and mechanical wear. (Materials and methods) Authors conducted tests on the basis of the "Nano-Center" center for collective use. A coating was applied on the BIG-4M unit with a VK-8 hard alloy electrode, tribological properties were evaluated on a CSM Instruments TRB-S-DE-0000 tribometer, the width of the friction track was measured after the test using an inverted OLYMPUS gx51 optical microscope, and samples were weighed before and after the test on a VLR-200 analytical balance. Conducted research in accordance with GOST 23.224-86 and RD 50-662-88 guidelines. (Results and discussion) The article presents performed tests on the run-in and wear resistance of the coating. The samples were worked on with a step-by-step increase in the load. During the tests, the friction force was drawed on the diagram. Authors compared the results with the reference sample, an uncoated surface. (Conclusions) The resulting coating has better run-in and wear resistance compared to the standard, and the increase in wear resistance in dry friction conditions is very significant.

scholarly journals ZnSnN 2 in Real Space and k‐Space: Lattice Constants, Dislocation Density, and Optical Band Gap

2021 ◽  
pp. 2100015
Author(s):  
Vegard Skiftestad Olsen ◽  
Vetle Øversjøen ◽  
Daniela Gogova ◽  
Béla Pécz ◽  
Augustinas Galeckas ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Band Gap ◽  
Optical Band Gap ◽  
Real Space ◽  
Lattice Constants ◽  
Space Lattice

Influences of two-step growth and off-angle Ge substrate on crystalline quality of GaAs buffer layers grown by MOVPE

2015 ◽  
Vol 414 ◽  
pp. 15-20 ◽  
Author(s):  
Pornsiri Wanarattikan ◽  
Sakuntam Sanorpim ◽  
Somyod Denchitcharoen ◽  
Kenjiro Uesugi ◽  
Shigeyuki Kuboya ◽  
...  
Keyword(s):  
Buffer Layers ◽  
Crystalline Quality ◽  
Step Growth

scholarly journals The Band-Gap Studies of Short-Period CdO/MgO Superlattices

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Ewa Przeździecka ◽  
P. Strąk ◽  
A. Wierzbicka ◽  
A. Adhikari ◽  
A. Lysak ◽  
...  
Keyword(s):  
Band Gap ◽  
Layer Thickness ◽  
Energy Gap ◽  
Band Gaps ◽  
Short Period ◽  
Wide Range ◽  
Salt Structure ◽  
Short Period Superlattices ◽  
Direct Band ◽  
Sublayer Thickness

AbstractTrends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

Photoconductivité dans l'alliage GaAsxSb1−x en présence d'un champ magnétique

1974 ◽  
Vol 52 (8) ◽  
pp. 743-747 ◽  
Author(s):  
A. Filion ◽  
E. Fortin
Keyword(s):  
Magnetic Fields ◽  
Band Gap ◽  
Effective Mass ◽  
Alloy Composition ◽  
Longitudinal Optical ◽  
Optical Phonons ◽  
Champ Magnétique

The intrinsic photoconductivity of several samples of the alloy GaAsxSb1−x has been studied at 4.2 K in the presence of magnetic fields of up to 65 kG. Values for the band-gap, the reduced effective mass of the carriers, the energy of the longitudinal optical phonons across the alloy composition are deduced from the measurements.

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