Extremely high electron mobilities in modulation-doped GaAs-AlxGa1−xAs heterojunction superlattices

1981 ◽  
Vol 17 (1) ◽  
pp. 36 ◽  
Author(s):  
W.I. Wang ◽  
C.E.C. Wood ◽  
L.F. Eastman
Keyword(s):  
High Electron

A correlation of CL emissions from Penrith sandstone with elemental distributions obtained by simultaneous SEM-CL and EDS analysis

1995 ◽  
Vol 53 ◽  
pp. 392-393
Author(s):  
Paul J. Wright
Keyword(s):  
Optical Microscope ◽  
Electron Gun ◽  
High Electron ◽  
Collection System ◽  
Electron Hole ◽  
Depositional Processes ◽  
Eds Analysis ◽  
Distribution Mapping ◽  
Backscattered Electron ◽  
Electron Imaging

Most industrial and academic geologists are familiar with the beautiful red and orange cathodoluminescence colours produced by carbonate minerals in an optical microscope with a cold cathode electron gun attached. The cement stratigraphies interpreted from colour photographs have been widely used to determine the post depositional processes which have modified sedimentary rock textures.However to study quartzose materials high electron densities and kV's are necessary to stimulate sufficient emission. A scanning electron microscope with an optical collection system and monochromator provides an adequate tool and gives the advantage of providing secondary and backscattered electron imaging as well as elemental analysis and distribution mapping via standard EDS/WDS facilities.It has been known that the incorporation of many elements modify the characteristics of the CL emissions from geological materials. They do this by taking up positions between the valence and conduction band thus providing sites to assist in the recombination of electron hole pairs.

Electron microscope study of the secretory activity of epithelial cells in embryonic thymus

1990 ◽  
Vol 48 (3) ◽  
pp. 382-383
Author(s):  
H. Alasam
Keyword(s):  
Cell Differentiation ◽  
T Cell ◽  
Epithelial Cells ◽  
Electron Density ◽  
Secretory Activity ◽  
T Cell Differentiation ◽  
High Electron ◽  
Transmission Electron ◽  
Medullary Epithelial Cells ◽  
Thymic Factor

The possibility that intrathymic T-cell differentiation involves stem cell-lymphoid interactions in embryos led us to study the ultrastructure of epithelial cell in normal embryonic thymus. Studies in adult thymus showed that it produces several peptides that induce T-cell differentiation. Several of them have been chemically characterized, such as thymosin α 1, thymopoietin, thymic humoral factor or the serum thymic factor. It was suggested that most of these factors are secreted by populations of A and B-epithelial cells.Embryonic materials were obtained from inbred matings of Swiss Albino mice. Thymuses were disected from embryos 17 days old and prepared for transmission electron microscopy. Our studies showed that embryonic thymus at this stage contains undifferentiated and differentiated epithelial cells, large lymphoblasts, medium and few small lymphocytes (Fig. 5). No differences were found between cortical and medullary epithelial cells, in contrast to the findings of Van Vliet et al,. Epithelial cells were mostly of the A-type with low electron density in both cytoplasm and nucleus. However few B-type with high electron density were also found (Fig. 7).

HVPE-GROWN AlGaN/GaN HEMTs

2003 ◽  
Vol 764 ◽  
Author(s):  
B. Luo ◽  
F. Ren ◽  
M. A. Mastro ◽  
D. Tsvetkov ◽  
A. Pechnikov ◽  
...  
Keyword(s):  
High Electron Mobility Transistors ◽  
Hydride Vapor Phase Epitaxy ◽  
Root Mean Square Roughness ◽  
High Electron ◽  
Electron Mobility Transistors ◽  
Current Collapse ◽  
Collapse Characteristics ◽  
Capacitance Voltage ◽  
Source Current ◽  
Measurement Area

AbstractHigh quality undoped AlGaN/GaN high electron mobility transistors(HEMTs) structures have been gorwn by Hydride Vapor Phase Epitaxy (HVPE). The morphology of the films grown on Al2O3 substrates is excellent with root-mean-square roughness of ∼0.2nm over 10×10μm2 measurement area. Capacitance-voltage measurements show formation of dense sheet of charge at the AlGaN/GaN interface. HEMTs with 1μm gate length fabricated on these structures show transconductances in excess of 110 mS/mm and drain-source current above 0.6A/mm. Gate lag measurements show similar current collapse characteristics to HEMTs fabricated in MBE- or MOCVD grown material.

Infrared and Visible—Near Infrared Electroluminescence Developments for FA in AlGaN/GaN HEMTS on SiC

2010 ◽  
Author(s):  
M. Bouya ◽  
D. Carisetti ◽  
J.C. Clement ◽  
N. Malbert ◽  
N. Labat ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Near Infrared ◽  
High Electron Mobility Transistor ◽  
Low Noise ◽  
Civil Defense ◽  
Base Stations ◽  
Infrared Range ◽  
High Electron ◽  
Radar Applications ◽  
Gan Hemts

Abstract HEMT (High Electron Mobility Transistor) are playing a key role for power and RF low noise applications. They are crucial components for the development of base stations in the telecommunications networks and for civil, defense and space radar applications. As well as the improvement of the MMIC performances, the localization of the defects and the failure analysis of these devices are very challenging. To face these challenges, we have developed a complete approach, without degrading the component, based on front side failure analysis by standard (Visible-NIR) and Infrared (range of wavelength: 3-5 µm) electroluminescence techniques. Its complementarities and efficiency have been demonstrated through two case studies.

IR Thermography for Temperature Measurements and Fault Location on AlGaN/GaN HEMTs and MMICs

2015 ◽  
Author(s):  
Lény Baczkowski ◽  
Franck Vouzelaud ◽  
Dominique Carisetti ◽  
Nicolas Sarazin ◽  
Jean-Claude Clément ◽  
...  
Keyword(s):  
Fault Location ◽  
Hot Spot ◽  
Life Time ◽  
High Electron Mobility Transistors ◽  
Junction Temperature ◽  
High Electron ◽  
Ir Thermography ◽  
Operating Life ◽  
Gan Hemt ◽  
Electron Mobility Transistors

Abstract This paper shows a specific approach based on infrared (IR) thermography to face the challenging aspects of thermal measurement, mapping, and failure analysis on AlGaN/GaN high electron-mobility transistors (HEMTs) and MMICs. In the first part of this paper, IR thermography is used for the temperature measurement. Results are compared with 3D thermal simulations (ANSYS) to validate the thermal model of an 8x125pm AIGaN/GaN HEMT on SiC substrate. Measurements at different baseplate temperature are also performed to highlight the non-linearity of the thermal properties of materials. Then, correlations between the junction temperature and the life time are also discussed. In the second part, IR thermography is used for hot spot detection. The interest of the system for defect localization on AIGaN/GaN HEMT technology is presented through two case studies: a high temperature operating life test and a temperature humidity bias test.

Modulation-doped (AlGa)As/GaAs quantum well structure with high electron sheet density

1989 ◽  
Vol 25 (17) ◽  
pp. 1147
Author(s):  
A.L. Powell ◽  
J.S. Roberts ◽  
P.I. Rockett ◽  
T.J. Foster ◽  
L. Eaves
Keyword(s):  
Quantum Well ◽  
High Electron ◽  
Quantum Well Structure ◽  
Electron Sheet ◽  
Sheet Density

scholarly journals A Comparative Study of GaN HEMT and Si MOSFET-Based Active Clamp Forward Converters

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4160
Author(s):  
Xiaobin Li ◽  
Hongbo Ma ◽  
Junhong Yi ◽  
Song Lu ◽  
Jianping Xu
Keyword(s):  
Comparative Analysis ◽  
Power Density ◽  
Load Condition ◽  
High Electron ◽  
Power Devices ◽  
Voltage Range ◽  
Gan Hemt ◽  
Active Clamp ◽  
Forward Converters ◽  
Bus Voltage

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution and comparative analysis, two 18~36 V input, 120 W/12 V output, synchronous rectification prototype with different power devices are built and compared in the lab. The experimental results show the GaN version can achieve the efficiency of 95.45%, which is around 1% higher than its counterpart under the whole load condition and the same power density of 2.2 W/cm3.

Effective Dielectric Function of Porous Silicon: the Transverse Component

1994 ◽  
Vol 358 ◽  
Author(s):  
G. Gumbs
Keyword(s):  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Electron Density ◽  
Quantum Wires ◽  
Interband Transition ◽  
Incident Light ◽  
Transverse Component ◽  
Effect Of Temperature ◽  
High Electron ◽  
Confining Potential

ABSTRACTA self-consistent many-body theory is developed to study the effect of temperature and electron density on the interband absorption coefficient and the frequency-dependent refractive index for an array of isolated quantum wires. The peaks in the absorption coefficient correspond to interband transitions resulting in the resonant absorption of light. The oscillations in the derivative spectrum are due to the quantization of the energy levels related to the in-plane confining potential for such reduced dimensional systems. There are appreciable changes in the absorption spectrum when the electron density or temperature is increased. One interband transition peak is suppressed in the high electron density limit and the thermal depopulation effect on the electron subbands can be easily seen when the temperature is high. We also find that the exciton coupling weakens the shoulder features in the absorption spectrum. This study is relevant to optical characterization of the confining potential and the areal density of electrons using photoreflectance. By using incident light with tunable frequencies in the interband excitation regime, contactless photoreflectance measurements may be carried out and the data compared with our calculations. By fitting the numerical results to the peak positions of the photoreflectance spectrum, the number of electrons in each wire may be extracted.

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