Francisco Machuca

Hospital Universitario de Valme

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Zhi Liu

ShanghaiTech University

P. Pianetta

SLAC National Accelerator Laboratory

R. F. W. Pease

Stanford University

W. E. Spicer

Stanford University

Bernardo Herrera‐Imbroda

Hospital Clínico Universitario Virgen de la Victoria

Yun Sun

Shandong Agricultural University

Juan Enríque Pérez

University of Pennsylvania

J. Herráez

Universitat de València

Robert E. Weiss

University of California, Los Angeles

Alex Welsh

Acree Technologies (United States)

Cooperative Institutions

Hospital Clínico Universitario Virgen de la Victoria

Instituto de Investigación Biomédica de Málaga

Stanford University

Stanford Synchrotron Radiation Lightsource

SLAC National Accelerator Laboratory

Hospital Universitario de Valme

Hospital Regional Universitario de Málaga

Universidad de Málaga

University of Florida

Spanish National Cancer Research Centre

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Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers

ECS Transactions (2015)

A. M. Dabiran Francisco Machuca Indranil De Robert E. Weiss

We discuss the development of high-quality ZrTi metal layers that are epitaxially deposited by sputtering on sapphire and Si, and which are c-axis oriented and lattice matched for growth of low-defect hexagonal GaN films. We also explain and discuss the nucleation and growth of thick GaN layers by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) on these metal layers. Finally, we present the results of thin-film measurements to demonstrate the high crystal qualities and very smooth surface morphologies of highly specular GaN layers grown on ZrTi buffers in this work.

10.1149/06601.0113ecst

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Citations (4)

A New Multi-Parameter Instrument for Photoconductance Quality Measurements Useful in the Development and Production of Solar Silicon Wafers and Solar Cells

World Conference on Photovoltaic Energy Conversion (2011)

Francisco Machuca Dennis E. House David G. Cornwell Phil Shaw

Silicon solar cell

10.4229/26theupvsec2011-2bv.4.19

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Citations (1)

Risk Prediction Tools Available for Germline BRCA1/2 Mutations Underperform in Prostate Cancer Patients

European Urology Oncology (2019)

L. Martinez Oliva Rebeca Lozano Casilda Llácer Isabel M. Aragón Bella I. Pajares

10.1016/j.euo.2019.06.019

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Citations (9)

Optimization and characterization of III–V surface cleaning

Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena (2003)

Zhi Liu Yun Sun Francisco Machuca P. Pianetta W. E. Spicer

Achieving clean surfaces is a major and challenging requirement for the study of surfaces and surface reactions. Nondestructive cleaning is a crucial step in semiconductor manufacturing, growth of materials, and processing. We use photoemission spectroscopy (PES) to systematically study the core and valence band electronic structure of various chemical treatments of InP(100), GaAs(100), and GaN(0001). These surfaces undergo wet chemical cleaning of H2SO2/H2O2/H2O followed by thermal heating. In order to achieve the necessary surface sensitivity and spectral resolution, synchrotron radiation in the energy range of 60–1000 eV is used for PES. In tuning the sulfuric acid based chemistry, we achieve oxygen free GaAs and InP surfaces, as shown in our valence band and core level PES analysis. Furthermore, core level PES shows oxygen coverage of the GaN surface is reduced to less than 0.1 monolayer (ML). The carbon coverage is also reduced dramatically for the III–V surfaces, <10% ML for InP and GaAs and approximately 1% ML for GaN. The chemical reactions and species at different cleaning stages are determined and cleaning mechanisms are proposed. Our study shows that material similarities do not imply exact correlation to the chemical cleaning properties among III–V materials.

10.1116/1.1593644

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Citations (40)

A thin film P-type gallium nitride photocathode: Prospect for a high performance electron emitter

Francisco Machuca

Photocathode

Source

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Citations (0)

Tumor primario de vena cava inferior con extensión infrarrenal, suprarrenal y suprahepática

Medicina Clínica Práctica (2018)

Ana Moreno Reina Guillermo Núñez de Arenas Baeza Francisco Machuca J. Herráez Andrés García León

Vena cava

10.1016/j.mcpsp.2018.11.009

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Primary tumor of inferior vena cava with infrarenal, suprarenal and suprahepatic extension.

Cancer Research and Cellular Therapeutics (2019)

Ana Moreno Reina Guillermo Núñez de Arenas Baeza Francisco Machuca J. Herráez Andrés García León

The patient was a 77-year-old woman with hypertension and no other history of interest. She presented with generalized edema, oliguria and weight gain, associated with asthenia and malaise of months of evolution.

Oliguria

Malaise

Primary tumor

10.31579/2640-1053/034

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AlGaN/GaN High Electron Mobility Transistor Grown and Fabricated on Lattice Matched Metallic Layers

Meeting abstracts/Meeting abstracts (Electrochemical Society. CD-ROM) (2016)

F. Ren S. J. Pearton Shihyun Ahn Yi-Hsuan Lin Francisco Machuca

AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. In order to lower the cost of HEMTs, larger diameters substrates are needed. Currently, the HEMT structures are grown on non-native sapphire, SiC and Si substrates or on native substrate of vapor phase epitaxy (VPE) GaN wafers. HEMTs grown on sapphire substrate suffer from poor heat dissipation and higher defect density due to the relative larger lattice mismatch to GaN. SiC has a very good thermal conductivity and is less lattice mismatch to GaN, but high quality semi-insulating SiC substrates are quite expensive. Although, Si substrates are fair low cost and available for larger diameter substrates, due to larger lattice mismatch to GaN, it requires to grow thick complex AlGaN buffers prior to the growth of GaN layer to reduce the threading dislocation density. These thick AlGaN layers are very defective and thermal resistive, which will hinder device heat dissipation. VPE grown GaN wafers are limited to 2-3” diameter and very expensive. Recently, it was reported that high quality GaN layers were grown by RF plasma-assisted molecular beam epitaxy (PA-MBE) or metal organic chemical vapor deposition (MOCVD) on high-quality, single crystal ZrTi refractory metal alloys deposited by plasma sputtering on c-plane sapphire and Si substrates. These ZrTi refractory metal alloys are not only lattice match to GaN, but have a similar coefficient of thermal expansion (CTE) as the CTE of GaN [1]. By employing these ZrTi alloys, there is no need to grow thick AlGaN buffer, both photonic and electronic GaN based device structure can be grown on large area Si substrates to achieve low cost GaN based device fabrication. In this work, we have demonstrated AlGaN/GaN HEMTs grown on ZrTi refractory metal alloys, which were deposited on both Si and sapphire substrates. HEMTs with a gate dimension of 1 µm × 100 um were fabricated and characterized. Both dc and rf performance of AlGaN/GaN HEMTs fabricated on the ZrTi metal alloys will be presented. 1. “Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers”, A.M. Dabiran, F. Machuca, I. De, and R. Weiss, ECS Trans. 66, 113-117 (2015).

Electron Mobility

10.1149/ma2016-02/31/2047

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Role of oxygen in semiconductor negative electron affinity photocathodes

Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena (2002)

Francisco Machuca Zhi Liu Yun Sun P. Pianetta W. E. Spicer

Source contamination, photovoltage effects, and stimulated electron desorption of cesium are factors that determine the initial high performance and longevity of negative electron affinity electron sources. As part of the study of these factors, we investigate the effect of oxygen contamination during the activation process and operation of a traditional GaAs (100) and a novel GaN (0001) emitter. We use synchrotron radiation photoemission spectroscopy, a focused mercury arc discharge lamp, and a helium neon (HeNe) laser to obtain simultaneously elemental analyses of the emitting surface and the corresponding total quantum yield at various stages, respectively, for GaN and GaAs. Our results indicate: (1) carbon uptake does not occur in our carbon free system over time, (2) oxygen uptake is observed for both GaN (0001) and GaAs (100) activated surfaces, a property common to the chemistry of the Cs/O adlayer, (3) the oxygen species appears to change over time and the initial species is assigned to an ion of nondissociated oxygen in the Cs/O activation layer, (4) the chemical changes of the Cs/O adlayer are not accompanied by a significant loss of cesium from the surface, and (5) the onset of decay of the quantum yield begins at a later time for the GaN (0001) emitter in comparison to the GaAs (100) electron source. A chemical model for the activation layer and its transformation over time is developed, consistent with points (1) through (4) in a separate report [F. Machuca et al. (unpublished)]. The complete account of the decay of the quantum yield of both Cs/O activated III–V emitters is compared and discussed in this article.

Quantum yield

Caesium

10.1116/1.1521742

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Citations (58)

Subpicosecond jitter in picosecond electron bunches

Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures Processing Measurement and Phenomena (2005)

K. Ioakeimidi S. Gradinaru Zhi Liu Francisco Machuca Jon‐Fredrik Nielsen

We have simulated and measured 60–120fs time jitter of photoelectron pulses emitted by a nitride photocathode at 100GHz rate as in order to evaluate the resolution performance of a previously proposed photonic analog to digital converter. Recently, there has been an increasing demand for high speed analog-to-digital converters (ADCs) for microwave bandwidth signals. State of the art electronic ADCs have reached 10Gigasamples∕second (GS/s), 6–12bit performance [P. W. Juodawlkis, J. C. Twichell, G. E. Betts, J. J. Hargreaves, R. D. Younger, J. L. Wasserman, F. J. O’Donnell, K. G. Ray, and R. C. Williamson, IEEE Microwave Theory Tech. 49, 1840 (2001)]. We have previously introduced a photoelectronic ADC implementation with measured performance of 3bits at 100GS∕s [K. Ioakeimidi, R. Leheny, S. Gradinaru, K. Ma, R. Aldana, J. Clendenin, J. S Harris, R. F. W. Pease, IEEE Trans. Microwave Theory Tech. (to be published); Conference on Lasers and Electro-Optics, Baltimore MD, 1–6 June 2003]. The basic operating principle of the ADC is based on a miniaturized cathode ray tube where a bunch of photoemitted electrons passing through an electric deflection system is directed to a specific detector whence a digital code word emanates. The electron bunch samples the analog deflecting voltage that is then quantized according to the position of the detector receiving the bunch. The fundamental limit of the number of distinguishable voltage levels is the ratio of the deflecting voltage to the energy spread due to diffraction of the electron beam. This allows for up to 12bits at 100GS∕s [R. F. Pease, K. Ioakeimidi, R. Aldana, and R. Leheny, J. Vac. Sci. Technol. B 21, 2826 (2003)]. At a more practical level, the bit resolution is primarily limited by the uncertainty in the emission of each electron bunch (temporal jitter). For 100fs time uncertainty 5bits of resolution are attainable with the nitride cathode for a 50GHz bandwidth analog signal.

Photocathode

Picosecond

10.1116/1.1849212

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Citations (2)