Michael W. Moseley
Sandia National Laboratories
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Featured researches published by Michael W. Moseley.
Applied Physics Letters | 2008
Gon Namkoong; Elaissa Trybus; Kyung Keun Lee; Michael W. Moseley; W. Alan Doolittle; David C. Look
The free hole carriers in GaN have been limited to concentrations in the low 1018cm−3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ∼10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ∼1.5×1019cm−3.
Applied Physics Letters | 2015
Yuewei Zhang; Sriram Krishnamoorthy; Jared M. Johnson; Fatih Akyol; Andrew A. Allerman; Michael W. Moseley; Andrew Armstrong; Jinwoo Hwang; Siddharth Rajan
Low p-type conductivity and high contact resistance remain a critical problem in wide band gap AlGaN-based ultraviolet light emitters due to the high acceptor ionization energy. In this work, interband tunneling is demonstrated for non-equilibrium injection of holes through the use of ultra-thin polarization-engineered layers that enhance tunneling probability by several orders of magnitude over a PN homojunction. Al0.3Ga0.7N interband tunnel junctions with a low resistance of 5.6 × 10−4 Ω cm2 were obtained and integrated on ultraviolet light emitting diodes. Tunnel injection of holes was used to realize GaN-free ultraviolet light emitters with bottom and top n-type Al0.3Ga0.7N contacts. At an emission wavelength of 327 nm, stable output power of 6 W/cm2 at a current density of 120 A/cm2 with a forward voltage of 5.9 V was achieved. This demonstration of efficient interband tunneling could enable device designs for higher efficiency ultraviolet emitters.
Journal of Applied Physics | 2012
Michael W. Moseley; Brendan P. Gunning; Jordan D. Greenlee; Jonathan Lowder; Gon Namkoong; W. Alan Doolittle
The growth of InGaN alloys via Metal-Modulated Epitaxy has been investigated. Transient reflection high-energy electron diffraction intensities for several modulation schemes during the growth of 20% InGaN were analyzed, and signatures associated with the accumulation, consumption, and segregation of excess metal adlayers were identified. A model for shuttered, metal-rich growth of InGaN was then developed, and a mechanism for indium surface segregation was elucidated. It was found that indium surface segregation only occurs after a threshold of excess metal is accumulated, and a method of quantifying this indium surface segregation onset dose is presented. The onset dose of surface segregation was found to be indium-composition dependent and between 1 and 2 monolayers of excess metal. Below this surface threshold off excess metal, metal-rich growth can occur without indium surface segregation. Since at least 2 monolayers of excess metal will accumulate in the case of metal-rich, unshuttered growth of InG...
Applied Physics Letters | 2012
Brendan P. Gunning; Jonathan Lowder; Michael W. Moseley; W. Alan Doolittle
Highly p-type GaN films with hole concentrations exceeding 6 × 1019 cm−3 grown by metal-modulated epitaxy are electrically characterized. Temperature-dependent Hall effect measurements at cryogenic temperatures reveal minimal carrier freeze-out in highly doped samples, while less heavily doped samples exhibited high resistivity and donor-compensated conductivity as is traditionally observed. Effective activation energies as low as 43 meV were extracted, and a maximum Mg activation efficiency of 52% was found. In addition, the effective activation energy was found to be negatively correlated to the hole concentration. These results indicate the onset of the Mott-Insulator transition leading to impurity band conduction.
Applied Physics Letters | 2013
Alec M. Fischer; Yong O. Wei; F. A. Ponce; Michael W. Moseley; Brendan P. Gunning; W. A. Doolittle
We have studied the properties of thick InxGa1−xN films, with indium content ranging from x ∼ 0.22 to 0.67, grown by metal-modulated epitaxy. While the low indium-content films exhibit high density of stacking faults and dislocations, a significant improvement in the crystalline quality and optical properties has been observed starting at x ∼ 0.6. Surprisingly, the InxGa1−xN film with x ∼ 0.67 exhibits high luminescence intensity, low defect density, and uniform full lattice-mismatch strain relaxation. The efficient strain relaxation is shown to be due to a critical thickness close to the monolayer range. These films were grown at low temperatures (∼400 °C) to facilitate indium incorporation and with precursor modulation to enhance surface morphology and metal adlayer diffusion. These findings should contribute to the development of growth techniques for nitride semiconductors under high lattice misfit conditions.
Applied Physics Letters | 2010
Michael W. Moseley; Jonathan Lowder; Daniel Billingsley; W. Alan Doolittle
The surface kinetics of InGaN alloys grown via metal-modulated epitaxy (MME) are explored in combination with transient reflection high-energy electron diffraction intensities. A method for monitoring and controlling indium segregation in situ is demonstrated. It is found that indium segregation is more accurately associated with the quantity of excess adsorbed metal, rather than the metal-rich growth regime in general. A modified form of MME is developed in which the excess metal dose is managed via shuttered growth, and high-quality InGaN films throughout the miscibility gap are grown.
Journal of Applied Physics | 2009
Michael W. Moseley; Daniel Billingsley; Walter Henderson; Elaissa Trybus; W. Alan Doolittle
An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.
Journal of Applied Physics | 2014
Michael W. Moseley; Andrew A. Allerman; Mary H. Crawford; Jonathan J. Wierer; Michael Smith; Laura Biedermann
Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al0.7Ga0.3N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these open-core threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al0.7Ga0.3N templates are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.
IEEE Journal of Photovoltaics | 2014
Chloe A. M. Fabien; Michael W. Moseley; Brendan P. Gunning; W. Alan Doolittle; Alec M. Fischer; Yong O. Wei; F. A. Ponce
Indium gallium nitride (InGaN) alloys exhibit substantial potential for high-efficiency photovoltaics. However, theoretical promise still needs to be experimentally realized. This paper presents a detailed theoretical study to provide guidelines to achieve high-efficiency InGaN solar cells. While the efficiency of heterojunction devices is limited to ~11%, homojunction devices can achieve suitable efficiencies, provided that highly p-type-doped InGaN layers and thick, single-phase InGaN films can be grown. Thus, we have developed a novel growth technology that facilitates growth of p-type nitride films with greatly improved hole concentration and growth of InGaN without phase separation, offering promise for future high-efficiency InGaN solar cells.
IEEE Transactions on Electron Devices | 2016
Jeramy Ray Dickerson; Andrew A. Allerman; Benjamin N. Bryant; Arthur J. Fischer; Michael P. King; Michael W. Moseley; Andrew Armstrong; Robert Kaplar; Isik C. Kizilyalli; Ozgur Aktas; Jonathan J. Wierer
Vertical GaN power diodes with a bilayer edge termination (ET) are demonstrated. The GaN p-n junction is formed on a low threading dislocation defect density (104 - 105 cm-2) GaN substrate, and has a 15-μm-thick n-type drift layer with a free carrier concentration of 5 × 1015 cm-3. The ET structure is formed by N implantation into the p+-GaN epilayer just outside the p-type contact to create compensating defects. The implant defect profile may be approximated by a bilayer structure consisting of a fully compensated layer near the surface, followed by a 90% compensated (p) layer near the n-type drift region. These devices exhibit avalanche breakdown as high as 2.6 kV at room temperature. Simulations show that the ET created by implantation is an effective way to laterally distribute the electric field over a large area. This increases the voltage at which impact ionization occurs and leads to the observed higher breakdown voltages.