Eric R. Heller

Bio: Eric R. Heller is an academic researcher from Wright-Patterson Air Force Base. The author has contributed to research in topics: High-electron-mobility transistor & Gallium nitride. The author has an hindex of 24, co-authored 88 publications receiving 2523 citations. Previous affiliations of Eric R. Heller include University of Alabama in Huntsville & Wright State University.

Analysis of Time Dependent Electric Field Degradation in AlGaN/GaN HEMTs (POSTPRINT)

Abstract: : The authors report on an electrical and optical analysis of AlGaN/GaN HEMTs stressed under high electric field conditions into a state of permanent degradation, evidenced by an increase in OFF-state leakage current and a reduction in breakdown voltage. A method of stress testing AlGaN/GaN HEMTs to voltages close to breakdown while protecting the device from catastrophic failure is presented. Using this stress method, a detailed study was performed to observe device degradation that limits safe operation in the OFF-state. Electrical analysis reveals that quantitatively the Schottky properties of the gate diode are degraded by the stress and suggests a localized defect. An optical analysis confirms localized degradation via electroluminescence (EL) spots on the stressed side of the gate finger. It is shown that the dominant EL site in the degraded device may be observed prior to the application of stress. Finally, it is confirmed that the localized EL emission of the stressed device is the dominant gate leakage path via thermal imaging. These results suggest a method for identifying and understanding the failure mechanisms that limit the safe operating area of GaN HEMTs.

Damage Characterization for Electronic Components Under Impact Loading

Abstract: A new experimental method has been develop to characterize critical interfacial damage parameters of solder interconnects subjected to high strain-rate mechanical loading, simulating shock or impact loading. A test apparatus and a test specimen were devised to experimentally characterize such critical damage parameters, particularly interfacial shear strength and fracture toughness. The test fixture was designed to easily mount and unmount test specimens, and accommodate various sizes of electronic components and solder layer thicknesses. Test specimens were fabricated with both metallic and polymeric solder materials, and tests were conducted under various shear load rates. It was found that both strength and fracture toughness exhibit significant rate-dependency.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

A review of Ga2O3 materials, processing, and devices

Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

Abstract: J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons