David V. Kerns

A multimechanism model for photon generation by silicon junctions in avalanche breakdown

Light emission from three device types ((1) commercial silicon JFETs, (2) bipolar transistors, and (3) a custom diode) with p-n junctions biased in controlled avalanche breakdown, has been measured over the photon energy range 1.4-3.4 eV, Previously published models are compared with these data to elucidate the mechanisms responsible for avalanche light emission in silicon. A multimechanism model fitting measured spectra and spectra measured by other researchers is presented and justified. The success of the model indicates that indirect recombination of electrons and holes is the dominant emission mechanism below the light intensity peak (/spl sim/1.8-2.0 eV), that indirect intraband recombination dominates at intermediate energies up to /spl sim/2.3 eV, and that direct interband recombination between high-field populations of carriers near k=0 dominates above /spl sim/2.3 eV. For junctions with overlayer passivation, an interference model must be applied to model measured spectra.

Micropatterned polycrystalline diamond field emitter vacuum diode arrays

Electron field emission from an array of patterned pyramids of polycrystalline diamond for vacuum diode applications has been investigated. High current emission from the patterned diamond microtip arrays was obtained at low electric fields. An emission current from the diamond microtips of 0.1 mA was observed for a field of <10 V/μm. Field emission for these diamond microtips exhibits significant enhancement in total emission current compared to silicon emitters. Moreover, field emission from patterned polycrystalline diamond pyramidal tip arrays is unique in that the applied field is found to be lower compared to that required for emission from Si, Ge, GaAs, and metal surfaces. The fabrication process utilizes selective deposition of diamond film in a silicon cavity mold and subsequent creation of free standing polycrystalline diamond diaphragm with diamond pyramidal microtip array. The processing techniques are compatible with integrated circuit fabrication technology.

Effect of sp2 content and tip treatment on the field emission of micropatterned pyramidal diamond tips

Electron field emission characteristics of uniformly constructed micro-pyramids of polycrystalline diamond with varying sp2 content have been systemically investigated. Concurrently, tip surface treatment was performed and emission characteristics of the post-treated tips were evaluated. The experimental results show that the field emission characteristics of the diamond can be enhanced by increasing the sp2 content and performing surface treatment. The emission current is significantly improved and the turn-on electric field is drastically reduced. Hypotheses are proposed for the effect of sp2 content and surface treatment on the field emission enhancement of diamond tips: (i) lowering of the work function due to sp2 defect induced band and impurity desorption, and (ii) increase in field enhancement factor due to sp2-diamond-sp2 microstructures and a field forming process. Analysis of the experimental results indicates that (ii) is the more probable explanation.

The Olin curriculum: thinking toward the future

In 1997, the F. W. Olin Foundation of New York established the Franklin W. Olin College of Engineering, Needham, MA, with the mission of creating an engineering school for the 21st century. Over the last five years, the college has transformed from an idea to a functioning entity that admitted its first freshman class in fall 2002. This paper describes the broad outlines of the Olin curriculum with some emphasis on the electrical and computer engineering degree. The curriculum incorporates the best practices from many other institutions as well as new ideas and approaches in an attempt to address the future of engineering education.

Recent development of diamond microtip field emitter cathodes and devices

Recent development of diamond field emitter cathodes and devices fabricated from molding process is presented. Practical modifications involving the sp2 content, surface treatment, boron doping, and tip sharpening to further enhance diamond field emission are discussed. A new fabrication process for achieving ultrasharp diamond tips with a radius of curvature less than 5 nm has been achieved and shows significant improvement in emission characteristics. Discussion of this enhanced emission in diamond microtips is presented in accordance with analysis of emission behavior. The development of high site density of uniform diamond microtip arrays is presented. We also report the development of a new technique to fabricate self-aligned gate diamond emitter diodes, which achieve very high emission characteristics at extremely low applied voltage. The latest development aims to integrate diamond field emitters with silicon-based MEMS processing technology and achieve totally monolithic diamond field emitter devi...

Comparison of contactless measurement and testing techniques to a all-silicon optical test and characterization method

The rapid improvement in performance and increased density of electronic devices in integrated circuits has provided a strong motivation for the development of contactless testing and diagnostic measurement methods. This paper first reviews existing contactless test methodologies and then compares these with an all-silicon contactless testing approach that has been recently developed and demonstrated. This cost-effective approach utilizes silicon-generated optical signals and has the advantages of easy test setup, low equipment cost, and noninvasiveness over existing contactless test and measurement methods.

Analysis of electroluminescence spectra of silicon and gallium arsenide p–n junctions in avalanche breakdown

We present a generalized study of light emission from reverse biased p–n junctions under avalanche breakdown conditions. A model is developed based on direct and indirect interband processes including self-absorption to describe measured electroluminescence spectra. This model was used to analyze experimental data for silicon (Si) and gallium arsenide p–n junctions and can be extended to several types of semiconductors regardless of their band gaps. This model can be used as a noninvasive technique for the determination of the junction depth. It has also been used to explain the observed changes of the Si p–n junction electroluminescence spectra after fast neutron irradiation. In particular, it is demonstrated that the neutron irradiation affects both the semiconductor and the overlying passivation oxide layer.

Modeling of the transistor characteristics of a monolithic diamond vacuum triode

Transistor emission characteristics from a monolithic diamond vacuum triode fabricated by a self-aligning gate technique have been studied and modeled. The anode emission current of diamond triodes has been modeled per the Fowler–Nordheim triode equation and an empirical model for the emission transport factor described. The model was applied to two different diamond field emission triodes with distinct emission characteristics. A procedure for modeling parameter extraction is developed and demonstrated. The modeling results agree well with the experimental data. The empirical model can be incorporated into programs for field emission device simulation.

Fabrication and field emission characteristics of lateral diamond field emitter

Lateral diamond field emitters were fabricated by a diamond patterning technique that utilizes oxide patterning and lift-off process on a silicon-on-insulator wafer. An anode–cathode spacing of 2 μm between the diamond anode and cathode was achieved. The fabricated lateral diamond emitter diode exhibits excellent emission characteristics with a low turn-on voltage of ∼5 V and a high emission current of 6 μA, from four diamond fingers, at an anode voltage of 25 V. The emission current is stable over time, even at high emission current. The low turn-on voltage (turn-on field ∼3 V/μm) and high emission characteristics are among the best of reported lateral field emitter structures. The lateral diamond field emitter has potential applications in vacuum microelectronics, sensors, and microelectromechanical systems.

Physical characterization of diamond pyramidal microtip emitters

Micropatterned diamond pyramidal tips have been demonstrated to have high emission current. This article presents in great detail the physical characterizations that have proceeded to characterize the topology, morphology, and microstructure of these diamond microtips using transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and Raman spectroscopy. The results show that the diamond microtips are indeed a polycrystalline diamond structure as evidenced by Raman spectroscopy and diffraction analysis of the TEM. AFM and STM results provide detail information as to the surface and tip shape of the diamond emitters. AFM/STM observations suggest a nucleation and growth process whereby the matter in which chemical vapor deposition diamond nucleates on the planar top surface of the tip substrate is distinct and different from the way the diamond grows in the cavity “mold.” Likewise, the TEM results contrast the diamond microstructure in the field area with th...