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Electronic Properties and Reliability of the SiO2 / SiC Interface
John Rozen, May 2008. Ph.D. Thesis, Vanderbilt University.

A global effort has been started towards the implementation of energy efficient electronics. In particular, there is much interest in silicon carbide (SiC), a large band-gap semiconductor which enables the control of high voltage signals with an efficiency orders of magnitude higher than the widespread silicon-based devices. Moreover, the reduced cooling requirements of SiC devices allow for less bulky and lighter components.

This thesis focused on the electrical properties and the reliability of the oxide and its interface with silicon carbide. In particular, the effects of processing parameters, such as (i) implant activation, (ii) oxidation conditions, and (iii) post-oxidation anneal, are considered. Measurements are performed on metal-oxide-semiconductor (MOS) capacitors formed on 4H-SiC, the most widely used polytype.

The findings and the analysis reported in the thesis have led to the publication of several peer-reviewed manuscripts. During this research effort, three experimental setups, detailed in the appendices, have been designed and implemented for (high pressure) semiconductor oxidation, automated carrier injection, and time-dependent dielectric breakdown measurements.

Download Files: PDF Manuscript 

Properties of Nanocrystalline Vanadium Dioxide
John Rozen, August 2005. Master's Thesis, Vanderbilt University.

Vanadium dioxide falls into the category of smart materials because it undergoes a semiconductor to metal phase transition at the convenient temperature of 68 oC. This transition is accompanied by large modifications of its optical and electrical properties which suggests its use in window coatings, infrared sensors or opto-electronic memories and switches.

The first chapter introduces the mechanisms underlying the phase transition and how scale can affect its properties. Then, different methods used to deposit thin films of vanadium dioxide are cited, together with the important parameters that control the quality of the obtained material. In particular, the principles of pulsed laser deposition are described before the properties of sputtered vanadium dioxide thin films are discussed. Percolation theory is introduced in the last chapter because it can model vanadium dioxide networks. The results of computer simulations are also reported and they justify the use of an effective medium approximation to quantitatively describe real systems. Finally, current percolation effects in a nanocrystalline vanadium dioxide film are studied using this approximation.

Download Files: PPT Slides / PDF Manuscript 

Current Percolation in Nanocrystalline Vanadium Dioxide Thin Films
John Rozen, May 2005. ME 343, Vanderbilt University.

Measurements on thin VO2 wires reveal an apparent offset between the electrical and optical critical temperatures of the semiconductor to metal phase transition, suggesting the possibility of designing tristate optoelectronic devices. This shift is explained by current percolation in a nanostructured system that can be modelled as a network of resistors in which sites switch independently from a semiconducting to a metallic state upon heating. A computer simulation was implemented in order to support this concept.

Download Files: PPT Slides /  PDF Manuscript 

Simulation of a High Performance 35nm Gate CMOS
John Rozen, May 2004. EECE 307, Vanderbilt University.

The 35 nm gate length CMOS devices have been simulated to study the feasibility of higher performance operation. The results are in good accordance with fabricated devices. This paper shows that halo doping and super steep retrograde profiles are required to reduce short channel effects. The best parameters lead to current drives of 1088 μA/μm in the nFET and 682 μA/μm in the pFET at Vdd = 0.85V

Download Files: PPT Slides /  PDF Manuscript 

Mechanical Properties of Nanocomposites
John Rozen, December 2003. CHEM 350, Vanderbilt University.

The purpose of this work is to show how the mechanical properties of a material can be enhanced when used as a host matrix for another compound. In order to understand the characteristics of the so-called composites, a first section introduces briefly what are the observed properties of a material when observed under mechanical stresses. Then, the second part of this work focus on the mechanical behavior of bulk polymers and single carbon nanotubes. After, some composites involving these at the nanoscale are introduced, demonstrating the effectiveness of such a patchwork.

Download Files: PPT Slides /  PDF Manuscript 

Intro to Pulsed Laser Deposition and Comparison with other Techniques
John Rozen and Enrique J. Montes, December 2003. CHE 284, Vanderbilt University.

The present work shows that Pulsed Laser Deposition (PLD) has the potential to be a useful tool as well if the transition from a laboratory to an industry process can be made. Before describing this energetic technique, a chapter is dedicated to the actual usage of thin films and depicts the steps common to the processes used for their deposition. The second chapter describes briefly the chemical vapor deposition (CVD) process as an example of thermal technique and introduce the deposition of silicon by this method for a comparison purpose. The third chapter discuss the PLD process in more details, describing the equipment and the energetic processes involved. It also contains the main problems that need to be overcome and some innovative solutions. Also, it is shown that silicon deposition is possible by this process. The last chapter defines some fundamental criteria to compare the different techniques without forgetting the practical parameters that are required for them in order to be part of an industrial process.

Download Files: PPT Slides /  PDF Manuscript 

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