Date of Award

2015

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

Goutam Koley

Abstract

Recent research trends in chemical and biological sensing have been geared toward developing molecular sensor devices that are fast, inexpensive, miniaturized, have low power consumption and are portable. The performance of these devices can be dramatically improved by utilizing multimodal detection techniques, new materials and nanofabrication technologies. To develop such sensor devices, we utilized Indium Nitride (InN) nanowires (NWs) to fabricate nanoelectromechanical system (NEMS) based sensors and Graphene/InN NW heterojunctions, and InN thin films to fabricate Graphene/InN thin film heterojunction based sensors. InN NWs, which exhibit interesting properties including high carrier density, superior electron mobility, strong surface charge accumulation, and chemical inertness, were synthesized using Chemical Vapor Deposition (CVD) technique by Vapor-Liquid-Solid (VLS) mechanism. A novel method for synthesis of high quality InN nanowires, at temperatures well above their decomposition temperature, has been demonstrated by utilizing controlled oxygen flow into the growth chamber. Detailed structural and chemical analyses indicate that the nanowires consist of pure InN, with no evidence of In2O3 detected by any of the characterization methods. It is proposed that the oxygen, pre-adsorbed on the Au catalyst surface, assists in accelerating the decomposition of NH3 at the growth temperature by providing high concentration of atomic nitrogen to assist in the growth, and prevent decomposition of the InN nanowires, without getting incorporated in them. The proposed role of oxygen is supported by improved material quality at higher oxygen flow rates.

In a related research effort, Indium Nitride based heterojunction sensor devices were investigated. We designed and fabricated graphene/InN heterojunction devices that are suitable for gas sensing because of a tunable barrier height controlling the conductivity across the heterojunction in presence of different analyte gas and vapor molecules. Electrical characterization of the device demonstrated good rectifying behavior across the graphene/InN heterojunction. Preliminary sensing experiments carried out with trace amount of water and acetone vapors, as well as, NH3 and NO2 gases showed highly promising results. It is observed that this sensor offers better sensitivity than simple graphene or InN based conductometric sensors, primarily because of the presence of a tunable Schottky barrier formed between graphene and InN that can be modulated by different analyte gas molecules, which affects the junction current exponentially.

To explore promising alternative device approaches addressing the challenges posed by continuous shrinking of Si based device dimensions in integrated circuits, we investigated for the first time an InN NW/graphene heterojunction based vertical threeterminal active device, a variable barrier transistor or barristor, where the interfacial current between two terminals were controlled by an insulated gate. A very promising on/off ratio exceeding 100 was achieved by adjusting the gate voltage to control the graphene/InN NW heterojunction Schottky barrier, which underlines the promise of these devices in low power device and sensing applications.

Rights

© 2015, Alina Wilson

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