Oxygen adsorption and photoconduction models for metal oxide photodetectors

Peterson, Amelia
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Shur, Michael
Chow, J. H. (Joe H.), 1951-
Plawsky, Joel L., 1957-
Sawyer, Shayla Maya Louise
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Computer Systems engineering
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Attribution-NonCommercial-NoDerivs 3.0 United States
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute (RPI), Troy, NY. Copyright of original work retained by author.
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There is a need for real-time biohazard detection in hospitals, water-treatment facilities, bodies of water, and food processing facilities to prevent bacterial infections and outbreaks. Detection of small concentrations of bacteria requires photodetectors with a large photoresponsivity and fast response time. Metal oxide Ultraviolet (UV) photodetectors are a good candidate for this application due to their large photoresponsivity compared to other material systems. However, metal oxide photodetectors generally have a response time that is too slow for bacterial detection, and it is difficult to predict device performance because the oxygen adsorption and photodesorption processes which control the UV response are not well understood.To aid in the development of metal oxide photodetectors for bacterial fluorescence detection, this thesis presents a new model for metal oxide photodetectors. This is accomplished by deriving and solving the oxygen adsorption and photodesorption rate equations which control the UV response of these devices. This interaction with oxygen molecules is modelled by a variation in the space charge width at surfaces, grain boundaries, and necks which in turn provides the surface concentration of electrons available for adsorption of oxygen. The model provides the transient photocurrent given the device geometry, material parameters, atmospheric environment, and illumination intensity and wavelength. From the transient photocurrent, figures of merit such as the photoresponsivity, current on-to-off ratio, response time, and signal-to-noise (SNR) ratio are derived. The model is integrated into a Graphical User Interface (GUI) in MATLAB to allow for fast design of metal oxide photodetectors. This model enables a comparison of the performance of metal oxide photodetectors based on material, geometry, morphology, doping, and atmospheric environment. This new model sheds light on the operation of metal oxide devices, and it also points to the types of devices that will enable remote bacterial fluorescence detection. Based on this model, a novel photodetector structure, called a Capacitive Mode photodetector, is proposed. This type of device enables ultra-fast response time for very low illumination intensities. A prototype of this device is fabricated and characterized. A ZnO thin film on Silicon thermal oxide with a p+-Si backgate is created. We demonstrate the ability to control the oxygen adsorption rate with the backgate, thereby reducing the recovery time and enabling detection of very low optical powers. The device is also operated in a novel mode, called Capacitive Mode, which decreases the response time from minutes to milliseconds at low optical powers. This work opens the door for real time biological detection. Significant future work is still required in the form of characterizing some material parameters and implementing novel photodetector device designs.
May 2022
School of Engineering
Dept. of Electrical, Computer, and Systems Engineering
Rensselaer Polytechnic Institute, Troy, NY
Rensselaer Theses and Dissertations Online Collection
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