Development of a UV photodetector using a Schottky diode and a transistor based on ZnO by spray pyrolysis

Author(s)

Douglas Henrique Vieira

• Document type: Master's Dissertation
• Press: Presidente Prudente. 2020-11-10.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências e Tecnologia. Presidente Prudente
• Defense date: 2020-09-24
• Advisor: Neri Alves

Abstract

Exposure to high levels of ultraviolet radiation (UV) can cause burns, immunological changes, neoplasms, skin cancer, among others disease. The advent of printed electronics makes it possible to develop sensors that monitor exposure to UV radiation through printed electronic circuits that are cheap, thin, light, flexible and that can be fixed on clothes or adornments. Electronic devices, such as transistors or Schottky diodes, commonly have several electrical parameters, which can be exploited in a beneficial way to provide more information than sensors based on a purely resistive or capacitive response. In this dissertation, Schottky diodes were manufactured using ZnO and PEDOT:PSS obtained by spray, as an easy, simple and low cost method for the production of photodetectors. The devices had achieved rectification ratio as high as 104, associated with an ideality factor as low as 1.3. The photoconduction of ZnO films was studied as a function of geometric parameters and UV irradiance on the device, demonstrating that the photocurrent in ZnO depends on relationships that involve the surface dynamics of oxygen exposure, identifying changes in bimolecular recombination regime to monomolecular at higher irradiance values. In addition, transistors were fabricated with gate-electrolyte using ZnO as the active layer. The devices showed a high on/off ratio of 3.0x105 associated with very interesting changes in threshold voltage, saturation mobility, on/off ratio, ratio Iuv/Idark and in transconductance, when under UV irradiation. β-Ga2O3 was used as an alternative to detect deep UV radiation, it is a promising material for high voltage and high frequency applications. In this work, a new approach based on the coupling of two Schottky diodes, using β-Ga2O3, is reported, which led to a substantial increase in photocurrent (~ 186 times) when compared to a conventional diode of the same material. Summarizing, this work had presented good photodetector devices based on diodes and transistors with solutions for detection in the entire UV spectrum. (AU)

• FAPESP's process: 18/04169-3 - Development of a UV photodetector using a Schottky diode and a transistor based on ZnO by spray pyrolysis
• Grantee: Douglas Henrique Vieira
• Support Opportunities: Scholarships in Brazil - Master