Journal of Sensor Science and Technology (센서학회지)

The Korean Sensors Society (한국센서학회)
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GaN-based Ultraviolet Passive Pixel Sensor for UV Imager

  • Lee, Chang-Ju (School of Electronics Engineering, Kyungpook National University) ;
  • Hahm, Sung-Ho (School of Electronics Engineering, Kyungpook National University) ;
  • Park, Hongsik (School of Electronics Engineering, Kyungpook National University)
  • Received : 2019.05.25
  • Accepted : 2019.05.30
  • Published : 2019.05.31
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Abstract

An ultraviolet (UV) image sensor is an extremely important optoelectronic device used in scientific and medical applications because it can detect images that cannot be obtained using visible or infrared image sensors. Because photodetectors and transistors are based on different materials, conventional UV imaging devices, which have a hybrid-type structure, require additional complex processes such as a backside etching of a GaN epi-wafer and a wafer-to-wafer bonding for the fabrication of the image sensors. In this study, we developed a monolithic GaN UV passive pixel sensor (PPS) by integrating a GaN-based Schottky-barrier type transistor and a GaN UV photodetector on a wafer. Both individual devices show good electrical and photoresponse characteristics, and the fabricated UV PPS was successfully operated under UV irradiation conditions with a high on/off extinction ratio of as high as $10^3$. This integration technique of a single pixel sensor will be a breakthrough for the development of GaN-based optoelectronic integrated circuits.

Keywords

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Fig. 1. (a) Micro-photograph image with the pad electrode names (scale bar, 100 μm), (b) circuit schematic, and (c) cross-sectional view with the epitaxial layer structure of the proposed GaN UV PPS.

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Fig. 2. Energy band structure of metal (ITO)/GaN contact interface with a Schottky barrier lowering effect using the gate bias at the gate overlapped region of the source contact.

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Fig. 3. (a) Dark and photoresponsive I–V characteristics and (b) spectral photoresponsivity characteristics of the fabricated GaN MSM UV sensor. The optical power density of a 365-nm UV light was 447 mW/㎠.

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Fig. 4. (a) Output IDS–VDS characteristics under dark, (b) output IDS– VDS characteristic under 365-nm UV irradiation, (c) linear and log-scale transfer IDS–VGS characteristics under dark, and (d) linear and log-scale transfer IDS–VGS characteristics under 365-nm UV irradiation of the fabricated GaN SB-MOSFET. The optical power density of a 365-nm UV light was 447 mW/㎠.

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Fig. 5. (a) Linear-scale and (b) log-scale output I–V characteristics of the fabricated GaN UV PPS with/without 365-nm UV irradiation. The GaN UV PPS was fabricated by integration of a GaN MSM UV sensor and a GaN SB-MOSFET.

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