| Summary: | 博士 === 國立中央大學 === 電機工程研究所 === 95 === This dissertation presents systematically fabricated GaN p-i-n ultraviolet (UV) photo detectors that have demonstrated improved device structure and superior sensor performance. Studies of the material growth, device fabrication and sensor characterization are described. GaN p-i-n UV-A sensor with a structure of 8-pairs of AlxGa1-xN/GaN superlattices (SLs) grown by MOCVD method, was incorporated into the device. Not only does this device structure eliminate material cracking through strain management, but also significantly decreases the threading dislocation density by acting itself as an effective dislocation filter. The proposed device structure has exhibited excellent epitaxial film qualities, such as improved crystallinity, higher carrier mobility, lower defect levels, and less etching pit density (EPD), and has shown improved performance such as lower dark current, superior response sensitivity in the UV spectrum, and higher UV/visible rejection ratio than those without the SLs structure.
GaN epitaxial material grown using epitaxial lateral overgrowth (ELOG) technique has shown its superiority for GaN p-i-n UV-A sensor application. Due to the minimization of threading dislocations, it is demonstrated that the ELOG technique has reduced the device dark current and increased the responsivity and sharpness of cut-off than that of the traditional design without ELOG design.
GaN layer grown on misorientation angles of a-plane 1o-off-axis sapphire substrate has exhibited excellent film qualities such as enhanced crystallinity, lower defect levels, and less etching pit density. Accordingly, the GaN p-i-n UV-A sensor was first proposed fabricated on 1o off-axis sapphire substrate. The dark current density is decreased by two orders magnitude and the spectrum responsivity is increased 20% than that of traditional on-axis design. A superior device performance can be achieved as device fabricated on 1o off-axis sapphire substrate.
In addition, for applications of AlxGa1-xN/GaN p-i-n UV sensor in UV-B range (310nm), an added a graded AlxGa1-xN (x=0.26
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