109. SCALABLE SILICON NANOWIRE PHOTODETECTORS FOR HIGH SENSITIVITY APPLICATIONS

Department: Electrical & Computer Engineering
Faculty Advisor(s): Yu-Hwa Lo

Primary Student
Name: Arthur Yasheng Zhang
Email: ayzhang@ucsd.edu
Phone: 858-534-4207
Grad Year: 2010

Student Collaborators
HongKwon Kim, hkk001@ucsd.edu

Abstract
Semiconductor devices, including devices used for photodetection, continue to shrink while becoming increasingly complex as we follow the roadmap dictated by Moore?s law. In addition, photodetectors must meet increasingly rigorous metrics including higher resolution and higher sensitivity. To meet these goals, we are creating the next generation photodetectors using silicon (Si) nanowire (NW) arrays fabricated with either e-beam or nanoimprint lithography, and dry etching. The top down approach used to fabricate these vertical NW devices allows for high density, ordered array formation and easy integration with CMOS circuits. By using nanoimprint lithography, we will be able to make these large area arrays quickly and cheaply. First, nickel dots are patterned onto an epi Si wafer using e-beam or nanoimprint lithography. This forms the template and self-aligned top contact for our NW?s. The substrate is then etched using reactive ion and inductively coupled plasma to form highly anisotropic, vertical arrays of NW?s between 100 nm and 200 nm in diameter and between 2 um to 4 um in length. The space between NW?s is then filled with an optically transparent insulator for structural support, and a top transparent contact of indium tin oxide is deposited. These devices can operate at low voltages and, at low light levels, show high photoconductive gain greater than 35,000 at 1 volt. These devices have the potential for many applications in medical, defense, and commercial areas. Si NW devices can greatly increase the resolution of high energy medical imaging which currently require the use of bulky photomultiplier tubes that operate at very high voltages. When paired with scintillators, they may also make possible handheld nuclear radiation detectors for homeland security and nuclear power plants. Finally, they may push commercial imaging arrays to even higher megapixels and sensitivity.

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