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Name (Title):
Masataka Imura (ICYS-MANA)
Affiliation:
International Center for Materials Nanoarchitectonics
Address:
1-1 Namiki, Tsukuba. Ibaraki 305-0044, Japan
Email: IMURA.Masataka@nims.go.jp
Home Page:
Presentation Title:
Deep-ultraviolet Diamond-based Photodetector for high-power excimer lamp
Abstract:
The next generation photolithography system, which uses a stepper with an excimer laser such
as an ArF laser (λ=193nm) and an F2 laser (λ=157nm), requires deep-ultraviolet (DUV) detection.
Currently, Si-based photodetectors are primarily used to detect UV light. However, they require
filters to stop energy photons from visible and infrared light and have low efficiency. In addition,
they easily degrade by the UV light. Diamond-based photodetector is a promising candidate for
UV and DUV detection and overcome these limitations. In order to achieve and demonstrate
diamond-based photodetector for UV and DUV detection, we fabricated Schottky barrier
photodiode (SPD) with the vertical-type by using heavily B-doped p + -diamond (100) substrates.
The p-diamond epilayers were homoepitaxially grown by microwave plasma chemical vapor
deposition (MPCVD) on the heavily B-doped p + -diamond (100) substrates commercialized by
Technological Institute for Super-hard and Novel Carbon Materials (TISNCM). The substrate
was 2.5 × 2.5 × 0.5 mm 3 in size, and the B concentration ([B]) was measured to be around 1×10 20
cm -3 by secondary-ion mass spectroscopy (SIMS). The unintentionally B-doped p-diamond
epilayers with [B] in the range 10 15 to 10 16 cm -3 analyzed by SIMS were grown by CH4 and H2
gases. The ratio of CH4 to H2 was 0.08 %, and the corresponding flow rates of CH4 and H2 were
0.4 and 500 sccm, respectively. The reactor pressure was fixed at 106 hPa during growth. The
growth was performed at ~800 °C. The thickness of epilayer was about 0.5 µm. To obtain Ohmic
contact, Ti (40 nm)/ WC (30 nm) films were deposited on the back-side of the diamond substrate,
subsequently annealed at 600 °C for 1 h in an argon ambient. The semitransparent WC Schottky
contact was deposited on the defined circle patterns on the diamond epilayer by a
photolithographic technique. The diameter of WC Schottky
contact was 1 mm.
Figure 1 shows a dark current and photocurrent under 220nm
light illumination as a function of applied voltage. Here, the
forward voltage and the reverse voltage correspond to positive
and negative biases, respectively. The reverse leakage current
of the SPD is smaller than the detection limit of 10 -14 A. The
rectification ratio is determined to be around 10 12 at ±3 V. The
ideality factor (n value) of the SPD is 1.1, and the Schottky
barrier height is determined to be 1.42±0.01 eV. The SPD is
operated in only the reverse bias mode. The photocurrent is
almost constant with increasing the reverse bias voltage.
References:
*M. Imura, M. Y. Liao, J. Alvarez, and Y. Koide “Schottky-Barrier Photodiode using p-Diamond
Epilayer Grown on p+-Diamond Substrate”: Diamond & Related Materials, (In press).
*M. Imura, M. Y. Liao, J. Alvarez, and Y. Koide “Vertical-type Schottky-Barrier Photodiode
using p-Diamond Epilayer Grown on Heavily Boron-doped p+-Diamond Substrate”: Diamond &
Related Materials, 17 (2008) 1916-1921.
120
Current (A)
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dark
220-nm illumination
Poster Session PIR-7
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Applied voltage (V)
Fig. 1. Dark current and photocurrent
under 220-nm light illumination as a
function of applied voltage