0 2 4 6 8 100
0.01
0.02
0.03
0.04
0.05
-dI/dx
[× I0]
Depth [μm]
I = I0exp(-αx)
W
−−×
L
Wxexp
Picture of pn-SiC
A pn-SiC diode as a radiation detectorAkimasa Kinoshitaa, Motohiro Iwamia, Itsuo Nakanoa, Reisaburo Tanakaa,
Tomihiro Kamiyab, Akihiko Ohib, Takeshi Ohshimab, Yasutaka Fukushimac
a Faculty of Science, Okayama University, 3-1-1, Tsushimanaka, Okayama 700-8530, Japanb Japan Atomic Energy Research Institute, 1233 Watanuki Takasaki, Gunma 370-1292, Japanc KEK, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
AbstractWe evaluated pn-SiC (silicon carbide) particle detectors exposed to 5.486 MeV alpha particles from a sealed radioactive source of 241Am and 3.26 eV (380 nm) pulsed Ultra-Violet (UV) light at 100Hz from a Light Emitting Diode (LED). The pn junction SiC diode was made by the implantation of phosphorus (P) ions (140, 60, 90 keV) into p-type 6H-SiC epitaxial layers (5µm) grown onto p+-type substrates. The mean pulse height from detector increased with the supplied reverse bias voltage for each irradiation, alpha particles and UV light. We discuss relation of the pulse height distribution obtained by the UV light and the alpha particles to the depletion width with diffusion length of carriers.
2nF
100M
Ω
2nF
2nF
1.5
MΩ
1.5
MΩ
1.5
MΩ
1pF
500M Ω
93 Ω
Preamplifier(EG&G 142AH)
Shaper Amplifier(EG&G ORTEC 672)
Discriminator
Gate Generator
Analog to Digital Converter(HOSHIN C008)
CAMAC Crate Controller
Bias Source(KIKUSUI PMC350)
2nF
Veto
Gate
α source241 Am
Bipolar Output
Uni
pola
r O
utpu
t
Output Register
SiC (Silicon Carbide)
0 10 20 30 40 500
1000
2000
Counts
Channel
0V -10V -50 -100 -200
0 50 100 150 2000
0.2
0.4
0.6
0.8
1 (1) (2) = + (3) (4)
CCE
Reverse Bias [V]
L = 2.5 μm
1/C2 versus applied voltage for pn junction diode. These capacitances, closed circles, ware subtracted stray capacitance, solid curve, from total capacitance, broken curve, at several reverse bias voltages.
○ I-V characteristics (KEITHLEY 2400 high voltage source meter) ○ 1/C2-V characteristics (HEWLETT PACKARD 4277A 1MHz LCZ meter)
0 1000 2000 30000
20
40
60
80
1000 1 2
Channel
Counts
Energy [MeV]
0 V -10 V
-50 V-100 V -200 V
The pn-SiC diode - 4.1 MeV alpha particles from a radioactive source of 241Am - 3.26 eV pulsed UV light from LED. For alpha measurement The charge collection efficiency was good agreement with the theoretical method using diffusion length. The diffusion with 2.5 µm was obtained.For UV measurement The effect of carrier diffusion on charge collection is not significant. No or small diffusion length is obtained. The difference of charge collection between alpha and UV irradiations can be interpreted in terms of the distribution of e-h pairs in the neutral region.
The pulse processing system consisting of a pre-amplifier, a main (shaping) amplifier, an Analog-to-Digital Converter, and a personal computer through the GPIB interface.
Pulse height spectra obtained by irradiating alpha particles to the pn-SiC diode at different reverse bias voltages, V=0, -10, -50, -100 and -200.
The Charge Collection Efficiency (CCE) as a function of the applied reverse bias in the range of 0 ~ -200V, these CCE is the ratio of the loss energy, 4.1MeV, of incident alpha particles to the energy calculated by using e-h pair producing energy 8.4 eV for SiC.
∫
∫
−−+
=
d
W
W
dxL
Wx
dx
dE
E
dxdx
dE
ECCE
)(exp
1
1
p
0p
UV light was introduced into the electrode of the pn-SiC diode using a guide pipe with diameter 100 µm which is used for forcing UV light to around center of pn junction area
The pulse height spectra obtained with the pn-SiC diode at different reverse bias voltages, V=0, -10, -50, -100 and -200V by UV light of 1µs width pulses at 100Hz.
Theoretical curve (1) with solid-line, curve (2) with broken-line and curve (3) with dash-dotted ware obtained by equation 1. The curve (1) without diffusion and the curve (2) with L=1.0 µm have good agreement to experimental open circles for measurement of 1µs pulse width.
Al Box
In air at room temperature.
LEDUV 100μmφ
The pulse processing system consisting of a pre-amplifier, a main (shaping) amplifier, an Analog-to-Digital Converter, and a personal computer through the GPIB interface. UV light was generated by LED connected to a function generator.
・UV-LED - NICHIA-NSHU590AE - 380 nm (peak) - 3.26 eV@ In air@ At room temperature
100 Ω
50
Ω
2nF
100M
Ω
2nF
2nF
1.5
MΩ
1.5
MΩ
1.5
MΩ
1pF
500M Ω
93 Ω
Preamplifier(EG&G 142AH)
Function Generator(WAVETEK datron 39A)
Spectroscopy Amplifier(EG&G ORTEC 672)
Analog to Digital Converter(HOSHIN C008)
CAMAC Crate Controller
Bias Source(KIKUSUI PMC350)
LED ( λ = 380nm )
2nF
Gate ADC
Discriminator
Gate Generator
Al Box
In vacuum (~1kPa) at room temperature.
α 300μmφ・Sealed alpha source - 4.1 MeV@ In vacuum (~1kPa)@ At room temperature
Alpha particles were introduced into the electrode of the pn-SiC diode using a guide pipe with diameter of 300µm witch is used for forcing alpha particles to the pn junction area.
Bragg ionization curve - SRIM2000 simulation - SiC - 4.1MeV - alpha particles
Equation 1
Equation 2
0 5 100
10
20
30
40
50
60
Depth [μm]
dE/dx [kev/μm]
・He- ion・4.1 MeV・SiC
W
−−×
L
Wxexp
The function of intensity absorbed per unit lengh in SiC for UV with intensity I0.
( )
( )∫
−−⋅−
+−−=d
Wdx
L
WxxI
WIPairs
expexp
)exp(1
0
0
αα
α
[] large bandgap[] high electrical breakdown field[] high electron saturation drift velocity[] high thermal conductivity
A superior material for[] high temperature[] high frequency[] high power electronics.
Schematic cross-section of pn-SiC Electrical Characteristics
UV Measurement
alpha Measurement
Summary
Figure A-1 Figure A-2 Figure A-3 Figure A-4
Figure B-1 Figure B-2 Figure B-3
Figure C-1 Figure C-2 Figure C-3
Normalizing
The instruments for I-V and C-V measurement were controlled by the PC through the GPIB interface. The pn-SiC diode was in a shielded fixture to minimize external spurious noise during I-V and C-V measurement. The linearity of 1/C2-V curve in Figure A-3 shows the good uniformity of doping concentration within the active layer. The built-in voltages estimated from Figure A-2 and Figure A-4 have good agreement, Vbi=2.2~2.4 V.
The I-V characteristic for forward bias in the region of 1.0 ~ 3.0 V.
The I-V characteristics for reverse bias in the region of 0 ~ -200 V. Leakage curents were of the order of several nA.
0 100 200
0.2
0.4
0.6
0.8
1
Reverse Bias [V]
Normalized pulse height and
intensity absorbed in depletion layer
no diffusion (1) 1.0μm (2) 2.5μm (3)
Pulse width : 1μsExperimental
Theoretical
The numerical least-squares fit
Depletion Region Neutral Region
UV light
alpha partcle
Diffusion
e-h pairsHigh
Low
Conclusion SiC is a promising material as particle detector. UV illumination is an alternative evaluation method for the capability of SiC particle detectors. For UV illumination, the channel number of charge collection increase with increasing reverse bias voltage applied to SiC diodes. This behavior is very similar to the result obtained in alpha irradiation.
Al
φ: 300μmbond pad
Al
SiO2 AlSiC n+-type
SiC p-type
SiC p+-type
Al
150 nm~5μm
~300μm