A pn-SiC diode as a radiation...

0 2 4 6 8 10 0 0.01 0.02 0.03 0.04 0.05 -dI/dx [ I 0 ] Depth [ m] I = I 0 exp(- x) W × L W x exp Picture of pn-SiC A pn-SiC diode as a radiation detector Akimasa Kinoshita a , Motohiro Iwami a , Itsuo Nakano a , Reisaburo Tanaka a , Tomihiro Kamiya b , Akihiko Ohi b , Takeshi Ohshima b , Yasutaka Fukushima c a Faculty of Science, Okayama University, 3-1-1, Tsushimanaka, Okayama 700-8530, Japan b Japan Atomic Energy Research Institute, 1233 Watanuki Takasaki, Gunma 370-1292, Japan c KEK, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan Abstract We evaluated pn-SiC (silicon carbide) particle detectors exposed to 5.486 MeV alpha particles from a sealed radioactive source of 241 Am 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. 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) Veto Gate α source 241 Am Bipolar Output Unipolar Output Output Register SiC (Silicon Carbide) 0 10 20 30 40 50 0 1000 2000 Counts Channel 0V -10V -50 -100 -200 0 50 100 150 200 0 0.2 0.4 0.6 0.8 1 (1) (2) = + (3) (4) CCE Reverse Bias [V] L = 2.5 m 1/C 2 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/C 2 -V characteristics (HEWLETT PACKARD 4277A 1MHz LCZ meter) 0 1000 2000 3000 0 20 40 60 80 100 0 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 241 Am - 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 dx L W x dx dE E dx dx dE E CCE ) ( exp 1 1 p 0 p 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 µ m have good agreement to experimental open circles for measurement of 1µs pulse width. Al Box In air at room temperature. LED UV 1 00μmφ 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 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) 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 10 0 10 20 30 40 50 60 Depth [ m] dE/dx [kev/ m] He - ion 4.1 MeV SiC W × L W x exp The function of intensity absorbed per unit lengh in SiC for UV with intensity I 0 . ( ) ( ) + = d W dx L W x x I W I Pairs exp exp ) exp( 1 0 0 α α 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/C 2 -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) 1.0 m (2) 2.5 m (3) Pulse width : 1 s Experimental Theoretical The numerical least-squares fit Depletion Region Neutral Region UV light alpha partcle Diffusion e-h pairs High 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: 300μm bond pad Al SiO 2 Al SiC n + -type SiC p-type SiC p+-type Al 150 nm ~5μm ~300μm

Transcript of A pn-SiC diode as a radiation...

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

1.5

1.5

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

1.5

1.5

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