Development of InP detector for solar pp/7Be neutrino measurement
Y.Fukudaa T.Izawad Y.Kaminagaa Y.Koshinob Y.Miyakea S.Moriyamab T.Nambac R.Onoa T.Satoa M.Shiozawaba Miyagi University of Educationb ICRR, University of Tokyo

c ICEPP, University of Tokyo d Soild state division, Hamamatsu Photonics K.K.

supported by the Grant-in-Aid Scientific Research (B)17340065 of Japanese Society for the Promotion of Science, Inamori Foundation, and Asahi Glass Foundation

4. Response for γ-rays

1. Introduction◆ Purpose : Precise measurement of ν oscillation mixing angle θ12◆Response from 57Co and 133Ba

γ spectrum obtained by InP detector◆ Status of determination for ν oscillation parameter・ Photo electric peak for 81keV (133Ba) and122keV (57Co) were observed,
・ However, two peaks were found.
・ Higher peak corresponds to photo electricpeak with charge collection efficiency (CCE)100%.
・ Average energy of electron/hole pair
production is obtained by 3.5eV.
・ Lower peak is equivalent to CCE 56%(57Co)
and 72%(133Ba), respectively.
・ Energy resolution σ=5%@122keV

・ 96%C.L. allowed region obtained by global fit
LMA solution (blue) : Cl + Ga + SK (D/N spectrum)
KamLAND (green) → confirm Δm122

27°< θ 12<37°
mixing angle θ12 is not constrained
compared with θ23 (obtained by Atm ν)
Survival probability tends to increase in 5MeV or lessin case of LMA solution, and shapes depend on θ12.

Spectral analysis with MC・ Assuming depletion layer formed at theohrmic contact of electrode and carrier drift
in remaining part.
・ Input parameter : depletion layer =30μm
Ld=250μm, ε=3.5eV・ MC reproduces spectral shape of data.

Amount of pp/7Be ν should be observed● future solar pp/7Be experiment
・ XMASS (LXe, elastic scatter(ES), DIRK MATTER)
・ LENS (Liquid scintillator loaded In/Ye, charged current(CC))
・ CLEAN (LNe, ES)・ MOON (100Mo,CC)・ SIREN (160Gd, CC)MCMCCarrier drift length Ld is not enough◆Response from 241Am

Y.Suzuki@Neutrino2004◆ Technique of low energy solar neutrino detection● Advantage
・ direct counting
・ sensitive to low energy ν(Eν ≧ 125keV)・ energy measurable (Ee = Eν － 125keV)・ Triple fold coincidence to extract
neutrino signal (e1 +γ2 + γ3 )● Disadvantage
・ natural β-decay of 115In(τ1/2 = 6.4 × 1014 yr)
・ BG due to correlated accidental
115In + ν → 115Sn* + ee
coincidence by Bremsstrahlung
115Sn*(4.76μs) → 115Sn + γ (115keV) + γ (497keV)

R.S.Raghavan Phs.Rev.Lett37(1976)259

1

2

60keV γpoto elec.
CCE=100%

Low CCE signal improved by applying higher bias voltage

increase carrier drift length (Ld)Assuming Ld ~1000mm, spectrum issingle peak with good E resolution◆ How to increase the carrier drift length
1. Increasing mobility (μ) Temperaturelower● μτ product value●Assuming observant of the 4tons of 115In in 5 years

57Co

MC

60keV γpoto elec.
CCE=100%

Liquid N2
Extrapolated Low-Field Electron Drift Mobility for InP

Detector

Drift Mobility (cm2/Vs)

・ Number of expected events assuming no ν oscillation → 1885
・ Number of expected event assuming LMA solution with Ee≧100keV → 720

θ12 = 29°- 34°
Statistical error and SSM theoretical error in total error → 3.9 %●We will use Semi-Insulating(SI) InP semi-conductor as both target and detector

Temperature(k)Ref:J.Costa and A.Peczalski, J.applo Phys.66(2),(1989)p674-479

2. Semi-Insulating InP semi-conductor

・ Increasing mobility by cooling

Dry ice (-79 ℃)・ Increasing μτ productvalue at lower temperature◆ InP crystal growth method
・Product
Sumitomo Electric Industries, Ltd.
・ ProcessInner chambar

http://www.sei.co.jp/sc/technical/inp.html

In inner chambar controlled by steam pressure of
As or P, covering material melt by B2O3 like LEC
method and pulling up single crystal growth from it.
Because of crystal growth in low temperature
gradient, transition density can reduce.

● Characteristic table
I-V characteristics

EPD～5,000cm-2

Conduct

Semi-insulation

2. Higher bias voltage (V0)Change electrode material (Au

DopantInP(Fe)(4.9～5.2)×107Ωcm

Mobility(2.8～2.7)×103Ωcm

Thickness456～459μm

Diameter

50.00mm

Orientation(100)±0.03°

・ Avoid electric noise due to dark current

5. Development of InP prototype
detector for solar neutrino experiment

1.0cm
28.5cm1.0cm

I [A] ∝T2/3 exp(-Eg/2kβT) Eg : band gap (1.29eV)

Dark current could be reduced bylowering temperature◆ New test module for prototype detector●Hybrid structure of InP and CsI
crystal scintillator
・InP detector module
10mmX10mmX200μm detectors
in 5x5 pixel・CsI crystal scintillator to detect γs
3cmX5cmX28.5cm●4tons of 115In for solar ν experiment
InP=5.1tons (2.1X106 modules)
CsI=934tons
size : 6.3m X 6.3m X 5.3m

kβ: Boltzmann constantT : element temperature● Actual module for proto- typedetector
・ 10mm X 10mm X 0.2mm
・ delivered from 12th of July !
・ first data has been taken andobserved same spectrum
・ proto-type detector consistsof 4 modules

3. Test Module with the SI InP◆ Detection of radiation with SI InP solid state detector
・ Electron produced by radiation loses theenergy, and produces electron-hole pairas carrier.
・ Carrier moves along electric field.
・ If drift length is not enough to the thicknessof detector, the carrier might be trapped by
impurity before reaching electrode.
・ Drift length is proportional to carrier mobility
and electric field.
●InP detector with cooling dewar

Pd, Ag)・ Shottky barrier height: 0.37eV(Au) / 0.41eV(Pd) / 0.54eV(Ag) Ref: J.Phys.III 1(1991) 749-758

3.0cm

Resistivity

Liquid N2(- 186℃)

Direct measurement for mobility using Hall EffectMeasurement System will be done at this summer● VCZ (Vapor Pressure Controlled Czochralski)
high pressurechambarCryostat for LN2 in preparation◆ 115In β-decay spectrum and bremsstrahlung
Background measurement at Kamioka mine
● estimate effect of accidental coincidence due to backgrounds.
● establish counting methods.
● scientific program in Kyoudou-riyou of ICRR, Univ. of Tokyo● experiment will start at the end of this year or early of next year
Schematic view of experimental setup

Size:
7mm×7mm×0.2mm
Electrode :・ Ohmic contact
・ Vacuum evaporationof Au base

Schematic view of InP detector

Oxygen free copper

CsI

Lead Shield