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Explore the use of GaAs as a sensor for LCAL development. Discover test results, simulations, advantages, and future directions. Collaboration with Lebedev Physical Institute, Moscow.
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LCAL Meeting – Zeuthen, August 26-27, 2004GaAs as sensor for LCAL M.Negodaev Lebedev Physical Institute, Moscow LPI, Moscow
LPI facilities Synchrotron S-60 • e test beam HELIS (ion accelerator) • thin films productionwith ion sputtering method Close connection with electronic industry LPI, Moscow
Proposal • Use of GaAs as a sensor for LCAL • We considered two types of material as sensitive elements of GaAs detector : • commercial semi-isolating plates (thickness 100-200 mm) • epitaxial structures (thickness 30 mm) grown in Zelenograd • Choice of the material is a subject to study • Participants • Lebedev Physical Institute, Moscow Laboratory of High Energy Electrons • Scientific and Educational Center on Quantum Devices and Nanotechnologies(joint venture of LebedevPhysical Institute and Moscow Federal Institute of Electronic Technology - Technical University (MIET)) LPI, Moscow
Proposal • Topology of the LCAL layer with GaAs sensors LPI, Moscow
History Some tests were performed last year.For these tests we used: • detectors of barrier type(metal-semiconductor or p-n junctions) with epitaxial layers of undoped GaAs as active layers (thickness 30 mm) • detectors of resistive type with commercial semiisolating GaAs (compensated EL2 deep level defects) as active layers (thickness 150 mm) LPI, Moscow
Test results (last year) • Spectrometric measurements were performed - GaAs detectors were irradiated by a-source(5.456and 5.499 MeV) I, nA DE, keV S/N I: M–n-GaAs–n+GаАs<15 35 II: M–p+GaAs–n-GaAs–n+GaAs 7 141 III: M–n-GaAs–n+GaAs 45 1515 IV: М-iGaAs-M (EL2)150 40 10 I-III types - epitaxial GaAs layers,IV type - semiisolating GaAs, I, nA - leakage current; DE, keV - energy resolution; S/N - signal to noise ratio Conclusion: detectors with epitaxial structure showed slightly better results compared to semi-isolating one. LPI, Moscow
Activity in 2004 Somesamples of detectors with epitaxial layers of GaAs was made in beginning 2004. In preparing this GaAs samples mesa-epitaxial approach was used. Detectors were manufactured either as twin linear integrated structures or discrete cells. Discrete cells were made of different shape (circle, ring) anddifferent size (50 mm - 2 cm). Detectorswere placed in a special casing. GaAs samples were irradiated by a-source. I, nA DE, keV S/N 3 mm <50 ~120 4 10 mm <200 1.5 20 mm <1000 1 200 mm <1 - First results on DEwere worse than those obtained on samples of last year (errors in grown process). Preliminary tests of uniformityfor linear integrated structuresgave accuracy (in summary signal) about 10 %. LPI, Moscow
Detectors: description of structure • Detectors had following contacts: • barrier (V-Au) of circular (or annular)shape - to doped epitaxial layers from front-side of the structure • ohmic (Ge/Ni/Au) - to heavily-doped n+GaAs substrate from the back-side of the structure • common guard ring in the case of twin linear integrated sructures and «Guard» electrods (three-ringtype) in the caseof discrete cells • layer thickness: 0.25 µm and 30 µm • substrate thickness 600 mm In July 2004 we produced new samples and sent it to Zeuthen for study. LPI, Moscow
Simulation of the LCAL • To compare characteristics of two different materials as sensitive layers of detector we (besides direct measurements) made first attempts of MC simulation of energy deposited in active layers • of calorimeter • Simulationhave been made by using Geant4 package • We used simple geometry • 1)63 layers: W 2 mm,GaAs 300 m • 2) 63 layers: W 2 mm,Si 300 m • 3) 63 layers: W 2 mm,GaAs 30 m • Primary particle e- , energy 1 GeV e- , E=1 GeV LPI, Moscow
Simulation of the LCAL Primary particle e- , energy1 GeV Geometry 1)63 layers: W 2 mm,GaAs 300 m 2) 63 layers: W 2 mm,Si 300 m 3) 63 layers: W 2 mm,GaAs 30 m Results: Signal from calorimeter with GaAs sensor is two times larger thansignal from Si sensor when thicknesses are equal. In case of epitaxial layerwith thickness of GaAs 30 menergy deposited in active layers ofthe calorimeter is several times smaller than that from thick sample of Si. To make final conclusion further MC simulations are required. e- , E=1 GeV LPI, Moscow
Advantages and disadvantages • GaAs detector on epitaxial layers has following advantages compared tothe case of semi-isolating layers: • low noise level • smaller values of working voltage • larger temperature range of stable work • (especially compared to Si) • and disadvantage • low level of signal (energy deposited in active layers of the calorimeter) LPI, Moscow
Directions of studies • At present there are at least two directions of developing • material parameters suitable for use in LCAL: • Preparation GaAs epitaxial layers with larger thicknesses • (up to 100 m). • In this case we shall havesignal (energy deposited in active • layers of the calorimeter) compared with that obtained in case • of Si -sensor. • Decreasing concentration of EL2 deep level defects (in the case of semi-isolating GaAs) without increasing background concentration of carriers. LPI, Moscow