LCAL Meeting – Zeuthen, August 26-27, 2004 GaAs as sensor for LCAL

1. LCAL Meeting – Zeuthen, August 26-27, 2004GaAs as sensor for LCAL M.Negodaev Lebedev Physical Institute, Moscow LPI, Moscow

2. LPI facilities Synchrotron S-60 • e test beam HELIS (ion accelerator) • thin films productionwith ion sputtering method Close connection with electronic industry LPI, Moscow

3. 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

4. Proposal • Topology of the LCAL layer with GaAs sensors LPI, Moscow

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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