Instrumentation of the Forward Region of a Linear Collider Detector Workshop at Prague 16 April 2004

1
Instrumentation of the Forward Region of a
Linear Collider Detector - Workshop at Prague
16 April 2004

• LPI group
• Lebedev Physical Institute, Moscow

2
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
  Lebedev
• Physical Institute and Moscow Federal
  Institute of Electronic
• Technology - Technical University (MIET))

3
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)

4
Test results (last year)

• Spectrometric measurements were performed -
• GaAs detectors were irradiated by a-source (5.456
  and 5.499 MeV)
• I, nA DE, keV S/N
• I Mn-GaAsnG??s lt15 35
• II MpGaAsn-GaAsnGaAs 7
  141
• III Mn-GaAsnGaAs 45 15
  15
• IV ?-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.

5
New party of GaAs detectors

• To continue investigations recently (2004) new
  party of detectors with epitaxial layers of GaAs
  was made. Detectors were manufactured either as
  twin linear integrated structures or discrete
  cells.
• Topology of the prepared detectors was
• pGaAs - n-GaAs -nGaAs (substrate)
• layer thickness 0.25 mm and 30 mm
• substrate thickness 600 mm
• dopant density 1018 cm-3 and 2.1013 cm-3

Discrete cells were made of different shape
(circle, ring) and different size (50 mm - 2
cm). In preparing new party of GaAs samples
mesa-epitaxial approach was used.
6
Detectors description of structure

• Two types of detectors were used
• twin linear integrated structure of galvanically
  disconnected recording cells separated with the
  guard rings
• discrete detection cells separated with the usage
  of guard rings
• Detectors had following contacts
• ohmic (Ge/Ni/Au) - to heavily-doped nGaAs
  substrate from the back-side of the structure
• barrier (V-Au) of circular (or annular) shape -
  to doped epitaxial layers from front-side of the
  structure
• common guard ring in the case of twin linear
  integrated sructures and Guard electrods
  (three-ring type) in the case of discrete cells
• GaAs detectors were placed in a special casing

7
Test results
We started measurements of the parameters of new
GaAs detectrors. We performed spectrometric
measurements GaAs detectors were irradiated by
a-source.

• I, nA DE, keV S/N
• ?3 mm lt50 120 4
• ?10 mm lt200 1.5
• ?20 mm lt1000 1
• ?200 mm lt1 -
• First results on DE were worse than those
• obtained on samples of last year. We could not
• optimize measurement procedure because of the
• time deficit.Measurements will be continued.
• There are also plans to extend measurements to
• the region of high energies (hundreds MeV
• and GeV region).
• Preliminary tests of uniformity for linear
  integrated
• structures gave accuracy (in summary signal)
• about 10 .
  

8
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
• Simulation have 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- , E1 GeV
9
Simulation of the LCAL

• Primary particle e- , energy 1 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 than signal from Si sensor
• when thicknesses are equal.
• In case of epitaxial layer with thickness of
• GaAs 30 ?m energy deposited in active
• layers of the calorimeter is several times
• smaller than that from thick sample of Si.
• To make final conclusion further MC
• simulations are required.

e- , E1 GeV
10
Advantages and disadvantages

• GaAs detector on epitaxial layers has following
  advantages compared to the 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)

11
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 have signal (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.
• (First samples with considerable decreasing of
  EL2 defects
• concentration were obtained).
• It will allow to decrease noise level

12
Plans tests in Russia

• Special setup is being preparing now for
• measurement of parameters GaAs detectors
• We intend to perform
• full-scale electrophysical tests of GaAs
  detectors
• spectrometric measurements using radioactive
  source
• Single channel amplifier was prepared on the
  basis of GaAs epitaxial layers
• We hope to use this amplifier for realization
  spectrometric
• measurements on electron beam (Emax 600 MeV) of
• Synchrotron S-60 (Lebedev Physical Institute)