GaAs:Cr detector testing for FCAL calorimeter at planned linear accelerator ILC V. Elkin, U.Kruchonak XVI научная конференция молодых учёных и специалистов ОМУС 2012

The International Linear Collider ILC Parameters of the ILC: e + e - accelerator, sc cavities, gradient 31.5 MV/m => 30km long CMS energy: 200 to 500 GeV (possible upgrade to 1 TeV) One interaction region, beam crossing angle of 14mrad and two detectors („push-pull“ scenario) Peak luminosity: 2 x cm -2 s -1 typical beam size: (h x v) 650 nm x 5.7nm & beam intensity 2 x e + e - ~ 30 km

C.Grah: Radhard Sensors for BeamCal3 Very Forward Region of the ILC Detectors R&D of the detectors in the forward region is done by the FCAL Collaboration. Precise (LumiCal) and fast (BeamCal) luminosity measurement Hermeticity (electron detection at low polar angles) Mask for the inner detectors Not shown here: GamCal, a beamstrahlung photon detector at about 180m post-IP. LumiCal TPC ECAL HCAL BeamCal

C.Grah: Radhard Sensors for BeamCal4 The Beam Calorimeter - BeamCal Interaction point  Compact EM calorimeter with sandwich structure:  30 layers of 1 X 0 o3.5mm W absorber and 0.3mm radiation hard sensor  Angular coverage from 5mrad to 28 mrad (6.0 > |η| > 4.3)  Moliére radius R M ≈ 1cm  Segmentation between 0.5 and 0.8 x R M BeamCal LDC ~10cm ~12cm Space for electronics

The Challenges for BeamCal  e+e- pairs from beamstrahlung are deflected into the BeamCal e + e - per BX => 10 – 20 TeV total energy dep.  ~ 10 MGy per year strongly dependent on the beam and magnetic field configuration => radiation hard sensors  Detect the signature of single high energetic particles on top of the background. => high dynamic range/linearity e-e- e+e+ e-e- e-e- γ e-e- γ e+e+ e.g. Breit-Wheeler process

GaAs:Cr Sensor Plane  Produced by the Siberian Institute of Technology, Tomsk  semi-insulating GaAs doped by Sn (shallow donor)  compensated by Cr (deep acceptor): to compensate electron trapping centers EL2+ and provide i-type conductivity.

8 Advantages of Cr impurity as compared to the EL2 centers for detector material production Deep acceptor Deep donor - + small value of the electron capture cross section and absence of the field increase of the capture cross section on the electric field intensity absence of current oscillations possibility to reach uniform high electric field distribution through whole the detector with the thickness up to 1 mm

9 Electrophysical characteristics of high resistivity GaAs Material  о (10 -9 /  *cм) n o (10 5 cm –3 ) p o (10 5 cm –3 ) L n (cm) GaAs EL GaAs Cr – 0.2 The hole concentration in GaAs:Cr exceeds the concentration of electrons. The difference changes from 10 to 100 times depending on conditions of the diffusion process and the initial material characteristics.

11 sector size GaAs sensors Thickness μm Metallization -1 μm Ni 12 rings 64 pads from 18 to 42 mm 2 Surrounded by 120 μm width guard ring GaAs:Cr Sensor Plane

№Detectorthickness, um collected charge, e metallization, Type of metallization pixelsGuard ring 1AG-84 № Ni 2 AG 84 № Ni 3 AG 84 № Ni 4 AG 84 № Ni 5 AG 84 № Ni 6 AG 84 № Ni 7 AG 84 № Ni 8 AG 84 № Ni 9 AG 84 № Ni 10 AG 84 № Ni 11 AG 221 № Ni GaAs:Cr Sensor producer data

Circuit of capacitance measurement Bias Adapter BP Guard Ring L H Bias Ring LCR Meter

Typical C-V, measured between pad and backplane for different rates 100Hz -100 kHz Capacitance decrease with frequency Chosen frequency 10kHz

Pads capacitance distribution for 8 sensors

Pads capacitance distribution

A DC-PADs BP Guard Ring Circuit for I/V pad measurement Typical IV measurement for single pad is symmetric and linear in the range +/-500V

Temperature dependence of the resistance Measured from -10 C to 50 C The range from 65 GΩ*cm to 0.12 G Ω*cm

Measurement of the barrier height on border of metal−semiinsulating gallium arsenide total current through the device R eff - effective resistance of the entire device I n or I sat - Saturation current - Limiting current from metal to semiconductor [1] S - Cross-sectional area, A * n = 8.16 A*cm -2 *K -2 - Richardson constant for GaAs T - Temperature of device, q - electron charge, k - Boltzmann constant - barrier height on border of metal−semiinsulating gallium arsenide

I-V in range +/-10V Parameterization of the IV curve by 4 parameters: I saturation - I saturation + Resestivity- Resestivity+

Average resistivity and barrier height of AG84N19

Average resistivity and barrier height of 11 sensors №Detectorthickness, um Resistivity, Ohm*cmDarrier height, volts ρ+ρ+ ρ-ρ- φ+φ+ φ-φ- 1AG-84 №13498Not processed 2 AG 84 № E91.10E AG 84 № E92.18E AG 84 № E92.79E AG 84 № E92.37E AG 84 № E93.04E AG 84 № E93.48E AG 84 № E93.84E AG 84 № E93.23E AG 84 № E91.92E AG 221 № E92.42E

Unusual pads Some pads or guard rings have untypical behavior. For now we’ve found 6 sensors with guard ring and one pad: that may be related to metallization defects or internal structure injury. It appears on the crystal boundary in all cases.

Unusual pad, unusual guardring and normal pad C-V Growth up to 110pF at 100 V Similar behavior with guard ring Break through while measuring with guard ring Typical C < 12pF at 10kHz

Unusual pad I-V Growth up for positive Vbias Normal behavior in negative area Similar behavior with guard ring

Unusual pads NoNo Pad N o Breakdown voltage, V AsGa84N7Guard ring-330 AsGa84N7Ring12-Pad1-310 AsGa84N13Guard ring-160; +200 AsGa84N13Ring12-Pad6-280 AsGa84N21Guard ring+30 AsGa84N21Ring1-Pad4+50 AsGa84N26Guard ring-110; +230 AsGa84N26Ring12-Pad1-210 AsGa84N28Guard ring-300 AsGa84N28Ring12-Pad6+330 AsGa84N41Guard ring+110 AsGa84N41Ring12-Pad6+110

Thank you for attention!

Forward region of the ILC Beam calorimeter (BeamCal) - monitor the beam parameters at the interaction point; adjacent to the beampipe. Luminosity detector (LumiCal) – covers larger polar angles; luminometer of the detector. The gamma detector (GamCal) – together with BeamCal, measures beamstrahlung photons, which are very collinear to the beam.

Изучение характеристик детекторов на основе GaAs компенсированного хромом для будущего калориметра FCAL линейного ускорителя ILC V. Elkin, U.Kruchonak

Gallium arsenide (GaAs) Compound semiconductor, direct bandgap Two sublattices of face centered cubic lattice (zinc-blende type) GaAs grown by Liquid Encapsulated Czochralski (LEC). doped by Te or Sn (shallow donor) to fill EL2+ trapping centers. Compensated by Cr (deep acceptor) to high-ohmic intrinsic material. Compensation is temperature controlled Semi-insulating - no p-n junction Signal charge transport mainly by electrons Structure provided by metallisation (similar to diamond)  Density 5.32 g/cm3  Pair creation E 4.3 eV/pair  Band gap 1.42 eV  Electron mobility 8500 cm2/Vs  Hole mobility 400 cm2/Vs  Dielectric const  Radiation length 2.3 cm  Ave. Edep/100 μm69.7 keV (by 10 MeV e-)  Ave. pairs/100 μm  Structure p-n or insul  Density 5.32 g/cm3  Pair creation E 4.3 eV/pair  Band gap 1.42 eV  Electron mobility 8500 cm2/Vs  Hole mobility 400 cm2/Vs  Dielectric const  Radiation length 2.3 cm  Ave. Edep/100 μm69.7 keV (by 10 MeV e-)  Ave. pairs/100 μm  Structure p-n or insul