Celso Figueiredo26/10/2015 Characterization and optimization of silicon sensors for intense...

Celso Figueiredo 26/10/2015

Characterization and optimization of silicon sensors for intense radiation fields

Traineeship project within the PH-DT-DD sectionIntegrated within the SSD (Solid State Detectors) team

Supervisor: Christian Gallrapp on behalf of Michael MollMichael Moll is deputy of the PH-DT group and co-spokesperson of the RD50 collaboration


Project Description:

Motivation

Defect Characterization

Performed Tasks:

Initial theoretical training

Initial practical training:

CV/IV

TCT

TCAD Simulations

Main project:

Aim

Performed Simulations

I-DLTS setup

Outlook on future work

Acknowledgements

Outline

2


Project Description - Motivation

3

As the luminosity of the LHC keeps being upgraded, silicon detectors used for particle tracking need to become radiation harder

The signal performance of the silicon detectors degrades with radiation damage, due to the generation of electrically active defects in the silicon bulk

(Michael Moll, 04/2010, “Recent advances in the development of radiation tolerant silicon detectors for the super-LHC”)


Project Description - Motivation

4

1013 5 1014 5 1015 5 1016

eq [cm-2]

5000

10000

15000

20000

25000

signa

l [el

ectro

ns]

n-in-n (FZ), 285m, 600V, 23 GeV p p-in-n (FZ), 300m, 500V, 23GeV pp-in-n (FZ), 300m, 500V, neutrons

p-in-n-FZ (500V)n-in-n FZ (600V)

M.Moll - 08/2008

References:

[1] p/n-FZ, 300m, (-30oC, 25ns), strip [Casse 2008][2] n/n-FZ, 285m, (-10oC, 40ns), pixel [Rohe et al. 2005]

FZ Silicon Strip and Pixel Sensors

strip sensorspixel sensors

Note: Measured partly under different conditions!

Lines to guide the eye (no modeling)!

Strip sensors: max. cumulated fluence for LHC and LHC upgrade

Pixel sensors: max. cumulated fluence for LHC and LHC upgrade

The LHC upgrade will require more radiation tolerant tracking detector concepts!

Also, it will be useful to study and clarify the underlying solid state mechanisms related to radiation damage and tolerance, which are not yet well understood!


Project Description – Defect Characterization

5

Leakage Current Generation

Most effective closer to the middle of the bandgap

Charge Trapping

Impacts Charge Collection Efficiency of electrons and holes

Create Space Charge

Impacts Doping Concentration and Depletion Voltage

According to Shockley-Read-Hall statistics, the impact of defects on detector properties can be calculated if the following parameters are known:

σe,h – capture cross sections for electrons and holesΔE – ionization energyNt – defect concentration

A large number of defects levels have already been characterized (CiOi, VV, VO, …)


Initial theoretical training:

- Solid State and particle physics

- Semiconductor detector technology

- Phenomena of performance degradation in semiconductor detectors in

high radiation environments

Performed Tasks – Theory

6

n+ layer

p+ layer

p-doped bulk

Transversing Particle

+

-

++++

+

- -- -

-Electron Drift

Hole Drift

VRB > Vdep


Initial practical training:

- Operation of silicon sensor characterization setups in the laboratories:

- IV: leakage current vs. applied reverse bias voltage analysis

- CV: capacitance vs. applied reverse bias voltage analysis

- TCT: Laser pulse induced transient current technique

- CV, IV and TCT measurements were performed on n-bulk silicon pad

detectors

- Introduction to Technology Computer Aided Design (TCAD) of silicon

detector structures, using the Sentaurus Synopsys TCAD software suite

Performed Tasks – Practice

7


CV/IV Setup

Performed Tasks – CV/IV Setup

8

Capacitancevs.

Reverse Bias Voltage Analysis

Leakage Currentvs.



TCT Setup

Performed Tasks – TCT Setup

9

Induced current vs. time analysisIllumination by picosecond laser pulse


Simulations with the Sentaurus Synopsys software suite

- Powerful tool for simulation of 2D/3D semiconductor structures and devices:

- using finite element methods

- solver of coupled differential equations for semiconductors:

- Poisson’s equation, continuity equations for electrons and holes

- includes a wide range of models to calculate solid state physics mechanisms:

- Mobility, Shockley-Read-Hall, Carrier trapping, …

Performed Tasks – TCAD Simulations

10



- The goal of the simulation work is to be able to reproduce the results obtained in IV, CV

and TCT measurements on unirradiated and irradiated detectors.

- Issues:

- There is a very large number of known defects and there is currently no computational power

to be able to include them all in a simulation;

- Need to build a simplified but functional radiation damage model based on a small number of

defects


11

Measured Defects TCAD input




12

Capacitancevs.


Red Laser

Laser Induced current vs.

time analysis

Leakage Currentvs.



Goal:To study the trapping and de-trapping behaviour of proton and neutron irradiated silicon

sensors by means of experiments and simulations in order to identify the radiation induced

defects responsible for charge trapping in silicon detectors.

- Evaluate previous results from Current-Deep Level Transient Spectrocopy (I-DLTS):

- Temperature controlled TCT setup with long, microsecond pulses

- Used to study charge carrier detrapping phenomena

- Match simulation with measurement results and extract defect parameters and

detrapping time constants

Main Project

13

Detector

Bias Tee

DC Power Supply

2.5 GHz Oscilloscope

µs pulsed red and IRlaser


Performed simulations

Main Project

14

Up to now, the results of the simulations match the measurements

only qualitatively. Further work is needed to match the results

obtained in the I-DLTS setup, tuning the following parameters:- Laser Intensity and spot size diameter

- Number of acceptor and donor traps/defects

- For each trap/defect:σe,h – capture cross sections for electrons and holesΔE – ionization energyNt – defect concentration

It is possible to calculate trap occupation in

any point in the silicon bulk


I-DLTS Setup

New I-DLTS measurements:

- Need for a better understanding of the measurement conditions, concerning the laser:

- Characterization of laser power with commercial reference diode

- Tuning and characterization of laser beam width

- New irradiated detector samples are available for measurement and can also be included in

the aim of this project

Main Project

15

Detector

Bias Tee

DC Power Supply

2.5 GHz Oscilloscopeµs pulsed red and IRlaser


Outlook on Future Work

16

Measurements:- Maintenance and characterization of the I-DLTS setup

- Repeat a set of previously done I-DLTS measurements, with better understanding of the used

laser intensity (power and beam width)

- Measure recently available samples (unirradiated and irradiated)

Simulations:

- Use characterization information of the I-DLTS setup as input of TCAD simulations

- Tune simulated defect parameters, aiming to match measurements and simulations results,

and to obtain a predictive radiation model

- Cooperate with other people in the SSD team and the RD50 community in the simulation of

other detector structures

Development:

- Continue to develop scripts for the extraction and plotting of TCAD simulation results (Tcl)

- Development of scripts for data fitting and extraction of detrapping time constants (ROOT, C++)


Acknowlegdements

17

CERN Solid State Detectors Team

Laboratories: 28/2-019, 28/2-020, 28/2-026, 186/R-G25Contact: [email protected]


End

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