Paul Sellin, Radiation Imaging Group Charge Drift in partially-depleted epitaxial GaAs detectors P.J. Sellin, H. El-Abbassi, S. Rath Department of Physics University of Surrey, Guildford, UK J.C. Bourgoin LMDH, Université Pierre et Marie Curie, Paris, France
25
Embed
Charge Drift in partially-depleted epitaxial GaAs detectors
Charge Drift in partially-depleted epitaxial GaAs detectors. P.J. Sellin, H. El-Abbassi, S. Rath Department of Physics University of Surrey, Guildford, UK J.C. Bourgoin LMDH, Université Pierre et Marie Curie, Paris, France. Overview. Chemical reaction growth of thick epitaxial GaAs layers - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Paul Sellin, Radiation Imaging Group
Charge Drift in partially-depleted epitaxial GaAs detectors
P.J. Sellin, H. El-Abbassi, S. RathDepartment of Physics
University of Surrey, Guildford, UK
J.C. BourgoinLMDH, Université Pierre et Marie Curie, Paris, France
Paul Sellin, Radiation Imaging Group
Overview
Chemical reaction growth of thick epitaxial GaAs layers
Depletion thickness and residual impurity concentration
Performance of partially depleted detectors
C-V measurements of impurity concentration at low temperature
Optical probing of charge transport using a focussed laser
Paul Sellin, Radiation Imaging Group
Potential challenges for epitaxial GaAs
Strengths of epitaxial GaAs: intermediate photon detection efficiency between Si and
CZT/CdTe metal-semiconductor contacts and device physics are well
understood epitaxial GaAs has low concentrations of native EL2 defect source of highly uniform whole wafer material, compatible with
flip-chip bonding and monolithic electronics
Existing problems: even high purity epitaxial is compensated due to residual
impurities- does not exhibit intrinsic carrier concentrations depletion thickness is severely limited charge carrier lifetimes are reduced
Paul Sellin, Radiation Imaging Group
Chemical Reaction growth of thick epitaxial GaAs
Epitaxial GaAs material studied in this work was grown by a Chemical Reaction Method by Jacques Bourgoin (Paris).
• An undoped GaAs wafer is used as the material source, which is decomposed in the presence of high temperature high pressure water vapour to produce volatile species.
•Typically, growth rates of <10 m/hr are used to achieve EL2 concentrations of ~1013 cm-3
L. El Mir, et al, “Compound semiconductor growth by chemical reaction”, Current Topics in Crystal Growth Research 5 (1999) 131-139.
Paul Sellin, Radiation Imaging Group
Whole wafer photoluminescence mapping
GaAs material uniformity is characterised using room temperature photo-luminescence mapping - a contact-less, whole wafer technique:
A 25 mW 633 nm HeNe laser is focussed to ~50 m on the wafer
the wafer is mounted on an XY stage, and scanned
PL intensity maps at peak the band edge emission wavelength (870 nm) are acquired
Paul Sellin, Radiation Imaging Group
PL maps of GaAs
Photoluminescence mapping clearly shows the uniformity of epitaxial GaAs compared to semi-insulating VGF material:
H. Samic et al., NIM A 487 (2002) 107-112.
Epitaxial GaAs Bulk GaAs
Paul Sellin, Radiation Imaging Group
Calculated depletion thickness
This material is nominally 1-5 x 1014 cm-3- corresponds to a 10-20 m depletion thickness @ 30V, and 15-30 m @ 80V
Width of GaAs Space Charge Region vs Reverse Bias Voltage
Reverse bias voltage (V)
0 50 100 150 200
SC
R w
idth
( m
)
0
50
100
150
200
250
0
50
100
150
200
250
N = 5x1012 cm-3
N = 1x1013 cm-3
N = 5x1013 cm-3
N = 1x1014 cm-3
N = 5x1014 cm-3
Paul Sellin, Radiation Imaging Group
-particle spectra taken with an applied bias of 30V
Channel no.
0 500 1000 1500 2000 2500
Cou
nts
1
10
100
1000
220C-540CV = 30VV = 80V
Alpha particle spectra
5.48 MeV alpha particles are irradiated through the Schottky (cathode) contact - range in GaAs ~20m.
A peltier cooler controlled the device temperature in the range +25°C to -55°C. Shaping time = 0.5 s.
Paul Sellin, Radiation Imaging Group
Alpha particle pulse shapes
Alpha particle pulses at room temperature:
preamplifier
shaping amplifier
time base = 1s per division
slow component
fast component
Paul Sellin, Radiation Imaging Group
Alpha particle tracks
An un-collimated alpha particle source produces a characteristic ‘double peak’ pulse height spectrum if the depletion thickness is shallower than the particle