Post-growth annealing

23 Pages·2013·4.06 MB·English

by  Joyce Fortunado

BNL-101614-2013-CP

Post-Growth Annealing of CdZnTe Crystals:
An Analysis of Defect-Structures and Opto-
Electronic Properties

Ge Yang

Presented at the 2013 SPIE Optics + Photonics
August 25-29, 2013
San Diego, CA

August 2013

Nonproliferation and National Security Department

Brookhaven National Laboratory
P.O. Box 5000
Upton, New York 11973
www.bnl.gov

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2013 SPIE Optics + Photonics
August 25-29, 2013, San Diego, California, U.S.A.

Post-growth annealing of CdZnTe crystals: an analysis
of defect-structures and opto-electronic properties
G. Yang1, A. E. Bolotnikov1, P. M. Fochuk1,2, G. S. Camarda1, A. Hossain1, U.
Roy1, Y. Cui1, R. Pinder1,3, J. Gray1,3, V. Dedic1,4, J. Franc4 and R. B. James1

1 Brookhaven National Laboratory, Upton, NY, USA

2 Chernivtsi National University, Chernivtsi, Ukraine
3 Alabama A&M University, Huntsville, AL, USA
4 Charles University Prague, Prague, Czech Republic
August 28, 2013
Outline
Goal: Investigate post-growth annealing to improve the
performance of CZT detectors
Experimental results and discussions
Origin and nature of star-like defects after Cd annealing
Resistivity change before and after annealing
Low-temperature photoluminescence measurement before and
after annealing
Summary
Background and motivation
Material quality is inextricably linked to supply, performance
and cost of large-volume CdZnTe (CZT) gamma-ray detectors
• Different material defects, e.g., tellurium inclusions, dislocations, grain
boundaries and sub-grain boundaries, are found in typical CZT crystals

(Csaba Szeles, IEEE transactions on nuclear science, 51, 1242, 2004)
• These material defects play an important role in determining the performance of
CZT detectors
An example
Post-growth annealing — A controllable and
reproducible way to address the challenge
heater
Thermocouple 2
Quartz ampoule
Annealing source Crystals
Thermocouple 1
heater
Uniform temperature field Temperature gradient field
Facilities for annealing study
Two-zone annealing furnace Single-zone annealing furnace # 1 Single-zone annealing furnace # 2
Temperature profile of the annealing Customized computer-controlling Sealed quartz tubes for
furnace (two-zone) interface annealing experiments
Our previous work demonstrated that the post-
growth annealing in Cd vapor helps to remove Te
inclusions
Low high Low high
100µm 100µm
• Large Te inclusions --- migrate to high temperature side

• Small Te inclusions --- eliminated by the diffusion of external Cd atoms into
CZT and their chemical bonding with Te inclusions
However, ‘star-like’ defects were formed in CdTe, CdZnTe
and CdMnTe after the annealing in Cd vapor
White beam X-ray diffraction topography (WBXDT) image
‘Star-like’ defects are
often observed in Cd
annealed CdTe,
CdZnTe and CdMnTe
crystals. Such ‘star-
like’ defects
deteriorate the
uniformity of charge
Optical image of etch pits X-ray response map
transport.
Star-like defects were observed after high, medium
and low temperature Cd annealing
White beam X-ray diffraction topography (WBXDT) image
Star-like defects
Before annealing After annealing
)
(770 , 2 hours, Cd ove rpressure
℃
Star-like defects
Before annealing After annealing
)
(510 , 60 hours, Cd overpressure
℃