BNL-100674-2013-CP

Correlation of Photoluminescence measurements with the Spatial Distribution of Dislocations in

CdZnTe Crystals

Ge Yang

Presented at the 2013 MRS Spring Meeting & Exhibit San Diego, CA

April 1 – 5, 2013

April 2013

Nonproliferation and National Security Department

Brookhaven National Laboratory P.O. Box 5000

Upton, New York 11973 Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This preprint is intended for publication in a journal or proceedings. Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.

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Correlation of photoluminescence measurements with the spatial distribution of dislocations in CdZnTe crystals

2013 MRS Spring Meeting & Exhibit April 1-5, 2013, San Francisco, California

April 3, 2013

G. Yang, A. E. Bolotnikov, Y. Cui, G. S. Camarda, A. Hossain, R. Utpal and R. B. James Brookhaven National Laboratory, Upton, NY 11973

V. Babentsov

Institute of Semiconductor Physics, Kiev, Ukraine

C. S. Korach State University of New York at Stony Brook, Stony Brook, NY 11794

Background Advantages of CdZnTe (CZT) — ideal candidate for room temperature X-ray and gamma-ray detectors High average atomic number efficient radiation-atomic interactions Large band-gap (1.4 -2.2 eV, tunable by Zn composition) high resistivity and low leakage current Good electron transport properties Available materials with acceptable cross-sectional areas and thickness Flexibility with different electrode configurations

One major challenge in the development of CZT detectors —Issue of material defects

Examples: dislocations, sub-grain boundaries, and Te inclusions Especially, dislocations interact with point defects and impurities, affecting the uniformity of charge-collection and deteriorating the detector

performance. (*Csaba Szeles, IEEE IEEE Trans. Nucl. Sci., 51,1242, 2004)

*

Plastic deformation (e.g., by micro-indentation) to study different types of dislocations in semiconductors

Cathodoluminescence (CL) of GaSb, showing the rosette structure and the dark ring surrounding the indentation

SEM-CL micrograph of deformed CdS

CL image of the dislocation pattern around an indentation on CdTe

*(1) M. F. Chioncel, et al., Semicond. Sci. Technol. 19, 490 (2004) (2) N. I. Tarbaev, et al., phys. stat. sol. (a) 110, 97 (1988) (3) H.S. Leipner, et al., Scanning Microscopy 12, 149 (1998)

Micro-indentation experiment and PL mapping technique to investigate the spatial distribution of dislocations in CdZnTe

Stage movement

Cold Finger Sample

Cryostat

Window

Laser PL signal

X Y

Laser Monochrometer Detector

PL System layout

CdZnTe, (110) surface

Micro-indentation experiment Indentation

(D0,X) (A0,X) (A0,X)-LO

DAP

DAP-LO D1 A center + D2

1.642 eV 1.633 eV 1.611eV 1.592eV 1.569eV 1.527eV 1.480 eV

Different 4.2 K PL spectrum from the studied area

(D0,X)

(A0,X)

(A0,X)-LO

DAP DAP-LO

D1 A center + D2

D1 and D2 are related to dislocations

(D0,X)

(A0,X)

(A0,X)-LO

DAP A center + D2

DAP-LO

(FE)

Near deformation region Far away from deformation region

Non-uniform spatial distribution of feature emissions was observed!

4.2 K PL intensity map of all peaks from 1.35eV to 1.66eV

Various line features (different types of dislocations) were revealed around the indent. It is consistent with the panchromatic cathodoluminesce (CL) micrograph (see below).

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Y (u

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X (um)

J. Schreiber, L. HoÈring, H. Uniewski, S. Hildebrandt, and H. S. Leipner, Phys. Stat. Sol. (a) 171, 89 (1999)

High spatial resolution PL maps provide detailed information about different feature emissions

Intensity map of (D0,X) peak

Donor-bound exciton (D0,X) peak and acceptor-bound exciton (A0,X) peaks are very sensitive to the presence of dislocations

Intensity map of (A0,X) peak

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X (um) X (um) Dislocations

4.2 K PL map of donor-acceptor pair (DAP) emission

Intensity map of DAP peak

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The corresponding dislocations are not clear in the PL map of donor-acceptor pair (DAP) emission.

Previous assumption for explaining contrast features in panchromatic CL micrograph of CdTe

(1) Te (g) dislocations behave as centers of radiative recombination

(2) Cd (g) dislocations behave as centers of nonradiative recombination

Panchromatic CL micrograph

* J. Schreiber, L. HoÈring, H. Uniewski, S. Hildebrandt, and H. S. Leipner, Phys. Stat. Sol. (a) 171, 89 (1999)

Effects of different types of dislocations on PL

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X (um)

A center + D2 D1

Relative intensity change of the dislocation-related peaks, compared to exciton peak

Origin of dislocation-related D1 and D2 peaks

A center + D2

D1

The peak at 1.480 eV is consistent with the well-known Y line, which was related to Te (g) 60o dislocations by some researchers. The peak at 1.527 eV could tentatively be assigned to Cd (g) 60o dislocations.*

*V. N. Babentsov, et al., Advanced Materials Research, 276, 195 (2011)

4.2 K PL map of D1 emission at 1.527 eV

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D1 (A0,X)

Distribution of white region and dark region is opposite in PL maps of D1 and exciton peak, supporting the assignment of D1 peak (Cd (g) 60o dislocations)

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Temperature Dependence of PL

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500

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PL In

tens

ity (a

.u.)

1.35 1.40 1.45 1.50 1.55Energy (eV)

17K21K25K30K35K40K45K52K

A center + D2

D1

The D1 peak at 1.527 eV is only distinguishable under 25 K. It diminishes much more quickly than another dislocation-related peak at 1.480 eV with increasing temperature. This can be due to the fact that the defect complexes related to D1 and D2 have different binding energies.

4.2 K 4.2 K

Stability of D1 peak after storage at room temperature

This is different from some report that D1 peak in CdTe only exists within several hours after making an indentation. The possible reason is that the addition of Zn restricts the movement of dislocations due to lattice hardening.

D1 peak can still be observed after 4 day’s storage at room temperature.

after 4 days

Summary

Our preliminary results show the spatially-resolved low-temperature PL mapping technique can be used to investigate the spatial distribution of dislocations in CdZnTe. The donor-bound exciton (D0,X) peak and acceptor-bound exciton (A0,X) peak are very sensitive to the presence of dislocations. The peak at 1.527 eV after the indentation could be related to Cd (g) 60o dislocations. The peak at 1.527 eV is relatively stable, compared with that in CdTe.

Future work: (1) Conduct micro-indentation and PL mapping on CdZnTe with different

orientations; (2) Conduct PL mapping around the indentation at elevated temperature to

compare the mobility of different types of dislocations

Acknowledgement

This work was supported by U.S. Department of Energy, Office of Defense Nuclear Nonproliferation Research and Development, DNN R&D.

Thank you for your attention!