Gamma ray detector

Details Gamma ray detector Gamma ray detector

2002-01-22

2003-11-11

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to corpuscular radiation

C250S370130

Reexamination Certificate

active

06645787

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to the manufacture of devices for the detection of high-energy electromagnetic radiation and, more particularly, to a method for providing gamma-ray detectors containing cadmium zinc telluride (CdZnTe) crystals with improved properties.
Gamma-ray detectors have wide applications, for example, in medicine, environmental monitoring and materials testing. As an example, in nuclear medicine a gamma-ray-emitting substance, a radiotracer, is typically injected into the body of a patient. The radiotracer travels through or is concentrated in parts of the body. By detecting the gamma rays emitted by the radiotracer using a gamma ray spectrometer, diagnostically useful information is gained.
In
FIG. 1
a typical gamma-ray spectrometer
10
is depicted. The heart of gamma-ray spectrometer
10
is gamma-ray detector
11
. Gamma-ray detector
11
detects and measures the energy of individual photons, such as photon
18
. Gamma-ray detectors, such as
11
, typically include a semiconductor crystal
12
, a forward contact
14
and a backward contact
16
. In detector
11
, semiconductor crystal
12
is a CdZnTe crystal. A gamma-ray photon
18
interacting with a semiconductor crystal
12
deposits energy in the bulk of semiconductor crystal
12
by ionization to form electron
20
and hole
22
pairs. Once produced, electrons
20
and holes
22
drift in opposite directions (
24
and
26
, respectively) under the influence of a strong electric field
28
within which semiconductor crystal
12
is found. The output signal of detector
11
is the induced charge corresponding to charge-motion
24
and
26
. Read-out electronics
30
, including pulse-shaping amplifier
32
and computer equipped multi-channel analyzer
34
, allow a spectral distribution (energy distribution) curve to be recorded. In
FIG. 2A
, detector
11
is depicted in perspective, showing CdZnTe crystal
12
, forward contact
14
and backward contact
16
. In
FIG. 2B
, an embodiment of a detector
11
is depicted, where in addition to CdZnTe crystal
12
, forward contact
14
and backward contact
16
, is a guard ring
38
maintained at the same potential as forward contact
14
so as to reduce surface leakage current.
The parameters important in defining the usefulness of a gamma ray detector for nuclear medicine are spatial resolution, energy resolution and counting efficiency. In order to minimize the exposure of a patient to radiation, it is preferable that only small amounts of radiotracer be injected. As a result, the absolute intensity of gamma-rays that are emitted by the radiotracer to be detected is low. It is thus important that a gamma-ray detector used in nuclear medicine have a high counting efficiency. In addition, the semiconducting crystal used in a gamma-ray detector must be made of a semi-insulating material. As described above and in
FIG. 1
, a gamma-ray detector must be located in an intense electric field. The intense electric field increases the level of charge collection. However, the typical intensity of an electric field used is such that large dark currents are induced in materials which are even slightly conductive and are thus not categorized as semi-insulating.
Amongst the suitable semiconducting materials used in gamma ray detectors is crystalline Cadmium Zinc Telluride (CdZnTe). Gamma-ray detectors made using CdZnTe have wide band-gaps, high resistivities and allow room-temperature operation.
Further background of radiation detectors in general and CdZnTe detectors in particular can be found in the prior art, for example in references [1-3]. Greater details concerning the specific background relating to CdZnTe detectors can be found in the prior art, for example in references [4-15].
Known semiconducting materials, including CdZnTe crystals, produced in accordance with the methods known in the art contain a large number of defects. The presence of a large number of defects renders a crystal unsuitable for use in a detector. In the first place, the presence of a large number of defects decreases the resistivity of a crystal, leading to high levels of dark current. In the second place, defects lead to charge-carrier trapping. Charge-carrier trapping occurs when charge-carriers become trapped at defects in the crystal and thus contribute only partially to the signal. When charge-carrier trapping occurs, pulse heights are different for different interaction depths resulting in a tailing or plateauing of a photopeak. This tailing or plateauing reduces the energy resolution of the detector and reduces the effective photopeak fraction. For any given energy window, charge-carrier trapping also reduces the detector counting-efficiency.
It would be highly advantageous to have a method for improving CdZnTe crystals and gamma-ray detectors. It would be highly advantageous to be able to supply CdZnTe crystals having a well-defined and predictable low level of defects so that gamma-ray detectors made using the crystals have a good spectral resolution, high sensitivity and low dark current level.
REFERENCES
[1] “Physics in Nuclear Medicine”, J. A. Sorenson and M. E. Phelps, Second Edition, W. B. Saunders Company, London (1987).
[2] “Foundation of medical imaging”, Z. H. Cho, J. P. Jones and M. Singh, Wiley, N.Y. (1993).
[3] H. B. Barber “Application of II-VI materials to nuclear medicine”,
J. Electronic Materials,
1996, 25, 1232.
[4] Y. Nemirovsky, A. Ruzin, G. Asa, J. Gorelik “Study of Charge Collection Efficiency of CdZnTe Radiation Detectors”,
J. Electronic Materials,
1996, 25, 1221-1231.
[5] Y. Nemirovsky, A. Ruzin, G. Asa, J. Gorelik “Study of Contacts to CdZnTe Radiation Detectors”,
J. Electronic Materials,
1997, 26, 756-764.
[6] A. Ruzin Y. Nemirovsky “Statistical Models for Charge Collection Efficiency and Variance in Semiconductor Spectrometers”,
J. Appl. Phys.,
1997, 82, 2754-2758.
[7] Y. Nemirovsky, G. Asa, C. G. Jakobson, A. Ruzin, J. Gorelik “Dark Noise Currents and Energy Resolution of CdZnTe Spectrometers”,
J. Electronic Materials,
1998, 27, 800-806.
[8] Y. Nemirovsky, G. Asa, A. Ruzin, J. Gorelik, R. Sudharsanan “Characterization of Dark Noise in CdZnTe Spectrometers”,
J. Electronic Materials,
1998, 27, 807-813.
[9] A. Ruzin, Y. Nemirovsky “Methodology for Evaluation of Mobility—Lifetime Product by Spectroscopy Measurements in CdZnTe Spectrometers”,
J. Appl. Phys.,
1997, 82, 4166-4171.
[10] A. Ruzin, Y. Nemirovsky “Passivation and Surface Leakage in CdZnTe Spectrometers”,
Appl. Phys. Lett.,
1997, 71, 2214-2215.
[11] Y. Nemirovsky, G. Gordon, D. Goren “Measurement of Band Offsets and Interface Charges by the C-V Matching Method”,
J. Appl. Phys.,
1998, 84, 1-8.
[12]Y. Nemirovsky “Statistical Modeling of Charge Collection in Semiconductor Gamma-Ray Spectrometers”,
J. Appl. Phys.,
1999, 85, 8-15.
[13] Y. Nemirovsky, M. Iframor, A. Ludwig “The Effect of the Geometrical Parameters on the Electric Field of Pixilated Two-Dimensional Arrays of Gamma-Ray Spectrometers”,
J. Appl. Phys.,
2000, 88, 5388-5394.
[14] Y. Nemirovsky, G. Asa, J. Gorelik, A. Peyser “Recent Progress in n-Type CdZnTe Arrays for Gamma-Ray Spectroscopy”,
Nuclear Instrument
&
Methods, A,
2001, 458, 325-333.
[15] M. Ifraimov, A. Ludwig, Y. Nemirovsky “Statistical Modeling of the Spectral Performance of a Two-Dimensional Array of Gamma-Ray Spectrometers” to be published in
J. Appl. Phys.,
2002.
[16] A. P. Zdebskii, N. V. Mironyuk, S. S. Ostapenko, A. U. Savchuk, M. K. Sheinkman
Sov. Phys. Semicond.,
1986, 20, 1167.
[17] A. P. Zdebskii, M. I. Lisyanskii, N. B. Lukyanchikov Sov. Tech. Phys. Lett., 1987, 13, 550.
[18] G. Garyagdiyev, I. Y. Gorodetskii, B. R. Dzhumayev
Sov. Phys. Semicond.,
1991, 25, 248.
[19] M. Lisiansky, V. Korchnoi, R. Weil, N. Nemirovsky “Stability of Electrical Parameters of Metalorganic Chemical Vapor Deposi

Affiliated with

Also associated with

Rating

Gamma ray detector does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Gamma ray detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gamma ray detector will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3184995