CdZnTe device using constrained design for high-flux x-ray spectroscopic imaging applications
View Patent ↗A CdZnTe photon counting detector includes a core material of Cd 1-x Zn x Te, where (0≦x<1), an anode terminal on one side of the core material and a cathode terminal on a side of the core material opposite the anode terminal. At least one of the following is selected in the design of the detector as a function of the maximum sustainable photon flux the core material is able to absorb in operation while avoiding polarization of the core material: electron lifetime-mobility product of the core material; de-trapping time of the core material; a value of a DC bias voltage applied between the anode and the cathode; a temperature of the core material in operation; a mean photon flux density to be absorbed by the core material in operation; and a thickness of the core material between the anode and the cathode.
1. A photon counting detector comprising:
a core material of Cd 1-x Zn x Te, where (0 ≦x <1);
an anode terminal on one side of the core material; and
a cathode terminal on a side of the core material opposite the anode terminal, wherein
the anode terminal comprises either a single terminal or a plurality of segmented terminals; and
the cathode terminal comprises a plurality of segmented terminals.
2. A method of designing a photon counting detector, comprising:
(a) selecting a value for a design maximum sustainable photon flux that a core material of Cd 1-x Zn x Te, where (0≦x<1), is able to absorb in operation while avoiding polarization of the core material;
(b) selecting a plurality of design parameters as a function of the maximum sustainable photon flux, wherein the plurality of design parameters comprises:
a hole lifetime-mobility product of the core material;
a hole de-trapping time of the core material; and
a thickness of the core material between an anode terminal and a cathode terminal;
(c) selecting a plurality of operating parameters as a function of the maximum sustainable photon flux, wherein the plurality of operating parameters comprises:
a value of a DC bias voltage applied between the anode terminal and the cathode terminal;
a temperature of the core material in operation; and
a mean photon energy to be absorbed by the core material in operation;
(d) applying a correlation to determine a calculated maximum sustainable photon flux based on the pluralities of the design and operating parameters;
(e) repeating steps (b)-(d) if the calculated maximum sustainable photon flux is not substantially equal to the design maximum sustainable photon flux;
(f) selecting a core material of Cd 1-x Zn x Te, where (0≦x<1), having the design parameters selected in step (b) and capable of operation at the operating parameters selected in step (c);
(g) forming the anode terminal on one side of the core material; and
(h) forming the cathode terminal on a side of the core material opposite the anode terminal.
3. The method of claim 2 wherein the design maximum sustainable photon flux is greater than 20 million counts/s/mm 2 .
4. The method of claim 2 wherein said applying a correlation step (d) consists of:
Φ
γ
*
=
ɛ
czt
ɛ
0
V
2
qL
E
_
γ
λ
2
[
β
-
L
λ
exp
(
-
L
λ
)
]
-
1
μ
h
τ
h
τ
h
+
τ
D
;
where Φ γ * is the maximum sustainable photon flux while avoiding polarization of the core material;
ε czt =pair-creation energy in Cd 1-x Zn x Te, where (0 ≦x<1);
ε 0 =electrical permittivity of free space;
V=bias voltage applied to the anode and cathode terminals;
q=1.6E-19 Coulombs;
L=detector thickness;
Ē γ =mean photon energy;
λ=photon absorption length scale defined by the linear photon absorption coefficient for Cd 1-x Zn x Te, where (0 ≦x<1);
β=1-exp(-L/λ);
μ h =hole mobility;
τ h =trapping time for holes; and
τ D =temperature-dependent de-trapping time for holes τ D ˜exp(E A /kT)
5. The method of claim 2 wherein the design maximum sustainable photon flux is more than 100 million counts/s/mm 2 .
6. The method of claim 2 wherein:
the anode terminal, the cathode terminal or both comprise a plurality of segmented terminals.
7. A method of controlling a maximum sustainable photon flux that a photon counting detector with a core material of Cd 1-x Zn x Te, where (0≦x<1), is able to absorb in operation while avoiding polarization of the core material, including an anode terminal on one side of the core material and a cathode terminal on a side of the core material opposite the anode terminal, the steps comprising:
setting a value of a DC bias voltage applied between the anode terminal and the cathode terminal;
controlling a temperature of the core material in operation; and
controlling or selecting an energy output of a photon energy source to regulate a mean photon energy to be absorbed by the core material in operation.
8. The method of claim 7 , wherein the following equation is utilized to determine the maximum sustainable photon flux of the core material in operation:
Φ
γ
*
=
ɛ
czt
ɛ
0
V
2
qL
E
_
γ
λ
2
[
β
-
L
λ
exp
(
-
L
λ
)
]
-
1
μ
h
τ
h
τ
h
+
τ
D
;
where Φ γ * is the maximum sustainable photon flux while avoiding polarization of the core material;
ε czt =pair-creation energy in Cd 1-x Zn x Te, where (0≦x<1);
ε 0 =electrical permittivity of free space;
V=bias voltage applied to the anode and cathode terminals;
q=1.6E-19 Coulombs;
L=detector thickness;
Ē γ =mean photon energy;
λ=photon absorption length scale defined by the linear photon absorption coefficient for Cd 1-x Zn x Te, where (0 ≦x<1);
β=1-exp(-L/λ);
μ h =hole mobility;
τ h =trapping time for holes; and
τ D =temperature-dependent de-trapping time for holes τ D ˜exp(E A /kT)
9. The method of claim 7 , wherein:
the anode terminal, the cathode terminal or both comprises a plurality of segmented terminals.
10. The method of claim 7 , wherein the maximum sustainable photon flux is greater than 20 million counts/s/mm 2 .
11. The method of claim 7 , wherein the maximum sustainable photon flux is greater than 100 million counts/s/mm 2 .