GaAs detectors for medical imaging G.I.Ayzenshtat a*, S.M. Gushin a, O.B. Koretskaya b, O.P....
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GaAs detectors for medical imaging G.I.Ayzenshtat a* , S.M. Gushin a , O.B. Koretskaya b , O.P. Tolbanov b , A.V. Tyazhev b , E.A. Babichev c , V.R. Groshev c , G.A. Savinov c , A.P. Vorobiev d a Research Inst. of Semicond. Dev., Tomsk, Russia b Siberian Physical Technical Institute, Tomsk, Russia c Budker Institute of Nuclear Physics, Novosibirsk, Russia d Institute of High Energy Physics, Protvino, Russia [email protected]
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Transcript of GaAs detectors for medical imaging G.I.Ayzenshtat a*, S.M. Gushin a, O.B. Koretskaya b, O.P....
GaAs detectors for medical imaging
G.I.Ayzenshtata*, S.M. Gushina, O.B. Koretskayab, O.P. Tolbanovb, A.V. Tyazhevb, E.A. Babichevc, V.R.
Groshevc, G.A. Savinovc , A.P. Vorobievd
a Research Inst. of Semicond. Dev., Tomsk, Russia
b Siberian Physical Technical Institute, Tomsk, Russiac Budker Institute of Nuclear Physics, Novosibirsk, Russia
d Institute of High Energy Physics, Protvino, Russia
Low dose digital radiographic device
with GaAs - detectors • The aim of this work
was to test GaAs detectors in a real
radiographic device• Gas detector was
replaced by a GaAs one in a Low Dose Digital Radiographic Device “LDRD SIBERIA-N”
Detector
+
Electronics
Low dose digital
radiographic device
The main properties of compensated SI-GaAs(Cr) detectors
• 1. SI-GaAs(Cr) detectors have no Schottky contacts, they have only ohmic ones. I-V characteristics are linear.
• 2.The electric field (E) occupies the whole volume of detector. E(kV/cm) const
• 3. Charge collection in GaAs-detectors is determined by electrons.
• 4. The detector material resistivity is extremely high (ρ>109 Ω∙cm).
-100 0 100
-5
5
0
I, nA
U, V
Cur
rent
Voltage
20 40 600
50
Energy
Cou
nts
keV
E const
Attachment of GaAs-detectors to electronics
Iz = 0I = +I0
I = -I0
+U1 - U1
zX-Rays
The problem: the dark current of detector is about 10 nA. It is necessary to reduce the current by a factor of 10 for the electronics to operate. Solution of the problem: we offer to attach the detectors to electronics as shown in the figure.
Symmetrical detector structures with the compensation of dark currents
The hypothetical detector structure
The real structure of the mammo- graphy detector (100 mkm pitch)
+ U - U
I = 0
The results of current compensation measurements in the symmetrical device.
• The output current of the detector decreases by a factor 30
X - ray s
A S IC
U 1 U 2
T h e sc reen
0 50 100 150 200
0
200
400
600
I = 20 pA
+ U2
U1 = -200 V
I, pA
X- rays
screen
+U0 -U0
D
etec
tor
1 D
etec
tor
2
Plane view of detector (h = m)
A fragment of hybrid circuit of
electronics
A fragment of detectors mounting
64-channel chip
0 10 20 30 40 50 60 700
2000
4000
6000
8000
10000
I, mA
80 keV
Cou
nt (
Arb
. un
its)
0 2000 4000 60000
2000
4000
6000
8000
10000
mR/min
60 keV 80 keV 120 keV
Cou
nt (
Arb
. uni
ts)
The magnitude of the output signal
as a function of the Roentgen tube current
The magnitude of the output signal as a function of dosage rate for various
quantum energy
0 1 2 3 4
500
1000
1500
2000
2500
With Pb screen
Without Pb screen
Sig
nal m
agni
tude
t, sec
Waveshape of the signal in vertical scanning of
the detector SNR2 as a function of
dosage rate
«Channel form» obtained by vertical scanning
0,9 1,0 1,1 1,2 1,30
100
200
300
400
500
21
Downx, mm
1 (U = - 200 V) 2 (U = + 250 V)
Sig
nal m
agni
tude
UDown
To electronics
X-rays
«Channel form» obtained by horizontal scanning
Detector
200 400 600 800 1000 12000,0
0,2
0,4
0,6
0,8
1,0Channel numbersU
x, mkm
30 31 32 33 34 35
The collimator moves along the horizontal axis
Collimator
The normalized amounts of signals for various channels during horizontal scanningTo electronics
X-rays
Image of the test pattern obtained by the GaAs detector with a 400 mkm pitch(The limiting image resolution is 1.4 pairs
of lines per mm)
-150 -100 -50 0 50 100 150-10
-5
0
5
10
15
SI-GaAs(Cr)
Epitaxy p-i-n GaAs(Cr)I, nA
U,V
Plane view of the detector (h = 200m) fabricated
from GaAs liquid-phase epitaxy
Comparision of I-V characteristics for two detectors.
1. The GaAs liquid-phase epitaxy detector 2.
The SI-GaAs(Cr) detector
IT The image of the test pattern obtained by GaAs detector with a 200 m pitch
(The limiting image resolution is 2.8 pairs of lines per mm)
Conclusion
1. It was shown experimentally that the GaAs material compensated with Cr can be used to fabricate efficient X-ray detectors.
2.The object image with the resolution 2.8 pairs of lines per mm has been obtained with GaAs detectors.
3.We consider the GaAs(Cr) liquid-phase epitaxy material to be a more promising material for obtaining the resolution more than 2.8 pairs of lines per mm.
