IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 60, NO. 6, DECEMBER 2013
4257
Sensors Based on Radiation-Induced Diffusion of
Silver in Germanium Selenide Glasses
Pradeep Dandamudi, Student Member, IEEE, M. N. Kozicki, Member, IEEE, H. J. Barnaby, Senior Member, IEEE,
Y. Gonzalez-Velo, Member, IEEE, M. Mitkova, Member, IEEE, K. E. Holbert, Senior Member, IEEE,
M. Ailavajhala, Student Member, IEEE, and W. Yu
Abstract—In this study we demonstrate the potential radiation
sensing capabilities of a metal-chalcogenide glass (ChG) device.
The lateral device senses radiation-induced migration of
ions
in germanium selenide glasses by measuring changes in electrical
resistance between electrodes. These devices exhibit a high-resistance ‘OFF-state’ (
) before irradiation, but following
gamma-rays or UV light, their resisirradiation with either
tance drops to a low-resistance ‘ON-state’ (
). The devices
have exhibited cyclical recovery with room temperature annealing
of Ag doped ChG, which suggests potential use in reusable radiation sensor applications. Furthermore, the mechanisms of radiation-induced
transport and reactions in ChG are modeled using a finite element device simulator. The essential reactions
captured by the simulator are radiation-induced carrier generation, combined with reduction/oxidation for both ionic and neutral Ag species in the chalcogenide film. The results provide strong
qualitative evidence that finite element codes can simulate ionic
transport reactions in the ChG and reveal plausible mechanisms
for radiation-induced metal doping.
Index Terms—Chalcogenide glass, dosimetry, photodoping,
reusable sensor, TCAD modeling, UV and gamma rays.
I. INTRODUCTION
C
UMULATIVE radiation measurement systems quantify
total ionizing dose (TID) which may cause undesirable
effects on equipment or subjects over time [1], [2]. Low cost
film badges, which are good for large-scale distributed applications, require time-delayed, and inconvenient wet chemical
processing for readout. Thermoluminescent dosimeters (TLDs)
need high-temperature processing for readout, and they suffer
from poor signal retention and relatively high cost. Detection
systems that provide an instantaneous electrical readout are
clearly more desirable. Ionization chamber detection systems
are expensive, bulky, require a high voltage supply, and therefore are not suitable for distributed applications. MOSFET
detectors are used in electronic sensors because of their small
Manuscript received July 02, 2013; revised August 31, 2013; accepted October 06, 2013. Date of publication November 13, 2013; date of current version
December 11, 2013. This work was supported by the Defense Threat Reduction Agency under Grant HDTRA1-11-1-0055 and the Battelle Energy Alliance
under Blanket Master Contract 41394.
P. Dandamudi, M. N. Kozicki, H. J. Barnaby, Y. Gonzalez-Velo, K. E. Holbert, and W. Yu are with the School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287-5706 USA (e-mail: pdandamu@asu.edu).
M. Mitkova and M. Ailavajhala are with the Department of Electrical and
Computer Engineering, Boise State University, Boise, ID 83725 USA.
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TNS.2013.2285343
size, good signal retention, and instantaneous readouts. However, limited range, lifetime, and drift in response over time can
result in loss of accuracy [1]–[3].
In this study we investigate simple and cost-effective radiation sensing devices based on changes in electrical resistance
due to radiation-induced diffusion of Ag metal into chalcogenide glass (ChG). We examine a lateral device configuration
and demonstrate the effect of film thickness and ChG composition on the device response. The sensors have a high-resistance
‘OFF-state’ (
) before irradiation. Post-irradiation,
from either
gamma-rays or ultraviolet (UV) light, the
sensors exhibit a low-resistance ‘ON-state’ (
) with
a tunable input dose range. We believe such devices provide
the possibility of a cost-effective, very low-voltage alternative
to currently available radiation sensor technologies. The ChG
sensor presented in this paper exhibits controllable sensor
performance characteristics, good state retention, and instantaneous readout. The device is compact in size, scalable, and
can be easily and inexpensively incorporated into a standard
integrated circuit process flow. These properties make it a good
candidate for the next generation of portable, electronic, field
dosimeters.
II. MATERIALS
Chalcogenide glasses containing chalcogen atoms (S, Se, Te)
are often used in conjunction with group IV and/or group V elements. These glasses are currently used in emerging memories,
known as resistive random access memories (ReRAM), that
have the potential to replace current flash technologies [4]–[10].
Exposure of Ag/ChG film stack(s) to UV light will initiate a
process known as photodoping, whereby Ag diffuses both laterally and vertically into the ChG, resulting in a large change in
the properties of the glass material [11]–[20]. The electrical rem,
sistivity of undoped ChG is typically high, more than
but with the incorporation of Ag, the resistivity decreases to less
than
m [14], [21].
In the case of the photo-dissolution of Ag, light illumination generates charged carriers (electron-hole pairs) in the ChG
which facilitate the diffusion of Ag into the glass. The presumed
mechanisms are: 1) Ag metal reacts with photo-generated holes
ions and 2) photo-generated electrons are trapped
to create
in the ChG film. An electrochemical potential is thus formed
ions and negatively charged,
between positively charged
trapped electrons [12]–[18]. The resulting electric field causes
ions to drift into the undoped ChG. Metal transport
mobile
into the undoped region will continue until the light source is
removed or the Ag supply is exhausted. The resulting Ag-ChG
0018-9499 © 2013 IEEE
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Fig. 1. Sensor fabrication sequence for lateral devices.
ternary [11], [22], [23] has a variety of interesting physical and
electrical properties, but the most important aspect for this study
is the significant change in film conductivity, which increases
with increasing Ag concentration [11]–[15]. Although much of
the previous work on photodiffusion has focused on the effects
of UV exposure, similar mechanisms are thought to be prevalent
in the case of exposure to much higher energy ionizing radiation. Previous work on
gamma exposures of a Ni/Ag/ChG
stack [24] shows that the irradiation causes Ag photo-doping in
ChG and post-radiation annealing enables un-neutralized
to transport back to the Ag top layer. In general, the absorption of ionizing radiation across a broad energy spectrum (from
“low energy” ultraviolet to “high energy” gamma rays) can induce the incorporation of Ag metal into a ChG film. This will
cause a significant change in the material resistance—a useful
effect for radiation measurement/sensing applications.
III. DEVICE FABRICATION
The sensors discussed in this paper are simple to make, as
the fabrication process involves only two main steps. The first
step involves deposition of a thin ChG film on a substrate and
the final step is formation of electrodes on the ChG. The electrodes supply the metal for photodoping as well as the terminals
for resistance measurement. The device resistance is measured
between two electrodes on the ChG film surface. The materials
we selected were
and
glasses and Ag electrodes. In general, Ag has high diffusivity in Ge-Se films and
many tens of atomic percent of Ag can be incorporated in them.
These particular Ge-Se compositions were chosen to assess the
effect of chalcogen content on device response since it is known
that Ag diffusivity is higher in more chalcogen rich material
[14]–[16], [22]. Several Ge-Se thicknesses were also used to
determine the effect of this parameter on sensor performance.
The processing steps are shown in Fig. 1. Blanket
and
films, of 5 nm, 10 nm, and 20 nm thickness, were
evaporated onto cleaned microscope glass slides in a Cressington 308 thermal evaporator at a deposition rate of 0.1 nm/s.
Then 35 nm of Ag were evaporated at 0.1 nm/s through a
shadow mask on top of the deposited ChG film in order to form
Fig. 2. Lateral device: (a) Cross-section view and (b) top view.
the Ag electrodes. Figs. 2(a) and 2(b) show the cross-sectional
view and top view of the lateral devices, respectively. The Ag
dots are 2 mm in diameter, with a spacing of 1 mm between
them.
IV. TEST PROTOCOL AND DEVICE CHARACTERIZATION
Step stress UV irradiation was first performed on test structures as a simple and quick means for assessing resistance
change as a function of exposure time/dose. The UV light
power density was
mW/cm at a wavelength of 324 nm
(1 h of UV exposure therefore corresponded to a total energy
density of
J/cm ). The dose is the energy density of the UV
source (measured by an external calibrator) that is delivered at
the point of incidence onto the sample.
For
gamma-ray exposures, the samples were placed in a
Gammacell 220 irradiator with a dose rate of 10.5 rad(GeSe)/s.
The doses are converted from
to a ChG equivalent using
the relative energy-absorption mass coefficients for the constituent elements (taken at the average energy of 1.25 MeV).
The samples were periodically removed from the Gammacell
to measure the change in electrical resistance with respect to
increasing dose levels. The samples were exposed at room temperature and were left floating (electrodes unconnected) during
the exposures.
Quasi-static DC electrical measurements were performed
using an Agilent 4155B/C Semiconductor Parameter Analyzer
(SPA) at room temperature. For lateral devices, the resistance
between two adjacent Ag electrodes was monitored for 500 s,
at 10 mV bias. The electrical measurements were carried out
at these low-voltages in order to minimize any Ag drift caused
by internal electric fields during measurements. Resistance
DANDAMUDI et al.: SENSORS BASED ON RADIATION-INDUCED DIFFUSION OF SILVER IN GERMANIUM SELENIDE GLASSES
Fig. 4. Resistance as a function of measurement time of 5 nm
devices, measured at incremental UV doses.
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lateral
the electrodes has been bridged by Ag-Ge-Se (doped) conducting material. At this stage, the device is in a low-resistance
‘ON-state’. The device resistance may be approximated by,
(1)
Fig. 3. Optical micrographs show evolution of UV light induced Ag lateral
diffusion in a 5 nm thick
film, (a) before irradiation, (b) after
J/cm of UV dose.
J/cm , (c) after
J/cm , and (d) after
measurements with respect to dose were taken when there
was a significant resistance difference (typically an order of
magnitude) between each TID level.
Optical microscopy was performed using a Zeiss Axiophot
Microscope. Bright-field images were taken in order to capture
the evolution of Ag diffusion into the ChG following UV and
gamma irradiation. Dark-field images were taken to investigate
the surface morphology of the Ag-Ge-Se film before and after
room temperature annealing experiments following exposure.
V. DEVICE OPERATION
Fig. 3 shows the evolution of Ag lateral diffusion in a
film with respect to UV exposure time. Fig. 3(a)
shows two Ag electrodes on top of 5 nm thick
.
These two electrodes are used as contact pads for electrical
measurements as well as providing the Ag into the ChG
layer. Before UV exposure, the device exhibits a very high
resistance ‘OFF-state’. This OFF state resistance cannot be
determined using the 4155B/C SPA, as the current is below
the measurement limit of the instrument. After
J/cm of
UV exposures, as shown in Fig. 3(b), Ag has diffused laterally
more than 0.5 mm between the two electrodes. At this stage,
the device is still in the OFF-state, as there remains a region of
undoped ChG between the electrodes. As shown in Fig. 3(c),
after
J/cm of UV exposures, the ChG layer between
(2)
where,
, is the resistivity of Ag-Ge-Se ( depends on
the atomic fraction of Ag in Ge-Se), is the distance between
two electrodes, is the thickness of ChG, and is the width of
doped or undoped region between the electrodes. So as the width
of Ag-Ge-Se between two electrodes is increased, the resistance
is decreased.
The threshold dose (
) for radiation measurement can be
defined as the point when the doped regions between two Ag
electrodes connect, i.e., when a low resistivity Ag-Ge-Se ‘conduction pathway’ between the two electrodes is formed. The
resistance measured at
is known as the threshold resistance (
). As shown in Fig. 3(c), although the ChG region
between two electrodes has been Ag-doped, the longer region
between 2 diagonal Ag electrodes has not been fully bridged.
After
J/cm of UV exposure, the undoped regions of ChG
film have been completely doped with Ag, as shown in Fig 3(d).
The dose and resistance at this stage can be defined as the saturation dose (
) corresponding to a saturation resistance (
).
At this point, no further significant change in resistance with additional light exposure is observed.
VI. EXPERIMENTAL RESULTS AND DISCUSSION
A. UV Exposure Results on Lateral Devices
UV irradiation tests were performed on 5 nm thick
devices and the average resistance with respect to total UV dose
was measured on a minimum of 20 devices. The devices were
exposed to a total UV dose of
J/cm . The resistance of
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Fig. 5. Resistance as a function of total UV dose for four different structures.
TABLE I
UV SENSOR PERFORMANCE CHARACTERISTICS
each device was monitored for 500 s and Fig. 4 shows the average resistance with respect to measurement time, at various
total UV dose levels.
Fig. 4 shows that the resistance of the devices decreases and
saturates in response to the total UV dose. The high OFF-state
resistance (
) is not plotted, since it is beyond the instrument range. After a dose of
J/cm , the resistance of the device was
k (
) and shows no significant change beyond
this, even after
J/cm of UV exposures. The average resistance also shows no significant change during the measurement time (i.e. 500 s), therefore suggesting that the application
of bias (at 10 mV) during measurements may not cause Ag diffusion and disturb the state of the device. The decrease in resistance at incremental UV doses is mainly due to UV induced
photodoping of Ag into the ChG and not due to measurement
bias.
Two different thicknesses of
(5 nm and 20 nm) and
5 nm and 20 nm) samples were studied in order to
analyze the effect of ChG thickness and composition on sensor
performance. Fig. 5 plots the average resistance with respect to
UV dose for the four different sample types and Table I shows
the effect of composition and thicknesses on
and
.
These results demonstrate that regardless of device type, the
sensors show a rapid reduction in resistance followed by a saturation in response, when exposed to UV irradiation.
As shown in Fig. 5, the devices with greatest sensitivity are
5 nm thick
devices and the second most are 5 nm thick
devices. From Table I, the threshold UV dose (
) of
5 nm and 20 nm
are 24.0 and
J/cm , respectively,
Fig. 6. Resistance as a function of
gamma TID of 10 nm thick
devices. The doses are ChG equivalent.
and for 5 nm and 20 nm
are 33.6 and
J/cm .
This shows that
can be increased by increasing the thickness of ChG layer. At
, the resistivity of 5 nm
is calculated as
m and of 5 nm
is
m. It is also evident that the composition of ChG
can also influence the
of the device. Also the difference,
, is smaller in
compared to
devices, indicating that
devices might have greater radiation sensitivity due to more rapid achievement of the threshold
condition. This is likely due to the greater Ag diffusivity in more
chalcogen rich materials.
B. Gamma-Ray Exposure Results on Lateral Devices
Exposure to gamma irradiation has also been performed on
device samples. Fig. 6 shows the average resistances (
devices) with respect to TID for 10 nm thick
devices. The average threshold dose
is 495 krad(GeSe), where
, and
is 694 krad(GeSe), where
. Comparing Figs. 5 and 6, the devices show similar resistance change response to both UV and
gamma
irradiations.
C. Effects of Agglomeration and Annealing
In order to study the effect of thickness on sensor performance, 5 nm thick
devices were fabricated
and exposed to gamma rays for a TID of 1.7 Mrad(GeSe)
(Figs. 7 and 8). Fig. 7 plots average resistances (
devices) up to a TID level of 940 krad(GeSe) and Fig. 8
from a TID of 940 krad(GeSe) to 1.7 Mrad(GeSe) (including room-temperature annealing intervals). For these
devices,
krad(GeSe), where
G , and
krad(GeSe), where
k . Although
no significant difference has been observed in
for the
5 nm and 10 nm devices, the
of 10 nm devices is higher
than that of the 5 nm devices, suggesting higher resistivity in
10 nm devices. Also, the response dose (
) is lower in
5 nm devices (105 krad(GeSe)), compared to 10 nm devices
DANDAMUDI et al.: SENSORS BASED ON RADIATION-INDUCED DIFFUSION OF SILVER IN GERMANIUM SELENIDE GLASSES
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Fig. 9. Optical microphotographs showing surface morphology of a 5 nm thick
saturated device. (a) Shows formation of Ag clusters on ChG after
TID of 1.303 Mrad(GeSe), and (b) shows disappearance of Ag clusters after
12 h of RT annealing interval.
Fig. 7. Average resistance as a function of gamma TID of 5 nm
lateral devices. The doses are ChG equivalent.
Fig. 8. Characteristics of reusable sensors: Average resistance as a function of
RT annealing time, measured at various step stress irradiation doses for 5 nm
devices. The figure shows switching-in resistance response of
thick
saturated devices when stressed to irradiations and anneals cycles. The doses
are ChG equivalent.
(199 krad(GeSe)), indicating that Ag diffusion (i.e. saturation)
is faster in thinner films.
After the devices reach a saturation dose at or below
660 krad(GeSe), as shown in Fig. 7, they were further stress
step irradiated to 725 krad(GeSe), 810 krad(GeSe) and
940 krad(GeSe) and no significant change in resistance was
observed (
k ). After incrementally reaching a TID of
940 krad(GeSe), these ‘saturated devices’ were left unbiased
at room temperature and resistance measurements were monitored during room-temperature (RT) annealing intervals (12 h,
24 h, 48 h, and 64 h). The anneal measurements show that the
saturated device resistances remained in the saturation state
(
k ), as shown in Fig. 8 (0 h on the x-axis represent the
measurements taken soon after irradiation).
The step-stress irradiations of these saturated and RT annealed devices were continued to TIDs of 1.17 Mrad(GeSe),
1.3 Mrad(GeSe), 1.49 Mrad(GeSe) and 1.7 Mrad(GeSe). Following each of these step stress doses, resistance measurements
were monitored during total RT annealing intervals (0 h, 12 h,
24 h, 48 h, 64 h). Fig. 8 plots the average resistance vs. RT
annealing time, measured at various doses.
The results in Fig. 8 demonstrate that once 5 nm thick Ge-Se
devices reach a resistance saturation state (
), further step
stress irradiation and subsequent RT annealing on ‘saturated devices’ causes switching of the resistance response. In the case of
irradiation of RT anneal devices, the resistance switches from a
low (
) to high (
) level, and in the case of RT anneal of irradiated and saturated devices, the resistance switches
from a high (
) to low (
) resistance level.
As shown in Fig. 8, the saturated devices step stressed to
a TID of 1.17 Mrad(GeSe) show significant change in resistance level, on the order of
, compared to its previous
state. Subsequent RT annealing measurements on these devices
show that the resistance dropped back to
. Several cycles
of step-stressed irradiation exposures and subsequent annealing
intervals were performed on these devices in order to study the
repeatability of the resistance switching behavior, as shown in
Fig. 8.
In order to further investigate the resistance switching characteristics, dark field optical microscopy was performed on saturated devices to reveal the surface morphology of Ag-Ge-Se
thin films. Fig. 9(a) shows the surface morphology of a saturated device after a step-stress irradiation of 1.303 Mrad(GeSe)
and Fig. 9(b) after 12 h RT anneal of this irradiated and saturated device. Fig. 9(a) reveals a large number of Ag clusters deposited/agglomerated on the surface of the irradiated Ag-Ge-Se
region. This gamma-ray induced surface deposition/agglomeration of Ag nanoparticles on top of ChG is due to the presence of
excess
ions present inside Ag-rich ChG film that migrates
towards the irradiated surface area. The migration of
is
due to counter flow of photoexcited holes during the radiation
process [14], [25].
Previous studies have observed a photo-induced surface
deposition (PSD) phenomena for 30-40 atom percent Ag in
films and electron-beam surface deposition (ESD)
on Ag-rich films on glass substrates. Such phenomena have
found applications in rewritable optical recording disks [14].
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As a result of discontinuous Ag metallic clusters deposited/agglomerated on the irradiated device, the conductivity of a
previously photodoped ChG film decreases, thereby increasing
the resistance of the device.
Fig. 9(b) shows that the Ag clusters deposited/agglomerated
during radiation exposure have disappeared after 12 h of RT
annealing, leaving little Ag residue on the surface. The disappearance of the Ag deposits is likely due to re-diffusion of
Ag back into the Ag-Ge-Se thin film by thermal effects [14].
The combination of radiation-induced agglomeration and RT
annealing effects suggests that the device may work as a reprogrammable/reusable radiation sensor.
Similar resistance characteristics were observed on 5 nm
thick
devices, which were step stress irradiated to a
TID of 1.632 Mrad(GeSe). In this case,
(
krad(GeSe)) and
k . These devices
showed similar radiation response characteristics and annealing
behavior when compared with 5 nm thick
devices.
D. Controlling Sensor Performance Characteristics
From UV and gamma irradiation experiments, the sensor performance parameters (
,
,
,
) likely depend on a
number of factors including: ChG thickness, ChG composition,
Ag thickness, distance between the two electrodes, substrate beneath the ChG (insulator, metal conductors, semiconductors or
flexible substrates), electrode configuration (bus bars, interdigitated fingers, array or ring electrodes), radiation sources (intensity, dose rate), and annealing intervals.
A ChG thickness of 20 nm or less has been shown to be a
significant factor for Ag lateral diffusion. In particular, the 5 nm
ChG film had a faster rate (or shorter saturation time) of Ag
lateral diffusion than 20 nm ChG films. The ChG composition
was also shown to have a considerable effect on the Ag diffusion
rate. An increase in the Se content leads to an increase in diffusion rate and higher Ag incorporation in the films. Ag photodissolution has also been observed in other ChG materials such
as Ge-Te, Ge-S, As-S, As-Se, As-Te, As–S–Te and As–Se-Te
[14]–[21], and the maximum lateral diffusion occurs along the
composition of lowest density. Studies have shown that lateral
diffusion in sulfide glasses is much slower than selenide glasses
[14], [26]. Therefore, as a result of changing the thickness and
composition of ChG materials, the dynamic range of
and
can be tuned for measuring different total ionizing doses.
Lower dose measurements can be achieved by reducing the
spacing between two adjacent Ag electrodes. The electrodes
spacing on our sensors were fixed at 1 mm, but can easily be
reduced to much smaller dimensions using conventional lithography techniques, thereby lowering
.
Fig. 10. Contour plot of two-dimensional finite element simulation structure
representative of lateral sensors. (a) Figure shows distribution of Ag in ChG at
.
an arbitrary fixed dose, and (b) after
is 2.5 eV, ChG affinity is 3.45 eV, ChG dielectric constant is
5.0, and the silver work function is 4.6 eV [27].
Key ion transport (oxidation and reduction reactions) equations used in the model are:
(3)
(4)
The electron-hole pair generation rate is defined as,
VII. FINITE ELEMENT MODELING
Finite element (FE) simulations were performed with
Silvaco’s numerical device simulator ATLAS on a two-dimensional structure representative of a lateral sensor structure.
As shown in Fig. 10(a), the structure is composed of a ChG
film (10 nm thick, 200 nm wide) sandwiched between silver
electrodes (10 nm thick, 350 nm wide). For the simulations,
the ChG film is modeled as a wide bandgap semiconductor.
Material constants used for the simulations are: ChG bandgap
(5)
where is the density of ChG, is the radiation dose rate, and
is the ionization energy for electron-hole pairs.
The ATLAS FE code solves the radiation-induced ion transport and reactions, combined with the code’s intrinsic radiation-induced carrier generation capability. Fig. 10(a) plots the
DANDAMUDI et al.: SENSORS BASED ON RADIATION-INDUCED DIFFUSION OF SILVER IN GERMANIUM SELENIDE GLASSES
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simulation models the diffusion of Ag concentration profiles
within ChG film under radiation doses. While work is in
progress to improve the accuracy of the simulations through
adjustments of the simulation parameters and additions to the
equation set, the results reported here provide strong qualitative
evidence that finite element codes can simulate ionic transport
and subsequent photodoping in ChG films.
Hence, the ChG sensor presented in this paper exhibits controllable sensor performance characteristics, good data retention, and instantaneous readout. The device is compact in size,
scalable, and can be easily and inexpensively incorporated into a
standard integrated circuit process flow, making it a good candidate for the next generation of portable, electronic, field dosimeters.
ACKNOWLEDGMENT
Fig. 11. Evolution of neutral Ag distribution in ChG, with increasing radiation
doses where is an arbitrary dose.
The authors would like to thank Dr. James Reed of DTRA for
his support of this work.
REFERENCES
Ag density distribution within the ChG film after an arbitrary
fixed dose, and Fig. 10(b) plots the distribution after 500 .
The figure shows that
that are oxidized at the electrodes
drift into ChG film and begin to reduce to neutral Ag with increasing total dose.
Fig. 11 plots the distribution of neutral Ag concentration
along the cutline shown in Fig. 10(a). The figure shows that
with increasing radiation dose, Ag diffuses into ChG film.
Increasing radiation dose causes the ChG film to be saturated
with higher Ag concentration, thereby lowering the resistivity
of the ChG film. The increase in neutral Ag demonstrates
that FE simulations, which include particle (ionic and neutral
species) transport and reactions, can model photodoping of Ag
in ChG film.
VIII. CONCLUSION
In this work, we studied radiation-sensing devices that exhibited a significant change in output resistance as a result of radiation-induced diffusion of Ag into chalcogenide glasses. We
studied lateral sensor structures with two different compositions
(
and
), three glass thicknesses (5 nm, 10 nm,
and 20 nm) that were exposed to UV light and
gamma-ray
irradiation. The irradiation results indicate that thickness and
composition of ChG material play major roles in the radiationinduced Ag photodoping process and in return influence the
sensor performance characteristics. Distance between the two
coplanar Ag electrodes shows linear dependence on
of the
sensor.
It has also been demonstrated that radiation induced Ag
doping is reversible through extended irradiation of saturated
ChG films. The combination of radiation induced silver surface
agglomeration and subsequent room-temperature/thermal annealing of Ag clusters in Ag-Ge-Se thin films has demonstrated
the devices potential use for reusable sensor applications.
The results of finite element simulations that incorporate
the ion transport equations and their reactions with electrons
and holes generated during exposures are shown to effectively
model the silver lateral photodoping in ChG film. The FE
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