In this work, the effects of 60Co γ-ray irradiation on high resistivity p-type diodes have been investigated. The diodes were exposed to dose values of 0.1, 0.2, 1, and 2MGy. Both macroscopic (I–V, ...C–V) and microscopic investigations, by means of Thermally Stimulated Current (TSC) and Deep Level Transient Spectroscopy (DLTS) techniques, were conducted to characterize the radiation-induced changes. The investigated diodes were manufactured on high resistivity p-type Float Zone (FZ) silicon and were further classified into two types based on the isolation technique between the pad and guard ring: p-stop and p-spray. After irradiation, the macroscopic results of current–voltage and capacitance–voltage measurements were obtained and compared with existing literature data. Additionally, the microscopic measurements focused on the development of the concentration of different radiation-induced defects, including the Boron interstitial-Oxygen interstitial (BiOi) complex, the Carbon interstitial-Oxygen interstitial (CiOi) defect, the H40K, and the so-called IP∗.
To investigate the thermal stability of induced defects in the bulk, isochronal annealing studies were performed in the temperature range of 100°C to 300°C. These annealing processes were carried out on diodes irradiated with doses of 1 and 2MGy. Furthermore, in order to investigate the unexpected results observed in the C–V measurements after irradiation with high dose values, the surface conductance between the pad and guard ring was measured as a function of both dose and annealing temperature.
In this work, the thermally stimulated current (TSC) technique has been used to investigate the properties of the radiation-induced interstitial boron and interstitial oxygen defect complex by 23-GeV ...(<inline-formula> <tex-math notation="LaTeX">E_{\text {kin}} </tex-math></inline-formula>) protons, including activation energy, defect concentration, as well as the annealing behavior. At first isothermal annealing (at 80 °C for 0-180 min) followed by isochronal annealing (for 15 min between 100 °C and 190 °C in steps of 10 °C), studies had been performed in order to get information about the thermal stability of the interstitial boron and interstitial oxygen defect in 50-<inline-formula> <tex-math notation="LaTeX">\Omega </tex-math></inline-formula>cm material after irradiation with 23-GeV protons to a fluence of <inline-formula> <tex-math notation="LaTeX">6.91\times 10^{13}\,\,{\text {p/cm}^{2}} </tex-math></inline-formula>. The results are presented and discussed. Furthermore, the extracted data from TSC measurements are compared with the macroscopic properties derived from current-voltage and capacitance-voltage characteristics. In addition, the introduction rate of interstitial boron and interstitial oxygen defect as a function of the initial doping concentration was determined by exposing diodes with different resistivities (10, 50, 250, and 2 <inline-formula> <tex-math notation="LaTeX">\text{k}\Omega </tex-math></inline-formula>cm) to 23-GeV protons. These results are compared with data from TSC and deep-level transient spectroscopy measurements achieved by the team of the CERN-RD50 "Acceptor removal project."
Charge multiplication (CM) in p+n epitaxial silicon pad diodes of 75, 100 and 150μm thickness at high voltages after proton irradiation with 1MeV neutron equivalent fluences in the order of 1016cm−2 ...was studied as an option to overcome the strong trapping of charge carriers in the innermost tracking region of future Super-LHC detectors. Charge collection efficiency (CCE) measurements using the Transient Current Technique (TCT) with radiation of different penetration (670, 830, 1060nm laser light and α-particles with optional absorbers) were used to locate the CM region close to the p+-implantation. The dependence of CM on material, thickness of the epitaxial layer, annealing and temperature was studied. The collected charge in the CM regime was found to be proportional to the deposited charge, uniform over the diode area and stable over a period of several days. Randomly occurring micro-discharges at high voltages turned out to be the largest challenge for operation of the diodes in the CM regime. Although at high voltages an increase of the TCT baseline noise was observed, the signal-to-noise ratio was found to improve due to CM for laser light. Possible effects on the charge spectra measured with laser light due to statistical fluctuations in the CM process were not observed. In contrast, the relative width of the spectra increased in the case of α-particles, probably due to varying charge deposited in the CM region.
An overview of the radiation-damage-induced problems connected with the application of silicon particle detectors in future high-energy physics experiments is given. Problems arising from the ...expected hadron fluences are summarized and the use of the nonionizing energy loss for normalization of bulk damage is explained. The present knowledge on the deterioration effects caused by irradiation is described leading to an appropriate modeling. Examples are given for a correlation between the change in the macroscopic performance parameters and effects to be seen on the microscopic level by defect analysis. Finally possible ways are out-lined for improving the radiation tolerance of silicon detectors either by operational conditions, process technology or defect engineering.
Proton-irradiated epitaxial pad diodes of 75, 100 and
150
μ
m
thickness and different oxygen concentrations were studied as an option to withstand the extreme radiation environment in the innermost ...tracking region of the future Super-LHC. With a new TCT setup using red laser light, time-resolved current signals could be measured in
150
μ
m
thin diodes. Thus the charge correction method (CCM) could be used to extract the effective trapping times. Similar results compared to previously investigated materials were obtained if the standard model of trapping is assumed, which is based on a constant trapping time at each fluence and neglects detrapping and charge multiplication. Charge collection efficiency (CCE) measured with 5.8
MeV
α
-particles
showed an increase for decreasing thickness, but no dependence on impurity concentration was seen. CCE simulations based on the effective trapping time constants determined with the CCM resulted in systematically lower values than the measurements. This is the case for the CCE of both
α
-particles
, red and infrared laser light. To account for this, possible modifications of the trapping model including voltage- or field-dependent trapping times will be discussed. Moreover, at high fluences and voltages anomalously high
CCE
>
1
was observed, which indicates charge multiplication effects.
The leakage current increase of silicon detectors irradiated with fast neutrons was measured in the fluence range from 10
11 to 10
15
cm
−2 for a wide range of different starting material. The oxygen ...concentration in the investigated silicon varied from 9×10
17
cm
−3 to below 2×10
14
cm
−3 and the carbon concentration from 2×10
16
cm
−3 to below 5×10
15
cm
−3. Furthermore the resistivity differed from 100
Ω
cm to 20
kΩ
cm for the used n-type and from 400
Ω
cm to 2
kΩ
cm for the p-type silicon. It is found that up to the highest fluence the current-related damage parameter alpha is almost independent of the initial resistivity and impurity concentration. After irradiation a universal annealing behavior for all material is observed which unmistakably indicates that the microscopic defects underlying the generation of leakage current are of intrinsic origin. Furthermore it is shown that the parameterization of the annealing behavior at an elevated temperature (here 60°C) provides an excellent tool for comparing the so-called hardness factors of different irradiation sources. As an example the hardness factors for the 24 GeV/
c CERN proton synchrotron and the TRIGA research reactor in Ljubljana were determined to be 0.51 and 0.90, respectively.
PDF
