The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated ...with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.
We have processed large-area strip sensors on silicon wafers grown by the magnetic Czochralski (MCZ) method. The n-type MCZ silicon wafers manufactured by Okmetic Oyj have nominal resistivity of ...900Ωcm and oxygen concentration of less than 10ppma. The Photoconductive Decay (PCD) measurements, current–voltage measurements and capacitance–voltage measurements were made to characterise the samples. The leakage current of 3μA at 900V bias voltage was measured on the 32.5cm2 detector. Detector depletion took place at about 420V. According to PCD measurements, process induced contamination was effectively bound and neutralised by the oxygen present in Czochralski silicon. During the sample processing, the silicon resistivity increased in spite of the lack of specific donor-killing heat treatment.
We have processed full-size strip detectors on Czochralski grown silicon wafers with resistivity of about 1.2
k
Ω
cm. Wafers grown with Czochralski method intrinsically contain high concentrations of ...oxygen, and thus have potential for high radiation tolerance. Detectors and test diodes were irradiated with 10
MeV protons. The 1-MeV neutron equivalent irradiation doses were 1.6×10
14 and 8.5×10
13
cm
−2 for detectors, and up to 5.0×10
14
cm
−3 for test diodes. After irradiations, depletion voltages and leakage currents were measured. Czochralski silicon devices proved to be significantly more radiation hard than the reference devices made on traditional detector materials.
We have processed pin-diodes on Czochralski silicon (Cz-Si), standard float zone silicon (Fz-Si), and diffusion oxygenated float zone silicon (DOF) and irradiated them with 10- and 20-MeV protons. ...Evolutions of depletion voltage and leakage current as a function of irradiation dose were measured. Space charge sign inversion (SCSI) was investigated by an annealing study and verified by transient current technique (TCT). Czochralski silicon was found to be significantly more radiation hard than the other materials.
We processed pin-diodes on Czochralski silicon (Cz-Si), standard Float Zone silicon (Fz-Si) and oxygenated Fz-Si. The diodes were irradiated with 10, 20, and
30
MeV
protons. Depletion voltages and ...leakage currents were measured as a function of the irradiation dose. Additionally, the samples were characterized by TCT and DLTS methods. The high-resistivity Cz-Si was found to be more radiation hard than the other studied materials.
A search for new dielectron-mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7 fb(-1) is presented. No significant excess over the ...expected standard model prediction is observed. In this data set, an event with the highest dielectron mass ever observed (960 GeV/c(2)) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4 fb(-1) diphoton analysis, the RS-graviton lower-mass limit for the coupling k/M¯(Pl)=0.1 is 1058 GeV/c(2), making it the strongest limit to date.