Search

The radiation response of a 0.25 um silicon-on-sapphire CMOS technology is characterized at the transistor and circuit levels utilizing both standard and enclosed layout devices. Device-level characterization showed threshold voltage change of less than 170 mV and leakage current change of less than 1 nA for individual nMOSFET and pMOSFET devices at a total dose of 100 krad(SiO2). The increase in power supply current at the circuit level was less than 5%, consistent with the small change in off-state transistor leakage current. The technology exhibits good characteristics for use in the electronics of the ATLAS experiment at the Large Hadron Collider., Comment: 5 pages, 5 figures

We investigate the influence of X-ray and gamma-ray irradiation on the photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs) immobilized in porous silica (PSiO2) scaffolds. The highly luminescent QD-PSiO2 thin films allow for straightforward monitoring of the optical properties of the QDs through continuous wave and time-resolved photoluminescence spectroscopy. The PSiO2 host matrix itself does not modify the QD properties. X-ray irradiation of the QD-PSiO2 films in air leads to an exponential decrease in QD emission intensity, an exponential blue-shift in peak emission energy, and substantially faster exciton decay rates with increasing exposure doses from 2.2 Mrad(SiO2) to 6.6 Mrad(SiO2). Gamma-ray irradiation of a QD-PSiO2 thin film at a total exposure dose of 700 krad(SiO2) in a nitrogen environment results in over 80% QD photodarkening but no concurrent blue-shift in peak emission energy due to a lack of photo-oxidative effects. Near-complete and partial reversal of irradiation-induced photodarkening was demonstrated on X-ray and gamma-ray irradiated samples, respectively, through the use of a surface re-passivating solution, suggesting that there are different contributing mechanisms responsible for photodarkening under different irradiation energies. This work contributes to improving the reliability and robustness of QD based heterogeneous devices that are exposed to high risk, high energy environments with the possibility of also developing QD-based large area, low-cost, re-useable, and flexible optical dosimeters.

Using a combination of continuous wave and time-resolved spectroscopy, we study the effects of interfacial conditions on the radiative lifetimes and photoluminescence intensities of colloidal CdTe/CdS quantum dots (QDs) embedded in a three-dimensional nanostructured silicon (NSi) matrix. The NSi matrix was thermally oxidized under different conditions to change the interfacial oxide thickness. QDs embedded in a NSi matrix with ~0.5 nm of interfacial oxide exhibited reduced photoluminescence intensity and nearly five times shorter radiative lifetimes (~16 ns) compared to QDs immobilized within completely oxidized, nanostructured silica (NSiO2) frameworks (~78 ns). Optical absorption by the sub-nm oxidized NSi matrix partially lowers QD emission intensities while non-radiative carrier recombination and phonon assisted transitions influenced by defect sites within the oxide and NSi are believed to be the primary factors limiting the QD exciton lifetimes in the heterostructures.