Radiation Effects

Harsh radiation environments present unique reliability concerns for devices operating in a variety of fields such as avionics, space missions, and nuclear facilities.  As prolonged exposure to a radiation environment typically results in degradation of device performance, accurate characterization of the total dose of radiation delivered to devices is critical for environment modeling and mission design. Traditionally, scintillator crystals are used for measuring the accumulation of ionizing radiation, but alternatives such as quantum dots have been used in more novel devices. Drawing inspiration from biosensing applications, incorporation of quantum dots into porous silicon provides the potential for a high-density quantum dot sensor. Exposure of the quantum dots in the porous silicon matrix displays decreasing photoluminescence as radiation exposure increases demonstrates a potential metric that could be used for measuring accumulated radiation.

Highly focused pulsed laser systems are commonly used to inject charge into circuits to emulate high energy particles passing through a device. In most cases, sub-bandgap wavelength photons are used to deposit charge through nonlinear, multiphoton absorptive processes that spatially confine charge generation to only the focus of the laser. While pulsed laser testing is extensively used for qualitative measurements, development of first-principle simulation tools for nonlinear optical energy deposition is critical for correlating pulsed laser measurements with traditional radiation testing techniques. Adaption of a commercial FDTD solvers to incorporate nonlinear absorption as well as free carrier effects has allowed for the simulation of 3D distribution of deposited energy from a single laser pulse. Incorporation of these optical simulations into charge transport code allows for complete simulation of the pulsed laser testing technique: from laser pulse to electrical signal output.