The Use of Lasers to Simulate Radiation-Induced Transients in Semiconductor Devices and Circuits

High levels of ionization can be created in semiconductor devices by irradiating the devices with short pulses of light. If the light frequency is properly selected, sufficient and relatively uniform energy deposition is obtained which results in ionization rates orders of magnitude above those presently attainable from other sources. It is shown that a pulsed-infrared laser can be used as a relatively simple, inexpensive, and effective means of simulating the effects caused by intense gamma ray sources on semiconductors. Experimental results are presented which show that the transients induced in various types of silicon transistors when exposed to a neodymium laser are essentially identical to those obtained when the transistors are exposed to pulses of 25 MeV electrons from a linear accelerator and 600 kvp flash X-ray machine. Good agreement exists between the peak photocurrents obtained using these three sources over a dose range of 10-1 to 104 rads. Calculations based upon published as well as experimental absorption data for silicon show that energy deposition is very nearly uniform for the wavelength of light obtained from neodymium lasers (1. 06 microns - 1. 17 ev photons). By defocusing the laser light beam, dose rates in excess of 10R12 rads/ sec (silicon) in 40 x 1-99 seconds over an area of 50 cm2 have been obtained from a Q-switched 10 megawatt neodymium laser. This greatly exceeds the maximum dose rate of 1011< rads/ sec silicon) over approximately 1 c2m attainable from linear accelerators.