Characterization of impact ionization rate in silicon over four orders of magnitude

Accurate experimental data on impact ionization rate in silicon have recently become achievable because of UV-resistant induced junction photodiodes, which eliminate the charge-carrier recombination losses in the bulk, leaving only a small contribution from surface recombination centers to be corrected in spectral responsivity data. We measured the spectral responsivity of trap detectors built from such photodiodes using low-uncertainty cryogenic radiometer setups, thereby gaining highly accurate responsivity data over the wavelength range of 250–476 nm. Reflectance correction of a three-element trap detector was measured at laser wavelengths of 325 and 405 nm and then modeled with low uncertainty between 250 and 410 nm. A minor correction due to recombination loss of electrons and holes was modeled over the spectral range of 250–476 nm. When combined, these measurements and models enabled us to achieve unprecedentedly accurate data on impact ionization. The results thus obtained are in good agreement with the theoretical impact ionization rate by Kamakura et al. [J. Appl. Phys. 75, 3500 (1994)] over four orders of magnitude, characterized by a power-law exponent of 4.6 describing the dependence on the energy of incident photons. These results have significance in developing silicon photodiode detectors with predictable spectral responsivity for photons or other particles and also in electronics when modeling electron tunneling in metal-oxide-semiconductor transistors.