Effect of Irradiation on the Hole Lifetime of N-Type Germanium

Abstract

The minority carrier lifetime of germanium is very sensitive to certain types of irradiation. The results of irradiating large single crystal samples of n-type germanium with fast neutrons and Co60 gamma rays are presented and discussed. Lifetime was determined from a transient measurement of the decay of holes following an injection pulse. The effect of initial carrier concentration has been considered. According to the James-Lark-Horovitz model, four energy levels are introduced by irradiation into the forbidden band of germanium, one above and three below the center of the band. Using the upper level, a one level recombination model serves to explain the experimental results approximately. The determination of the recombination level agrees well with the position of the first ionization level of the interstitial produced by irradiation at about 0.2 ev below the conduction band. On this basis, the effective cross section for hole capture by these recombination centers is found to be about 4×10−15 cm2 and 5×10−16 cm2 for neutron and gamma-irradiated germanium, respectively. A lower level may also be responsible for the recombination process.

Carrier recombination and trapping processes in irradiated germanium

“…Fortunately, the trqping centres present in arsenic-doped specimens do not occur in antimony-doped specimens. However, at low temperatures, trapping centres become important even in low-resistivity (2)(3)(4) ohm cm) antimony-doped samples. (In high-resistivity->lO ohm cm-antimony-doped material, trapping effects are important at relatively high temperatures.…”

The Effects of High Energy Radiation on Failure Mechanisms in Semiconductors Devices

“…It is known that minority carrier lifetime is the most sensitive indicator of the production of atomic displacements. From the work of Curtis, et al (4) it has been established that the threshold for an observable change in minority carrier lifetime in n-type germanium under Co00 irradiation occurs at an integrated flux of about 3-5 X 1014 photons/cm2. The corresponding value for silicon does not appear to be known for gamma radiation.…”