Electron-Irradiation Effects in Silicon at Liquid-Helium Temperatures Using ac Hopping Conductivity

Abstract

Changes in ac hopping conductivity with electron irradiation have been measured in n-type silicon, p-type silicon, and high purity silicon. • Irradiations were carried out at both 4.8 and 1.6 degrees kelvin, with measurements made at reference temperatures of 4.2 and 1.3 degrees kelvin, respectively. In the p-type crystals, the changes in ac hopping conductivity depended strongly on the concentration of chemical acceptors, indicating a / /. concentration dependence on impurities in the defect production rate. The production rates at 1.6'K were generally very similar to those for a 4.8'K ' irradiation. No significant thermal annealing stages below room temperature were observed in any of the crystals. A small amount of "reverse annealing, " i.e. an increase in ac hopping conductivity was'observed below 30'K. No radiation annealing effects due to a beam of either .500 Mev or .350 Mev electrons were observed, either at 4.5'K or at 1.45°K.

Evidence of Defect Levels in P and N-Type Electron Irradiated Si

“…The defects introduced into Si specimens are monitored by bridge measurements of capacitance C and loss factor D formed by the evaporation of gold electrodes on opposite faces of a thin slab of the specimen which had a thickness of Z40um. Following McKeighen and Koehler [3,4] we obtain for reasonably low D the a.c. conductivity oac =6,395 f'Dwhere f'is the frequency of the bridge oscilator. The results of the measurements between 4.2K and ~100'.K or above are attributed in two different temperatur.e regimes to (a) a silicondielectric capacitor with loss arising from a.c. hopping,for T<20K and (b) two surface-barrier layer capacitors connected in series by band conduction in the bulk semiconductor at higher temperatures,T>20K.…”

“…The n-type pulled specimens had a phosphorus concentration. of 3xl0 4 cm'. The defects introduced into Si specimens are monitored by bridge measurements of capacitance C and loss factor D formed by the evaporation of gold electrodes on opposite faces of a thin slab of the specimen which had a thickness of Z40um.…”

Frequency Dependence of Hopping Conductance in Electron Irradiated Semiconductors

“…In doped semiconductors it has been observed [1,2,3] that irradiation-induced defects can produce localized states at low temperatures. During conduction the charged carriers are presumed to migrate between localized centers and the ac conductivity exhibits a frequency dependence of the form s oc ws with s _< 1.…”

Effects of electron irradiation on p-type germanium at liquid helium temperatures using ac hopping conductivity

“…If we assume that -I = ·7 throughout the irradiation, then at cp = 9.8 x 10 2 14 e/cm , the · donor concentration produced by irradiation would be 6.9. x 10 -3 4 cm . .Adding to this the upper limit for chemical donors present, we have a total of 1.4 X 10 cm .…”

“…4 Note that the production rate curves at 10 Hz have an "s" shape between 13 2 13 2 3.7 x 10 e/cm and 18.5 x 10 e/cm . The production rate reaches a maxi-14 ' 2 mum near 1 X 10 e/cm .…”