The capture of hot electrons by Au-and Au2-centres in germanium at 20 K

The time constants associated with the capture of hot electrons by gold centres in germanium at 20 °K have been measured as a function of electric field in specimens containing N Sb antimony and N Au gold atoms per cubic centimetre where N Au < N Sb < 2 N Au . Capture by Au 2- centres dominated at high fields. The capture rate per Au 2- centre at high fields was a factor 2 × 10 3 higher than the zero-field value, which confirmed previous results. A direct measurement of the capture rate per Au - centre at high fields was not possible and the value had to be estimated from current density measurements. This estimate gave an increase of capture rate per Au - centre over the zero-field value by a factor of about 20. The zero-field value of the capture rate per Au - centre at 20 °K was found to be 3 × 10 -12 cm 3 sec -1 . The hot electron results for both Au - and Au 2- centres were conveniently summarized by assuming an energy dependence of the capture rate α( E ) of the form α( E ) = AS ( E ) E p +½ , where A was temperature dependent and S ( E ) was the coulombic tunnelling factor for the transverse effective mass. For Au 2- centres p = -0.8 ± 0 1. For Au - centres p = -1.0 ± 0.1 from the 77 °K results, and this was adequate to explain the 20 °K results. For low electron energies the approximate formula of Bonch-Bruevitch for the zero-field capture rate, α = A exp{-( T 0 / T ) 1/3 }, was applicable, with T 0 = 1.34 × 10 4 °K for Au - centres and T 0 = 5.35 × 10 4 °K for Au 2- centres.