Low‐Temperature Conductivity and Mobility in Semiconductors

Abstract

The influence of the free-carrier concentration upon the low-temperature conductivity is investigated. The variation may be due either to temperature effects (under thermal equilibrium conditions) or to the influence of a n electric field (under non-equilibrium conditions). The effect considered is significant up to the temperature a t which the free-carrier concentration saturates and for the thermal electrons a t low compensation ratio. Then the low-temperature conductivity considered as a function of the temperature and electric field strength acquires a sharp minimum while the maximum of the conductivity becomes higher and shifts towards lower temperatures and snidler fields. The comparison with experimental data shows quite a good agreement between the csperimental and theoretical curves. This suggests that the mobility minimum which for rather a long time wiis being observed and not understood is due t o the effects discussed above. The cascade electron capture cross-scction of the ionized donors is re-calculated using the sticking probability corrected by Abakomov and Yassevich. The result is used to ralculate the capture coefficicnt in a strong electric field.Es wird der EinflnB der Konzentration frcier Trager auf die Tieftempcraturlcitfiihigkeit untersurht. Die Bndcrnng k m n entweder durch Temperatnreffekte (untci thermischen Gleichgemiehtsbcdingtingcn) oder durch den EinfluB eines elektrischen Feldcs (unter Piichtgleicligewiclitsbedingitngen) hrrvorgernfen werden. Der betrachtete Effekt ist bis zu der Temperatnr signifikant, bei der sich die freie Ladnngstragerkonzentration siittigt und ftir thermische Elektronen bt.i kleincm KompensationsvcrhLItnis. Dann erreicht die Tieftemperaturleitf%higkcit als Funktion der Temperatnr und elektrischen Feldstarke ein scharfes Minimum wahrend das Leitfaliigkeitsmaximum hoher wird und sich zu tieferen Temperaturen und kleineren Feldern vcrsehiebt. Ein Vergleich rnit experimentellen Wertcn zeigt eine ziemlich gute Ubereinstimmung zwischen experimentellen und theoretischen Kurven. Dies weist darauf hin, dal? das Beweglichkeituminimum, das schon seit langerer Zeit beobachtet und nicht verstanden wurde. durch die oben diskutierten Effekte hervorgerufen wird. Elcktronenkaskadeneinfangquerschnitte der ionisierten Donatoren 1 1 erden erneut berechnet, wobei die durch Abakomov und Yassevich korrigierte Anhaftwahrscheinlichkeit benutzt wird. Das Ergebnis wird weiter benutzt, um den Einfangkoeffizienten im starken elektrischen Feld zu bereehnen.

Impurity breakdown under transverse runaway of hot electrons

“…where A I ða IB Þ is the impact ionization coefficient which is calculated using the differential crosssection obtained by Drawin [6], and B T ða IB Þ is the recombination coefficient which is calculated using the effective capture cross-section obtained in [7] by the corrected Lax theory [8]. It should be emphasized that the a IB is defined from (10) for each compensation degree and magnetic field, and using Eq.…”

Temperature Dependence of Electron Mobility in Doped n-Ge

“…5, it was shown that at low temperatures in doped semiconductors with low compensation degrees (C = N A /N D < C 1 ) charge carriers mobility µ i determined by ion impurity scattering first reaches its maximum with increasing temperature (T ), then drops to a minimum and increases again according to the T +3/2 law. Such a non-monotonous mobility behavior at low C values is determined by an increase in the number of energetic free electrons, a decrease in the impurity potential and by an increase in the concentration of scattering ionized impurity centers.…”

“…5 Tin contacts were welded to the samples at 400 • C in hydrogen atmosphere. Copper wires were soldered to the above-mentioned contacts and helped to fix the sample on a teflon substrate.…”