摘要:

An exact calculation of the acoustic‐phonon‐assisted jump rate has been carried out. It is found that although the Miller and Abrahams jump‐rate expression constitutes an adequate approximation to the jump rate in the highly restrictive situation to which they have applied it (impurity conduction between very shallow impurity states at helium temperatures), their expression does not generally provide even a qualitatively correct representation of the jump rate. Specifically, multiphonon transitions will, in many instances, provide the dominant contribution to the jump rate even as the temperature approaches absolute zero. The multiphonon jump rate will manifest a non‐activated temperature‐dependence, resembling aexp[ −(T0/T)1/4]behavior, between helium temperatures and some fraction of the Debye temperature. In fact, the present study suggests that the non‐activated temperature dependence of the electrical conductivity, which is observed in a number of non‐ crystalline solids in this temperature range, may arise, in the main, from the jump‐rate itself rather than from the percolation aspects of hopping conduction in disordered materials.

ISSN:0094-243X    

DOI:10.1063/1.2945981

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Electron tunneling throughAl ‐ Al2O3 ‐ Ge ‐ Mtunnel junctions was studied between 300 ‐ 1.2 K for different thicknesses t of the amorphous Ge layer. Depending on temperature T and thickness t two competing processes are observed: (i) fort < ddirect tunneling to the metallic top electrode M, which was Al or Sn, and (ii) fort > dtunneling to an intermediate localized state in a‐Ge. The critical thickness d increases linearly with T−1/4. Using the variable range tunneling model of Sauvageet al.and the slope of this curve one obtains∝−1 = 8 Åfor the decay parameter of the localized state wavefunction. Effects of alloying at the Ge‐M interface are seen in the tunnel characteristics when Al and M are superconducting. Magnetic fields up to 65 KG had no effect on the very sharp minimum of the tunneling conductance at zero bias and 4.2 K. Different models leading to a tunnel characteristic which is symmetric with respect to bias reversal are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2945982

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Electron tunneling into various amorphous semiconductors (Ge, Ge alloys, Si and InSb) resulted in qualitatively similar data: The tunneling conductance increases smoothly and symmetrically with bias voltage and exhibits the same temperature dependence as the conductance of the amorphous semiconductors, which suggests tunneling into localized states. However, the number of localized states deduced from the tunneling experiments is generally higher than the value obtained from conductivity measurements. These tunneling experiments seem to indicate that deep level impurities increase the number of localized states within the mobility gap, leaving the Fermi level at the center of the pseudo‐gap.

ISSN:0094-243X    

DOI:10.1063/1.2945983

出版商:AIP    

年代:1974

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2945985

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Junctions between amorphous and crystalline semiconductors are investigated theoretically. A new type of junction is formed if the dominant conduction mechanism in the amorphous semiconductor is hopping near the Fermi level. In this case the junctions are expected to exhibit qualitatively different behavior than conventional semiconductor‐ semiconductor or semiconductor‐metal junctions. Current and capacitance as a function of applied voltage are calculated for a simple model. We point out how these measurements can give information about the position of the Fermi‐level and the density of states in the amorphous material.

ISSN:0094-243X    

DOI:10.1063/1.2945986

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The origin of magnetoconductivity in tetrahedral amorphous films is not yet understood. Nevertheless, this property offers the possibility to obtain additional information on the ac conduction and on the transport in high electric fields. Similar to the alternating current j(&ohgr;) also &Dgr;j(&ohgr;) due to the magnetic field increases with frequency &ohgr;. The increase of &Dgr;j(&ohgr;) is, however, smaller than that of j(&ohgr;) and sets in at higher frequencies. In high dc electric fields F the relative change of conductivity &Dgr;&sgr;(F)/&sgr;(F) is almost independent of F although &sgr;(F) varies by orders of magnitude. These results indicate that neither the ac conductivity nor the high field dc conductivity in amorphous Ge can be due to mechanisms which are basically different from the charge carrier motion in low direct electric fields.

ISSN:0094-243X    

DOI:10.1063/1.2945987

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Temperature dependence (77K‐room temperature) of evaporated germanium films and their annealed samples is investigated in the frequency range70×103∼ 60×106Hz. A transition from an &ohgr;sdependence to essentially dc behavior is observed, depending on temperature. Annealing at 250 °C decreases the conductivity and shifts the transition to a lower frequency. These behaviors are shown to be explained by the stochastic transport theory of impurity hopping conduction developed recently by Scher and Lax.

ISSN:0094-243X    

DOI:10.1063/1.2945988

出版商:AIP    

年代:1974

数据来源: AIP