Das elektrische Verhalten von AlSb

In previous papers the authors have reported on the semiconducting character of intermetallic compounds as CdSb. Here they describe similar experiments on AlSb which should be a semiconductor as saturated chemical compound. The present measurements confirm the semiconducting mechanism of AlSb also in the extrinsic range near room temperature, i.e. a decrease of resistivity with increasing temperature. The accuracy of these measurements and the purity of the AslSb-samples makes it possible to find below the intrinsic range two other activation energies of 0,53 and 0,08 eV, which were unknown hitherto. The positive sign of the thermoeletric force and of the rectifying curve prove that AlSb is a p-type conductor; perhaps the hole conduction is caused in analogy to CdSb by an impurity content of 0,01% Pb in the purest Sb-samples now available. Rectifying characteristics are measured for both low and high resistivity specimens, depending on different hole concentration. The authors could increase the barrier voltages from about 5 till 12 volts to more than 300 volts. The maximal rectifying ratio obtained is greater than 1:10^4. Specimens with high back voltages show small forward currents and vice versa. The metallurgical process and the corrosion of AlSb-samples observed but not overcome by Tammann and Rühenbeck are discussed in detail. The present authors observed precipitations of metallic Al on the grain boundaries and supposed that the corrosion by water vapor is starting from these Al-spots and is proceeding by an autocalalytic process. Infact, the corrosion velocity could be lowered by some orders of magnitude by avoiding or removing such precipitations of metallic Al

Neue Versuche zur Deutung der Feinwanderung in elektrischen Abhebekontakten

The well known bridge transfer ("Feinwanderung") - occurring even in non-arcing electric breaking contacts - is caused by the formation of bridges of molten metal between the separating electrodes. The hottest cross-section of the bridge seems nearly always to be displaced to the anode; the repeated rupture of such asymmetrical bridges forms a crater in the anode and a cone on the cathode. Only Pt contacts show a change of the direction of the transfer with increasing current. The inversion current strength can be shifted by changing the length and diameter of contacts; thus one can make contacts which are free of disturbances by transfer when used with currents between 10-20 amperes. The temperature asymmetry of the liquid bridge was explained by the superposition of the Thomson- and Peltiereffects over the Joulean heat. These effects have not been measured up to now but we have computed them approximately from the Thomson formulae using the measured Seebeck-effects in the case of Zn and Bi. The observed "positive" direction of material transfer (anode -> cathode) can not be satisfactorily explained by this theory. A supposition about the possible influence of the second Benedicks-effect was quite surprisingly confirmed in discussions with M. Kohler, who had formerly proved that this thermoelectric effect between identical electrodes is caused by their adsorbed gas layers. Thus the electron tunnelling through the potential wall of the contact space preheats the anode by its kinetic energy and supports a positive sign of bridge transfer. Experiments to avoid bridge transfer by use of higher melting anodes failed to be 100% successful; but the reduction of the work function of the cathode by oxidation diminishes the kinetic energy of the tunnelling electrons and seems to be successful in Au alloy contacts

Über die Halbleitereigenschaften intermetallischer Verbindungen (CdSb)

The well known stoichiometric intermetallic compounds of binary systems, as f.i. Au-Cu, show minima of electrical resistivity connected with their high crystallographic order. Such compounds reach approximately the resistivity of the pure components. In contradiction to these older statements the authors report about new experiments with other binary alloys, f.ex. Cd-Sb which show a sharp increase of resistivity by 4 to 5 orders of magnitude when stoichiometric composition is being reached. The new measurements of the temperature dependence of resistivity between 10° to 700° abs. prove in accordance with the Halleffect, the magnetic increase of resistance, the thermoelectric force and the rectifying properties that these intermetallic compounds behave as veritable intrinsic resp. extrinsic semiconductors. Pure stoichiometric CdSb can reach [rho]293°=2,4 Ohm x cm. A theoretical explanation of these experimental statements is given in terms of the electron theory of metals. The authors point out how the CdSb with its known rhombic crystal structure becomes semiconductive by completion of the seventh Brillouinzone. In conclusion the authors discuss the possibilities of technical use of such intermetallic semiconducting compounds instead of Ge and Si in diodes or transistors

Weglängenprobleme der Elektronen in Metallen und Halbleitern

In general the electrical resistivity of metal specimens does not depend on their size. At low temperatures, however, the mean free path of the electrons can be comparable with the geometric dimensions of the specimens. In this paper the theory of K. Fuchs and R.B. Dingle is discussed in detail, and it is shown that there is a discrepancy between their formulae and the experimental results of van den Berg and hitherto unpublished own measurements for gold at liquid helium temperatures. On the assumption of Rutherford-scattering in a semiconductor one can see that in first approximation the mechanism of electron scattering has only little influence on the formulae derived by Fuchs for thin films. In agreement with similar observations on the anomalous skin-effect the authors propose to explain· the discrepancy by the increase of residual resistivity with cold working of the surface layer and therefore by the enlargement of the effective surface-area. As to thin wires the assumption of a "surface-resistivity" yields some approximated results in good agreement with those of Dingle. In conclusion, the authors give a report of the above discussed resistivity measurements on cylindrical specimens of Mylius-gold, perhaps the purest metal ever obtained

Verfeinerte Theorie der elektrothermischen Kälteerzeugung

Forty years ago E. Altenkirch had developed a theory concerning the use of the electrothermic Peltier effect for refrigerating purposes. This theory is too much simplified in comparison with the practical difficulties and the present authors give a more detailed calculation here. First they consider the influence of non cylindric forms of the thermoelements. Secondly the new calculations demonstrate the great influence even of small contact resistances on the maximal temperature diminuition and efficiency of electrothermic cooling plants. In conclusion the authors discuss the diminuition of the practical chances of the electrothermic cooling method from the standpoint of the new detailed theory