An diffusiven MOS-Strukturen auf p-Typ InAs wurde der Einfluß der Ladungsträgerdichte auf die Spinaufspaltung untersucht. In den Shubnikov-de Haas Oszillationen zeigt sich ein deutliches Schwebungsmuster. Der Rashba-Parameter α wird für die ersten beiden Subbänder bestimmt, wobei die Nichtparabolizität berücksichtigt wird. Der Rashba-Parameter steigt bei beiden stark an und sättigt bei α = 3 x 10-11 eVm bzw. α = 2 x 10-11 eVm. In der differentiellen Kennlinie dU/dVg ist eine Reihe ausgeprägter Peaks zu beobachten, die als Transport-Resonanzen interpretiert werden können.
In the present thesis Josephson field-effect transistors (JoFETs) with superconducting Nb contacts on p-type InAs single crystals are studied. The width of the junctions is 50 μm, their channel length varies between 105 and 230 nm. The carrier density in the natural inversion layer on p-type InAs can be changed via the gate voltage from total depletion to ns= 3 x 1012 cm-2 . The normal resistance is comparable with the Sharvin resistance and does not depend notably on the channel length, indicating the quasi ballistic transport. The effective transmission for the single interface estimated from the ratio of normal and Sharvin resistance increases with electron density and saturates at DSN = 0.85. A very weak oscillation is observed in the dependence of the critical current on the electron density. The peak positions are described quite well by the ballistic Brouwer and Beenakker model. The temperature characteristic agrees very well with this model. However, a larger channel length than the electrode spacing has to be used. The coherence length is estimated from the exponential length dependence of the critical current. The calculated coherence length is about twice as large. The current-phase relationship is measured in collaboration with Il'ichev (IPHT, Jena). A significant deviation from the sinusoidal behavior is observed, which can be described by the Brouwer and Beenakker model. The current distribution is retrieved from the magnetic field dependence of the critical current. The subharmonic energy-gap structure (SGS) is observed in the differential resistance up to the order n = 6. The SGS can be described by the SNININS model considered by Samuelsson (Chalmers University, Sweden). The peak position and the excess current depend on the channel length, which is not fully understood yet. At higher electron densities the current voltage characteristics are hysteretic. Only at the highest carrier density the I-V characteristic can be described by the RCSJ model.
The dependence of the spin splitting on electron density is studied by magnetoresistance of diffusive MOS structures on p-type InAs. A clear beating pattern is observed in the Shubnikov-de Haas oscillations. The Rashba parameter α of the first two subbands are calculated taking subband nonparabolicity into account. The Rashba parameter of the ground and the first excited subband increase strongly and saturate at α = 3 x 10-11 eVm and α = 2 x 10-11 eVm, respectively. In the differential characteristics dV/dVg of the JoFETs a rich series of strong peaks is observed, which could be interpreted as transport resonaces.