QUANTUM POINT CONTACTS ON INGAAS INP HETEROSTRUCTURES/

For the first time we have observed quantized conductance in a split g ate quantum point contact prepared in a strained In0.77Ga0.23As/InP tw o-dimensional electron gas (2DEG). Although quantization effects in ga ted two-dimensional semiconductor structures are theoretically well kn own and proven in various experiments on AlGaAs/GaAs and also on In0.0 4Ga0.96As/GaAs, no quantum point contact has been presented in the InG aAs/InP material with an indium fraction as high as 77% so far. The ma jor problem is the comparatively low Schottky barrier of the InGaAs (p hi(B) x 0.2 eV) making leakage-free gate structures difficult to obtai n. Nevertheless this heterostructure-especially with the highest possi ble indium content-has remarkable properties concerning quantum interf erence devices and semiconductor/superconductor hybrid devices because of its large phase coherence length and the small depletion zone, res pectively. In order to produce leakage-free split gate point contacts the samples were covered with an insulating SiO2 layer prior to metal deposition. The gate geometry was defined by electron-beam lithography . In this paper we present first measurements of a point contact on an In0.77Ga0.23As/InP 2DEG clearly showing quantized conductance. (C) 19 98 Academic Press Limited.