Quantum point contacts on InGaAs/InP heterostructures

For the first time we have observed quantized conductance in a split gate quantum point contact prepared in a strained In_0.77Ga_0.23As/InP two-dimensional electron gas (2DEG). Although quantization effects in gated two-dimensional semiconductor structures are theoretically well known and proven in various experiments on AlGaAs/GaAs and also on In_0.04Ga_0.96As/GaAs, no quantum point contact has been presented in the InGaAs/InP material with an indium fraction as high as 77% so far. The major problem is the comparatively low Schottky barrier of the InGaAs (φ_B≈ 0.2 eV) making leakage-free gate structures difficult to obtain. Nevertheless this heterostructure—especially with the highest possible indium content—has remarkable properties concerning quantum interference devices and semiconductor/superconductor hybrid devices because of its large phase coherence length and the small depletion zone, respectively. In order to produce leakage-free split gate point contacts the samples were covered with an insulating SiO₂layer 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 In_0.77Ga_0.23As/InP 2DEG clearly showing quantized conductance.