Experimental determination of the Andreev reflection probability using ballistic point contact spectroscopy

In this article, we present an experimental technique to determine the Andr eev reflection probability-a quantity of central importance for superconduc tor/semiconductor-hybride structures. This is achieved with a point contact (PC) formed in a two-dimensional electron gas (2DEG) in front of a superco nductor/semiconductor (SN) interface. The PC in the InGaAs/InP heterostruct ure emits electrons towards the SN interface and detects the reflected carr iers. Due to the specific sample setup, the vast majority of the detected c arriers are retroreflected holes and the signal is a direct measurement of the Andreev reflection probability. A(E) is found to be up to 20% by measur ing the point contact conductance. The experimental results are compared wi th the predictions of two theoretical models. It is found that the Andreev reflection probability significantly differs from theoretical expectations. The main advantage of the presented technique is the direct way of measuri ng the Andreev reflection probability, independent of any model describing the SN interface. (C) 2001 Elsevier Science B.V. All rights reserved.