Direct determination of the Andreev reflection probability by means of point contact spectroscopy

In this letter, we describe a technique for determining the Andreev reflection probability of electrons impinging on a semiconductor–superconductor interface. A two-dimensional electron gas (2DEG) in an InGaAs/InP heterostructure is linked to a niobium superconductor. A point contact in the 2DEG emits ballistic electrons and detects the reflected carriers. The vast majority of the detected carriers are retroreflected holes because of our specific sample setup. We have found an Andreev reflection probability of up to 20%. The experimental results are compared with the predictions of two theoretical models.