Optical beam-induced current in planar two-dimensional n–p–n devices

We have fabricated two-dimensional lateral n–p–n devices from a p-doped pseudomorphic GaAs/In0.11Ga0.89As/Al0.33Ga0.67As heterostructure employing Si compensation doping by focused ion-beam implantation. Optical beam-induced current (OBIC) measurements on such devices show that the two p–n junctions produce a signal of opposite polarity. Between the junctions, the signal varies linearly with the position of the laser spot, reaching zero approximately in the middle of the p-region. A qualitative understanding of this behavior is obtained by adding the OBIC traces for two individual junctions.