Highly NO2 sensitive pseudo Schottky barrier diodes on p-type InP with improved electrical characteristics

We have studied the NO2 sensing properties of p-type InP-based Schottky barrier diodes. In the light of theoretical considerations concerning metal/semiconductor contacts, we describe a fabrication process which leads to electrically improved Schottky contacts, with high barrier heights and low reverse leakage currents. This simple process involves the use of a thin shallow n-type InP layer between the contact metallization and the p-type bulk InP. This inversion layer is created by diffusion of n-type doping species present in the contact metallization during controlled annealing sequences. Calculations from classical J–V characterizations indicate barrier height elevations of 0.1–0.15 eV in good agreement with C–V measurements. Submitted to nitrogen dioxide flow, the diodes show a drastic increase of their reverse current under a fixed bias. This effect can be attributed to the reduction of the barrier height of the Schottky contact arising from electronic exchange between the NO2 molecules and the thin n-InP inter facial layer. Studies on several diodes show that they exhibit high sensitivities as well as rather short response times towards nitrogen dioxide, but that aging effects occur after several uses.