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 bar rier diodes. In the light of theoretical considerations concerning metal/se miconductor contacts, we describe a fabrication process which leads to elec trically improved Schottky contacts, with high barrier heights and low reve rse leakage currents. This simple process involves the use of a thin shallo w n-type InP layer between the contact metallization and the p-type bulk In P. This inversion layer is created by diffusion of n-type doping species pr esent in the contact metallization during controlled annealing sequences. C alculations from classical J-V characterizations indicate barrier height el evations 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 rever se current under a fixed bias. This effect can be attributed to the reducti on of the barrier height of the Schottky contact arising from electronic ex change between the NO2 molecules and the thin n-InP inter facial layer. Stu dies on several diodes show that they exhibit high sensitivities as well as rather short response times rewards nitrogen dioxide, but that aging effec ts occur after several uses. (C) 2001 Elsevier Science B.V. All rights rese rved.