Al–GaAs (001) Schottky barrier formation

Abstract

Schottky diodes have been fabricated by in situ deposition of Al on GaAs (001) grown by molecular beam epitaxy. A detailed study of the Schottky barrier height (φb ) dependence on surface geometry and composition has been undertaken. Reconstructed, as well as very As- and very Ga-rich surfaces have been prepared. For comparison also samples with a thin interfacial AlAs layer were produced. The barrier height was determined by the capacitance–voltage (C–V) and current–voltage (I–V) techniques. The quality of the material was controlled by deep level transient spectroscopy revealing a total concentration of levels in the upper part of the band gap in the mid 1012 cm−3 range. Measuring the barrier heights of different diodes across a wafer showed lateral variations which were preserved also after annealing. A number of possible explanations for these variations were investigated but none proved satisfactory. Averaging over a large number of diodes revealed no apparent reconstruction dependence of the barrier height. The two measurement techniques gave the same barrier height φb ≊0.75 eV. By defining the Auger As (MVV)/Ga(MMM) signal ratio as a measure on the surface composition it was found that reconstructed surfaces appeared in the interval 2<As/Ga<5. Going outside this interval the barrier increased for As/Ga<2 and decreased for 5<As/Ga<10. For As/Ga>10 an increase was again found. Annealing at 573 K led to a rapid initial increase of the barrier height for the samples with reconstructed GaAs surfaces followed by a slower interdiffusion related increase during prolonged annealing.