ON THE RICHARDSON CONSTANT OF INTIMATE METAL-GAAS (111)B SCHOTTKY DIODES GROWN BY MOLECULAR-BEAM EPITAXY

Careful measurements have been made of the temperature dependence of t he barrier height (phi(b)) and the Richardson constant (A(c)*) for se veral metal/GaAs (111)B Schottky diodes using current-voltage and capa citance-voltage techniques. The metals used, aluminium, copper, and go ld, were evaporated at a base pressure of 10(-10) Torr, to ensure no n ative oxide at the interface. The values obtained for the temperature dependence of the barrier height were - (4.3+/-0.1) x 10(-4) eV K-1 fo r all diodes except for the Cu/GaAs (111) B diode where it was - (4.7/-0.1) x 10(-4) eV K-1. The calculated Richardson constants were 0.51 X 10(4), 0.88 X 10(4), and 1.37 X 10(4) A m-2 K-2 for the Al, Au, and Cu GaAs (111) B diodes respectively, and 0.50 X 10(4) A m-2 K-2 for th e Al/GaAs (100) comparison diode. The exactness of results between the Al/GaAs (111) B and the Al/GaAs (100) Schottky diodes is believed to indicate the formation of a thin interfacial layer of AlAs, probably f ormed during the metal evaporation. It was found that the semiconducto r orientation had a subtle effect upon the Richardson constant compare d to similar Schottky diodes fabricated on (100) GaAs. The variation i n A(c)* indicates that the band structure of the metal plays a part i n the formation of a Schottky barrier, and the similarity in the value of alpha indicates that the barriers are pinned relative to the same position. In comparison to the GaAs band gap variation with temperatur e, this appears to be pinned relative to the valence band of the semic onductor.