Current–voltage and capacitance–voltage techniques have been used to characterize the electrical properties of annealed epitaxial aluminum contacts to In0.53Al0.47As grown by molecular beam epitaxy. These as-deposited diodes were found to have electrical characteristics that were dominated by thermionic emission, with an ideality factor of 1.06–1.08 and a barrier height of 0.55–0.56 eV. As the anneal temperature is increased, there is a slight increase in the value of the barrier height, which is believed to be related to an increasing interfacial reaction occurring, promoting the formation of AlAs. For anneals above 400 °C, the electrical characteristics start to degrade rapidly. For comparison, conventionally evaporated Au/InAlAs diodes were also characterized. These diodes had an ideality factor of 1.14–1.18 and a barrier height of 0.63–0.67 eV. Although the electrical characteristics showed little variation in the forward direction, the reverse characteristics exhibited a significant variation between diodes. Upon annealing, the characteristics show variations between diodes, with the characteristics significantly degraded for anneals of 300 °C, showing the poor thermal stability exhibited by conventionally evaporated contacts. The observed characteristics for the epitaxial aluminum contacts to InAlAs, compared with those from conventionally evaporated gold contacts, have implications for the Schottky gate contact in the manufacture of InAlAs–InGaAs high electron mobility transistors.
Careful measurements have been made of the temperature dependence of the barrier height (φb) and the Richardson constant (A**c) for several metal/GaAs (111)B Schottky diodes using current-voltage and capacitance-voltage techniques. The metals used, aluminium, copper, and gold, were evaporated at a base pressure of 10−10 Torr, to ensure no native oxide at the interface. The values obtained for the temperature dependence of the barrier height were −(4.3±0.1)×10−4 eV K−1 for all diodes except for the Cu/GaAs (111)B diode where it was −(4.7±0.1)×10−4 eV K−1. The calculated Richardson constants were 0.51×104, 0.88×104, and 1.37×104 A m−2 K−2 for the Al, Au, and Cu GaAs (111)B diodes respectively, and 0.50×104 A m−2 K−2 for the 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 formed during the metal evaporation. It was found that the semiconductor orientation had a subtle effect upon the Richardson constant compared to similar Schottky diodes fabricated on (100) GaAs. The variation in A**c indicates that the band structure of the metal plays a part in the formation of a Schottky barrier, and the similarity in the value of α indicates that the barriers are pinned relative to the same position. In comparison to the GaAs band gap variation with temperature, this appears to be pinned relative to the valence band of the semiconductor.
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