A comparative study of Mg and Pt contacts on semi-insulating GaAs: Electrical and XPS characterization

• Published in: Applied surface science 2017-02, Vol.395, p.131-135
• Main Authors: Dubecký, F., Kindl, D., Hubík, P., Mičušík, M., Dubecký, M., Boháček, P., Vanko, G., Gombia, E., Nečas, V., Mudroň, J.
• Format: Article
• Language: English
• Subjects: Electrical charge transport; Interface; M-S contact; Metal-semiconductor; Semi-insulating GaAs; Work function; XPS
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2016.04.176

•Explored were diodes with full-area low/high work function metal contacts on semi-insulating GaAs (S).•The Mg-S-Mg diode is promising for radiation detectors for its low high-field current.•The XPS analysis of Mg-S interface shows presence of MgO instead of Mg metal. We present a comparative study of the symmetric metal-SI GaAs-metal (M-S-M) diodes with full-area contacts on both device sides, in order to demonstrate the effect of contact metal work function in a straightforward way. We compare the conventional high work function Pt contact versus the less explored low work function Mg contact. The Pt-S-Pt, Mg-S-Mg and mixed Mg-S-Pt structures are characterized by the current-voltage measurements, and individual Pt-S and Mg-S contacts are investigated by the X-ray photoelectron spectroscopy (XPS). The transport measurements of Mg-S-Pt structure show a significant current decrease at low bias while the Mg-S-Mg structure shows saturation current at high voltages more than an order of magnitude lower with respect to the Pt-S-Pt reference. The phenomena observed in Mg-containing samples are explained by the presence of insulating MgO layer at the M-S interface, instead of the elementary Mg, as confirmed by the XPS analysis. Alternative explanations of the influence of MgO layer on the effective resistance of the structures are presented. The reported findings have potential applications in M-S-M sensors and radiation detectors based on SI GaAs.