Peculiarities of metal contacts on semi-insulating GaAs: electrical, photoelectronic and XPS characterization

The present work reports on peculiarities in the charge transport observed with novel electrodes applied to SI GaAs in relation to our previous results. The novel electrode uses a metal with rather low work function (such as e.g. In, Mg, Gd) used in our previous paper as a quasi-ohmic contact. Fabricated structures with the small 'blocking' top contacts and full area quasi-ohmic backside metallization, are compared with full area contacts on both sides. Structures based on the same 'detector-grade' SI GaAs are characterized by the current-voltage (I-V) measurements, photocurrent spectroscopy (PCS), and X-ray photo-emission spectroscopy (XPS). We observed an anomalous lowering of the reverse current at low bias voltages (<10 V) for electrodes formed by Gd and Mg. Possible explanation of the observed effects is presented and applications utilizing the investigated effect are discussed. (authors)