へき開した自立n-GaN基板のm面に形成したAu/Niショットキー接触における表面処理の影響

抄録

We fabricated and characterized Au/Ni Schottky contacts on cleaved m-plane free-standing n-GaN surfaces (i) without any surface treatment, (ii) with H₂O₂ treatment, or (iii) with HCl treatment by current-voltage (I-V), capacitance-voltage (C-V), and photoresponse (PR) measurements. 50-nm-thick Ni films and 50-nm-thick Au films were deposited in turn on the m-plane surface by electron-beam evaporation to form Schottky contacts. All of the Schottky contacts were circular and 100µm in diameter. The highest step determined by the laser microscope was 5 nm, but in some dots, steps were not observed. The as-cleaved samples showed I-V characteristics with small n-values and less diode-to-diode variation. However, the H₂O₂ samples had much smaller Schottky barrier height (qϕ_B). Whereas the HCl samples exhibited significantly large diode-to-diode variation. The qϕ_B and n-values obtained from the I-V, C-V, and PR results are nearly constant, independent of the step height. This is probably because the steps also consist of m-plane facets, which have no effect on the electrical characteristics of the Schottky diodes. It is confirmed that cleaving without any surface treatment can provide a cleaner surface to form Schottky diodes on m-plane n-GaN surfaces than that with conventional HCl treatment.