Interface and Transport Properties of Metallization Contacts to Flat and Wet-Etching Roughed N-Polar n-Type GaN

The electrical characteristics of metallization contacts to flat (F-sample, without wet-etching roughed) and wet-etching roughed (R-sample) N-polar (Nitrogen-polar) n-GaN have been investigated. R-sample shows higher contact resistance (R-c) to Al/Ti/Au (similar to 2.5 x 10(-5) Omega.cm(2)) and higher Schottky barriers height (SBH, similar to 0.386 eV) to Ni/Au, compared with that of F-sample (similar to 1.3 x 10(-6) Omega.cm(2), similar to 0.154 eV). Reasons accounting for this discrepancy has been detail investigated and discussed: for R-sample, wet-etching process caused surface state and spontaneous polarization variation will degraded its electrical characteristics. Metal on R-sample shows smoother morphology, however, the effect of metal deposition state on electrical characteristics is negligible. Metallization contact area for both samples has also been further considered. Electrical characteristics of metallization contact to both samples show degradation upon annealing. The VLED chip (1 mm x 1 mm), which was fabricated on the basis of a hybrid scheme, coupling the advantage of F- and R-sample, shows the lowest forward voltage (2.75 V@350 mA) and the highest light output power.