The characteristics of the GaN/InGaN multiquantum-well light-emitting diode ͑LED͒ have been examined from the view point of uniform current spreading. By means of simple modeling, it was found that the current density and the length of the lateral current path through the transparent layer represent dominant parameters in determining uniform current spreading. In this regard, we studied the effect of current density on the reliability characteristics of the LED. We were able to significantly improve the electrical, optical, and reliability characteristics of the LED in terms of reducing the length of the lateral current path through the transparent layer.

The dry etching characteristics of ZnO using an inductively couple plasma (ICP) have been investigated, for the first time, as functions of plasma chemistry, radio frequency (rf) table power, and ICP power. The CH 4 /H 2 etchant gases resulted in the highest etch rate of ZnO, suggesting that the etching of Zn in ZnO largely involves a process in which a volatile metallorganic zinc compound, such as Zn(CH 3) y is formed. The etch rate was increased with increasing rf table power, and the highest etch rate of 2000 Å/min was achieved at an rf table power of 200 W (dc bias: Ϫ80 V). As the ICP power was increased, the etch rate also increased, which suggests that the plasma density is also an important factor in this process. Furthermore, it was observed that hydrogen-containing plasma etching enhances the band-edge photoluminescence of the ZnO film.

Low-resistance and nonalloyed ohmic contacts to epitaxially grown n-ZnO were formed by exposing n-ZnO to an inductively coupled hydrogen and an argon plasma. Using Ti/Au, the specific contact resistivity of the ohmic contact was drastically decreased from 7.3×10−3 to 4.3×10−5 Ω cm2 by hydrogen plasma treatment. The photoluminescence spectrum of the hydrogen plasma treated ZnO showed a large enhancement in band-edge emission and a strong suppression in deep-level emission. These results suggest that the low contact resistivity can be attributed to an increase in carrier concentration on the ZnO surface. The specific contact resistivity of the Ar-plasma treated sample was also decreased to 5.0×10−4 Ω cm2, presumably due to the formation of shallow donor on the ZnO surface by ion bombardment.

The fabrication and characterization of an InGaN/GaN multiple-quantum well ͑MQW͒ light-emitting diode ͑LED͒ with a SiO 2 current blocking layer inserted beneath the p-pad electrode is described. The light-output power and external quantum efficiency for the InGaN/GaN MQW LED chip with a current blocking layer were significantly increased compared to those for the conventional InGaN/GaN MQW LED chip. The increase in the light-output power can be attributed to the injection of additional current into the light-emitting quantum well layer of the LED by the SiO 2 current blocking layer and a reduction in parasitic optical absorption in the p-pad electrode.

The etching characteristics and evolution of the surface morphology of ZnO and GaN thin films during wet chemical etching were investigated. While the ZnO etch rates using acidic solutions were similar, regardless of etchant or polarity, the etch rate of the Ga-polar GaN surface was dependent on the etchant. N-polar GaN could be etched in alkali-based solutions such as KOH. The surface morphologies of etched ZnO were very similar to those of the GaN surface: hexagonal pyramids and stepped hexagonal pits formed during the etching of O-polar ZnO and N-polar GaN and of Zn-polar ZnO and Ga-polar GaN, respectively. The formation of a hexagonal etch pit on the etched Zn-polar and Ga-polar surfaces was enhanced by surface defects such as pits or threading dislocations. The etching of N-polar GaN by KOH proceeded through the evolutionary stages of hexagonal pyramids: formation, growth, dissociation, and isolation. Ga-polar GaN was etched through the formation, widening, and merging of hexagonal pits.