Abstract
Because wet etching poses many advantages over dry etching, development of GaN wet etching has drawn more and more attentions in recent years. First of all, wet etching avoids surface damages and thus improves both device characteristics and production yield. Second, wet etching reduces the number of processing steps, shortens the processing time and improves the overall throughput. In terms of cost reduction, wet etching obviously is a better choice. Therefore, laboratories worldwide have put enormous amount of efforts in the development of GaN wet etching process. This thesis focused on applying UV-LEDs to n-type GaN PhotoElectroChemical (PEC) wet etching. In our experiment, KOH solutions with PH values lying between 11.0 and 14.0 are used as etchants. We also examined both Ti/Au 300/3000 and Ti/Al/Ni/Au 250/1250/450/550 contacts as wet etching masks. Two UV-LEDs, whose peak wavelengths are 373nm and 365nm, respectively, were used as the light sources of wet etching. The UV-LEDs were also made from GaN based materials. Although cooling is not required for UV-LED operation, we attached a ThermoElectric Cooler (TEC) to control the temperature and performed the etching under a constant wavelength. Finally, we have demonstrated that UV-LED made from Nichia with 365 nm peak wavelength can be used to etch the n-GaN and stop on top of the p-GaN in a PH=14.0 KOH solution and the etching depth is around 1.4μm.