| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 87 === Etching in GaN is an important priori for device processing due to the chemical inertness, hardness, and easily introducing damage in device process. The plasma/energetic ion etching with high reactive gas will provide a smooth etching bottom and vertical sidewall. But the ion bombardment induced damage will degrade the device performance. Another disadvantage was the different volatility of Ga and N reactant which will produce a non-stoichiometric surface. The damaged surface will limit the device application. So a mild etching process of wet etching was considered. Due to the chemical inertness of GaN, chemical wet etching can not be used for etching process, although wet etching is a low damage etching technology.
From the discussion above, we want to find an etching process with high etching rate, smooth etching surface, vertical sidewall and near damage free for etching GaN. In this thesis, photoelectrochemical (PEC) etching GaN was shown to yield high etching rate comparable with dry etching and vertical sidewall. But the enhancement in etching surface roughness and etching induced damage related to yellow luminescence also appeared in this etching process. The boiled KOH solution was used to remove the PEC etching damage successfully from the PL identification. The etching surface was also smoothed by post-treatment with boiled KOH solution.
Another important contribution is the rapidly identify threading dislocation density of the film by PEC etching. From selective etching of the threading dislocation and crystalline GaN, we could rapidly identify the dislocation density without using the TEM. We also use this skill to identify the dislocation related luminescence. This is the first report on the origin of this dislocation related PL peak.
In this work, we have developed an etching process of PEC etching with boiled KOH solution to obtain a high etching rate, smoothing etching surface, vertical sidewall and near damage free etching. We also showed the etching mechanism and studied the etching damage. The etching process could be applied for device processing, laser cavity formation, nanostructure fabrication and surface damage removal.
|
|---|
