| Summary: | 博士 === 國立中興大學 === 材料科學與工程學系所 === 101 === The major topics in this thesis were focused the characteristic of the fabrication and analysis about GaN-based optoelectronic devices through wet oxidation and etching process. In first part, a photoelectrichemical (PEC) wet mesa etching process was used to fabricate InGaN-based light-emitting diodes as a substitute for the conventional plasema mesa dry etching process. The etching process were consisted of photoelectrochemical wet oxidation and oxide-removed processes occurred on p-type GaN:Mg layer, InGaN active layer, and n-type GaN:Si layer to define mesa region. Furthermore, the wet mesa etching process produced lateral etching under p-GaN at mesa sidewall region and this process reduced strain in InGaN quantum well layers. We divided the three regions to discuss the piezoelectric fields of dry mesa etching and wet mesa etching process. From the results of the μ-PL spectra, bias-dependent μ-PL and other measurement, the piezoelectric fields from mesa center to TCL edge became smaller and smaller; additionally, the smaller piezoelectric fields of WME-LED were compared with the ST-LED.
In second part, the light emitting diodes with the air-channel structure were fabricated by regrowth on a nanorods structure template. And then utilizing selective wet etching process formed nanoporous structure to embed in air-channel light-emitting diodes (A-LEDs). The nanorods structure was formed through the Ni film coated on u-GaN template was subsequently formed as the self-assembled Ni metal clusters using a rapid thermal annealing system, and then the u-GaN template layer was etched using a dry etching system. The selective wet etching was a dopant selective etching in oxalic acid by using PEC etching process to produce a different etching rate and morphology. For the A-LEDs and the nanoporous/air-channel LEDs (NA-LEDs), the light output powers were respectively enhanced 1.48- and 1.75-fold, and divergent angles was became smaller.
In final part, the wet etching process was applied on chemical lift-off process of LEDs. The technique was different from other conventional chemical lift-off and it separated the LEDs from a nanorods structure template in a hot KOH solution (80 ℃, 2.2 M). The wet etching processes consisted of a reducing diameter process on a GaN nanorod structure and a crystallographic wet etched process on an N-face GaN surface. The N-face crystallographic etching process was limited by the boundary of the nanorod structure that InGaN active layer can prevent from the etching damage. The light output power of the lift-off LED had 2.28 times enhancement compared with the non-treated LED due to pyramidal-roughened structure formed.
|
|---|
