| Summary: | 博士 === 國立交通大學 === 電子物理系所 === 102 === Although it is a well-known effect that hydrogen can increase the decomposition rate of gallium nitride (GaN), most studies focus on the role of it as a carrier gas during epitaxial growth. Studies of hydrogen etch are therefore scarce. Moreover, there is almost no research investigating on the specific surface morphology produced by hydrogen.
In this work, we systematically analyzed the etching behavior of hydrogen on GaN, and found that it can produce various surface structures depending on the conditions. Among the etching parameters, temperature and pressure are the most dominative factors determining the morphology, but their tendencies are opposite. If the temperature is fixed, a high-pressure hydrogen etch will produce a surface decorated by mooring-post-like GaN columns; in contrast, a low-pressure etch will produce a cavity-ridden surface. On the other hand, modulating temperature can also obtain similar results. We also proposed a mechanism to elaborate on the evolution of the surfaces and performed some examinations to verify it.
Besides studying the mechanism, we also applied hydrogen etch to thick-film overgrowth and the enhancement of internal quantum efficiency (IQE) of a light-emitting diode (LED). In the thick-film application, by inserting a hydrogen etching step to a GaN template before overgrowth, the stress in the film can be relieved. Furthermore, by combining different etching conditions, such as a two-step etch, we can obtain a "stilt GaN template," which can assist in self-separation of a thick film grown on it. In the IQE application, given that dislocation sites are the prior locations to be etched, hydrogen can therefore be used to remove the existing dislocations in an LED; consequentially, IQE can be elevated. PL measurement authenticated that after hydrogen etch, the IQE of an LED is enhanced; this can probably be accredited to the removal of dislocations. Nevertheless, the drawback is the difficulty of electrode deposition.
|
|---|
