Free-Standing GaN Layer by Combination of Electrochemical and Photo-Electrochemical Etching

Abstract

A free-standing GaN layer was produced by combining electrochemical (EC) etching from the front surface, photo-electrochemical (PEC) etching from the back surface, and subsequent regrowth of GaN on the porous template thus produced. The EC etching resulted in the formation of etch channels on the surface portion of the starting film, whereas the back-side PEC etching gave rise to a columnar structure supporting the entire film. When the n-GaN layer was regrown on such template, the underlying columnar structure provided weak places for easy separation and transfer of the film by mechanical bonding.

Epitaxial growth of (0001) oriented porous GaN layers by chemical vapour deposition

“…9,10 However, porous GaN has been typically fabricated using (photo)electrochemical and chemical etching methods. [11][12][13] These methods generally suffer from a lack of control over the size, morphology and distribution of the pores, making the fabrication of optoelectronic devices difficult. Furthermore, the use of these techniques might induce unwanted interface states and surface contamination as well as defects that can affect properties of the crystals, which negatively affect the performance of the systems based on them.…”

III‐Nitride Nanowires as Building Blocks for Advanced Light Emitting Diodes

“…Epitaxial layer of n‐GaN/undoped GaN/substrate (a), morphology after ECE (b), PECE (c), GaN regrowth (d), separation of GaN layers from substrate (e), and concept showing substrate recycling (f). Reproduced with permission . Copyright 2013, The Japan Society of Applied Physics.…”

“…Approaches in separation and transfer, again, are similar to the ones developed for top‐down microLEDs and bottom‐up NW LEDs. One final thing to be mentioned here is that the top‐down NW LEDs seem to be particularly amenable to the new separation technology developed for MOCVD grown planar LEDs in our earlier papers . In this technology a combination of electrochemical etching (ECE) and photoelectrochemical etching (PECE) of undoped GaN/n + ‐GaN is applied to fabricate porous templates schematically displayed in Figure .…”

“…These ECE‐PECE templates are then used to grow the standard LED structures that can be easily separated from the substrate by mechanical peeling off using the weak places presented by the ECE‐PECE template as breaking points. The advantages of LED structures thus prepared are related to lower strain and lower density of structural defects, such as V‐pits . This technique can come very handy when organizing the efficient separation and transfer of the NW LEDs prepared by the top‐down approach described above.…”

Photo-electrochemical etching of free-standing GaN wafer surfaces grown by hydride vapor phase epitaxy

“…This generates electron-hole pairs, which then initiate a redox reaction at the semiconductor/ electrolyte interface. This method has been used for the chemical lift off of GaN layers [5] and in light-emitting diode (LED) fabrications [6] with a practical etching efficiency, but has so far only been used with epitaxial GaN thin films [7][8][9][10] applied to a substrate by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). However, free-standing GaN bulk wafers have been produced quite recently by hydride vapor phase epitaxy (HVPE) [11][12][13][14], and the demand for these has significantly increased due to the fact that they represent high-quality GaN crystals with a low dislocation density.…”