| Abstract: | This study aims at investigating the etching methods of acid solution to GaN epitaxial layer. It produced the surface roughening GaN structure by the GaN epitaxial layer on the sapphire which was etched by three different acid solutions, which were H2SO4, H3PO4, and H2SO4+H3PO4 (HH). The researcher investigated the influence of different time and etching etchant to surface morphology and etching depth and used SEM, AFM, and XPS to analyze the samples after etching.
The results show that the choice of different acid solutions will produce different etching morphologies. Under the H2SO4 etching, the thickness of the GaN epitaxial layer does not change significantly, but the pits of the inverted hexagonal pyramid are generated on the surface, and expand and combine with time, finally remain on the etched surface(101 ̅5 ̅); Under the H3PO4 etching, the thickness of the GaN epitaxial layer decreases with time, and the etch pit will change from inverted hexagonal pyramid to hexagonal prism over time, and the pits will be combined with each other, and the size of the pit and the depth will increase with time; Under the HH etching, the thickness of the GaN epitaxial layer decreases with time, and the etch pit will change from inverted hexagonal to dodecagonal pyramid over time, and finally maintained at an angle of about 9.3°. These etching pits are generated because of the dislocation. When GaN is growth on the sapphire substrate, A lattice mismatch between the two causes dislocation, and the acidic solution begins to etch and create pits from these defects.
For the product, the peak of Ga-OEx can be found to increase, and a characteristic peak of a sulfide is generated at 169.1 eV, corresponding product Ga2(SO4)3; in the experimental group of H2SO4 etching; in the H3PO4 experiment, the bonding peak of O 1s and P 2p was found to rise after etching, and it was confirmed that phosphate may be the main cause of etching; In the HH experiment, there was no significant difference in the bonding energy after the reaction, so no product was found on the surface of the sample. |
