The impact of wet treatment using an (NH4)2S-alcohol solution on the interface state of the p-GaN/Ni/Au/Pt contact system and laser diode processing was investigated. Sulfur wet cleaning resulted in reduced surface roughness and contact resistivity. The lowest specific contact resistance (ρc < 1 × 10−4 Ω·cm2) was achieved with samples treated with an (NH4)2S-isopropanol solution, whereas the highest resistivity (ρc = 3.3 × 10−4 Ω·cm2) and surface roughness (Ra = 16 nm) were observed in samples prepared by standard methods. Annealing the contact system in an N2 + O2 + H2O atmosphere caused degradation through species inter-diffusion and metal-metal solid solution formation, irrespective of the preparation method. Standard prepared substrates developed a thin GaN-Au intermediate layer at the interface after heat treatment. Enhanced adhesion and the absence of GaN decomposition were observed in samples additionally cleaned with the (NH4)2S-solvent solution. Complete oxidation of nickel to NiO was observed in samples that underwent additional sulfur solution treatment. The intensity of metal species mixing and nickel oxidation was influenced by the metal diffusion rate and was affected by the initial state of the GaN substrate obtained through different wet treatment methods.
The names of files corespond to the numbering of the figures in the paper Iryna Levchenko,Serhii Kryvyi,Eliana Kamińska,Julita Smalc-Koziorowska,Szymon Grzanka,Jacek Kacperski,Grzegorz Nowak,Sławomir Kret,Łucja Marona and Piotr Perlin. Pros and Cons of (NH4)2S Solution Treatment of p-GaN/Metallization Interface: Perspectives for Laser Diode. https://doi.org/10.3390/ma17184520.
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Figure 1. AFM overview scan of p-GaN surface after (a) standard cleaning and (b) standard and (NH4)2S-t-(CH3)3COH treatment.
Figure 2. AFM maps (a–d) and SEM images (e–h) of the surface of annealed p-GaN/Ni/Au/Pt contact system.
Figure 3. c-AFM current maps (a–d) and AFM images (e–h) of annealed p-GaN/Ni/Au/Pt.
Figure 4. STEM image of annealed p-GaN/Ni/Au/Pt, after standard preparation (a) and with additional treatment by (NH4)2S solution (b).
Figure 5. STEM image (a) and EDX maps of the element propagation (b–f) for the annealed p-GaN/Ni/Au/Pt system with treatment in (NH4)2S-based solution.
Figure 6. Schematic view on evolution of the annealed p-GaN/Ni/Au/Pt system with treatment in (NH4)2S-based solution (grey circles represent the voids).
Figure 7. STEM image (a) and EDX maps of the element dispersion (b–f) for the annealed p-GaN/Ni/Au/Pt system after standard cleaning.
Figure 8. Schematic view on evolution of the annealed p-GaN/Ni/Au/Pt system after standard cleaning.
(2024)
