DOI: 10.18150/cebljl
title: Palladium-Based Contacts on p-GaN and Their Application in Laser Diodes

description: Palladium-Based Contacts on p-GaN and Their Application in Laser Diodes. Iryna Levchenko, Serhii Kryvyi, Eliana Kamińska, Szymon Grzanka, Ewa Grzanka, Łucja Marona and Piotr Perlin. Materials 2023, 16(19), 6568; https://doi.org/10.3390/ma16196568In this paper, we investigate the effect of Pd thickness and heat treatment on Pd/Ni/Au/p-GaN metal contacts. The as-deposited samples exhibit a smooth morphology and non-linear I–V characteristics. Heat treatment in a N2 atmosphere leads to degradation of the contact microstructure, resulting in diffusion of Ga, void formation on the interface and mixing of metals. Annealing in a mixture of N2 and O2 improves adhesion and reduces contact resistance. However, this process also induces GaN decomposition and species mixing. The mixing of metal–Ga and metal–metal remains unaffected by the method of thermal treatment but depends on gas composition for thin Pd contacts. To achieve low-resistance contacts (≈1 × 10−4 Ω cm2), we found that increasing the Pd thickness and using N2 + O2 as the annealing environment are effective measures. Nevertheless, the degradation effect of the annealed contact microstructure in the form of the void generation becomes evident as the thickness of Pd increases. Laser diodes (LDs) with optimized palladium-based contacts operate at a voltage of 4.1 V and a current density of 3.3 kA/cm².The names of files correspond to the nnumbering of the figures in the paper. It includes:Figure 1. SEM image of the surface of as-deposited Pd/Ni/Au (10/10/30 nm) metallization on p-GaN. The provided layer thicknesses correspond to the settings used for evaporation.Figure 2. XRD profile for investigated Pd/Ni/Au (10/10/30 nm) as-grown sample. The powder diffraction patterns with corresponding reference numbers in PDF-2 and ICSD databases are shown.Figure 3. HR-STEM image (a) of as-deposited Pd/Ni/Au (10/10/30 nm) together with the interplanar distance for the indicated lattice planes (b) determined from measurements by FFT. ZA—zone axis.Figure 4. Crystallographic orientation of GaN (a) and metal layers (b,c).Figure 5. I−V plots for the as-deposited and annealed contacts.Figure 6. SEM (a) and STEM (b) images of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 flow at 530 °C.Figure 7. EDX elemental mapping data for p-GaN/Pd/Ni/Au (10/10/30 nm) contact annealed in N2 (a–f). Schematic view of the contact composition (g).Figure 8. XRD profiles for investigated as-grown sample and after annealing in N2.Figure 9. SEM data of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 + O2 flow at 530 °C.Figure 10. EDX elemental mapping data (a–f) and schematic view (g) of Pd/Ni/Au (10/10/30 nm) annealed in RTA in N2 + O2 flow at 530 °C.Figure 11. XRD profiles for investigated as-grown sample after annealing by RTA in N2 + O2 flow.Figure 12. SEM data of Pd/Ni/Au (90/10/30 nm) after annealing by (a) oven in N2 + O2 + H2O and (b) RTA in N2 + O2.Figure 13. EDX maps of Pd/Ni/Au (90/10/30 nm) after annealing by oven in N2 + O2 + H2O (a–f) and scheme of Pd/Ni/Au (90/10/30 nm) composition (g).Figure 14. XRD profiles for investigated as-grown sample and after annealing.