Formation of High-Quality Ag-Based Ohmic Contact to p-Type GaN for UV LEDs Using a Tin-Zinc Oxide Interlayer

Ohmic Contacts on p‐GaN

“…Furthermore, annealing in oxygen causes Ag to become oxidized and/or to agglomerate . Therefore, materials with good conductivity and high transparency were deposited together with the Ag layer, with the goal of forming a passivation layer without annealing, or after annealing in an oxygen‐containing ambient atmosphere with the oxidized materials, thus suppressing the agglomeration of the Ag layer. Examples are the contact scheme of CeO 2 ‐doped In 2 O 3 (ICO)/Ag, Ag/Cu‐doped indium oxide (CIO), Ni/Au/W/Ag, Ag/La, and Pd/Zn/Ag .…”

“…They proposed the conductance mechanism of annealed contacts to be via defect‐assisted tunneling and hopping . Thin layers of tin‐zinc oxide (TZO) (2.5 nm) and ITO (2 nm) were investigated as intermediate layers between Ag and p‐GaN. In both contacts, the TZO and ITO films were observed to break up into nanodots and contacted the GaN surface together with Ag.…”

“…Thin layers of tin‐zinc oxide (TZO) (2.5 nm) and ITO (2 nm) were investigated as intermediate layers between Ag and p‐GaN. In both contacts, the TZO and ITO films were observed to break up into nanodots and contacted the GaN surface together with Ag. Thus, inhomogeneous barrier contacts formed at the contact/GaN interfaces; it was proposed that this yields a reduction in contact resistivity, together with the formation of Ag‐Ga solid solutions at the interface.…”

Insights into the Silver Reflection Layer of a Vertical LED for Light Emission Optimization

“…Possible reasons involve poor adhesion between the Ag reflective (metal) and GaN (semiconductor) layers, different thermal annealing (temperature cycle), and lattice mismatch (stress) during the fabrication of GaN and Ag layers. , Furthermore, thermal annealing performed in O 2 ambient environment exhibited interdiffusion between Ag and GaN, which disrupts the Ag/GaN interface (Figure d) . In this case, interfacial Ga vacancies will be generated substantially, which can degrade the Ohmic contact (metal–semiconductor junction) or change energy levels (e.g., Schottky barrier height). , In addition, dissimilar properties between the Ag metal and the GaN semiconductor materials (Table S3) can potentially result in unwanted diffusion and intermixing. For instance, lattice mismatch (strain) and different miscibility between different materials can cause segregation of Ag atoms into the upper layer of GaN (as no barrier layer exists), which will lead to inhomogeneous distribution of carrier concentration or photon transport at the Ag/p-GaN interface and ultimately influence the optical and electrical performances of VLEDs.…”

“…Moreover, these results suggest the different diffusion widths that originate from the growth temperature variation (between GaN, InGaN, and Ag layers) and the nonavailability of the diffusion barrier between the Ag and GaN interface. To mitigate such in-/out-diffusion issues, the Ag/GaN interface needs to be optimized by incorporating appropriate transparent barrier layers, for example, tin–zinc oxide interlayer . Also, the formation of Ag–O and Ag alloys (Ag–Ga) during the thermal annealing process can be suppressed by having a multilayer stack of Me/Ag/Ru/Ni/Au (where Me = Ni, Ir, Pt, or Ru) contacts or barriers for high-power GaN-based VLEDs .…”