Electrical Characteristics of Ti/Al Ohmic Contacts to Molecular Beam Epitaxy-Grown N-polar n-type GaN for Vertical-Structure Light-Emitting Diodes

• Published in: Journal of electronic materials 2012-08, Vol.41 (8), p.2145-2150
• Main Authors: Jeon, Joon-Woo, Seong, Tae-Yeon, Namgoong, Gon
• Format: Article
• Language: English
• Subjects: Annealing; Carrier density; Characterization and Evaluation of Materials; Chemistry and Materials Science; Contact resistance; Electronics and Microelectronics; Gallium nitrides; Instrumentation; Interfacial bonding; Light-emitting diodes; Materials Science; Molecular beam epitaxy; Ohmic; Optical and Electronic Materials; Scanning electron microscopy; Scanning transmission electron microscopy; Semiconductor annealing; Solid State Physics; Wurtzite; X-ray photoelectron spectroscopy
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-012-2136-0

We investigated the electrical properties of Ti(30 nm)/Al(200 nm) contacts to molecular beam epitaxy-grown N-polar n -GaN with different carrier concentrations. Samples with carrier concentration of 1.2 × 10 18  cm −3 showed nonohmic behaviors when annealed at 300°C, but ohmic at 500°C and 700°C. All samples with carrier concentration of 2.0 × 10 19  cm −3 exhibited ohmic behavior. x-Ray photoemission spectroscopy (XPS) results showed that, for samples with carrier concentration of 1.2 × 10 18  cm −3 , the Ga 2 p core levels shift to lower or higher binding energy upon annealing at 300°C or above 500°C, respectively. Scanning transmission electron microscopy (STEM) results showed that, for samples with carrier concentration of 1.2 × 10 18  cm −3 , a wurtzite AlN layer (∼2 nm thick) formed at the metal/GaN interface when the samples were annealed at 500°C. An interfacial wurtzite AlN layer also formed upon annealing at 700°C, but its thickness was ∼4 nm. Based on the XPS and STEM results, the ohmic contact formation and degradation mechanisms are described and discussed.