Formation of Low-Resistance Ohmic Contact by Damage-Proof Selective-Area Growth of Single-Crystal n+-GaN Using Plasma-Assisted Molecular Beam Epitaxy

• Published in: Journal of electronic materials 2008-05, Vol.37 (5), p.635-640
• Main Authors: Seo, Hui-Chan, Hong, Seung Jae, Chapman, Patrick, Kim, Kyekyoon(Kevin)
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Electronics and Microelectronics; Instrumentation; Materials Science; Optical and Electronic Materials; Solid State Physics
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-008-0390-y

To achieve very low ohmic contact resistance, an n + -GaN layer was selectively deposited using plasma-assisted molecular beam epitaxy (PAMBE). During this process polycrystalline GaN grew on the patterned SiO 2 region, which was subsequently removed by a heated KOH solution, resulting in damage to the n + -GaN surface. To prevent this damage, an additional SiO 2 layer was selectively deposited only on the n + -GaN region. To optimize the fabrication process the KOH etching time and n + -GaN layer thickness were adjusted. This damage-proof scheme resulted in a specific contact resistance of 4.6 × 10 −7 Ω cm 2 . In comparison, the resistance with the KOH etching damage was 4.9 × 10 −6  Ω cm 2 to 24 × 10 −6  Ω cm 2 . The KOH etching produced a large number of pits (4.1 × 10 8  cm −2 ) and degraded the current transport. X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectrometry (SIMS) analysis indicated that KOH etching was very effective in removing the oxide from the GaN surface and that the O-H bonding at the GaN surface was likely responsible for the degraded contact performance. The optimum n + -GaN thickness was found to be 54 nm.