Effects of surface plasma treatment on n-GaN ohmic contact formation

Abstract

Elemental compositions of GaN surfaces treated by N2 and BCl3/Cl2 plasmas have been investigated via AES and XPS analyses. The AES results indicate a low N/Ga ratio of 0.1 for N2 plasma-treated GaN surface and a relatively high N/Ga ratio of 0.5 for BCl 3/Cl2 plasma-treated GaN surface. Although the N/Ga ratio has often been used as an indicator for N-vacancies (VN) formation, ohmic contacts fabricated on plasma treated n-GaN surfaces with a lower N/Ga ratio do not necessarily have a correspondingly lower specific contact resistance (ρc). Ohmic contacts on N2 plasma treated n-GaN (Si∼2.6×1018cm-3) yield a higher ρc of 6.7×10-5Ωcm2, despite a lower N/Ga ratio, than similar samples with BCl3/Cl2 plasma treatment, which is 6.1×10-6Ωcm2. XPS analysis of the Ga 3d peak shows a high degree of oxidation on N2 plasma treated GaN. Hence, its low N/Ga ratio is not indicative of V N abundance at the GaN surface but a high concentration of Ga in the form of an oxide (GaxOy), thus translating to a higher ρc. © 2004 Elsevier B.V. All rights reserved.