Assembly of phosphonic acids on GaN and AlGaN

• Published in: Journal of physics. D, Applied physics Vol. 43; no. 1; pp. 015303 - 015303 (5)
• Main Authors: Simpkins, B S, Hong, S, Stine, R, Mäkinen, A J, Theodore, N D, Mastro, M A, Eddy, C R, Pehrsson, P E
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 13.01.2010; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Physics; Thin films and multilayers; Semiconductor materials; Self-assembled layers; Gallium nitride; Chemical modification; Electronic structure; Sheet resistivity; Aluminium Gallium Nitrides Mixed; Chemical bonds; Ultraviolet photoelectron spectra; Phosphonic acid derivatives; Fourier-transformed infrared spectrometry; Defect structure; Heterostructures; X-ray photoelectron spectra
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/43/1/015303

Self-assembled monolayers of octadecylphosphonic acid and 16-phosphonohexadecanoic acid (PHDA) were formed on the semiconductor substrates gallium nitride (GaN) and aluminium gallium nitride (AlGaN). The presence of the molecular layers was verified through x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Structural information was acquired with infrared spectroscopy which verified the bonding orientation of the carboxyl-containing PHDA. The impact of the molecular layers on the channel conductivity and the surface electronic structure of an AlGaN/GaN heterostructure was measured. Our results indicate that pinning of the surface Fermi level prohibits modification of the channel conductivity by the layer. However, a surface dipole of ~0.8 eV is present and associated with both phosphonic acid layers. These results are of direct relevance to field-effect-based biochemical sensors and metal-semiconductor contact formation for this system and provide a fundamental basis for further applications of GaN and AlGaN technology in the fields of biosensing and microelectronics.