Deposition and Characterization of Amorphous GaN Thin Films
Theoretical study by Stumm and Drabold [P. Stumm and D. A. Drabold, Phys. Rev. Lett 79, 677 (1997).] showed that amorphous GaN could be a promising wide bandgap semiconductor material for electronic and optoelectronic device applications. In this dissertation, a-GaN and a-GaN:Er thin films were prepared by means of ion beam assisted evaporation at room temperature in an ultra-high vacuum chamber. The properties of as-deposited and thermal annealed films were studied by a variety of characterization methods. X-ray diffraction, electron diffraction, and Raman spectroscopy results confirmed that the films are amorphous. Depending on the deposition condition, films with Ga to N ratio of 1.0:0.5 to 1.0:1.4 were obtained. The film with the Ga:N ratio of 1.0:1.3±0.1 has an optical bandgap of ?2.5eV measured at the absorption coefficient of 10 ^4 cm ?1 , whereas the optical bandgap is ?2.0eV from a Tauc plot. The film is highly transparent for light with energy lower than the bandgap energy, while gallium rich films showed much higher absorption in the same region, which indicate that a clean band gap can be obtained for a-GaN film by preparing nitrogen rich films. Oxidation at room temperature has been observed for some films, while others are stable against oxidation until annealed above 500°C. The densities of the a-GaN and a-GaN:O films in this work are 62 to 78 at % and 68 to 85 at % respectively, of that of crystalline GaN, and the more the N or N+O in the film, the lower the density of the film. XPS and AES results showed that the binding energies for N and Ga to be consisted with Ga-N bonding. The XPS valence band spectrum showed that the highest valence band state is about 1.5eV below the Fermi level. Both as-deposited and annealed (at 900°C in N 2 ) a-GaN:Er film showed IR emissions in the range of 950-1000nm by PL measurement. The annealed film also showed visible emissions near 700nm by PL measurement.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:amorphous gallium nitride thin films optical properties electron spectroscopy structure
Date of Publication:01/01/2002