Preparation and lithium doping of gallium oxynitride by ammonia nitridation via a citrate precursor route

• Published in: Journal of solid state chemistry Vol. 180; no. 7; pp. 1984 - 1989
• Main Authors: Kikkawa, Shinichi, Nagasaka, Kazuteru, Takeda, Takashi, Bailey, Mark, Sakurai, Toshitaka, Miyamoto, Yoshinari
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.07.2007; Elsevier
• Subjects: AMMONIA; AQUEOUS SOLUTIONS; Citrate route; CITRATES; CITRIC ACID; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; DOPED MATERIALS; ELECTRIC CONDUCTIVITY; Exact sciences and technology; GALLIUM IONS; GALLIUM NITRATES; Gallium nitride; GALLIUM NITRIDES; HEXAGONAL LATTICES; Inorganic compounds; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Lithium doping; LITHIUM IONS; LITHIUM NITRATES; LUMINESCENCE; Materials science; NITRIDATION; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; OXYGEN COMPOUNDS; Oxynitride; Physics; SEMICONDUCTOR MATERIALS; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Surface treatments; VACANCIES; Citrate route; Gallium nitride; Lithium doping; Oxynitride; Temperature dependence; Electrical conductivity; Crystal lattices; Gallium nitrides; Citrates; Luminescence; Gallium additions; Precursor; Ammonia; Hexagonal lattices; Aqueous solutions; Optical properties; Nitridation; Codoping; Gallium Oxynitrides; Lithium additions; III-V semiconductors; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2007.04.011

Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga 0.89□ 0.11) (N 0.66O 0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750–850 °C. Approximately, 10 at% Li + was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga 3+ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li 2Ga 3NO 4, was also obtained with Li 2CN 2 impurity using similar preparations from a mixture of Li/Ga⩾1. The crystal structure was isostructural with h-GaN, and was refined as P6 3 mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2 b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2 b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li 2CN 2 impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO 2. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm. Schematic gallium vacancy distribution within a Ga-plane in wurtzite-type gallium oxynitride prepared via a citrate precursor route. Closed and open circles represent gallium and its vacancy sites, respectively. This is the most probable case among various kinds of statistical vacancy distribution, where Ga/vacancy=6/1 in atomic ratio. About 10 at% Li + could be doped to the gallium oxynitride by substituting Ga 3+. Well-crystallized new oxynitride, Li 2Ga 3NO 4, isostructural with h-GaN, was also obtained in the preparation with Li/Ga⩾1.