The growth and optical properties of large, high-quality AlN single crystals

Abstract

The effect of impurities and defects on the optical properties of AlN was investigated. High-quality AlN single crystals of more than 20mm2 size were examined. Different crucible materials and growth procedures were applied to the growth of bulk AlN by physical vapor transport method to vary the defect and the impurity concentrations. The crystalline orientation was investigated by Raman spectroscopy. Glow discharge mass spectrometry was used to determine the trace concentration of the incorporated impurities such as oxygen and carbon. The photoluminescence emission and absorption properties of the crystals revealed bands around 3.5 and 4.3eV at room temperature. Absorption edges ranging between 4.1 and 5.95eV were observed. Since no straight correlation of the oxygen concentration was obtained, a major contribution of oxygen or oxygen-related impurities was ruled out to generate the observed emission and absorption bands in the Ultraviolet spectral range. The carbon-related impurities and intrinsic defects might contribute to the observed optical properties. The absorption coefficient for AlN single crystals has been derived for the spectral range below the band edge.

Broadband white light emission from Ce:AlN ceramics: High thermal conductivity down-converters for LED and laser-driven solid state lighting

“…For example, in Ce doped garnets, the range of peak positions is in the 500-550 nm range. 1 Since, consistent with previous studies, [22][23][24][25] the un-doped AlN (sample 7) does not show the 490 nm peak, we attribute the deconvoluted peak centered at 490 in Ce:AlN to the 4f to 5d electronic transitions of the Ce 3+ dopant.…”

“…PL caused by intrinsic defects such as vacancies, O impurities, and their complexes in AlN is well known. [22][23][24][25] AlN is extremely susceptible to O contamination, so O impurities are typically considered intrinsic. Studies on AlN ceramics 22,23 observed a PL peak in the ∼300 to 375 nm region and attributed it to an O related defect complex [V A1 -O N · ].…”

Stress and its effect on optical properties of AlN nanorods

“…It shifts from 3.3 to 4.0 eV with the oxygen concentration as reported. 20 The nitrogen vacancy and Al interstitial point defects are responsible for the visible emission as suggested by Strassburg et al 21 Unlike the extremely broadband emission from AlN, 22,23 the FWHM of the emissions of AlN nanorods is about 15 and 70 nm, corresponding to UV and visible emission, respectively. The PL measurement provides strong evidence for the existence of a shortening phonon lifetime mechanism via impurities and defects.…”

Development of 2" AlN Substrates Using SiC Seeds

“…Another kind of the two-stage procedure was reported by M. Strassburg et al (Strassburg et al, 2004) where the temperature was gradually ramped between the two stages and by Z. Sitar et al (Sitar et al, 2004) who used vaporization of Al (use of the metal vapour source is called direct synthesis method by K. Nishino et al (Nishino et al, 2002)) 13 at the first and the AlN powder source at higher temperature at the second stage; two-stage growth was also used by R. Dalmau et al with stages differing in the growth temperature and, thus, growth rate.…”