Luminescence Excitation Spectrum for Excitation in the Region of Fundamental Absorption, and the Electronic Structure of Aluminum Nitride

In the present work we investigate the band structure of aluminum nitride crystals and the nature of the electronic transitions excited by photons in the region of the fundamental absorption. The band structure of crystals is usually studied in terms of the spectral variation of the reflection coefficient R. This method has many shortcomings, however. In the first place it involves laborious calculations, starting from the Kramers-Kronig relations, of the absorption coefficient K, as it is the latter that is directly associated with the band structure. The absorption coefficient K determined in this manner is very imprecise, as the directly measured quantity, R, can vary by a factor of not more than 5–6 (from 15–20% in the region of transparency to almost 100% in the region of large K) whereas the corresponding variation of the quantity of interest, K, can be more than 5–6 orders of magnitude (for example, from 0.1 to 105 cm−1).