Photochromism and influence of point defect charge states on optical absorption in aluminum nitride (AlN)

Abstract

In this work, we study the absorption properties of AlN in the range of 1.5 -5.5 eV, as well as the meta-stable change in absorption induced by ultraviolet (UV) irradiation (photochromism), and the restoration of the initial state under the action of irradiation of 2 -4 eV or elevated temperatures. UV irradiation results in a decrease of the absorption coefficient from 110 cm -1 to 55 cm -1 at 4.7 eV while in the visible range the absorption coefficient increases from values below 5 cm -1 to ~35 cm -1 . Measurements with two linear polarizations, E∥c and E⊥c, provide determination of several different absorption bands at 2. 6, 2.8, 3.4, 4.0, 4.5, and 4.8 eV. The bands at 2.6 eV and 3.4 eV identify the defect levels near to the valence band, while the band peaking at 2.8 eV is related to the conduction band. The photochromism allows controlling the absorption of light in two related spectral ranges because the decrease of UV absorption and increase of the visible absorption are related to switching the charge state of the same defects.

Tracking of Point Defects in the Full Compositional Range of AlGaN via Photoluminescence Spectroscopy

“…[ 13,27,30 ] Absorption measurements have also confirmed the presence of carbon‐related defects in AlN. [ 17,31–33 ] Based on these studies, it has been determined that carbon is mainly a substitutional impurity on the nitrogen site in the n‐type material, with the possibility of complex formation with other carbon species. [ 31,33 ] However, recent results have shown that carbon occupies the metal site in semi‐insulating or p‐type material, so the site occupation depends on the dopant and can be manipulated by the Fermi level.…”

“…[17,[31][32][33] Based on these studies, it has been determined that carbon is mainly a substitutional impurity on the nitrogen site in the n-type material, with the possibility of complex formation with other carbon species. [31,33] However, recent results have shown that carbon occupies the metal site in semi-insulating or p-type material, so the site occupation depends on the dopant and can be manipulated by the Fermi level. [16,21,34] This identification and control of C configuration is important due to its impact on the electrical and optical properties.…”