Poster abstract

Aluminum nitride AlN is a wide-gap crystalline material (Eg = 6.2 eV). Due to its hardness, thermal and chemical stability and high thermal conductivity it is widely used in microelectronics in the form of thin layers and ceramics. We have studied AlN ceramics using methods of optical spectroscopy, thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL). AlN grains are characterized by a lattice of wurtzite type easily incorporating oxygen as a natural dopant, which substitutes nitrogen in the regular lattice site during the crystallization process forming several types of oxygen-related defects. Charge transfer processes between the oxygen-related defects occur under irradiation with both ultraviolet radiation (UVR) and ionizing radiation producing donor and acceptor pairs with different separation distances. Recombination of close donor-acceptor pairs during irradiation process and shortly after its ceasing is accompanied by a strong luminescence emission peaking around 400 nm. The donor - acceptor pairs with larger separation distances survive until their recombination is initiated by heating or illuminating the sample with visible or infrared light, producing TL or OSL, respectively. These phenomena form the basis for the application of AlN as a dosimetric material.

The properties of TL and OSL of AlN ceramics were studied after exposure both to ionising radiation and UVR. The TL signal of the irradiated material is characterized with a very high sensitivity, 5 decades wide linear dynamic dose range, good repeatability of measurements and a minor influence of the heating rate on the TL. Though the OSL signal was found to be much weaker than the TL response, it is still high enough to be used for dosimetric applications. This material has a spectral sensitivity in a broad region from 200 to 360 nm covering almost the whole UVR spectrum. In the UV-A and UV-B regions of the solar emission (280-360 nm) the character of the AlN spectral sensitivity is in good agreement with the human skin erythemal response, making the material potentially applicable for personal UV dosimetry.

A practical application of the AlN ceramics for dosimetry is hampered by the serious disadvantage of the material - the high fading rate of the TL and OSL signals after exposure to ionising radiation and UVR during storage at room temperature. The fading of the stimulated signal is explained by the uncontrollable recombination of the donor-acceptor pair due to charge carriers release from the trapping centres. Introducing additional dopants, providing stable deep trap levels inside energy gap could eliminate the fading process. The search for such impurities improving dosimetric properties of the material is the aim of further study.