Shallow donors and deep level color centers in AlN single crystals: EPR, ODMR and optical studies

EPR studies presented here reveal the presence of three different types of shallow donor (SD) impurities in AlN single crystals: one impurity is located at the N site (preferentially oxygen, labeled D1) and two impurities are located at the Al site (preferentially carbon and silicon, labeled D2 and D3) of the AlN lattice. We show that D1 and D2 centers exhibit a DX-like relaxation. The light-induced EPR signals of the D1 and D2 centers are characterized by slightly anisotropic g factors typical for SD in AlN but strongly different anisotropic EPR linewidths ΔB. The D3 center shows the SD behavior at the room temperature and can be observed without light excitation at the temperatures above 200 K. Combining EPR, optical absorption and thermoluminescence induced by the X-ray irradiation we establish the structure of deep level color centers in AlN - a neutral nitrogen vacancy VN. The an optical absorption band of the center is in the visible region with a maximum at ∼450 nm and the energy level at ∼0.75 eV relative to the bottom of AlN conduction band (