Abstract:
The results of measurements of AlN polarization in the range of 4.3–300 K are presented. These results are used for calculating the pyroelectric coefficients as a function of temperature. The experiment was carried out both with an original sample grown from gas phase in nitrogen atmosphere at $T\approx$ 2400 K and with the sample subjected to external electric action in a field of different polarity. The sample polarization at $T$ = 4.2 K results in a radical modification of the polar state of real AlN sample: due to the structural defects, ferroelectric ordering arises and the total sample polarization dependent on $T$ increases by an order of magnitude. First of all, the revealed anomalies are related to the occurrence of oxygen in the crystalline structure resulting in considerable deformations of coordination tetrahedra in the wurtzite structure. The process of replacement of the nitrogen vacancies by oppositely charged oxygen ions also leads to changing the dipolemoment orientation for the coordination tetrahedra in the structure instead of changing only their magnitudes. The ferroelectric ordering “in pure form” exists in this AlN sample only below $T\approx$ 80 K.
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