Search

By using first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory, the maximally localized Wannier functions of N vacancy and Al vacancy with different charge states in wurtzite AlN are calculated. With the shape and center of the computed Wannier function, the electronic structure and the spontaneous polarization of vacancy are studied respectively. The results show that N–Al bond possesses a large ionicity. It is found that the electrons of the dangling bonds displace to the positions of vacancies in N vacancy structure, while in Al vacancy structure the electrons of dangling bonds keep away from vacancies and move to the other side of N atoms. Since the vacancy breaks the centrosymmetry of the [1010] and [1210] orientations, the polarization will be induced in these two directions, and the polarization will increase as the charge increases. In the [0001] orientation, the spontaneous polarization in N vacancy will reverse as charge increases because of the dramatic variation of the electronic structure. Contrary to N vacancy, the reversion does not occur although the spontaneous polarization of Al vacancy increases as charge increases.

In a stainless steel autoclave of 25ml capacity, pure hexagonal aluminum nitride (h-AlN) nanowire has been successfully synthesized by direct reaction of AlCl3 with NaN3 in non-solvent system at low temperature. The obtained grayish-white powder is characterized by high-resolution transmission election microscopy, which shows that the grayish-white products consist of long straight-wires with diameter from 40nm to 60nm and the longest ones were up to several micrometers. The electron diffraction and XRD analysis indicat that the AlN manowire has hexagonal/cubicl monocrystal structure. A possible growth mechanism for h-AlN nanowire is disscussed.

The change of atom configuration in hexagonal AlN, caused by native point defects (N and Al vacancies, N and Al antisites, N and Al interstitials), are calculated firstly by plan-wave pseudopotential method with the generalized gradient approximation in the frame of density functional theory, and the most stable structure are obtained. Then the formation energy of each kind of native point defect is calculated, by which the possibilities of the six kinds of native defects to be formed during crystal growth are analyzed. Finally, the defect energy levels responding to every kind of native point defect and their electron occupancy are analyzed from the aspect of density of states. The results show that all the native defects form very deep energy levels in the band gap except N vacancy, and foreign impurities are needed to realize n- or p-type AlN. The values of defect energy levels obtained will be helpful in ascertaining the luminescence mechanism of some AlN non-band-edge emissions.