Among the III-nitride semiconductors AlN exhibits the largest direct band gap, 6.2 eV and is thus suitable for solid-state white-light-emitting devices. It is promising in spintronics because of its high Curie temperature if doped with transition metals. AlN shows excellent field-emission performance in vacuum microelectronic devices due to its small electron affinity value, which is from negative to 0.6 eV, therefore, study of nanostructured AlN, such as AlN nanowires and nanorods are important for nanodevice applications.
Aluminium nitride (AlN) crystals were grown by physical vapour transport (PVT) method. In this method a thermal gradient drives the sublimation of a polycrystalline AlN source material and recondensation occurs at the colder substrate. The growth was carried out at a temperature between 1600 and 1850 °C in pure nitrogen (N2) ambient, maintained at pressures between 200 and 700 mbar.
Here we focused on growth dependences and morphological forms of AlN crystals. The effects of different conditions such as nitrogen pressure, growth temperature and temperature ramp-up was studied. By varying the growth conditions, we were able to scale down crystal dimensions from micrometer to nanometer size. One can see that the parameter window in the relationship temperature–pressure for the evolution of different structural forms is narrow. The temperature ramp-up is a critical step in the growth process. This will be discussed in relation to the formation mechanism of AlN nanowires.
The AlN surface morphology was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy. X-ray diffraction and Cathodoluminescence were used to examine the crystalline quality of the grown crystals.
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