We report here the fabrication and characterization of ultra-long AlN whiskers by physical vapor transport method. The obtained whiskers are 1–3 µm in diameter and up to millimeters in length. The whiskers grow along the [0001] crystallographic direction and are well crystallized. They exhibit a strong ultraviolet emission at 345 nm, the shortest wavelength reported in AlN whiskers or nanowires. Our results indicate that these large scales of AlN whiskers are less contaminated by oxygen and other impurities compared with the previously reported ones, which may find wide applications in fabricating ultraviolet optoelectronic devices.

A technique of controlling growth gas flow rate for adjusting crystal resistivity is presented in this paper. The experimental results showed that high growth gas flow rate could affect SiC crystal resistivity remarkably. The SiC crystal resistivity would get higher and higher with increasing growth gas flow rate. The purifying effect of gas flow rate was contributing to resistivity increase at a relatively low flow rate range. As for the high gas flow rate, increase of resistivity might be explained by the well-known site competition effect. Then, one explanation for reducing nitrogen content in the crystal via increasing gas flow rate was put forward. Namely, the Si component in the gas species may more easily go through the graphite crucible at the initial stage to make the growth ambient C-rich when the gas flow rate is ∼800 sccm or more and hence suppress nitrogen incorporation into carbon site to increase crystal resistivity. This result is very helpful to grow high purity high resistivity SiC ingots.