Aluminum nitride (AlN) films were grown on sapphire by reactive magnetron sputter deposition in N 2 discharges at plasma self-heating conditions. The growth temperature was as low as 94°C. The structural properties resulting from different substrate biases and growth pressures were investigated by atomic force microscopy, x-ray diffraction (XRD) measurements, and transmission electron microscopy (TEM). At 20 mTorr of N 2 with most sputtered species thermalized, films exhibited both AlN (0002) and ð1011Þ XRD peaks, with the AlN (0002) intensity initially increasing with ion energy above 15 eV, showing enhanced film quality with an optimum of 25 eV. At a lower growth pressure of 5 mTorr with energetic sputtered species, the AlN ð1011Þ peak disappeared and the crystallinity of AlN improved, exhibiting relaxed epitaxial AlN. The measured lattice parameter was 0.4975 nm, which was 0.10% smaller than that of bulk. The epitaxial relationship of a single-crystal AlN film was confirmed by pole figure and cross-sectional TEM. These results demonstrate that control of ion energy and energy of the sputter-deposited species is critical for film deposition at low temperature.
Development of high-performance fully depleted silicon-on-insulator based extended-gate field-effect transistor using the parasitic bipolar junction transistor effect Appl. Phys. Lett. 101, 133703 (2012) Abnormal interface state generation under positive bias stress in TiN/HfO2 p-channel metal-oxide-semiconductor field effect transistors Appl. Phys. Lett. 101, 133505 (2012) Top-gate staggered poly(3,3″′-dialkyl-quarterthiophene) organic thin-film transistors with reverse-offset-printed silver source/drain electrodes Appl. Phys. Lett. 101, 133306 (2012) Subthreshold swings below 60mV/dec in three-terminal nanojunctions at room temperature Appl. Phys. Lett. 101, 133504 (2012) Top-gate staggered poly(3,3″′-dialkyl-quarterthiophene) organic thin-film transistors with reverse-offset-printed silver source/drain electrodes APL: Org. Electron. Photonics 5, 220 (2012) Additional information on Appl. Phys. Lett.
Selective-area growth (SAG) based on plasma-assisted molecular-beam epitaxy (PAMBE) was shown to facilitate improvement of Ohmic contacts and directcurrent (DC) characteristics for GaN-based field-effect transistors (FETs) over the widely accepted ion-implantation technique. Twofold improvements in breakdown voltage were also demonstrated for samples grown on both sapphire and silicon substrates. An AlGaN/GaN high-electron-mobility transistor (HEMT) fabricated with PAMBE-SAG exhibited a low specific contact resistivity of 5.86 9 10 À7 X cm 2 , peak drain current of 420 mA/mm, and high breakdown voltage of 77 V. These results demonstrate that PAMBE-SAG is suited to fabricating HEMTs for high-power applications.
For optoelectronic applications requiring unconventional substrates, use of flexible forms of semiconductors may be inevitable. We have fabricated a flexible form of single crystalline AlN ribbons with periodic and wavelike structures on an elastomeric substrate. Single crystalline AlN films were grown on Si (111) substrate using high vacuum unbalanced magnetron sputtering. Crystallinity of the AlN films was confirmed with x-ray diffraction and pole figure. The AlN ribbons were transferred to a prestrained (3.1%) elastomeric substrate and the resulting “wavy” ribbons on the substrate were flexible up to 30% strain without any crack formation on the surface. As the film thickness changed from 300 to 900 nm, the periods of the waves varied from 95 to 277 μm, which were within a 10% error of the calculated values. When we applied more than 30% strain, mechanical instability, such as the failure of AlN ribbons due to the cracks on the surface and the merged ribbons, was observed.
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