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The improved resistively-heated furnace with two heaters established a vertical thermal gradient to control nucleation during AlN single crystals Physical Vapor Transport (PVT) growth on polycrystal tungsten substrates. During the high temperature (> 1850 °C) heating process, the reverse temperature field (i.e., the temperature difference between the sublimation zone and the crystalline zone ΔT < 0) was obtained to reduce the number of nuclei on the tungsten substrate. During growth, the proper positive values of ΔT T were chosen to content the supersaturation values (0.25 < S < 0.3). The reverse temperature condition during high temperature (> 1850 °C) cooling was fulfilled to avoid recrystallization on grown AlN crystal. AlN single crystals made through the method were characterized by X-ray diffractions (XRD) and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Bandgap engineering offers opportunities for tailoring the properties of semiconductor materials for desired applications in microelectronics and optoelectronics. Alloys of different semiconductor materials can lead to the continuously tuning of the bandgap. Here, we report the bandgap engineering in layered InSe single crystals by substituting the Se atoms with S atoms. The formation of InSxSe1-x single crystal alloy with x ≤ 0.3 is evidenced by the X-ray diffraction and resonant Raman spectra. The photoluminescence (PL) spectra peak position blue shifts from ~1.27 to ~1.42 eV as S composition increases from 0 to 0.3 in the alloys, which is consistent with the bandgap shifts calculated by density functional theory. Temperature dependence of the PL spectra indicate that the presence of S atoms decreases the strength of the electron-phonon interaction but increases the average phonon energy in InSxSe1-x alloys. Our findings will open an intriguing avenue in understanding the fundamental physics in the III-VI layered semiconductor materials and their potential applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]