Исследование свойств двумерных пленок МоS-=SUB=-2-=/SUB=- и WS-=SUB=-2-=/SUB=-, синтезированных химическим газофазным методом

Molybdenum- and tungsten-disulfide films are synthesized by chemical-vapor deposition. The set of optimal synthesis parameters (temperature, time, and amount and ratio of precursors) is established at which MoS_2 domains with maximum lateral sizes of up to 250 μm on sapphire and MoS_2 and WS_2 domains up to 80 μm in size on SiO_2 can be grown. Domain intergrowth leads to the formation of homogeneous single-layer MoS_2 films. The Raman spectra of the synthesized films contain two characteristic peaks corresponding to the atomic vibrations in MoS_2 and WS_2. Photoluminescence of the single-layer and bilayer MoS_2 films with a maximum intensity of 670 ± 2 nm and of the single-layer WS_2 films with a maximum intensity of 630 ± 2 nm is detected. The photoluminescence spectral maps (the dependences of the photoluminescence intensity on the luminescence and excitation-light wavelengths) are measured. According to the measured data, the photoluminescence excitation spectrum of MoS_2 has a maximum at 350 ± 5 nm and the photoluminescence excitation spectrum of WS_2 has a maximum at 330 ± 5 nm. The I – V characteristics of the synthesized films are photosensitive in the visible spectral range.

Excitation Wavelength and Saturation Effects on Gallium Nitride Photoluminescence

ABSTRACTWe report on the excitation wavelength and power dependence of LPMOCVD grown GaN photoluminescence (PL). A mode-locked Ti:Sapphire laser that is doubled to provide a tunable wavelength range of 350-500 nm is used to pump the GaN samples. Special attention has been paid to the “yellow” (∼567 nm) luminescence. Different power dependence characteristics of the yellow emission are observed when pumping above and below the bandgap. A measurement of the photoluminescence excitation spectrum of the yellow peak (∼567 nm) is also performed and this spectrum shows a peak at room temperature at 3.36 eV (369 nm), an additional broad peak at 77 K and only the broad peak at 7 K. An excitation model is used to explain the behavior of the yellow emission, suggesting the neutral donor serves as a key species for the yellow emission.