Novel materials suitable for optoelectronics are of great interest due to limited and diminishing energy resources and the movement toward a green earth. We report a simple film growth method to tune the S composition, x from 1 to 2 in semiconductor ultrathin SnS x films on quartz substrates, that is, single phase SnS, single phase SnS2, and mixed phases of both SnS and SnS2 by varying the sulfurization temperature from 150 to 500 °C. Due to the ultrathin nature of the SnS x films, their structural and optical properties are characterized and cross-checked by multiple surface-sensitive techniques. The grazing incidence X-ray diffraction (GIXRD) shows that the single phase SnS forms at 150 °C, single phase SnS2 forms at 350 °C and higher, and mixed phases of SnS and SnS2 form at temperature between. GIXRD shows structures of SnS film and SnS2 film are orthorhombic and 2H hexagonal, respectively. To complement the GIXRD, the reflection high energy electron diffraction pattern analysis shows that both pure phases are polycrystalline on the surface. Raman spectra support existence of pure phase SnS, pure phase SnS2, and mixed phases of SnS and SnS2. X-ray photoelectron spectroscopy reveals that the near surface stoichiometry of both single phase SnS and single phase SnS2 are close to Sn/S ratios of 1:1 and 1:2, respectively. UV–vis spectroscopy shows the optical absorption coefficient of SnS film is higher than 105 cm–1 above the optical bandgap of 1.38 ± 0.02 eV, an ideal optical absorber. A two-terminal device made of SnS film grown on SiO2 substrates shows good photoresponse. The SnS2 has an optical bandgap of 2.21 ± 0.02 eV. A photoluminescence (PL) peak of SnS2 film is observed at ∼542 nm. Time-resolved PL of the single phase ultrathin SnS2 film indicates a carrier lifetime of 1.62 ns, longer than sub nanosecond lifetime from multilayer SnS2. Our comprehensive results show that ultrathin SnS and SnS2 films have the required properties for potential photodetectors and solar cell applications but consume much less material as compared with current thin film devices.

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Single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (~21-55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection highenergy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [1 � 21 � ] CdTe //[1100] CdS //[010] mica , respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. The use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.

We have performed the epitaxial growth of GaInN based deep green (540–570 nm) light emitting diodes (LEDs) by introducing processes to avoid the formation of V‐defects in the active region of the GaInN/GaN multiple quantum wells. For 541 and 559 nm LED wafers, the light output power (LOP) at 90 A/cm2 reaches as high as 14 and 8 mW, respectively. These values are 4 times larger than those of typical deep green LED wafers with average V‐defect density of 2–5 × 108cm–2. Under pulsed operation (pulse width of 50 μs, duty cycle 1%), the external quantum efficiency exhibits a maximum of 39% at 16 A/cm2 in 558 nm LED die of size (350 μm)2. This type of V‐defect‐free LED die also shows excellent lifetime behaviour. In 168 hr stress test of 30 mA at 80 °C, LOP declines less than 5%. Apparently, eliminating V‐defects from the active region significantly enhances the reliability of deep green LEDs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)