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Silicon–germanium (SiGe) films have been grown using chemical vapor deposition on c-plane sapphire substrates. Optical and material characterization of the films show successful alloying of SiGe up to 22.4% Si. X-ray diffraction characterizations show that the SiGe films are oriented in the (111) direction on the sapphire (0001) substrates. However, 60°-rotated twin defects are observed as well. Transmission electron microscopy (TEM) shows crystalline growth of the film. The high surface roughness observed in the TEM images and the atomic force microscopy scans of the films indicates the formation of two different orientations of SiGe on sapphire substrates. [ABSTRACT FROM AUTHOR]

Germanium (Ge) films have been grown on silicon (Si) substrate by ultrahigh-vacuum chemical vapor deposition with plasma enhancement (PE). Argon plasma was generated using high-power radiofrequency (50 W) to assist in germane decomposition at low temperature. The growth temperature was varied in the low range of 250°C to 450°C to make this growth process compatible with complementary metal-oxide-semiconductor technology. The material and optical properties of the grown Ge films were investigated. The material quality was determined by Raman and x-ray diffraction techniques, revealing growth of crystalline films in the temperature range of 350°C to 450°C. Photoluminescence spectra revealed improved optical quality at growth temperatures of 400°C and 450°C. Furthermore, material quality study using transmission electron microscopy revealed existence of defects in the Ge layer grown at 400°C. Based on the etch pit density, the average threading dislocation density in the Ge layer obtained at this growth temperature was measured to be 4.5 × 108 cm−2. This result was achieved without any material improvement steps such as use of graded buffer or thermal annealing. Comparison between PE and non-plasma-enhanced growth, in the same machine at otherwise the same growth conditions, indicated increased growth rate and improved material and optical qualities for PE growth. [ABSTRACT FROM AUTHOR]

Germanium-tin (GeSn) films with Sn compositions from 5% to 11% were grown on Ge-buffered Si using a reduced pressure chemical vapor deposition system with low-cost SnCl and GeH precursors. Material characterization showed that relaxed GeSn layers with thicknesses ranging from 400 nm to 1 μm were achieved. The strong photoluminescence (PL) intensity and the low defect density indicated very high material quality. In addition, temperature-dependent 10-300 K photoluminescence spectra showed that, due to strain relaxation of the material, the emission wavelength is longer than that of strained GeSn thin film samples ( t < 200 nm) having the same Sn composition. At 300 K, the PL peak at 2520 nm was observed from the sample with a 1- μm-thick GeSn layer and 11% Sn composition. [ABSTRACT FROM AUTHOR]

This paper reports the study of GeSn/GeSn/GeSn single quantum well (SQW) and double quantum wells (DQWs). The quantum well (QW) structures were grown on Ge buffered Si substrates using an industrial standard reduced-pressure chemical vapor deposition system. Pseudomorphically grown structures were observed using x-ray diffraction measurements. Defect-free interfaces between each layer were revealed using cross-sectional transmission electron microscopy. Atomic-scale high-resolution transmission electron microscopy and Fourier transform patterns exhibited the high crystalline quality of QWs. Temperature-dependent photoluminescence (PL) was performed, and the emission peaks attributed to the QW region were identified. The dominant optical transition changed from direct bandgap transition at 300 K to indirect bandgap transition at 10 K. Theoretical calculation showed the type-I band alignment for the QWs. Moreover, the Γ and L valley electron distributions and non-radiative lifetimes were evaluated, which further explained the PL characteristics of the QW samples. [ABSTRACT FROM AUTHOR]

Optical properties of germanium tin (GeSn) alloys have been comprehensively studied with Sn compositions from 0 (Ge) to 12%. Raman spectra of the GeSn samples with various Sn compositions were measured. The room temperature photoluminescence (PL) spectra show a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Temperature dependent PL shows the PL intensity variation along with the temperature change, which reveals the indirectness or directness of the bandgap of the material. As temperature decreases, the PL intensity decreases with Sn composition less than 8%, indicating the indirect bandgap GeSn; while the PL intensity increases with Sn composition higher than 10%, implying the direct bandgap GeSn. Moreover, the PL study of n-doped samples shows bandgap narrowing compared to the unintentionally (Boron) doped thin film with similar Sn compositions due to the doping. [ABSTRACT FROM AUTHOR]

Buffer-free GeSn and SiGeSn films have been deposited on Si via a cold-wall, ultra-high vacuum chemical vapor deposition reactor using in situ gas mixing of deuterated stannane, silane and germane. Material characterization of the films using x-ray diffraction and transmission electron microscopy shows crystalline growth with an array of misfit dislocation formed at the Si substrate interface. Energy dispersive x-ray maps attained from the samples show uniform incorporation of the elements. The Z-contrast map of the high-angle annular dark-field of the film cross section shows uniform incorporation along the growth as well. Optical characterization of the GeSn films through photoluminescence technique shows reduction in the bandgap edge of the materials. [ABSTRACT FROM AUTHOR]