Si1−x−yGexCy films ( x≊0.90, y⩽0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x-ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C-resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions.
Arsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700 ˚C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure. Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced "composition pulling".
In this paper we demonstrate the successful integration of in-situ doped embedded Si:C stressors epitaxially grown in the source and drain areas of nMOS devices using a novel Cyclic Deposition Etch (CDE) process. These layers have substitutional C content ranging between 1% and 2% with potential of achieving even higher substitutional carbon concentration. Another distinctive feature of this process is that it allows for high in-situ P doping for ease of integration within a CMOS platform. We demonstrate superior performance of strained nMOS devices with embedded Si:C showing up to 12.5% on-state current improvement over the unstrained reference process. We report on material characterization results of embedded Si:C stressors, in particular, strain retention properties as a function of subsequent post-epitaxy processing.
High quality thin films of ZnO have been successfully grown by the pulsed laser deposition (PLD) technique since 1983. [1][2][3][4][5][6][7] More recently PLD has been used to grow epitaxial ZnO films on sapphire in order to investigate their nonlinear optical and piezoelectric properties and their use as a buffer layer for epitaxial GaN growth. [8][9][10][11][12] The relatively low substrate temperatures required during the deposition of thin films have been used as an argument in favor of the PLD technique. However, the growth of high quality epitaxial ZnO layers on sapphire (001) substrates has been achieved only at higher temperatures, 750-800ЊC. [8][9][10][11][12] The growth of high quality epitaxial ZnO films at temperatures below 550ЊC using an in situ ultravioletassisted PLD technique (UVPLD) is reported in this paper. Experimental The PLD system employed for this study 13 and the optimum conditions for the ZnO growth of oxide films were presented elsewhere. 4,5 An excimer laser (KrF, ϭ 248 nm, laser fluence 1.8-2.3 J/cm 2 , repetition rate 5 Hz) was used to ablate ZnO targets (99.99% purity). The oxygen pressure for conventional deposition (without UV radiation) was 1 ϫ 10 Ϫ3 Torr, while lower oxygen pressures of around 7-8 ϫ 10 Ϫ4 Torr were used during UVPLD. To increase the oxygen incorporation within the grown layer a vacuum compatible, low pressure Hg lamp, which allows for in situ UV irradiation of the substrate during the laser ablation-growth process and the cooling down stage was added to the PLD system. The photodissociation reactions of molecular oxygen induced by the UV photons emitted by the lamp (254 and 184 nm) are well known. 14 Films were deposited onto Si(100) wafers and sapphire (001) substrates.The crystalline structure of the grown films was investigated by X-ray diffraction (XRD) with the aid of an X'Pert MRD Philips system. The chemical composition was determined by Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS, Perkin Elmer 5100, Mg K␣ radiation, h ϭ 1253.6 eV). The optical properties of films grown on Si substrates were investigated by variable angle spectroscopic ellipsometry (VASE, Woollam Co.) at 70, 75, and 80Њ. The sheet resistance was measured by a four-point probe method.Results and Discussion Previous investigations by transmission electron microscopy showed that crystalline and textured (in the direction of the c axis of the hexagonal unit cell of the ZnO) films can be deposited by UVPLD at a substrate temperature of only 100ЊC. 15 Films grown on sapphire at temperatures higher than 400ЊC were found to exhibit in plane orientation as well. In Fig. 1, the diffraction patterns acquired from ZnO layers grown on sapphire substrates at 550ЊC by UVPLD and conventional PLD under otherwise identical conditions are shown. One can see that the layers are highly textured, with the c axis perpendicular to the substrate, [001] ZnO || [001] sap . To investigate the
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