Advanced optoelectronic devices, the backbone of modern communication technology, require the monolithic integration of different functions at chip level. An example of devices fulfilling this requirement are multi-quantum well (MQW) electroabsorption-modulated lasers (EMLs) employed in long-distance, high-frequency optical fiber communications technology. Such devices are realized by using the selective area growth (SAG) technique. Optimization of the growth parameters is carried out by empirical approaches as direct structural characterization of the MQW is not possible with laboratory X-ray sources, owing to the micrometer-variation of composition and thickness inherent to the SAG technique. Micrometer-resolved X-ray (m-X-ray) beam available at third generation synchrotron radiation sources, such as the ID22 at the European Synchrotron Radiation Facility (ESRF), allowed us to directly measure the determinant structural parameters of MQW EML structures such as well and barrier widths and mismatches with a 2 mm spatial resolution.In more detail, optoelectronic devices, widely used in the generation and detection of optical signal for telecom and datacom applications, consist of different III-V semiconductors alloys deposited on suitable substrates. The deposition can be performed by different techniques that are based on the crystal rebuilding of a semiconductor used as substrate, such as metal organic vapor phase epitaxy (MOVPE). [1,2] The reaction takes place between free atoms and the substrate's surface with the rebuilding of the crystal lattice. During the growth different layers are sequentially and uniformly deposited on the entire substrate, resulting in the aimed structure relative to the specific device function (e.g., LED, laser, amplifier, modulator, photodiode, waveguide, etc.).As an example, uncooled distributed feedback (DFB) lasers, operating in the second window of telecommunications at 1310 nm, are MQW semiconductor lasers directly modulated at high frequency (up to 10 Gb s À1) and are a key element for connections typically up to 10 km. For longer distances a directly modulated laser cannot be used. The devices operate at 1550 nm (third-window) to take advantage of the limited fiber attenuation. However, in the presence of chromatic-dispersion on a standard single-mode fiber at this wavelength, the high positive chirp [3] of the optical pulses, generated by directly modulated DFB, severely limits the propagation span ($10 km at 10 Gb s À1). For 40-80 km propagation of 10 Gb s À1 optical signals, external modulation is needed. An external MQW electroabsorption modulator (EAM) can produce near-zero or even negatively chirped pulses, allowing propagation spans of more than 80 km. An EML, [4,5] obtained by monolithic integration of an EAM with a constant-injected DFB laser (Fig. 1b), is often the most convenient and compact solution. The modulation of the laser emission is ensured by the switching between an opaque and transparent state of the EAM due to the Stark effect [6] (Fig. 1c) induced by a...

In the past few years, strong efforts have been devoted to improving the frequency of optical-fiber communications. In particular, the use of a special kind of integrated optoelectronic device called an electroabsorption modulated laser (EML) allows communication at 10 Gb s(-1) or higher over long propagation spans (up to 80 km). Such devices are realized using the selective area growth (SAG) technique and are based on a multiple quantum well (MQW) distributed-feedback laser (DFB) monolithically integrated with a MQW electroabsorption modulator (EAM). Since the variation in the chemical composition between these two structures takes place on the micrometer scale, in order to study the spatial variation of the relevant parameters of the MQW EML structures, the X-ray microbeam available at the ESRF ID22 beamline is used. The effectiveness of the SAG technique in modulating the chemical composition of the quaternary alloy is proven by a micrometer-resolved X-ray fluorescence (μ-XRF) map. Here, reported micrometer-resolved extended X-ray absorption fine structure (μ-EXAFS) spectra represent the state of the art of μ-EXAFS achievable at third-generation synchrotron radiation sources. The results are in qualitative agreement with X-ray diffraction (XRD) and micrometer-resolved photoluminescence (μ-PL) data, but a technical improvement is still crucial in order to make μ-EXAFS really quantitative on such complex heterostructures.

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ZrO 2 thin films were deposited on polycrystalline alumina, glass, á100ñ silicon, and stainless steel substrates by metal-organic chemical vapor deposition (MOCVD). Depositions were carried out in a hot wall reactor at reduced pressure (0.6 torr) in the temperature range 400±550 C, using zirconium cyclopentadienyl derivatives as precursors, both in a flux of oxygen and of an oxygen/water vapor mixture. High quality zirconia films with high growth rates were obtained by employing (C 5 H 5 ) 2 Zr(CH 3 ) 2 . Scanning electron microscopy (SEM) images display, in both cases, a tapered polycrystalline columnar structure of the deposits. Films grown under O 2 flux show a cracked surface with a variable carbon contamination depending on the experimental conditions, while those prepared in a O 2 /H 2 O mixture are smooth and well adherent to the substrate with 5 % carbon presence according to X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction shows that samples grown in O 2 flux consist of the tetragonal phase with a small amount of the monoclinic polymorph, whose percentage increases with the growth temperature. The presence of water vapor led to larger crystalline domains predominantly composed of monoclinic phase.

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