Laser Induced Synthesis of Compound Semiconductors
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LASER INDUCED SYNTHESIS OF COMPOUND SEMICONDUCTORS
L. D. LAUDE Universitg de l'Etat, Mons,
Belgium
ABSTRACT A review is given of a technique in which compound semiconductor films are produced by direct synthesis from multilayered, polymetallic films deposited onto insulating substrates and laser-irradiated in the CW or pulsed regime. Such films are characterized by a high degree of crystallinity together with optical and transport properties sufficiently close to single crystal ones to allow for various applications in optoelectronics.
INTRODUCTION Laser-processing has been considered to be an efficient (if not sufficient) means to restore periodicity in implanted semiconductors. In such processes, high power fluxes are required to melt and regrow epitaxially the damaged material onto the single crystal base. Nothing else is required from the laser beam and, to some extent, it does the job without perturbing the spatial distribution of implanted species. Recently, an increasingly large variety of laser-processing techniques (noted transient thermal processes) have been developed for silicon. They are designed to promote inovative solutions in the field of microelectronics, as for instance metal silicide formation or silicon-on-insulator thin film technology. As far as laserprocessing of compound semiconductors is concerned, interest has been so far almost exclusively restricted to implanted GaAs single crystals. Little attention has been paid to other compounds and to films of such materials. Part of this attitude resides in the well-known stoichiometry difficulties which are further enhanced in film preparation. It must be stressed however that such materials may have distinct advantages over silicon in fields like optoelectronics and photovoltaics for instance. Would such difficulties be encompassed, then a wider range of development could be envisaged aiming at more efficient devices. Other ways have been proposed to produce high quality thin films of such compounds, like chemical vapor deposition and molecular beam epitaxy. In both cases, and despite the quality of the materials being produced, sophistication, cost, time consumption and the reduced dimensions of the end-product are limitations to mass production. In such instances and given the flexibility of laser sources of energy, a laser-based technique may provide for the necessary conditions to allow large fabrication of semiconducting compound films. To be ideal, such a technique would have to be cheap, versatile and yet able to produce materials compatible with optoelectronics applications. As usual, compromises between these characteristics would determine the competitivity of the products. In this paper, a review is given of the results obtained using a laser processing technique adapted to the fabrication of compound semiconductor films on insulating substrates. This technique is essentially based on the synthesis of such materials which result from the laser (CW or pulsed) irradiation of polymetallic, multilayered films. Characterization of the
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