Laser Interference Structuring of a-GeN for the Production of Optical Diffraction Gratings
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A17.4.1
Laser interference structuring of a-GeN for the production of optical diffraction gratings M. Mulato1, A. R. Zanatta2, D. Toet3,*, and I. E. Chambouleyron4 1 Departamento de Física e Matemática, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, Ribeirão Preto, SP, Brazil 2 Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP, Brazil 3 FlexICs Inc.,165 Topaz Street, Milpitas, CA, 95035, USA 4 Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas - Unicamp, Campinas, SP, Brazil * Present address: Photon Dynamics, Inc., 17 Great Oaks Blvd., San Jose CA 95117, USA
ABSTRACT In this work, we study the pulsed laser crystallization of hydrogen-free amorphous germanium-nitrogen alloys (a-GeN). We discuss the role of nitrogen during phase transitions and the possible application of the resulting structure as an optical diffraction grating. The crystallized region results of pure microcrystalline germanium (µc-Ge). An indication that Ge-N bonds have broken and nitrogen outdiffused of the film is obtained from infrared spectroscopy and confirmed by Raman spectra. A pattern of alternating a-GeN and µc-Ge lines with a period of about 4 µm acts as an optical diffraction grating due to the difference in optical properties between the two materials, and the three dimensional surface profile, caused by N2 effusion, that is formed on the sample.
INTRODUCTION In the last decade a growing interest in laser processing technologies was observed at the semiconductor industry [1-19]. Amorphous semiconductors have been crystallized by treatments with short laser pulses. This process has attracted a lot of attention since it enables the fabrication of high performance devices base on polycrystalline materials that are produced on low temperature substrates, e.g. for flat panel display applications [9-11]. The same process could be applied in the near future for the development of new generation X-ray medical imaging systems. Experimental and theoretical studies have shown that laser crystallization involves ultra-fast melting and solidification processes occurring far from thermal equilibrium [12-17]. In addition to that, when more than one laser beam is used for the crystallization process, new interesting phenomena take place also. Bringing two laser beams to interference on the surface of an amorphous film results in a sinusoidal modulation of the light intensity. This modulation of the light intensity leads as a consequence to a modulation of the temperature of the sample. The last one thus controls the selective crystallization process. As a result, a pattern consisting of alternating amorphous and polycrystalline lines (dots are obtained when 3 beams are used) is obtained. In summary, the technique seems to be very promising for controlled grain growth, and reduced lithographic processes in industrial applications, among others. This technique was first demonstrated on hydrogen-free amorphous silicon (a-Si) in 1994 [18], and was
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