Cristalização uniforme e seletiva de materiais semicondutores amorfos utilizando pulsos curtos de uma fonte de luz laser

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

We have investigated the laser induced crystallization of amorphous semiconductors using short-pulses (5-7 ns wide) from the second harmonic (l = 532 nm) of a Nd:Yag laser source. The main studied material was the amorphous germanium (a-Ge), while some alloys like its hydrogenated counterpart (a-Ge:H), silicon-germanium (a-SiGe) and germanium nitride (a-GeN) were also used for comparisons. We have used time resolved reflection measurements to determine the thresholds for melting (36 m.J/cm2) and for damaging of the surface of the sample (66 m.J/cm2). Analysis of Raman scattering experiments show that the grain size distribution (between 5 and 20 nm) in polycrystalline material varies with the laser intensity .The effect of the grain size distribution on the Raman spectrum is more important than stress effects. The relative small size of the final grains is neither a function of the incoming laser wavelength nor of the substrate temperature (from room temperature up to 350 ºC). The fast hydrogen effusion during laser processing of a-Ge:H leads to a disruption of the top surface layer, leading to the formation of a self-suported 110-nm thick crystalline membrane. No segregation effects were observed after laser crystallization of a-SiGe, while it seems that no nitrogen remains bonded in the germanium matrix after the crystallization of a-GeN. We prove that it is possible to selectively crystallize a-Ge to obtain periodic arrays of micrometer-sized stripes and dots, by using the interference of two and three laser beams on the surface of the sample, respectively. The dots-array structure shows an increased surface roughness of about 50-nm, and the small crystallites seem to be weakly bonded or connected. This is corroborated by the use of plasma-etching, which removes preferentially the crystallized structures. We demonstrate that the original dots-array can be used as seeds for solid-phase growth of large crystalline areas upon thermal annealing bellow 450 ºC .The dots growth until complete coalescence, thus providing a way to crystallize large areas at low temperatures

ASSUNTO(S)

semicondutores amorfos cristalização fusão a laser semicondutores policristalinos

ACESSO AO ARTIGO

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