Synthesis and characterization of Ge nanocrystal by LPCVD / Sintese e caracterização de nanocristais de Ge por LPCVD

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

In this thesis we studied the synthesis of Ge nanocrystals (NCs) by the LPCVD technique (Low Pressure Chemical Vapor Deposition). We looked for NCs with characteristics of sizes, density and uniformity of sizes that are necessary for applications in floating gate memory devices. To reach those characteristics we have optimized the process conditions. The NCs were fabricated by a process of two steps: 1) formation of Si nuclei on SiO2 surface, through the silane (SiH4) decomposition; 2) Ge growth on Si nuclei through germane (GeH4) deposition. We accomplished deposition cycles and characterization of the samples. The process parameters: temperature, total pressure, silana and germana flow and deposition time, were altered conveniently based on the literature and results obtained at each production cycle. The morphology of the samples was analyzed by atomic force microscopy (AFM) and the NCs structures were analyzed by high resolution transmission electron microscopy (HRTEM). We studied the influence of the process parameters in the NCs characteristics and we have observed tendencies of NCs density increase with rise of the temperature, total pressure and SiH4 flow of step 1. The NCs size tends to decrease with the reduction of temperature, total pressure and deposition time of step 2. The results show that with the parameters: 600 ºC / 5 Torr / 20 sccm de SiH4 / 20 sec. for the Si nucleation and 550 ºC / 2 Torr / 5 sccm / 30 sec. for the Ge deposition, it?s possible to reach a high density of NCs (4x1010 NCs/cm2) with diameter of 19 nm and average height of 4,5 nm

ASSUNTO(S)

silicon semicondutores semiconductor silicio germanium nanocrystals nanocristais germanio

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