STUDY OF MULTIPLE QUANTUM WELL STRUCTURES WITH NIPI DOPING FOR ELECTRO ABSORPTION MODULATION / ESTUDO DE ESTRUTURAS DE POÇOS QUÂNTICOS MÚLTIPLOS COM DOPAGEM NIPI PARA MODULAÇÃO POR ELETRO-ABSORÇÃO

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

In this thesis we have studied multiple quantum well structures with Si delta doping inside the GaAs quantum wells and C delta doping in the AlGaAs barriers (nipi). This structure was proposed by W. Batty and D. W. E. Allsopp ( ¤ )as an alternativeto maximize the Stark shift and improve the performance of electroabsorption amplitude modulators.The samples were grown by the MOCVD technique, using respectively as Si and C sources, silane (SiH4) and carbon tetrabromide (CBr4). Particularly, the C doping of AlGaAs was carefully studied because of the difficulties in controlling the C incorporation.Despite the little flexibility in the growth conditions, in particular in the V to III fluxes ratio, it was possible to control the C doping level in the AlGaAs layers.The nipi structures were studied in detail to evaluate their potential for use in the fabrication of optical modulators. It has been observed that the required balance between n and p type doping levels is not trivial to be achieved due to the presence of interface hole traps whose population depends on the GaAs quantum well doping concentration.Photoluminescence measurements, supported by calculations, point out that an spatially indirect transition which involves electrons in the GaAs quantum well and holes in the AlGaAs barrier occurs, at low temperatures, at energies below the gap of the quantum well. At room temperature this transition has not been observed and the measured optical emission occurs at essentially the same energy as that of an equivalent undoped structure. These results led to the conclusion that insertion losses problems will not occur due to absorption below the gap since, at room temperature, there are no energy levels below the quantum well fundamental transition energy.

ASSUNTO(S)

dopagem delta delta-doping moduladores modulators

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