Analysis of Layer Structure Variation of Periodic Porous Silicon Multilayer

Abstract

Structures of periodic porous silicon multilayer, which were formed by the current density modulation method, were investigated by cross-sectional scanning electron microscopy (SEM) observation. When the layers were formed with a current density of 20 mA/cm2 or less the thickness of the layers was constant regardless of the stack position of the layer. When the layers were formed with a current density of 50 mA/cm2 or more, the thickness of the layers decreased and the porosity of the layers increased as the stack position of the layer became deep. The layer peeled off when the porosity of the layer increased up to aproximately 100%. The thickness variation of the layers and the peeling were prevented by raising the temperature of the electrolyte.

Optical characterization of one-dimensional porous silicon photonic crystals with effective refractive index gradient in depth

“…As commented in the experimental section, to project our 1D‐PSPC devices, we estimate the d H and d L values using the etch rate value determined from the thick monolayers (Eq. (2)), however this rate may be different from those observed in thin multilayers structures, as reported by many authors , and also the ERI could also be dependent on the layer thickness . These effects are attributed to: (i) difficulties in HF diffusion from the first outer porous layer to the deep layers where the reaction surface is placed (PS/c‐Si interface); and (ii) local consumption of HF concentration during silicon dissolution .…”

“…(2)), however this rate may be different from those observed in thin multilayers structures, as reported by many authors , and also the ERI could also be dependent on the layer thickness . These effects are attributed to: (i) difficulties in HF diffusion from the first outer porous layer to the deep layers where the reaction surface is placed (PS/c‐Si interface); and (ii) local consumption of HF concentration during silicon dissolution . For this reason the HF concentration at the etching front is lower than in the electrolyte bulk , so for a given current density, the larger the HF concentration, the larger the etch rate.…”

“…These effects are attributed to: (i) difficulties in HF diffusion from the first outer porous layer to the deep layers where the reaction surface is placed (PS/c‐Si interface); and (ii) local consumption of HF concentration during silicon dissolution . For this reason the HF concentration at the etching front is lower than in the electrolyte bulk , so for a given current density, the larger the HF concentration, the larger the etch rate. If the HF concentration changes locally with time, then the etch rate will also .…”

Estruturas multicamadas de silício poroso para aplicação em dispositivos de cristais fotônicos.

“…No entanto em [90] foi reportado que a taxa de corrosão permanece sendo aproximadamente constante para as camadas formadas com baixa densidade de corrente (alto índice de refração). Esta discrepância em relação aos resultados obtidos no presente trabalho pode ser atribuída à diferença de tempo de anodização utilizada, já que foram utilizados tempos da ordem de 600 segundos promovendo camadas mais espessas e profundas do que os reportados em [90].…”

“…No entanto em [90] foi reportado que a taxa de corrosão permanece sendo aproximadamente constante para as camadas formadas com baixa densidade de corrente (alto índice de refração). Esta discrepância em relação aos resultados obtidos no presente trabalho pode ser atribuída à diferença de tempo de anodização utilizada, já que foram utilizados tempos da ordem de 600 segundos promovendo camadas mais espessas e profundas do que os reportados em [90]. A dependência da taxa de corrosão em função da profundidade do filme tem como conseqüência a formação de camadas com diferente índice de refração e diferente espessura mesmo elas tendo sido formadas em iguais condições Devido à alta superfície específica, de 200-250m 2 /cm 3 , nas estrutras mesoporosas, os filmes de PS apresentam problemas de envelhecimento [80,81] devido à sua elevada reatividade química, provocando mudanças nas suas propriedades ópticas [81,86].…”