Direct excitation spectroscopy of Er centers in porous silicon

Abstract

We report direct excitation of optically active Er centers in porous Si. Excitation spectroscopy performed close to the intracenter I415/2→I411/2 and I415/2→I49/2 transitions of Er3+ (4f11) ions allows us to identify two kinds of Er centers in porous Si: (i) Er diffused into porous nanograins with lower than cubic symmetry and (ii) Er centers incorporated in an amorphous silicalike matrix. The latter show much weaker thermal quenching of the Er3+ emission which decreases only by a factor of eight when the temperature is increased from 4.2 K up to 360 K.

The Selective Growth of Silicon Nanowires and Their Optical Activation

“…As above mentioned, the optimum location for Er 3+ is not inside Si, but in the nanometerthin oxide shell right next to Si (Shin et al, 2000b;Kimura et al, 2003;Stepikhova et al, 1997, as cited in Suh et al, 2005). This suggests that rather than trying to dope Si-NWs directly, it would be preferable to coat the Si-NWs with high-quality Er-doped silica in order to optically activate the Si-NWs.…”

“…Then, the long SiNWs were dipped into Sol-gel solutions by surface coating with Er-doped silica or other materials. That is because the optimum locations for Er ions are not inside Si, but in the nanometer thin oxide shell right next to Si (Kimura et al, 2003;Shin et al, 2000b;Stepikhova et al, 1997). As a result, rather than trying to dope SiNWs directly, it would be preferable to coat the SiNWs with high quality, Er-doped oxides by sol-gel in order to optically activate the SiNWs.…”

“…Given the identical temperature dependence of the Er 3+ luminescence lifetime, the reduction of the Er 3+ luminescence lifetime by Si-NWs is attributed to the effect of increased effective refractive index (Snoeks et al, 1995) rather than any degradation of the quality of sol-gel derived silica film. Thus, it could be ensured that the Er 3+ ions excited via carriers generated in Si-NWs are actually in the sol-gel derived Erdoped silica film that is coating the Si-NWs (Shin et al, 2000b;Kimura et al, 2003;Stepikhova et al, 1997), indicating that Si-NWs, even without quantum confinement effects, are much more effective for exciting Er 3+ ions in an oxide layer on their surface. This conclusion is supported by the low-temperature PL spectra, as shown in Figure 2.5.…”

“…This conclusion is supported by the low-temperature PL spectra, as shown in Figure 2.5. The 4 I 13/2 → 4 I 15/2 transition responsible for the 1.54 µm Er 3+ luminescence is a parity-forbidden transition that occurs in part due to the effects of the crystal field, and the exact shape and position of the luminescence spectra depend on the chemical and structural environment of Er (Stepikhova et al, 1997). Therefore, the results indicate that by using sol-gel derived Er-doped silica to optically activate Si-NWs, we can simultaneously achieve the ease of carrier injection, high carriermediated Er 3+ excitation efficiency, and high Er 3+ luminescence efficiency in a thick, easily produced film with a very high areal density of Er 3+ ions, thus providing a promising material platform for Si photonics.…”

Optical activation of Si nanowires using Er-doped sol-gel derived silica

“…The 4 I 13/2 → 4 I 15/2 transition responsible for the 1.54 µm Er 3+ luminescence is a parity-forbidden transition that occurs in part due to the effects of the crystal field, and the exact shape and position of the luminescence spectra depend on the chemical and structural environment of Er [13]. However, the Er 3+ PL spectra obtained from the Si-NWs and pure silica film are completely identical irrespective of the pump wavelengths, indicating that the optically-excited and carrier-excited Er 3+ ions are all in the same environment -i.e., in silica.…”