Photoluminescence ofEr3+-implanted amorphous hydrogenated silicon suboxides

Abstract

Erbium ions incorporated into amorphous hydrogenated silicon suboxides (a-SiO x :H) allow to overcome the disadvantages of Er 3ϩ in c-Si such as the limited solubility, the strong quenching of the luminescence at room temperature, and the need for co-doping with electronegative atoms. a-SiO x :H alloys have an enhanced Er solubility and easily variable oxygen content, thereby providing favorable atomic environments for an efficient Er luminescence and reduced excitation backtransfer due to deeper localized band-tail states. In the present study, Er 3ϩ doses up to 7ϫ10 14 cm Ϫ2 were implanted into a-SiO x :H with oxygen content between 0 and 44 at. %. Optical properties such as the absorption coefficients and the photoluminescence ͑PL͒ spectra of the Er 3ϩ ions and of the SiO x host were investigated as a function of erbium implantation dose, oxygen content, defect density, temperature, and annealing treatment. It was found that annealing is a requirement for activating the characteristic Er PL at 1.54 m mainly due to a reduction of implantation induced defects. The intensity of both the intrinsic SiO x and the Er PL was found to be inversely proportional to the defect density as measured by electron spin resonance or subgap absorption. The Er PL is additionally enhanced upon annealing, probably as a result of better structural arrangements of the Er ions. The Er PL intensity increases approximately linearly with the implantation dose. An increase of the oxygen content ͑and correspondingly of the optical band gap͒ of a-SiO x :H causes no drastic changes in the erbium luminescence energy and intensity, whereas the intrinsic PL shifts to higher photon energies according to the larger band gap. Already low O concentrations of a few percent provide favorable Er environments. The main advantage of a-SiO x :H as a host matrix is revealed by temperature-dependent PL measurements. For high oxygen contents, the thermal quenching of both the Er 3ϩ and the intrinsic PL is strongly reduced. In an a-SiO x sample with 44 at. % oxygen, the Er PL is only quenched by 20% between 77 and 300 K. In contrast, the quenching of the intrinsic PL for all ͓O͔ is roughly one order of magnitude stronger than that of the Er PL. These PL measurements were complemented by PL excitation experiments over a wide spectral range. We have observed that the Er 3ϩ PL is excited about one order of magnitude more efficiently when pumped with sub-band-gap light compared to band-toband excitation. The experimental results are discussed with regard to the two currently proposed Er 3ϩ excitation models, the defect-related Auger effect and the Förster transfer mechanism.

Low energy shifted photoluminescence of Er3+ incorporated in amorphous hydrogenated silicon–germanium alloys

“…4 I 15/2 at 0.75 eV is of the order of 0.025 eV in full width at half maximum (FWHM), which is of almost identical magnitude as those widths observed in a-SiO x :H by Jannotta et al [1] The FWHM of the 1.50 eV transition reported in this work is slightly larger than 0.05 eV. It is necessary to remark that this FWHM is surprisingly narrow in the a-(Si xGe 1Àx ) 1Ày O y :H(Er) amorphous compound reported in this work, and its lineshape is strikingly similar to that of the direct ionic broadened fundamental emission 4 I 13/2 ?…”

“…4 I 13/2 transition, which has already been observed in absorption at 1.458 eV, [13] which in this case ought to be blue-shifted by an amount of around 40 meV [13]. However, several authors report strong and somewhat broader PL emission, centered between 1.3 and 1.55 eV, which is attributed either to the emission of SiO x , in a-SiO x :H, or to Si nanocrystallites embedded in SiO 2 [1,[13][14][15]. It is also necessary to remark that, in particular in the report of Janotta et al …”

“…Under these conditions, erbium as an impurity in amorphous silicon shows photoluminescence at room temperature. This result opens the possibility to fabricate electro-optic devices in this important spectral region [1]. Due to the extended interest to grow semiconductors that may be compatible with modern silicon technology, and to the importance of the Er 3+ emission, it is of interest to study, as an additional system to crystalline or amorphous silicon, erbium doped silicon germanium alloys.…”

“…These last limitations of the Er 3+ in c-Si result in a moderate luminescence yield at room temperature uncompetitive for the moment with that obtained from, e.g., III-V compounds. a-SiO x :H alloys have an enhanced erbium solubility and easily variable oxygen content, thereby providing what may be more favorable atomic environments for efficient Er 3+ luminescence [1][2][3][4][5].…”

“…Amorphous hydrogenated silicon suboxides (a-SiO x :H) implanted with erbium ions have been the subject of recent interest due to their possible application as an on-chip laser source for use in optical fiber communications [1][2][3]. This may be possible due to the luminescence emitted by this material at a wavelength of approximately 1.54 lm, which corresponds to the absolute absorption and local dispersion minima in optical fibers.…”