We report silicon band-edge photoluminescence ͑PL͒ with photon energy of 1.1 eV and external quantum efficiency ͑EQE͒ better than 10 Ϫ3 in samples prepared by high-temperature oxidation of porous silicon. The integrated PL intensity is insensitive to temperature. The EQE strongly depends on the annealing conditions: temperature, time, and ambient. A model is proposed in which the PL originates from silicon clusters within a nonstoichiometric silicon-rich silicon oxide matrix. ͓S0163-1829͑96͒52336-2͔A number of groups have investigated different types of photoluminescence ͑PL͒ in crystalline silicon (c-Si͒ during the last decades. Recent interest has focused on the visible PL that is observed in Si nanoclusters and in porous Si ͑PSi͒, 1 the infrared PL in silicon-germanium superlattices, 2 and the subgap PL due to impurities in c-Si. 3 Band-edge PL in bulk Si is inefficient and usually observed at low temperatures only because c-Si has an indirect band gap. 4 However, there are a few reports in the literature of room-temperature band-edge PL in Si. 5 The typical external quantum efficiency ͑EQE͒ of this PL is understandably low (р10 Ϫ5 ) but can be increased by better surface passivation. 6 In this work we report a significant increase of the Si band-edge PL EQE to greater than 0.1% and its unexpected weak dependence on temperature. During sample preparation, a large number of parameters may be varied opening additional room for further improvements.The samples were prepared by anodically etching borondoped p ϩ c-Si wafers with a resistivity Ϸ0.05 ⍀ cm in an HF-ethanol solution ͑1:1͒ under a current density JϷ20 mA/cm 2 . After anodization the samples were annealed in dilute oxygen ͑10% O 2 in N 2 ) from 10 min up to 3 h, at temperatures ranging from 800 to 990°C. Fouriertransform infrared ͑FTIR͒ spectra of the oxidized samples show the presence of silicon oxide with an absorption peak near 1080 cm Ϫ1 and the absence of Si-H bonds. The PL measurements were performed using the experimental setup in Ref. 5. Figure 1 compares the PL spectra measured over a temperature range from 12 to 300 K for a sample annealed at 950°C for 30 min. The inset shows a detailed PL spectrum at 12 K with a weak no-phonon ͑NP͒ line at 1.158 eV, a TA-phonon line near 1.14 eV, and a TO-phonon line at 1.1 eV with a replica at 1.04 eV. These PL spectral lines are well known in c-Si and tabulated in Ref. 3. The PL spectrum peak is shifted and becomes broader as the temperature is raised. In the temperature region from 12 to 50 K the PL peak undergoes a small blueshift ͑to shorter wavelength͒ and at temperatures greater than 70 K the PL peak is redshifted ͑to longer wavelength͒. We do not observe any blueshift in the PL spectra attributable to quantum confinement effects.Increasing the temperature broadens the PL spectra. Figure 2 shows that the intensity of the high-energy tail of the PL spectrum is linear on a semilogarithmic scale. The slope increases linearly with temperature, as expected when the carriers follow a Boltzmann distribution. 7...

Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures Appl. Phys. Lett. 94, 101916 (2009); 10.1063/1.3098474 Room-temperature 1.54 μm photoluminescence from Er-doped Si-rich silica layers obtained by reactive magnetron sputtering J. Appl. Phys. 94, 3869 (2003); 10.1063/1.1604479 Room-temperature 1.54 μm electroluminescence from Er-doped silicon-rich silicon oxide films deposited on n + -Si substrates by magnetron sputtering J. Appl. Phys. 90, 5835 (2001); 10.1063/1.1413231Effect of hydrogenation on room-temperature 1.54 μm Er 3+ photoluminescent properties of erbium-doped silicon-rich silicon oxide

Photoluminescence ͑PL͒ from the recombination of excitons bound to isoelectronic Be 2 dopants in bulk silicon is measured for pressures up to 60 kbar and temperatures down to 9 K. PL from excitons bound to this Be 2 trap is analyzed by using the Hopfield-Thomas-Lynch model, extended to treat more complex isoelectronic dopants, and several different binding potentials. This modified model describes the change in exciton binding energy with pressure determined from the PL spectrum and the loss of PL at and above 60 kbar when short-range potentials are used. The depth of the potential in this model is relatively insensitive to pressure. Coulomb-based models do not explain these observations as well.

We have achieved room-temperature electroluminescence (EL) at 1.1 eV from a light-emitting diode with an active layer prepared by high-temperature partial oxidation of electrochemically etched crystalline silicon. The EL is easily measurable under a forward bias ≥ 1 V and a current density <10 mA/cm2 and is only weakly temperature dependent from 12 to 300 K. The luminescence is due to Si band edge radiative recombination and originates from large silicon clusters within a nonstoichiometric silicon-rich silicon oxide matrix.

Radiative isoelectronic impurity complexes consisting of pairs of Be atoms that bind excitons can be formed in both Si and SiGe/Si superlattices during growth by molecular beam epitaxy. We describe in this letter the conditions under which these radiative complexes can be formed, show that they can be localized in the alloy layers of a superlattice, and demonstrate that the blueshift of the bound-exciton’s no-phonon line that occurs for Be-implanted superlattices is absent for grown-in Be complexes. Be densities in excess of 5×1017 cm−3 can be achieved.

Silicon-rich silicon oxide (SRSO) films were prepared by thermal oxidation (700°C-950°C) of electrochemically etched crystalline silicon (c-Si). The annealing-oxidation conditions are responsible for the chemical and structural modification of SRSO as well as for the intrinsic light-emission in the visible and near infra-red spectral regions (2.0–1.8 eV, 1.6 eV and 1.1 eV). The extrinsic photoluminescence (PL) is produced by doping (via electroplating or ion implantation) with rare-earth (R-E) ions (Nd at 1.06 μm, Er at 1.5 μm) and chalcogens (S at ∼1.6 μm). The impurities can be localized within the Si grains (S), in the SiO matrix (Nd, Er) or at the Si-SiO interface (Er). The Er-related PL in SRSO was studied in detail: the maximum PL external quantum efficiency (EQE) of 0.01–0.1% was found in samples annealed at 900°C in diluted oxygen (∼ 10% in N2). The integrated PL temperature dependence is weak from 12K to 300K. Light emitting diodes (LEDs) with an active layer made of an intrinsic and doped SRSO are manufactured and studied: room temperature electroluminescence (EL) from the visible to 1.6 μmhas been demonstrated.

No abstract

The photoluminescence (PL) in crystalline silicon (c-Si) has been investigated during the last decades. Recent interest has focused on the visible PL that is observed in Si nanoclusters and in porous Si (PSi), the infrared PL in silicon-germanium superlattices, and the subgap PL due to impurities in c-Si [1]. Band edge PL in bulk Si is inefficient and usually observed only at low temperatures because c-Si has an indirect bandgap. The electroluminescence (EL) is as inefficient as the photoluminescence (PL) and, in addition, the EL is quenched by an electric field E ≥ 104 V/cm due to field-induced dissociation of the exciton. In this work we report a significant increase of the Si band edge photoluminescence and electroluminescence and its unexpectedly weak temperature dependence in large Si nanocrystals produced by the recrystallization of oxidized porous Si.