S. Lombardo

Room‐temperature luminescence from Er‐implanted semi‐insulating polycrystalline silicon

Semi‐insulating polycrystalline silicon films with oxygen concentrations in the range 4–27 at.u2009% were deposited by low‐pressure chemical vapor deposition of SiH4 and N2O onto silicon substrates, annealed at 920u2009°C, and then implanted with 2×1015 500 keV Er ions/cm2. After annealing at temperatures in the range 300–900u2009°C, the samples show intense room‐temperature luminescence around 1.54 μm, characteristic of intra‐4f emission from Er3+, upon excitation using an Ar ion laser. The luminescence intensity increases with increasing oxygen concentration in the film. The luminescence is attributed to Er3+ ions in oxygen‐rich shells around Si nanograins, excited by a photocarrier‐mediated process.

Erbium in oxygen-doped silicon: Optical excitation

The photoluminescence of erbium‐doped semi‐insulating polycrystalline and amorphous silicon containing 30 at.u2009% oxygen is studied. The films were deposited on single‐crystal Si substrates by chemical vapor deposition, implanted with 500 keV Er to fluences ranging from 0.05 to 6×1015 ions/cm2, and annealed at 300–1000u2009°C. Upon optical pumping near 500 nm, the samples show room‐temperature luminescence around 1.54 μm due to intra‐4f transitions in Er3+, excited by photogenerated carriers. The strongest luminescence is obtained after 400u2009°C annealing. Two classes of Er3+ can be distinguished, characterized by luminescence lifetimes of 170 and 800 μs. The classes are attributed to Er3+ in Si‐rich and in O‐rich environments. Photoluminescence excitation spectroscopy on a sample with 1×1015 Er/cm2 shows that ∼2% of the implanted Er is optically active. No quenching of the Er luminescence efficiency is observed between 77 K and room temperature in this Si‐based semiconductor. The internal quantum efficiency for ...

Erbium in oxygen‐doped silicon: Electroluminescence

Room‐temperature electroluminescence at 1.54 μm is demonstrated in erbium‐implanted oxygen‐doped silicon (27 at.u2009% O), due to intra‐4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal‐(Si:O, Er)‐p+ silicon diodes. The 30‐nm‐thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical‐vapor deposition of SiH4 and N2O, doped by ion implantation with Er to a concentration up to ≊1.5 at.u2009%, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400u2009°C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≊6×10−16 cm2 is obtained.

Characterization by x‐ray photoelectron spectroscopy of the chemical structure of semi‐insulating polycrystalline silicon thin films

The x‐ray photoelectron spectroscopy (XPS) technique has been used to investigate the composition of semi‐insulating polycrystalline silicon (SIPOS) films having oxygen contents of 10 and 35 at.u2009% prepared by low pressure chemical vapor deposition. XPS analysis has demonstrated that the film compositions can be qualitatively described by means of the five Si‐SixO4−x tetrahedra (with 0≤x≤4 and integer) predicted by the statistical random bonding model (RBM). However, the quantitative analysis of the XPS spectra has demonstrated that the concentrations of the various tetrahedra found in the SIPOS films are remarkably different from those predicted by a statistical approach, i.e., by assuming that each Si atom forms with equal probability bonds with either Si or O. We have also found that the composition of high temperature (up to 1000u2009°C) annealed films further departs from that predicted by the RBM model; indeed, the anneal promotes the decomposition of partially oxidized Si‐SixO4−x tetrahedra in Si‐Si4 te...

Electrical and optical properties of semi-insulating polycrystalline silicon thin films: the role of microstructure and doping

We have investigated the relationship between microstructure and electrical conductivity in semi-insulating polycrystalline silicon (SIPOS) with oxygen concentrations in the 2–35 at.% range and the effect of doping with boron, phosphorus, arsenic and erbium by ion implantation. SIPOS thin films are mixtures of silicon and silicon oxide phases. The chemical and morphological evolution of these phases upon annealing is emphasized. Electrical conductivity measurements are interpreted in terms of a physical model containing few free parameters related to the material microstructure. A direct extension of this model explains also the conductivity increase in SIPOS doped with elements of the third or the fifth group. In the last part of the paper, data of electroluminescence at 1.54 μm in Er-implanted SIPOS due to intra-4f transitions of the Er3+ ion are shown and discussed.

Structural properties of fluorinated SiO 2 thin films

Abstract Fluorinated SiO2 (SiOF) films, prepared by plasma enhanced chemical vapour deposition from SiH4, N2O and CF4 precursors, have been analysed by infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to extract chemical and structural information. Notwithstanding XPS reveals that fluorine concentrations are quite low (less than 4 at.%), the analysis of the Si–O–Si vibration modes in the IR spectra indicates that CF4 addition involves a deeper modification of the film structure, than the simple formation of Si–F bonds. In particular, by increasing the F concentration in the oxides, the stretching frequency of the Si–O–Si bonds increases, while the bending frequency decreases. On the basis of the central force model, both observations are consistent with the occurrence of a Si–O–Si bond angle relaxation phenomenon, the importance of which increases with the fluorine concentration in the films.

Room-temperature luminescence in semi-insulating polycrystalline silicon implanted with Er

We demonstrate sharp room-temperature electroluminescence at 1.54 μm due to intra-4f transitions of Er3+ in semi-insulating polycrystalline silicon (SIPOS) implanted with Er and annealed for implant damage recovery. Our measurements refer to SIPOS containing ≈ 30 at.% O, doped with Er to concentrations of about 1 at.% and annealed at a temperature in the 400–1100°C range. The luminescence has been excited either by optically pumping with an Ar laser or by biasing suitable metal-SIPOS-p+ silicon devices.

OPTICAL DOPING OF MATERIALS BY ERBIUM ION IMPLANTATION

Abstract The development of silicon compatible optoelectronics would require the fabrication and integration of several optical functions such as waveguides, amplifiers, signal processing components and light emitters in silicon or on thin films deposited on silicon. In this paper the optical doping by erbium ion implantation of sodalime silica glass and silicon is presented with the aim to fabricate an amplifier and a light source operating at 1.5 μm. The materials issues currently limiting the performances of these devices are analyzed in detail and the possible future developments are discussed.

Erbium doping of crystalline and amorphous silicon for optoelectronic applications

SummaryIn this work we demonstrate that efficient light emission at 1.54 μm can be achieved when Er ions are incorporated into crystalline Si or in heavily oxygen-doped amorphous and polycrystalline Si films (SIPOS). We have found that temperature quenching of photo- and electroluminescence, which is the major limitation towards the achievement of room temperature luminescence, can be strongly reduced by codoping these films with oxygen. This impurity is already present in as-prepared SIPOS and it is introduced by ion-implantation in crystalline Si. Er luminescence is obtained under both optical and electrical excitation and we demonstrate that excitation occurs through a carrier-mediated process. Electrical excitation is obtained by incorporating Er in properly designed device structures. It is found that this excitation can occur both through the recombination of hole-electron pairs and through impact excitation of the Er ions by hot electrons. These two mechanisms have different efficiencies and impact excitation is shown to prevail at room temperature. These data are presented and possible future developments are discussed.

Electroluminescence of Erbium in Oxygen Doped Silicon

It is demonstrated room-temperature electroluminescence at 1.54 μm in erbiumimplanted oxygen doped silicon (27 at. 0), due to intra-4f transitions of the Er 3+ . The luminescence is electrically stimulated by biasing metal-(Si:O,Er)-p + silicon diodes. The 30 nm thick Si:O,Er films are amorphous layers deposited onto silicon substrates by chemical vapour deposition of S i H 4 and N 2 0, doped by ion implantation with Er to a concentration up to ≈ 1.5 at.%, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400°C in reverse bias under breakdown condition and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O,Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross-section of ≈6×10 −16 cm 2 is obtained.