The electroluminescence from p-i-n diode structures with Si1-yCy/Si1-xGex layers in the depletion region has been studied. Emission attributed to an overlap of the wavefunction associated with electrons confined in the Si1-yCy layer and the wavefunction associated with holes confined in the Si1-xGe, layer has been observed. For low injection currents, emission due to recombination occurring in the Si1-xGex layer is more dominant. For structures with higher C concentration, the interface related emission can persist up to higher temperatures.

Photoluminescence (PL) and electroluminescence (EL) from Si+- and Ge+-implanted SiO2 layers thermally-grown on a Si substrate were studied. The PL spectra were recorded after annealing at temperatures in the range of 400° to 1200°C. Single-peak PL at 460 nm and doublepeak PL at 420 and 385 nm due to Si+-implanted and Ge+-implanted oxide layers, respectively, reached a maximum following heat treatment at 500°C for 30 min. The EL spectra from the Gerich oxides after annealing at 1000°C correlated very well with the PL signal, and showed a linear dependence on the injection current. The EL emission was strong enough to be readily seen with the naked eye, and the EL efficiency was estimated to be about 5×10−4. High-resolution transmission electron microscopy (HRTEM) analysis showed that the formation of nanocrystals in the implanted oxide layers occurred at annealing temperatures in excess of 800°C. The observed light emission is attributable to the presence of-≡Si-Si≡, ≡Si-Ge≡ and ≡Ge-Ge≡ centres in SiO2.

We have studied the optical and the electrical properties of deuterium-terminated porous silicon. The photoluminescence spectrum was different from that of usual hydrogen-terminated porous Si despite both porous Si showing the same structure and the same absorption spectrum. In addition to these basic results, it is found that the replacement of hydrogen with deuterium reduces the degradation not only of photoluminescence but also of electroluminescence. The luminescence degradation mechanism will be discussed from the point of a photoinduced oxidation model.

Germanium (Ge) photodiodes are capable of high quantum yields and can operate at gigahertz frequencies in the 1–1.6 μm wavelength regime. The compatibility of SiGe alloys with Si substrates makes Ge a natural choice for photodetectors in Si-based optoelectronics applications. The large lattice mismatch (≈4%) between Si and Ge, however, leads to the formation of a high density of misfit and associated threading dislocations when uniform Ge layers are grown on Si substrates. High quality Ge layers were grown on relaxed graded SiGe/Si layers by ultra-high vacuum chemical vapor deposition (UHVCVD). Typically, as the Ge concentration in the graded layers increases, strain fields from underlying misfit dislocations result in increased surface roughness and the formation of dislocation pile-ups. The generation of pile-ups increases the threading dislocation density in the relaxed layers. In this study the pileup formation was minimized by growing on miscut (001) substrates employing a chemical mechanical polishing (CMP) step within the epitaxial structure. Other problems such as the thermal mismatch between Si and Ge, results in unwanted residual tensile stresses and surface microcracks when the substrates are cooled from the growth temperature. Compressive strain has been incorporated into the graded layers to overcome the thermal mismatch problem, resulting in crack-free relaxed cubic Ge on Si at room temperature. The overall result of the CMP step and the growth modifications have eliminated dislocation pile-ups, decreased gas-phase nucleation of particles, and eliminated the increase in threading dislocation density that occurs when grading to Ge concentrations greater than 70% Ge. The threading dislocation density in the Ge layers determined through plan view transmission electron microscopy (TEM) and etch pit density (EPD) was found to be in the range of 2 × 106/cm2. Ge p-n diodes were fabricated to assess the electronic quality and prove the feasibility of high quality photodetectors on Si substrates.

In the present work we investigate photo-detectors based on thick relaxed Ge layers, epitaxially grown on silicon after insertion of a low-temperature-grown Ge buffer layer. By using this procedure it was possible to grow films having thicknesses comparable with light penetration depth in the 1.3–1.6μm spectral range. The films exhibited flatness on the atomic scale. Two kinds of detectors were investigated: vertical heterojunction diodes and a planar Metal-Semiconductor-Metal structure. The detectors show a good responsivity at normal incidence at both 1.3 and 1.55μm. The photocurrent increases with the voltage applied, reaching a maximum responsivity of 0.24 A/W at 1.3μm under a bias of IV. A complete optoelectronic characterization of the fabricated devices is performed. The results confirm the feasibility of the proposed approach for the fabrication of 1.3–1.55μm near infrared photodetectors integrated on silicon chips.

We have studied optical properties and electronic structures of zero-dimensional (OD) Si nanocrystals and two-dimensional (2D) Si quantum wells by means of resonant excitation spectroscopy. Resonantly excited luminescence spectra of 0D Si nanocrystals are sensitive to the surface structure. The size dependence of the photoluminescence (PL) properties and resonantly excited PL spectra of SiO2-capped Si nanocrystals indicate that excitons are localized at the interface between the c-Si and SiO2 surface layer. The TO-phonon related structure in resonantly excited luminescence is clearly observed in H-passivated Si nanocrystals. Hpassivated Si nanocrystals show their crystalline nature, while the oxidized Si nanocrystals show their disordered nature. Luminescence properties of Si/SiO2 nanocrystals are similar to those of Si/SiO2 quantum wells. The electronic structures and luminescence properties of Si nanostructures are discussed.

Si nanocrystals (diameter 2 – 5 nm) were formed by 35 keV Si+ implantation at a fluence of 6×1016 Si/cm2 into a 100 nm thick thermally grown SiO2 film on Si (100), followed by thermal annealing at 1100 °C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O2 at 1000 °C for times up to 30 min. results in oxidation of the Si nanocrystals, first close to the SiO2 film surface and later at greater depths. Upon oxidation for 30 min. the photoluminescence peak wavelength blue-shifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The fabrication of a laser based on SiO2 waveguides doped with Si nanocrystals seems possible, if the nanocrystal size distribution can be narrowed down into the percent range.

The inert-gas-ambient pulsed laser ablation technique is a promising method for preparing Si nanocrystallites. We measured the temperature dependence of photoluminescence (PL) spectra to investigate radiative and nonradiative recombination processes in the nanocrystallites prepared using this method. The Si nanocrystallites showed visible PL bands in the red (1.6 eV) and green (2.1 eV) spectral regions. The intensities of the red and green PL increased with decreasing temperature and then saturated below 80 K. This temperature dependence was compared with that of other photoluminescent Si materials. It was shown that the PL quantum efficiency of the Si nanocrystallites was larger than that of a-Si:H at high temperatures. One of the reasons for the difference in the temperature dependence between the Si nanocrystallite and a-Si:H is the change in the role of defects in the nonradiative recombination process.

Si nanograins embedded in silicon oxide matrix have been obtained by thermal annealing at 1100°C during one hour, either after implantation of Si+ into thermal SiO2 layers or after magnetron cosputtering of both Si and SiO2. The spectral distribution of the photoluminescence (PL) in both systems is similar and peaks in the red visible region (1.45–1.60 eV). The results obtained indicate that for high PL efficiency, the films have to be annealed at temperatures high enough to achieve phase separation. This was observed from the gradual shift of the infrared bands of the silica matrix toward those of thermal SiO2, together with the appearance of the crystalline silicon Raman vibrational mode in the spectra. The similar behavior of samples obtained by ion implantation and by sputtering suggests a more complex origin of the PL than quantum confinement.

Nano-crystalline silicon (nc-Si) thin films were directly deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) and ion beam assisted electron beam deposition (IBAED) method. In the sample deposited by ECR-CVD, the room temperature photoluminescence originated from the nc-Si and the silicon-hydrogen bond were appeared. It was confirmed that the size of the nc-Si could be controlled up to about 3 nm with the low substrate temperature during the deposition process and then the hydrogen atoms play a very important role in the formation of the nc-Si. The IBAED method was also found to an useful technique for nc-Si formation by the control of ion beam power.

Dual Si+C implantations at high doses (3×1017 cm−2) were performed in thermal SiO2 layers. The C implantation energy was fixed at 60 keV while the Si ones were performed at different energies (150 keV and 60 keV) with the aim of synthetizing carbon rich luminescent centers. Annealings up to 1100 °C were performed in an inert N2 atmosphere either for short times in a rapid thermal processing furnace and up to two hours in a conventional furnace. Evidence of the formation of silicon and carbon-rich clusters was provided by XPS, SIMS, Raman and TEM experiments. Photoluminescence experiments under blue and ultraviolet excitations showed intense emission bands peaking at 1.5–1.7 eV (red), 2.20 eV (yellowgreen) and 2.75 eV (blue). The relative intensity and spectral shape of the emission bands was found to depend strongly upon implantation and annealing conditions and offered the possibility of tuning the desired dominant emission wavelength. The possible formation of SiC clusters and even SiC crystallites at the SiO2/Si interface could explain the origin of the highly intense blue emission band found for these samples.

Recently, intrinsic localized excitonic radiative surface states belonging to interacting dangling bonds of expanded, unstrained Si-Si dimers on the surface of nanocrystallites have been predicted. Those are connected, via a potential barrier, to the nonradiative delocalized excitonic states on the unexpanded, strained dimer. We present a theoretical analysis of the photoexcitation pathways involved in populating the radiative states. We include both direct above barrier, and indirect excitation from the photoexcited delocalized excitonic states via quantum tunneling and thermal activation. Our calculation gives an enhancement in the efficiency for sizes below a critical size of 1.4 nm, the size for which the outer trapped states become stable against tunneling and thermal activation. It is as if the material were changed from an indirect gap to a somewhat direct gap material. The results show that the photoluminescence exhibits a large Stokes shift resulting from the expansion of the radiative dimers. Moreover, the emission bandwidth is found to be quite wide especially for the ultra small crystallites (0.8 nm) where it encompasses nearly all of the visible spectrum, and the near infrared. Spectra simulated over size distributions are presented.

Time resolved photoluminescence (PL) decays have been measured for Si nanocrystals embedded in silicon dioxide. The nanocrystals were formed by Si implantation followed by thermal annealing at 800 – 1200 °C. The observed PL peaked in the wavelength range 640 – 850 nm and the PL decay exhibited a stretched exponential lineshape, characterized by a relatively large time constant. A nonlinear dose dependence of the PL yield and an observed redshifting for increasing doses and/or higher annealing temperatures is discussed in terms of a nucleation and growth mechanism for the nanocrystals. Finally, we argue that Auger recombination is effective at high excitation densities explaining a wavelength dependent saturation of the PL intensity.

A new way of preparing wafer sized SiGe and Ge quantum dots at extremely low cost is presented. The results show that two different controlled nanometer sizes of the quantum dots can be formed simultaneously into two layers on the same wafer with good dot size uniformity. Our initial experiments on SiGe and Ge system suggest that it is possible to squeeze the SiGe dots for much improved optical emission. The advantages of this dot preparation method are its fully compatibility with the Sitechnology, its simplicity in dot preparation and extremely low cost.

Fourier transform infrared spectroscopy is used to determine the time evolution of oxygen incorporation onto the surface of silicon nanocrystals. Oxygen concentrations up to one monolayer are investigated. The temporal progress of surface oxidation of Si nanocrystals in porous silicon shows a linear dependence on the square root of the oxidation time. This is similar to the oxidation of bulk Si and mesoporous silicon.

We report on the lattice location of 167Er in Si measured by conversion electron emission channeling. In both FZ and CZ Si, a high fraction of Er (>65%) occupies near-tetrahedral interstitial (T) sites directly following 60 keV room temperature implantation at doses of 6× 1012 cm−2 For higher doses, the as-implanted near-T fractions of Er visible by emission channeling are smaller, due to the beginning of amorphization. Following the recovery of implantation damage at 600°C, more than 70% of Er is found on near-T sites in both FZ and CZ Si. In FZ Si, Er exhibits a remarkable thermal stability and only prolonged annealing for several hours reduces the near-T fraction. On the other hand, annealing of CZ Si at 900°C for more than 10 minutes results in the majority of Er probes in sites of very low symmetry or disordered surroundings.

The composition dependence of room temperature 1.54 μ Er3+ photoluminescence of erbium doped silicon:oxygen thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium is investigated. The Si:O ratio was varied from 3:1 to 1:2 and the annealing temperature was varied from 500 to 900 °C. The most intense Er3+ luminescence is observed from the sample with Si:O ratio of 1:1.2 after 900 °C anneal and formation of silicon nanoclusters embedded in SiO2 matrix. High active erbium fraction, efficient excitation via carriers, and high luminescence efficiency due to high quality SiO2 matrix are identified as key factors in producing the intense Er3+ luminescence.

Deposition of a rare earth salt layer on a silicon substrate with subsequent spark processing yields a porous Si layer and SiO 2 cap doped with the rare earth ion. We have characterized luminescent Er-doped porous SiO2 on Si by scanning electron microscopy, energy dispersive Xray spectroscopy, as well as visible and near IR photoluminescence (PL) spectroscopies. Energydispersive x-ray maps indicate that the erbium concentration in the porous layer can be controlled by varying the molarity of the erbium solution deposited on the substrate prior to spark processing. Visible PL measurements reveal that the concentration of Er3+ is proportional to the resultant intensity of the visible fluorescence transitions; however, for the near IR fluorescence peak at 1.54 gim, self-quenching due to erbium clustering occurs at higher concentrations. Erbium-doped porous silicon layers can also be obtained by diffusion of an erbium salt into porous silicon formed by anodic etching of Si in hydrofluoric acid. Densification of the porous Si layers through high temperature oxidation after erbium diffusion forms erbium-doped SiO2 layers.

Er3+;-doped porous silicon (Er:PS) shows strong room temperature emissions at ˜ 1.54μm. However, its spectrum is usually much broader than that of Er-doped crystalline silicon (fullwidth at half maximum - FWHM - is ˜ 10 nm). It is probably because Er ions are located in amorphous phases. We report in this paper that strong and very sharp Er3+ 1.54μm emissions are obtained, when Er:PS samples are treated in a hydrogen plasma. Porous silicon layers are formed by anodic etching and then doped with Er3+ ions in an ErCl3/ethanol solution by an electrochemical method, and then treated in a hydrogen plasma at ˜ 1000°C from 0.5 min to 90 min for the optical activation. Several sharp peaks are observed at 20K, of which the strongest peak is located at 1.538 μm with an FWHM less than 1 nm. This value is comparable to that obtained from Er3+-doped crystalline silicon formed by means of molecular beam epitaxy (MBE) or ion implantation. Comparisons are made among hydrogen plasma, argon plasma, H2 flow and vacuum for the post-dope annealing atmosphere. Fourier-transform infrared (FT-IR) absorption and secondary ions mass spectrometry (SIMS) measurements are also carried out. We conclude that preferential etching of amorphous surface layers, and termination of dangling bonds of silicon nanocrystallites with hydrogen atoms and formation of Er-H complexes may be responsible for the strong and sharp Er3+-related luminescence.

Enhanced emissions at 0.98 μm of Yb3+ ions (2F5/2 → 2F7/2) incorporated in porous silicon are obtained when the host porous silicon is pre-annealed in an O2 containing atmosphere. Time decay characteristics are measured for the Yb 3+-related 0.98 μm emissions as well as for the emissions of these host porous silicon between 20 K and 300 K. The decay of the Yb3+ peak at 20 K is characterized with a fast (˜ 30 μs) and a slow decay time (≤ ˜ 400 μs), whereas it is fitted with one slow decay time (˜ 390 μs) at 300 K. The results are explained in terms of two optical centers: one has a fast fluorescent lifetime with a large temperature quenching, and the other has a slow fluorescent lifetime which is nearly constant between 20 K and 300 K.