With the growing use of optoelectronics in information technology, manipulating light is almost as important as manipulating electrons. Unfortunately silicon, workhorse of modern microelectronics, is next to useless in optical applications. There has been a massive effort to overcome silicon's inadequacies, and ways of coaxing silicon to handle light are under development but a key component — the laser — has been problematic. Last year a silicon laser was produced, but it involved metres of optical fibre. Now workers in Intel's research labs have come up with an all-silicon laser on a single chip. The device is compact and readily integrated with other silicon components. The possibility of light generation and/or amplification in silicon has attracted a great deal of attention1 for silicon-based optoelectronic applications owing to the potential for forming inexpensive, monolithic integrated optical components. Because of its indirect bandgap, bulk silicon shows very inefficient band-to-band radiative electron–hole recombination. Light emission in silicon has thus focused on the use of silicon engineered materials such as nanocrystals2,3,4,5, Si/SiO2 superlattices6, erbium-doped silicon-rich oxides7,8,9,10, surface-textured bulk silicon11 and Si/SiGe quantum cascade structures12. Stimulated Raman scattering (SRS) has recently been demonstrated as a mechanism to generate optical gain in planar silicon waveguide structures13,14,15,16,17,18,19,20,21. In fact, net optical gain in the range 2–11 dB due to SRS has been reported in centimetre-sized silicon waveguides using pulsed pumping18,19,20,21. Recently, a lasing experiment involving silicon as the gain medium by way of SRS was reported, where the ring laser cavity was formed by an 8-m-long optical fibre22. Here we report the experimental demonstration of Raman lasing in a compact, all-silicon, waveguide cavity on a single silicon chip. This demonstration represents an important step towards producing practical continuous-wave optical amplifiers and lasers that could be integrated with other optoelectronic components onto CMOS-compatible silicon chips.

An all-silicon Raman laser

Recent developments in rare-earth doped materials for optoelectronics

A threshold-shifting, single transistor memory structure with fast read and write times and long retention time is described. The structure consists of a silicon field-effect transistor with nano-crystals of germanium or silicon placed in the gate oxide in close proximity of the inversion surface. Electron charge is stored in these isolated 2-5 nm size nano-crystals which are separated from each other by greater than 5 nm of SiO/sub 2/ and from the inversion layer of the substrate surface by less than 5 nm of SiO/sub 2/. Direct tunneling of charge from the inversion layer and its storage in the nano-crystal causes a shift in the threshold voltage which is detected via current sensing. The nano-crystals are formed using implantation and annealing or using direct deposition of the distributed floating gate region. Threshold shift of 0.3 V is obtained in Ge-implanted devices with 2 nm of SiO/sub 2/ injection layer by a 4 V write pulse of 300 ns duration. The nano-crystal memories achieve improved programming characteristics as a nonvolatile memory as well as simplicity of the single poly-Si-gate process. The V/sub T/ window is scarcely degraded after greater than 10/sup 9/ write/erase cycles or greater than 10/sup 5/ s retention time. Nano-crystal memories are promising for nonvolatile memory applications.

Fast and long retention-time nano-crystal memory

Strong room-temperature photoluminescence (PL) in the wavelength range 650–950 nm has been observed in high temperature annealed (1000–1300 °C) substoichiometric silicon oxide (SiOx) thin films prepared by plasma enhanced chemical vapor deposition. A marked redshift of the luminescence peak has been detected by increasing the Si concentration of the SiOx films, as well as the annealing temperature. The integrated intensity of the PL peaks spans along two orders of magnitude, and, as a general trend, increases with the annealing temperature up to 1250 °C. Transmission electron microscopy analyses have demonstrated that Si nanocrystals (nc), having a mean radius ranging between 0.7 and 2.1 nm, are present in the annealed samples. Each sample is characterized by a peculiar Si nc size distribution that can be fitted with a Gaussian curve; by increasing the Si content and/or the annealing temperature of the SiOx samples, the distributions become wider and their mean value increases. The strong correlation betw...

Correlation between luminescence and structural properties of Si nanocrystals

Visualization of stress distribution has been realized by a nondestructive mechanoluminescence (ML) from SrAl2O4:Eu, which can emit three magnitudes higher visible light than that of well-known ML substance of quartz. A simulation result confirms that such a ML image successfully reflects the stress distribution. A kinetic model for ML of SrAl2O4:Eu is proposed.

Direct view of stress distribution in solid by mechanoluminescence

We have investigated visible photoluminescence excited by Ar‐ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted silica glass, as‐implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as‐implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E’ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+‐implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron‐hole recombination in Si‐rich SiO2 and the 1.7 eV band to the electron‐hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.

Visible photoluminescence in Si+‐implanted silica glass

We have investigated visible photoluminescence excited by Ar ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted thermal oxide films grown on crystalline Si wafer, as‐implanted and after subsequent annealing in vacuum. We found two types of visible luminescence bands similar to those of silica glasses; one band is observed in as‐implanted specimens and disappears after heating to about 600 °C, and the other band is observed only after heating the specimens to about 1100 °C. Though the shapes of these luminescence spectra are different from those having been observed in Si+‐implanted silica glass, the origins of these bands are the same as in silica glass. We discuss the similarities and the differences of luminescence bands in Si+‐implanted silica glasses and thermal oxide films grown on crystalline Si.

Visible photoluminescence in Si+‐implanted thermal oxide films on crystalline Si

The authors have investigated visible photoluminescence from Si+-implanted SiO2. It is found that a luminescence band observed around 2.0 eV in as-implanted specimens disappears on annealing to 500 degrees C and then a band around 1.7 eV appears on annealing to 1100 degrees C. They discuss the origin of the luminescence hands in terms of the defects in SiO2 and the Si nanocrystals grown in SiO2.

https://iopscience.iop.org/article/10.1088/0953-8984/5/31/002/pdf

Kazuo Saitoh

Papers

Visible photoluminescence in Si+‐implanted silica glass

Visible photoluminescence in Si+‐implanted thermal oxide films on crystalline Si

Visible photoluminescence related to Si precipitates in Si+-implanted SiO2

Correlation of microstructure and photoluminescence for nanometer-sized Si crystals formed in an amorphous SiO2 matrix by ion implantation

Visible photoluminescence from silicon nanocrystals formed in silicon dioxide by ion implantation and thermal processing