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 $({\mathrm{SiO}}_x)$ 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 ${\mathrm{SiO}}_x$ 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 ${\mathrm{SiO}}_x$ samples, the distributions become wider and their mean value increases. The strong correlation between structural (nanocrystal radius and width of the size distributions) and optical (wavelength and width of the PL peaks) data indicates that light emission from the annealed ${\mathrm{SiO}}_x$ films is due to carrier recombination in the Si nc, and it can be interpreted in terms of carrier quantum confinement. The possible reasons for the quantitative discrepancy between the experimentally measured luminescence energy values and the theoretical calculations for the enlargement of the band gap with decreasing the crystal size are also discussed.

We have obtained room‐temperature electroluminescence (EL) at ∼1.54 μm from Er and O co‐doped crystalline p‐n Si diodes fabricated by ion implantation, under both forward and reverse bias conditions. Under forward bias, the EL intensity decreases by a factor of ∼15 on going from 110 to 300 K, where a weak peak is still visible. In contrast, we report the first sharp luminescence peak obtained under reverse bias conditions in the breakdown regime. In this case the EL intensity decreases only by a factor of 4 on going from 110 to 300 K and the room‐temperature yield is more than one order of magnitude higher than under forward bias. The data suggest that Er excitation occurs through electron‐hole mediated processes under forward bias and through impact excitation under reverse bias.

In this article the luminescence properties of Si nanocrystals (nc) formed by plasma enhanced chemical vapor deposition and their interaction with Er ions introduced by ion implantation are investigated in detail. Si nc with different size distributions and densities were produced and all show quite intense room temperature luminescence (PL) in the range 700–1100 nm. It is shown that the time-decay of the luminescence follows a stretched exponential function whose shape tends towards a single exponential for almost isolated nc. This suggests that stretched exponential decays are related to the energy transfer from smaller towards larger nc. Indeed, by comparing samples with similar nc size distributions, but with very different nc densities, it is demonstrated that the PL has a quite strong redshift in the high density case, demonstrating a clear energy redistribution within the sample. Excitation cross sections have been measured in all samples yielding a value of ∼1.8×10−16 cm2 for isolated nc excited with 2.54 eV photons. This effective excitation cross section is shown to increase by a factor of 4 in interacting nc as a result of the energy transfer within the sample. When Er ions are introduced in these samples a strong nc–Er interaction sets in and the energy is preferentially transferred from the nc to the Er ions. The nc-related luminescence is quenched and the Er-related luminescence at 1.54 μm appears. The effective excitation cross section of Er ions through Si nc has been determined to be ∼1.1×10−16 cm2. This number resembles the excitation cross section of nc themselves demonstrating that the coupling is extremely strong. Moreover, by increasing the Er content the effective excitation cross section is seen to increase. In the same concentration range the Er lifetime decreases demonstrating that “concentration quenching” effects, with the energy transferred among Er ions, are setting in. These Er–Er interactions are responsible for the effective increase of the cross section. However, since the increase in the cross section is related to a simultaneous decrease in lifetime the net effect for the luminescence efficiency is negative. The best Er content to take advantage of the sensitizer action of Si nc avoiding the detrimental Er–Er interactions has been determined to be ∼2×1020/cm3. These data are presented and their implications discussed.

A detailed investigation on the excitation and deexcitation processes of ${\mathrm{Er}}^{3+}$ in Si is reported. In particular, we explored Er pumping through electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and holes. Since Er donor behavior would result in a free-carrier concentration varying along its profile, experiments have been performed by embedding the whole Er profile within previously prepared $n$-doped or $p$-doped regions. Multiple P (B) implants were performed in $n$-type ($p$-type) Czochralski Si samples in order to realize uniform dopant concentrations from $4\times {10}^{16}$ to $1.2\times {10}^{18}/{\mathrm{cm}}^3$ at depths between 0.5 and 2.5 μm below the surface. These samples have been subsequently implanted with 4 MeV $3.3\times {10}^{13}{\mathrm{E}\mathrm{r}/\mathrm{c}\mathrm{m}}^2$ and annealed at 900 °C for 30 min. Free electrons or holes concentrations in the region where Er sits were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and acceptors, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 μm. These phenomena are produced by Auger deexcitation of the ${\mathrm{Er}}^{3+}$ intra-$4f$ electrons with energy transfer to free carriers. The Auger coefficient of this process has been measured to be $C_A\sim 5\times {10}^{-13}{\mathrm{cm}}^3{\mathrm{}\mathrm{s}}^{\mathrm{-}1}$ for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the ${\mathrm{Er}}^{3+}$ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (acceptors): the efficiency of this process has been determined to be two orders of magnitude smaller with respect to the Auger deexcitation with free carriers. Furthermore, at temperatures above 100 K a nonradiative back-transfer decay process, characterized by an activation energy of 0.15 eV, is seen to set in for both $p$-type and $n$-type samples. This suggests that the back-transfer process, which severely limits the high-temperature luminescence efficiency, is always completed by a thermalization of an electron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescence yield at 15 K, we have found that excitation of Er through the recombination of an electron-hole pair is a very efficient process, characterized by an effective cross section of $3\times {10}^{-15}{\mathrm{cm}}^2$ and able to provide an internal quantum efficiency as high as 10% at low temperatures (15 K) and pump powers (below 1 mW). This efficiency is significantly reduced when, at higher temperatures and/or high pump powers, strong nonradiative decay processes set in. These phenomena are investigated in detail and their impact on device operation perspectives are analyzed and discussed.

The luminescence quenching of Er in crystalline Si at temperatures between 77 and 300 K is investigated. Samples were prepared by solid-phase epitaxy of Er-implanted amorphous Si layers with or without O codoping. After epitaxial regrowth at 620 °C, thermal annealing at 900 °C for 30 sec was performed in order to eliminate residual defects in the regrown layer and electrically and optically activate the Er ions. Measurements of photoluminescence intensity and time decay were performed as a function of temperature and pump power. By increasing the temperature from 77 K to room temperature the luminescence intensity decreases by ∼ three orders of magnitude in the Er-doped sample without O codoping, but only by a factor of 30 in the O-doped sample. In this sample room-temperature photo-luminescence and electroluminescence have been observed. Time-decay curves show a fast initial decay (∼100 μsec) followed by a slow decay (∼1 msec), with the relative intensity of these two components depending on temperature, pump power, and O codoping. The decay curves can be fitted by a sum of two exponential functions revealing the existence, in both samples, of two different classes of optically active Er sites. The concentration of excitable sites belonging to the slow-decaying class is similar for the samples with or without O codoping and rapidly decreases when temperature is increased. At temperatures above 150 K the Er luminescence is dominated by the fast-decaying centers the concentration of which is greatly increased by the presence of O. It is found that in the absence of oxygen room-temperature luminescence is hampered by the limited amount of excitable Er ions. In contrast, in O-doped samples the nonradiative decay of excited Er is the main quenching mechanism. The main factors determining the temperature quenching of Er luminescence and the crucial role of oxygen are discussed.