Dislocation-related photoluminescence in silicon

Photoluminescence is studied in silicon, deformed in a well-defined and reproducible way. Usual deformation conditions (high temperature, low stress) result in sharp spectra of the D1 through D4 lines as recently described in the literature. New lines D5 and D6 emerge for predeformation as above and subsequent low-temperature, high-stress deformation. Another new sharp line, D12, is observed when both the familiar and the novel lines appear simultaneously. Annealing for 1 h atT _A 300 °C causes all new lines to disappear and the D1–D4 spectra to reappear. Quantitative annealing and TEM micrographs suggest that D5 is related to straight dislocations and D6 to stacking faults, whereas D1–D4 are due to relaxed dislocations. Photoluminescence under uniaxial stress shows that D1/D2 originate in tetragonal defects with random orientation relative to 100 directions, whereas D6 stems from triclinic centers, preferentially oriented — as are the D3/D4 centers. We conclude that the D3/D4 and the D5 and D6 defects are closely related, whereas the independent D1/D2 centers might be deformation-produced point defects in the strain region of dislocations.     

On the nature of the spectral shift caused by photoluminescence fatigue in porous silicon

Luminescence spectra of porous silicon with a regular columnar-layered structure have been studied. A substantial narrowing of the luminescence band in samples of this type and a considerable shift of the band induced by fatigue have been established. An explanation for the spectral shift of the luminescence band resulting from fatigue relaxation is proposed for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 2137–2140 (December 1997)     

Enhanced photoluminescence in grooved silicon microstructures

Grooved silicon structures formed by anisotropic chemical etching of crystalline silicon (c-Si) wafers in alkaline solution and composed by c-Si walls and voids (grooves) with thicknesses of several micrometers were found to exhibit efficient photoluminescence after excitation with laser radiation at 1.06 μm. The photoluminescence emission which originates from the interband radiative recombination of charge carriers in c-Si walls was represented by a broad spectral band centered at 1.1 eV. Independently on the polarization direction of the excitation light the photoluminescence of grooved silicon structures was partially linear-polarized with the polarization degree of 0.15–0.24 along c-Si walls and the photoluminescence intensity was strongly enhanced in comparison with that of c-Si substrate. These experimental observations are explained by considering an enhancement of the photoluminescence excitation due to both partial light localization in c-Si walls and a low rate of the non-radiative recombination at surface defects on c-Si walls. The defect density could be modified by additional chemical treatment or thermal annealing, which resulted in significant changes of the photoluminescence intensity of the grooved Si structures. The obtained results are discussed in view of possible applications of grooved Si in optoelectronics and molecular sensorics.     

Instability of the photoluminescence of porous silicon

Results of studies of the photoluminescence of porous silicon with different prehistories have revealed the mechanism and nature of the instability of the luminescence properties of freshly prepared samples. It was established that the initial quenching and subsequent rise of the photoluminescence is attributable to the intermediate formation of silicon monoxide (photoluminescence degradation) and subsequent additional oxidation to form SiO₂ (photoluminescence rise). Ultraviolet laser irradiation accelerates this process by a factor of 200–250 compared with passive storage of the samples in air. Plasma-chemical treatment in an oxygen environment merely results in a subsequent rise in the photoluminescence as a result of the formation of monoxide on the porous silicon surface. A kinetic model is proposed for this process. Zh. Tekh. Fiz. 69, 135–137 (June 1999)     

On the calculation of the tunnelling probability in a heavily-doped p-n junction

Abstract

The one-dimensional Schrodinger's equation for a triangular potential barrier (appropriate to tunnel diodes) is solved directly to obtain an expression for the probability of tunnelling of an electron through it. The result has been compared with that of Kane and the W.K.B. method. It is concluded that the results based on this calculation predict the same functional dependence of the tunnelling probability on m?, E_g and F as that predicted by earlier methods.     

多孔硅的时间延迟光谱

利用时间延迟光谱技术测量了多孔硅的发光光谱. 实验结果表明,多孔硅的发光是复杂的动力学发光弛豫过程,时间延迟光谱测量技术在研究复杂动力学发光过程方面比稳态光谱测量方法更有效.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

Synthesis and photoluminescence studies of silicon nanoparticles embedded in silicon compound films

High-density silicon nanoparticles with well-controlled sizes were grown onto cold substrates in amorphous SiN_x and SiC matrices by plasma-enhanced chemical vapor deposition. Strong, tunable photoluminescence across the whole visible light range has been measured at room temperature from such samples without invoking any post-treatment, and the spectral features can find a qualitative explanation in the framework of quantum confinement effect. Moreover, the decay time was for the first time brought down to within one nanosecond. These excellent features make the silicon nanostructures discussed here very promising candidates for light-emitting units in photonic and optoelectronic applications.     

Synthesis and photoluminescence studies of silicon nanoparticles embedded in silicon compound films

High-density silicon nanoparticles with well-controlled sizes were grown onto cold substrates in amorphous SiN _x and SiC matrices by plasma-enhanced chemical vapor deposition. Strong, tunable photoluminescence across the whole visible light range has been measured at room temperature from such samples without invoking any post-treatment, and the spectral features can find a qualitative explanation in the framework of quantum confinement effect. Moreover, the decay time was for the first time brought down to within one nanosecond. These excellent features make the silicon nanostructures discussed here very promising candidates for light-emitting units in photonic and optoelectronic applications.      

Influence of the temperature on the photoluminescence of silicon clusters embedded in a silicon oxide matrix

Amorphous silicon oxide thin films were prepared by co-evaporation of Si and SiO in ultra-high vacuum. Different compositions were obtained by changing the evaporation rate of silicon. After thermal annealing treatments, the dissociation of the silicon oxide in pure silicon and silicon dioxide leads to the formation of silicon clusters embedded in a silicon oxide matrix. Thus the samples were annealed to different temperatures up to 950°C. Depending on the annealing temperature and on the composition, different cluster sizes were obtained. The photoluminescence (PL) energy depends on the cluster size and a large range of wavelengths is obtained from 500 to 750 nm. The PL, attributed to a confinement effect of the electron–hole pairs in the silicon particles, is studied as a function of the temperature. It is demonstrated that the continuous decrease of PL intensity with the temperature from 77 to 500 K depends on the structure of the samples. For samples with well-separated clusters, the PL decreases rapidly with the temperature. For samples containing clusters separated by a small distance, the PL weakly depends on the temperature. No shift of the energy is observed. The results are discussed by taking into account the competition between the radiative recombination in the silicon clusters and the non-radiative escape of the carriers via a hopping mechanism.     

Effect of surface Si-Si dimers on photoluminescence of silicon nanocrystals in the silicon dioxide matrix

The effect of surface states of silicon nanocrystals embedded in silicon dioxide on the photoluminescent properties of the nanocrystals is reported. We have investigated the time-resolved and stationary photoluminescence of silicon nanocrystals in the matrix of silicon dioxide in the visible and infrared spectral ranges at 77 and 300 K. The structures containing silicon nanocrystals were prepared by the high-temperature annealing of multilayer SiO _x /SiO₂ films. The understanding of the experimental results on photoluminescence is underlain by a model of autolocalized states arising on surface Si-Si dimers. The emission of autocatalized excitons is found for the first time, and the energy level of the autolocalized states is determined. The effect of these states on the mechanism of the excitation and the photoluminescence properties of nanocrystals is discussed for a wide range of their dimensions. It is reliably shown that the cause of the known blue boundary of photoluminescence of silicon nanocrystals in the silicon dioxide matrix is the capture of free excitons on autolocalized surface states.     

Relative enhancement of photoluminescence intensity of passivated silicon nanocrystals in silicon dioxide matrix

Photoluminescence (PL) intensity of passivated silicon nanocrystals (Si NCs) embeded in an SiO₂ matrix is compared with that of unpassivated ones. We investigate the relative enhancement of PL intensity (I_R) as a function of annealing temperature and implanted Si ion dose. The I_R increases simultaneously with the annealing temperature. This demonstrates an increase in the number of dangling bonds (DBs) with the degree of Si crystallization via varying the annealing temperature. The increase in I_R with implanted Si ion dose is also observed. We believe that the near-field interaction between DBs and neighboring Si NCs is an additional factor that reduces the PL efficiency of unpassivated Si NCs.     

Stable ultraviolet photoluminescence emission in n-type porous silicon

This very paper is focusing on the investigation of porous silicon preparation with n-type silicon wafer by means of electrochemical anodization in the dark and, particularly, on its stable ultraviolet photoluminescence emission. A lateral electrical potential was applied, for this purpose, on silicon wafers, driving the electrons away and letting holes appear on the surface of the silicon wafer to enhance the electrochemical etching process. Characterizations have been made with scanning electronic microscope, fluorescence spectrophotometer and Fourier transform infrared spectroscope. An ultraviolet photoluminescence emission of 370 nm is found in the as-prepared n-type porous silicon, which seems to be well associated with the formation of oxygen-related species (twofold coordinated silicon defect) during the anodic oxidation. The result characterized by photo-bleaching performance indicates that the ultraviolet photoluminescence emission is so stable—only 7% reduction within 3600 s. Meanwhile the morphology of as-prepared n-type porous silicon is investigated.     

Simple fabrication of nanostructured silicon and photoluminescence

Porous Si (PS) was fabricated simply by electrochemical anodic etching of a Si wafer. By a combination of SEM, EDX and infrared spectrum measurements hydrogen-terminated crystalline Si surfaces were identified. Transparent Si nanocolloids were obtained via thermally-initiated hydrosilation of the hydrogenated Si surfaces reaction with unsaturated 1-undecene. In contrast to weak luminescence in the hydrogenated PS dispersed in toluene, intense luminescence was observed in the Si nanocolloid. In the Si nanocolloid, both strong luminescence and long-term stability can be correlated with alkylated passivation, as formation of Si–C bonds identified in infrared spectrum. Additionally, the oxidation effect was noticeable in affecting the luminescence of nano-Si during the process.     

Observation of two-step excitation of photoluminescence in silicon nanostructures

Efficient visible-range photoluminescence with photon energy higher than the photon energy of the exciting radiation is observed in nanostructures of porous silicon subjected to heat treatment in vacuum. The photoluminescence intensity is found to be virtually identical for cw and femtosecond excitation by Ti:sapphire laser radiation with the same average power. The results can be explained by a two-step cascade photoluminescence excitation process in which optical passivation of defects of the dangling silicon bond type occurs. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 732–736 (25 November 1998)     

Thermally induced defect photoluminescence in hydrogenated amorphous silicon

The intrinsic defect photoluminescence of hydrogenated amorphous silicon (a-Si:H) films has been investigated at high intensities of optical pumping that lead to heating of the film. It has been revealed that, for short heating times, the intensity of the defect photoluminescence increases exponentially with an increase in the temperature with an activation energy of 0.85 eV, which is considerably higher than the activation energy (∼0.2 eV) determined from experiments on classical annealing. This and other experimental results on the temperature dependence of the intensity and kinetics of the defect photoluminescence have been explained in terms of the “hydrogen glass” model by thermally induced generation of intrinsic defects in amorphous silicon. The results of the calculations are in good agreement with the experimental data on the defect photoluminescence that reflects the formation and annihilation of defects for short heating times under optical excitation.     

Dislocation-induced photoluminescence in silicon crystals of various impurity composition

The effect of oxygen on the dislocation-induced photoluminescence (DPL) spectra at 4.2 K is studied in silicon crystals with different impurity compositions subjected to plastic deformation at temperatures above 1000°C. A strong effect of doping impurities on the DPL spectra is observed for concentrations above 10¹⁶ cm^?3. It is shown that the peculiarities of many DPL spectra in silicon can be explained by assuming that the D1 and D2 lines are associated with edge-type dislocation steps on glide dislocations.