E.A. Steinman

The origin of the 0.78 eV luminescence band in dislocated silicon

We report the results of a study into the influence of implanted impurities on luminescence in the region of the well-known D1 luminescence band that is associated with dislocations in silicon. A photoluminescence band at around 0.78 eV, which is sometimes seen in silicon containing a high density of dislocations, has been attributed to the presence of oxygen complexes. In this study we have deposited layers of Si0.9Ge0.1 onto single-crystal Si substrates by MBE in order to induce dislocations in the silicon substrate. The samples have subsequently been implanted with iron, erbium or oxygen in order to study the effect of implanted impurities on D-band photoluminescence at around 800 meV. Following implantation with oxygen, two luminescence bands appear at around 0.85 and 0.78 eV, respectively. These bands are not present in either the unimplanted sample or those subject to Er or Fe implantation. The correlation between oxygen doping and the appearance of these bands supports the conjecture that they are associated with oxygen complexes.

Crystal structure and photoluminescence of single crystals of fullerene-9,9′-trans-bis(telluraxanthenyl) molecular complex: C26H18Te2 · C60 · CS2

Abstract The crystal structure of novel molecular complex of fullerene C60 with 9,9′-trans-bis(telluraxantheny):C26H18Te2 · C60 · CS2 (BTX · C60 · CS2) has been investigated by X-ray structural analysis. Its photoluminescence (PL) and optical reflectivity spectra have been examined. We have found that fullerene C60, donor BTX and carbon disulfide CS2 molecules are situated at the inversion centers (1,0, 1 2 ), ( 1 2 , 1 1 2 ,1), ( 1 2 , 1 2 ,1),( 1 2 , 1 2 , 1 2 ), respectively. The PL spectrum in C60+BTX is shifted by 0.16eV towards lower energies compared to C60. The optical reflectivity spectrum of C60 + BTX is also different from that of C60. The results are explained in terms of a decrease of the singlet exciton energy due to the strong interaction between C60 and BTX molecules. The decrease of PL intensity in the new complex has been found to begin at much lower temperature as compared to the pure C60 crystals.

Electrical and Optical Properties of Dislocations Generated under Pure Conditions

The PL, DLTS and EBIC investigations of p-Si samples plastical ly deformed in the clean conditions were carried out. For a comparison the samples deformed using set-up made from steel were studied. Oxygen effect on the PL spectra of samples deformed in the clean conditions is revealed. The effect of contamination during deformation was observed by the all thr e methods.

Photoluminescence of solid C60 polymerized under high pressure

Abstract Photoluminescence (PL) spectra were measured on the C 60 polymeric phase prepared from a single crystal and from a microcrystalline powder treated at pressures to 15 kbar and temperatures to 600 K. It was found that the high-pressure treatment resulted in a shift of the spectral intensity distribution to lower energies compared to the well-known spectrum of pristine C 60 . A set of new lines was observed. The PL spectrum of the high-pressure phase exhibited a distinct structure contrary to that of photopolymerized C 60 . The PL intensity of the high-pressure phase showed a non-monotomic temperature dependence with a slight minimumum around 150 K.

Low-temperature strain relaxation in SiGe/Si heterostructures implanted with Ge ions

Pseudomorphic Si0.76Ge0.24/Si heterostructures grown by molecular beam epitaxy were implanted with Ge ions at 400 8 Ci n such a way that an ion-damaged region was located below the SiGe/Si interface. The effect of Ge-ion irradiation on strainrelaxation rate and defect structure in the heterostructures was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and low-temperature photoluminescence (PL). It was found that annealing at a temperature as low as 600 8C resulted in very high degree of strain relaxation, while density of threading dislocations was low (B/ 10 5 cm 2 ). The enhanced strain relaxation was attributed to the fact that complexes of point defects produced by the heavy-ion implantation at the elevated temperature acted as nucleation sites for dislocations. The obtained results allowed us to propose a method for preparation of thin highly relaxed SiGe layer with low threading dislocation density and good surface morphology. # 2003 Elsevier Science B.V. All rights reserved.

Time-resolved measurements of dislocation-related photoluminescence bands in silicon

Time decay measurements of dislocation-related PL have been performed for plastically deformed Si samples. Dislocation structures with different spectra were realized by deformation and subsequent thermal treatment. In all cases the decay time of the D1 band is less than that of the D2 band. Intrinsic properties of dislocations may therefore define the difference in decay times between the two bands. We compare this observation with previous results and propose a model of recombination between shallow and deep levels for D1/D2 bands. Different decay times are attributed to different spatial separation of shallow traps from a common deep trap.

Possible Polymerisation at Dislocations in C60 Crystals

It is known that under hydrostatic pressures of about 1 GPa the polymerisation of molecules in C 60 crystals occurs in a temperature range of about 400-600 K. The same strain of a lattice can be achieved in the vicinity of a dislocation core. Therefore, one can suppose that the polymerisation of C 60 molecules can be possible in the vicinity of dislocations in C 60 crystals at elevated temperature. Here we report the results of stress-strain measurements made on C 60 single crystals and the photoluminescence (PL) spectra of plastically deformed samples. A hardening of samples with increase of the deformation temperature from 20 to 300 °C was observed together with a strong enhancement of some defect-related lines in PL spectra. We suppose that the appearance of covalently bonded C 60 molecules at dislocations is a possible reason for that.

Charge transfer state of novel molecular complex C26H18Te2·C60·CS2 detected in single crystals by photoluminescence and ESR

Abstract Photoluminescence (PL), time resolved PL and optical absorption spectra near the band gap energy and in the range of IR active vibration modes of a novel molecular complex of fullerene, C 26 H 18 Te 2 ·C 60 ·CS 2 (BTX C 60 ·CS 2 ), have been investigated. The new absorption band in the range 1100 cm −1 , and a novel broad ESR signal have been found, indicating the optically excited charge transfer transition in the complex. The shift of the PL spectrum by 0.32 Ev towards lower energies (with respect to one in the C 60 crystal), together with a long time decay of all PL lines, allows us to assume that the recombination is also accompanied by a charge transfer.

Luminescence induced in diamond by He+ ion implantation into SiC/C composites with an inverse opal structure

The photoluminescence induced in diamond by helium ion implantation into SiC/C nanocomposite samples and their structure revealed by high-resolution transmission electron microscopy have been investigated. It has been found that, apart from crystallites of silicon carbide, graphite, and amorphous carbon, in the structure of the composites there are spherical carbon particles containing concentric graphite-like shells (onion-like particles). It has been established that onion-like particles are formed during high-temperature treatment of SiC/C nanocomposites in the course of their preparation. It has been shown that, after the implantation with the subsequent thermal treatment, nanocomposite samples exhibit a luminescence characteristic of N-V centers in diamonds. The assumption has been made that the diamond crystallites are formed at the center of onion-like particles during high-temperature treatment of the composite.

The Unusual Temperature Shift of Dislocation Related D1/D2 PL Bands in Donor Doped Silicon

The samples of p- and n-doped Fz Si were deformed in 3-point bending mode in the temperature range 800-950flC. Dislocation related PL (DRL) spectra were measured at temperature in the range 4.2 – 200K. Several features of DRL turned out to be sensitive to donor level doping. First, the low energy components of D1/D2 bands disappear at middle and high doping level. Second, the intensity of D1 band showed much more dependence on the donor doping level than other DRL bands and almost disappeared at the concentration of donors around 1017cm-3. Finally, it has been found that the temperature variation of the D1/D2 line positions depend on the donor doping level. Namely, at the donor concentration higher than 1015cm-3 the D1/D2 bands demonstrate the blue shift when the sample temperature goes up from 4K. At higher temperature the band positions more or less follow the temperature behavior of the band gap. The effect does not depend on chemical nature of donor except a value of ionization energy. No such behavior has been observed for different levels of acceptor doping. Taking into account that the ionization of shallow donors happens in the temperature range of above 30K, the effect of blue shift has been attributed to the influence of free electrons released from donors.