A.N. Tereshchenko

Dislocation Photoluminescence in Silicon and Germanium

Dislocation photoluminescence (DPL) is studied at 4.2K in plastically deformed germanium single crystals containing predominantly 60fl dislocations of “relaxed” morphology. The DPL spectra were deconvolved into Gaussian (Gm) lines of two groups over the range 0.5-0.6 eV. One of these lines corresponds to the radiation of 60fl dislocations with the equilibrium stacking fault width F0. To clarify the origin of the other Gm lines, the effect of both the dislocation density ND, ranging from106 to 109 cm-2, and the annealing at temperatures above 600flC on the intensity of Gm lines was investigated. The origin of different lines in the DPL spectra of germanium and silicon is discussed.

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.

Features and mechanisms of growth of cubic silicon carbide films on silicon

The mechanisms and specific features of the growth of silicon carbide layers through vacuum chemical epitaxy in the range of growth temperatures from 1000 to 700°C have been considered. The structure of the heterojunction formed has been studied using the results of the performed investigations of photoluminescence spectra in the near-infrared wavelength range and the data obtained from the mass spectrometric analysis. It has been found that, in the silicon layer adjacent to the 3C-SiC/Si heterojunction, the concentration of point defects significantly increases and the dislocation structure is not pronounced. According to the morphological examinations of the surface of the growing film, by analogy with the theory of thermal oxidation of silicon, the theory of carbidization of surface silicon layers has been constructed. A distinctive feature of the model under consideration is the inclusion of the counter diffusion fluxes of silicon atoms from the substrate to the surface of the structure. The growth rate of films and the activation energy of diffusion processes have been estimated. The performed experiments in combination with the developed growth model have explained the aggregates of voids observed in practice under the silicon carbide layer formed in the silicon matrix and the possibility of forming a developed surface morphology (the island growth of films) even under conditions using only one flow of hydrocarbons in the reactor.

Dislocation Related PL of Multi-Step Annealed Cz-Si Samples

The samples of Cz Si were subjected to multi-step annealing at different temperatures. After high temperature consequent steps the dislocation related spectra (DRL) were detected from the samples. The main feature of the DRL spectra was the very narrow low energy bands D1/D2, which are unusual for Cz Si. TEM analysis shown that the only candidates for DRL spectra are dislocation loops, punched out from precipitates. To explain the absence of influence of oxygen it was assumed that the distribution of interstitial oxygen is nonuniform in such samples and has some depletion regions in the vicinity of precipitates.

Effect of copper on dislocation luminescence centers in silicon

The effect of copper on dislocation luminescence centers in silicon has been investigated using photoluminescence and transmission electron microscopy. It has been demonstrated that there exist two main mechanisms responsible for quenching of dislocation luminescence by the copper impurity. The first mechanism is dominant at high copper concentrations and associated with the decrease in the time of nonradiative recombination of nonequilibrium charge carriers due to the formation of copper precipitates in silicon. This leads to the quenching of the entire dislocation luminescence and the edge exciton luminescence. The second mechanism is associated with the interaction of individual copper atoms with deep dislocation centers D1/D2, which results in the passivation of the recombination activity of these centers. This mechanism takes place even at room temperature and is highly effective at low copper concentrations.

Dislocation states and deformation-induced point defects in plastically deformed germanium

We used the DLTS and photoluminescence (PL) techniques to study the deep states due to dislocations and deformation-induced point defects (PDs) in plastically deformed p-type germanium single crystals containing predominantly 60 dislocations with density ND, ranging from 105 to 106 cm-2. The narrow line near the temperature 140K dominates in the DLTS spectra. The ionization enthalpy and the capture cross section for holes traps indicate that the substitution copper atoms Cus are the main type of PDs. A decrease of the Cus atoms concentration and redistribution of the intensity in the PL spectra after the heat treatment of deformed samples at a temperature 500 °C are attributed to the diffusion of copper atoms to dislocations resulting in the appearance of “dirty” regular segments of 60 dislocations.

Dependence of Luminescence Properties of Bonded Si Wafers on Surface Orientation and Twist Angle.

PL spectra of SOI wafers with buried oxide (BOX) layer were measured after dissolution annealing at 1200°. Depending on mutual orientation of starting base and top wafers different patterns of luminescence bands were observed after annealing. While the small fraction of luminescence clearly originated from dislocation related centers, another intensive band appeared in the range 0.8 – 0.95eV with certain dependence of maximum position on the twist misorientation. TEM investigation confirmed the existence of dislocation net at the interface. On the other hand some peculiarities of PL spectra did not support their relation to dislocations. Though a stepped chemical etch of surface layer confirmed the origin of new band being at the interface too. Therefore a nature of possible defects generated due to dissolution of BOX layer is discussed.

Peculiarities of Dislocation Related D1/D2 Bands Behavior under Copper Contamination in Silicon

In this paper we present a detailed investigation of peculiarities of dislocation related D1/D2 bands behavior in silicon doped with Cu. For this purpose float zone grown (FZ) p-type silicon with B-doping 2.85·1015cm-3 was deformed by 3-point bending method at 950flC up to dislocation density of 2±0.2·106 cm-2. The deformed samples were contaminated with Cu up to several concentrations from 6·1013 cm-3 to 5·1016 cm-3. The variation in dislocation related spectra were traced after different thermal treatments. A decrease of D1/D2 bands intensity in quenched samples was observed even after their storage at room temperature. Taking into account the fact that Cu has a high mobility even at room temperature the decrease of D1/D2 bands intensity can be attributed to passivation of corresponding luminescence centers by Cu atoms. The influence of Cu contamination on D2 band is much more complicated as compared to D1 band. New line in position about 883 meV was observed as a result of storage of samples at room temperature and subsequent isochronous anneals. It was observed that D1/D2 band luminescence sharply increased in 30K – 50K range in samples with high Cu doping level. In addition the line in about 830 meV position became stronger at these temperatures whereas its intensity was negligible at 6K.

Fine Structure of Dislocation Related PL Bands D1 and D2 in Silicon

The samples of p- and n-doped Fz Si were deformed in 3-point bending mode in the temperature range 800-950°C. The fine structure of dislocation related luminescence in the region of D1 and D2 bands was most pronounced at lowest rate of deformation. The temperature variation of intensity of individual lines did not reveal any thermalization effects. It implies that centers responsible for different individual lines are situated in diverse places. The most narrow lines with maximum positions of 802 meV and 807 meV (D1 band) and 869 meV and 873 meV (D2 band) are rapidly quenched with increase in temperature, while the broader background lines survive at higher temperature. The new line with maximum position at about 882 meV appears in the D2 band with enhanced carbon doping. It was found that at higher P-doping the low energy fine structure lines 802 meV and 869 meV are absent. Besides, the Fz samples with different P doping level from 6×1014 cm-3 to 1.2×1016 cm-3 demonstrate quite a different temperature variation of broad background lines. At lowest level of P-doping they move to low energy side at temperature above 30K, while at P-doping above 1015 cm-3 these lines move to higher energy in the same temperature range. A possible explanation of this observation can be related to distribution of electrons in the cband. It implies that the corresponding electronic transitions occur between the edge of conduction band and deep states.