Dislocation-related Lines Research Articles

Deep-level photoluminescence due to dislocations and oxygen precipitates in multicrystalline Si

We have demonstrated the presence of a dislocation-related component and a component due to oxygen precipitates in a broad deep-level photoluminescence (PL) band in multicrystalline Si at room temperature. In PL intensity mapping, the lower-energy side of the deep-level PL band at about 0.79 eV appeared as a dark line along a small-angle grain boundary (SA-GB) surrounded by a bright band on either side, while the higher-energy side at about 0.87 eV as a bright line along the SA-GB. These intensity variations agree with the low-temperature PL intensity patterns for well-established dislocation-related lines of D1/D2 and those for oxygen precipitates, respectively. These patterns were observed around SA-GBs with a misorientation angle of 1–2°, and were assumed to be due to the distribution of secondary defects or impurities trapped by the strain field around dislocation clusters forming SA-GBs and that of preferential oxygen precipitation on the dislocations. A spectral component associated with the D3/D4 lines was also extractable from the deep-level PL at about 0.94 eV. The intensity increased on SA-GBs with the angle of <1°, where oxygen precipitation did not occur. This corresponds to the generally accepted idea that the D3/D4 lines are related to the intrinsic nature of dislocations.

Photoluminescence in silicon implanted with silicon ions at amorphizing doses

Luminescent and structural properties of n-FZ-Si and n-Cz-Si implanted with Si ions at amorphizing doses and annealed at 1100°C in a chlorine-containing atmosphere have been studied. An analysis of proton Rutherford backscattering spectra of implanted samples demonstrated that an amorphous layer is formed, and its position and thickness depend on the implantation dose. An X-ray diffraction analysis revealed that defects of the interstitial type are formed in the samples upon annealing. Photoluminescence spectra measured at 78 K and low excitation levels are dominated by the dislocation-related line D1, which is also observed at 300 K. The peak position of this line, its full width at half-maximum, and intensity depend on the conduction type of Si and implantation dose. As the luminescence excitation power is raised, a continuous band appears in the spectrum. A model is suggested that explains the fundamental aspects of the behavior of the photoluminescence spectra in relation to the experimental conditions.

Microscopic and spectroscopic mapping of dislocation-related photoluminescence in multicrystalline silicon wafers

Microscopic and spectroscopic photoluminescence (PL) mapping was performed on a region including intra-grain defects in multicrystalline silicon wafers in the temperature range between 15 and 300 K, and the temperature dependence of PL spectra from the region was studied. We confirmed that the origin of deep-level emission with an intensity maximum at 0.78 eV at room temperature was different from that of dislocation-related lines at low temperature. We believe that the 0.78 eV emission is associated with oxygen precipitation, and that the intra-grain defects are dislocation clusters decorated with not only heavy-metal but also oxygen impurities.

Dislocation-related luminescence in silicon, caused by implantation of oxygen ions and subsequent annealing

Multiple implantation of oxygen ions with energies of 0.1–1.5 MeV at doses of 7 × 1013−2 × 1014 cm−2 and subsequent annealing in a chlorine-containing atmosphere at 900°C for 4 h give rise to dislocation-related luminescence in p-Si. A p → n conductivity-type conversion is also observed in this case in the surface layer of Si, which indicates that electrically active donor centers are formed in the process. Preliminary heat treatment of wafers covered with an erbium-doped film of tetraethoxysilane (TEOS) in argon at 1250°C for 1 h does not preclude the appearance of dislocation-related luminescence, but affects the parameters of the dislocation-related lines (peak positions and intensities).

Defect-related light emission from processed He-implanted silicon

Photoluminescence (PL) from He +-implanted Si (Si:He, He + dose—2×10 16 cm −2, at 150 keV) is related to its microstructure; it has been tuned by processing at 720–1400 K under hydrostatic Ar pressure (HP, up to 1.2 GPa). Processing of Si:He at 720 K for 10 h results in an appearance of the D2 and D3 dislocation-related PL lines, these last of the highest intensity. Only the D1 dislocation-related line of intensity increasing with HP has been detected after processing at 920–1070 K. The D1 (of the highest intensity), D2 and D3 PL lines are observed after the treatment at 1270 K. No dislocation-related PL has been detected for Si:He processed at 1400 K. The treatment of Si:He at 720–1270 K under HP makes it possible to produce Si:He of specific microstructure resulting in strong PL at 0.81, 0.87 or 0.94 eV.

Structures prepared by implantation of silicon with nitrogen and annealing under high hydrostatic pressure

The effect of treatment up to 1130 °C under hydrostatic argon pressure up to 1.1 GPa on the structure of silicon implanted with nitrogen, Si:N (nitrogen dose, D=2×10 16 cm −2, ion energy, E=150 keV) was investigated by TEM, photoluminescence (PL) and other methods. The high-temperature pressure treatment produces typically strongly disturbed buried nitrogen-containing layers. The Fz-Si:N samples treated at 450 °C—HP indicate the PL peaks at about 0.81 eV (the dislocation-related D1 peak) with the intensity increasing with HP (no PL at 0.81 eV was detected for the sample treated under 0.01 GPa), and at about 0.93 eV (the dislocation-related D3 peak). The Fz-Si:N sample treated at higher temperature (650 °C) and under the highest pressure (1.1 GPa) indicates the presence of PL only at about 0.87 eV (the D2 dislocation-related line). Our investigations help in understanding the mechanisms of creation of buried insulating layers in nitrogen-implanted silicon.

Temperature behaviour of extended defects in solar grade silicon investigated by photoluminescence and EBIC

Spatially resolved photoluminescence and EBIC were used to characterise a sample of multicrystalline silicon in the temperature range 80–300 K. The dislocation related lines in the spectrum-D1, D2, D3 and D4 correlate with the total recombination activity measured by EBIC. The temperature dependent EBIC behaviour was utilised to access the contamination level at the dislocations in low quality regions of the sample. The temperature dependence of D1 line shows a maximum at about 150 K. The decrement of D1 peak area upon temperature decreasing below 150 K could be related to the appearance of D3 and D4 lines in the photoluminescence spectra. The peak widths of D1 and D2 show opposite temperature dependence. D1 width decreases and D2 becomes broader upon decreasing temperature. Two additional lines with energies below the energy of band-to-band luminescence were observed together with the D bands at 80 K. They could be related to phonon replication of the band edge luminescence peak and can be seen on FZ-Si too.

Correlation between defect structure and luminescence spectra in monocrystallineerbium-implanted silicon

The transformation of structural defects and photoluminescence (PL) spectra ofn- and p-type Cz-Si after implantation with erbium ions at 1 MeV energy to dosesof 1 × 1013 and 1 × 1014 cm−2 followed by annealing at 620–1100°C for 0.25–3.0 h inchlorine-containing atmosphere or oxygen have been studied by transmissionelectron microscopy, optical microscopy in combination with selective chemicaletching, and PL. For the doses used, annealing at a temperature lower than1100°C leads to the formation of different extended defects (partial Frank orperfect prismatic dislocation loops) of submicron sizes which do not prevent theappearance of Er-related lines and do not give rise to dislocation-related lines inthe PL spectrum. In contrast, high-temperature annealing at 1100°C resultsin the development of similar three-dimensional networks of pure edgedislocations with a density of ∼107 cm−2. These dislocations are responsible for theappearance of quite intensive dislocation-related luminescence (DRL).For high-dose implantation, when annealing at 1100°C is used, the samedislocation networks have been found to form in the n- and p-Si wafers withdifferent low-temperature annealing stages (if any). However, all theseparameters exert the peculiar influence upon the intensity of DRL lines.

Structural defects and dislocation-related photoluminescence in erbium-implanted silicon

Structural defects and optical features of p-type CzSi after implantation of erbium ions with 1 MeV energy and 1×10 14 cm −2 dose followed by annealing at (620–1100 °C) for 0.5–1.0 h in chlorine-containing atmosphere (CCA) or argon have been studied by transmission electron microscopy (TEM), optical microscopy in combination with selective chemical etching, and photoluminescence (PL). High temperature annealing in the chlorine-containing ambience gives rise to perfect prismatic dislocation loops as well as 60° and pure edge dislocations with dominant dislocation-related lines in the PL spectrum. Pure edge dislocations are responsible for the appearance of the lines. The Er-related lines due to the intra-4f shell transitions in the rare earth ions dominate in the PL spectra and no structural defects are observed after high temperature annealing in argon. The role of the intrinsic point defects in the transformation of structural defects and optically active centers is discussed.

Separation of dislocation- and erbium-related photoluminescence by time resolved studies

The luminescence of Er in silicon occurs at 1.54 μm, which is very close to the dislocation-related PL signal in silicon known as D1. Photoluminescence decay measurements have been carried out on silicon co-implanted with Er and O. Decays were recorded using a transient capture card designed in-house, and decays over nearly three decades were routinely measured with a system response time of 10 μs. The decay transient always shows a component with a decay time of up to 1100 μs, and also a component with a much faster decay time. It is shown, that the presence of the fast decay component correlates with a broadening of the signal at 1.54 μm, indicative of radiative emission due to the dislocation-related line D1, and also with the observation in electron and optical microscopy of small extended defects.

Effect of dislocations on the photoluminescence decay of 1.54 μm emission from erbium-doped silicon

The decay of the photoluminescence at 1.54 μm from erbium-implanted silicon has been recorded over nearly three decades of intensity. Two components of the decay are observed at 7.5 K, one with a decay time constant of ∼40–160 μs, and the other with a characteristic time of between 800 and 1200 μs. It is found that the proportions of fast and slow components can vary depending upon the amount of implantation-induced damage, and this variation correlates with a broadening on the high energy side of the erbium related emission. The temperature dependence of the fastest decay is not consistent with it being due to an Auger process involving free carriers, and it is suggested that extended defects in the layers are responsible for this part of the decay curve. The broadening of the erbium line is attributed to the overlap of the dislocation-related line D1 with the erbium emission. Selective chemical etching and scanning electron microscopy show that there are extended defects present in samples with a short fast decay component.

Dislocation-related luminescence in Er-implanted silicon

The behavior of luminescence spectra and structural defects in single crystal Czochralski silicon after erbium implantation at 1–1.8 MeV energies and 1×10 13 cm −2 dose with subsequent annealing at 1000–1200°C for 0.25–3 h in argon and a chlorine-containing ambience (CCA) was studied by photoluminescence (PL), transmission electron microscopy and chemical etching/Nomarski microscopy. We have found that annealing in CCA gives rise to dislocation loops and pure edge dislocations with dominant dislocation-related lines in the PL spectrum. Pure edge dislocations are responsible for the appearance of the lines.

Photoluminescence and structural defects in erbium-implanted silicon annealed at high temperature

The behavior of luminescence spectra and structural defects in single crystal Czochralski silicon after erbium implantation at 1 MeV energy and 1×1013 cm−2 dose with subsequent annealing at 1100 °C for 0.25–3 h in an argon or chlorine-containing ambience was studied by photoluminescence (PL), transmission electron microscopy, and chemical etching/Nomarski microscopy. We have found that annealing in the chlorine-containing ambience gives rise to dislocation loops and pure edge dislocations with dominant dislocation-related lines in the PL spectrum. Pure edge dislocations are responsible for the appearance of the lines. The Er-related lines due to the intra-4f shell transitions in the rare-earth ions dominate in the PL spectra and no structural defects are observed after annealing in argon. The observed differences in the optical and structural properties of Si:Er are associated with intrinsic point defects generated during the implantation and annealing.

Electrical and optical properties of gold-doped n-type silicon

Different measurement techniques, both electrical and optical, were utilized in this work to characterize gold diffusion in n-type, float-zoned silicon in the temperature range 600–1150 °C. In the lower temperature region (≤750 °C), the gold diffusion is observed by the introduction of the Au acceptor state at 0.53 eV below the conduction band, and is correlated to the electrical behavior of the samples deduced from Hall effect and resistivity data. Also, the effects of Au diffusion on the free-carrier concentration and mobilities are discussed. It was shown that high temperatures and long times for gold diffusion change the conductivity type in the samples from n to p. In the samples that converted to p type, a limiting room-temperature resistivity of 2.0×103 Ω cm was attained, when the conduction is mainly influenced by the Au-related deep electronic states in the band gap. In this case, the diffusion mechanism is also investigated by secondary ion mass spectroscopy data determining the equilibrium Au solubility, which is close to the equilibrium solubility of interstitial gold. Low-temperature photoluminescence measurements have shown that the intensity of the lines often attributed to dislocations, increases significantly by gold diffusion in the lower temperature region. At higher diffusion temperatures, a decrease of the dislocation-related lines was found, associated with formation of gold-related precipitates. Introducing an inhomogeneous internal stress distribution in the Si matrix, these precipitates cause line shifts as well as line broadenings of the free exciton, the phosphorus bound exciton, and the electron-hole droplet photoluminescence emissions. The concentration of substitutional phosphorus is found to decrease with increasing diffusion temperatures.