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The charge carrier lifetime and accordingly the diffusion length in polycrystalline semiconductor materials is known to be detrimentally influenced by disordered interfaces like grain boundaries (GBs). The GB light beam induced current (GB-LBIC) technique is suitable for the extraction of the minority charge carrier diffusion length in unprocessed polycrystalline materials. This measurement method is based on the GB itself acting as a charge collector. A spatially-resolved light beam induced current can thus be measured even without a collecting p–n junction or Schottky contact, and without biasing the sample. In this contribution we present a simulation based analysis of measured GB-LBIC line scans on bonded silicon wafers and polycrystalline silicon thin films with different laser wavelengths and intensities.

We analyzed multi quantum well light emitting diodes, consisting of ten alternating GeSn/Ge-layers, were grown by molecular beam epitaxy on Si. The Ge barriers were 10 nm thick and the GeSn wells were grown with 7% Sn and thicknesses between 6 and 12 nm. Despite the high threading dislocation density of 109to 1010cm−2the electroluminescence spectra measured at 300 and 80 K yield a broad and intensive luminescence band. Deconvolution revealed three major lines produced by the GeSn wells that can be interpreted in terms of quantum confinement. Biaxial compressive strain causes a splitting of light and heavy holes in the GeSn wells. We interpret the three lines to represent two direct lines, formed by transitions with the light and heavy hole band, respectively, andan indirect line.

The heteroepitaxial growth of GeSn and Ge crystals on Si substrates are investigated for Si-based photonic applications. Light Emitting Diodes with emission wavelengths from 2,100 to 1,550 nm could be demonstrated with active intrinsic GeSn light emitting layers between Ge barriers. A clear shift of the direct band gap toward the infrared beyond 2 μm is measured. Emission intensity is increased compared to Ge Light Emitting Diodes. Room temperature lasing from electrically pumped n-type doped Ge edge emitting devices are demonstrated. The edge emitter is formed by cleaving Si-Ge waveguide heterodiodes, providing optical feedback through a Fabry-Pérot resonator. The electroluminescence spectra of the devices showed optical bleaching and intensity gain for wavelengths between 1,660 nm and 1,700 nm.

A significant increase of the drain current is verified if defined numbers and types of dislocations are present in the channel of MOSFETs. For pMOSFETs, analysed here, an enhancement by a factor of eight exists if mixed dislocations are placed in the channel. The drain current increase is caused by higher concentration and higher mobility of holes on dislocations. It is shown that cores of mixed dislocations possess uniaxial compressive strain components in the order of e ≅ –0.1 which are significantly higher than in the strain field surrounding a dislocation. The exceptional high uniaxial strain results in dramatic alterations of the silicon band structure. Upward shifts of the upper valence bands appear forming a quantum wire. The generation of the quantum wire forces hole confinement along dislocations and generates a one-dimensional hole gas (1DHG). Confinement and energy quantization are assumed to be most important for the increased carrier transport along dislocations. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In conjunction with the two-level model the temperature behaviour of the dislocation-related D1-peak follows the T-behaviour of the band gap. Based on luminescence observations in our laboratory and on literature data we propose a ∼30 meV wide domain of the D1 peak. Altogether, the D1-peak position ranges between about 0.76 eV at 300 K and nearly 0.84 eV at a few K. It was shown that the energetic shift for a certain temperature is caused by external electric fields, by excitation level, that affects the intrinsic dislocation field, and by elastic stress. The luminescence of oxygen-related defects / precipitates might be described by a line at ∼ 0.77 eV (P-line) that does not depend on temperature. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

For mono-crystalline Ge the indirect luminescence intensity declines upon growing temperature from 80 to 300 K, whereas for dislocated Ge structures the opposite behavior occurs. These findings are comparable to earlier observations on Si. The drop of the luminescence in dislocated material upon lowering temperature was attributed to the increase of the competing non-radiative recombination due to shallow dislocation states. In opposition to the indirect luminescence, the character of the direct Ge luminescence, i.e. incline of intensity upon growing temperature, is not converted by dislocations. The measured behavior of the direct peak position of Ge, in the temperature range between 80 and 300 K, is in accordance with calculated dependence and reflects the direct bandgap energy. The observed red shifts in dislocated Ge structures are shown to be produced by tensile strain, bandgap narrowing and by the Sn-content of GeSn quantum wells, respectively. A direct influence of dislocations could not be observed. Satisfying understanding of the existing temperature behavior of the indirect Ge peak position is on embryonic stage.

Antimony-doped Ge-LEDs were subjected to electroluminescence studies at temperatures about 300 K and 80 K. The LEDs were grown on Si substrates by MBE. The thickness of the active layer was 300 nm. For the p+nn+-LEDs the Sb concentrations were 1 × 1018, 1 × 1019, 3 × 1019, 4 × 1019, 7 × 1019 or 1 × 1020 cm–3, respectively. As reference a p+in+-LED without intentional doping in the active layer was used. The investigated specimen exhibited dominance of the direct transition line at about 0.8 eV. Moreover, luminescence indirect transition was observed. In general, the spectra reveal higher EL intensities at room temperature as compared to 80 K. With decreasing temperature the direct peak was blue shifted. The highest EL intensity was found for the LED with Sb concentration of 3 × 1019 cm–3. With increasing Sb doping a red-shift of the direct peak was observed, caused by band gap narrowing. In addition, a simulated curve of the direct transition was compared with our samples and fits well with the measured spectra. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two- dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one- dimensional channels for holes.

Local electronic states of regular dislocation networks produced by n- and p-type silicon wafer bonding with different screw dislocation density were studied with deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). A drastic sadden changes of the electric level spectrum with increasing of dislocation density from two shallow bands located near the edges of valence and conduction bands towards two deep bands with energy positions about Ec - (0.22-0.26) eV and Ev + (0.4-0.53) eV were found. The origin of the electric level spectrum changes is ascribed to the changes of dislocation core structure from dissociated to perfect ones that occur when interdislocation distances became comparable with the dislocation equilibrium dissociation width. The obtained results correlate well with the results of recent studies of recombination activity of grain boundaries in mc-Si.

The formation of dislocation pile-ups and related small-angle subgrain boundaries in block-cast multicrystalline silicon for photovoltaic applications has been studied by means of white-beam X-ray topography (WB-XRT). For this purpose, samples sliced perpendicular and parallel to the growth direction have been investigated in reflection and transmission geometry, respectively. During the growth process of the silicon ingot, the dislocation density increases. WB-XRT measurements revealed the formation of small-angle subgrain boundaries. The subgrains have a slightly changed orientation related to a rotation of ∼0.07–0.80° around an axis parallel to the growth direction. This tilt results from the high number of dislocations forming dislocation pile-ups and walls. The spacings between dislocations in such subgrain boundaries were found to be between 297 and 28 nm. A qualitative model for the formation of dislocation pile-ups is proposed.

We present an overview on generation of direct gap photo- and electroluminescence in Ge bulk wafers, Ge thin films deposited on Si, and Ge p-i-n diodes prepared on Si substrates. We analyzed the emission in a spectral range from 0.45 eV to 0.95 eV, covering the radiation caused by direct gap transitions, the indirect one, and also the luminescence related to transition on dislocations. The temperature and excitation level strongly influence the intensities of direct and indirect photoluminescence in bulk samples. As it could be expected, high temperature and excitation favour the generation of direct gap luminescence. Intrinsic bulk Ge shows a quadratic dependence of the direct gap luminescence on the excitation and a sub-quadratic one for the indirect. The photoluminescence spectra taken from intrinsic Ge on Si layers show features related to dislocations. There are two spectral regions associated with dislocation recombination. At room temperature one is at around 0.45 eV and the other at 0.72 eV. We found strong direct gap radiation from the Ge p-i-n diodes with intrinsic, highly dislocated active area (dislocation density of about 108-1010 cm-2). There is a threshold current density of 8 kA/cm2, at which the direct band luminescence becomes a super-quadratic. The dependence of the radiation intensity on the excitation is governed by a power law with exponent of 1.7 before reaching that threshold and 4.5 after exceeding it. Above the threshold the dislocation radiation shows similar dependence on the excitation as the direct band luminescence.

We report on 0.93 eV luminescence observed in multicrystalline silicon. The spectral line is close to the well known D3 one, but its properties are different. The new feature shows a remarkable intensity at room temperature, exceeding the intensity of the band to band radiative transition. Moreover, it appears as a single line in the entire temperature range 10-300K, in contrast to the D3, which is usually accompanied by D4. Cathodoluminescence (CL) and electron beam induced current (EBIC) micrographs revealed that the centers causing 0.93 eV emission are irregularly distributed along certain grain boundaries. Electron backscattering diffraction examination showed that the 0.93 eV luminescence appears at grain boundaries characterized by a lattice rotation around a axis. The EBIC contrast at those irregularities indicates strong total recombination. Based on an analysis of the temperature dependence of the CL intensity and the EBIC contrast we obtained an activation energy of about 120 meV.

An amorphous Si (a-Si) film, 60 nm thick, embedded between SiO2 layers and deposited on quartz substrate was crystallized in the regime of light-induced solid-phase crystallization (LISPC). The high quality of the film after LISPC was proved by high-resolution transmission electron microscopy (HRTEM), by Raman spectroscopy (RS) measurements, and by electron energy loss spectroscopy (EELS). The crystallized film consisted of fully crystalline grains with lateral sizes of 200–600 nm. Only a few stacking faults and/or dislocations were detected inside these grains. Besides the large grains, regions with fully crystalline material containing a higher density of lattice defects were also observed. An intermixing of phases, i.e., SiO2 or a-Si clusters inside the crystallized Si film and/or Si-clysters inside the SiO2 layers, was not detected.

The influence of GBs contained in the channel of MOS-FETs - fabricated in thin SOI layers - is demonstrated. The drain current measured at room temperature increases about 50 times for nFETs and about 10 times for pFETs, respectively, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

Techniques, such as photoluminescence (PL) and electron-beam-induced current (EBIC), have already proven their effectiveness and applicability for solar materials. Although, the methods are standard techniques for multicrystalline Si PV, their application to thin films is challenging and requires special adjustment and a careful selection of the measuring parameters. Here we report on the investigation of thin-film tandem solar cells consisting of hydrogenated amorphous (a-Si:H) and microcrystalline silicon (µc-Si:H) on glass substrates. We observe a homogeneous spatial distribution of the PL signals caused by the dominance of the surface recombination. A typical PL spectrum exhibits sub-band gap features of a-Si:H. We relate the sub-band-gap spectral features mainly to transitions of carriers trapped in deep states. Observations on partially processed stacks support this supposition. PL is only detectable on the a-Si:H layer, while EBIC signal is generated mainly in the µc-Si:H layer. It is found out that the luminescence features of the thin a-Si:H layer resemble those on bulk a-Si:H.

To enlarge the tensile strain in Ge light emission diodes (s-Ge LED) we applied a GeSn virtual substrate (VS) on Si (001) with a Sn content of 4.5 %, to produce s-Ge LEDs. The LED stack was grown by molecular beam epitaxy. Electroluminescence investigations of the s-Ge LED show a major direct Ge peak and a minor peak at lower energy, which is formed by the GeSn-VS and the s-Ge indirect transition. The main peak of a 100 nm thick s-Ge LED is red-shifted as compared to the Ge peak of an unstrained reference Ge LED grown on Ge-VS. At a temperature of T = 80 K the increased tensile strain, produced by the GeSn-VS, causes a redshift of the direct Ge peak from 0.809 eV to 0.745 and 0.769 eV, namely for the s-Ge LED with a 100 and 200 nm thick active layer. At T = 300 K the direct Ge peak is shifted from 0.777 eV of the reference Ge LED to 0.725 eV (for 100 nm) and 0.743 eV (for 200 nm). The peak positions do not differ much between the 50 and 100 nm thick s-Ge LEDs. The intensities of the direct Ge peak increase with the s-Ge layer thickness. Moreover, the intensity of the 50 nm thick s-Ge sample is found to be larger than that of the 100 nm thick reference Ge LED.

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

The electrical behaviour of only a few dislocations was analysed. Such small numbers of defined dislocations were produced by hydrophobic semiconductor wafer direct bonding. The dislocation networks were placed in the channel of SOI MOSFETs where the source and drain regions of these devices act as contacts. Varying the channel width allows one to control the number of dislocations measured. Analyses of nMOSFETs proved an increase of the drain current caused by dislocations by more than one order of magnitude, while a decrease of the current is obtained for pMOSFETs. This indicates that electrons are present on the dislocation core in p-type material. The concentration of electrons on dislocations was estimated to be about 200 electrons per micrometer dislocation length, corresponding to a distance of about 5 nm between free electrons. This distance agrees with the space between Coulomb islands proved by low-temperature measurements. The investigations refer to a metallic-like conductance along dislocations caused by a two-dimensional carrier confinement. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic states of dislocation networks produced by Si wafers bonding was studied by means of deep level transient and admittance spectroscopy methods. A strong field-enhanced hole thermoemission was established for one shallow and one deep states in p-type Si that was explained in the framework of dislocation-related Poole-Frenkel-effect model. The shallow dislocation related states situated close to the valence as well as to the conduction band of silicon were found to be associated with the broad energetic bands with rapid interstate exchange. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocation related electroluminescence was detected in germanium p-i-n diodes grown on silicon using a virtual substrate. It appears at room temperature and above a certain threshold of the excitation current. The spectral feature characterizing dislocation related radiation consists of three peaks at around 0.45 eV. The appearance of the dislocation related peaks in the spectrum goes along with a change in the growth rate of the direct band-to-band luminescence upon increasing of the current through the structure. The observation is consistent with an injection of minority carriers in the p+ and n+ regions of the diode. As the p+ region contains the misfit dislocation rich virtual substrate it becomes a source of dislocation luminescence. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thin absorber films grown by the CuInS2-on-Cu-tape (CISCuT) method were studied by Raman spectroscopy and deep-level transient spectroscopy (DLTS). Raman measurements revealed a degradation of crystalline quality and a growth of the CuAu fraction with the increase of Cu-tape velocity through the sulfur chamber, whereas DLTS method – corresponding variations in the magnitude of the dominating peak E1. The origin of the E1 peak was established from the correlation of Raman and DLTS results and ascribed to defect states at the interface between chalcopyrite and CuAu phase.

We report on a method for fast detection of defect rich areas in multicrystalline silicon solar wafers. It is based on photoluminescence imaging of the whole wafers and detects both the band-to-band radiation as well as the dislocation specific radiation D1. To illustrate the capabilities of the method we examined 5.0 × 5.0 cm2 wafer pieces in different stages of their processing. The achieved resolution of the D1 images was ∼120 μm, within a total recording time of 550 ms.

We studied the correlation between the appearance of defects and of breakdowns in fully processed solar cells by electroluminescence imaging. Images under forward and reverse bias were recorded, revealing defective areas and breakdown sites of the cells, respectively. In the experiments presented here an InGaAs camera system was used, which allows us to detect short wave infrared light in the 900–1700 nm range. Applying a forward bias the band-to-band luminescence (1.1 eV/1150 nm) and the defect-related luminescence (0.8 eV/1550 nm) were imaged. Both imaging techniques reveal mainly dislocation-rich areas and grain boundaries. Applying a reverse bias (approximately −10 V), breakdown luminescence occurs. It was found that the distribution of the breakdown sites across the solar cells is different from the distribution of the defects showing luminescence at 0.8 eV (grain boundaries, dislocations). The spatial separation between those defects and the breakdown sites was clearly evidenced by high resolution imaging. Possible reasons for such spatial separation are discussed.

Germanium (Ge) pin photodiodes show clear direct band gap emission at room temperature, as grown on bulk silicon in both photoluminescence (PL) and electroluminescence (EL). PL stems from the top contact layer with highly doped Ge because of strong absorption of visible laser light excitation (532 nm). EL stems from the recombination of injected carriers in the undoped intrinsic layer. The difference in peak positions for PL (0.73 eV) and EL (0.80 eV) is explained by band gap narrowing from high doping in n+-top layer. A superlinear increase of EL with current density is explained by a rising ratio of direct/indirect electron densities when quasi Fermi energy level rises into the conduction band. An analytical model for the direct/indirect electron density ratio is given using simplifying assumptions.

Electroluminescence imaging under forward (EL) and reverse bias (ReBEL) has been applied to correlate defect distribution and breakdown sites in solar cells made of UMG-Si. An InGaAs camera system is used for luminescence detection, providing access to band-to-band and to the sub-band gap radiative transition in silicon. In contrast to previous papers the ReBEL reported here is observed only in the near-infrared (1.25 eV - 0.6 eV) spectral range and no visible luminescence has been detected. It is found that ReBEL intensity correlates with dark I-V characteristics. The overall distribution of breakdown sites in cells is different from the distribution of dislocations exhibiting luminescence at 0.8 eV (grain boundaries, defects). For the first time, a spatial separation between such defects and breakdown sites is clearly established by high resolution images, giving evidence that the defects showing sub-band gap luminescence do not take part in breakdown. It is further concluded that such radiative defects reduce the affinity for breakdown in their vicinity.

The results of investigations of solar grade mc-Si by means of combination of scanning X-ray beam excited optical luminescence microscopy (SXEOL), X-ray beam induced current (XBIC) and X-ray fluorescence (XRF) are presented. It was found, that for relatively clean sample SXEOL and XBIC provide similar information about the recombination activity of defects while for the samples with a high transition metal content there are significant differences in the provided information. The reasons of the revealed XBIC - SXEOL differences are discussed.

Thin crystalline silicon films on glass substrate, fabricated using solid phase crystallization for application in thin-film solar cells, were investigated by deep level transient spectroscopy (DLTS). The analyses of the DLTS spectra obtained during temperature scans revealed presence of carrier traps related to dislocations in silicon. Other carrier traps of yet unknown nature were detected as well. Variations of electrical activity of the traps were achieved applying variations in the process of the film formation. These changes were also detected during DLTS measurements, suggesting a possibility for applying of DLTS for the investigation and characterization of the thin-film Si material on glass.

We present a novel Ge on Si based LED with unstrained i-Ge active region. The device operates at room temperature and emits photons with energy of 0.8 eV. It basically resembles a p-i-n structure formed on a sub-micrometer thin Ge layer. The Ge layer has been grown on Si substrate by utilizing thin virtual buffer, so it becomes stress free but with high threading dislocation density. We show that such forward biased diode generates strong emission, caused by direct band to band transition in Ge. Using an InSb based detector we were able to analyze the emission spectrum in a broad energy range. We show that at low and moderate currents, features belonging to the direct and the indirect band to band electronic transitions are present which are characteristic for Ge. Clearly dominating is the direct transition related peak. Due to the missing stress-related red shift this peak appears close to the desired communication wave length of 1.55 μm. The dependence of radiation intensity on the excitation current follows a power low with exponent of 1.7, indicating that the recombination rate of the competitive nonradiative processes is relatively low. At high excitation currents features appear in the low energetic part of the spectrum. All results presented here are discussed in view of the outcome from measurements on Ge high quality bulk material. The role of the dislocation in the Ge films is discussed.

Multi-quantum wells (MQW) with nanometer thick crystalline Si layers are considered among the promising light absorbers for application in the next generation of photovoltaic cells. Proper crystallization of the initially amorphous Si (a-Si) layers in such MQW presents a challenge. Recently it was shown that light-induced solid-phase crystallization (LISPC) leads to almost complete crystallization of Si layers in the MQW. In this report we present and discuss recent results, problems and prospects related to the large-scale LISPC process of MQW structures on glass.

Threading dislocation density as function of Ge thickness deposited with different annealing processes. AFM images of 4.7 μm thick Ge deposited without annealing process and Ge deposited with cyclic annealing process.► Smooth Ge layer growth on Si (100) surface without graded SiGe buffer is performed using RPCVD. ► Threading dislocation density (TDD) is decreased with increasing Ge thickness. ► TDD is decreased by postannealing and further decease is observed by cyclic annealing. ► TDD of 7×10 5 cm −2 without degrading surface roughness is achieved.

Thin film of amorphous Si deposited on glass substrate was crystallized at 600 °C using solid phase crystallization and further processed for PV application using Crystalline Silicon on Glass technology. The resulting film was polycrystalline and contained dislocations in large density. Photoluminescence (PL) and SunsVoc measurements were applied for characterization of the material properties. The intensity of radiative transitions related to dislocations (DRL) measured at room temperature supplied information about specificities of non-radiative recombination in the material and nicely correlated with open circuit voltage, measured using SunsVoc method. The PL measurements at room temperature showed a capability of fast and reliable prediction of PV performance of the film. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Here we report on two different approaches, which allow rapid photoluminescence imaging of dislocation-related D1, and band-to-band radiation on multicrystalline solar cell wafers at room temperature. We compared a new light emitting diode based method with the recently introduced pulsed laser based method. With both techniques we obtained spatially resolved images from 15.6 × 15.6 cm2 wafers originating from different stages of the standard solar cell production process, showing that these techniques are highly interesting for inline quality control. Both methods provide homogeneous illumination over the whole sample area. With a resolution around 300 μm, and a total recording time of ∼45 s, full D1 images could be captured by the new diode technique. The most promising fact was that surface artifacts did not lead to any noticeable disturbance in the D1 image. For acid textured wafers, the pulsed laser based method was clearly in advantage over the continuous diode technique. Possible explanations are discussed in the text. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Schottky diodes prepared on silicon bonded wafers with dislocation network (DN) lying parallel to the sample surface at the depth of ∼2 μm were investigated by means of capacitance-voltage (CV), current-voltage (IV) measurements at 80 K under optical illumination. A model of the interpretation of CV and IV data is presented and discussed. It is shown that electron-beam induced current (EBIC) mapping under the proper chosen forward bias voltages allows one to trace the inhomogeneities of the potential barrier at DN. The observed non-uniformity of the DN barrier heights was ascribed to inhomogeneous distribution of small oxide precipitates lying at the dislocation network plane (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The process of light induced solid phase crystallization (LISPC) of thin layers of amorphous silicon (a-Si) embedded in silicon oxide (SiO2) was investigated using Atomic Force Microscopy (AFM). The results achieved by different modes of AFM, namely Phase Contrast Imaging, Lateral Force Mapping and Scanning Kelvin Probe microscopy reveal several steps of light-matter interaction. There is clear evidence that the very first steps take place inside of the structure leaving the surface pristine.Also, the findings well agree with that achieved by micro Raman spectroscopy yielding information on the local crystalline structure. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on electro-luminescence from metal-insulator-semiconductor diodes (MISLED). MISLEDs prepared on silicon with HfO2 layers of different thicknesses were investigated and their properties compared with such prepared by using SiO2 insulator layer. The role of the insulator layer was studied in view of the efficiency of the band-to-band radiation from silicon. We show that the luminescence efficiency depends on the dielectric constant of the insulator as well as on its ability to conduct carriers by tunnelling. Efficiency enhancement of 3.3 times was detected when the SiO2 insulator was substituted by HfO2 in the MIS emitter. Optimal injection current exists, which leads to a maximal efficiency of the luminescence. The optimal current depends strongly on the thickness of the oxide. We relate the existence of an optimal current with the depth at which the injected minority carriers recombine radiatively. Thus the electric field in the semiconductor and the surface recombination are the factors determining the optimal injection (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Multi-crystalline Ge (mc-Ge) and Ge layers on Si substrate grown by MBE and CVD are studied. The photoluminescence (PL) spectra are analysed by comparison with those obtained for bulk Ge. We present a scheme which explains the temperature dependence of the peak positions of the direct and indirect lines observed in the PL spectra. The complex fine structure of the indirect band, consisting of different sub-peaks, can be understood in terms of phonon assisted processes. Around 80 K emission of longitudinal acoustic (LA) phonons is the decisive process whereas at room temperature absorption of LA phonons dominates. Moreover, PL spectra measured in material with crystal defects suggest that multi-phonon absorption is involved in the formation of the indirect sub-peaks. As compared to mono-Ge the overall luminescence intensity of MBE and CVD grown Ge layers on Si substrate is strongly reduced. In the CVD grown Ge layers the direct line dominates at room temperature whereas in the MBE grown layers the indirect lines are found to be decisive. A shift of the peak positions for the Ge layers to lower energy (10 meV and more) is caused by tensile strain. In the Ge layers on Si and in mc-Ge, respectively, at 300 or 80 K several lines are observed, ranging roughly between 0.45 and 0.6 eV, which are originated by crystal defects/dislocations.

Regular dislocation networks (DN) formed by direct bonding of Si wafers actively participate in recombination of minority carriers. Besides nonradiative recombination (NRR), dislocation-related luminescence (DRL), i.e. radiative recombination could be observed. We show that the type of recombination is defined by the type of the dislocations and the structure of the network. Screw dislocations are mostly DRL active, while NRR is mostly related to edge dislocations. Moreover, the DRL intensity strongly depends on the misalignment angle between the crystal orientations of both bonded wafers. There exists an optimal alignment between bonded Si wafers, for which the DRL intensity has a maximum. Such alignment could be used for dislocation based all-Si light emitting devices in the future on-chip optical communication components. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Here we report on a novel method, which allows rapid photoluminescence imaging of band-to-band and dislocation-related radiation, D1, on multicrystalline silicon wafers at room temperature. We demonstrate spatially resolved 5.0 × 5.0 cm2 D1-images, with a resolution of ∼120 µm, within a total recording time of 550 ms. The method provides homogeneous illumination over the whole sample area. Comparison with results from a conventional photoluminescence mapping technique demonstrates the potential of this new method for application as an in-line wafer characterization technique.

The selective emitter formation by laser doping is a well known process to increase the efficiency of silicon solar cells [1] , [2] . For the characterization of laser doped emitters, SIMS (Secondary Ion Mass Spectroscopy) and ECV (Electrochemical Capacitance Voltage Measurement) techniques are used to analyze the emitter profile [3] . It is very difficult to get acceptable result by SIMS on a textured surface, so only ECV can be used. It has been shown, that a charge carrier depth profile can be measured on a homogeneous emitter only by ECV. The use of laser doping results in a non-homogeneous emitter. We have shown that the emitter depth is not just a function of the pulse power, but in addition of the surface structure of the wafer. The texture seems responsible for a strong variability in the doping profile. It has been shown, that the ECV measurement is not applicable to characterize the emitter depth on laser doped areas, because of the microscopic inhomogeneities in the emitter on the macroscopic measurement area. The real emitter profiles are to complex to be characterized by SIMS or ECV. We have shown that the variation in the emitter profile is resulting from the texture in the laser-doped regions.

Comparative structural analyses of a crystallized, 60 nm thick silicon film deposited on quartz substrate were performed using high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy (RS). Both methods suggest high degree of crystallization of the film. The material of the film consists of crystalline grains with sizes up to 20 nm (HRTEM) and the mean size of the grains is ∼4 nm (RS). HRTEM results suggest large scatter of the crystal orientations of the grains. The existence of boundary defects between grains grouped in large agglomerates was also detected by HRTEM. RS analyses indicate large compressive strain in the system and the existence of high pressure Si phases in the material of the film.

A temperature dependence of intensity for band to band (BB) luminescence of a solar cell excited by constant current in forward biasing was investigated. The obtained temperature dependence is untypical for silicon, i.e. the intensity of the BB luminescence increases with temperature. We analyse our results in view of thermally induced change of excess carrier concentration. Two temperature dependent nonradiative recombination processes limit the carrier concentration. One is the recombination in the bulk, mediated by deep impurity levels and the other is the surface recombination. The surface recombination limits the minority carrier diffusion length to the thickness of the solar cell. We show that the interference of both recombination processes causes the effective lifetime to increase upon increasing temperature. Thereby the deep level mediated recombination dominates at high temperature, whilst the surface recombination is dominant at low temperatures. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In X-ray beam induced current (XBIC) in combination with X-ray fluorescence (XRF) and X-ray absorption (XAS) microscopy techniques is now widely used as a powerful tool for the investigation of transition metal (TM) behavior in Si. The aim of this work was to replace XBIC with a new recombination-sensitive, but contactless technique, that is, scanning X-ray beam excited optical luminescence microscopy (μ-SXEOL). We report for the first time the successful realization of μ-SXEOL to register the spatial distribution of band-band luminescence in silicon in a reasonable time of 1 s/pixel with X-ray flux of 10 11 /s. Results of simultaneous μ-SXEOL/XBIC/ μ-XRF measurements on multi-crystalline silicon are presented. A correlation between XBIC and μ-SXEOL maps of the same sample as well as significant differences are found. The magnitude of μ-SXEOL signal is shown to anti-correlate with the averaged amount of copper detected by μ-XRF.

The results of the investigations of the interaction between the different impurities in intentionally contaminated block-cast multi-crystalline silicon by means of synchrotron-based microprobe techniques XBIC (X-ray beam induced current), μ-XRF (X-ray fluorescence microscopy) and μ-XAS (X-ray absorption microspectroscopy) recently implemented at beamlines ID-21 and ID-22 of ESRF, Grenoble, are presented. It was found that Si 3 N 4 /SiC particles frequently observed in the upper part of multi-crystalline Si blocks represent effective sinks for Fe and Cu impurities. The amount of precipitated iron was the same order magnitude both at nitride and carbide particles. The amount of Cu precipitated at the SiC inclusions was significantly larger than that at Si 3 N 4 rods. Chemical state of the copper precipitates was identified as copper-rich silicide Cu 3 Si. The anneal at 950 °C that is known to enhance oxygen precipitation in silicon was found to accompany with the enhanced formation of nanoscale iron disilicide precipitates both inside the grains and at grain boundaries.

Iron–oxygen interaction in the Czochralski-grown silicon (CZ-Si) giving rise to their final precipitated state was investigated by means of a combination of electrical and element-sensitive techniques. The samples studied were intentionally contaminated with iron at 1150 °C and then they were annealed at temperatures of 850 and 950 °C to stimulate precipitate formation. Fe-related defect levels in silicon band gap and spatial distributions of iron-related precipitates were monitored after each annealing step. It was found that FeB-pairs being the dominant defects in as-contaminated sample transformed completely to the stable FeO-related complexes that served as precursors for further iron–oxygen co-precipitation.

We report on the optical and mechanical properties of Si3N4 inclusions, formed in the upper part of mc-Si blocks during the crystallization process. Those inclusions usually appear as crystalline hexagonal tubes or rods. Here we show that in many cases the Si3N4 inclusions contain crystalline Si in their core. The presence of the Si phase in the centre was proven by means of cathodoluminescence spectroscopy and imaging, electron beam induced current measurements and Raman spectroscopy. The crystalline Si3N4 phase was identified as β-Si3N4. Residual stress was revealed at the particles. While the stress is compressive in the Si material surrounding the Si3N4 particles tensile stress is found in the Si core. We assume that the stress is formed during cool down of the Si block and is a consequence of the larger thermal expansion coefficient of Si in comparison to that of β-Si3N4. Iron assisted nitridation of Si at temperatures below 1400 °C is considered a possible mechanism of Si3N4 formation.

The investigation of regular dislocation networks (DN) formed by direct wafer bonding suggests that the D1 and D2 peaks of dislocation-related luminescence (DRL) in silicon is linked to screw dislocations, whereas edge dislocations are responsible for D3 and D4 DRL peaks. Non-radiative recombination activity in DN could be attributed to edge dislocations and could be related to enhanced ability of these dislocations to getter impurity atoms. Obtained relation of DRL intensity with the density of screw dislocations suggests existence of the optimum twist angle for the wafer-bonding geometry for which the DRL intensity has a maximum. The dependence of DRL intensity on the spacing between screw dislocations has the maximum at about 7 nm. Reported radiative and non-radiative recombination properties of DN present substantial interest not only for possible LED applications in all-Si photonics but also for photovoltaics, since DNs represent a model system for grain boundaries controlling carrier lifetime in microcrystalline-Si material.

Electrical and structural properties of thin-film photovoltaic (PV) material fabricated using Crystal Silicon on Glass (CSG) technology was investigated applying photoluminescence (PL) and Raman spectroscopy (RS). The obtained results and their correlation with the PV properties of the cells prepared from the same material showed that PL is applicable for in-line characterization of the material before the electrical contact fabrication processes. The results obtained using RS gave useful information on crystallization grade of the material during the fabrication process.

The results of experimental investigations of the dislocation-related DLTS-peaks originated from the dislocation networks (DN) are presented. Samples with DNs were produced by direct bonding of p-type silicon wafers and no enhancement of oxygen concentration was detected near the DN plane. Origins of the DLTS peaks were proposed and a correlation with the dislocation-related photoluminescence data was established based on known dislocation structure of the samples. Two types of shallow DLTS peaks exhibited Pool-Frenkel effect, which could be linked to the dislocation deformation potential. One of the shallow DLTS peaks was related to straight parts of screw dislocations and another - to the intersections of the dislocations.