S. Pizzini

Grain boundary segregation of oxygen and carbon in polycrystalline silicon

The electrical activity of grain boundaries (GB’s) in polycrystalline silicon is strongly affected by heat treatments, which are known to induce the segregation of oxygen. The large, quantitative variations of the electrical activity of GB’s observed experimentally, which are a function not only of the heat treatments but also of the carbon and oxygen content of the specific sample examined, could not be explained however, without assuming that carbon and oxygen play a synergistic role. We demonstrate in this work, by using secondary ion mass spectrometry, that oxygen and carbon segregate simultaneously, albeit spatially resolved, at grain boundaries. This result appears to be of major importance when interpreting electron or light beam induced current profiles at grain boundaries in polycrystalline silicon.

Effect of nitrogen contamination by crucible encapsulation on polycrystalline silicon material quality

Abstract This paper reports some results about a recently discovered source of lifetime degradation found in polycrystalline silicon ingots grown in silicon-nitride-lined silica crucibles. A systematic analysis of the low lifetime areas, which preferentially are found corresponding to the ingot edges and corners, carried out using different structural, spectroscopical and electrical techniques, shows that the lifetime drop is associated with the presence of a high density of silicon nitride and iron silicide submicrometre particles, revealed by transmission electron microscopy and electron diffraction measurements. An at least partial recovery of the lifetime is obtained by P gettering at 900°C, which seems to be effective in dissolving the iron silicide from the nitride-rich areas.

About the D1 and d2 dislocation luminescence and its correlation with oxygen segregation

It is well known that the dislocation luminescence (DL) in silicon consists of four main bands, conventionally labelled D1 to D4, where E 1 = 0.807 eV, E 2 = 0.874 eV, E 3 = 0.95 eV and E 4 = 0.99 eV, of which the D1 is considered of interest for optoelectronic devices working in the third window of optical communications. Although DL has been the subject of a number of investigations in the last twenty years, still some questions remain open, concerning both the origin of the dislocation luminescence and its intrinsic or extrinsic nature. We report in this paper the results of a combination of complementary dislocation generation processes (deformation and oxide segregation) and characterisation procedures (photoluminescence and surface photovoltage), which give a strong evidence that the Dl band is correlated in a very complex manner with the presence of optically active silicon self-interstitials and oxygen clusters.

Crystallinity and microstructure in Si films grown by plasma-enhanced chemical vapor deposition: A simple atomic-scale model validated by experiments

A joint theoretical and experimental analysis of the crystalline fraction in nanocrystalline films grown by low-energy plasma enhanced chemical vapor deposition is presented. The effect of key growth parameters such as temperature, silane flux, and hydrogen dilution ratio is analyzed and modeled at the atomic scale, introducing an environment-dependent crystallization probability. A very good agreement between experiments and theory is found, despite the use of a single fitting parameter.

Detection of junction failures and other defects in silicon and III–v devices using the LBIC technique in lateral configuration

Abstract A scanning light microscope was used to obtain light beam induced current (LBIC) profiles in samples containing a p-n junction either parallel or perpendicular to the surface scanned by the beam. Using this technique we studied the quality of the junction of InP(n)-InP(p) diodes, which are one of the intermediate structures obtained during the processing of InGaAsP/InP lasers. The same technique was successfully employed also for the quality control of silicon power diodes. It was thus demonstrated that the LBIC technique, operated in the standard and in the lateral configuration at a resolution better than 10 μm, is a powerful, nondestructive tool which can be efficiently used for the quantitative measure of the damage present at any kind of diode junctions.

Luminescence from Erbium‐Doped Silicon Epi Layers Grown by Liquid‐Phase Epitaxy

Dislocation-related photoluminescence at 0.806 and 0.873 eV is observed in erbium-doped silicon epi layers grown by liquid-phase epitaxy on (100) Si wafers. These signals are detected at T = 2 K only on epi layers deposited on Czochralski grown silicon substrates. No luminescence is observed when float zone-grown substrates are used. The peak intensity shows temperature quenching, but the signal remains detectable up to 195 K. The luminescence apparently is due to dislocations in silicon in the simultaneous presence of high oxygen concentration and erbium impurities. A comparison with the typical infrared emission from erbium-implanted silicon samples is presented.

Deep levels in Er-doped liquid phase epitaxy grown silicon

The optical activity of Er-doped silicon is related to the presence of defects which enhance the typical radiative transition at 0.8 eV but whose nature and properties are still largely unknown. We have investigated the deep levels present in Er-doped liquid phase epitaxy silicon to identify the traps possibly related to the luminescence. Among the observed levels, two minority carrier traps labeled E2 (EC−0.20u2009eV) and E3 (EC−0.39u2009eV), and one majority carrier trap labeled H1 (Ev+0.32u2009eV) are good candidates for the material optical activity. The onset of luminescence occurs after a thermal treatment and is accompanied by a high space charge density localization at the epilayer-substrate interface.

Local structure of erbium-oxygen complexes in erbium-doped silicon and its correlation with the optical activity of erbium

Abstract It is well-known that the sharp luminescence emission at 1.54 μm from erbium-doped silicon has set off a great interest for this material in view of its applications in the third window of optical telecommunications. It is also known that the erbium luminescence is very poor in the absence of impurities like oxygen, carbon and nitrogen, but in spite of the large amount of research work devoted to this material, it is not yet completely clear what is the local structure of the optically active Er centre in oxygen-doped Er–Si alloys. The aim of this paper is to present and discuss the results of the analysis of the EXAFS spectra of two sets of Er-doped silicon samples, of which one was obtained by erbium and oxygen co-implantation and the other was grown by LPE (liquid phase epitaxy). The EXAFS spectra of these samples were satisfactorily fitted by assuming that Er sits in three different configurations, depending on the presence or the absence of oxygen and dislocations in the epi-layer. The relevance of these results in terms of optical and electrical activity of erbium is discussed in details.

Radiative recombination processes of thermal donors in silicon

Abstract : There is a recent, renewed attention on the possible development of optical emitters compatible with silicon microelectronic technology and it has been recently shown that light emitting diodes could be manufactured on dislocated silicon, where dislocations were generated by plastic deformation or ion implantation. Among other potential sources of room temperature light emission, compatible with standard silicon-based ULSI technology, we have studied old thermal donors (OTD), as the origin of their luminescence is still matter of controversy and demands further investigation. In this work we discuss the results of a spectroscopical study of OTD using photoluminescence (PL) and Deep Level Transient Spectroscopy (DLTS) on standard Czochralsky (Cz) silicon samples and on carbon-doped samples. We were able to show that their main optical activity, which consists of a narrow band at 0.767 eV (P line), is correlated to a transition from a shallow donor level of OTD to a deep level at E(sub v)+0.37 eV which is tentatively associated to C-O complexes. As we have shown that the P line emission persists at room temperature, we discuss about its potentialities to silicon in optoelectronic applications.

Erbium-doped silicon epilayers grown by liquid-phase epitaxy

A careful analysis of the features of the spectroscopic properties of Er-doped and undoped epitaxial silicon films grown by liquid-phase epitaxy at 950 °C in silicon-saturated indium melts shows that threading dislocations work as effective gettering sites for erbium and oxygen. The last impurity is incorporated in the epitaxial film by back diffusion from the Czochralski substrate during the growth. The photoluminescence emitted by these films appears to be related to the dislocation and is enforced by the presence of erbium-oxygen complexes.