V. V. Kveder

Room-temperature silicon light-emitting diodes based on dislocation luminescence

We demonstrate electroluminescence (EL) with an external efficiency of more than 0.1% at room temperature from glide dislocations in silicon. The key to this achievement is a considerable reduction of nonradiative carrier recombination at dislocations due to impurities and core defects by impurity gettering and hydrogen passivation, respectively, which is shown by means of deep-level transient spectroscopy. Time-resolved EL measurements reveal a response time below 1.8 μs, which is much faster, compared to the band-to-band luminescence of bulk silicon.

Simulation of Al and phosphorus diffusion gettering in Si

Abstract We present a quantitative computer model (‘Gettering Simulator’) of phosphorus diffusion gettering (PDG) that allows to simulate the PDG process. The model was checked for Au as a typical substitutional metallic impurity elements and for Co as an example of the fast diffusing interstitial 3d metals in Si. Here we will only discuss the gettering of substitutional metals. The ‘Gettering Simulator’ includes a model for P diffusion for phosphorus concentrations [P] up to the solubility limit. In this model, the main contribution to phosphorus diffusion at [P] 19 cm −3 comes from the kick-out mechanism, while at higher P concentrations the diffusion is dominated by phosphorus vacancy complexes. The latter results in the development of the well-known ‘kink-and-tail’ P and specific self-interstitial profiles. The gettering mechanism is described by a combination of three factors: (1) the Fermi level effect; (2) the formation of phosphorus–metal pairs; (3) the high concentration of self-interstitials in the bulk together with nearly equilibrium concentration in the region of high phosphorus concentration near the surface. The third factor was found to be very important for the PDG of substitutional metals. No local equilibrium is assumed in the model. Instead. the calculations are based on the reaction rates between different species.

Atomic structure and electronic states of nickel and copper silicides in silicon

Abstract This paper summarizes current understanding of structural and electronic properties of nickel and copper silicide precipitates in silicon. From high-resolution electron microscopy studies it has been concluded that metastable structures form during early stages of precipitation which transform into energetically more favourable configurations during additional annealing or slow cooling. These structural transformations are related to changes of the electronic structure of the precipitates as revealed by deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC). Deep bandlike states at initially formed NiSi2- and Cu3Si-platelets detected by DLTS have been attributed to a bounding dislocation and precipitate/matrix interfaces, respectively. Large NiSi2-precipitates act as internal Schottky barriers and may control the minority carrier lifetime of silicon samples. Recent advances in modeling EBIC contrasts provide insight how metal impurities affect the electrical behaviour of dislocations at different degrees of decoration.

Hydrogen effect on the optical activity of dislocations in silicon introduced at room temperature

Dislocations were introduced into silicon crystals by mechanical scratching at room temperature. The optical property of such dislocations was investigated by means of cathodoluminescence. Neither deformation‐induced luminescence nor the exciton luminescence was detected in the scratched region, showing that a high density of nonradiative recombination centers is induced on or around dislocations. Hydrogen plasma treatment of a scratched crystal led to the appearance of the so‐called D1–D4 luminescence lines along the scratch. Deep‐level transient spectroscopy revealed that deep traps were induced by scratching and diminished drastically due to subsequent hydrogen plasma treatment. Thus, it was concluded that hydrogen passivated nonradiative recombination centers but not the luminescence centers. The characteristics in spatial distribution of D1 and D2 lines and those of D3 and D4 lines showed that these two groups of luminescence lines were of different origins. Since the specimens used were thought to b...

Measurements of energy spectra of extended defects

The density of states of two different dislocation types in silicon has been studied by computer modelling and fitting to available deep-level transient spectroscopic data. Our preliminary fit results indicate that one type, which is ad islocation bounding thin platelets consisting of two NiSi2(111) planes and supposed to be free of jogs, kinks, reconstruction defects and also point defect decoration, is associated with a one-dimensional band of states in the middle of the bandgap, 0.3 eV wide and with an electron occupation of 0.3 in the neutral state. Two fit parameter sa renot consistent with independent results and require the potential drop along the platelet to be incorporated in our model. For dislocations that move from a scratch under an applied stress at high temperatures, our fits, possible at present to only some of the data, show th ee xistence of point defect clouds in the dislocation strain field and indicate the existence of core defects.

Mechanisms and computer modelling of transition element gettering in silicon

Abstract This paper starts out by summarising the modelling and computer simulation of phosphorus diffusion gettering (PDG) of Au. The mobilisation of precipitated impurity atoms is discussed in the light of the silicon interstitial supersaturation provided by the phosphorus diffusion (PD). We then extend the gettering model to Co using bulk solubility data of highly P-doped Si, and find satisfactory agreement with experimental profiles of the total Co-concentration. Yet the pointed disagreement between the CoP/Cos-ratio obtained through simulation and Mosbauer data leads to the conclusion that, in the case of phosphorus silicate glass (PSG) growth, segregation alone cannot unambigiously account for the observed gettering efficiency. Instead, it is proposed that PD induced silicide formation provides a more suitable explanation of the high efficiency of PDG accompanied with PSG growth.

Nonstoichiometry and electrocoloration due to injection of Li+ and O2− ions into lithium niobate crystals

The high oxygen and lithium ion conductivity in LiNbO3 was investigated and interpreted in terms of lithium and oxygen vacancies being intrinsically present in congruently grown single crystals. As a result of this, it was found that the stoichiometry of lithium niobate crystals may be changed with respect to lithium and oxygen. The optical and electrical properties of electrically colored LiNbO3 crystals were studied and it was shown that the absorption spectra of thermally reduced and electrocolored samples are identical. Therefore, the origin of the absorption processes is considered to be the same in both cases. The formation of regions with different stoichiometry due to the injection of additional lithium or oxygen into the LiNbO3 crystals was also observed and investigated. The motion of these stoichiometric domains through a LiNbO3 crystal from one electrode to the other was studied and described in terms of electrodiffusion of the ions and electrons. A model is proposed which considers the injection of oxygen and lithium vacancies for the generation of concentration profiles in the originally homogeneous material. The numerical calculation of the concentration profiles shows good agreement with the experimental results.The high oxygen and lithium ion conductivity in LiNbO3 was investigated and interpreted in terms of lithium and oxygen vacancies being intrinsically present in congruently grown single crystals. As a result of this, it was found that the stoichiometry of lithium niobate crystals may be changed with respect to lithium and oxygen. The optical and electrical properties of electrically colored LiNbO3 crystals were studied and it was shown that the absorption spectra of thermally reduced and electrocolored samples are identical. Therefore, the origin of the absorption processes is considered to be the same in both cases. The formation of regions with different stoichiometry due to the injection of additional lithium or oxygen into the LiNbO3 crystals was also observed and investigated. The motion of these stoichiometric domains through a LiNbO3 crystal from one electrode to the other was studied and described in terms of electrodiffusion of the ions and electrons. A model is proposed which considers the inject...

Aluminum gettering of iron in silicon as a problem of the ternary phase diagram

Deep level transient spectroscopy is used to study the segregation of Fe from crystalline Si to an Al:Si liquid at its surface, which is the basic mechanism of aluminum gettering used in silicon photovoltaics. The measured segregation coefficient is smaller than estimates from the binary Fe:Si and Al:Fe phase diagrams. This apparent discrepancy originates from the ternary character of the system where the solubility of Fe in Si in equilibrium with the Al-doped α-FeSi2 has to be taken as a reference. Our data suggest that this solubility exceeds that in the binary Fe:Si system by two orders of magnitude.

Dislocations in Silicon and D-Band Luminescence for Infrared Light Emitters

There is a growing demand for a silicon-based light emitters generating a light with a wavelength in of 1.3-1.6 μm range, which can be integrated into silicon chips and used for in-chip opto-electronic interconnects. Among other possibilities, the D1 luminescence at about 1.55 m, caused by dislocations in Si, can be a suitable candidate for such in-chip light emitters. Here we present a brief review of today knowledge about electronic properties of dislocations in silicon and dislocation-related luminescence in connection with possible application of this luminescence for silicon infrared light-emitting diodes (Si-LEDs).

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.