Wolfgang Schröter

Mechanisms of transition-metal gettering in silicon

The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed. Methods for mathematical modeling of gettering are discussed and illustrated. Needs for further research are considered.

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.

Yield point and dislocation mobility in silicon and germanium

Measurements of the lower yield point in silicon and germanium, covering wide ranges of temperature and strain rate, are presented. The results indicate that Haasen’s model for the beginning of the plastic deformation of semiconductors has to be modified for germanium, while it is confirmed for silicon.

Recombination properties of structurally well defined NiSi2 precipitates in silicon

We report first results on the recombination properties of structurally well defined NiSi2 precipitates in n‐type silicon. Under the conditions applied, precipitates form without the occurrence of punched out dislocations or any other secondary defects. We find that the minority‐carrier diffusion length (LD) measured by electron beam induced current (EBIC) is related to the precipitate density NV and LD ≂ 0.7 × NV−1/3. EBIC investigations of individual precipitates reveal contrasts up to 40% demonstrating NiSi2 particles to be efficient recombination centers.

Formation and Properties of Copper Silicide Precipitates in Silicon

We report results of a detailed study of structural and electrical properties of copper silicide precipitates in silicon. Using conventional and high-resolution transmission electron microscopy: we observe that metastable platelets surrounded by extrinsic stacking faults form upon quenching from high temperatures. By ripening experiments at low temperatures as well as by a variation of cooling rates it is shown how homogeneous copper precipitation merges into the heterogeneous precipitation mode of colony growth. The application of recently developed criteria for the interpretation of deep level transient spectra from extended defects allows to conclude that deep electronic states associated with the precipitates have bandlike character.

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.

Energy Spectra Of Dislocations In Silicon And Germanium

The properties of edge‐type dislocations are strongly dependent on the temperature at which they have been introduced into the crystal. Dislocations produced at T < 0·6 Tm (Tm melting point) exhibit a richer variety of properties than those introduced at T > 0·6 Tm: in germanium a strong increase of the hole density, in silicon an electron para‐magnetic resource (EPR)‐signal, showing many fine details, and several peaks in the deep level transient spectroscopy (DLTS)‐signal, are only found after low‐temperature deformation. The increase in the hole density has been ascribed to point defect clouds, which surround the dislocation, and seem to control their mobility. The clouds are not stable at the deformation temperature.

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.

Diffusion of manganese in silicon studied by deep‐level transient spectroscopy and tracer measurements

The diffusion of manganese in silicon was studied in the temperature range 900–1200 °C by deep‐level transient spectroscopy and the tracer method, with particular emphasis on well‐defined boundary conditions. The surface concentrations from the tracer method agree with solubility data and the concentration of electrically active interstitial manganese is found to be 60–70% of the total manganese concentration. Both methods yield identical diffusion coefficients which are described by an Arrhenius law, D(T)=(6.9±2.2)×10−4 cm2 s−1 exp [(−0.63±0.03)eV/kT].

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.