A SOGICON type instability in silicon

A current oscillation phenomenon in SOGICON type Si device fabricated by the use of a planar process is studied. The oscillation is generated in the region between anode and notch which is located at the center on the sample. A considerably high electric field is observed in the notch region. Considering the hot-electron effect due to the high electric field, the mechanism underlying the current oscillation is discussed.     

In-situ formation of p-n junctions in semiconducting TiO2

Application of small voltages in the range from 0.5 V to 1 V to an originally homogeneously Fe-doped (0.5 mol-%) TiO₂ semiconductor at temperatures between 700° C and 750° C caused the formation of a p-n junction within the sample. This is indicated by a change of the U-I characteristics from a symmetrical to a diode type behavior. By inversion of the polarity of the applied voltage, the p-n junction could be removed. This process is completely reversible. The results are explained by an asymmetric change in the concentration of lattice defects, which act as dopants in addition to the extrinsic dopants, caused by the application of the voltage to the sample.     

Mechanism and kinetics of the diffusion of gold in silicon

The diffusion of Au in Si is known to take place via the interchange of Au atoms between substitutional (Au _s ) and interstitial (Au _i ) sites. So far it has generally been believed that this interchange involves lattice vacancies (V) and that it occurs via the Frank-Turnbull mechanism V+Au _i ⇆Au _s . It is stated in the literature that this model explains the observation that the Au _s concentrationC _s ^m in the centre of Au-diffused Si wafers increases with timet according to . We show that this statement is incorrect, i.e., the Frank-Turnbull model cannot account for the law. Such a dependence is expected in the case of Si wafers with a sufficiently low density of internal sinks for self-interstitials if the Au _i −Au _s interchange is controlled by the so-called kick-out mechanism Au _i ⇆Au _s +1. Since this mechanism involves self-interstitials (I) the present result is in accordance with the fact that under high-temperature equilibrium conditions the dominating intrinsic point defects in Si are self-interstitials and not vacancies as in Ge or metals.     

The electrical activity of stacking faults in Czochralski silicon

A spectroscopic analysis by the light-beam-induced-current technique has been carried out to study the electrical properties of stacking faults in Czochralski silicon subjected to internal gettering treatments. By changing the wavelength of the light beam probing the sample, we have obtained the depth profiling of the stacking fault electrical activity. Occurrence of minority carrier recombination and generation processes at some stacking faults, corresponding, respectively, to dark and bright levels in a grey-shade imaging, has been observed. The presence of fixed charges at the defect-silicon matrix interface is hypothesized as a possible cause of the observed images.     

Oxygen diffusion and thermal donor formation in silicon

The information available on the diffusion of oxygen and on the formation of thermal donors in silicon is critically reviewed. In this context the effects of intrinsic point defects on the diffusion-controlled growth of oxygen precipitates is investigated in some detail. Seemingly contradictory experimental results on the diffusivity of oxygen in silicon at temperatures around 400° C are explained in terms offast-diffusing gas-like molecular oxygen in silicon. The concept of molecular oxygen is also invoked in a newly suggested model of thermal donor formation in silicon. The diffusivity of molecular oxygen in silicon is estimated to be around 10^–9cm²s^–1 at 450° C, almost nine orders of magnitude higher than the diffusivity of atomic oxygen in interstitial position.     

On the theory of the diffusion of gold into dislocated silicon wafers

The paper presents a theoretical study of the diffusion of gold into dislocated silicon wafers in terms of the kick-out mechanism Au _i Au _s +I, where Au _i , Au _s , andI mean Au interstitials, substitutional Au atoms, and Si self-interstitials, respectively. In agreement with experiments it is found that the Au _s concentration in the centre of a wafer,C _s ^m , increases with the durationt of the diffusion anneal according toC _s ^m =C _s ^eq (k ₀ t)^1/2 except forC _s ^m values in the vicinity of the solubility limitC _s ^eq of Au _s . Approximate analytical expressions fork ₀ as a function of the densityN _I of the dislocations acting asI sinks are given for the entire regime 0N_I<+t8.     

On the recombination behaviour of iron in moderately boron-doped p-type silicon

The recombination lifetime and diffusion length of intentionally iron-contaminated samples were measured by the Surface Photo Voltage (SPV) and the Elymat technique. The lifetime results from these techniques for intentionally iron-contaminated samples were analysed, in particular for the aspect of the injection-level dependency of recombination lifetime. Based on theoretical considerations, a method for the analysis of deep-level parameters combining constant photon flux SPV and Elymat measurements has been developed. This method is based on a detailed numerical analysis of the Elymat technique, including the Dember electric field, the characteristics of the laser beam, the transport parameters of the semiconductor and multilevel Shockley-Read-Hall (SRH) recombination kinetics. The results of the numerical simulation are applied to the analysis of recombination lifetime measurements on intentionally iron-contaminated samples. We compared numerical simulations and experimental results from SPV and Elymat for p-type samples using the classical acceptor level atE _v +0.1 eV and the donor level of FeB pairs atE _c -0.3 eV as recombination centre. Better consistency in the interpretation of the results has been found in the doping range 10¹⁴–10¹⁶ cm^–3 supposing theE _c -0.3 eV level as predominant recombination centre. An attempt to extract the electron and hole capture cross-sections for this defect is made.     

Diffusion of gold in dislocation-free or highly dislocated silicon measured by the spreading-resistance technique

The diffusion of Au in dislocation-free or plastically deformed Si (10¹¹ to 10¹³ dislocations/m²) was measured with the aid of the spreading-resistance technique. The Au profiles produced indislocation-free Si slices by in-diffusion from both surfaces possess nonerfc-type U shapes as predicted by the so-called kick-out diffusion model. This model is used to calculate the contribution of self-interstitials to the (uncorrelated) Si self-diffusion coefficient,D _I ^SD =0.064×exp(–4.80 eV/kT)m² s^–1, from the present and previous data on the diffusivity and solubility of Au in Si in the temperature range 1073–1473 K. Inhighly dislocated Si the diffusion of Au is considerably faster than in dislocation-free Si. From the erfc-type penetration profiles found in this case, effective Au diffusion coefficients were deduced and combined with data on the solubility of Au in Si. ThusC _i ^eq D _i=0.0064 ×exp(–3.93 eV/kT)m² s^–1 was obtained in the temperature range 1180–1427 K, whereC _i ^eq andD _i are the solubility and diffusivity of interstitial Au in Si.     

High-temperature thermal evolution of SiAs precipitates in silicon

The thermal evolution of monoclinic SiAs precipitates at 1050° C in silicon samples implanted with 1 and 1.5×10¹⁷ As/cm² was followed by transmission electron microscopy (TEM) and secondary neutral mass spectrometry (SNMS). These experiments show, for the first time, the coexistence of two different states of As in silicon, i.e., the electrically active and the inactive mobile dopant, in equilibrium with monoclinic SiAs precipitates. Moreover, they provide, for the saturation concentration of As in silicon, which includes both these states, a value of 3×10²¹ cm^–3 at 1050° C.     

On the nature of point defects and the effect of oxidation on substitutional dopant diffusion in silicon

An extensive analysis of the substitutional dopant diffusion phenomena in silicon during oxidation is presented. The analysis covers qualitative as well as quantitative aspects of the oxidation-enhanced and -retarded diffusion (OED and ORD) phenomena, and examines three different possible assumptions that can be made on the nature of the silicon thermal equilibrium point defect species: silicon self-interstitials (I) only, vacancies (V) only, coexistence of I and V. The only consistent way to interpret all properly documented OED/ORD data is to assume that I and V coexist under oxidation as well as under thermal equilibrium conditions at high temperatures.     

A model for the occurrence of transient negative photoconductivity in silicon doped with gold

A transient negative photoconductivity phenomenon observed in silicon doped with gold atoms has been investigated. On the basis of the trapping of photo-excited carriers into two deep levels of gold atoms, a model for the occurrence of transient negative photoconductivity is proposed and related qualitatively to some experimental results.     

Point defects,diffusion processes,and swirl defect formation in silicon

The paper consists of three parts. In the first part we review the basic experimental and theoretical results which shaped our present knowledge on point defects and diffusion processes in silicon. These results concern on one side oxidation effects which established that silicon self-interstitials and vacancies coexist in silicon and on the other side diffusion of gold into dislocation-free silicon which allowed to determine the self-interstitial contribution to silicon self-diffusion and to estimate the corresponding vacancy contribution. In the second part we discuss topics for which an understanding is just emerging within the framework of coexisting self-interstitials and vacancies: reaching of local dynamical equilibrium between self-interstitials and vacancies; rough estimates of the thermal equilibrium concentrations of self-interstitials and vacancies and their respective diffusivities, and finally, various possibilities to generate an undersaturation of self-interstitials. In the third part we examine swirl defect formation in silicon in terms of vacancies and self-interstitials.     

Au gettering by Ne and Ar implantation in silicon

The gettering efficiency for Au induced by Ne⁺ and Ar⁺ implantation has been studied. The depth distribution of gettered Au as a function of annealing temperature and dose of implanted Ne⁺ and Ar⁺ ions are presented. The experiment shows that the maximum efficiency of gettering occurs when the implantation doses are comparable with amorphization dose.     

Annealing behavior ot trap-centers in silicon containing A-swirl defects

The annealing behavior of trap-centers was studied in float-zone silicon wafers containing A-swirl defects. Samples from areas of high and low A-swirl density were annealed in nitrogen ambient between 100° and 900 °C, and analysed using the Deep Level Transient Spectroscopy. The results indicate, that two levels atE _c }-0.07 eV, _n=4.6×10^–16 cm², andE _c–0.49eV, _n=6.6×10^–16cm² are caused by one defect, for which the silicon di-selfinterstitial is a likely interpretation. A level atE _c }-0.11 eV was assigned to interstitial carbon. Both defects annealed out at about 170 °C. After 600 °C annealing an additional level atE _c–0.2 eV was detected, which was attributed to an interstitial silicon carbon complex. Heat treatment at 800 °C generated a new level atE _c–0.49 eV, _n=2.9×10^–16cm² only in the area of high A-swirl defect density. This level was also observed after oxidation and subsequent annealing of silicon.     

Structural and electrical properties of Au/Pt/Ti ohmic contacts to degenerated doped n-GaAs

The ohmic contact characteristics of Au/Pt/Ti on degenerated doped n-GaAs were evaluated. Structural and electrical properties were studied by means of X-ray diffraction (XRD), Auger Energy Spectrum (AES) and a HP4145B parameter analyzer. The structural analysis revealed a TiAs phase in the interface between metal multilayer and GaAs at higher annealing temperatures. Electrical measurement showed a minimum ohmic contact resistance of 3×10^-4 Ω cm². The dominant current mechanism was found to be thermionic emission with a barrier height of Φ_b, of 0.09 V by comparing the experimental data with different theoretical models. Received: 14 December 2001 / Accepted: 4 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6226-4397, E-mail: zhoujian999@163.net     

Effect of temperature on the validity of the einstein relation in heavily doped semiconductors

An analytical expression of the modified form of the Einstein relation in heavily doped semiconductors in which Gaussian band tails are formed near the lower limit of heavy doping is derived for studying the temperature dependence of the diffusivity-mobility ratio of the carriers in such semiconductors. It is found that, with increasing temperature from relatively low values, the ratio first increases in a nonlinear manner and then decreases till, at high temperatures, it approaches its value corresponding to the non-degenerate condition resulting in a peak over a narrow range of temperatures.     

X-ray Photoelectron Spectroscopy of silicon oxynitride layers obtained by low-energy ion implantation

Simultaneous oxygen and nitrogen low-energy ion implantation in silicon single crystals have been used to obtain surface layers of silicon oxynitride. In-depth concentration profiles, measured by XPS, showed all the possible tetrahedral configurations of silicon with the neighboring atoms. The most important feature of these profiles has been found to be the accumulation of a so-called Si³⁺ state just below the surface and about 20 nm deep. This amphoteric state has interesting properties for impurity passivation or electron trapping.     

Electron and hole traps in N-GaAs crystals

Deep traps were measured and their electronic and optical properties were determined by junction capacitance techniques in n-GaAs crystals grown by different methods. Four electron-traps and four hole-traps were detected. An electron trap was not observed in LPE wafers. A hole trap at 0.45 eV above the top of the valence band was detected in all wafers measured here.     

Spin-dependent recombination in a silicon p-n junction

Like the spin-denendent photoconductivity in pure silicon, the current of a silicon n⁺-p junction is found to be affected by electron spin resonance. The experiment shows that the same centers are responsible for the recombination in the diode and in pure silicon, that only the recombination in the space-charge region of the junction is spin-dependent and that the effect in this region is very large. A tentative model for the electron-hole recombination in silicon is proposed.     

Instability of photoexcited electron-hole plasma in short semiconductor structures

The instability of the electron-hole plasma produced by continuous photoexcitation in short semiconductor structures is investigated theoretically. The applied electric field is considerably disturbed by photogenerated charge carriers. At a sufficiently intensive photogeneration plasma instability occurs. The frequency of current oscillations due to the instability, as shown by numerical simulation for a GaAs structure, is in the range of 10¹¹–10¹²s^–1.