P. Pellegrino

ELECTRICALLY ACTIVE POINT DEFECTS IN N-TYPE 4H-SIC

An electrically active defect has been observed at a level position of ∼ 0.70 eV below the conduction band edge (Ec) with an extrapolated capture cross section of ∼ 5×10−14 cm2 in epitaxial layers ...

Nitrogen deactivation by implantation-induced defects in 4H–SiC epitaxial layers

Ion implantation causes free charge carrier reduction due to damage in the crystalline structure. Here, nitrogen-doped 4H silicon carbide (n type) epitaxial layers have been investigated using low ion doses in order to resolve the initial stage of the charge carrier reduction. It was found that the reduction of free carriers per ion-induced vacancy increases with increasing nitrogen content. Nitrogen is suggested to be deactivated through reaction with migrating point defects, and silicon vacancies or alternatively interstitials are proposed as the most likely candidates.

Ion implantation induced defects in epitaxial 4H-SiC

Thick epitaxial layers of 4H-SiC are implanted with MeV He and B ions at low doses. The epi layers are nitrogen doped and have donor concentrations around I × 10 15 cm - 3 . The ion energies are selected to give a mean projected range of 4 μm for both He and B (1.7 and 5.0 MeV, respectively) and the implantations are performed both at nominal room temperature and 700°C. Capacitance-voltage measurements show that the samples are strongly compensated despite the low ion doses. In silicon the prompt vacancy-interstitial recombination is known to reduce the number of free migrating interstitials and vacancies with around 95%. For SiC this is not the case and the resulting concentration of implantation induced defects stable at room temperature becomes much higher than in Si. Deep level transient spectroscopy measurements between 77 and 350 K show two acceptor peaks at E C -0.18 and E C -0.67 eV (±0.03 eV), but the major part of the compensation is shown to be caused by deeper lying acceptor traps.

Separation of vacancy and interstitial depth profiles in ion-implanted silicon: Experimental observation

Financial support was kindly provided by the Swedish Research Council for Engineering Sciences (TFR), the Swedish Foundation for International Cooperation in Research and Higher Education (STINT), and the EU Commission, Contract No. ERBFMRXCT980208 (ENDEASD—TMR network).

Vacancy and interstitial depth profiles in ion-implanted silicon

The authors gratefully acknowledge support from the European Commission TMR Program, network Contract No. ERBFMRXCT 980228. Partial financial support was also received from the Swedish Research Council for Engineering Science (TFR) and the Swedish Foundation for International Cooperation in Research and Higher Education (STINT).

Hydrogen-related defect centers in float-zone and epitaxial n-type proton implanted silicon

Abstract Hydrogen-related defects in float zone (Fz) and epitaxial (Epi) n-type silicon crystals have been studied by means of deep level transient spectroscopy. These defects, as well as the characteristic vacancy-oxygen (VO) and divacancy (V 2 ) centers were introduced by proton implantation (1.3 MeV) using a dose of 1×10 10 /cm 2 . A hydrogen-related defect level located at 0.45 eV below the conduction band edge ( E c ) appears in both kind of samples. Another hydrogen-related defect appears predominantly in the Fz samples with a level at E c −0.32 eV. Depth profiling as well as annealing studies strongly suggest that the level at E c −0.45 eV is due to a complex involving hydrogen and V 2 . The level at E c −0.32 eV is strongly suppressed in the high purity Epi samples and the same holds for VO center. These results together with annealing data provide substantial evidence that the E c −0.32 eV level originates from a VO-center partly saturated with hydrogen (a VOH complex). Finally, in the Epi samples a new level at ∼ E c −0.31 eV is resolved, which exhibits a concentration versus depth profile strongly confined to the damage peak region. The origin of this level is not known but the extremely narrow depth profile may indicate a higher-order defect of either vacancy or interstitial type.

Dose-rate influence on the defect production in MeV proton-implanted float-zone and epitaxial n-type silicon

Abstract The production of stable vacancy-related point defects in proton-implanted float-zone and epitaxial silicon has been studied in the low dose range (⩽10 10 /cm 2 ) as a function of dose-rate. The well-known “inverse dose-rate” effect has been observed in both types of materials with a decrease in the concentration of vacancy-related defects as the dose-rate increases. The effect is less pronounced in oxygen lean epitaxial silicon. Moreover, a continuous decrease of the vacancy-related defect concentration as a function of the flux was measured while a threshold was expected according to previous studies. Both of these results can be explained by a simple calculation, taking into account the influence of the oxygen concentration as well as the influence of the diffusion coefficient of point defects on the “inverse dose-rate” effect.

Reverse annealing effects in heavy ion implanted silicon

Silicon samples of both n- and p-type have been implanted with low doses of In and I ions using energies between 15 and 30 MeV. The resulting electrically active defects were characterized by deep level transient spectroscopy (DLTS). The well-known vacancy-oxygen (VO) center is observed to show a reverse annealing. For annealing temperatures between 150°C and 250°C the concentration of VO is increased by about 40%, while the concentration of deep levels about 0.43 eV below the conduction band edge (divacancy defect, phosphorus–vacancy pair (PV) and others) is reduced by more than 40%. The growth of VO can to a large extent be explained by a release of vacancies during annealing from defect-rich zones generated by the heavy ions, although a part of the increase is also caused by vacancies originating from dissociation of PV centers. It has previously been shown that the interstitial carbon–interstitial oxygen (CiOi) complex is formed at room temperature by pairing of slowly diffusing interstitial carbon, released by the self-interstitials from the collision cascades, and oxygen. An increase by more than 15% of the initial concentration of the CiOi center is observed upon annealing between 75°C and 200°C in n-type material. The effect can be explained by a release of interstitials from the defect-rich zones during annealing at moderate temperatures. The increase is not observed in p-type material, which might be explained by a more effective trapping of the interstitials, released during annealing, by substitutional boron rather than substitutional carbon.

Nitrogen passivation by implantation-induced point defects in 4H–SiC epitaxial layers

Ion implantation causes damage to the crystal lattice resulting in the loss of free charge carriers. In this study, low dose implantations using different ions and implantation doses are made to resolve the initial carrier loss in nitrogen-doped epitaxial layers. A strong dependence of compensation on nitrogen concentration is seen, showing that nitrogen is passivated by implantation-induced point defects. An activation energy of 3.2 eV for the dissociation of the passivated nitrogen center is obtained.

Separation of vacancy and interstitial depth profiles in proton- and boron-implanted silicon

Anew experimental method of studying shifts between concentration-versus-depth profiles of vacancy-type and interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy (DLTS) measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy-oxygen center and the interstitial profile, represented by the substitutional carbon-interstitial carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. Thus the two profiles can be recorded with a high relative depth resolution. Point defects have been introduced in low doped float zone n-type silicon by implantation with 6 MeV boron ions and 1.3 MeV protons at room temperature, using low doses. For each implantation condition the peak of the interstitial profile is shown to be displaced by � 0:5 lm towards larger depths compared to that of the vacancy profile. This shift is primarily attributed to the preferential forward momentum of recoiling Si atoms, in accordance with theoretical predictions. 2002 Elsevier Science B.V. All rights reserved.