Solid State Phenomena Vols. 178-179

Abstract: ZnO/n-Si and ZnO/p-Si heterostructures were prepared by Atomic layer deposition (ALD) and the electronic properties have been investigated by Current-Voltage (I-V), Capacitance-Voltage (C-V) and Deep level transient spectroscopy (DLTS) measurements. DLTS measurements show two dominants electron traps at the interface of the ZnO/n-Si junction with energy position at 0.07 eV and 0.15 eV below the conduction band edge, labelled E(0.07) and E(0.15), respectively, and no electrically active defects at the interface of the ZnO/p-Si junction. E(0.07) is reduced by annealing up to 400°C while E(0.15) is created at 500°C. The best heterostructure is found after heat treatment at 400°C with a substantial improvement of the current rectification for ZnO/n-Si and the formation of Ohmic contact on ZnO/p-Si. A reduction of the interface defects correlates with an improvement of the crystal structure of the ZnO film with a preferred orientation along the c-axis.

Abstract: Illumination-induced degradation of minority carrier lifetime was studied in n-type Czochralski silicon co-doped with phosphorus and boron. The recombination centre that emerges is found to be identical to the fast-stage centre (FRC) known for p-Si where it is produced at a rate proportional to the squared hole concentration, p2. Since holes in n-Si are excess carriers of a relatively low concentration, the time scale of FRC generation in n-Si is increased by several orders of magnitude. The generation kinetics is non-linear, due to the dependence of p on the concentration of FRC and this non-linearity is well reproduced by simulations. The injection level dependence of the lifetime shows that FRC exists in 3 charge states (-1, 0, +1) possessing 2 energy levels. The recombination is controlled by both levels. The proper identification of FRC is a BsO2 complex of a substitutional boron and an oxygen dimer. The nature of the major lifetime-degrading centre in n-Si is thus different from that in p-Si - where the dominant one (a slow-stage centre, SRC) was found to be BiO2 – a complex involving an interstitial boron.

Abstract: This paper reports experimental results on the production and annealing of oxygen-vacancy related (VO_n, 1<n<5) and carbon-related (C_iO_i, C_iO_iI, and C_iC_s) defects in Ge-doped Czochralski-grown silicon (Cz-Si) materials containing carbon. The samples were irradiated by 2 MeV fast electrons and the behavior of radiation-produced defects is studied by means of infrared (IR) spectroscopy, monitoring the relevant bands in spectra. Regarding the VO_n family, it was found that the presence of Ge affects the annealing temperature of VO defects as well as their fraction that is converted to VO₂ defects. Both effects are discussed in relation with an impact of Ge on the concentration of self-interstitials that take part in the annealing of VO defects via two reaction paths VO + I → O_i and VO + O_i → VO₂. Furthermore, two bands at 1037 and 1051 cm^-1 are attributed to the VO₅ defect, although three other bands at 762, 967 and 1005 cm^-1 are believed to be associated with V_nO_m clusters containing carbon, most likely having a VO_nC_s structure. Regarding carbon-related complexes, it has been established that the annealing of the 862 cm^-1 band belonging to the C_iO_i defect is accompanied by the emergence of the 1048 cm^-1 band previously assigned to the C_sO_2i center. The evolution of the C_iC_s and the C_iO_iI bands is monitored and the identification of bands at 947, 967 and 1020 cm^-1 making their appearance in IR spectra over the temperature range where C_iC_s and C_iO_iI defects are annealed out is discussed.

Abstract: Results of a DLTS study on the deep-level centers in the copper-contaminated electron-irradiated FZ-Si are presented. Copper was diffused from the Cu-contaminated surface into previously irradiated samples at 350 K. The most abundant Cu-related complexes formed due to this procedure are the same as in the case of previously studied Cu-diffused Cz-Si.

Abstract: The evolution of Fe-related defects is simulated for di erent P di usion gettering (PDG) processes which are applied during silicon solar cell processing. It is shown that the introduction of an extended PDG is bene cial for some as-grown Si materials but not essential for all of them. For mc-Si wafers with an as-grown Fe concentration 14 cm³, a good reduction of the Fe_i concentration and increase of the electron lifetime is achieved during standard PDG. For mc-Si wafers with a higher as-grown Fe concentration the introduction of defect engineering tools into the solar cell process seems to be advantageous. From comparison of standard PDG with extended PDG it is concluded that the latter leads to a stronger reduction of highly recombination active Fe_i atoms due to an enhanced segregation gettering e ect. For an as-grown Fe concentration between 10¹⁴ cm³ and 10¹⁵ cm³, this enhanced Fe_i reduction results in an appreciable increase in the electron lifetime. However, for an as-grown Fe concentration >10¹⁵ cm³, the PDG process needs to be optimized in order to reduce the total Fe concentration within the wafer as the electron lifetime after extended PDG keeps being limited by recombination at precipitated Fe.

Abstract: The effect of tin on the formation and temperature transformation of VO centers in Ge upon annealing has been investigated. It was found that the doping of Ge with tin leads to a change of reactions involving oxygen and vacancies and the new defect SnVO appears upon VO annealing. Doping Ge with tin gives rise to a considerable decrease in the formation efficiency of divacancies and VO centers and the latter exist in a very narrow temperatures range. VO2 complexes appear only upon annealing of SnVO centers. The assumption is made that the absorption bands situated at 718.9 and 733.6 cm^-1 belong to the less stable configuration VO₂* and the bands at 731.5 and 771.7 cm^-1 correspond to stable configuration of VO₂ centers.

Abstract: Silicon wafers with different carbon contents have been characterized by Fourier transform infrared spectroscopy technique. An infrared absorption band at 1207cm-1 can be newly observed in the case of carbon content being above 1.7×1017/cm3, whose intensity increases with an increase of carbon concentration in silicon crystal. More interestingly, the 1207cm-1 band cannot be influenced by the long-time annealing in the temperature range of 450-1250oC, suggesting the high thermal stability of this carbon-related defect, which might be related to the presence of silicon carbide in silicon crystals.

Abstract: In silicon with high oxygen and boron content a new absorption band situated near 1026 cm-1 was found in Si after light illumin^{Superscript text}ation with intensity of 70 mW/cm². It was shown that both oxygen and boron are the component of the defect to which found band corresponds. It was revealed that defect occurs also during thermal treatments of silicon without illumination when a weak current was applied to the sample upon the treatment. The assumption was made that the formation of defect occurs both as result of direct interaction of components and through intermediate metastable states.

Abstract: The interaction between hydrogen and the iron-boron pair (Fe-B) has been investigated in iron-contaminated boron-doped Cz-Si using capacitance-voltage measurements (CV) and deep level transient spectroscopy (DLTS). Introduction of hydrogen was performed by wet chemical etching and subsequent reverve bias annealing of Al Schottky diodes. The treatment led to the appearance of the defect level characteristic to interstitial iron (Fe_i) with a corresponding decrease in the concentration of the Fe-B pair. Concentration versus depth profiles of the defects show that dissociation of Fe-B occurs in the depletion region and capacitance-voltage measurements unveil a decrease in the charge carrier concentration due to passivation of B. These quantitative observations imply strongly that H promotes dissociation of Fe-B releasing Fe_i whereas no detectable passivation of Fe-B or Fe_i by H occurs.

Abstract: High temperature annealing effects on Oxygen-induced defects formation has been studied by IR-LST, FTIR and TEM techniques. The results show that most defects are amorphous oxygen precipitates and/or dislocations. Ham’s theory has been modified in order to take into account the variations of interstitial oxygen concentration during the formation of precipitates. Comparison between experimental data and simulation shows that the specificity of annealing cycle is to combine both nucleation and growth stages. The morphology and stoechiometry of SiOx precipitates are also studied.