ALBERT

Notes: We have investigated the electronic properties of Er in crystalline Si using deep-level transient spectroscopy and capacitance-voltage measurements. Erbium was incorporated by ion implantation in a p+-n junction structure. In order to explore the role of oxygen and defects some samples were coimplanted with O and the annealing behavior of the deep-level spectra was explored in the temperature range 800–1000 °C for annealing times ranging from 5 s to 30 min. We show that O-codoping produces large modifications in the Er-related deep-level spectra and, in particular, a promotion from deep to shallow levels, thus enhancing the donor behavior of Er in Si. For erbium implanted in pure crystalline Si the spectrum is dominated by deep levels arising from Er-defect complexes which are easily dissociated upon thermal annealing. In O-coimplanted samples the formation of Er-O complexes with a characteristic level at EC−0.15 eV is observed. These complexes form upon thermal annealing and are stable up to 900 °C. These results are presented and possible implications for our current understanding of the mechanisms of Er photoluminescence in Si are discussed. © 1995 American Institute of Physics.

Notes: A method to control carrier lifetime in silicon locally and efficiently is presented. Voids, formed by high dose He implants, have been characterized by transmission electron microscopy demonstrating they are well localized in depth within layers thinner than 100 nm while their lateral extent is limited only by the masking capability during He implantation. Deep level transient spectroscopy measurements, performed on diodes containing different void densities, revealed the presence of two well defined trap levels, independent of void characteristics, at Ev+0.53 for holes and Ec−0.55 for electrons. These characteristics make them ideal for lifetime control in reducing parasitic transistor gain. Gummel plots on transistors have shown that when voids are formed the gain decreases from 1 to 10−3. The other transistor characteristics are only slightly influenced by the presence of voids. © 1996 American Institute of Physics.

Notes: We have studied the effect of erbium-impurity interactions on the 1.54 μm luminescence of Er3+ in crystalline Si. Float-zone and Czochralski-grown (100) oriented Si wafers were implanted with Er at a total dose of ∼1×1015/cm2. Some samples were also coimplanted with O, C, and F to realize uniform concentrations (up to 1020/cm3) of these impurities in the Er-doped region. Samples were analyzed by photoluminescence spectroscopy (PL) and electron paramagnetic resonance (EPR). Deep-level transient spectroscopy (DLTS) was also performed on p-n diodes implanted with Er at a dose of 6×1011/cm2 and codoped with impurities at a constant concentration of 1×1018/cm3. It was found that impurity codoping reduces the temperature quenching of the PL yield and that this reduction is more marked when the impurity concentration is increased. An EPR spectrum of sharp, anisotropic, lines is obtained for the sample codoped with 1020 O/cm3 but no clear EPR signal is observed without this codoping. The spectrum for the magnetic field B parallel to the [100] direction is similar to that expected for Er3+ in an approximately octahedral crystal field. DLTS analyses confirmed the formation of new Er3+ sites in the presence of the codoping impurities. In particular, a reduction in the density of the deepest levels has been observed and an impurity+Er-related level at ∼0.15 eV below the conduction band has been identified.This level is present in Er+O-, Er+F-, and Er+C-doped Si samples while it is not observed in samples solely doped with Er or with the codoping impurity only. We suggest that this new level causes efficient excitation of Er through the recombination of e-h pairs bound to this level. Temperature quenching is ascribed to the thermalization of bound electrons to the conduction band. We show that the attainment of well-defined impurity-related luminescent Er centers is responsible for both the luminescence enhancement at low temperatures and for the reduction of the temperature quenching of the luminescence. A quantitative model for the excitation and deexcitation processes of Er in Si is also proposed and shows good agreement with the experimental results. © 1995 American Institute of Physics.

Notes: We have quantitatively analyzed the structure and the annealing behavior of the point defects introduced by ion implantation in Si. We used deep-level transient spectroscopy to monitor and count interstitial-type (e.g., carbon–oxygen complexes) and vacancy-type (e.g., divacancies) defects introduced by MeV Si implants in crystalline Si and to monitor their annealing behavior for temperatures up to 400 °C. A small fraction (∼4%) of the initial interstitial–vacancy pairs generated by the ions escapes recombination and forms equal concentrations of interstitial- and vacancy-type room-temperature stable defect pairs. At T≤300 °C, vacancy-type defects dissociate, releasing free vacancies, which recombine with interstitial-type defects, producing their dissolution. This defect annihilation occurs preferentially in the bulk. At temperatures above 300 °C, all vacancy-type defects are annealed and the residual damage contains only ∼3 interstitial-type defects per implanted ion. This imbalance between vacancies and interstitials is not observed in electron-irradiated samples, demonstrating that it is the direct consequence of the extra ion introduced by the implantation process. © 1997 American Institute of Physics.

Notes: We compare the defect complexes generated in crystalline Si by electron irradiation and ion implantation, using irradiation fluences which deposit the same total energy in nuclear collisions. Deep level transient spectroscopy was used to monitor both vacancy-type (e.g., divacancies) and interstitial-type (e.g., carbon–oxygen complexes) defects produced on p-type Si samples. We show that identical defect structures and annealing behavior, T≤300 °C, are produced by both Si implantation and electron irradiation. After annealing at higher temperatures, we observe a higher residual damage in ion implanted samples, which is a direct consequence of the extra incorporated ions. We demonstrate that the substrate impurity content rather than the ion cascade dominates defect formation and evolution. In high purity Si, B-related instead of C-related (e.g., the carbon–oxygen complex) defects preferentially store the interstitials which escape direct recombination with vacancies, and the thermal stability of the CiOi complexes is decreased in Si containing low concentration of impurities. © 1997 American Institute of Physics.

Notes: Deep level transient spectroscopy (DLTS) investigations have been used to characterize the electrical properties of interstitial clusters in ion-implanted Si. Both n- and p-type samples were implanted with 145 keV–1.2 MeV Si ions to doses of 1×1010–5×1013 cm−2 and annealed at 450–750 °C. On samples annealed at temperatures above 550 °C, the residual damage is dominated by two hole traps (B lines) in p-type and five electron traps (K lines) in n-type samples. Analyses of the spectra and defect depth profiles reveal that these signatures are related to Si self-interstitial clusters, and experiments confirm that these clusters do not embody large numbers of impurities such as C, O, B, or P. Four deep level signatures exhibit similar annealing behavior, suggesting that they arise from the same defect structure. On the other hand, the remaining signatures exhibit different annealing behaviors and are tentatively associated with different cluster configurations. We have found that the thermal stability of the clusters is enhanced by either increasing the Si dose or by reducing the impurity content of the substrate. The explanation of these effects proposes that bigger and more stable clusters are formed when the concentration of free interstitials available for clustering is increased and the competing interstitial trapping at impurities is inhibited. Finally, in samples implanted at doses of ≥1×1013 cm−2, most of the DLTS signals exhibit a complex and nonmonotonic annealing behavior providing evidence that the clusters can transform between electronic configurations. © 1998 American Institute of Physics.

Notes: We present a quantitative study of the evolution of point defects into clusters and extended defects in ion-implanted Si. Deep level transient spectroscopy (DLTS) measurements are used to identify and count the electrically active defects in the damaged region produced by Si ion implantation at energies of 145 keV–2 MeV, and fluences from 1×108 to 5×1013 Si/cm2. Analyses of silicon annealed in the temperature range 100–680 °C allow us to monitor the transition from simple point defects to defect clusters and extended defects that occur upon increasing the ion fluence and the annealing temperature. At low doses, 〈1010 Si/cm2, only about 2% of the Frenkel pairs generated by the ion beam escape recombination and are stored into an equal number of interstitial and vacancy-type point defects. Thermal treatments produce a concomitant annealing of interstitial and vacancy-type defects until, at temperatures above 350 °C, only two to three interstitial-type defects per ion are left, and the DLTS spectra contain signatures of second-order point defects. Interstitial clusters at Ev+0.29 and Ev+0.48 eV are found to dominate the residual damage of silicon implanted at higher fluences, 1×1012–7×1013 Si/cm2, and at annealing temperatures, T≥600 °C. These interstitial clusters have point defect capture kinetics and are not observable in transmission electron microscopy (TEM), suggesting that they are smaller than (approximate)50 Å. Finally, for silicon implanted at higher Si doses, ≥5×1013 Si/cm2, thermal treatments at 680 °C result in a strong decrease in the concentration of the interstitial cluster signatures and in the introduction of a different DLTS signal, Ev+0.50 eV, which exhibits logarithmic rather than exponential carrier capture kinetics, a feature typical of an extended defect. Comparison of the formation and dissolution of this extended defect signature with TEM analyses indicates that this level is a signature of the rodlike {311} defects that are known to store the interstitials responsible for transient enhanced diffusion. These results suggest that the small interstitial clusters are either the precursors of the {311} defects or that they compete with {311} defects as sinks for self-interstitials. © 1997 American Institute of Physics.