Boron-oxygen defect imaging in p-type Czochralski silicon

In this work, we demonstrate an accurate method for determining the effective boron-oxygen (BO) related defect density on Czochralski-grown silicon wafers using photoluminescence imaging. Furthermore, by combining a recently developed dopant density imaging technique and microscopic Fourier transform infrared spectroscopy measurements of the local interstitial oxygen concentration [Oi ], the BO-related defect density, [Oi ], and the boron dopant density from the same wafer were determined, all with a spatial resolution of 160 μm. The results clearly confirm the established dependencies of the BO-related defect density on [Oi ] and the boron dopant density and demonstrate a powerful technique for studying this important defect.This work was supported by the Australian Research Council (ARC) Future Fellowships program and the Australian Renewable Energy Agency (ARENA) fellowships program

Impact of incomplete ionization of dopants on the electrical properties of compensated p-type silicon

This paper investigates the importance of incomplete ionization of dopants in compensated p-type Si and its impact on the majority-carrier density and mobility and thus on the resistivity. Both theoretical calculations and temperature-dependent Hall-effect measurements demonstrate that the carrier density is more strongly affected by incomplete ionization in compensated Si than in uncompensated Si with the same net doping. The previously suggested existence of a compensation-specific scattering mechanism to explain the reduction of mobility in compensated Si is shown not to be consistent with the T-dependence of the measuredcarrier mobility. The experiment also shows that, in the vicinity of 300 K, the resistivity of compensated Si has a much weaker dependence on temperature than that of uncompensated silicon

Reading data stored in the state of metastable defects in silicon using band-band photoluminescence: Proof of concept and physical limits to the data storage density

The state of bistable defects in crystalline silicon such as iron-boron pairs or the boron-oxygen defect can be changed at room temperature. In this letter, we experimentally demonstrate that the chemical state of a group of defects can be changed to represent a bit of information. The state can then be read without direct contact via the intensity of the emitted band-band photoluminescence signal of the group of defects, via their impact on the carrier lifetime. The theoretical limit of the information density is then computed. The information density is shown to be low for two-dimensional storage but significant for three-dimensional data storage. Finally, we compute the maximum storage capacity as a function of the lower limit of the photoluminescence detector sensitivity.This work has been supported by the Australian Research Council (ARC) Future Fellowships program and the Australian Renewable Energy Agency (ARENA) fellowships program

Grown-in defects limiting the bulk lifetime of p-type float-zone silicon wafers

We investigate a recombination active grown-in defect limiting the bulk lifetime (τ bulk ) of high quality float-zone (FZ) p-type silicon wafers. After annealing the samples at temperatures between 80 °C and 400 °C, τ bulk was found to increase from ∼500 μs to ∼1.5 ms. By isochronal annealing the p-type samples between 80 °C and 400 °C for 30 min, the annihilation energy (Eann ) of the defect was determined to be 0.3 < Eann  < 0.7 eV. When the annihilated samples were phosphorus gettered at 880 °C or subject to 0.2 sun illumination for 24 h, τ bulk was found to degrade. However, when the samples were subsequently annealed at temperatures between 250 and 400 °C, the defect could be re-annihilated. The experimental results suggest that the defect limiting the lifetime in the p-type FZ silicon is not related to fast diffusing metallic impurities but rather to a lattice-impurity or an impurity-impurity metastable defect.This work has been supported by the Australian Renewable Energy Agency (ARENA) fellowships program and the Australian Research Council (ARC) Future Fellowships program

Influence of net doping, excess carrier density and annealing on the boron oxygen related defect density in compensated n-type silicon

In this study, we present experimental data regarding the concentration of the boron-oxygen complex in compensated n-type silicon when subjected to illumination. We find that the defect density is independent of the net dopant concentration and is strongly dependent on the minority carrier concentration during illumination. We show that annealing at temperatures in the range 500 C to 700 C permanently reduces the defect density possibly via a decrease in the oxygen dimer concentration.This work was supported by the Australian Research Council (ARC)

Boron-oxygen defect in Czochralski-silicon co-doped with gallium and boron

We study the boron-oxygen defect in Si co-doped with gallium and boron with the hole density 10 times higher than the boron concentration. Instead of the linear dependence of the defect density on the hole density observed in boron and phosphorus compensated silicon, we find a proportionality to the boron concentration. This indicates the participation of substitutional, rather than interstitial,boron in the defect complex. The measured defectformationrate constant is proportional to the hole density squared, which gives credit to latent defect models against defectreactions limited by the diffusion and trapping of oxygen dimers by boron atoms

Electron and hole mobility reduction and Hall factor in phosphorus-compensated p-type silicon

The conductivity mobility for majority carrier holes in compensated p-type silicon is determined by combined measurement of the resistivity and the net doping, the latter via electrochemical capacitance-voltage measurements. The minority electron mobility was also measured with a technique based on measurements of surface-limited effective carrier lifetimes. While both minority and majority carrier mobilities are found to be significantly reduced by compensation, the impact is greater on the minority electron mobility. The Hall factor, which relates the Hall mobility to the conductivity mobility, has also been determined using the Hall method combined with the capacitance-voltage measurements. Our results indicate a similar Hall factor in both compensated and noncompensated samples.This work was supported by the Australian Research Council ARC and by the DAAD/Go8 researcher exchange funding scheme

Upgraded metallurgical-grade silicon solar cells with efficiency above 20%

We present solar cells fabricated with n-type Czochralski–silicon wafers grown with strongly compensated 100% upgraded metallurgical-grade feedstock, with efficiencies above 20%. The cells have a passivated boron-diffused front surface, and a rear locally phosphorus-diffused structure fabricated using an etch-back process. The local heavy phosphorus diffusion on the rear helps to maintain a high bulk lifetime in the substrates via phosphorus gettering, whilst also reducing recombination under the rear-side metal contacts. The independently measured results yield a peak efficiency of 20.9% for the best upgraded metallurgical-grade silicon cell and 21.9% for a control device made with electronic-grade float-zone silicon. The presence of boron-oxygen related defects in the cells is also investigated, and we confirm that these defects can be partially deactivated permanently by annealing under illumination.This work was supported by the Australian Renewable Energy Agency (ARENA) through the Australian Center for Advanced Photovoltaics (ACAP), Project RND009, and their Postdoctoral Fellowships program. D.M. acknowledges the support from the Australian Research Council through the Future Fellowships program

Impact of grown-in point-defects on the minority carrier lifetime in Czochralski-grown silicon wafers

In this study, we investigate the nature of some recombination active defects limiting the lifetime in Czochralski (CZ) silicon wafers, in the millisecond range. Due to their low concentrations, the observed defects are unlikely to be identified through Deep-Level Transient Spectroscopy (DLTS) or Electron Paramagnetic Resonance (EPR), hence we use lifetime spectroscopy combine with several annealing steps to help identify the defect. We demonstrate that the defect can be deactivated by annealing above 300°C. Our experimental findings suggest that vacancy-related pairs incorporated during ingot growth may be responsible for the decreased minority carrier lifetime.This work was supported by the Australian Renewable Energy Agency postdoctoral fellowship program (ARENA), and the Australian Research Council future fellowship program (ARC)