J. S. Christensen

Gettering of transition metal impurities during phosphorus emitter diffusion in multicrystalline silicon solar cell processing

We have investigated the gettering of transition metals in multicrystalline silicon wafers during a phosphorus emitter diffusion for solar cell processing. The results show that mainly regions of high initial recombination lifetime exhibit a significant lifetime enhancement upon phosphorus diffusion gettering. Nevertheless, transition metal profiles extracted by secondary ion mass spectrometry in a region of low initial lifetime reveal significant gradients in Cr, Fe, and Cu concentrations towards the surface after the emitter diffusion, without exhibiting a significant enhancement in the lifetime. In a region of higher initial lifetime, however, diminutive concentration gradients of the transition metal impurities are revealed, indicating a significantly lower initial concentration in these regions. From spatial maps of the dislocation density in the wafers, we find that lifetime enhancements mainly occur in regions of low dislocation density. Thus, it is believed that a generally higher concentration of...

High concentration in-diffusion of phosphorus in Si from a spray-on source

High concentration in-diffusion of phosphorus in both Czochralski grown and solar grade multicrystalline Si from a spray-on liquid source has been studied by secondary ion mass spectrometry and electrochemical capacitance-voltage profiling. By extraction of the concentration dependent effective diffusivity employing the Boltzmann-Matano analysis, we adapt an integrated diffusion model based on a previous work by Uematsu [J. Appl. Phys. 82, 2228 (1997)], in order to gain insight into the mechanisms governing such in-diffusions. We find that in the tail region of the profiles, diffusion is mediated by interaction with Si self-interstitials, whereas a vacancy mechanism via doubly negative vacancies dominates in the higher concentration region towards the surface, in correspondence with a previous analysis by Fair and Tsai [J. Electrochem. Soc. 124, 1107 (1977)]. Moreover, we find that both the vacancy and interstitial mechanisms can be described by an Arrhenius behavior, exhibiting apparent activation energi...

Hydrogen implantation into ZnO for n+-layer formation

Bulk ZnO crystals were implanted using 100keV H+ ions with doses 5×1016 and 2×1017cm−2 and subsequently annealed at 200–600°C to study the evolution of the implanted H by employing secondary ion mass spectrometry and scanning spreading resistance microscopy. It is shown that the heat treatment results in a decrease of H concentration in the implanted region, while no significant broadening of the H profiles is observed. This suggests that the implanted H is trapped in immobile complexes which dissociate during annealing with subsequent outdiffusion of H from the implanted region. The formation of a highly conductive n+-layer is observed in the implanted region, and the n+-layer is found to be stable up to 600°C. A correlation between electrical activity of H and presence of radiation damage is discussed.

Deuterium diffusion and trapping in hydrothermally grown single crystalline ZnO

Secondary ion mass spectrometry is employed to investigate diffusion of H2 implanted in hydrothermally grown single crystal ZnO. Diffusion profiles have been studied after 30 min isochronal heat treatments from 100 to 400 °C and evaluated using three different models: the infinite source model, a solid solubility limited model, and a trap limited model. Only the latter one reproduces closely the measured values. From this model an activation energy Ea=0.85 eV is extracted, and it is speculated that trapping may be a source of the discrepancies between the reported values of Ea in the literature.

Impurity diffusion of (141)Pr in LaMnO(3), LaCoO(3) and LaFeO(3) materials.

The impurity diffusion of Pr(3+) in dense polycrystalline LaMnO(3), LaCoO(3) and LaFeO(3) was studied at 1373-1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr(3+) had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients. The activation energies for bulk diffusion of Pr(3+) in LaMnO(3), LaCoO(3) and LaFeO(3) were 126 +/- 6, 334 +/- 68 and 258 +/- 75 kJ mol(-1), respectively, which are significantly lower than previously predicted by atomistic simulations. The bulk diffusion of Pr(3+) in LaMnO(3) was enhanced compared to LaCoO(3) and LaFeO(3) due to higher concentrations of intrinsic point defects in LaMnO(3), especially La site vacancies. Grain-boundary diffusion coefficients of Pr(3+) in LaCoO(3) and LaFeO(3) materials were evaluated according to the Whipple-Le Claire equation. Activation energies for grain-boundary diffusion of Pr(3+) in LaCoO(3) and LaFeO(3) materials were 264 +/- 41 kJ mol(-1) and 290 +/- 36 kJ mol(-1) respectively. Finally, a correlation between activation energies for cation diffusion in bulk and along grain boundaries in pure and substituted LaBO(3) materials (B = Cr, Fe, Co) is discussed.

Phosphorus and boron diffusion in silicon under equilibrium conditions

The intrinsic diffusion of phosphorus and boron in high-purity epitaxial silicon films has been studied. Phosphorus diffusion in a wide temperature range (810 to 1100 °C) revealed diffusion coefficients with an Arrhenius behavior exhibiting an activation energy of 2.74±0.07 eV and a pre-exponential factor of (8±5)×10−4 cm2/s. In the temperature range of 810 to 1050 °C, boron was found to diffuse with an activation energy of 3.12±0.04 eV and a pre-exponential factor of 0.06±0.02 cm2/s. These results differ from those of many previous studies, but this deviation may to a large extent be attributed to slow transients before equilibrium concentrations of point defects are established at temperatures below ∼1000 °C. Despite a similar diffusion mechanism mediated by Si self-interstitials, P exhibits a lower activation energy than B because of stronger bonding to the Si self-interstitial.

Diffusion of phosphorus in relaxed Si1−xGex films and strained Si/Si1−xGex heterostructures

Phosphorus diffusion has been studied in relaxed Si1−xGex samples (x=0.11 and 0.19) and strained Si/Si1−xGex/Si heterostructures (x=0.08, 0.13, and 0.18). The diffusivity of P is found to increase with increasing Ge content, while the influence of compressive strain results in a decrease in diffusivity as compared to that in relaxed material. The effect of strain is found to be equivalent to an apparent activation energy of −13 eV per unit strain, where the negative sign indicates that the P diffusion is mediated by interstitials in Si1−xGex (x<0.20). This conclusion is also supported by an experiment utilizing injection of Si self-interstitials, which results in an enhanced P diffusion in strained Si1−xGex. Further, P is found to segregate into Si across Si/Si1−xGex interfaces and the segregation coefficient increases with increasing Ge concentration.

Spatial distribution of cavities in silicon formed by ion implantation generated excess vacancies

The spatial distribution of nanosized cavities in silicon formed by high energy Ge ion implantation and annealing is determined. The cavities are directly observed by transmission electron microsco ...

Excess vacancies in high energy ion implanted SiGe

Excess vacancies generated by high energy implantation with 1.2MeV Si+ and 2MeV Ge+ ions in SiGe were investigated after rapid thermal annealing at 900°C. Excess vacancies were probed by decoration with Cu and measuring the Cu profile by secondary ion mass spectrometry. Cross section transmission electron microscopy of cleaved specimen enabled to visualize nanocavities resulting from agglomeration of excess vacancies. The ion-induced damage in SiGe increases with increasing Ge fraction of the alloy. The amorphization threshold decreases and the extension of a buried amorphous layer increases for given implantation and annealing conditions. In contrast to ballistic simulations of excess defect generation where perfect local self-annihilation is assumed the concentrations of excess vacancies and excess interstitials in SiGe increase with increasing Ge fraction. The main contribution to the high excess vacancy concentration in SiGe results from the inefficient recombination of vacancies and interstitials. Th...

Rearrangement of the oxide-semiconductor interface in annealed Al2O3∕4H-SiC structures

Al2O3 films with different thicknesses have been deposited on n-type (nitrogen-doped) 4H-SiC(0001) epitaxial samples by atomic layer chemical vapor deposition at 300°C and subsequently annealed in Ar atmosphere at temperatures up to 1000°C. The Al2O3∕4H-SiC structures were analyzed by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). The XPS and SIMS results indicate that the average composition in the wider interface area does not significantly change due to the annealing. However, as revealed by the TEM investigations in combination with XPS, the as-grown samples exhibit a double interface created by an intermediate suboxide SiOx layer (x<2). After annealing, this intermediate suboxide layer breaks up and transforms into SiO2 islands, resulting in a rather rough interface region and a high concentration of pure Si in the Al2O3 film. Furthermore, a pronounced accumulation of H is found in the rough interface region and this may pla...