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Recombination at textured silicon surfaces passivated with silicon dioxide
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View: Figures


Image of FIG. 1.
FIG. 1.

A textured front surface increases (1) transmission and (2) light trapping. (Refs. 1–5) Transmission increases when light is reflected from one facet onto a neighboring facet, and light trapping increases because the transmitted light has an angle to the perpendicular leading to (2a) a longer first pass through the absorber and usually (2b) a higher internal reflection at the rear surface. A textured front surface also tends to have (2c) a high internal reflection at the front surface. Note that when transmitted at an angle to the perpendicular, more light is absorbed near the front surface; this can be beneficial or deleterious depending on the location of the collecting junction and the relative rates of recombination within the cell.

Image of FIG. 2.
FIG. 2.

SEM images of {100} silicon wafers textured with random upright pyramids where the wafers were subsequently submitted to an rounding etch at the time and concentration stated on each image.

Image of FIG. 3.
FIG. 3.

The ratio of for textured and planar {100} wafers submitted to the same phosphorus diffusion and passivation step, plotted as a function of (a) , (b) diffusion sheet resistance, and (c) surface doping of the planar wafer (when available). The data is taken from King et al., (Ref. 41) Glunz et al.,(Ref. 38) Kerr et al., (Ref. 42) Schultz et al., (Ref. 35) Jin et al., (Ref. 43) and this work, where the sheet resistance of King et al. (Ref. 41) was calculated from the surface concentration and junction depth assuming an ERFC diffusion profile. The legend lists and the available detail regarding the texture and passivation.

Image of FIG. 4.
FIG. 4.

ratio of oxide-passivated, phosphorus-diffused silicon after exposure to a rapid thermal anneal (RTA) at in for 0, 0.5, 1, 3, and 6 min. (Ref. 43)

Image of FIG. 5.
FIG. 5.

A diffused and oxidized rantex surface illustrating how the diffusion and its associated depletion region might not conform to the textured surface. The figure also shows the location of stress and how the oxide grows nonuniformly. (Ref. 39)

Image of FIG. 6.
FIG. 6.

Data of Kerr et al. (Ref. 42) from Fig. 3(b) replotted such that the ratio refers to samples of equivalent sheet resistance rather than diffusion conditions.

Image of FIG. 7.
FIG. 7.

Hemispherical reflection of -coated rantex silicon after a rounding etch at various concentrations of (symbols) and calculated reflection for 110 nm of on rantex and 101 nm of on planar (lines) for light normally incident to the plane of the wafer.

Image of FIG. 8.
FIG. 8.

(a) SWR, (b) oxide thickness, (c) fraction of nonleaky MOS structures, (d) accumulation capacitance , (e) metal area, (f) flat-band voltage and equivalent insulator charge located at the interface , (g) density of interface states at midgap, and (h) emitter saturation current density and high-injection bulk lifetime , where all parameters are measured on MOS structures created on rantex that has been etched in for the times and concentrations listed in the figure. The various etches lead to a gradual change from rantex (no etch) to planar {100} (1 min, 1:5). For comparison, results of planar {111} silicon are also presented. Error bars associated with the experiments represent the standard deviation from the mean of the nonleaky MOS measurements.

Image of FIG. 9.
FIG. 9.

(a) High frequency (solid symbols) and quasistatic (open symbols) data, and (b) the density of interface states calculated by a Castagne analysis as a function of energy , where the data was measured from MOS structures fabricated on planar {100} (1 min, 1:5 ) and near-textured (1 min, 1:60 ) silicon. For comparison, is also plotted for a representative planar {111} sample. In the case of the near-textured sample, corresponds to the effective surface area determined from .

Image of FIG. 10.
FIG. 10.

Insulator charge density as a function of the midgap , where is determined at flat band from and the work function difference between the aluminum and silicon assuming all charge is located at the interface. Both axes refer to a surface-area density.

Image of FIG. 11.
FIG. 11.

Effective lifetime as a function of excess carrier concentration of rantex and planar {100} samples.

Image of FIG. 12.
FIG. 12.

Emitter saturation current density from the PC experiment plotted against the midgap from the experiment for samples of the same morphology. Both axes refer to the cross-sectional area of the test structures.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Recombination at textured silicon surfaces passivated with silicon dioxide