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Effect of incomplete ionization for the description of highly aluminum-doped silicon
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10.1063/1.3603043
/content/aip/journal/jap/110/2/10.1063/1.3603043
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/2/10.1063/1.3603043

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Al dopant density in Si as a function of depth measured by ECV. The Gaussian-shaped characteristic of the profile decay is mainly caused by the lateral doping inhomogeneities within the measuring area. Thus, according to Ref. 15 , the determined profiles have been assumed as a convolution of the real Al profile and a Gaussian function. stands for the depth, at which the profile decreases abruptly.

Image of FIG. 2.
FIG. 2.

SEM image of the cross section of an Al-doped  +  region at the Si surface. The Al doping profile ends abruptly, clearly indicated by the sharp contrast at the interface between the Al-  +  region and the Si bulk. Thickness inhomogeneities within the ECV measurement area (Ø = 3.55 mm ± 0.06 mm) lead to the Gaussian-shaped characteristics of the measured profiles (cf. Fig. 1 ).

Image of FIG. 3.
FIG. 3.

(Color online) Measured saturation current densities of the test samples (squares) with surface-passivated (open) and non-surface-passivated (closed) Al-  +  regions and calculated influence of Auger recombination (lines) using an empirical Al doping profile (inset), without taking defect recombination into account. The profile depth and the minority carrier surface recombination velocity have been varied. The inset shows the simplified profile used for our simulations.

Image of FIG. 4.
FIG. 4.

(Color online) Measured saturation current densities of the test samples (squares) and calculated influence of Auger and SRH recombination (lines) for varied effective defect densities *σ. The two curves for each * value indicate calculations for passivated (  = 100 cm/s) and nonpassivated (  = 107 cm/s) Al-  +  surfaces, respectively.

Image of FIG. 5.
FIG. 5.

(Color online) Measured saturation current densities of the test samples (squares) and calculated influence of Auger and SRH recombination with * = 1.7 cm−1 (named the SRH model) and the lifetime parameterization (τ model) proposed in Refs. 1 and 2 .

Image of FIG. 6.
FIG. 6.

(Color online) Gaussian function vs standard deviation σ. The medium variation of the measured depth Δ = 0.75 μm has been determined from fits to the measured ECV profiles (cf. Fig. 1 ). The different depths have been accounted for in our simulations (inset), according to their Gaussian probability.

Image of FIG. 7.
FIG. 7.

(Color online) Measured saturation current densities of the test samples (squares) and calculated influence of Auger and SRH recombination without (dash dotted) and with (dotted) taking into account Al-  +  thickness inhomogeneities (i.) (cf. Fig. 6 ). For non-surface-passivated thin Al-  +  regions, a lower shielding for the minority carriers in the Si bulk leads to increased recombination activities at the surface and thus to an increase of . Taking into account incomplete ionization (i.i.) of the Al acceptors without (line) and with (dashed) Al-  +  thickness inhomogeneities, the effect of the latter behaves similar. The lower amount of free majority carriers in the Al-  +  region due to i.i. leads to a significant overall increase of and, furthermore, to a more pronounced difference for passivated and nonpassivated surfaces.

Image of FIG. 8.
FIG. 8.

(Color online) Effect of incomplete ionization dependent on the acceptor concentration . Shown are the results of our simulations with the integrated model in Sentaurus TCAD (line) and calculations by Huster and Schubert (Ref. 15 ).

Image of FIG. 9.
FIG. 9.

(Color online) Measured saturation current densities of the test samples (squares) and calculated (squares) influence of Auger and SRH recombination taking into account incomplete ionization of the Al acceptors. In this case (compared to Fig. 7 ), each simulation result is calculated with the corresponding measured profile at the same Al profile depth, respectively. The influence of profile inhomogeneities has been neglected. Excellent agreement of measured and calculated values has been achieved.

Tables

Generic image for table
Table I.

Parameters used for our simulations of the saturation current densities of Al-doped Si.

Generic image for table
Table II.

Defect level and capture cross sections for Al-contaminated Si reported in literature.

Generic image for table
Table III.

Experimental data and simulation results for our -type Si solar cell with Al- +  rear emitter. By counting the Al atoms simply as acceptor occupancies (1), calculations show an overestimation of the open-circuit voltage of 2.5%. While incorporating the τ model (2) still leads to a significant overestimation, the model presented in this work (3) shows very good agreement with the measured values.

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/content/aip/journal/jap/110/2/10.1063/1.3603043
2011-07-25
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Effect of incomplete ionization for the description of highly aluminum-doped silicon
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/2/10.1063/1.3603043
10.1063/1.3603043
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