Dopant Diffusion and Segregation

Kamins, T. I.

doi:10.1007/978-1-4613-1681-7_3

Cited by 2 publications

(1 citation statement)

References 56 publications

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“…This finding indicates that the laser-activated poly Si layers are supersaturated with boron atoms. Grain boundaries in poly Si provide an easy path for boron atoms to diffuse, and, therefore, allow for high dopant diffusivity [22]. We speculate that rapid boron migration along this path strongly enhances boron diffusion during the furnace BBr 3 diffusion step in our experiment.…”

Section: Supersaturationmentioning

confidence: 68%

Laser Activation for Highly Boron-Doped Passivated Contacts

Sharbaf Kalaghichi,

Hoß,

Zapf-Gottwick

et al. 2023

Solar

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Passivated, selective contacts in silicon solar cells consist of a double layer of highly doped polycrystalline silicon (poly Si) and thin interfacial silicon dioxide (SiO2). This design concept allows for the highest efficiencies. Here, we report on a selective laser activation process, resulting in highly doped p++-type poly Si on top of the SiO2. In this double-layer structure, the p++-poly Si layer serves as a layer for transporting the generated holes from the bulk to a metal contact and, therefore, needs to be highly conductive for holes. High boron-doping of the poly Si layers is one approach to establish the desired high conductivity. In a laser activation step, a laser pulse melts the poly Si layer, and subsequent rapid cooling of the Si melt enables electrically active boron concentrations exceeding the solid solubility limit. In addition to the high conductivity, the high active boron concentration in the poly Si layer allows maskless patterning of p++-poly Si/SiO2 layers by providing an etch stop layer in the Si etchant solution, which results in a locally structured p++-poly Si/SiO2 after the etching process. The challenge in the laser activation technique is not to destroy the thin SiO2, which necessitates fine tuning of the laser process. In order to find the optimal processing window, we test laser pulse energy densities (Hp) in a broad range of 0.7 J/cm2 ≤ Hp ≤ 5 J/cm2 on poly Si layers with two different thicknesses dpoly Si,1 = 155 nm and dpoly Si,2 = 264 nm. Finally, the processing window 2.8 J/cm2≤ Hp ≤ 4 J/cm2 leads to the highest sheet conductance (Gsh) without destroying the SiO2 for both poly Si layer thicknesses. For both tested poly Si layers, the majority of the symmetric lifetime samples processed using these Hp achieve a good passivation quality with a high implied open circuit voltage (iVOC) and a low saturation current density (J0). The best sample achieves iVOC = 722 mV and J0 = 6.7 fA/cm2 per side. This low surface recombination current density, together with the accompanying measurements of the doping profiles, suggests that the SiO2 is not damaged during the laser process. We also observe that the passivation quality is independent of the tested poly Si layer thicknesses. The findings of this study show that laser-activated p++-poly Si/SiO2 are not only suitable for integration into advanced passivated contact solar cells, but also offer the possibility of maskless patterning of these stacks, substantially simplifying such solar cell production.

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Section: Supersaturationmentioning

confidence: 68%

Laser Activation for Highly Boron-Doped Passivated Contacts

Sharbaf Kalaghichi,

Hoß,

Zapf-Gottwick

et al. 2023

Solar

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Dopant Implantation and Activation in Polycrystalline-SiGe

et al. 1994

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The activation of dopants and theevolution of the microstructure of poly-SiGe films during the activation anneal are of interest for applications such as removable diffusion sources for shallow junctions in CMOS circuit processing, low resistance contact layers and elements for thin film transistors in active matrix flat panel displays. To study these effects, 2300A poly-SiGe films with Ge content between 20 and 48% were deposited on 600A poly-Si seed layers by APCVD on thermally oxidized Si substrates. Growth temperatures were between 600 and 700'C. These films were then implanted with B and As at energies of 40 and 80 keV, respectively, at two different doses of 5 x 101 3 /cm 2 and 5 x 106/cm2 . To activate the dopants, the samples were furnace annealed at temperatures from 600 to 1000'C in an N2 ambient. Additional samples were rapidly annealed at temperatures between 800 and 1050'C for times up to 120 seconds. The sheet resistance, measured using a four-point probe, of 5 x 10 16/cm2 arsenic implanted films increased by a factor of two as the Ge content in the film increased from 20 to 48%. The boron doped film, on the other hand, showed no increase in sheet resistance with Ge content. TEM showed that in all cases the grain size increased after anneal. However, the grain sizes of the annealed, arsenic doped samples were on average 5 times larger than those of the boron-doped samples with the same anneal. The sub-grain structure of these films also changed after implantation and annealing. In particular, the twin planes increased in size in boron doped samples and sub-grain twinning virtually disappeared in the arsenic doped samples. In 25x 10 /cm As implanted samples, precipitates were formed which may indicate that the As solubility limit in the films has been exceeded. These precipitates are believed to be As or Asrich and could be responsible for the sheet resistance increase with Ge fraction, since the maximum solubility for As in Ge is lower than in Si by about a factor often.

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Dopant Diffusion and Segregation

Cited by 2 publications

References 56 publications

Laser Activation for Highly Boron-Doped Passivated Contacts

Laser Activation for Highly Boron-Doped Passivated Contacts

Dopant Implantation and Activation in Polycrystalline-SiGe

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