Properties of interfaces in amorphous/crystalline silicon heterojunctions

Abstract

To study recombination at the amorphous/crystalline Si (aSi:H/c-Si) heterointerface, the amphoteric nature of silicon (Si) dangling bonds is taken into account. Modeling interface recombination measured on various test structures provides insight into the microscopic passivation mechanisms, yielding an excellent interface defect density reduction by intrinsic aSi:H and tunable field-effect passivation by doped layers. The potential of this model's applicability to recombination at other Si heterointerfaces is demonstrated. Solar cell properties of aSi:H/c-Si heterojunctions are in good accordance with the microscopic interface properties revealed by modeling, that are, e.g., slight asymmetries in the neutral capture cross-sections and band offsets. The importance of atomically abrupt interfaces and the difficulties to obtain them on pyramidally textured c-Si is studied in combination with transmission electron microscopy.

High-efficiency Silicon Heterojunction Solar Cells: A Review

“…Most aSi:H(i/ films are deposited by PECVD with silane (SiH 4 ), possibly diluted in H 2 , as a precursor. A plasma excitation frequency of 13.56 MHz is often used [63][64][65][66]92], though the successful use of very high frequencies (VHF, e.g., 40 MHz [67,92], or 70 MHz) [52,68] was reported too. For device-grade films, typical deposition temperatures and pressures are 200°C and 0.1-1 Torr.…”

>21% Efficient Silicon Heterojunction Solar Cells on n- and p-Type Wafers Compared

“…Since electrons (minority carriers in p-doped c-Si) are more easily lost at the interface than holes, p-type samples suffer more from surface defect-assisted minority carrier recombination than n-type samples, especially at low injection. Even if the asymmetry in the respective cross sections is much less pronounced for defects at the a-Si:H/cSi interface than for defects at the SiO 2 /c-Si interface [15], it is nevertheless sufficient to reduce the low-injection lifetime on p-type samples. This behavior cannot be attributed to bulk defects: High-quality FZ wafers were used here, and longer low-injection lifetimes are observed when similar wafers are passivated with the negative fixed-charge dielectric aluminum oxide (Al 2 O 3 ) [16].…”

Conductive Atomic Force Microscopy Measurements of Localized over Dark Current along Pyramidal Ridge Lines of Intrinsic Hydrogenated Amorphous Silicon Layer on Textured Crystalline

“…The reduced V oc has been attributed to degradation of the intrinsic amorphous hydrogenated silicon (i-a-Si:H) layer, which works as a passivation layer. 8) Film deposition on at and textured surfaces differs primarily by the multiple deposition conditions engendered by the pyramidal textures. 8) Particularly in the textured case, epitaxial growth and/or mixed phase probably occurs on a nanoscopically uneven surface.…”

“…8) Film deposition on at and textured surfaces differs primarily by the multiple deposition conditions engendered by the pyramidal textures. 8) Particularly in the textured case, epitaxial growth and/or mixed phase probably occurs on a nanoscopically uneven surface. 8) Fesquet reported that the carrier lifetime increased in proportion to the size of the pyramidal texture, and that V oc could be increased by reducing the sharpness of the pyramids as well as the sub-micron pyramid density using isotropic etching.…”

“…8) Particularly in the textured case, epitaxial growth and/or mixed phase probably occurs on a nanoscopically uneven surface. 8) Fesquet reported that the carrier lifetime increased in proportion to the size of the pyramidal texture, and that V oc could be increased by reducing the sharpness of the pyramids as well as the sub-micron pyramid density using isotropic etching. 9) In the pyramid valleys, the lm is not conformal, and epitaxial growth occurs.…”