High Si content SRO/SiO2 bilayer superlattices with boron and phosphorus doping for next generation Si quantum dot photovoltaics

Abstract

Si quantum dots or interchangeably Si nanocrystals are promising materials for all-Si tandem solar cells in next generation photovoltaics. Si QDs in this study were fabricated by annealing sputtered Si rich oxide/SiO 2 (SRO/SiO 2 ) bilayer superlattice thin-films. Advantages of high Si content SRO layers include lower resistivity and higher light absorption crosssections which are more suitable for photovoltaic devices. However, theoretically high Si content SRO produces greater size distribution and larger Si nanocrystals which in this case slightly lowers the bandgap towards that of crystalline Si. This study investigates the properties of high Si content SRO/SiO 2 bilayer superlattice thin-films and the effect of boron and phosphorus doping.Index Terms -Boron, Doping, Phosphorus, Magnetron Sputtering, Si Quantum Dots, Si Nanocrystals. 978-1-4799-7944-8/15/$31.00 ©2015 IEEE 978-1-4799-7944-8/15/$31.00 ©2015 IEEE

Structural, optical, and electrical properties of silicon nanocrystals fabricated by high silicon content silicon-rich oxide and silicon dioxide bilayers

“…1(a), 1(c), and 1(e). After hightemperature annealing, the crystallization of Si was confirmed for all samples by conventional TEM, X-ray diffraction, or Raman spectroscopy as demonstrated previously; 13) however, the morphology of the Si NCs was different between samples as shown in Figs. On the other hand, the P-doped Si NCs were separated by neighboring Si NCs.…”

“…We suggest that this difference was due to the differences in Si NC sizes. 13) Next, we quantitatively demonstrate that the Si NC size contributes to the peak position and intensity between samples. Figures 4(a)-4(c) show the size distribution of Si NCs for all samples in a small volume range.…”

“…18) Our previous work also indicated that the film contained an amorphous Si phase. 13) Here, it is worth noting that the density of amorphous Si is approximately 1.8% less than that of crystalline Si. 19) Although the size of Si NCs might be affected by the presence of amorphous Si, the uncertainty in the size should be very small considering that the criterion for creating Si NCs in the image relies on the atomic density as previously discussed.…”

“…The high Si content in SRO is more suitable for solar cell devices to improve their performance, with advantages such as (1) lower resistivity of devices and (2) higher light absorption as previously reported. 13) In this study, we compare the structural, optical, and electrical properties of individual intrinsic, boron (B)-doped, and phosphorus (P)-doped Si NCs with high Si content. The structural properties were revealed using transmission electron microscopy (TEM)=energy-filtered TEM (EFTEM) 14) and atom probe tomography (APT).…”

“…Details of the sample preparation have been described previously. 13) EFTEM specimens were prepared by typical mechanical polishing and Ar ion milling, resulting in sample thicknesses of approximately 50 nm or thinner. Si mapping was performed with an energy shift of 17 eV and an energy slit width of 2 eV to distinguish energies between Si (17 eV) and SiO 2 (23 eV) using a JEOL 2200FS TEM.…”