REAL-TIME SPECTROSCOPIC ELLIPSOMETRY CHARACTERIZATION OF STRUCTURAL AND THERMAL EQUILIBRATION OF AMORPHOUS SILICON-CARBON ALLOY P LAYERS INP-I-N SOLAR-CELL FABRICATION

Real time spectroscopic ellipsometry (RTSE) has been applied to invest igate the near-surface optical changes that occur during p/i interface processing for hydrogenated amorphous silicon carbon alloy (a-Si1-xCx :H, x approximate to 0.05)p layers prepared at similar to 200 degrees C by plasma-enhanced chemical vapor deposition in the p-i-n solar cell configuration. Trimethylboron [B(CH3)(3)] was used as the p-type dopa nt source gas in order to avoid p-layer surface contamination that occ urs when using diborane (B2H6). We have analyzed the changes in the RT SE data detected after extinguishing the plasma for a-Si1-xCx:H p-laye r deposition while maintaining the p layer near its growth temperature . We have attributed these changes to: (i) structural equilibration ch aracterized by the emission of bonded hydrogen (similar to 2 at. %) fr om the p layer into the vacuum, and (ii) thermal equilibration charact erized by near-surface temperature variations (similar to 7 degrees C) due to gas composition and pressure variations within the reactor. Fr om the RTSE data, the kinetics of Il emission and the time evolution o f the near-surface temperature have been determined separately. We hav e found that a significant fraction of the H emitted from the a-Si1-xC x:H p layer at similar to 200 degrees C is lost within minutes of term inating the p-layer plasma. To restore the p-layer Il content and impr ove the p/i interface characteristics in a-Si:H p-i-n solar cells, we applied a H-2 plasma treatment to the p layer just prior to i-layer de position at 200 degrees C. Such a treatment yielded a 0.05 V increase in the open circuit voltage of the cell. (C) 1998 American Institute o f Physics. [S0021-8979(98)02816-3].