Second-harmonic spectroscopy of a Si(001) surface during calibrated variations in temperature and hydrogen coverage

Abstract

The epitaxial growth of silicon films by chemical vapor deposition ͑CVD͒ is strongly affected by temperature and hydrogen ͑H͒ termination. We report measurements of p-polarized optical second-harmonic ͑SH͒ spectra generated in reflection from clean 2ϫ1-reconstructed and H-terminated epitaxial Si͑001͒ surfaces with no intentional doping by Ti:sapphire femtosecond laser pulses for SH photon energies 3.0р2បр3.5 eV near the bulk E 1 resonance. Temperatures were varied from 200 to 900 K and H coverages from 0 to 1.5 monolayers ͑ML͒. Increases in temperature at fixed H-coverage redshift and broaden the E 1 resonance, as observed in linear bulk spectroscopy. Increases in H coverage from 0 to 1 ML at fixed temperature strongly quench, redshift, and distort the lineshape of the E 1 resonance even though reflection high-energy electron diffraction shows that the surface maintains the dimerized 2ϫ1 reconstruction. The latter spectroscopic variations cannot be explained by vertical strain relaxation in the selvedge region, nor by bulk electric-field-induced SH ͑EFISH͒ effects. We instead attribute these variations to a monohydride-induced surface chemical modification, which we parametrize as a surface EFISH effect because submonolayer H strongly alters surface electric fields by redistributing charge from surface dimers into the bulk. The effects of vertical strain relaxation are weakly evident as a blueshift of the E 1 resonance accompanying dihydride termination ͑1.0-1.5 ML͒, which breaks the surface dimer bond. This modification is parametrized as a separate field-independent alteration to the surface dipole susceptibility surface (2) . Finally, guided by these SH spectroscopic studies, we demonstrate dynamic real-time ͑100-ms resolution͒ SH monitoring of H coverage ͑5% accuracy͒ during temperature programmed hydrogen desorption and CVD epitaxial growth of silicon from disilane. ͓S0163-1829͑97͒07144-0͔

Electric field induced surface passivation of Si by atomic layer deposited Al<inf>2</inf>O<inf>3</inf> studied by optical second-harmonic generation

“…2). Also, the parameters of the resonances at 3.32 ± 0.01 eV and 3.38 ± 0.01 eV correspond well to values reported for the c-Si/Si0 2 interface [28], as well as to values reported for clean and H dosed c-Si surfaces [24]. In addition to the good reproduction of the experimental data, this similarity supports the validity of the fitting results .…”

“…3(a) and (b) SHG spectra for p-polarized fundamental and SHG radiation are shown for the 11 nm thick AI 203 film on Si(100), as-deposited and after anneal, respectively. Both show a distinct resonance in the 3.3 -3.4 eV range, indicating that the SHG response is dominated by c-Si interband transitions at the E'dE 1 critical point (CP) [23,24]. The anneal very clearly modifies the SHG spectrum; the amplitude increases with more than an order of magnitude, whereas the peak shifts from -3.3 to -3.4 eV resulting in a more symmetric feature.…”

“…The first contribution has redshifted to 3.25 ± 0.02 eV and has minor impact. This contribution can be assigned to interband transitions related to Si-Si bonds modified due to the vicinity of the interface with the film [23,24] . The redshift of this "modified Si-Si interface contribution" after anneal might be related to further weakening of Si-Si bonds [23,27], indicating structural changes in the (interfacial) oxide .…”

Improvedab initiocalculation of surface second-harmonic generation from Si(111)(1×1):H

“…2 that our calculation for χ (−2ω; ω,ω) coincides with the measurement taken at a low temperature of 80 K. It is well known that temperature causes shifting in the peak position of SSHG spectra [49]. As R pS only depends on this component [see Eq.…”

“…Additionally, Ref. [49] shows that low-temperature measurements of R pP will blueshift the spectrum away from room-temperature measurements such as those shown in Figs. 7 and 8, and towards our theoretical results.…”