Electronic resonant images of an ion implanted Si(111) substrate observed by wavelength tunable optical second harmonic microscopy

Abstract

This paper demonstrates that the spatial distribution of electronic states of an arsenic ion implanted Si(111) substrate can be observed by using a wavelength tunable second harmonic (SH) microscope in a wide photon energy range from 2ℏω=1.96to5.19eV. The contrast in the SH intensity images between the As-doped area and the nondoped area depends greatly on the SH photon energy. For 2ℏω>3eV, optical second harmonic generation (SHG) from the nondoped area was stronger than from the doped area, and the contrast was reversed for 2ℏω⩽2.33eV. The contrast in the SH intensity images was considerably different from that in the linear optical reflection images, indicating that spectroscopic SH microscopy can provide different informations on electronic levels from that associated with the linear optical response. It is suggested that the larger SH intensity from the nondoped area for 2ℏω>3eV results from the resonant SHG enhancement effect associated with the bulk Si E1 (3.4eV) and E2 (4.3eV) gaps. In the case of the doped area, a small resonant enhancement of the SH intensity was observed around 2ℏω=2.33eV. This resonance may result from an energy level created by the ion implantation.