Optical properties of an SiOx porous silicon (PS) interface,
prepared by stain etching of the laser modified p-Si surface, were
investigated. The electroreflectance spectra (ERS) were measured in the
region of 3.0-3.8 eV. A correlation between the existence of
photoluminescence (PL) and the polarity inversion of the ERS signal of PS,
compared to the laser modified Si or PS samples without PL, is
established. It is shown that PL appears due to the electron enrichment of
the near interface region caused by the positive charge imbedded into the
oxide layer. The transition energy experiences a red shift with the
increasing thickness of the oxide film. The intrinsic field between the
oxide layer and Si increased with the ageing of the PS samples displaying
PL. The results obtained support the surface localization model of PS PL
controlled by the tunnelling mechanism of photocarriers through the
Si/SiOx barrier.
Nanohill formations were found on a surface of 6H-SiC by the N 2 laser focused beam. These nanohills are situated along the circular line with diameter smaller than that of the focused laser beam. Results of photoluminescence and studies of friction force microscopy speak in favor of an increase in the nitrogen concentration in the nanohills. The pressure of liquid matter in the subsurface area and the pressure of the laser beam on the surface of the sample are taken into account in explaining this phenomenon. The threshold character of the effect, accumulation effect and increase of N band on PL spectra testify to the major role of the thermogradient effect in this phenomenon.
The influence of strongly absorbing N¬2 laser radiation on pores formation on a surface of Si single crystal has been investigated using optical microscope, atomic force microscope and photoluminescence. After irradiation by the laser and subsequent electrochemical etching in HF acid solution morphological changes of the irradiated parts of a surface of Si were not observed. At the same time, pores formation on the non-irradiated parts of Si surface took place. The porous part of the Si surface is characterized by strong photoluminescence in red part of spectra with maximum at 1.88 eV and intensity of photoluminescence increases with current density. Suppression of the pores formation by the laser radiation is explained with inversion of Si type conductivity from p-type to n-type. This fact is explained by Thermogradient effect – generation and redistribution of the intrinsic defects in gradient of temperature. It was shown that the depth of n-Si layer on p-Si substrate depends on intensity of laser radiation and it increases with intensity of laser radiation. The results of the investigation can be used for optical recording and storage of information on surface of semiconductors.
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