https://doi.org/10.15407/jopt.2018.53.268

Optoelectron. Semicond. Tech. 53, 268-272 (2018)

N.I. Karas, V.F. Onyshchenko

MONOPOLAR PHOTOCONDUCTIVITY OF THE INVERSION LAYER AND “SLOW”-SURFACE LEVELS IN THE STRUCTURES OF MACROPOROUS AND MONOCRYSTALLINE SILICON IN CONDITIONS OF STRONG SURFACE LIGHTNING

The surface photoconductivity in the structures of macroporous and monocrystalline silicon has been studied with an absorption coefficient in the range of 200 - 104 cm – 1. At the same time, positive and negative photoconductivity was observed. The starting material consisted of n-type silicon with [100] orientation and 4.5 Ohm cm resistivity. Macropores with diameter Dp=2 μm, depth hp= 60 μm and period a= 4 μm were formed by electrochemical etching. It was found that when light is absorbed with a wavelength of 0.52 μm, a “slow” negative photoconductivity is observed on the thickness of the space charge region of 1 μm. When light is absorbed with a wavelength of 0.935 and 0.62 μm at a depth of 50 and 2.5 μm, respectively, positive photoconductivity is observed. The cause of negative photoconductivity is capture on the “slow” surface levels of the majority charge carriers, positive surface photoconductivity is manifested when capture of minority charge carriers. On the basis of the measured negative photoconductivity, the photoconductivity of the inversion layer was calculated, and from it the estimated values of the concentration of “slow” surface levels were obtained both in the macroporous structure (N> 1013 cm – 2) and in monocrystalline silicon (N <1013 cm – 2). It is shown that the ratio of negative photoconductivity in the structure of macroporous and monocrystalline silicon almost coincides with the ratio of illuminated areas of the structure of macroporous and monocrystalline silicon (27 and 25, respectively), which confirms the purely surface nature of negative photoconductivity under conditions of strong surface absorption of light.

Keywords: "slow" monopolar surface negative photoconductivity, concentration of "slow" surface levels, inversion layer.