On theory of doping in nanosized crystallographic voids

For determining the position of an impurity level in the band gap within the frame of the proposed model, it is also necessary to know the positions of edges of both valence and conduction bands of the semiconductor or its electron work function and band gap width. The beta-rhombohedral boron (β-B) band gap width E_G is well known: 1.56 eV. As for the β-B work function E_WF, there are only old and to some extent contradictory measurements of this parameter. The values of the β-B work function measured by different (photoelectric, thermoelectric and high-energy electron's surface-diffraction) methods show a fairly wide spread: 3.80 - 6.13 eV and there are suggestions explaining both under- and overestimated values. The reference book's value of 4.45 eV is placed near the midpoint of this interval. However, we are inclined to accept the highest value proposed for the β-B work function, 6.13 eV. Such choice of the zero reference point on the energy scale yields the location of the conduction band edge E_C at 6.13 eV-1.56 eV=4.57 eV giving quite a good estimate for the work function of contaminated and imperfect crystals, i.e. when electrons are exciting in vacuum not from the valence band edge of an ideal crystal, but in the vicinity of the conduction band edge. In any case, evaluating the calculated energy levels we should take into account the possible spread in values associated with the spread in input parameters, namely the band edges' positions on the energy axis. (author)