Portal de Periódicos da CAPES

General expressions of positive- and negative-ionic emission currents in dissociative self-surface ionization of binary salt

1983; Elsevier BV; Volume: 54; Issue: 1-2 Linguagem: Inglês

10.1016/0168-1176(83)85012-5

1873-2801

Hiroyuki Kawano, Tsutomu Kenpō,

Semiconductor materials and devices

Abstract General expressions for thermal positive- and negative-ion currents ( i ±) emitted from a thick layer surface of binary salt (MX) such as alkali-metal halide are derived theoretically. These are i ± = e η ± S ± [ m (M) m (X)] − 1 4 (2π kT ) − 1 2 × exp[(Δ S = + Δ S ° + Δ S ± )/2 R ] × exp[(± φ ± ∓ Z ± − D = − D °)/2 kT ]. Here, e is the elementary electric charge; η ± the collection efficiency of the emitted ion M + or X − ; S ± the actual surface area for the positive- or negative-ion emission, generally much smaller than that for simultaneous emission of the neutral molecule MX; m (M) and m (X) the masses of M and X, respectively; T the surface temperature; Δ S = , Δ S °, and Δ S ± the standard entropy changes due to dissociation of the molecule MX, to sublimation of MX, and to positive- or negative-ion formation, respectively; φ ± the effective work function for the emission of M + or X − from the layer surface; Z ± the first ionization energy of M or the electron affinity of X; D = the dissociation energy of MX; and D ° the heat of sublimation of MX. Values of the above factors except S ± and φ ± are usually known. The expression for i + of Li + , for example, is found to explain reasonably the experimental results obtained with LiF (about 2 × 10 2 molecular layers) in the range 720–860 K.