H. Navarrocontreras et al., OBSERVATION OF CONFINEMENT EFFECTS ON ACCEPTORS IN SI SI1-XGEX SUPERLATTICES/, Solid state communications, 90(5), 1994, pp. 311-316
We have used photothermal ionization spectroscopy to study boron accep
tors in p-Si/Si1-xGex, MBE grown on n-Si substrates. The Si1-xGex laye
rs were center-doped with boron in concentrations between 10(17) to 10
(18) cm-3. For constant Si layer width, at Si1-xGex widths of 100 angs
trom and smaller, bands of acceptor transitions appeared between 120 t
o 400 cm-1 depending on the width. For 100 angstrom wells, the observa
tions are explained by the simple hydrogenic model of a confined accep
tor of Bastard and the assumption that they form states associated to
the heavy hole valence band. This assumption is justified by the well
known fact that the valence band is splitted from the ligth hole band
by the stress present in these superlattices. For the 30 angstrom supe
rlattice, appreciable differences with respect to the Bastard model ax
e observed. This indicate the need to include the finite height of the
confining barrier and the effect of the ligth and heavy hole band sta
tes for acceptors confined in wells of 30 angstrom in width and smalle
r.