Groups-II and -IV Acceptors in III-V Compounds

In III-V compounds, group-II acceptors are located on the atom-III sublattice and group-IV acceptors on the atom-V sublattice. In GaAs, however, the Si atom can also be found on atom-III sublattice, where it behaves as a donor. Two main types of GaAs LEC crystals can be considered a) the semi-insulating (SI) crystals, with a Fermi level pinned near Ec — 0.8 eV because of the presence of the Asca deep donor (EL2), where the residual acceptors are ionized at LHeT under TEC and b) the Ga-rich samples which can be made p-type by doping with shallow acceptors. 

The measured FWHMs of the acceptor lines are usually broader ( 1.5 — 2 cm-1 or 0.19 — 0.25 meV) than those observed in silicon and germanium, but a FWHM of 0.7 cm-1 (87 ieV) has been reported by Atzmuller et al. [11] for the G line of the Cas acceptor. 

The positions of the absorption lines of some shallow acceptors in GaAs are given in Table 7.21. The attributions are those of [97]. The GeAs lines are closer to the one-phonon absorption of GaAs and their positions have been deduced from selective-pair PL measurements [98]. 

Two lines at 192.5 and 195.3 cm-1 (23.87 and 24.21 meV) have been observed in the Cas spectrum by Kirkman et al. [97] between lines B and A of Table 7.21. They have been attributed to the equivalent for GaAs of the A4 and A3 lines of Table 7.9 for germanium. 

The ionization energies of Be, Mg, Zn, and C are close to the low-energy onset of the one-phonon absorption of GaAs, but those of Si and Ge are within this strong intrinsic absorption and most of the discrete electronic transitions of these latter acceptors are resonant with the one-phonon absorption. Hence, their energies have been deduced from PL measurements near from the GaAs band gap. 

---