Shallow acceptor-bound exciton

DAP and Shallow Acceptor-Bound Exciton Transitions and LO-Phonon Replicas in PL... 

In a semiconductor, substitutional FAs from the same column of the periodic table as the one of the crystal atom they replace are usually electrically inactive and they are called isoelectronic with respect to the semiconductor. It can occur, however, that for some isoelectronic impurities or electrically-inactive complexes, the combination of the atomic potential at the impurity centre with the potential produced by the local lattice distortion produces an overall electron- or hole-attractive potential in a given semiconductor. This potential can bind an electron or a hole to the centre with energies much larger than those for shallow electrically-active acceptors or donors. The interaction of these isoelectronic impurities traps the free excitons producing isoelectronic bound excitons which display pseudo-donor or pseudo-acceptor properties. This is discussed later in this chapter in connection with the bound excitons, and examples of these centres are given in Chaps. 6 and 7. 

In ZnO doped with As, which is another potential acceptor in ZnO, a line at about 3.23-3.24 eV, followed by two LO-phonon replicas has been observed in the PL spectrum with an intensity exceeding the exciton emission intensity [83]. This emission has been attributed to the shallow As acceptor, the activation energy of which was estimated at 180 lOmeV from the temperature dependence of the PL spectrum. Concurrently with the DAP emission line, a sharp line at 3.325 eV appeared in these samples, tentatively attributed to the As acceptor-bound exd-ton [83]. In yet another study [84], the 3.322 and 3.273 eV lines greatly increased with... 

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