Acceptors in II-VI Compounds

The II-VI compounds have a larger ionicity than the III-V compounds, and it was first assumed that most of the residual donors and acceptors were due to the lattice defects like the anion and cation vacancies (Vn and VVi) and to group-II and group)-VI interstitial atoms, but it was later found that in most cases, group-1 and group)-V impurities were involved [118]. In some of these compounds, Li occupies a group-II site, where it is an acceptor, but it can also be present in the interstitial form, leading to self-compensation. 

A few acceptor absorption spectra have been identified in ZnSe, ZnTe and CdTe, but most of the results have been obtained by PL. Table 7.28 gives the transition energies for Li and Na in cubic ZnSe deduced from PL excitation spectra and from SPL. 

More absorption data exist for acceptors in ZnTe, together with PL measurements and they are given in Table 7.29. 

The calculated transition energies of the last column are the difference between the ground and excited states energies (in parentheses) calculated by [61]. The acceptor ionization energies are obtained by adding 15.4 meV to the energy of the 2Pb/2 (Ts) transition 

In II-VI compounds, the cation vacancy Vm2 is a deep double acceptor and in CdTe, the most recent estimations give Ev +0.76eV for Vcy2-/Vcd [29], It combines with the Cl e donor to give a relatively shallow acceptor complex which has been identified by the conjunction of PL and ODMR measurements as a centre with trigonal symmetry and i 120meV [79]. 

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