Spectroscopic studies of ZnSe grown by liquid phase epitaxy

The application of modern LPE techniques to ZnSe has recently resulted in material which shows a relatively small number of sharp lines in the bound exciton (BE) region and negligible deep level emission. BE transitions reveal the presence of Al and In donors and Li acceptors. Occasionally BE´s related to Cl and Ga donors and Na acceptors are also observed. The sole unidentified line at 2.79 eV appears to be related to an isoelectronic center, on the basis of its moderate phonon coupling and lack of 2-electron transitions. These sharp narrow (<0.2 meV) BE lines indicate that the total shallow donor concentration is < 5 × 10¹⁶/cm³. No manifestation of vacancies or interstitials has been seen, and thus all the shallow donor or acceptor states in undoped material appear to be impurity related. In the donor-acceptor pair (DAP) region, the formerly observed Al-Li pair lines [1] are seen as doublets, suggesting a new shallow donor with a binding energy ~0.3 meV different from Al. Correlation with growth conditions suggests that the new donor is likely to be boron. N, P, and As-doped samples show DAP bands which indicate that they form shallow acceptors, but confirmation of their presence as simple substitutional acceptors has not yet been achieved. The activation energies, derived from DAP band positions, are 80, 85, and 100 meV, respectively, for N, P, and As.