We have studied the optical properties of the ␦-doped ZnSe:Te system using photoluminescence ͑PL͒ and x-ray and Raman scattering. Two different types of sample were investigated, ͑1͒ with a single ␦ layer and ͑2͒ with three adjacent ␦ layers separated by undoped layers. All of these samples are of reasonable crystalline quality and have the symmetry of the host ZnSe lattice as determined by x-ray and Raman scattering. The PL from each sample is very similar to the PL from bulk Zn-Se-Te solutions at low Te concentrations. The PL from the single-␦-doped material shows emission relatively close to the band edge which we attribute partly to Te 2 clusters ͑nearest-neighbor pairs͒ and partly to non-nearest pairs. This PL changes with storage time, from which we conclude that the nearest-neighbor pairs are more stable than non-nearest-neighbor pairs. The triple-␦-doped material also shows a deeper PL feature, with a peak at about 2.48 eV, which we attribute to Te nу3 clusters as well as to corresponding non-nearest-neighbors pairs.

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Delta doping techniques have been investigated to enhance the p-type doping of ZnSe. Tellurium was used as a codopant for improving the nitrogen doping efficiency. The net acceptor concentration (N A ϪN D) increased to 1.5ϫ10 18 cm Ϫ3 using single ␦ doping of N and Te ͑NϩTe͒, while it was limited to 8ϫ10 17 cm Ϫ3 by ␦ doping of N alone. A promising approach was developed in which three consecutive ␦-doped layers of NϩTe were deposited for each ␦-doping cycle. An enhancement in the (N A ϪN D) level to 6ϫ10 18 cm Ϫ3 has been achieved in ZnSe using this technique. The resultant layer has an average ZnTe content of only about 3%. This doping method shows potential for obtaining highly p-type doped ohmic contact layers without introducing significant lattice mismatch to ZnSe. Low-temperature photoluminescence spectra reveal some Te-related emissions.