Self-Compensation-Limited Conductivity in Binary Semiconductors. II.n-ZnTe

Paramagnetic resonance has geen observed in Al-doped ZnTe grown in excess Te vapor. The resonance is due to a hole trapped at a defect consisting of a doubly negatively charged zinc vacancy ${V_{\mathrm{Zn}}}^{2-}$ and an ${\mathrm{Al}}^{3+}$ donor ion on one of the twelve zinc sites nearest the ${V_{\mathrm{Zn}}}^{2-}$. The hole is trapped at the defect after irradiating the sample at 77°K with light of energy less than that of the band gap. The $g$ tensor is orthorhombic, as expected for such a defect. Compensation of donor or acceptor impurities by doubly as opposed to singly ionized defects has been shown to be important in II-VI compounds. The observed resonance shows that compensation of Al donors in ZnTe by doubly charged zinc vacancies does indeed occur. A consequence of the self-compensation of donor impurities in ZnTe is that there is a limit to how $n$-type the material can be made. Similar attempts to dope ZnTe $n$-type were carried out with Ga, In, Br, and I. Only insulating crystals were produced, even after subsequent firing in Zn vapor. No analogous resonance signals were observed in these sample, however.