| Research Abstract |
Atomic configuration and charge states of Cl or P in ZnSe and ZnTe were investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy. By measuring Cl K-edge EXAFS,it was found that the Cl atoms in ZnSe are incorporated into four coordinated Se lattice sites, however in ZnTe, the Cl atoms are displaced from Te lattice sites, and probably moved toward [111] direction and from one-coordination. On the other hand, XANES spectra of P K-edge indicates the existence of two kinds of charge states in ZnSe. The carrir compensation mechanism seems to be different between Cl doped ZnTe and P doped ZnSe.
Almost all II-VI compounds are unipolar materials. Though the cause of the unipolarity is not well understood yet, some models have been suggested such as 1) self-compensation by creating point defects, 2) solubility limit of impurities and 3) formation of DX centers by a displcement of dopant atoms. It is important to cl
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arify the atomic structure around dopant atoms to understand the cause of the unipolarity.
The Cl doped ZnSe and ZnTe were grown on GaAs (100) substrate by molecular beam epitaxy. The atomic configuration of Cl dopant is about 1x10E19 cm-3 for both materials. The P doped materials were prepared by ion implantation into undoped ZnSe and undoped ZnTe grown on GaAs substrates by MBE.The dose of P ions were 4x10E14 cm-2 with 350 keV for both ZnSe and ZnTe. The EXAFS and XANES measurements were performed by fluorescence yield method at 100K.
In the Cl doped ZnTe, two kinds of atomic distances, 0.24 and 0.32nm, between Cl and Zn were observed. The atomic distance between Zn and Te in ZnTe is 0.265nm, so it can be said that the Cl atom in ZnTe is not incorporated into the substiutional Te lattice site. The coordination number of Cl corresponding to shorter bond length (0.24nm) to that of longer one (0.32nm) is just 1 : 3. Therefore, Cl atoms may be displaced toward [111] direction and formed one-coordination.
The XANES spectra of P doped ZnSe shows two absortion edges, indicating two kinds of charge states. The positive P ion may cause the carrier compensation in ZnSe. Less
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