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We report the properties of ordered ZnO x S 1-x alloys calculated in various structures (CuAu -I, Cu 3 Au, Luzonite and Famatinite) using a first-principles total-energy formalism based on the hybrid full-potential augmented plane-wave plus local orbitals (APW + lo) method, within the local-density approximation (LDA). The calculated band gaps of the alloys are direct and range from 0.49 for O-rich to 1.55 eV for S-rich ZnO x S 1-x . The non linear variation of the band gap energy is related to the large electronegativity difference between O and S.

In order to investigate the electronic and magnetic properties of Co-ZnO alloys, we used a full potential linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT), as implement in the WIEN2K package. This work is carried out within the LSDA approximation as the exchange-correlation potential. We have modeled ZnO doped with 6.25, 12.5, and 18.75% of Co. It pointed out that the band gap decrease and the magnetic moments increase with the atomic fraction of Cobalt. The Zn x Co 1-x O is found to be a semiconductor, where the filled-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty d-states are also shown to shift downwards and upwards in the valence and the conduction bands, respectively, with increase in the U potential. The analysis of the partial density of states reveals that the reduction of the ZnO band gap is due principally to the strong p-d interaction of O and Co. 1 Introduction The recent discovery of ferromagnetism in Co-doped ZnO [1, 2] has added a new dimension to the importance of this material. The s, p electrons of ZnO are responsible for transport, while the d electrons of Co are responsible for the magnetic properties. Consequently, the coupling between these electrons can be exploited in new magnetic devices for information processing and data storage. This possibility has generated much interest in the study of dilute magnetic semiconductors (DMSs) where transition metal atoms are doped in II-VI and III-V semiconductors. In particular, ZnO attracts large research attention, since it due to become a ferromagnetic FM-DMS with a Curie temperature of T C % 110 K. Along this line, attempts have been made to fabricate ZnO-based DMSs. ZnO offers other desirable features as a semiconductor host. It has a direct wide band-gap of 3.3 eV [3], and therefore should have an extensive use in the optoelectronics industry [4,5]. Its strong piezoelectricity [6] is exploited in a variety of transducer applications [7] and has possible application in polarization field effect transistors [8]. The predictions of high temperature ferromagnetism [9] spawned a large number of experimental [10][11][12][13][14][15][16][17] and computational [18][19][20] studies of transition metal (TM) doped ZnO. The reported experimental values of Curie temperature and

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