Electronic Structure And Magnetism of Novel Diluted Magnetic Semiconductors CdGeP 2 : Mn and ZnGeP 2 : Mn

Chalcopyrite II-IV-V 2 semiconductors CdGeP 2 : Mn and ZnGeP 2 : Mn are new types of diluted magnetic semiconductors (DMSs). Since their ferromagnetic Curie temperatures are much higher than room temperature, these DMSs are good candidates for materials to be used in spintronics devices. Their electronic and magnetic structures have been investigated using the first-principles calculations based on the Korringa-Kohn-Rostoker coherent-potential-approximation and local-density-approximation (KKR-CPA-LDA) methods. When Cd or Zn atoms are substituted by Mn atoms, the ground state magnetic structure is spinglass-like. On the other hand, if Mn atoms substitute Ge atoms, the system becomes ferromagnetic through the double-exchange mechanism. However, the calculation of the formation energies shows that this system is not energetically favorable. Instead, the system with vacancies (Cd, Vc, Mn)GeP 2 or a non-stoichiometric (Cd, Ge, Mn)GeP 2 are also ferromagnetic and, moreover, energetically stable. We conclude that either of these variants possess a ferromagnetic phase of the kind CdGeP 2 : Mn. Similar conclusions are obtained for ZnGeP 2 : Mn.     

Fabrication of p-CuGaS2/n-ZnO:Al heterojunction light-emitting diode grown by metalorganic vapor phase epitaxy and helicon-wave-excited-plasma sputtering methods

Greenish-white electroluminescence (EL) was observed from the heterojunction light-emitting diodes (LEDs) composed of p-type (001) CuGaS₂ chalcopyrite semiconductor epilayers and preferentially (0001)-oriented polycrystalline n-type ZnO thin films. The CuGaS₂ layers were grown on a (001) GaP substrate by metalorganic vapor phase epitaxy and the ZnO films were deposited by the surface-damage-free helicon-wave-excited-plasma sputtering method. The n-ZnO/p-CuGaS₂ LED structure was designed to enable an electron injection from the n-type wider band gap material forming a TYPE-I heterojunction. The EL spectra exhibited emission peaks and bands between 1.6 and 2.5 eV, although their higher energy portions were absorbed by the GaP substrate. Since the spectral lineshape resembled that of the photoluminescence from identical CuGaS₂ epilayers, the EL was assigned to originate from p-CuGaS₂.     

Optical absorption and electrical conductivity of flash evaporated CuGaTe2 thin films

The optical absorption edge of CuGaTe₂ thin films in the energy range 1 to 2·3 eV was studied. The characteristic band gaps were found to be 1·23 eV and 1·28 eV whereas the acceptor ionization energy was 170 meV. Electrical conductivity measurements were carried out in the temperature range 300–550 K and two acceptor states with ionization energies 400 meV and 140 meV were found. The origin of acceptor states is explained based on covalent model.