The dielectric function ͑͒ of polycrystalline bulk samples of the quaternary chalcopyrite semiconductors Ag 1−x Cu x InSe 2 with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 has been determined by spectroscopic ellipsometry in the energy range from 0.5 to 4.7 eV at room temperature. Accurate values of refractive indices n and extinction coefficients k representative of bulk materials are obtained from the data. The value of the main energy gap is very sensitive to the composition and varies from 1.225 to 1.009 eV as x increases ͑Cu content͒. The structures observed in ͑͒ have been analyzed by fitting the numerically differentiated experimental spectrum ͑second derivative͒ to analytical line shapes. As a result, the energies corresponding to different electronic transitions have been determined as a function of the composition, and they have been identified within the electronic band structure of chalcopyrites.

The electrical properties between 80 and 300 K and the optical absorption a t room temperature of both n-and p-type CuInTe, are studied. The n-type sample is obtained by annealing p-type CuInTe, in the presence of indium for a prolonged period of time. The p-type samples are grown by programmed directional freezing technique with slight excess of indium in the stoichiometry. Two defect levels with E D = 58 meV and EA around 15 meV are identified from the analysis of the temperature dependence of the carrier concentration. The origin of these levels, consistent with the covalent bonding model, is attributed to Incu and V T~, respectively. From a theoretical fit to the experimental data, the density of states effective mass of the electrons is found to be rn: = 0.16me. The estimated values of the conduction and valence-band deformation potentials are in agreement with the general trend observed in other I-111-VI, compounds. Using the model proposed for the band-gap shrinkage, the energy gap of n-type CuInTe, in the dilute limit is calculated to be 1.026 eV.On a &die les proprietes Blectriques entre 80 et 300 K, et l'absorption optique B temperature ambiante de CuInTe, type n et type p. L'bchantillon type n a At6 obtenu par recuit et celui type p par mise en presence de 1'Indium durant une periode de temps prolong& On a fait croitre les Bchantillons type p par la technique de refroidissement directionnel programme avec un lBger excBs #Indium dans la stoechiometrie. Par l'analyse de la dbpendance de la temperature de concentration des porteurs, on a identifie deux niveaux de dBfauts avec E D = 58 meV et EA environ 15 meV. L'origine de ces niveaux, compatible avec le modBle de liaison covalente, est attribue B Incu et a V T~, respectivement. AprBs un ajustement theorique aux donnees expbrimentales, la densite des Btats de la masse effective des 6lectrons est de m* = 0,16me. Les valeurs estimees des potentiels de deformation des bandes de conduction et de valence sont en accord avec la tendance gen6rale observBe dans les composes I-111-VI,. En utilisant le modBle propose pour la contraction de la bande du gap, le rBsultat de gap d'Bneigie de CuInTe, type n dani la fimite diluke est de 1,026 eV.

No abstract

From a combined study of the electrical properties between room temperature and 77 K and optical absorption at 300 K of bulk CuInSe 2 samples doped with different oxygen concentrations, two shallow acceptor levels are found. The activation energy E A1 and E A2 of these levels in the dilute limit tends to be around 30 and 36 meV, respectively. The increase of E A1 and decrease of E A2 with the increase of oxygen content can be explained consistently on the basis that the ratio of Cu to In atoms increases with the increase of oxygen incorporated into CuInSe 2 lattice.

Electrical conduction by Mott's variable range hopping mechanism and cross-over above liquid helium temperatures in the same samples to Efros and Shklovskii's type conduction in the presence of a Coulomb gap is observed in p-type CuInSe2. The behaviour of the hopping parameters is discussed.