We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...

Diluted magnetic semiconductors

Synthesis and magnetic properties of Zn1−xMnxO films prepared by the sol–gel method

Recently, the family of semimagnetic semiconductors (SMSC) or diluted magnetic semiconductors(DMS) typically involving manganeseions, i.e., Cd1−x Mn x Te, Cd1−x Mn x Se, Zn1−x Mn x Te, Hg1−x Mn x Te, was extended to include ironions in selenium and tellurium II‐VI compounds. Contrary to Mn‐based DMS where d states of Mn are energetically superimposed on the valence‐band continuum, for Cd1−x Fe x Se and Zn1−x Fe x Se the Fe2 +(3d 6) is a donor whose energy level lies deeply in the energy gap. On the other hand, for Hg1−v−x Cd v Fe x Se with x≤0.15 and v≲0.40, the Fe2 + level is a resonant donor located in the conduction band. Also in the case of this material, the mobility of free electrons is surprisingly high, while the Dingle temperature is low. Because of the Coulomb interaction between the ionized donors Fe3 +(3d 5) at low T, there will appear a correlation of the positions of charges in this system. This leads to a kind of ‘‘condensation’’ of the charges in the system of donors and to their ‘‘crystallization’’ at even lower T (i.e., formation of a ‘‘charge superlattice’’ or a localized Wigner crystal of ionized donors). The space ordering of ionized donors dramatically influences the free‐carrier scattering and consequently leads to high mobilities and low Dingle temperatures. Another implication of intersite repulsion is the existence of the Coulomb gap in the one‐electron d‐band density of states. We discuss some of the effects related to its formation. We shall also present some magnetic properties of these new DMS: the specific heat, magnetic susceptibility, and the magnetization.

Fe‐based semimagnetic semiconductors (invited)

Physics and applications of II-VI semimagnetics

Polycrystalline samples of the semimagnetic semiconductor alloys (AgIn)1−zMn2zTe2 and (CuIn)1−zMn2zTe2 are used in lattice parameter, optical energy gap E0, and differential thermal analysis (DTA) measurements. The results indicate that in both, the zinc blende and chalcopyrite ranges of composition, ordering of the manganese can occur at lower temperatures, and a combination of the results is used to delineate the composition and temperature ranges in which disordered α and ordered α′ chalcopyrite and disordered s and ordered β′ zinc blende is the equilibrium structure. It is shown that while the manganese ordering has little effect on the lattice parameter, it has appreciable effect on the values of E0. This is demonstrated by the different aiming points at z = 1.0 for the E0 vs. z lines in the different fields, the values being 2.8 eV for β, 1.95 eV for β′, and 1.35 eV for α′.



Polykristalline Proben der semimagnetischen Halbleiterlegierungen (AgIn)1−zMn2zTe2 und (CuIn)1−zMn2zTe2 werden fur Messungen der Gitterparameter, optischen Bandlucken E0 und differentiellen Thermoanalyse (DTA) benutzt. Die Ergebnisse zeigen, das sowohl im Zinkblende- als auch im Chalkopyrit-Bereich der Zusammensetzung die Ordnung des Mangans bei tieferen Temperaturen auftritt, und eine Kombination der Ergebnisse wird benutzt, die Zusammensetzungs-und Temperaturbereiche zu zeichnen, in denen fehlgeordnetes α- und geordnetes α′-Chalkopyrit und fehlgeordnete β- und geordnete β′-Zinkblende die Gleichgewichtsstrukutren sind. Wahrend der Manganordnungsprozes nur einen geringen Einflus auf den Gitterparameter hat, wird gezeigt, das er einen wesentlichen Einflus auf die Werte von E0 hat. Dies wird durch die verschiedenen Zielpunkte bei z = 1,0 fur die E0–z-Linien in den verschiedenen Feldern demonstriert, wobei die Werte 2,8 eV fur β, 1,95 eV fur β′ und 1,35 eV fur α′ betragen.

J. Mycielski

Papers

Band structure and impurity states in diluted magnetic semiconductors