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

Optical Properties of (Zn, Mn) and (Cd, Mn) Chalcogenide Mixed Crystals and Superlattices

A diffusion-based synthesis of doped colloidal semiconductor nanocrystals is demonstrated. This approach involves thermodynamically controlled addition of both impurity cations and host anions to preformed seed nanocrystals under equilibrium conditions, rather than kinetically controlled doping during growth. This chemistry allows thermodynamic crystal compositions to be prepared without sacrificing other kinetically trapped properties such as shape, size, or crystallographic phase. This doping chemistry thus shares some similarities with cation-exchange reactions, but proceeds without the loss of host cations and excels at the introduction of relatively unreactive impurity ions that have not been previously accessible using cation exchange. Specifically, we demonstrate the preparation of Cd1–xMnxSe (0 ≤ x ≤ ∼0.2) nanocrystals with narrow size distribution, unprecedentedly high Mn2+ content, and very large magneto-optical effects by diffusion of Mn2+ into seed CdSe nanocrystals grown by hot injection. Con...

Nanocrystal Diffusion Doping

Co-doped ZnO(Zn1−xCoxO) and Co, Al codoped ZnO(Zn1−xCoxO:Al) films were grown on c-plane sapphire (0001) substrates by pulsed laser deposition using a KrF excimer laser. In order to enhance homogeneous substitution of Co2+ for Zn2+ in the ZnO film, an alternating deposition (AD) method was employed for doping. ZnO films doped with the same elements were grown without employing the AD method under the same fabrication conditions to compare with the corresponding AD films. Despite Co incorporation, the Zn1−xCoxO film by AD methods showed better crystallinity than pure ZnO film. Also, the crystallinity of Zn1−xCoxO:Al films by AD methods was better than those of Zn1−xCoxO and ZnO:Al films by conventional doping methods. Root mean square roughnesses of the films by AD methods were less than 1.6 nm. Absorption peaks caused by d–d transitions were observed at 1.88, 2.01, and 2.19 eV in Zn1−xCoxO films. The electric conductivity of Zn1−xCoxO:Al film by AD methods was comparable to that of ZnO:Al film by conventi...

ZnO–CoO solid solution thin films

Diluted magnetic semiconductors (DMS) are semiconducting alloys containing a random distribution of substitutional magnetic ions (e.g., Mn++ in Cd1−xMnxSe). Magnetic properties of DMS—such as spin glass behavior due to lattice frustration, magnon excitations in a random system of spins, superexchange, and short range antiferromagnetic order—are of considerable interest in their own right. In addition, understanding these properties is important because they strongly influence the electronic phenomena in DMS via the sp‐d exchange interaction between the band electrons and the localized magnetic moments. We review the most recent results concerning magnetic susceptibility, Mn++‐Mn++ nearest‐neighbor exchange, and magnetic short‐range order in these materials. On this basis, we can present a fairly complete and unified picture of magnetic properties of DMS. In addition, we point out some of the issues and challenges that lie ahead.

Magnetic properties of diluted magnetic semiconductors: A review (invited)

A model for the high-field magnetization of II-VI semimagnetic compound semiconductors at low temperatures is presented. It applies for low Mn concentrations. The model explains quantitatively and without adjustable parameters the magnetization of ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$, ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$, ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{S}$, ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$, and ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{S}$ near 100 kOe for $Tl2$ K. At higher magnetic fields, magnetization steps are predicted. The first step is observed in ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$ and ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Se}$, and is used to determine the nearest-neighbor exchange constant. The results support a random distribution of Mn ions.

Technical saturation and magnetization steps in diluted magnetic semiconductors: Predictions and observations

Field-induced exchange effects in (Cd,Mn)Te and (Cd,Mn)Se from photoluminescence measurements.

Picosecond time-resolved photoluminescence studies of exciton-magnetic polaron complexes in Cd1−xMnxSe

Resistivity and Hall measurements were made on n-type ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se samples with x=0.01, 0.05, and 0.10 at temperatures 0.3\ensuremath{\le}T\ensuremath{\le}300 K and in magnetic fields H\ensuremath{\le}80 kOe. For each value of x, several samples with different room-temperature carrier concentrations ${n}_{\mathrm{RT}}$ were studied. They cover the range from slightly below ${n}_{c}$ to ng${n}_{c}$, where ${n}_{c}$ is the carrier concentration at the metal-insulator transition. The zero-field data indicate that for samples grown in the same manner ${n}_{c}$ increases with increasing x. For T\ensuremath{\le}4.2 K a large magnetoresistance (MR), and large changes in the Hall coefficient R with H, are observed. In some cases the H-induced change in the resistivity exceeds a factor of 10. At low H the MR is always positive. For samples with x=0.05 and 0.10 the MR goes through a maximum at a field ${H}_{\mathrm{max}}$, and it then decreases at higher H. The value of ${H}_{\mathrm{max}}$ decreases with decreasing T. For x=0.01 the resistivity at T\ensuremath{\gtrsim}2 K increases monotonically with H, but well below 2 K a weak peak in the MR is observed. The variation of the shape of the MR curve with x and with ${n}_{\mathrm{RT}}$ is discussed. The positive MR at low H is accompanied by an increase in \ensuremath{\Vert}R\ensuremath{\Vert}, but the behavior of R at high fields depends on x and on ${n}_{\mathrm{RT}}$. A strong correlation between the MR and the magnetization of the Mn spins is found. This correlation indicates that the s-d interaction is primarily responsible for the MR. Several competing mechanisms by which the s-d interaction can produce large MR effects are discussed. However, the precise mechanisms which are responsible for the effects observed here have not been identified as yet.

D. Ridgley

Papers

Technical saturation and magnetization steps in diluted magnetic semiconductors: Predictions and observations

Field-induced exchange effects in (Cd,Mn)Te and (Cd,Mn)Se from photoluminescence measurements.

Picosecond time-resolved photoluminescence studies of exciton-magnetic polaron complexes in Cd1−xMnxSe

Magnetoresistance and Hall effect near the metal-insulator transition of Cd 1 − x Mn x Se

Dynamics of magnetic-polaron formation in Cd1-xMnxSe and Cd1-xMnxTe.