The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

A comprehensive review of zno materials and devices

This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.

http://science.sciencemag.org/content/sci/294/5546/1488.full.pdf

Spintronics: a spin-based electronics vision for the future.

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

/pdf/spintronics-fundamentals-and-applications-2dx38n6phu.pdf

Spintronics: Fundamentals and applications

Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.

http://info.ifpan.edu.pl/SL-2/sl23sub/science_dietl.pdf

Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors

REVIEW Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.

https://science.sciencemag.org/content/sci/281/5379/951.full.pdf

Making Nonmagnetic Semiconductors Ferromagnetic

Effects of spin-orbit and $s\text{\ensuremath{-}}d$ exchange interactions are probed by magnetoresistance (MR) measurements carried out down to $50\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ on ZnO and ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{O}$ with $x=3$ and 7% and electron concentration $\ensuremath{\sim}{10}^{20}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. A description of the data for ZnO:Al in terms of weak-localization theory leads to the coupling constant ${\ensuremath{\lambda}}_{\mathrm{so}}=(4.4\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}\phantom{\rule{0.2em}{0ex}}\mathrm{cm}$ of the $kp$ hamiltonian for the wurzite structure, ${H}_{\mathrm{so}}={\ensuremath{\lambda}}_{\mathrm{so}}\mathbit{c}(\mathbit{s}\ifmmode\times\else\texttimes\fi{}\mathbit{k})$. A complex and large MR of ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{O}:\mathrm{Al}$ is interpreted in terms of the influence of the $s\text{\ensuremath{-}}d$ spin-splitting on the disorder-modified electron-electron interactions, which explains positive MR. A large negative MR is tentatively assigned to a precursor effect of the magnetic polaron formation. It is suggested that the proposed model explains the origin of MR observed recently in many magnetic oxide systems.

Spin-related magnetoresistance of n -type ZnO:Al and Zn 1 − x Mn x O : Al thin films

This paper reviews the present understanding of the origin of ferromagnetic response of diluted magnetic semiconductors and diluted magnetic oxides as well as in some nominally magnetically undoped materials. It is argued that these systems can be grouped into four classes. To the first belong composite materials in which precipitations of a known ferromagnetic, ferrimagnetic or antiferromagnetic compound account for magnetic characteristics at high temperatures. The second class forms alloys showing chemical nano-scale phase separation into the regions with small and large concentrations of the magnetic constituent. To the third class belong (Ga,Mn)As, heavily doped p-(Zn,Mn)Te, and related semiconductors. In these solid solutions the theory built on p-d Zener's model of hole-mediated ferromagnetism and on either the Kohn-Luttinger kp theory or the multi-orbital tight-binding approach describes qualitatively, and often quantitatively many relevant properties. Finally, in a number of carrier-doped DMS and DMO a competition between long-range ferromagnetic and short-range antiferromagnetic interactions and/or the proximity of the localisation boundary lead to an electronic nano-scale phase separation.

Origin of ferromagnetic response in diluted magnetic semiconductors and oxides

Magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As have been investigated. Measurements at low temperature (50 mK) and high magnetic field ( ⩽27 T ) have been employed in order to determine the hole concentration p=3.5×10 20 cm −3 of a metallic (Ga 0.947 Mn 0.053 )As layer. The analysis of the temperature and magnetic field dependencies of the resistivity in the paramagnetic region was performed using the above value of p , which gave the magnitude of p – d exchange energy |N 0 β|∼1.5 eV .

Tomasz Dietl

Papers

Spin-related magnetoresistance of n -type ZnO:Al and Zn 1 − x Mn x O : Al thin films

Origin of ferromagnetic response in diluted magnetic semiconductors and oxides

Magnetotransport properties of (Ga,Mn)As investigated at low temperature and high magnetic field

Self-organized growth controlled by charge states of magnetic impurities.

The study of the s-d type exchange interaction in Zn1−xMnxSe mixed crystals