Diluted magnetic semiconductors: Actual structure and magnetic and transport properties

An experimental investigation is conducted into electrical-transport, magnetic, optical, and structural properties of GaAs-based diluted-magnetic-semiconductor heterostructures containing a Ga_1?x In _x As quantum well and a Mn delta layer 0.5–1.8 ML thick, separated by a GaAs spacer of thickness 3 nm. Ferromagnetic features are observed in the electrical transport and the Hall effect, which involve the flow of holes across the quantum well. They indicate carrier spin polarization in the quantum well. The combined use of high-resolution x-ray diffraction and x-ray reflectivity has made it possible to reliably identify structural-parameter profiles for both the quantum well and the Mn delta layer. It is thus established that the distribution of Mn atoms is nonuniform, both horizontally and vertically. This finding suggests a conception whereby the Mn delta layer divides into nanoscale ferromagnetic-ordering regions and paramagnetic regions. Magnetic and electrical-transport properties of the heterostructures are discussed within this framework.     

AIN-based dilute magnetic semiconductors

AlMnN and AlCrN have been synthesized by gas-source molecular beam epitaxy (GSMBE). Using optimized growth conditions and compositions, sccm films as determined by x-ray diffraction (XRD) and transmission electron microscopy, which also show room-temperature magnetic behavior were obtained for both materials. Chromium was found to produce greater magnetic ordering as evidenced by a higher technical saturation. The AlCrN also exhibited a higher remanent magnetization and a M versus T behavior more typical of ferromagnetism than that observed for AlMnN. These results suggest that Cr is a superior dopant for formation of AlN-based, dilute magnetic semiconductors.     

Nanostructures, magnetic semiconductors and spintronics

The aim of this paper is to give a brief overview of recent advances in the area of semiconductor nanomaterials, which represent extremely promising applications for materials with the spin-polarized transport of the charge carriers. It is shown on the basis of the last theoretical and experimental achievements that the development of diluted semiconductors with the controlled disorder and the wide energy gaps as well as the study of their molecular structures are very prospective routes for producing of novel magnetic semiconductors.     

Picosecond magnetic spectroscopy of two- and three-dimensionaldiluted magnetic semiconductors

The authors have developed a novel type of magnetic spectroscopy which relies on an integrated multichip SQUID (superconducting quantum interference devices) microsusceptometer to obtain nearly quantum-limited spin resolution. The susceptometer, including two DC SQUIDs, pickup loops, and field coils, was fabricated using VLSI technology to achieve an unprecedented scale of magnetic sensitivity, optimized for the study of microscopic samples or thin layers. Furthermore, in combination with an ultrafast pulsed laser system, measurements can be made at picosecond time scales, providing an understanding of the dynamics of the magnetic phenomena in these materials and the effects of quantum confinement on magnetic behavior     

The magnetic properties in transition metal-doped chalcopyrite semiconductors

We calculated the chemical trends of transition metal-doped chalcopyrite diluted magnetic semiconductors by use of the Korringa–Kohn–Rostoker Green's function method and the coherent potential approximation combined with the local density approximation. The ferromagnetism was stable in V- and Cr-doped chalcopyrite diluted magnetic semiconductors (DMSs). In the cases of Fe and Co doping, however, the spinglass-like state was realized. On the other hand, in the cases of Mn-doped I–III–VI₂ and II–IV–V₂-type DMSs, the ground state was ferromagnetic and spinglass-like states, respectively. We explained these chemical trends by considering the electron configurations and the crystal field effect. Moreover, we evaluated Curie temperatures (T_cs) of Cr-doped chalcopyrite semiconductors and expected that T_cs of Cu(Al,Cr)S₂ and Ag(Ga,Cr)S₂ were much higher than room temperature.     

The predicaments and expectations in development of magnetic semiconductors

Over the past half a century, considerable research activities have been directing towards the development of magnetic semiconductors that can work at room temperature. These efforts were aimed at seeking room temperature magnetic semiconductors with strong and controllable s, p-d exchange interaction. With this s, p-d exchange interaction, one can utilize the spin degree of freedom to design applicable spintronics devices with very attractive functions that are not available in conventional semiconductors. Here, we first review the progress in understanding of this particular material and the dilemma to prepare a room temperature magnetic semiconductor. Then we discuss recent experimental progresses to pursue strong s, p-d interaction to realize room temperature magnetic semiconductors, which are achieved by introducing a very high concentration of magnetic atoms by means of low-temperature nonequilibrium growth.     

Amorphous magnetic semiconductors with Curie temperatures above room temperature

Recently, amorphous magnetic semiconductors as a new family of magnetic semiconductors have been developed by oxidizing ferromagnetic amorphous metals/alloys. Intriguingly, tuning the relative atomic ratios of Co and Fe in a Co-Fe-Ta-B-O system leads to the formation of an intrinsic magnetic semiconductor. Starting from high Curie-temperature amorphous ferromagnets, these amorphous magnetic semiconductors show Curie temperatures well above room temperature. Among them, one typical example is a p-type Co_28.6Fe_12.4Ta_4.3B_8.7O₄₆ magnetic semiconductor, which has an optical bandgap of ~2.4 eV, room-temperature saturation magnetization of ~433 emu/cm³, and the Curie temperature above 600 K. The amorphous Co_28.6Fe_12.4Ta_4.3B_8.7O₄₆ magnetic semiconductor can be integrated with n-type Si to form p–n heterojunctions with a threshold voltage of ~1.6 V, validating its p-type semiconducting character. Furthermore, the demonstration of electric field control of its room-temperature ferromagnetism reflects the interplay between the electricity and ferromagnetism in this material. It is suggested that the carrier density, ferromagnetism and conduction type of an intrinsic magnetic semiconductor are controllable by means of an electric field effect. These findings may pave a new way to realize magnetic semiconductor-based spintronic devices that work at room temperature.     

The room temperature ferromagnetism in highly strained two-dimensional magnetic semiconductors

<正>In spintronics, it is still a challenge in experiments to realize the ferromagnetic semiconductors with Curie temperature T_c above room temperature. In 2017, the successful synthesis of two-dimensional(2D) van der Waals ferromagnetic semiconductors, including the monolayer CrI₃ with T_c = 45 K^[1]and the bilayer Cr₂Ge₂Te₆ with T_c = 28 K^[2] in experiments,has attracted extensive attention in ...     

The second harmonic generation in semiconductors in the DC magnetic field

The second harmonic radiation in millimeter wave region is found in semiconductors in the absence of the dc electric field. The observed resonant maximum of radiation intensity is shown to be related to the excitation of the free-electron plasma oscillations in the dc magnetic field.     

MOCVD制备过掺杂GaN基稀磁半导体微结构研究

应用MOCVD方法我们在c轴取向的蓝宝石衬底上生长出Fe掺杂和Mn掺杂GaN薄膜。通过改变前驱物的通入量,我们制备出不同掺杂浓度的样品。应用高分辨透射电镜,我们对样品的微结构进行了分析。对于Fe过掺杂GaN样品,我们发现了六角结构的Fe3N团簇的存在,并且Fe3N(0002)面平行于GaN(0002)面;对于Mn过掺杂GaN样品,我们发现了六角结构的Mn6N2.58相的存在,并且Mn6N2.58(0002)面平行于GaN(0002)面。同时,由于晶格中掺入了大量掺杂离子,GaN晶格取向遭到了破坏,导致了部分GaN(0002)面的倾斜。磁学测量表明均一相的Fe掺杂GaN显现铁磁性,而均一相Mn掺杂GaN没有铁磁性。由于铁磁性Fe单晶和Fe3N团簇的存在,相比于均一性Fe掺杂GaN,过掺杂GaN样品的磁性大幅度增强,而Mn过掺杂GaN样品显现出很弱的铁磁性,这有可能来源于Mn6N2.58相。     

High temperature magnetic semiconductors: narrow band gaps and two-dimensional systems

Magnetic semiconductors have been demonstrated to work at low temperatures, but not yet at room temperature for spin electronic applications. In contrast to the p-type diluted magnetic semiconductors, n-type diluted magnetic semiconductors are few. Using a combined method of the density function theory and quantum Monte Carlo simulation, we briefly discuss the recent progress to obtain diluted magnetic semiconductors with both p- and n-type carriers by choosing host semiconductors with a narrow band gap. In addition, the recent progress on two-dimensional intrinsic magnetic semiconductors with possible room temperature ferromangetism and quantum anomalous Hall effect are also discussed.     

Features of obtaining diluted magnetic semiconductors in the system of narrow-gap GaInAsSb alloys

Nanotechnology of obtainment of diluted magnetic semiconductors based on the GaInAsSb compounds is developed using the laser deposition of Mn atoms on the surface of the epitaxial layer of a quaternary alloy obtained by liquid-phase epitaxy. Fabricated heterostructures were studied using high-resolution X-ray diffraction for the Bragg and grazing diffraction geometries, and the layer-by-layer analysis is performed by secondary-ion mass spectrometry. It is established that the near-boundary region of the Ga_0.96In_0.04As_0.11Sb_0.89 layer near the deposition surface of atomic Mn exhibits the presence of a quinary compound with Mn atoms in the lattice and Mn₃As₂-type binary inclusions. Saturation of the GaIn(Mn)AsSb multicomponent diluted semiconductor with the Mn compounds makes it possible to specify the concentration of the magnetic impurity in the crystal and control the magnetic properties of the heterostructure.     

Advances in new generation diluted magnetic semiconductors with independent spin and charge doping

As one branch of spintronics, diluted magnetic semiconductors (DMSs) are extensively investigated due to their fundamental significance and potential application in modern information society. The classical materials (Ga,Mn)As of III–V group based DMSs has been well studied for its high compatibility with the high-mobility semiconductor GaAs. But the Curie temperature in (Ga,Mn)As film is still far below room temperature because the spin &; charge doping is bundled to the same element that makes the fabrication very difficult. Alternatively, the discovery of a new generation DMSs with independent spin and charge doping, such as (Ba,K)(Zn,Mn)₂As₂ (briefly named BZA), attracted considerable attention due to their unique advantages in physical properties and heterojunction fabrication. In this review we focus on this series of new DMSs including (I) materials in terms of three types of new DMSs, i.e. the " 111”, " 122” and " 1111” system; (II) the physical properties of BZA; (III) single crystals &; prototype device based on BZA. The prospective of new type of DMSs with independent spin and charge doping is briefly discussed.     

On magnetic quantization of the energy states in semiconductors having non-parabolic energy bands

An extremum principle is developed which permits analytical solutions to be obtained, together with a maximum error bound, for boundary-value problems satisfying the Laplace or Poisson equations under Dirichlet boundary conditions.     

Hot carrier magnetophonon spectroscopy of semiconductors in high magnetic fields up to 40 T

Hot carrier magnetophonon resonances of n-type Si, short channel InP and p-type InSb were investigated in pulsed high magnetic fields up to 40 T. Using a recently developed high resolution technique in pulsed high fields, many new features of the hot carrier-phonon interactions in high magnetic fields were found.     

InP基稀释光波导特性分析

从InP基稀释光波导的基本模型出发,利用有限差分波束传播（FD-BPM）算法,推导了InP基稀释光波导的有效折射率,对其进行了数值计算;根据光传输损耗方程,分析了稀释波导传输损耗产生的原因;对稀释光波导中TE/TM模式传输进行了详细的数值分析和模拟计算,并分析了其模场分布曲线。