稀磁半导体CdMnTe单晶的制备新技术

ＣｄＭｎＴｅ是近年来出现的一种新型半导体材料，由于材料中含有磁性Ｍｎ２＋离子，所以又称之为稀释磁性半导体。它具有独特的磁学、光学、电学性质，同时也可用作红外探测器制备中的衬底材料，但是，受材料本身特性的限制，采用传统的长晶工艺制备这种材料存在有较大的困难。本文采用ＡＣＲＴ—Ｂ技术来进行晶体生长，使混料和长晶一次完成，成功的制备出了国内首批ＣｄＭｎＴｅ单晶     

Carrier-Density Dependence of Faraday Rotation and Spin Splitting in Cd1−x Mn x Te

We employ spin-quantum-beat spectroscopy to investigate the carrier-density dependence of the spin-precession frequency and the magnitude of the Faraday rotation of Cd_1?x Mn _x Te samples at fixed magnetic field. We find an onset of saturation of the Faraday rotation at carrier densities as low as 4× 10¹⁶ cm^?3 and attribute it to electrons (not holes which dominate in other types of experiments). The spin splitting at fixed magnetic field remains density dependent down to 3 × 10¹⁵ cm^?3 (the lowest density accessible in our measurements) which suggests a direct influence of the carrier-density on the sp–d exchange not mediated by screening effects.     

Cd/sub 1-x/Mn/sub x/Te semimagnetic semiconductors for ultrafast spintronics and magnetooptics

We present ultrafast optical characterization of Cd/sub 1-x/Mn/sub x/Te single crystals with high (x>0.5-Mn) concentration, studied by magnetooptical sampling and time-resolved magnetization modulation spectroscopy. We have demonstrated that the dynamics of both Mn spins and carrier spins in Cd/sub 1-x/Mn/sub x/Te is extremely fast (in the subpicosecond range), making the nanostructures based on this material very promising for applications in spintronics and magnetooptics.     

Magnetic, optical, and kinetic properties of Hg1 − x − y Mn x Dy y Te crystals

We have studied the magnetic, optical, and kinetic properties of Hg_{1 ? x ? y} Mn _x Dy _y Te crystals. The behavior of their magnetic susceptibility can be accounted for by the presence of clusters of various sizes. The Hg_{1 ? x ? y} Mn _x Dy _y Te crystals are shown to be n-type. Absorption data are used to determine the optical band gap of the crystals.     

Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSe(x)Te(1-x) nanocrystals

A series of ternary tetrapodal nanocrystals of CdSe(x)Te(1-x) with x = 0?(CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V(oc)), short-circuit current (J(sc)) and power conversion efficiency (η) of the devices all increased with increasing Se content in the CdSe(x)Te(1-x) nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1?w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80?mW?cm(-2), and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510?nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals.     

Ellipsometric characterization of Cd1−x Mn x Te thin films in the presence of perturbative fields

Ellipsometric studies in the 1·5 to 5 eV range have been carried out on thin films of Cd_1−x Mn _x Te and exhibitE ₀,E ₁ andE ₁+Δ₁ transitions of the cubic semiconductors. The effect on these transitions upon irradiation by HeNe laser light, application of small alternating magnetic fields and the influence of both the fields, applied simultaneously, has been investigated. The observed critical point shifts have been interpreted on the basis of changes in the band structure of these thin films. This has been corroborated by theoretically calculating the effective number of electrons contributing to the transition per atom —N _eff. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995.     

Control of Magnetic Properties in (Cd,Mn)Te Quantum Wells Inserted in Pin Diodes

Using photoluminescence and photoluminescence excitation, weinvestigate the magnetic properties of (Cd,Mn)Te quantum wells inserted in pin diodes. Such structures give us the opportunity to tune the carrier density by applying a bias of the order of 1 V. Results obtained in a small magnetic field show the presence of magnetic domains, which persist as long as the quantum well is populated.     

Microhardness and polarity in Cd x Hg1−x Te

The Vickers microhardness of Cd _x Hg_1–x Te alloys has been measured at room temperature as a function of composition and of the nature of the {111} faces for different conduction types. The hardness-composition curve shows a maximum at aboutx = 0.75. On the {111} faces, it has been found that the metal face (A face) is harder than the metalloid face for all studied doping types and is related to the different mobilities of the A(g) and B(g) dislocations. This behaviour is compared with a model previously developed for hardness polarity in GaAs.     

CdSe/Cd(x)Zn1-xS core/shell nanocrystals: core morphology and luminescent property

CdSe cores with rod (an aspect ratio of 1.8, d-5 nm) and spherical (an aspect ratio of 1, d-5 nm) morphologies were fabricated by two kinds of organic approaches through adjusting growth processes. Because of large difference of size and morphology, two kinds of cores revealed different absorption spectra. However, these cores exhibited almost same photoluminescence (PL) spectra with a red-emitting PL peak of around 625 nm. This is ascribed that they have a similar size in diameter. A graded Cd(x)Zn1-xS shell of larger band gap was grown around CdSe rods and spheres using oleic acid as a capping agent. Based on the growth kinetics of CdS and ZnS, interfacial segregation was created to preferentially deposit CdS near the core, providing relaxation of the strain at the core/shell interface. For spherical CdSe cores, the homogeneous deposition of the Cd(x)Zn1-xS shell created spherical core/shell nanocrystals (NCs) with a size of 7.1 nm in diameter. In the case of using CdSe cores with rod morphology, the anisotropic aggregation behaviors of CdS monomers on CdSe rods led to the size (approximately 10 nm in diameter) of spherical CdSe/Cd(x)Zn1-xS core/shell NCs with a small difference to the length of the CdSe rod (approximately 8.9 nm). The resulting spherical core/shell NCs created by the rod and spherical cores exhibited almost same PL peak wavelength (652 and 653 nm for using rod and spherical cores, respectively), high PL efficiency up to 50%, and narrow PL spectra (36 and 28 nm of full with at half maximum of PL spectra for the core/shell NCs with CdSe spheres and rods, respectively). These core/shell NCs provide an opportunity for the study of the evolution of PL properties as the shape of semiconductor NCs.     

The Magnetic Properties of Mn x Fe1−x NiSi (x=0,0.25,0.5,0.75,1) Alloys

The magnetic properties of Mn _x Fe_1?x NiSi (x=0,0.25,0.5,0.75,1) alloys are studied using density functional theory and the WIEN2k package. The exchange correlation potential is treated by generalized gradient approximation (GGA). The total energy calculations of these alloys confirm the stability of the ferromagnetic phase as compared to a nonmagnetic phase. The total magnetic moment is not a linear function of x. By increasing x, it increases and then decreases. The peak position of the magnetic moment is near x=0.75.     

Electrical and optical properties of Hg1-x-y Zn x Mn y Te crystals

Hg_1-x-y Zn _x Mn _y Te (x ≤ 0.10,y ≤ 0.15) crystals were grown, and their electrical and optical properties were studied in the temperature range from 80 to 295 K. Heat treatment of the crystals in Hg vapor made it possible to vary the concentration of electrically active defects and preparen- andp- type materials with various carrier concentrations. The band gaps and band-gap temperature coefficients of Hg_1-x-y Zn _x Mn _y Te were determined from the 80- and 295-K optical absorption spectra.     

Thermal Conductivity of Pb1 – x Mn x Te Single Crystals

The thermal conductivity of Pb_{1 – x} Mn _x Te single crystals is measured in the range 80–300 K. The electronic and lattice components of thermal conductivity in the crystals are evaluated for a parabolic conduction band, arbitrary degeneracy, and elastic scattering of charge carriers. The total thermal conductivity and lattice component are found to decrease with increasing temperature. Increasing the Mn content of the solid solutions also reduces the total and lattice thermal conductivities, while annealing increases them. The density of point defects in the crystals is evaluated. The heat conduction in Pb_{1 – x} Mn _x Te is shown to be dominated by phonons.     

Growth and Electrical Properties of Pb1 – x Mn x Te Crystals

Pb_{1 – x} Mn _x Te single crystals were grown, and their electrical conductivity, thermoelectric power, and Hall coefficient were measured from 80 to 300 K. The results indicate that the transport properties of the crystals are determined by lattice defects, the structure of the valence band, and Mn content.     

Anomalous Hall Effect in Sn1−x−y Mn x Eu y Te and Sn1−x−y Mn x Er y Te Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1?x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Thermal conductivity of tellurium-enriched Pb1 − x Mn x Te single crystals

We have studied the effect of excess tellurium atoms (up to 0.5 at %) on the thermal conductivity of single-crystal Pb_{1 ? x} Mn _x Te (x = 0.04) samples annealed at 570K for 120 h. We have evaluated the lattice and electron thermal conductivities of the samples, their additional thermal resistance due to structural defects, and the coefficient in the expression for the effective phonon scattering cross section. We assume that some of the excess Te atoms fill lead vacancies, thereby reducing the effective phonon scattering cross section.     

Control of luminescence emitted by Cd 1-x Mn x S nanocrystals in a glass matrix: x concentration and thermal annealing

Cd(1-x)Mn(x)S nanocrystals (NCs) were successfully grown in a glass matrix and investigated by photoluminescence (PL), electron paramagnetic resonance (EPR) and magnetic force microscopy (MFM). We verified that the luminescent properties of these NCs can be controlled both by changing the x concentration and by thermal annealing of the samples. The EPR and PL data showed that the characteristic emission of Mn(2+) ions ((4)T(1)-(6)A(1)) is only observed when this magnetic impurity is substitutionally incorporated in the Cd(1-x)Mn(x)S NC core (site S(I)). Besides, it was observed that the emission ((4)T(1)-(6)A(1)) suppression, caused by the Mn(2+) ion presence near the surface (site S(II)) of the Cd(1-x)Mn(x)S NCs, is independent of the host material. The MFM images also confirmed the high quality of the Cd(1 - x)Mn(x)S NC samples, showing a uniform distribution of total magnetic moments in the nanoparticles.     

CdTe/CdMnTe多量子阱的生长和激子复合动力学性质的研究

用分子束外延在GaAs衬底上生长了CdTe/Cd0.8Mn0.2Te多量子 结构,利用X射线衍射（XRD）、低激发密度下的PL光谱和变密度激发的ps时间分辨光谱研究了CdTe/CdMnTe多量子阱的结构和激子复合特性。在变密度激发的ps时间分辨光谱中,发现不同激发密度下发光衰减时间不同,认为它的机理可能是无辐射复合引起的。