We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by pulsed laser annealing. Benefiting from the short time annealing, the hole concentration in Mn-implanted Ge has been increased by two orders of magnitude from 10 18 to over 10 20 cm −3 . Likely due to the high hole concentration, we observe that the longitudinal and Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated ferromagnetism.
In the present work, we have prepared Mn-doped Ge using different annealing approaches after Mn ion implantation, and obtained samples with hole concentrations ranging from 10 18 to 2.1×10 20 cm −3 , the latter being the highest reported so far. Based on the magnetotransport properties of Mn doped Ge, we argue that the hole concentration is a decisive parameter in establishing carrier-mediated ferromagnetism in magnetic Ge.Mn doped GaAs (Ref. 1) and ZnTe (Ref. 2) are considered as the prototype diluted ferromagnetic semiconductors (FMS). In both systems, a large enough hole concentration is a prerequisite to establish the carrier-mediated ferromagnetism, which allows the electrical control over magnetism. 3 Practically, it is highly desirable to realize a FMS compatible with silicon technology. Whereas attempts to fabricate magnetically doped silicon (Si:Mn) have been rather discouraging, 4 germanium appears to be a promising candidate due to the wellaccepted substitutional occupation of Mn in the Ge matrix. 5,6,7,8 The substitutional Mn ions produce double-acceptor levels and supply holes. 9 The ferromagnetism in Ge:Mn has been nonquantitatively but plausibly explained by the formation of bound magnetic polarons (BMP). 10,11,12,13 According to the model by Kaminski and Das Sarma, 14 the percolation of BMP over the entire sample depends on the temperature and on the hole concentration. If GaAs:Mn can be any guide, a large enough hole concentration is required to establish carrier-mediated ferromagnetism. 15,16
Differential cross sections have been measured for He(2 3S)+Ne at kinetic energies between 28 and 370meV. For energies above 90meV the elastic cross sections show Sttickelberg oscillations from curve crossings, which lead to the energy exchange process: He(23 S) +Ne~He(t 1S) + Ne(2p 5 4s, 3 d, 4p). Differential cross sections for this inelastic process could be measured above 200meV..A fit to the data gives the potentials for He(2 3S)+Ne and, less accurately, for He +Ne*. These results offer a simple explanation, why the exothermic pumping process of the infrared lines of the HeNe laser has a threshold of about 80 meV and a small cross section. l. lntroductionThree different types of electronic excitation transfer can be distinguished for collisions of metastable helium atoms (He*) with groundstate atoms or molecules: I. For He* +He collisions the excitation transfer is due to the inherent symmetry of the problem and can be treated as an elastic process [1][2][3][4]. 2. For He*+Ar, Kr, Xe and any molecular collision Penning ionization can occur besides elastic scattering, because the excitation energy of the metastable helium atom, 19.8 eV for He(2 3S), is higher than the ionization energy of all atoms and molecules save Ne [5-73. 3. For He* +Ne collisions an ionizing collision is not possible at our kinetic energies due to the high ionization energy of the Ne atom (21.6eV). But transfer of the excitation energy from He* to a highly excited state of Ne can occur. This energy exchange plays a large role in HeNe gas discharges, and it is the dominant pumping process of the HeNe laser [8]. It has been shown recently by Miller and Morgner [9] that Penning ionization (excitation to a continuum) and energy transfer to highly excited states (excitation to a quasicontinuum) is not only conceptually very similar, but can be treated theoretically in a uniform manner. The principle of the HeNe laser is shown schematically in Fig. 1. He atoms are excited by electron collisions to their metastable states and transfer their energy to the excited Ne states, which are the upper laser levels. Some of the laser transitions are indicated in the figure. For isolated neon atoms roughly half of them end up in one of the two metastable states of the 2p53s configuration. The lifetimes of the metastable states 3P 0 and 3P 2 are longer than 0.8s [10 I. In a beam experiment these long living excited atoms are easily detected and can be used as a probe in the study of the energy transfer processes. Because of its importance this reaction was studied in many experiments [11][12][13][14][15]. All these experiments used discharges or afterglows which have a wide spread in collision energy, while we performed a crossed molecular beam experiment with good angle and velocity resolution. The technique of molecular beams has been improved considerably during the last years and is now an excellent tool to study collision processes. The use of nozzle beams gives the opportunity for beams in the thermal energy range with good velocity resolution and ...
In this work, amorphous silicon films with preformed a-Si lines were crystallized using a diode pumped solid state green laser irradiating at 532 nm. The possibility of controllable formation of grain boundaries was investigated. The crystallization processes in the rapidly melted silicon films were discussed. The influence of the crystallization parameters (i.e., energy density, scan velocity, etc.) and structure type (i.e., with and without preformed lines) on properties of the crystallized films was studied. The laser treatment with an energy density of 1.00 J/cm2 at a laser pulse overlapping of 90% provided the optimal crystallization process with predefined grain boundary location. X-ray diffraction (XRD), SEM and AFM microscopy have been used to characterize the crystallized silicon films.
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