jia Chen

Ferromagnetic properties and structures of the Mn-implanted GaAs semiconductor

Submicron ferromagnets have been successfully incorporated into semi-insulating (001) GaAs crystals by Mn+ ion implantation and subsequent rapid annealing. Magnetization measurements reveal room-temperature ferromagnetism. The structural and compositional properties of crystallites have been analyzed by transmission electron microscopy, energy dispersion x-ray spectrum, and electron microdiffraction. The results show that crystallites of MnGa and MnAs with a small amount of Ga are formed. Atomic force microscopy and magnetic force microscopy images indicate that the single-domain magnetic state is dominant in submicron ferromagnets under our annealing conditions (750 °C–900 °C).

Magnetization and magnetic susceptibility of the diluted magnetic semiconductors Zn1-xCoxS and Zn1-xCoxSe

Magnetization measurements have been done at 1.5 K and magnetic fields up to 7 T by using extraction method on the samples with x=0.0055, 0.048, 0.063 for Zn1−xCoxS and x=0.0097, 0.030, 0.037, 0.042 for Zn1−xCoxSe. In both Co‐based systems, the magnetization increases with x. A modified Brillouin function fits the data and the fitting parameters T0( ≳ 0) and Seff are obtained. These results reflect that there exists a strong antiferromagnetic interaction among Co++ ions and the antiferromagnetic interaction in Zn1−xCoxSe is stronger than that in Zn1−xCoxS. Magnetic susceptibility was measured in the temperature range 1.5 K≤T≤300 K by using a vibrating‐sample magnetometer. The susceptibility displays a high‐temperature Curie–Weiss behavior. From quantitative analysis we obtain the nearest‐neighbor Co++–Co++ exchange integral constant J1/kB for sulfides and selenides to be −51±6 K and −57±8 K, respectively. This value is at least three times as large as that in their Mn‐based counterparts, and we confirm th...

Optical study of self‐annealing in high‐current arsenic‐implanted silicon

Silicon samples implanted with As in the 1014–1016 cm−2 dose range and at a beam current density of 10 μA cm−2 were analyzed by reflectance and Rutherford backscattering measurements. The E1 and E2 reflectance structures disappear at a dose of 1015 cm−2 and reappear red shifted at 1016 cm−2, as a consequence of the self‐annealing during high‐dose‐rate implantation. The red shift of E1 and E2 has been quantitatively accounted for by calculations in a multilayer damage structure. The free‐carrier density determined by the infrared response correlates with the substitutional concentration of As measured by channeling effect. The optical response has been measured in laser annealed samples for comparison.

Faraday-rotation spectra of the diluted magnetic semiconductor Cd1−xGdxTe

The Faraday rotation as a function of photon energy for Cd1−xGdxTe with x=0.012 and 0.030 in the temperature range of 85–300 K has been measured. The Verdet constant includes a positive part and negative part due to pure Zeeman and sp-f exchange interaction contributions, respectively. The sp-f exchange interaction parameter has been determined in Cd1−xGdxTe: (q=9.3×10−4 at 85 K and q=5.3×10−4 at 300 K) in terms of a microscopic model, which takes into account the k dependence of the spin-spin exchange interaction. The normalization parameter C has been found to be independent of both the compositions of Gd and temperature. The agreement between the data and the microscopic model is very good in the whole spectra region even far from the band gap.

Giant Faraday rotation in diluted magnetic semiconductor Cd1−χFeχTeχ

Abstract The Faraday rotation as a function of photon energy and composition for Cd1−xFexTe with x=0.01, 0.03, 0.06 in temperature range 70 K to 300 K has been measured. The samples exhibit giant Faraday rotation characteristic of diluted magnetic semiconductors as in Cd1−xMnxTe. Exciton energy at Γ and band gap energy at L points of Brillouin zone for different composition have been obtained for the first time in terms of the multioscillator model.

Magnetic and optical properties of Cd1−xGdxTe diluted magnetic semiconductor

We report on a new type of diluted magnetic semiconductor materials with rare-earth ions: Cd1−xGdxTe. Magnetization measurements have been done at 1.5 K with magnetic fields up to 7T. A modified Brillouin function fits the data very well and the fitting parameters To ( > 0) and Seff are obtained. The susceptibility displays a high temperature Curie-Weiss law behavior when x ≤ 0.03, the value of GdGd ions exchange integral constant has been evaluated. The absorption edge shifts toward the low energy with increase of x.

Magnetization and magnetic susceptibility of the diluted magnetic semiconductor Cd1−xMnxGa2Se4

Results of experiments done to measure the magnetization and magnetic susceptibility in Cd1−xMnxS are given. The measurements were performed on the samples with x=0.03, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, and 0.45 in the temperature range 1.5 K≤T≤300 K and with magnetic fields up to 7 T by using a vibrating‐sample magnetometer and the extraction method. A modified Brillouin function fits the magnetization data and the fitting parameters T0 and xeff are obtained at T=1.5 K for different compositions. The susceptibility displays a high‐temperature Curie–Weiss behavior. From quantitative analysis we obtain the value of the exchange integral constant 2J/kB to be −25.9 K. By using our results in conjunction with a direct measurement of the nearest‐neighbor exchange JNN from high‐field magnetization steps and Raman scattering, we obtain an estimate of the next‐nearest‐neighbor exchange constant J2/kB = −4.7 K.

Optical properties of Cd1−xMnxTe∕Cd1−yMnyTe superlattices with high difference of Mn concentration between wells and barriers

We studied the optical properties of Cd1−xMnxTe∕Cd1−yMnyTe semiconductor superlattices with medium (x=0.3,y=0.01) and high (x=0.8,y=0) difference of the Mn concentration between wells and barriers, by means of photoluminescence and photoreflectance spectroscopy. Photoluminescence allows us to study the emission due to the fundamental heavy (H) hole 11H interminiband excitonic transition and evidences the emission characteristics. Photoreflectance reveals several heavy and light (L) holes interminiband excitonic transitions, up to the 33H. The experiments are in good agreement with the theory with an envelope-function approximation approach, taking into account strain effects due to lattice mismatch between wells and barriers. The combined use of photoluminescence and photoreflectance gives a complete information on the electronic configuration of these Cd1−xMnxTe∕Cd1−yMnyTe superlattices that can find specific applications in spintronic devices.

Spectroscopic ellipsometry study of Cd1-xMnxTe/CdTe superlattices

We studied, by means of spectroscopic ellipsometry, dilute magnetic Cd1−xMnxTe∕CdTe semiconductor superlattices and Cd1−xMnxTe thin films grown by molecular beam epitaxy. In superlattices, the pseudodielectric function measured by ellipsometry shows specific features related to the excitonic transition between quantized minibands. In thin films, ellipsometry allows the clear identification of the energy gap. Additionally, critical point transitions are observable both in the spectra of the superlattices and films. Photoluminescence experiments have also been measured in order to evidence the fundamental interminiband excitonic transitions in superlattices and the energy gap in thin films, respectively. The electronic structure of the superlattices has been calculated in the framework of the envelope function approximation and compared with the experimental spectra. Ellipsometry appears to be a suitable technique to monitor the molecular beam epitaxy growth, ultimately also in situ, of dilute magnetic low-...

Studies of photoreflectance spectra in Cd1−xMnxTe/CdTe superlattices with high compositions

Cd1−xMnxTe/CdTe superlattices were grown by molecular beam epitaxy with a CdTe buffer layer on GaAs(001) substrate. Photoreflectance spectra were performed on Cd1−xMnxTe/CdTe superlattices with high compositions of x=0.4, 0.8 at room temperature and liquid nitrogen temperature. The exciton transitions related to the heavy (H) and light (L) holes of 11H, 11L, 22H, and 33H are observed. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with the photoreflectance measurement results except x=0.8 of 33H. Photoluminescence measurements were also performed at room temperature and low temperature in order to compare with our photoreflectance results. Our results show that the photoreflectance spectroscopy technique is a powerful probe for the study of quantized state structures in superlattices systems.