BAND-STRUCTURE OF MG1-XZNXSYSE1-Y

The empirical pseudopotential method within the virtual crystal approximation is used to calculate the band structure of Mg1-xZnySySe1-y, which has recently been proved to be a potential semiconductor material for optoelectronic device applications in the blue spectral region. It is shown that MgZnSSe can be a direct or an indirect semiconductor depending on the alloy composition. Electron and hole effective masses are calculated for different compositions. Polynomial approximations are obtained for both the energy gap and the effective mass as functions of alloy composition at the GAMMA valley. This information will be useful for the future design of blue wavelength optoelectronic devices as well as for assessment of their properties.

EMPIRICAL PSEUDOPOTENTIAL BAND-STRUCTURE CALCULATION FOR ZN1-XCDXSYSE1-Y QUATERNARY ALLOY

The band structure of the Zn1-xCdxSySe1-y quaternary alloy is calculated using the empirical pseudopotential method and the virtual crystal approximation. The alloy is found to be a direct-gap semiconductor for all x and y composition. Polynomial approximation is obtained for the energy gap as a function of the composition x and y. Electron and hole effective masses are also calculated along various symmetry axes for different compositions and the results agree fairly well with available experimental values.

Correlation of electrical and optical properties in dually Cd+ and N+ ion-implanted GaAs

Cd in GaAs is an acceptor atom and has the largest atomic diameter among the four commonly-used group-II shallow acceptor impurities (Be, Mg, Zn and Cd). The activation energy of Cd (34.7 meV) is also the largest one in the above four impurities, When Cd is doped by ion implantation, the effects of lattice distortion are expected to be apparently different from those samples ion-implanted by acceptor impurities with smaller atomic diameter. In order to compensate the lattice expansion and simultaneously to adjust the crystal stoichiometry, dual incorporation of Cd and nitrogen (N) was carried out into GaAs, Ion implantation of Cd was made at room temperature, using three energies (400 keV, 210 keV, 110 keV) to establish a flat distribution, The spatial profile of N atoms was adjusted so as to match that of Cd ones, The concentration of Cd and N atoms, [Cd] and [N] varied between 1 x 10(16) cm(-3) and 1 x 10(20) cm(-3). Two type of samples, i.e., solely Cd+ ion-implanted and dually (Cd+ + N+) ion-implanted with [Cd] = [N] were prepared, For characterization, Hall effects and photoluminescence (PL) measurements were performed at room temperature and 2 K, respectively. Hall effects measurements revealed that for dually ion-implanted samples, the highest activation efficiency was similar to 40% for [Cd] (= [N])= 1 x 10(18) cm(-3). PL measurements indicated that [g-g] and [g-g](i) (i = 2, 3, alpha, beta,...), the emissions due to the multiple energy levels of acceptor-acceptor pairs are significantly suppressed by the incorporation of N atoms, For [Cd] = [N] greater than or equal to 1 x 10(19) cm(-3), a moderately deep emission denoted by (Cd, N) is formed at around 1.45-1.41 eV. PL measurements using a Ge detector indicated that (Cd, N) is increasingly red-shifted in energy and its intensity is enhanced with increasing [Cd] = [N], (Cd, N) becomes a dominant emission for [Cd] = [N] = 1 x 10(20) cm(-3). The steep reduction of net hole carrier concentration observed for [Cd]/[N] less than or equal to 1 was ascribed to the formation of (Cd, N) which is presumed to be a novel radiative complex center between acceptor and isoelectronic atoms in GaAs.

Correlation between Er3+ emission and the microstructure of a-SiOx : H < Er > films

Photoluminescence (PL) from Er-implanted hydrogenated amorphous silicon suboxide (a-SiOX:H(x<2.0)) films was measured. Two luminescence bands with maxima at lambda congruent to 750 nm and lambda congruent to 1.54mum, ascribed to the a-SiOX:H intrinsic emission and Er3+ emission, were observed. Peak intensities of the two bands follow the same trend as a function of annealing temperature from 300 to 1000degreesC. Micro-Raman results indicate that the a-SiOX:H films are a mixture of two phases, an amorphous SiOX matrix and amorphous silicon (a-Si) domains embedded there in. FTIR spectra confirm that hydrogen effusion from a-SiOX:H films occurs during annealing. Hydrogen effusion leads to a reconstruction of the microstructure of a-Si domains, thus having a strong influence on Er3+ emission. Our study emphasizes the role of a-Si domains on Er3+ emission in a-SiOX:H films.

Theoretical foundation of Zisman's empirical equation for wetting of liquids on solid surfaces

Theories of wetting of liquids on solid surfaces under the condition that van der Waals force is dominant are briefly reviewed. We show theoretically that Zisman's empirical equation for wetting of liquids on solid surfaces is a linear approximation of the Young-van der Waals equation in the wetting region, and we express the two parameters in Zisman's empirical equation in terms of the dielectric polarizabilities of the solid and liquids. The materials contained in this paper are suitable for physics teaching of wetting phenomena for undergraduate, graduate, general physicist, etc.

Effects of magnetic configuration on hot electrons in highly charged ECR plasma

To investigate the hot electrons in highly charged electron cyclotron resonance (ECR) plasma, Bremsstrahlung radiations were measured on two ECR ion sources at the Institute of Modern Physics. Used as a comparative index of the mean energy of the hot electrons, a spectral temperature, Tspe, is derived through a linear fitting of the spectra in a semi-logarithmic representation. The influences of the external source parameters, especially the magnetic configuration, on the hot electrons are studied systematically. This study has experimentally demonstrated the importance of high microwave frequency and high magnetic field in the electron resonance heating to produce a high density of hot electrons, which is consistent with the empirical ECR scaling laws. The experimental results have again shown that a good compromise is needed between the ion extraction and the plasma confinement for an efficient production of highly charged ion beams. In addition, this investigation has shown that the correlation between the mean energy of the hot electrons and the magnetic field gradient at the ECR is well in agreement with the theoretical models.中文摘要：ECR(电子回旋共振)离子源是产生稳定的强流多电荷态离子束流最有效装置。全永磁 ECR 离子源因其独特的特点为很多中小型多电荷态离子束流实验平台与离子注入机等系统所采用，为后者产生重复性好、稳定性强的多电荷态离子束流。本文着重论述了中国科学院近代物理研究所研制的几台全永磁多电荷态ECR离子源及其特性与典型性能，如能产生强流高电荷态离子束流的高性能全永磁离子源LAPECR2，能产生强流中低电荷态离子束流的LAPECR1，能产生多电荷态重金属离子束流的LAPECR1-M等。这些性能稳定的离子源为提高近代物理研究所相关试验平台的性能提供了关键的束流品质保障。