We report the growth of zinc-blende ZnSe/MgS superlattices ͑SLs͒ on GaAs ͑001͒ substrates. The SLs were grown with metalorganic vapor phase epitaxy by selecting appropriate precursors for Mg and S. MgS naturally forms rocksalt structures, but zinc-blende MgS layers were grown. The lattice constant of MgS was estimated to be 5.59 Å. X-ray diffraction measurements show that the ZnSe/MgS SLs are grown coherently to the GaAs substrates up to the total thicknesses of ϳ3000 Å. © 1996 American Institute of Physics. ͓S0003-6951͑96͒04506-8͔Wide band gap II-VI semiconductor superlattices ͑SLs͒ have attracted much attention for realizing blue/green light emitting devices. It is well known that the band offset plays an important role in determining the characteristics of heterostructures. However, most of II-VI heterostructures proposed up to now have band offsets localized to either conduction or valence band edges. In the case of ZnSe/ZnSSe SLs, the band offset is localized to valence bands, while the conduction band discontinuity is very small. 1 For ZnMnSe/ AnMnSe/ZnSe SLs, the heterojunctions exhibit very small valence band offsets. 2 Recently II-VI compound semiconductors containing group-IIA elements like Mg are expected to be the most promising materials to realize heterostructures. [3][4][5][6][7][8] In particular, ZnMgSSe 3-5,7 has been extensively studied since Zn͑Cd͒Se/ZnMgSSe heterostructures can confine both electrons and holes. Nakayama et al. demonstrated first continuous-wave operation of blue-green laser diodes using ZnMgSSe as the cladding layer. 9 ZnMgSSe films of the zinc-blende structure can be grown on GaAs ͑001͒ substrates, and the band gap energies can be changed from 2.8 to 4 eV maintaining lattice matching to the GaAs substrates. 3 However it is reported that the crystalline quality of ZnMgSSe layers tends to be worse with the increase of the Mg composition. For binary Mg chalcogenides of the zinc-blende structure, the lattice constants of 5.89 and 5.62 Å and the band gap energies of 3.6 and 4.5 eV are estimated for MgSe and MgS, respectively. 3 However the binary compound MgS naturally forms the rocksalt structure, and the reported lattice constants and bandgap energies were extrapolated from the experimental data on the quaternary alloys.Although the zinc-blende MgS has not previously been reported, the largest band gap among II-VI semiconductors is estimated in MgS. Therefore in the combination of ZnSe and MgS, the band offsets of the conduction band and the valence band are expected to be very large. 10 This will offer large quantum confinement effects on both electrons and holes. In addition, ZnSe/MgS heterostructures will have small lattice mismatch of 0.87% and are reasonably latticematched to GaAs substrates. These attractive features motivate us to try to grow the zinc-blende MgS. In this letter, we report the first successful epitaxy of zinc-blende ZnSe/MgS SLs on GaAs ͑001͒ substrates.The growth apparatus used in the present experiment was an atmospheric-pressure metalorganic vapor phas...

Optical properties of a ZnSe/MgS superlattice (SL) were studied by reflection and photoluminescence (PL) spectroscopies. Excitonic structures were clearly observed in the reflection spectra up to room temperature, and the exciton absorption peak energy and linewidth were well coincident with the PL peak energy and linewidth. The origin of the lowest luminescence peak was indicated to be C1-HH1 exciton up to room temperature. The lineshape broadening due to longitudinal-optical-phonon scattering of excitons is much decreased in this SL compared to bulk ZnSe.

Excitonic properties of newly developed zinc-blende ZnSe/MgS superlattices ͑SL's͒ were measured by reflection spectroscopy. The modification of the excitonic peaks by the multiple reflection in the SL films was treated theoretically and a fitting method to estimate the exciton absorption peak positions and exciton linewidths was developed. Although zinc-blende MgS did not exist before, excellent optical properties were observed in the ZnSe/MgS SL's. Excitonic structures were clearly observed from 13 K up to the measured room temperature. In spite of strong ionicity of MgS barrier layers in the ZnSe/MgS SL's, the reduction of exciton-LO-phonon coupling was clearly observed in narrower wells. This indicates that the quantum confinement effect on excitons is large due to the large band offsets and it overcomes the enhancement of exciton-LO-phonon scattering due to high ionicity in barrier layers. ͓S0163-1829͑97͒03307-9͔

A one-boson-exchange potential (OBEP) with retardation represented in coordinate space is proposed, that produces a good fit to the experimental data such as the nuclear phase shifts, the deuteron properties and two-nucleon low-energy parameters. In. addition to the scalar IJo and iJ mesons, the well-established n, "YJ, ()) a~d p mesons have .been exchanged in vur OBEP. In the core region the hard core, Gaussian soft core and velocitydependent core potentials are adopted. The characteristics of the retardation :J.re discussed in detail as compared with those given in momentum space calculations. The OBEP's with and without retardation reproduce essentially the same phase shifts in spite of very different potential shapes, in particular in the central-to-tensor ratio.

Several kinds of phase-shift equivalent one-boson-exchange potential (OBEP) including velocity-dependent term are constructed so as to reproduce the two-nucleon data. Here we propose an "extended Green's method" to treat the velocity-dependent tensor potential. Nuclear matter and neutron matter properties are calculated for our nonstatic OBEP. The phase-shift equivalent OBEP's, however, give different nuclear matter properties owing to the difference of the softness of core potential and the retardation. The retardation strengthens the tensor-to-central ratio of OBEP in the triplet even state, and reduces the nuclear matter binding energy per particle by 2.6~5.0 MeV with a decrease in density by 0.05~0.08 fm-1 • However, the retarded effect on neutron matter is relatively small.