Daming Huang

GERMANIUM DOTS WITH HIGHLY UNIFORM SIZE DISTRIBUTION GROWN ON SI(100) SUBSTRATE BY MOLECULAR BEAM EPITAXY

The growth of very uniform Ge dots on Si(100) is achieved by using molecular beam epitaxy. The atomic force microscopy and the transmission electron microscopic observations illustrate that the size uniformity of the dots is not worse than ±3%, i.e., the base dimension is 100±3 nm. The Raman spectrum reveals a peak downward shift of Ge-Ge mode caused by the phonon confinement in the Ge dots. A very narrow photoluminescence peak with the width of 1.6 meV at the energy of 0.767 eV is observed at the temperature of 16 K. We attribute this peak to the free exciton longitudinal acoustic phonon replica originated from the Ge dots.

Crystal structure and Raman scattering in Zn1−xMgxSe alloys

Zn1−xMgxSe alloys have been grown on (100) GaAs substrates by molecular beam epitaxy. Their crystal structures are determined form x‐ray diffraction spectra and are found to be zinc blende, rocksalt, and their mixture for x<0.5, x=1, and x∼0.6, respectively. The Raman spectra are measured and show two‐mode behavior for those alloys with zinc blende structure. The long‐wavelength frequencies of ZnSe‐ and MgSe‐like optical phonons are determined and the results can be expressed as linear functions of x. The first‐order Raman spectra are observed for MgSe and Mg‐rich Zn1−xMgxSe alloys with rocksalt structure. Those Raman spectra are attributed to the scattering from optical phonons activated by disorders and impurities, and their line shapes represent the phonon density of states.

Effect of Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate

Abstract Cross-sectional transmission electron microscopy and Raman spectra are used to investigate the effect of monolayer Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate. Without Sb, inner diffusion of the epilayer Ge atoms into the Si substrate occurs, resulting in a severe intermixing of atoms at the Ge–Si interface. With the presence of Sb as a surfactant, the inner diffusion of epitaxial Ge atoms into the Si substrate is greatly suppressed. This result is explained in terms of the strain relief in the Si substrate by the Sb surfactant.

Phonon modes of ZnS1−xTex alloys epitaxially grown on (100) GaAs substrates

ZnS1−xTex(0<x<1) alloys grown on (100) GaAs substrates by molecular beam epitaxy are investigated using the x-ray diffraction and Raman scattering. The frequencies of long wavelength ZnTe-like and ZnS-like longitudinal optical phonons determined from Raman scattering show linear variation with the composition x. The frequency of the zone-center optical phonons as a function of x of the ZnS1−xTex mixed crystal shows a typical two-mode behavior, which is in good agreement with the theoretical results from a modified random-element isodisplacement model.

Thickness dependence of exciton and polariton spectra from ZnSe films grown on GaAs substrates

ZnSe films with thicknesses from 0.05 to 1.45 μm were grown on GaAs substrates by molecular beam epitaxy. Low temperature photoluminescence (PL) and reflectance spectra are presented to show the thickness dependence of the exciton and polariton properties in the films. In addition to sharp PL peaks from free and donor bound excitons, an acceptor bound exciton peak was observed in the thin films and its intensity decreases rapidly with the film thickness. The PL characteristics show the acceptor centers being the defect states near the ZnSe/GaAs interface. The classical theory of exciton–polaritons was used to calculate the reflectance spectra and compared to the measured results. The comparison reveals the effects of strain, surface, and interface on the reflectance spectra from both heavy- and light-hole excitons. In addition to the strain-induced light- and heavy-hole splitting, the light-hole excitons show a larger damping and less sensitivity to the surface dead layer than the heavy-hole excitons. Whe...

Surfactant influence on the Ge heteroepilayer on Si(0 0 1) studied by X-ray diffraction and atomic force microscopy

X-ray diffraction and atomic force microscope were used to investigate the effect of Sb atoms as a surfactant on the morphology and strain relaxation of 6 nm-thick Ge epilayers grown on Si(0 0 1). Without Sb atoms, Ge atoms accumulate and form fully relaxed islands. With the presence of Sb atoms, the Ge epilayer is smooth with a roughness of 0.28 nm and partially relaxed.

High efficient biexciton photoluminescence observed from single ZnCdSe quantum wells with continuous wave cold carrier generation

Biexciton photoluminescence was observed from single ZnCdSe quantum wells with excitation densities at least three orders of magnitudes lower than those reported in the literature. The very efficient biexciton photoluminescence is essentially due to the cold carrier generation under which the biexciton dissociation by hot carrier collision is greatly suppressed.

Raman spectra of Zn1−xMgxSySe1−y quaternary alloys

Semiconductor quaternary alloys Zn1−xMgxSySe1−y were grown on GaAs substrates by molecular beam epitaxy. The crystal structures were determined from x‐ray diffraction spectra. The Raman spectra of both perpendicular and parallel polarization geometries were measured. The following long‐wavelength optical‐phonon modes were identified: ZnSe‐like TO and LO modes, and MgSe‐like and ZnMgS‐like LO modes. For the alloys with the same Mg composition x, the vibration frequencies of ZnSe‐like TO and LO modes were observed to change linearly with S composition y for y<0.5. The vibration frequency of the MgSe‐like LO mode was also observed to change linearly with y for 0.1

Effects of rapid thermal annealing on electrical properties of heavily doped silicon molecular‐beam‐epitaxial layer with B2O3 doping source

The effect of rapid thermal annealing (RTA) on the electrical properties of heavily boron‐doped silicon epilayer grown at 680 °C by molecular‐beam epitaxy and coevaporation of B2O3 is studied. Through the RTA process, the boron clusters in the epilayer break into boron atoms and the interstitial boron enters the substitutional site. These two effects cause the improvement of the electrical properties of the silicon epilayer. After RTA at 1100 °C for 10 s, the hole concentration can reach 3.1×1020 cm−3 with the mobility of 39 cm2/V s, which is about the same as that of the bulk silicon, while the oxygen concentration is less than 1018 cm−3. It is also shown that the full width at half‐maximum of the x‐ray‐diffraction rocking curve decreases as the RTA temperature increases. The RTA process does not affect the steep distribution of carrier concentration at the epilayer/substrate interface which differs by about 6 orders of magnitude across the interface with the leading edge slope of 25–30 nm/decade.

Structural characteristics of diluted magnetic semiconductor Zn1 − xMnxSe films grown by hot wall epitaxy on GaAs(100) substrates

Abstract In this paper, we report the growth of Zn 1 − x Mn x Se films on GaAs(100) substrates by hot wall epitaxy up to an Mn concentration of x = 0.52. The crystalline structures of the Zn 1 − x Mn x Se layers were characterized by X-ray diffraction and Raman scattering. At a low growth rate of 1 μm/h, Zn 1 − x Mn x Se films have demonstrated pure zinc-blende structure up to a composition of x = 0.50. At a high growth rate of above 2 μm/h, the films exhibited mixed phases of zinc-blende and hexagonal structures over the range 0.19 ≤ x ≤ 0.52. The achievement of (111) oriented single crystal Zn 1 − x Mn x Se epilayers on GaAs(100) substrates and its explanation are presented.