Jianbao Wang

Effects of quantum confinement and strain in Zn1-xCdxSe/ZnSe strained-layer superlattices

The effects of strain and quantum confinement in Zn1-xCdxSe/ZnSe strained-layer superlattices grown by molecular beam epitaxy on the GaAs(100) substrates were studied using photoluminescence (PL) at 4.4 K. The sample with 30 periods and total thickness of 3600 AA was directly grown on the substrate without a buffer layer. The PL spectrum shows a single peak that is attributed to the free excitons between the lowest electron subband and ground heavy-hole subband of the Zn1-xCdxSe wells. The blue shifts of the excitonic peaks in the PL spectra induced by the effects of strain and quantum confinements were calculated on the basis of deformation potential theory and Bastards method, respectively. In addition, the temperature dependence of the PL features of the sample was studied both theoretically and experimentally in detail. The experimental results coincide with the theoretical predictions very well.

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.

Photovoltaic investigations of interband transitions in SiGe/Si multiple quantum wells

Photovoltaic effect measurements have been carried out for the strained Si1−xGex/Si multiple quantum well samples. The absorption structures of the transitions from heavy‐hole ground state (HH0) to the unconfined conduction (EC) states, light‐hole ground state to EC states as well as the transitions of phonon (transverse acoustic and transverse optical)‐assisted HH0‐EC excitons of the sample with x=0.25 are identified by the photovoltaic measurement at the temperature of 18 K. The agreement between the experimental results and the calculations based on simple theoretical models is fairly good. Due to the rapid increase of the background absorption, the structures of the transitions from excited hole subbands to the conduction states are very difficult to identify. For the sample with x=0.5, the absorption related to the defects originated from the partial relaxation of the large misfit strain between Si0.5Ge0.5 and Si gives a great influence upon the identification of the interband absorption structures o...

Transport properties of a Fe0.04Si0.96 film at low temperatures

The transport properties of a Fe0.04Si0.96 film are studied. From the relationship between the resistivity of the film and the temperature, two activation energies, 40 and 2.5?meV, are obtained in two low-temperature regions below 50?K. Temperature-dependent magnetoresistance (MR) shows a peak feature with the largest value of 935% at 30?K. MR values are also measured under different configurations of field direction with respect to the current direction and the film plane, and their relationship in magnitude is discussed in terms of curving of carrier trajectories and shrinkage of wave function of localized states in a magnetic field.

A deep level transient spectroscopic study of boron-ion-implanted single quantum wells

The defects induced by boron-ion implantation with a relatively low dosage of 1 x 10 12 cm -2 in Si 1-x Ge x /Si single quantum wells are studied by deep level transient spectroscopy (DLTS). For low Ge content x, a defect level H 2 at an energy of 0.52 eV above the silicon valence band edge was found in the well region and its boundaries. For samples with higher Ge content, such that the strain is released, an electron trap E 2 rather than H 2 is formed by the ion implantation. Rapid thermal annealing at 600°C removes most of the H 2 defects induced by the ion implantation without changing the properties of the quantum well.

Hot Wall Epitaxial Growth of Diluted Magnetic Semiconductor Zn 1-x Mn x Se(111) GaAs(100) Substrate

We report the growth of Zn 1-x Mn x Se films on GaAs(100) by hot wall epitaxy (HWE) up to a Mn concentration of 52%. The crystal structures of Zn 1-x Mn x Se layers were characterized by x-ray diffraction and Raman scattering. For the first time Zn 1-x Mn x Se(111) layers on GaAs(100) substrate have been grown and mixed phases of zinc-blende and hexagonal structure have been observed over the range 0.19≤x≤0.52.