Yasutomo Kajikawa

Optical Matrix Elements in (110)-Oriented Quantum Wells

Optical matrix elements at the Brillouion zone center in (110)-oriented quantum wells (QWs) for linearly polarized light are theoretically investigated on the basis of an envelope-function approximation. For linear polarization parallel to the QW planes, the optical matrix elements in (110) QWs depend on the polarization direction, which is in contrast with polarization-independent character in (001)- or (111)-oriented QWs.

Growth of TlGaAs by low-temperature molecular-beam epitaxy

Abstract TlGaAs and GaAs were grown by molecular-beam epitaxy at temperatures lower than 350°C and were investigated by means of X-ray diffraction as well as by secondary ion mass spectrometry combined with Rutherford backscattering spectrometry. At the growth temperature of 250°C, the incorporation of Tl into Tl x Ga 1− x As was limited to x =1.2%, while the limit was extended beyond 2.8% at the growth temperature of 200°C. Taking into account the lattice expansion effect of As antisites, the expression of the lattice mismatch of Tl x Ga 1− x − ω As 1+ ω to GaAs is deduced as a function of the Tl content x .

Optical anisotropy of (11l)-oriented strained quantum-wells calculated with the effect of the spin-orbit split-off band

We theoretically investigate the polarization anisotropies of the interband transitions in heteroepitaxial layers of zinc-blende type semiconductors pseudomorphically grown on (11l) substrates with arbitrary l. As the grown layers, quantum well (QW) layers, as well as layers which are thick enough to be regarded as the bulk, are investigated on the assumption that the strain due to the lattice mismatch is not released at all and is fully involved. Calculation of polarization-dependent optical matrix elements at the Brillouin-zone center is carried out based on the multiband effective-mass theory with and without the spin-orbit split-off (SO) band. For the QW, an infinite-high-barrier model is adopted. The calculated results are presented for GaxIn1−xP heteroepitaxial layers having various Ga contents grown on (11l) GaAs substrates. The dependence of polarization anisotropies upon lattice mismatch, quantum confinement, and substrate orientation is discussed in connection with the effect of mixing between h...

Surface diffusion and sticking coefficient of adatoms to atomic steps during molecular beam epitaxy growth

The surface diffusion of adatoms coming from the vapor phase during molecular beam epitaxy growth is examined theoretically for the case in which the sticking coefficient of adatoms to atomic steps in 1/n. It is derived that the surface diffusion length is n times as large as the distance between neighboring two-dimensional nuclei. The temporal evolution of the surface morphology on the atomic-layer scale is also investigated. It is shown that flat surfaces grow in a layer-by-layer mode, even when the sticking coefficient is smaller than unity. It is demonstrated that the growth mode on vicinal surfaces depends on whether not the surface diffusion length but the distance between neighboring nuclei is larger than the terrace width on the surface.

X-Ray Diffraction Measurements on Lattice Mismatch of InTlAs Grown on InAs Substrates

InTlAs layers were grown by molecular-beam epitaxy on InAs(001) substrates, and their lattice mismatch to the substrate was characterized by X-ray diffraction measurements. In each X-ray rocking curve, a distinct peak of InTlAs was observed at a higher diffraction angle than the substrate peak, indicating a smaller lattice constant of InTlAs than InAs. The lattice mismatch, δ=(aepi-asub)/asub, was estimated to be -0.08% for a sample whose thallium composition x of In1-xTlxAs was determined to be 0.12(±0.02)% by Rutherford backscattering spectrometry.

Effect of Tl content on the growth of TlGaAs films by low-temperature molecular-beam epitaxy

TlGaAs layers with various Tl contents have been grown on GaAs(001) substrates by solid-source molecular-beam epitaxy at a substrate temperature of 210 °C and an As/Ga beam equivalent pressure ratio of 100. The Tl content was characterized by Rutherford backscattering spectrometry, secondary-ion mass spectrometry, and electron microprobe analysis. Nomarski microscope observation revealed that the surfaces of the TlxGa1−xAs layers were mirror like until a Tl content of x=7.0% while Tl droplets appeared on the surfaces of samples with a Tl content of x=7.7%. X-ray diffraction (XRD) curves showed clearly resolved epi-layer peaks until a Tl content of x=6.4%. We estimated the epitaxial thickness hepi, at which single-crystalline growth is replaced by polycrystalline growth, by two different methods using the XRD data. In one method we measured the change in diffracted intensity of the epi-layer peak after progressive gradual etching of the TlGaAs layers grown. The other was on the basis of a simulation of the...

Effects of As pressure and growth temperature on the growth of TlGaAs films by molecular-beam epitaxy

Growth of Tl0.05Ga0.95As on GaAs (001) substrates by molecular-beam epitaxy has been performed at substrate temperatures of 230, 210, and 190 °C under various As pressures. At a growth temperature of 230 °C, Tl droplets were observed on the surfaces after the growth under low As pressures, while no droplets were observed when As pressure was increased. On the other hand, when grown at 190 °C, no droplets were observed over the entire range of the As pressure examined. Except for a sample grown at 230 °C under the lowest As pressure, a clearly resolved peak appeared in addition to a substrate peak in each x-ray diffraction curve, indicating the existence of an epitaxial TlGaAs layer. However, the weak intensity of the diffracted peaks due to the TlGaAs layers suggested that single-crystalline growth is replaced by polycrystalline growth at some thickness, hepi. We estimated the epitaxial thickness, hepi, through fitting theoretical simulation to the experimental diffraction curves, and found that hepi incr...

Low-Temperature Growth of InAs on Glass and Plastic Film Substrates by Molecular-Beam Deposition

InAs layers were deposited on glass and plastic (polyimide) film substrates by molecular-beam deposition at substrate temperatures of 180-280degC. Atomic force microscopy revealed flat surfaces with RMS roughness of about 10 nm. X-ray diffraction patterns indicated that the InAs layers are poly crystalline textured in the (111) plane with crystallite sizes around 30 nm. Hall effect measurements showed that the films exhibit the n-type conduction with electron concentrations around 5 times 1018 cm-3. An InAs film deposited on polyimide showed electron mobility of 460 cm2/Vs at room temperature.

Photoluminescence from Ultrathin InAs/GaAs Single Quantum Wells Grown on GaAs (111)A Substrates

We have made the first observation of photoluminescence (PL) from an ultrathin InAs/GaAs single quantum well (SQW) grown on GaAs (111)A substrate by means of molecular beam epitaxy (MBE). When the thickness of the InAs wells in the SQW increases from 1 to 6 monolayers (MLs), the PL peak energy at 10 K decreases from 1.47 to 1.36 eV and the intensity abruptly decreases. The PL intensity appears to be closely related to the quality of the GaAs cap layer as well as the InAs wells. The PL peak energies significantly exceed the calculated values. This discrepancy may be due to the diffusion into GaAs of In atoms at the GaAs/InAs interfaces.

Effective masses of holes in non-(001) ultrathin Si layers

We investigate the effects of crystallographic orientation on the quantization masses and the in-plane masses of valence subbands in ultrathin layers of Si within a six-band effective-mass theory. In order to provide physical insight on the difference in the quantum-confinement effects on these masses due to different crystal orientations, we adopt a square-well potential model with an infinite-barrier height. We show that in contrast to the case of (001)-oriented Si layers, the quantization mass of the heavy-hole subbands in (110)-oriented Si layers varies as a function of d/n, where d is the well width and n is the quantum number. In addition, we show that the sum of the reciprocal quantization masses of the heavy-hole, light-hole, and spin-orbit split-off subbands is constant, irrespective of d/n, in layers with an arbitrary orientation. The nonparabolicity of the in-plane dispersion of the first heavy-hole (h1) subband is shown to be reduced in (110)-oriented layers than in (001)-oriented ones of the ...