Intersubband absorption from In0.26Ga0.74As/GaAs quantum dot superlattice

We have grown a high-quality 20 period InGaAs/GaAs quantum dot superlattice with a standard structure typically used for quantum well infrared photodetector. Normal incident absorption was observed around 13-15 mu m. Potential applications for this work include high-performance quantum dot infrared detectors.

Characteristics of InAs epilayers for Hall effect devices grown on GaAs substrates by MBE

InAs thin films with good characteristics were grown on GaAs (0 0 1) substrates by molecular beam epitaxy. Cross-sectional transmission electron microscopy indicated that most of the threading dislocations formed by the interaction of misfit dislocations are annihilated above a small thickness. The high electron mobility and small temperature dependence of InAs epilayers are useful for magnetic sensors which is demonstrated by the properties of Hall effect devices.

Magnetospectroscopy of bound phonons in high purity GaAs

Far infrared magnetophotoconductivity performed on high purity GaAs reveals the existence of fine structures in the resonant magnetopolaron regions. The fine structures are attributed to the presence of bound phonons due to multiphonon processes. We demonstrate that the magnetopolaron energy spectrum consists of bound phonon branches and magnetopolaron branches. Our results also indicate that different phonons are bound to a single impurity, and that the bound phonon in Si-doped GaAs is a quasilocalized mode.

Optical characterization of InAs monolayer quantum structures grown on (311)A, (311)B, and (100)GaAs substrates

Low-temperature photoluminescence and excitation spectra from InAs monolayer quantum structures, grown on (311)A, (311)B, and (100) GaAs substrates, are investigated, The structures were grown simultaneously by conventional molecular-beam epitaxy (MBE), The experimental results show that the quality of InAs monolayer on (311)B GaAs substrate is obviously better in crystal quality than those on the two other oriented GaAs substrates. In addition, the transition peaks of the InAs layer grown on (311) GaAs substrates shift to higher energy with respect to that from the InAs layer grown on (100) GaAs substrate.

Interfacial behaviour of quantum well electrode/electrolyte: effect of redox species on EER spectra of a single quantum well GaAs vertical bar AlxGa1-xAs electrode

The EER spectra of a single quantum well GaAs\AlxGa1-xAs electrode were studied as a function of applied reverse bias in ferrocene, p-methyl nitrobenzene and hydroquinone+benzoquinone non-aqueous solutions. EER spectra were compared for different redox species and showed that a pronounced quantum-confined Stark effect and a Franz-Keldysh oscillation for a single quantum well electrode were obtained in the p-methyl-nitrobenzene- and hydroquinone+benzoquinone-containing solutions. A surface interaction of the single quantum well electrode with ferrocene led to fewer changes in the electric field of the space charge layer for reverse bias; this was suggested to explain the weak quantum-confined Stark effect and Franz-Keldysh oscillation effect observed for the single quantum well electrode in the ferrocene-containing solution. (C) 1997 Elsevier Science S.A.

A theoretical model for the tilt of the GaAs/Si epilayers

The crystallographic tilt of the epilayers with respect to their substrates has been observed in many heteroepitaxial systems. Many models have been proposed to explain this phenomenon, but none of them is suitable for the large mismatched system, such as GaAs/Si. Here a new model is proposed for GaAs/Si epilayers, which can also be used in other large mismatched systems. The magnitude of the tilt calculated from this model coincide well with the experimental results. Especially, this model can correctly predict the tilt direction of the GaAs/Si epilayers.

Growth of GaN layers on GaAs and GaP (111) and (001) substrates by molecular beam epitaxy

Films of GaN have been grown using a modified MBE technique in which the active nitrogen is supplied from an RF plasma source. Wurtzite films grown on (001) oriented GaAs substrates show highly defective, ordered polycrystalline growth with a columnar structure, the (0001) planes of the layers being parallel to the (001) planes of the GaAs substrate. Films grown using a coincident As flux, however, have a single crystal zinc-blende growth mode. They have better structural and optical properties. To improve the properties of the wurtzite films we have studied the growth of such films on (111) oriented GaAs and GaP substrates. The improved structural properties of such films, assessed using X-ray and TEM method, correlate with better low-temperature FL.

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.

Stoichiometric defects in semi-insulating GaAs

The influences of arsenic interstitials and dislocations on the lattice parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve as effective gettering sites for arsenic interstitials due to the deformation energy of dislocations. The average excess arsenic in GaAs epilayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) is about 1%, and the lattice parameters of these epilayers are larger than those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by about 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by low-pressure (LP) LEC is the nearest to the strict stoichiometry compared with those grown by high-pressure (HP) LEC and vertical gradient freeze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.

Self-formed InGaAs/GaAs quantum dot superlattice and direct observation on strain distribution in the capped superlattice

We have demonstrated a 20 period dislocation-free InGaAs/GaAs quantum dot superlattice which is self-formed by the strain from the superlattice taken as a whole rather than by the strain from the strained single layer. The island formation does not take place while growing the corresponding strained single layer. From the variation of the average dot height in each layer, the strain distribution and relaxation process in the capped superlattice have been examined. It is found that the strain is not uniformly distributed and the greatest strains occur at two interfaces between the superlattice and the substrate and the cap layer in the capped superlattice. (C) 1997 American Institute of Physics.

Photoelectric behaviour of lattice-matched GaAs/AlxGa1-xAs quantum well electrodes

The photoelectric properties of the lattice-matched GaAs/AlxGa1-xAs quantum well electrodes and the influence of the electrode structure such as well width, the thickness of outer barrier and the number of period were studied in a nonaqueous electrolyte. A new kind of structure of multiple quantum well electrode with varied well width, possessing the quantum yield three times that of GaAs bulk materials, was designed and fabricated.

Current oscillations and stable electric field domains in doped GaAs/AlAs superlattices

The crossover between two regimes has been observed in the vertical electric transport of weakly coupled GaAs/AlAs superlattices (SLs). At fixed d.c. bias, the SLs can be triggered by illumination to switch from a regime of temporal current oscillation to the formation of a stable electric field domain. The conversion can be reversed by raising the sample temperature to about 200 K. An effective carrier injection model is proposed to explain the conversion processes, taking into account the contact resistance originating from DX centres in the n(+)-Al0.5Ga0.5As contact layers which is sensitive to light illumination and temperature. In addition, quasiperiodic oscillations have been observed at a particular d.c. bias voltage.

Reflectance-difference spectroscopy study of the Fermi-level position of low-temperature-grown GaAs

The results of a reflectance-difference spectroscopy study of GaAs grown on (100) GaAs substrates by low-temperature molecular-beam epitaxy (LT-GaAs) are presented. In-plane optical anisotropy resonances which come from the linear electro-optic effect produced by the surface electric field are observed. The RDS line shape of the resonances clearly shows that the depletion region of LT-GaAs is indeed extremely narrow (much less than 200 Angstrom). The surface potential is obtained from the RDS resonance amplitude without the knowledge of space-charge density. The change of the surface potential with post-growth annealing temperatures reflects a complicated movement of the Fermi level in LT-GaAs. The Fermi level still moves for samples annealed at above 600 degrees C, instead of being pinned to the As precipitates. This behavior can be explained by the dynamic properties of defects in the annealing process.

Photoluminescence studies on the interaction of near-surface GaAs/AlxGa1-xAs quantum wells with chemical adsorbates

The chemical adsorption of sodium sulphide, ferrocene, hydroquinone and p-methyl-nitrobenzene onto the surface of a GaAs/AlxGa1-xAs multiquantum well semiconductor was characterized by steady state and time-resolved photoluminescence (PL) spectroscopy. The changes in the PL response, including the red shift of the emission peak of the exciton in the quantum well and the enhancement of the PL intensity, are discussed in terms of the interactions of the adsorbed molecules with surface states.