Effect In GaAs Research Articles

Excess photo-carriers and cumulative Auger effects in GaAs–Ge quantum wells for high efficiency p–i (qw)–n solar cells

We report on carrier photo-excitation in GaAs–Ge quantum wells in the intrinsic region of p–i–n solar cells. In the process of the analysis, we solve for diffused photo-carriers in the quantum wells. We propose a wide gap/narrow gap/∼ 1 eV-gap via quantum well/narrow gap solar cell design. Our device model overcomes mobility problems (as is the case of III–N–V currently studied designs) and capitalizes on thermal escape of excess photo-excited carriers from quantum wells. We include the only significant effect of recombination losses via Auger Cooling on photo-excited carriers in intrinsic quantum wells, as found in the middle region of p–i–n solar cells, along with interface losses. We derive an explicit account of photo-carriers in quantum wells as a strong function of device parameters, Auger cumulative effect via a coefficient c n as follows: δ n = n ph + n o , with n ph ∼ c n − 1 / 3 .

Formation and dissolution of D-N complexes in dilute nitrides

Deuterium (hydrogen) incorporation in dilute nitrides (e.g., GaAsN and GaPN) modifies dramatically the crystal's electronic and structural properties and represents a prominent example of defect engineering in semiconductors. However, the microscopic origin of D-related effects is still an experimentally unresolved issue. In this paper, we used nuclear reaction analyses and/or channeling, high resolution x-ray diffraction, photoluminescence, and x-ray absorption fine structure measurements to determine how the stoichiometric $[\mathrm{D}]∕[\mathrm{N}]$ ratio and the local structure of the N-D complexes parallel the evolution of the GaAsN electronic and strain properties upon irradiation and controlled removal of D. The experimental results provide the following picture: (i) Upon deuteration, nitrogen-deuterium complexes form with $[\mathrm{D}]∕[\mathrm{N}]=3$, leading to a neutralization of the N electronic effects in GaAs and to a strain reversal (from tensile to compressive) of the N-containing layer. (ii) A moderate annealing at $250\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ gives $[\mathrm{D}]∕[\mathrm{N}]=2$ and removes the compressive strain, therefore the lattice parameter approaches that of the N-free alloy, whereas the N-induced electronic properties are still passivated. (iii) Finally, annealings at higher temperature $(330\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ dissolve the deuterium-nitrogen complexes, and consequently the electronic properties and the tensile strain of the as-grown GaAsN lattice are recovered. Therefore, we conclude that the complex responsible for N passivation contains two deuterium atoms per nitrogen atom, while strain reversal in deuterated GaAsN is due to a complex with a third, less tightly bound deuterium atom.

Observation of the anomalous Hall effect in GaAs

Devices for the direct detection of the spin current, based on the anomalous Hall effect (AHE), are fabricated on n-type GaAs bulk semiconductor materials. The AHE is observed in the device when the photoinduced spin-polarized electrons are injected into it, and it is found that the effect depends on the applied electric field. The origin of the field-dependent observed Hall effect is discussed based on the D'yakonov–Perel' (DP) spin relaxation mechanism. The spin-dependent Hall effect is also found to be enhanced with increasing doping concentration. The present experimental results might have potential applications in semiconductor spintronic devices since the effect is closely related to the spin Hall effect.

Spatial electric and axial magnetic fields effect in GaAs–AlAs quantum wires

In this work, we investigated the effect of both spatial electric and axial magnetic fields on the impurity ground state energy and the polarization of a donor impurity in square GaAs/AlAs QWWs. We show that the impurity ground state energy and the polarization depends strongly not only on the width of QWW, but also on the applied spatial component of the electric field and the impurity position.

Aging and detergent washing effects of the surface of (001) and (110) GaAs passivated with hexadecanethiol

We report on aging and detergent washing effects in GaAs wafers passivated with hexadecanethiol (HDT) [HS(CH2)15CH3]. The evolution of the photoluminescence (PL) signal from GaAs was measured at room temperature as a function of time, up to 1000h, for thiolated (001) GaAs that was solvent cleaned and etched using standard procedures, and for thiolated (110) GaAs that was obtained by cleaving in air. For 2h of thiolation time, the decay of the PL signal from (001) GaAs and (110) GaAs could be fitted, respectively, with double and single exponential functions. This indicates that at least two different types of non-adiative recombination centers (NRRC) form on the (001) surface. The overall density of surface states formed on (110) GaAs is significantly lower than those on (001) GaAs. A single exponential decay of the PL signal has been observed for 18h thiolated samples. The strong increase of the PL signal after detergent washing of (001) GaAs suggests that this treatment is effective in removal of some of the NRRC. The 19-fold enhancement of the PL signal, in comparison to that of the oxidized sample, has been obtained using the sample that, following the etching and detergent washing procedures, was thiolated with HDT.

Injection and detection of spin current and spin Hall effect in GaAs

A spin current is optically generated in GaAs and is detected by the spin Hall effect based on the extraordinary Hall effect. When photogenerated spin-polarized electrons are injected into the nonmagnetic semiconductor device by dragging them by a moderate electric field (0.35–1.20 kV/cm), a spin Hall voltage (transverse electric field) of 0.41 μV is obtained due to the induced nonequilibrium magnetization, which is proportional to the spin current in GaAs. The findings resulting from this experiment might have practical applications in the field of spintronics.

Effect of GaAs(1 0 0) 2° surface misorientation on the formation and optical properties of MOCVD grown InAs quantum dots

The influence of GaAs(1 0 0) 2° substrate misorientation on the formation and optical properties of InAs quantum dots (QDs) has been studied in compare with dots on exact GaAs(1 0 0) substrates. It is shown that, while QDs on exact substrates have only one dominant size, dots on misoriented substrates are formed in lines with a clear bimodal size distribution. Room temperature photoluminescence measurements show that QDs on misoriented substrates have narrower FWHM, longer emission wavelength and much larger PL intensity relative to those of dots on exact substrates. However, our rapid thermal annealing (RTA) experiments indicate that annealing shows a stronger effect on dots with misoriented substrates by greatly accelerating the degradation of material quality.

Spin-dependent electron many-body effects in GaAs

Time- and polarization-resolved differential transmission measurements employing same and oppositely circularly polarized $150\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ optical pulses are used to investigate spin characteristics of conduction band electrons in bulk GaAs at $295\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Electrons and holes with densities in the $2\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}--{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ range are generated and probed with pulses whose center wavelength is between 865 and $775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The transmissivity results can be explained in terms of the spin sensitivity of both phase-space filling and many-body effects (band-gap renormalization and screening of the Coulomb enhancement factor). For excitation and probing at $865\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, just above the band-gap edge, the transmissivity changes mainly reflect spin-dependent phase-space filling which is dominated by the electron Fermi factors. However, for $775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ probing, the influence of many-body effects on the induced transmission change are comparable with those from reduced phase space filling, exposing the spin dependence of the many-body effects. If one does not take account of these spin-dependent effects one can misinterpret both the magnitude and time evolution of the electron spin polarization. For suitable measurements we find that the electron spin relaxation time is $130\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$.

Interference of non-aligned Airy diffraction patterns in transmission acoustic microscopy images of crystals

This paper describes interference effects present in narrow band transmission acoustic microscopy images of crystals that arise from the superposition of pairs of non-aligned but symmetry equivalent Airy diffraction patterns. In the cases we examine, these Airy patterns are associated with folded portions of the slow transverse (ST) sheet of the acoustic wave surface of cubic crystals intersecting in the {110} symmetry planes. Each set of Airy fringes is inclined in the (001) observation plane to its overlapping counterpart, giving rise to curved Moiré-like fringes. Also, because of tilting of the two portions of the wave surface in opposite directions out of the (001) plane, each composite Airy fringe breaks up along its length into a large number of narrow, regularly spaced fringes, in a manner akin to wedge diffraction. We present calculations of these effects in GaAs and Ge, based on the elastodynamic Green's function, , for the infinitely extended anisotropic elastic continuum. A measured time-gated diffraction image is presented for GaAs, which is in good agreement with calculation.

DC-to-RF dispersion effects in GaAs- and GaN-based heterostructure FETs: performance and reliability issues

The performance and reliability implications of DC-to-RF dispersion effects are addressed. The proposed physical explanations and technological counteractions are reviewed. GaAs- and GaN-based FET technologies are considered, trying to point out both similar and peculiar aspects.

Asymmetric quantum-confined Stark effects of hierarchical self-assembly of GaAs∕AlxGa1−xAs quantum dots

Quantum-confined Stark effects in GaAs∕AlxGa1−xAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that the electron and hole energy levels and the optical transition energies can cause blueshifts when the electric field is applied along the opposite to the growth direction. Our calculated results are useful for the application of hierarchical self-assembly of GaAs∕AlxGa1−xAs quantum dots to photoelectric devices.

Jahn-Teller distortion and ferromagnetism in the dilute magnetic semiconductors GaAs:Mn and cubic GaN:Mn

Using first-principles total-energy methods, we investigate Jahn-Teller distortions in III-V dilute magnetic semiconductors, GaAs:Mn and GaN:Mn in the cubic zinc blende structure. The results for an isolated Mn impurity on a Ga site show that there is no appreciable effect in GaAs, whereas, in GaN there is a Jahn-Teller effect in which the symmetry around the impurity changes from T$_{d}$ to D$_{2d}$ or to C$_{2v}$. The large effect in GaN occurs because of the localized d$^4$ character, which is further enhanced by the distortion. The lower symmetry should be detectable experimentally in cubic GaN with low Mn concentration, and should be affected by charge compensation (reductions of holes and conversion of Mn ions to d$^5$ with no Jahn-Teller effect). Jahn-Teller effect is greatly reduced because the symmetry at each Mn site is lowered due to the Mn-Mn interaction. The tendency toward ferromagnetism is found to be stronger in GaN:Mn than in GaAs:Mn and to be only slightly reduced by charge compensation.

Biexcitonic blue Stark shift in semiconductor quantum dots

The effect of biexcitons on the Stark effect in GaAs and CdS quantum dots (QDs) has been investigated theoretically using a time-dependent perturbation technique. Our results show that the redshift, which usually occurs in QD energy levels, changes to a blueshift when account is taken of biexciton effects. The results are obtained for a single-quantum dot as well as for an inhomogeneous distribution of quantum dots. A comparison has also been made between the Stark effect in GaAs and in CdS crystals and it has been found that the Stark effect in GaAs is stronger than in CdS quantum dots. This can be attributed to the difference in biexciton binding energies of the two materials.

Spin-dependent localization effects in GaAs:Mn/MnAs granular paramagnetic–ferromagnetic hybrids at low temperatures

We compare the magneto-transport in paramagnetic–ferromagnetic GaAs:Mn/MnAs granular hybrids and paramagnetic GaAs:Mn reference samples. The differences in the hole transport between the two systems at low temperatures arise due to carrier localization effects at the cluster–matrix interface in the hybrids. The localization is caused by a Schottky barrier formation at the interface as well as spin-dependent shifts of the hole bands caused by the stray field of the ferromagnetic clusters. The application of an external magnetic field leads to a delocalization of the carriers and thus a negative magneto-resistance effect. These effects can be simulated using a network model approach.

Pure Spin Current from One-Photon Absorption of Linearly Polarized Light in Noncentrosymmetric Semiconductors

We show that one-photon absorption of linearly polarized light should produce pure spin currents in noncentrosymmetric semiconductors, including even bulk GaAs. We present 14x14 k.p model calculations of the effect in GaAs, including strain, and pseudopotential calculations of the effect in wurtzite CdSe.

Spatial electric field effect in GaAs–AlAs quantum wires

The response of an electron to a three-dimensional electric field in an infinite quantum well wire of square cross-section is investigated within a variational scheme. The ionization energy and the polarization are calculated for different locations of impurity ion. It is found that the results for the spatial electric field differ from the previous results found for the electric field applied in the direction perpendicular to the wire axis. The ionization energy weakens rapidly with the axial component of the field as the polarization of the carrier distribution intensifies.

Two-photon-absorption-induced nonlinear photoresponse in GaAs∕AlGaAs quantum-well infrared photodetectors

Using a free-electron laser(FEL) source, we have studied the two-photon-absorption (TPA) effect in GaAs∕AlGaAs quantum-well infrared photodetector (QWIP). The TPA-induced photoresponse in QWIPs has been measured under different FEL excitation power by the photoconductivity method. The effective-mass approximation theory is used for the QWIP structure to explain the photoresponse behavior. It is demonstrated that the TPA-induced photocarrier density is proportional to the square of the excitation power. Based on the experimental results, the TPA coefficients of QWIPs were obtained to be 0.0045, 0.0030, 0.0103, and 0.0061cm∕MW for the excitation lines of 10.6, 10.7, 11.9 and 13.2μm, respectively. The dependence the TPA coefficients on the excitation wavelength is explained by our theoretical model.

Photo-induced anomalous Hall effect in GaAs:MnAs granular films

We investigated the temperature-dependent Hall resistance and magnetization of the semiconductor/ferromagnetic hybrid structure of GaAs:MnAs granular films under dark and laser irradiated conditions. Under the laser irradiation with the energy above the band gap energy of GaAs, negative large Hall resistance due to the anomalous Hall effect was observed below the blocking temperature T b of the MnAs clusters. The intrinsic photo-induced magnetization of the MnAs clusters was, however, hardly observed. These results indicate that the blocking phenomena correlate with the photo-induced anomalous Hall resistance of the GaAs:MnAs granular films. Therefore, the magnetic interaction between the photo-induced carriers and the blocked magnetization of the MnAs clusters plays an important role in the photo-induced phenomena in the GaAs:MnAs granular films.

Comparison of photon recycling effect in GaAs and GaN structures

Comparison of photon recycling effect in GaAs and GaN structures

Quantum interference control of free-carrier density in GaAs

We have carried out theoretical and experimental investigations of optical phase controlled-free carrier injection in semiconductors via quantum interference between different absorption pathways connecting the same initial and final states in the valence and conduction bands. The interference schemes are theoretically modeled within a Fermi Golden rule approximation which also allows for a description in terms of the susceptibility formalism of nonlinear optics. Two different types of schemes involving interference between n and m multiphoton absorption events are considered depending on whether $n+m$ is even or odd. If $n+m$ is odd, phase control of carrier density can be observed only in a noncentrosymmetric crystal; if $n+m$ is even, interference can be observed in both centrosymmetric and noncentrosymmetric materials. The interference contribution to the density control is related to the imaginary part of the nonlinear electric susceptibility ${\ensuremath{\chi}}_{n+m\ensuremath{-}1}.$ Experimentally we have investigated carrier density control effects in GaAs at room temperature using nominally 150 fs optical pulses and considered an example for each of the two schemes: one-photon vs two-photon absorption with 0.775 and $1.55\ensuremath{\mu}\mathrm{m}$ pulses and one-photon vs three-photon absorption with 0.675 and $2.03\ensuremath{\mu}\mathrm{m}$ pulses. The main experimental features, including degree of phase control, are in good agreement with theory. We extract the relative magnitude of the imaginary and real components of ${\ensuremath{\chi}}_{2}$ and ${\ensuremath{\chi}}_{3}$ for GaAs at $1.55\ensuremath{\mu}\mathrm{m}$ and $2.03\ensuremath{\mu}\mathrm{m},$ respectively.