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Recent work has shown that GaN1-xAsx can be grown across the entire composition range by low temperature molecular beam epitaxy with intermediate compositions being amorphous, but control of the electrical properties through doping is critical for functionalizing this material. Here we report the bipolar doping of GaN1-xAsx with high As content to conductivities above 4 S/cm at room temperature using Mg or Te. The carrier type was confirmed by thermopower measurements. Doping requires an increase in Ga flux during growth resulting in a mixed phase material of polycrystalline GaAs:N embedded in amorphous GaN1-xAsx. [ABSTRACT FROM AUTHOR]

The steady state and time-resolved photoluminescence (PL) spectra of cubic AlxGa1-xN have been measured for 0 < x < 1. The intensity of the room temperature PL increases by an order of magnitude when the AlN content increases from x = 0 to x = 0.95. Additionally, the PL decay slows down with the decrease of temperature and increase of x. These results show that strong localization of carriers on alloy composition fluctuations plays a large role in determining the intensity and temporal evolution of the PL. The activation energy for the localized carriers increases with the increase of x and reaches the value of 55 meV at x = 0.95. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and electronic properties of (Ga,Mn)As ferromagnetic semiconductor layers containing low concentrations of room temperature magnetic MnAs precipitates, using x-ray magnetic circular dichroism in x-ray absorption spectroscopy. Measurements below and above the Curie temperature of the (Ga,Mn)As show localized multiplet structures and broad metallic-like line shapes, respectively. By applying magnetic fields below the coercivity of the (Ga,Mn)As layer, the magnetization reversal behavior of the ferromagnetic semiconductor and the MnAs precipitates can be resolved and are found to be independent of each other. [ABSTRACT FROM AUTHOR]

We have used scanning Hall probe microscopy to image domain structures and magnetization reversal in optimally annealed Ga0.91Mn0.09As films grown on (311)B GaAs substrates. Unmagnetized films exhibit a disordered mazelike domain structure consistent with a composite state of regions with magnetization along [0,1,0] and [0,0,1] out-of-plane easy axes. The characteristic stripe width of ∼3 μm exhibits almost no temperature dependence in the range of 5–90 K, consistent with recent theoretical predictions, while the peak domain fields drop almost linearly with increasing temperature. With an applied field perpendicular to the zero-field-cooled film magnetization proceeds by the motion of rather ordered stripe-shaped domains which form preferentially along one of the [0,1,0]/[0,0,1] easy axes. Surprisingly, stripelike domains are not clearly observed during reversal from the magnetized state, which appears to involve the propagation of magnetic “bubbles.” Weak image contrast in the magnetized state points to the existence of residual magnetic disorder in the films on an ∼2–3 μm length scale. Abrupt breaks within single images indicate the occurrence of large Barkhausen events when domain walls suddenly jump over ∼1 μm distances. This implies the existence of strong pinning sites on this length scale and this, as well as the residual magnetic disorder, may be related to microscopic Mn-rich regions formed during sample growth. [ABSTRACT FROM AUTHOR]

Examines the band gaps of both hexagonal and cubic thin films deposited by a modified molecular-beam-epitaxy process on gallium arsenide and gallium phosphide substrates. Significance of the method of supplying nitrogen to the growing film; Application of x-ray diffraction and arsenic beam; Factors that may cause errors in band-gap measurements; Structural properties of the film.

Deals with a study that presented a model for the spectral response of gallium arsenide and Al[subx]Ga[sub1-x]As p-n and p-i-n solar cells based on a standard solution of the minority-carrier equations. Application of the quantum well solar cell; Capability of the model; Strengths and weaknesses of the model; Disadvantages from the use of intercell connection.

Focuses on a study which discussed the effects of practical properties of gallium arsenide-aluminum gallium arsenide heterostructures on the accuracy of a quantum-Hall resistance standard. Methods of conduction that were addressed; Details of the measurement concerning the influences of sample size and mobility; Aspects of mobility that were investigated; Recommendations on sample geometry and mobility.

Presents information on a study which investigated the temperature dependence of the photoluminescence decay kinetics of a series of gallium arsenide (GaAs)/aluminum arsenide (AlAs) quantum-well structures where GaAs thickness was kept constants and AlAs was varied. Methodology of the study; Results and discussion; Conclusions.

Deals with a study that investigated the effects of undoped spacer layers on the electrical properties of single barrier heterostructures by measuring incremental slope resistance. Aspects that increase with spacer thickness; Capability of arsenic/gallium arsenide double barrier resonant tunneling devices; Components of the devices.

We present an experimental investigation of the magnetic, electrical, and structural properties of Ga0.94Mn0.06As1-yPy layers grown by molecular beam epitaxy on GaAs substrates for y≤0.3. X-ray diffraction measurements reveal that the layers are under tensile strain, which gives rise to a magnetic easy axis perpendicular to the plane of the layers. The strength of the magnetic anisotropy and the coercive field increases as the phosphorous concentration is increased. The resistivity of all samples shows metallic behavior with the resistivity increasing as y increases. These materials will be useful for studies of micromagnetic phenomena requiring metallic ferromagnetic material with perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We have performed spatially resolved polar magneto-optical Kerr effect microscopy measurements on as-grown and annealed Ga0.95Mn0.05As thin films with tensile strain. We find that the films exhibit very strong perpendicular magnetic anisotropy which is increased upon annealing. During magnetic reversal, the domain walls propagate along the direction of surface ripples for the as-grown sample at low temperatures and along the [110] direction for the annealed sample. This indicates that the magnetic domain pattern during reversal is determined by a combination of magnetocrystalline anisotropy and a distribution of pinning sites along the surface ripples that can be altered by annealing. These mechanisms could lead to an effective method of controlling domain wall propagation. [ABSTRACT FROM AUTHOR]

Examines the mobility of two-dimensional electron gas structures. Influence of aluminum gallium arsenide on the mobility; Trend of carrier density and mobility with undoped spacer thickness observed following the cleanup phase; Production of a sample with mobility in excess of 3×10[sup6] cm²V[sup-1]s[sup-1].

We demonstrate a detection mechanism for 2-5 THz radiation using intersubband transitions between anticrossing electron levels in a GaAs/AlGaAs coupled-quantum-well photodiode. The THz radiation is detected as a modulation in the photocurrent generated by a visible laser. This modulation is caused by carrier heating effects due to absorption of energy by intersubband transitions. Since the frequency of the intersubband transitions varies with the electric-field strength, the device can function as a voltage-tunable THz detector. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Direct measurements of the desorption rate of gallium from GaAs and (Al,Ga)As during growth by molecular beam epitaxy at high temperatures have been made by modulated beam mass spectrometry. The activation energy for desorption is dependent upon the nature of the site from which the gallium is lost. From free gallium atoms not incorporated into the lattice, behavior similar to that encountered under equilibrium conditions for gallium over gallium or gallium over GaAs is observed. For gallium lost from the GaAs lattice the apparent activation energy is higher and is influenced by the arsenic flux reaching the surface. [ABSTRACT FROM AUTHOR]

We report on low-temperature photoluminescence from an ultrapure GaAs-Al0.33Ga0.67As heterostructure grown with molecular beam epitaxy. A luminescence band centered at 1.509–1.510 eV is observed. In spectral shape and polarization this band distinguishes itself from the defect related lines of H. Kuenzel and K. Ploog [Appl. Phys. Lett. 37, 416 (1980)]. Furthermore, this band disappears when the top cladding Al0.33Ga0.67As layer is removed. The emission band is further characterized by measuring its dependence on excitation density and temperature as well as its temporal behavior. We discuss possible recombination mechanisms for this band. The most likely candidate is luminescence related to a defect pair situated at or near the interface of the heterojunction. [ABSTRACT FROM AUTHOR]

Measurements of the incremental slope resistance of a GaAs-(Al,Ga)As-GaAs single barrier structure have been made at temperatures between 70 and 230 K. In contrast with other work we deliberately concentrate on the region close to zero applied bias. The deficiencies in the often-used Wentzel–Kramers–Brillouin analysis of the electrical characteristics are exposed in this regime, and an exact, Airy function approach is found to be essential to describe our observations. [ABSTRACT FROM AUTHOR]

The authors have succeeded in growing GaN1-xAsx alloys over a large composition range (02 flux at low (as low as 100 °C) growth temperatures, which is much below the normal GaN growth temperature range. Using x-ray and transmission electron microscopy, they found that the GaNAs alloys with high As content x>0.17 are amorphous. Optical absorption measurements together with x-ray absorption and emission spectroscopy results reveal a continuous gradual decrease in band gap from ∼3.4 to <1 eV with increasing As content. The energy gap reaches its minimum of ∼0.8 eV at x∼0.8. The composition dependence of the band gap of the crystalline GaN1-xAsx alloys follows the prediction of the band anticrossing model (BAC). However, our measured band gap of amorphous GaN1-xAsx with 0.31-xAsx alloys have short-range ordering that resembles random crystalline GaN1-xAsx alloys. They have demonstrated the possibility of the growth of amorphous GaN1-xAsx layers with variable As content on glass substrates. [ABSTRACT FROM AUTHOR]

Mass spectrometer studies provide a powerful means to evaluate both the major species coming from a Knudsen source used for molecular beam epitaxy and also impurities, which may be detrimental to device performance. To distinguish signals from the source from those due to background gases in the ultrahigh vacuum system it is essential to have direct line of sight from the source to the ionizer of the mass spectrometer. For condensable species this criterion combined with a liquid nitrogen cryopanel is sufficient to ensure the species detected come from the source. However, for volatile species, such as arsenic, this is not the case and to adequately identify material from the source it is necessary to use modulated beam mass spectrometer studies as has previously been demonstrated in studies of the evaporation of GaAs [C. T. Foxon et al., J. Phys. Chem. Solids 34, 1693 (1973)]. The authors have recently constructed a new version of this apparatus using a Hiden HAL IV mass spectrometer, which has both pre and postfilters to improve transmission and sensitivity at high mass numbers. The new apparatus has several improvements compared to the original system used by one of the authors. In particular, in addition to the improved intrinsic sensitivity of the mass spectrometer, it is now possible to tune the electron ionization energy to a low enough value to prevent cracking of species within the ionizer of the mass spectrometer, thus simplifying the interpretation of the data. This new system has been used to study the performance of a Veeco Mark V arsenic valved cracker equipped with a variety of different baffles. In all cases, at a sufficiently high temperature of the hot (cracker) zone, complete decomposition of the arsenic from tetramers (As4) to dimers (As2) is achieved. Surprisingly, the source with an open tube achieves significant cracking at very low cracker temperatures. In this case the flux would not be sufficiently uniform over the area of a growth sample, so additional beam forming apertures or a series of baffle plates are typically used to alleviate this situation. With such apertures or baffles present, complete decomposition can also be achieved, but at a slightly higher operating temperature, suggesting some recombination takes place. In this article, the authors concentrate on baffle assemblies that will be familiar to users of most of the current models of cracker in service today. Aperture plates of various designs will be the subject of future work. [ABSTRACT FROM AUTHOR]

The integration of ferroelectric polymer gates on a Mn-doped GaAs magnetic channel provides a promising route for the persistent field-effect control of magnetic properties in high-quality diluted magnetic semiconductors (DMSs) that are otherwise incompatible with traditional oxide ferroelectrics. That control demands the thinnest possible DMS layers, for which to date the Curie temperature (Tc) is severely depressed. Here we show that reducing the channel thickness from 7 to 3-4 nm by etching, followed by a brief 135°C anneal, does not degrade the Tc (∼70 K) of the 7-nm film. The channel thinning results in a dramatic threefold increase of the Tc shift controlled by the ferroelectric polarization reversal. Furthermore, we obtain the same exponent (∂ in Tc/∂ In R) ≡ γ -0.3 for all channels with different thicknesses, regardless of the technique used for Tc determination. These results suggest that the ferromagnetic coupling in an ultrathin 3-nni channel is far from the two-dimensional limit and shows a rather bulklike behavior, similar to well-established 7-nm films. [ABSTRACT FROM AUTHOR]

We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found. [ABSTRACT FROM AUTHOR]