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Notes: The properties of deep donor states (DX centers) in III-V alloys are discussed in relation to their influence on device characteristics and performance. The techniques to avoid or minimize such deleterious effects in AlGaAs-based devices are discussed, along with their physical basis, and some guidelines for improved III-V device design are established. New results about the benefits of proper donor selection, the role of In alloying, the advantage of δ doping in layers and in modulation-doped devices, and the use of AlInAs and InGaP as alternative wide band-gap III-V alloys are presented.

Notes: Transient capacitance and photocapacitance techniques have been used to study the characteristics of two electron traps related to Te in GaAs1−xPx: Te. Levels En1 and En2 have thermal activation energies of 0.17 and 0.27 eV, respectively, and their thermal electron emission and capture rates deviate markedly from Schockley–Read–Hall theory for near band gap crossover compositions. Such centers are found for 0.3〈x≤1, are linked to the X conduction band minima, and their photoionization thresholds are 0.5 and 1 eV, respectively. Trap concentrations have been studied as a function of Te doping level, Zn diffusion temperature, and N content (x〉0.4) in GaAsP LEDs. It is suggested that both defects belong to the DX type, and they have been described by a large lattice relaxation model. Franck–Condon energies of 0.3 and 0.95 eV have been determined, respectively. The properties of present Te-related defects are quite similar to donor related centers in AlxGa1−xAs, including the nonexponential capacitance transients found in near x∼0.4 compositions. It is important to mention that both centers have very large hole capture coefficients (σp〉10−14 cm2) and behave as efficient recombination centers.

Notes: SnTe-doped InP layers were grown at low temperature by solid-source atomic layer molecular beam epitaxy. The samples were characterized by Hall measurements versus temperature, low temperature photoluminescence, x-ray diffraction, and secondary ion mass spectroscopy. The temperature of the SnTe effusion cell was varied from 320 to 440 °C, and the free electron concentration measured at room temperature ranged between 2.0×1016 cm−3 and 5.6×1018 cm−3 with the corresponding Hall mobility varying from 2320 to 1042 cm2/V s. © 2001 American Institute of Physics.

Notes: Beryllium-doped InP layers have been grown by solid source atomic layer molecular beam epitaxy at low substrate temperature. The residual n-type doping was reduced by controlling both the amplitude and the length of the phosphorus pulse. We have shown a well controlled p-type doping and obtained a hole concentration in the range 4×1017–3×1019 cm−3 at room temperature. The electrical and optical properties of InP layers grown at low temperatures were investigated by Hall effect and photoluminescence (PL) measurements. PL spectra for lightly doped samples have a near band emission at 1.41 eV and Be-related emissions around 1.38 eV. © 1999 American Institute of Physics.

Notes: We have devised a technique of manufacturing temperature sensor calibration devices based on the magnetic properties of the pseudobinary compounds of formula (RxR′1−x)Co2, where R and R′ are heavy rare earth elements. The device is a solid sensor which provides an easily detectable first order magnetic phase transition at fixed temperature points. It is known that a first order magnetic phase transition from ferrimagnetism to paramagnetism is observed in compounds as TmCo2 (3.70 K), ErCo2 (32.05 K), HoCo2 (77.12 K), and DyCo2 (136.55 K). These transitions correspond to a large anomaly in the characteristic properties as function of temperature. In this work, we present the electrical resistivity and magnetization measurements of (Er, Ho)Co2 series and DyCo2 compounds showing the viability of the proposed devices from 32.05 up to 136.55 K. This range can be extended below and above by substitution of the chemical components and the stoichiometric composition. The number of transitions can be fixed by a convenient arrangement of several elements. © 1999 American Institute of Physics.

Notes: In this work, we have succeeded in preparing γ′-(Fe1−xNix)4N powder samples for x up to 0.9 and have undertaken a systematic study of their structural and magnetic properties by x-ray diffraction and vibrating sample magnetometry. The lattice parameters of the nitrides decrease monotonically from 0.3795 to 0.3747 nm with increasing Ni concentration. The saturation magnetization, measured at room temperature and liquid nitrogen, was found to decrease with increasing Ni concentration. The Curie temperature TC also decrease with increasing Ni concentration, as well as with decreasing lattice parameter. Our results show that the lattice parameters, σs and TC behave in contrast with those of the corresponding fcc γ-Fe1−xNix alloys, for which each of these properties exhibits a maximum at some intermediate composition. © 1999 American Institute of Physics.

Notes: We have performed a temperature-dependent study of the rare earth L2,3 and Co K edges x-ray magnetic circular dichroism (XMCD) in HoCo2 and PrCo2. We have found in both samples that the L2/L3 ratio is temperature independent. This result contradicts previous findings that indicated a possible different behavior for L2 and L3 edges owing to modifications in the degree of 3d–5d hybridization. A further interesting result is that the temperature dependence of ratio E1/E2 for the L3 edge — where E1 and E2 correspond to the two area under the dichroic signal separated in two peaks, positive dipolar dominant, negative with significant contributions of both dipolar and quadrupolar channels — is also constant, suggesting that the dipolar and quadrupolar channels follow the same temperature dependence. This effect might be interpreted as the dominant 4f contribution to the 5d polarization (much larger than the 3d-induced contribution) to create the L-edge XMCD signal. The microscopic origin of the metamagnetic Co subsystem is also addressed. © 2000 American Institute of Physics.

Notes: Abstract The Santiago Schists are located in the Basal Unit of the Ordenes Complex, one of the allochthonous complexes outcropping in the inner part of the Hercynian Belt in the north-west of the Iberian Peninsula. Their tectonothermal evolution is characterized by the development of an eo-Hercynian metamorphic episode (c. 374 Ma) of high-P, low- to intermediate-T. The mineral assemblage of the high-P episode is preserved as a very thin Si= S1 foliation included in albite porphyroblasts, being composed of: albite + garnet-I + white mica-1 + chlorite-1 + epidote + quartz + rutile ± ilmenite. The equilibrium conditions for this mineral assemblage have been estimated by means of different thermobarometers at 495 ± 10 °C and 14.7 ± 0.7 kbar (probably minimum pressure). The later evolution (syn-D2) of the schists defines a decompressive and slightly prograde P-T path which reached its thermal peak at c. 525 ± 10 °C and 7 kbar. Decompression of the unit occurred contemporaneously with an inversion of the metamorphic gradient, so that the zones of garnet-II, biotite (with an upper subzone with chloritoid) and staurolite developed from bottom to top of the formation.The estimated P-T path for the Santiago Schists suggests that the Basal Unit, probably a fragment of the Gondwana continental margin, was uplifted immediately after its subduction at the beginning of the Hercynian Orogeny. It also suggests that the greater part of the unroofing history of the unit took place in a context of ductile extension, probably related to the continued subduction of the Gondwana continental margin and the contemporaneous development of compensatory extension above it. The inverted metamorphic gradient seems related to conductive heat transferred from a zone of the mantle wedge above the subducted continental margin, when it came into contact with the upper parts of the schists along a detachment, probably of extensional character.The general metamorphic evolution of the Santiago Schists, with the development of high-P assemblages with garnet prior to decompressive and prograde parageneses with biotite, is unusual in the context of the European Hercynian Belt, and shows a close similarity to the tectonothermal evolution of several high-P, low- to intermediate-T circum-Pacific belts.

Notes: The rare-earth intermetallic compounds RCo2, cubic Laves phases, are very suitable to study the magnetism of the 3d. Depending on the R magnetism we have an induced moment for the Co. For R=Dy, Ho, or Er the magnetic transition is of first order, whereas for Gd and Tb it is of second order. This behavior has been observed in this work by electrical resistivity and dc magnetization measurements in function of concentration in the system Er1−xTbx)Co2 where the internal field of the nearest R neighbors can induce the Co moment. Magnetization measurements of field cooling (FC) and zero field cooling (ZFC) samples are different for T〈Tc. This difference collapses for higher applied magnetic fields. The minimum for T just above Tc in ρ vs T curves disappears for x=0.2 with the onset of the second-order transition up to x=1.0. This minimum can result from the conduction electrons scattering on the spin fluctuations, enhanced by the 4f moments and the scattering by phonons. The idea of the metamagnetism of Co moments in the origin of this minimum is discarded. From our results we can conclude that a small amount of Tb in ErCo2 changes the first-order to second-order transition. Since the localization of the Fermi energy in the density of state of the 3d band is very important, a comparison study has been done with the system Er1−xTbx)Ni2. The concentration dependence of the lattice parameter differs a little from Vegard's law. Here we can infer from our results that all the magnetic transitions are second-order type. © 1996 American Institute of Physics.