Microwave-stimulated relaxation of internal strains in GaAs-based device heterostructures

We have studied the effect of microwave radiation (frequency, 2.45 GHz; specific power density, 1.5 W/cm²) on the relaxation of internal mechanical strains in the (i)n-n ⁺-GaAs structures, (ii) Au-Ti-n-n ⁺-GaAs diode structures with Schottky barriers, and (iii) GaAs-based Schottky-barrier field-effect transistors (SFETs). It is shown that exposure of the samples to the microwave radiation for a few seconds leads to relaxation of the internal mechanical strains and improves the quality of the semiconductor surface layer structure. This results in improved parameters of the GaAs-based device structures of both (diode and SFET) types, as manifested by increased Schottky barrier height, reduced ideality factor and back current in the diode structures, and increased gain slope and initial drain current in the SFETs.     

Photovoltaic X-ray detectors based on epitaxial GaAs structures

A new type of the photovoltaic X-ray detector based on epitaxial p ⁺-n-n′-n ⁺ GaAs structures is proposed, which provides for a high efficiency of charge carrier collection in a nonbiased operation regime at room temperature. The GaAs structures were grown by vapor phase epitaxy on heavily doped n ⁺-GaAs substrates. The X-ray sensitivity range covers the effective energies from 8 to 120 keV. The maximum output signal in the short-circuit regime is 30 μA min/(Gy cm²). The detector response to γ-radiation from a ¹³⁷Cs[660 keV] radioactive isotope was measured.     

Photoelectrochemical reactions on semiconductor materials

The cathodic reduction of Fe³⁺ ions and I₂ on ann-GaAs electrode was studied. The variation in the current density with the concentration of the oxidant has been interpreted as being the result of a reduction mechanism involving interface or surface states, an interpretation that is amply substantiated by experimental data. The effect of the surface modification with SiW₁₂O₄₀ ^4– on the reduction process was studied. Prior to this electrode activation, the rate constant for electrons being transferred from the conduction-band to the interface or surface states,k _S, was observed to be independent of electrode potential, whereas in the case of the modifiedn-GaAs,k _S depends on band-bending. On the other hand, the rate constant for electrons being transferred from the interface or surface states to oxidant species,k _ox, does depend on electrode potential in the case of the unmodifiedn-GaAs, and is independent of band-bending in the case of the modifiedn-GaAs. This change may be attributed to the filling of the active surface or interface states or their redistribution after the electrode surface activation.     

Complexation and Disproportionation of Np(V) in K10P2W17O61 Solutions

Complexation of NpO₂ ⁺ and NpO₂ ^{2 +} with unsaturated K _n P₂W₁₇O₆₁ ^{n - 1 0} (L ^x-) heteropolyanion and disproportionation of Np(V) in the presence of L ^x- were studied spectrophotometrically. The logarithms (logK) of the formation constants of NpO₂ ^VL and NpO₂ ^{V I}L are 3 and 7, respectively. The K⁺ and Na⁺ cations bind the L ^x- anions, thus decreasing the yield of the complexes. Neptunium(V) disproportionation in K₁₀P₂W₁₇O₆₁ solutions containing 1 M (HClO₄ + NaClO₄) (pH from 0 to 4) and free from NaClO₄ (pH 2-6.5) was studied. The disproportionation rate is described by the equation -d[Np(V)]/dt = k[Np(V)][L ^x-]. The pH dependence of the rate constant passes through a maximum at pH 1. The rate constant decreases with increasing [Na⁺]. The reaction is inhibited by its product, Np(IV). The Np(V) complex is not involved in disproportionation; the reactive species is NpO₂ ⁺ aqua ion, which is probably converted into NpO^{3 +}L ^x-. Then NpO^{3 +}L ^x- rapidly reacts with NpO₂ ⁺, which occurs simultaneously with, or is preceded by release of the second oxygen atom.     

Correlation between the electrical and luminescent properties of high-purity gallium arsenide

Epitaxial n-GaAs layers with a background impurity concentration of N_D-N_A<10¹⁵ cm^?3, grown by chloride vapor phase epitaxy in an open system, exhibit correlation between the electrical properties and the long persistence of the edge photoluminescence lines D⁰x and D⁰h related to the hole trapping centers. An increase in the concentration of such trapping centers in n-GaAs leads to a decrease in the mobility of free charge carriers.     

Electrical Electron Spin Injection with a p+-(Ga,Mn)As/n+-GaAs Tunnel Junction

We demonstrate electrical electron spin injection in a p⁺-(Ga,Mn)As/n⁺-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p⁺-(Ga,Mn)As/n⁺-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.     

Electrical Electron Spin Injection with a p+-(Ga,Mn)As/n+-GaAs Tunnel Junction

We demonstrate electrical electron spin injection in a p⁺-(Ga,Mn)As/n⁺-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p⁺-(Ga,Mn)As/n⁺-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.     

Investigation of the process of voltage distribution over elements of a high-power semiconductor current interrupter

The process of voltage distribution over serially connected elements of a high-power semiconductor current interrupter in the stage of current breakage is studied within the framework of a previously developed physicomathematical model. It is established that a mechanism is operative that provides for the voltage drop leveling between unit structures of the p ⁺-p-n-n ⁺ type with various depths X _p of the p-n junctions. The mechanism is related to the fact that the formation of a strong field region on the stage of current breakage in the unit structures with larger X _p begins later, but the expansion of this region proceeds faster than the same processes in the units with smaller X _p .     

Influence of interfacial structural defects on the development of avalanche breakdown in heterojunctions

The reverse I–V characteristics of Cr/nn⁺-Si and Cr/nn⁺-GaAs Schottky barrier diodes and of heterodiodes produced by the vacuum epitaxy of germanium or Si_xGe_1?x onto nn⁺-silicon and nn⁺-GaAs were measured. The interfacial structural defects were studied by metallographic and transmission electron microscopy techniques. The effect of the density of structural defects at the interface on the I–V characteristics was investigated.     

Studying electric field profiles in GaAs-based detector structures by Kelvin probe force microscopy

The method of scanning Kelvin probe force microscopy has been used to study the electric field distribution in GaAs-based p ⁺-π-n-n ⁺ detector structures. In the active layer volume, two maxima in the field strength profiles have been found, which are localized in the regions of p ⁺-π and π-n junctions. A volt-age drop on the π-n junction expands the region of collection of nonequilibrium holes, thus increasing the charge collection efficiency for the absorption of γ photons with an energy of 59.5 keV.     

Effect of electron irradiation attenuated by aluminum screens on the electrical parameters of p-n silicon structures

We have studied the influence of irradiation by 6-MeV electrons via flat aluminum screens with thicknesses d = 2−14 mm (mass thicknesses, 0.5–3.8 g/cm²) on the properties of p ⁺-n-n ⁺ silicon structures, including the nonequilibrium charge carrier lifetime (τ), reverse current (I _R), and forward current-voltage (I-U) characteristics. In the case of a screen with d = 14 mm (3.8 g/cm²), the irradiated structures exhibit significantly smaller changes in I _R values and I-U curves compared to those for d = 2–12 mm, whereas a decrease in τ (from 20 to 1.5 μs) is the same.     

Electrical characteristics of Au/n-GaAs Schottky barrier diodes with and without SiO2 insulator layer at room temperature

In this study, our main goal is fabricated with and without insulator layer Au/n-GaAs Schottky barrier diodes (SBDs) to explain whether or not the insulator layer is effective on some electric parameters such as Φ_B, n, N_ss, and R_s. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-semiconductor (Au/n-GaAs) are investigated and compared with metal-insulator-semiconductor (Au/SiO₂/n-GaAs) Schottky diodes. From the room temperature I-V characteristics of these devices, the main electrical parameters such as, ideality factor (n) and zero bias barrier height (Φ_bo) values of 1.25 and 0.73 eV for Au/n-GaAs, and 1.51 and 0.75 eV for Au/SiO₂/n-GaAs, were obtained. The interface distribution profile (N_ss) as a function of (E_c − E_ss) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) and series resistance (R_s) for the Schottky diodes. The N_ss values obtained taking into account the series resistance values are lower than those obtained without considering the series resistance. The diodes show non-ideal I-V behavior with ideality factor greater than unity. This behavior is attributed to the interfacial insulator layer and the interface states. The I-V characteristics confirmed that the distribution of N_ss, R_s, and interfacial insulator layer are important parameters that influence the electrical characteristics of metal-semiconductor and metal-insulator-semiconductor Schottky diodes.     

The effect of neutron irradiation on the microhardness of gallium arsenide

We have studied the effect of neutron irradiation on the microhardness of n-GaAs crystals. It is shown that the growth and saturation of microhardness with increasing radiation dose Φ, as previously reported in the literature, take place only in the dose range Φ∼10¹⁵−5×10¹⁶ cm⁻². As the neutron dose is increased further, the microhardness continues to grow due to the increasing role of the radiation-induced disordered regions in n-GaAs.     

Extraction of microamounts of Eu and Am into nitrobenzene using a synergistic mixture of chlorinated hydrogen dicarbollylcobaltate and <Emphasis Type="Italic">N,N′</Emphasis>-diethyl-<Emphasis Type="Italic">N,N′</Emphasis>-diphenyl-2,6-dipicolinamide

Extraction of microamounts of Eu and Am with a nitrobenzene solution of chlorinated hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of N,N′-diethyl-N,N′-diphenyl-2,6-dipicolinamide (EtPhDPA, L) was studied. The equilibrium data were interpreted assuming that the complexes HL⁺, HL₂⁺, ML₂³⁺, ML₃³⁺, and ML^4/3+ (M³⁺ = Eu³⁺, Am³⁺) are extracted into the organic phase. The extraction and stability constants of the species in water-saturated nitrobenzene were determined. The stability constants of the related complexes EuL _n ³⁺ and AmL _n ³⁺, where n = 2, 3, 4, in this medium are comparable.     

Investigation of the thermal stability of picosecond gallium arsenide dynistor switches

The operation of GaAs n⁺-p-i-n ⁰-p ⁺ dynistor structures has been demonstrated experimentally under conditions of reversible avalanche breakdown at temperatures up to 200 °C with switching times remaining under 140 ps. A numerical simulation refined the influence of various parameters of the semiconductor on the temperature dependence of the switching characteristics. Pis’ma Zh. Tekh. Fiz. 24, 73–78 (August 12, 1998)     

Specific features of technology of electron irradiation of large-area <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> silicon structures

We have studied the influence of irradiation by 4-MeV electrons via flat metal screens on the main electrical characteristics of high-power silicon diodes intended to operate at currents up to 600 A. The electron irradiation was performed via metal masks, which led to the formation of enhanced recombination zones (ERZs) in the base region of p ⁺-n-n ⁺ silicon structures. It is shown that the local irradiation of a large-area diode structure improves (as compared to the total irradiation) the relationship been the reverse recovery time (t _rr ) and energy loss in the conducting state (U _f ), while decreasing the temperature sensitivity of the reverse current (I _R ). It is established that the relationships between t _rr , U _F , and I _R in locally irradiated structures depends on the experimental conditions (ERZ size).     

Effect of iodine doping on the luminescent properties of the photochromic material CdBr<Subscript>2</Subscript>:Cu<Superscript>+</Superscript>

The effect of iodine doping on the roentgenoluminescence (RL) and thermoluminescence (TL) of CdBr₂:Cu⁺ is studied using CdBr₂:(Cu⁺ ,I^-) crystals grown by the Bridgman-Stockbarger method from melts containing 0.5 wt % CuBr and 0.15, 0.5, or 5.0 wt % CdI₂. The results demonstrate that, with increasing iodine content, the RL intensity first rises and then drops; in addition, the RL band shifts from 560 to 490–510 nm. At low CdI₂ levels, the TL curve shows peaks at 110, 130, 152, and 168 K, characteristic of CdBr₂:Cu⁺. At the maximum iodine concentration, the TL curve shows a weak peak at 115 K. The TL spectrum of lightly iodine-doped crystals is dominated by the 490-nm emission, which is attributable to heteronuclear anion excitons. The formation of nI^- clusters in heavily doped CdBr₂:(Cu⁺,I^-) crystals reduces the concentration of (BrI)^- hetero-nuclear centers. The nature of the trapping levels responsible for the TL of the crystals is discussed.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 235–239.Original Russian Text Copyright © 2005 by S. Novosad, I. Novosad, Borodchuk.     

Acoustic wave corrected current-voltage characteristics of GaAs-based structures with Schottky contacts

The effect of ultrasonic treatment (UST) on the current-voltage (I-U) characteristics of Au-TiB_x-n-n ⁺-GaAs diode structures has been studied. Upon acoustic loading with an intensity below 2 W/cm², the character of the UST-induced changes in the reverse branches of I-U curves depends on the predominating mechanism of current transfer. UST at a power density above 2.5 W/cm² increases the reverse current by one or two orders of magnitude. It is shown that UST favors a significant increase in the homogeneity of the characteristics of devices manufactured using integral heat sink technology.     

Photoluminescence of i-GaxIn1 ? xAs/n-GaAs heterostructures containing a random InAs quantum dot array

i-Ga _x In_{1 − x} As/n-GaAs heterostructures containing InAs quantum dots have been grown by ion beam deposition and their photoluminescence has been studied. The photoluminescence spectrum of the heterostructures contains three characteristic peaks. The peak at 1.1 eV has a large width and is due to the array of InAs quantum dots of different sizes, randomly arranged on the surface of the i-Ga _x In_{1 − x} As layer. From the position of another peak (hν = 0.94 eV), we have evaluated the composition of the Ga _x In_{1 − x} As solid solution: x = 0.64. The third photoluminescence peak corresponds to the intrinsic absorption edge of the n-GaAs substrate. The key features of luminescence photoexcitation in the heterostructures are discussed. We show that the Ga_0.64In_0.36As quantum well may accumulate not only photogenerated electrons but also electrons that come from a thin interfacial n-GaAs layer through ballistic transport.     

Crystal Structure and Electronic Absorption Spectrum of Double Neptunium(V) Phthalate Co(NH3)6NpO2[(OOC)2C6H4]2·2H2O

Single crystals of Co(NH₃)₆NpO₂[(OOC)₂C₆H₄]₂·2H₂O were grown. The crystal structure of this compound [monoclinic cell: a = 7.748(2), b = 23.051(5), c = 14.608(3) Å, = 96.21(3)°, space group P2₁/c, Z = 4, V = 2593.7(9) ų, d _calc = 2.034 g cm^{- 3}, CAD4 automatic diffractometer, MoK , graphite monochromator, R ₁ = 0.041 for all 3567 reflections observed, wR ₂ = 0.1344 for all 4445 unique reflections, 325 refined parameters] was studied. The structure consists of infinite anionic chains {NpO₂[(OOC)₂C₆H₄]₂} _n ^{3 n -}, [Co(NH₃)₆]^{3 +} cations, and molecules of crystallization water. Neptunium(V) atom is in pentagonal-bipyramidal oxygen surrounding (CN 7); the neptunyl(V) group is linear and symmetrical; the Np = O bond lengths are 1.830(6) and 1.833(5)Å, the O = Np = O angle is 176.4(2)°. The equatorial plane of the bipyramid is formed by five oxygen atoms of phthalate anions. The Np-Oeq bond length correlates with the denticity of the phthalate anions. Two types of phthalate anions are localized in the structure. The first tridentate ligand is a bridge between Np(V) atoms in the chains. The second ligand is coordinated to Np in the bidentate fashion to form NpOCCCCO seven-membered chelate ring. The cation [Co(NH₃)₆]^{3 +} has an octahedral structure. The average Co-N distance in the octahedron is 1.961 Å the N-Co-N bond angles are close to 90°. Two water molecules along with [Co(NH₃)₆]^{3 +} cations are located between the anionic chains {NpO₂[(OOC)₂C₆H₄]₂} _n ^{3 n -}. The chains are additionally bonded along the Z-axis of the crystal by O_w-H···O hydrogen bonds.