Silicon-doped Gallium Arsenide Research Articles

Resistive Switching of GaAs Oxide Nanostructures

The paper presents the results of experimental studies of the influence of the local anodic oxidation control parameters on the geometric parameters of oxide nanoscale structures (ONS) and profiled nanoscale structures (PNS) on the surface of epitaxial structures of silicon doped gallium arsenide with an impurity concentration of 5 × 1017 cm−3. X-ray photoelectron spectroscopy measurements showed that GaAs oxide consists of oxide phases Ga2O3 and As2O3, and the thickness of the Ga2O3 layer is 2–3 times greater than the thickness of As2O3 area—i.e., the oxidized GaAs region consists mainly of Ga2O3. The experimental studies of the influence of ONS thickness on the resistive switching effect were obtained. An increase in the ONS thickness from 0.8 ± 0.3 to 7.6 ± 0.6 nm leads to an increase in the switching voltage Uset from 2.8 ± 0.3 to 6.8 ± 0.9 V. The results can be used in the development of technological processes for the manufacturing of nano-electronic elements, such as ReRAM, as well as a high-efficiency quantum dot laser.

Simultaneously Mapping of In-Depth Thermal Diffusivity and Effective Infrared Absorption Coefficient of Silicon-Doped Gallium Arsenide Wafer Using Lock-in Thermography

ABSTRACTIn this work, we report on simultaneously mapping of the thermal diffusivity and effective infrared absorption coefficient of GaAs wafer using infrared lock-in thermography. The phase images were extracted from the temperature modulation of the investigated surface at different excitation frequencies, by applying the lock-in detection for each pixel of the recorded image. The resulting images were analyzed using the thermal wave model in the transmission configuration. The thermal diffusivity and the effective infrared absorption coefficient were estimated from the best fit of the theoretical model to the experimental data applied for each pixels of the phase images. Finally, we used different image filters to decrease the estimation errors of the parameters and to enhance the quality of the images. The results demonstrate that the lock-in thermography technique in transmission configuration provides spatial information for both (effective) infrared absorption coefficient and thermal diffusivity of semiconductor crystals. Moreover, the possibility of using lock-in thermography and photothermal radiometry microscopy in investigation of large area and thin films is discussed.

Irreversible phase transformation in a CoCrFeMnNi high entropy alloy under hydrostatic compression

An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system is investigated using in-situ angular-dispersive X-ray diffraction under hydrostatic compression up to 20GPa via diamond anvil cell. The evolutions of multiple diffraction peaks are collected simultaneously to elucidate the phase stability field. The results indicated that an irreversible phase transformation had occurred in the high entropy alloy upon decompression to ambient pressure. A reference material (n-type silicon-doped gallium arsenide) was investigated following the same protocol to demonstrate the different deformation mechanisms. It is suggested that the atomic bonding characteristics on the phase stability may play an important role in the high entropy alloys.

Structural properties of pressure-induced structural phase transition of Si-doped GaAs by angular-dispersive X-ray diffraction

Pressure-induced phase transitions in n-type silicon-doped gallium arsenide (GaAs:Si) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 18.6 (1) GPa, with a 4:1 (in volume ratio) methanol–ethanol mixture as the pressure-transmitting medium. In situ ADXRD measurements revealed that n-type GaAs:Si starts to transform from zinc-blende structure to an orthorhombic structure [GaAs-II phase], space group Pmm2, at 16.4 (1) GPa. In contrast to previous studies of pure GaAs under pressure, our results show no evidence of structural transition to Fmmm or Cmcm phase. The fitting of volume compression data to the third-order Birch–Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 75 (3) GPa and 6.4 (9) for the B3 phase, respectively. After decompressing to the ambient pressure, the GaAs:Si appears to revert to the B3 phase completely. By fitting to the empirical relations, the Knoop microhardness numbers are between HPK = 6.21 and HA = 5.85, respectively, which are substantially smaller than the values of 7–7.5 for pure GaAs reported previously. A discontinuous drop in the pressure-dependent lattice parameter, N–N distances, and V/V0 was observed at a pressure of 11.5 (1) GPa, which was tentatively attributed to the pressure-induced dislocation activities in the crystal grown by vertical gradient freeze method.

Compensation mechanism in silicon-doped gallium arsenide nanowires

P-type gallium arsenide nanowires were grown with different silicon doping concentrations. The incorporation is monitored by Raman spectroscopy of the local vibrational modes. For Si-concentrations up to 1.4×1018 cm−3, silicon incorporates mainly in arsenic sites. For higher concentrations, we observe the formation of silicon pairs. This is related to the Coulomb interaction between charged defects during growth. An electrical deactivation of more than 85% of the silicon acceptors is deduced for nominal silicon concentration of 4×1019 cm−3. This work is important to understand the limiting mechanisms of doping in compound semiconductor nanowires.

Photo-carrier and Electronic Studies of Silicon-Doped GaAs Grown by MBE Using PCR

Photo-carrier radiometry (PCR) has been used to study the distribution of impurities and the lattice damage in silicon-doped gallium arsenide in a noncontact way. The results from the PCR study are correlated with Hall effect measurements. Samples for this study were grown by molecular beam epitaxy. Of all possible parameters that can be manipulated, the silicon effusion cell temperature was the only one that was varied, in order to obtain samples with different silicon concentrations. The distribution of impurities was obtained by scanning the surface of each sample. The PCR amplitude and phase images were obtained as a function of the x–y position. According to the PCR images, it is evident that the impurities are not uniformly distributed across the sample. From these images, the average value of the amplitude and phase data across the surface was obtained for each sample in order to study the PCR signal behavior as a function of the silicon effusion cell temperature.

Enhanced Donor Binding Energy Close to a Semiconductor Surface

We measured the ionization threshold voltage of individual impurities close to a semiconductor-vacuum interface, where we use the STM tip to ionize individual donors. We observe a reversed order of ionization with depth below the surface, which proves that the binding energy is enhanced towards the surface. This is in contrast to the predicted reduction for a Coulombic impurity in the effective mass approach. We can estimate the binding energy from the ionization threshold and show experimentally that in the case of silicon doped gallium arsenide the binding energy gradually increases over the last 1.2 nm below the (110) surface.

Spark-source mass spectrometric assessment of silicon concentrations in silicon-doped gallium arsenide single crystals.

The spark-source mass spectrometric assessment of silicon concentrations in silicon-doped vertical-gradient-freeze gallium arsenide is presented. The silicon concentrations determined are compared with the charge-carrier densities measured by means of the Hall effect with van der Pauw symmetry along the axis of a single crystal.

Interaction of Copper with Dislocations in GaAs

The interaction of copper with dislocations was studied in silicon-doped gallium arsenide by means of cathodoluminescence, analytical, and transmission electron microscopy. Several structures of defect complexes or microdefects surrounding the dislocations were found depending on the diffusion temperature and cooling rate. The results could be explained by considering the local nonequilibrium of intrinsic point defects induced by Cu in- or outdiffusion. The appearance of a bright or dark dislocation contrast in the cathodoluminescence pictures is related for different diffusion conditions: i) to the enrichment of copper acceptors at dislocations, ii) to the distribution of silicon-vacancy complexes, and iii) to non-radiative recombination at Cu-As precipitates or clouds of small dislocation loops.

Residual disorder in low pressure, low thermal gradient liquid encapsulated Czochralski gallium arsenide observed in high resolution synchrotron diffraction imaging

High resolution synchrotron X-radiation diffraction images of low thermal gradient, low pressure, liquid encapsulated Czochralski (LEC) silicon-doped gallium arsenide display a degree of crystalline order that is far higher than that found in undoped conventional LEC material. No distinct volume irregularity is observed in one crystal where it is unstrained. Only a set of surface-treatment-related dislocations is prominent in a second. A third crystal exhibits two distinct sets of quasi periodic dislocations, which have been analyzed in detail. The results support a model previously proposed for the evolution of disorder in gallium arsenide and suggest the role that silicon plays in its control.

Infrared photoconductivity via deep copper acceptors in silicon-doped, copper-compensated gallium arsenide photoconductive switches

Silicon-doped, copper-compensated, semi-insulated gallium arsenide of various doping parameters was studied with respect to infrared photoconductivity. This material is used as a photoconductive switch, the bistable optically controlled semiconductor switch (BOSS). One limitation was the relatively low conductivity of the device during the on-state. Typically, silicon-doped gallium arsenide is converted to semi-insulating gallium arsenide by the thermal diffusion of copper into the GaAs:Si. It is shown that variation of the diffusion parameters can improve the on-state conductivity by the enhancement of the concentration of a copper center known as Cu/sub B/. The conductivity of the device 150 ns after irradiation from a 20-ns FWHM laser pulse ( lambda =1.1 mu m) is recorded for various incident energies. This on-state conductivity saturates at a value that is predicted by the densities of the copper levels and the mobility.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of arsenic vapor pressure during copper diffusion on deep level formation in silicon-doped gallium arsenide

The effect of arsenic vapor pressure during copper diffusion on deep level formation in silicon-doped gallium arsenide has been studied using photoinduced current transient spectroscopy. From the findings, models for the copper-related complexes in GaAs are identified. Capping effect of deposited copper layer is investigated. Deep levels with activation energies of 0.14 eV, 0.32 eV, and 0.45 eVhave been identified, which are attributed to CuGa, SiGa CuGa complex, and VAsCuGaVAs complex, respectively.

Defect reactions by heat treatment of heavily silicon doped gallium arsenide

Silicon is an amphoteric impurity of gallium arsenide that is present in different defect configurations. This work reports on the effects of heat treatment on defect reactions of heavily silicon-doped gallium arsenide crystals. The distribution of segregation, lattice parameter, and electrical properties was studied for several heat treatments. When the crystals were bulk-annealed at between 700 °C and 1000 °C for 20 h, zone-distributed segregation was observed at the area with a silicon concentration of about 1×1019 cm−3 by etching and x-ray topography. Regions observed to have silicon-related segregation exhibited a decrease in lattice parameter when the crystals were annealed below 850 °C for 20 h then quenched. In addition, such regions exhibited little change in lattice parameter when the crystals were annealed above 850 °C. For electrical properties, the largest decrease in carrier concentration and mobility of such regions was observed when the crystals were annealed at 700 °C. This change in the characteristics of such regions seems to be affected not only by heavily doped silicon but also by excess arsenic.

Evidence of pre-thermalization trapping of positrons in neutron-irradiated silicon-doped gallium arsenide

Abstract Positron lifetime spectroscopy has been used to make an isochronal annealing study of neutron-irradiated silicon-doped GaAs. Lifetime spectra have been collected for the temperature range 29C-825 K and analysed using conventional trapping models. Large deviations of the estimated positron free lifetime from its value in the annealed state are shown to occur; they have been interpreted as an indication of a strong trapping of positrons by defects prior to the positrons achieving thermal energies.

Infrared quenching of conductivity at high electric fields in a bulk, copper-compensated, optically activated GaAs switch

Controlled compensation of silicon-doped gallium arsenide with copper has been obtained by a process of thermal annealing at ascending temperatures. By using compensated Cu:Si:GaAs as switch material it is possible to activate and deactivate photoconductivity with two laser pulses of different wavelengths. Persistent photoconductivity is first induced by 1064-nm radiation that is absorbed at copper centers in the bandgap. Later, the photoconductivity is extinguished by stimulating quenching with 1620-nm radiation. This process is shown to be temporarily effective against lock-on currents at fields greater than 3.5 kV/cm-that is after a delay of approximately 25 ns, the lock current reappeared at a lower magnitude, whereas, at low fields, the photocurrent was permanently quenched.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of copper doping on the performance of optically controlled GaAs switches

The influence of the copper concentration in silicon-doped gallium arsenide on the photoionization and photoquenching of charge carriers was studied both experimentally and theoretically. The studies indicate that the compensation ratio (NCu/NSi) is an important parameter for the GaAs:Si:Cu switch systems with regard to the turn-on and turn-off performance. The optimum copper concentration for the use of GaAs:Si:Cu as an optically controlled closing and opening switch is determined.

Dislocations and microdefects in LEC-grown silicon-doped gallium arsenide crystals

This contribution refers to systematic research on silicon-doped LEC-grown GaAs crystals, aimed at lowering the dislocation density. By Si-doping in the range (1-5) × 10 18 atoms/cm 3 large dislocation-free regions can be obtained. It is shown that Si-doping entails large boron contamination. Results on the effect of deviations in the melt stoichiometry from which the crystals are grown are reported as regards dislocations and microdefects. From etching and photoetching studies, evidence is given that (i) most of the dislocations are not of a glide type and (ii) only dislocations in crystals grown from As-rich melts show characteristic As-type precipitates, while in crystals grown from stoichiometric and Ga-rich melts the nature of decorating microdefects is not yet clear.

Photoluminescence study of acceptors in silicon-doped gallium arsenide grown by metalorganic chemical vapor deposition

Epitaxial silicon-doped GaAs layers were grown by metalorganic vapor deposition (MOCVD) using a silane-argon mixture as a dopant source. Two different dopant sources with silane mole fractions 2.4×10 −4 and 2.3×10 −5 were used. For both sources the electron concentration increased with the silane mole fraction in the gas flow, reached a maximum, and then fell abruptly. The maximum electron concentration was substantially higher (up to 2.1×10 19 cm −3) for layers grown with a more concentrated dopant source. The difference in silicon incorporation from different silane sources is thought to be caused by uncontrollable impurities in the diluting gas - argon. The low temperature (12 and 80 K) photoluminscence investigation revealed the presence of at least three types of acceptors in the layers: residual impurity zinc, group IV acceptors silicon versus carbon and the deep acceptor complex, silicon donor-gallium vacancy, responsible for the emission band with peak energy 1.24 eV. As a rule, this emission band was dominant in the most heavily doped layers with low electron mobilities, and its intensity was low for layers with good mobility values. Therefore the silicon donor-gallium vacancy complex is thought to be the main compensating acceptor in most heavily doped layers.

A nuclear magnetic resonance field cycling investigation of chromium and silicon doped gallium arsenide

The results of an NMR field cycling study of GaAs doped with Cr and Si are reported. The two materials give significantly different spectra. In view of the different doping it is suggested that the results can be interpreted in terms of quadrupolar and hyperfine enhanced Zeeman energy level cross coupling around the impurities and that NMR field cycling can therefore distinguish between deep and shallow band gap states.

Mechanism of compensation in heavily silicon-doped gallium arsenide grown by molecular beam epitaxy

Silicon-doped GaAs grown by molecular beam epitaxy has been characterized by Hall measurements, infrared local vibrational mode (LVM) absorption, secondary ion and laser source mass spectroscopy. Highly doped samples with [Si]∼3×1019 cm−3 show only a low carrier concentration of 8×1017 cm−3. LVM spectroscopy shows that SiGa donors are compensated predominantly by [Si-X] complexes, where X has been assigned previously to a gallium vacancy (VGa). Other compensating impurities are not present in the layers at significant concentrations.