Activation Energy Of Mg Research Articles

Effects of Mg doping on the electrical and luminescence characterizations of p-type GaAsN alloys grown by MBE

We have demonstrated that Mg is a controllable acceptor element for p-type GaAsN alloys grown by solid-source molecular-beam epitaxy (MBE), where a hole concentration has been realized up to 1.5×10 20 cm −3 and has been controlled along the vapor pressure curve of Mg using a standard effusion cell. In addition, electrical and luminescence characterizations have been investigated for GaAsN:Mg samples grown by solid-source MBE. The activation energy of Mg for the GaAsN:Mg samples is close to the impurity energy of Mg in GaAs (28 meV). Thus Mg is a very shallow acceptor element for GaAsN alloys. From photoluminescence (PL) measurements, the integrated PL intensity drastically increases with increasing a hole concentration up to 8.6×10 19 cm −3 at 300 K. This result suggests that the hole concentration can increase up to 8.6×10 19 cm −3 without significantly increasing the non-radiative recombination centers related to Mg doping when Mg is the acceptor element.

Low-temperature characteristics of the current gain of GaN/InGaN double-heterojunction bipolar transistors

We investigated the temperature dependence of the current gain of npn-type GaN/InGaN double-heterojunction bipolar transistors (DHBTs) in the low-temperature region. The current gain increased with decrease in device temperature due to the reduction of the recombination current in the p-type base layer. The current gain reached as high as 5000 at 40 K, which is the highest among nitride-based HBTs. For conventional HBTs made of InP or GaAs, the current gain decreased with decreasing device temperature. However, no reduction of the current gain was observed in this study, suggesting that the minority carrier mobility in the p-type InGaN base layer has negative temperature dependence, presumably because the ionized impurity scattering is relatively unaffected owing to the carrier freezeout and the high activation energy of Mg in the p-InGaN base layer.

Interface microstructure and diffusion kinetics in diffusion bonded Mg/Al joint

The interface microstructure, formation of diffusion bonded joint and regulation of atom diffusion were studied by means of scanning electron microscope (SEM), energy dispersion spectroscopy (EDS) and electron probe microanalyser (EPMA). The experimental results indicated that an obvious interfacial transition zone was formed between Mg and Al, and there are three intermetallic layers Mg17Al12, MgAl and Mg2Al3 in this zone. Diffusion activation energy of Mg and Al in the above layers was lower than that in the Mg and Al base metals. The thickness (x) of each layer can be expressed as x2 = 4.14exp(−28780/RT)(t−t0), x2 = 31.4exp(−25550/RT)(t−t0) and x2 = 0.6exp(−22600/RT)(t−t0) corresponding to Mg17Al12, MgAl and Mg2Al3 with heating temperature (T) and holding time (t).

The size effect of raw materials on the phase formation of polycrystallineMgB2

The effect of the size of the B powder and the Mg powder onMgB2 phase formation has been studied by the technique of in situ high-temperature resistivity(HT-ρ(T)) measurement. Two characteristic temperatures indicating the phase formation, the onset point,Tonset, and thecompletion point, TPF, were directly determined during the continuous heating process. These two temperaturesof the samples synthesized using nanometer-size B powder (Nano-B) and micrometer-sizeB powder (Micro-B) with nanometer-size Mg (Nano-Mg) are almost the same,i.e. Tonset = 713 Kand TPF∼763 K, respectively, indicating that the phase formation temperature ofMgB2 does not primarily depend on the particle size of the B powder. A similar process was thencarried out on Mg powders with the same B powder. An exponential relationshipbetween the onset phase formation temperature and the Mg powder size is clearlyshown, which can be fully fitted by a modulated diffusion equation and which givesQ = 421 kJ mol−1 describing the grain boundary activation energy of Mg diffusing into B. We also find that theMgB2 crystallites along the [101] direction have the lowest formation energy, revealed byx-ray diffraction (XRD) analysis on raw Mg powders, and the correspondingMgB2 crystallites aligned along [101] will be formed preferentially in thesintering process. This result is useful for the understanding ofMgB2 phase formation in the solid reaction process.

Magnesium Doping of In-rich InGaN

InN and In-rich InGaN were grown by metal organic vapor phase epitaxy with magnesium doping. A set of samples were grown at 550 °C, whereas a second set of samples were grown at increasing temperature with Ga content. Upon annealing, p-InGaN was obtained from the second set up to an In content above 50%, with an acceptor concentration of ∼1×1019 cm-3 and a mobility of 1–2 cm2 V-1 s-1. None of the samples grown at a constant temperature of 550 °C showed a p-behavior after heat treatment. The electrical, optical, structural and morphological characteristics of the films grown were analyzed, and the leveling off of hole concentration beyond an In content of 30% was consistent with the reported decreasing activation energy of Mg with increasing In content.

Correlation between optical and electrical properties of Mg-doped AlN epilayers

Deep UV photoluminescence and Hall-effect measurements were employed to characterize Mg-doped AlN grown by metal organic chemical vapor deposition. A strong correlation between the optical and electrical properties was identified and utilized for material and p-type conductivity optimization. An impurity emission peak at 4.7eV, attributed to the transition of electrons bound to triply charged nitrogen vacancies to neutral magnesium impurities, was observed in highly resistive epilayers. Improved conductivity was obtained by suppressing the intensity of the 4.7eV emission line. Mg-doped AlN epilayers with improved conductivities predominantly emit the acceptor-bound exciton transition at 5.94eV. From the Hall-effect measurements performed at elevated temperatures, the activation energy of Mg in AlN was measured to be about 0.5eV, which is consistent with the value obtained from previous optical measurements. Energy levels of nitrogen vacancies and Mg acceptors in Mg-doped AlN have been constructed.

Investigation of high hole concentration Mg-doped InGaN epilayer

We investigated the optical and electrical properties of Mg-doped InxGa1-xN(0≤x≤0.3) grown by metalorganic chemical vapor deposition with different In and Mg contents. When the Mg doping concentration was fixed, the hole concentration of samples increased remarkably with the elevation of In mole fraction. The highest hole concentration achieved was 2.4×1019cm-3,the doping efficiency increased nearly by two orders. We explained the carrier transition mechanism with the help of the photoluminesce spectra. In addition, we obtained the activation energy of Mg and the band position of deep donor in InGaN:Mg samples.

Analyses of hydrogen sorption kinetics and thermodynamics of magnesium–misch metal alloys

The multi-component Mg– x wt.% Mm alloys are synthesized using the mechanical ball-milling technique and their hydrogen storage capacities, absorption/desorption kinetics, and thermodynamic parameters are quantified. The analysis of kinetic properties presented here is based on the method of exponential peeling. It is seen that the presence of misch metal (Mm) in the alloy samples dramatically decreases their rate of decrepitation and increases their cyclic stability. However, the increased concentration of misch metal in the samples has an adverse effect on their hydrogen storage capacity and their reaction rate. The hydrogen storage properties also vary with reaction temperature. The best hydrogen absorption kinetics are observed at temperatures around 300 °C and the desorption kinetics are quite fast at temperatures of 400 °C and above. The hydrogen desorption activation energy of Mg– x wt.% Mm hydride is much lower than that of MgH 2. The pressure–composition–isotherm ( P– C– T) plots of the samples at 300–420 °C indicate that the alloys possess good cyclic stability but very poor reversibility, making the study of their thermodynamic properties difficult. The P– C– T plots also indicate that the increase of the concentration of the misch metal's rare earths leads to an increase of the hydrogen equilibrium pressure and decrease of hydrogen storage capacity.

Characterization of optical and electrical quality of Mg-doped In xGa 1− xN grown by MOCVD

We investigated the optical and electrical quality of Mg-doped In x Ga 1− x N (0⩽ x⩽0.045) grown by metalorganic chemical vapor deposition with different In and Mg contents. The band edge emission of p- In x Ga 1− x N layer depended on the Mg incorporation. The emission intensity of InGaN band edge peak was drastically reduced with increasing Mg incorporation, indicating that the concentration of nonradiative recombination centers increased with Mg doping concentration in InGaN layer. Mg-related emission of p-In x Ga 1− x N was changed from the shallow acceptor level to deep acceptor level as Mg concentration increased. Additionally, photoluminescence spectra showed that the band to acceptor emission energy E(e −, A 0) decreased with increasing In composition under the same Mg concentration of 2×10 19/cm 3. The activation energy of Mg obtained from PL spectra is reduced from 170 to 123 meV with increasing In content. Although the intensity of InGaN band edge emission and the donor–acceptor pair emission drastically decreased with increasing Mg concentration, the hole concentration increased up to 2.5×10 18/cm 3 with Mg concentration for p-In 0.045Ga 0.955N.

Upper critical field and the effect of Li doping on the activation energy in MgB 2

MgB 2 and Mg 0.93Li 0.07B 2 superconductors have been prepared by solid-state reaction. The temperature dependence of electrical resistivity in MgB 2 and Mg 0.93Li 0.07B 2 have been measured in magnetic field up to 14 T. They have almost the same superconducting transition temperature T c. The upper critical fields H c2(0) were determined. The activation energy of MgB 2 and Mg 0.93Li 0.07B 2 bulk sample have been calculated from the Arrhenius activation law ρ= ρ 0exp(− U/ k B T). Compared to MgB 2, the activation energy of Mg 0.93Li 0.07B 2 rises by 25.0%, 20.4% and 16.5% at the magnetic field 14, 10 and 7 T, respectively. A small amount of Li doping in MgB 2 that almost not changes the T c of MgB 2 has raised the activation energy U, especially at high magnetic field.

Temperature dependence of the radiative recombination zone in InGaN/GaN multiple quantum well light-emitting diodes

The temperature dependence of the radiative recombination zone in InGaN/GaN multiple quantum well light-emitting diodes is investigated. From the electroluminescence spectra measured at various temperatures, it is found that there are two peaks at about 400 and 460 nm, which can be assigned as Mg-related and quantum well transitions, respectively. The behavior of these two peaks with temperature is modeled by the two rate equation. Based on this model, we deduce the activation energy of Mg in GaN films to be about 126 meV, which is consistent with reported results obtained by other techniques.

Features of dynamic strain aging in high strength Al-Zn-Mg-Cu alloy

The present work investigates mainly the regulation and features of the occurrence of serrated yielding phenomenon of a high strength Al-Zn-Mg-Cu alloy LC4 under various heat treatments and loading conditions. The main results are: (1) In the serrated yielding temperature region a critical transition temperature T t exists. The critical plastic strain has a negative or positive temperature coefficient within the temperature region lower or higher than T t; (2) The reason for this phenomenon might be the existence of an absorbed resource which diminishes the pinning effect of solute atoms to mobile dislocations; (3) in the positive coefficient region two reverse thermal activation processes occur simultaneously. One is the solute atoms diffuse to the moving dislocations and pin the dislocations. The other one is the absorbed resource absorbs the solute and diminishes the pinning effect; (4) for LC4, the activation energy of the first process is equivalent to the diffusion activation energy of Mg in Al matrix and the second one is equivalent to that of the interface absorbed solute atoms.

Effect of electric fields on solid-state reactions between oxides

Interdiffusion in sintered polycrystalline pellets of MgO and Al2O3 at temperatures in the range 1300 to 1450° C was shown by scanning electron microscope energy dispersive X-ray probe (EDAX) and X-ray diffraction techniques to be enhanced by the application of direct current electric fields, particularly when the alumina pellet is of negative polarity, under which conditions the diffusion activation energy of Mg in Al2O3 is significantly increased. The diffusion process involved, principally, the transport of Mg by grain-boundary diffusion and possibly vapour-phase transport into the interstices of the comparatively porous alumina pellets; only minimal counter-migration of aluminium was observed in these experiments. The Mg-content of the discrete spinel grains within the reaction interface region is increased by electrolysis above the values calculated from solid solubility data, particularly where the alumina pellet is of positive polarity. The excess Mg is most apparent at the side of the spinel grains nearest the reaction interface, and precipitates as a surface MgO layer on the grains. The effective electrical mobility of the migrating species was calculated from the down-field shift of the diffusion profile and compared with values calculated from the electrical conductivity of the system.