Electrical Properties of Praseodymium-doped GaAs and Al0.3Ga0.7As Epilayers

Praseodymium-doped GaAs and Al_0.3Ga_0.7As epilayers grown on Semi-Insulating (SI) GaAs substrates by Liquid Phase Epitaxy (LPE) were first studied in this present work. Measurement techniques, such as microscopic observation, X-ray diffraction, Secondary Ion Mass Spectroscopy (SIMS), and Hall measurement were employed. Layers doped with Pr resulted in a mirror-like surface, except several high Pr-doped layers having droplet surfaces. Hall measurements reveal that the grown layers contained p-type layers, carrier concentrations from 6.3 × 10¹⁵ to 1.2 × 10¹⁶ cm⁻³, and from 6.3 × 10¹⁵ to 3.5 × 10¹⁶ cm⁻³ for Pr-doped GaAs and Al_0.3Ga_0.7As epilayers, respectively. Although p-type conduction exists, in the light of electrical features, doping of Pr into the GaAs and Al_0.3Ga_0.7As growth melts, is still considered to exhibit gettering properties rather than to become a new acceptor itself. Additional photoluminescence examinations were taken. Their results also indicate that Pr-doped layers produce no new emission lines and support the electrical observations.     

Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts

Electrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n-GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm²/V · sat n = 2.5 · 10¹⁴ cm⁻³ has been grown).     

A study of the Growth-Temperature-dependent Surface Morphology in InSb Liquid Phase Epitaxy

InSb LPE layers were grown on (111) InSb substrates, their phase diagram and growth rates studied. The InSb activity coefficient α(T), determined by fitting the experimental data, had a value of 2556–11.11 · T cal · mole⁻¹. The terraces on the surface were reduced by increasing the temperature to 350 °C. Hall measurements of InSb/CdTe heterostructure failed due to the high Te segregation. The carrier concentration of these InSb epilayers, however, was determined by C-V measurements with values between 7.5 · 10¹⁴ cm⁻³ and 5 · 10¹⁵ cm⁻³.     

Doping Properties of Pr2O3 Associate InP Liquid Phase Epitaxy

InP epilayers were grown on semi-insulating InP substrates by liquid phase epitaxy with Pr₂O₃-doping. Most grown layers yield mirror-like surfaces and good crystal quality. Hall measurements indicate that n-type background concentration of those grown InP layers will decrease from a value of 2.8 × 10¹⁷ to 3.0 × 10¹⁶ cm⁻³. Their correspondent 77 K mobility also varied from a value of 1326 to 3775 cm²/V s. The photoluminescence (PL) spectra of Pr₂O₃-doped InP epilayers display narrower FWHM and stronger intensity ratios (for band peak to the impurity peak). These PL spectra also demonstrate that the grown layers exhibit a pure crystal quality.     

Organometallic vapour phase epitaxy of galliumarsenide using Ga(CH3)3 · N(CH3)3-adduct as precursor

Epitaxial layers of GaAs have been grown by MOVPE using trimethylgallium-trimethylamin-adduct (TMGa-TMN) as the Ga-precursor. In comparison to the growth system using pure TMGa no significant influence on growth conditions and materials parameters could be found. The deposited GaAs is of fairly high quality with room temperature mobilities of 6700 cm²/Vs at free electron concentrations of about 1 × 10¹⁵ cm⁻³. No hints to nitrogen incorporation could be found.     

Growth of Zn3As2 on GaAs by liquid phase epitaxy and their characterization

Zn₃As₂ epitaxial layers were grown on GaAs (1 0 0) substrates by liquid phase epitaxy (LPE) using Ga as the solvent. Zinc mole fraction in the growth melt was varied from 1.07×10^?2 to 6×10^?2. X-ray diffraction spectrum exhibits a sharp peak at 43.3° characteristic of Zn₃As₂ crystalline layer. The peak intensity increases with increase in zinc mole fraction in the growth melt. The compositions of the as-grown Zn₃As₂ layers were confirmed by energy dispersive X-ray (EDX) analysis. Surface morphology was studied using scanning electron microscopy (SEM) and the thickness of the epilayers was also determined. The Hall measurements at 300 K indicate that Zn₃As₂ epilayers are unintentionally p-doped. With an increase of zinc mole fraction in the growth melt, carrier concentration increases and carrier mobility decreases. Infrared optical absorption spectroscopy showed a sharp absorption edge at 1.0 eV corresponding to the reported band gap of Zn₃As₂.     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Crystal growth and spectral properties of Nd:Ca5(BO3)3F

A neodymium doped Ca₅(BO₃)₃F single crystal with size up to 51×48×8 mm³ has been grown by the top seeded solution growth (TSSG) technique with a Li₂O‐B₂O₃‐LiF flux. The spectra of absorption and fluorescence were measured at room temperature. According to Judd‐Ofelt (J‐O) theory, the spectroscopic parameters were calculated and the J‐O parameters Ω₂, Ω₄, Ω₆ were obtained as follows: Ω₂ = 1.41×10⁻²⁰cm², Ω₄ = 3.18×10⁻²⁰cm², Ω₆ = 2.11×10⁻²⁰cm². The room temperature fluorescence lifetime of NCBF was measured to be 51.8 μs. According to the J‐O paramenters, the emission probabilities of transitions, branching ratios, the radiative lifetime and the quantum efficiency from the Nd^{3+ 4}F_3/2 metastable state to lower lying J manifolds were also obtained. In comparasion with other Nd‐doped borate crystals, the calculated and experimental parameters show that NCBF is a promising SFD crystal.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Crystal growth of PbTe and (Pb,Sn)Te by the bridgman method and by THM

Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8–12 × 10⁴ cm⁻². All the materials were p-type with carrier concentrations from 1 to 2 × 10¹⁸ cm⁻³.     

Temperature dependence of electrical conductivity and hall effect of Ga2Se3 single crystal

Electrical conductivity (σ) and Hall coefficient (R_H) of single crystal grown from the melt have been investigated over the temperature range from 398 K to 673 K. Our investigation showed that our samples are p-type conducting. The dependence of Hall mobility an charge carrier concentration on temperature were presented graphically. The forbidden energy gap was calculated and found to be 1.79 eV. The ionization energy of impurity level equals 0.32 eV approximately. At 398 K the mobility equals to 8670 cm² V⁻¹ s⁻¹ and could described by the law μ = aTⁿ (n = 1.6) in the low temperature range. In the high temperature range, adopting the law μ = bT^–m (as m = 1.67), the mobility decreases. This result indicates that in the low temperature range the dominant effect is scattering by ionized impurity atoms, whereas in the high temperature range the major role is played by electron scattering on lattice vibrations (phonons). At 398 K the concentration of free carriers showed a value of about 1.98 × 10⁷ cm⁻³.     

Thermoelectric power of indium sesquisulphide single crystals

The investigation covers a temperature range from 200 to 450 K. Thermoelectric power measurements of In₂S₃ crystals showed that all samples under investigation have a positive TEP in all temperature ranges, indicating n-type conductivity for In₂S₃ crystals. The ratio of the electron and hole mobilities is μ_n/μ_p = 4.71. The effective mass of electrons m is found to be 0.00008 × 10⁻³¹ kg. The obtained effective masses of holes m = 1.893 × 10⁻³¹ kg. The diffusion coefficient for both carriers (electrons and holes) is evaluated to be 84.71 cm²/s and 17.985 cm²/s respectively. The mean free time between collision is estimated to be τ_n = 1.7 × 10⁻²⁰s, and τ_p = 8.5 × 10⁻¹⁷s. The estimated diffusion length for electrons is found to be L_n = 1.2 × 10⁻⁹ cm and L_p = 3.9 × 10⁻⁸ cm.     

Crystallization and Thermoelectric Power of Tl2Te3 Single Crystals

Thermoelectric power (TEP) of Tl₂Te₃ was measured in the temperature range from 150 to 480 K. The crystal was found to have a p-type conductivity throughout the whole range of temperature. The effective masses of holes and electrons were determined at room temperature and found to be m = 1.1 × 10⁻³⁴ kg and m = 1.72 × 10⁻³⁵ kg, respectively. Also at the same temperature the mobility μ_p was found to be 1737.8 cm²/V.s and μ_n was 3962.2 cm²/V.s. The hole and electron diffusion coefficients were obtained as 44.84 cm²/s, and 102.23 cm²/s. The relaxation times for holes and electrons were calculated and yielded the values τ_p = 1.19 × 10¹² s and τ_n = 4.25 × 10¹³ s, respectively.     

Temperature dependences of the electrical conductivity and hall coefficient of indium telluride single crystals

Conductivity type, carrier concentration and carrier mobility of InTe samples grown by Bridgmann technique were determined by the Hall effect and electrical conductivity measurements. The study was performed in the temperature range 150–480 K. Two samples with different growth rate were used in the investigation. The samples under test were P-type conducting, in accordance with previous measurements of undoped material. The Hall coefficient was found to be isotropic yielding room temperature hole concentration in the range 10¹⁵ – 10¹⁶ cm⁻³. The hole mobilities of InTe samples were in the range 1.17 × 10³ – 2.06 × 10³ cm²/V · sec at room temperature. The band – gap of InTe determined from Hall coefficient studies has been obtained equal to 0.34 ev. The scattering mechanism was checked, and the electrical properties were found to be sensitive to the crystal growth rate.     

Er doping of Si and Si0.88Ge0.12 using Er2O3 and ErF3 evaporation during molecular beam epitaxy A transmission electron microscopy study

The incorporation behavior of Er into Si and Si_0.88Ge_0.12 using ErF₃ and Er₂O₃ as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. Dissociation of Er₂O₃ took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4×10¹⁹ cm⁻³ using Er₂O₃ and a high F background pressure. Using ErF₃ compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF₃ molecules, but also from CF_x (x=1–4) and F background species, which are present due to a reaction between the ErF₃ source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1×10¹⁹ cm⁻³ and without observable defects using ErF₃ as source material. For the case of Er-doping of Si_0.88Ge_0.12 using ErF₃, we observed contrast along lines in the growth direction at an Er concentration of 1×10¹⁹ cm⁻³, which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence.     

An EPR Study of Scapolite

In single crystals of scapolite from two different localities, three paramagnetic centres are detected by electron paramagnetic resonance (EPR): 1. One isotropic singlet with g_iso = 2.005; 2. One triclinic singlet with g‖ = 2.005 ± 0.001 and g⟂= 2.009; 3. One triclinic sextet with g‖= 2.005 ± 0.001, g⟂ = 2.011; A‖ = 85.4 × 10⁻⁴ cm⁻⁴, A⟂ = 85.3 × 10⁻⁴ cm⁻¹. Centres 1 and 2 can be attributed to colour centres as they are bleached after annealing. Centre 3 can be due to Mn²⁺ (only the central M_s = ± 1/2 transition is observable) most likely substituting for Ca²⁺ The site symmetry must be triclinic but due to Al, Si disorder and mixed Na, Ca composition the different components from magnetically non-equivalent sites are averaged out for many orientations.     

Thermoelectric properties of indium sesquiselenide single crystals

Single crystals of δ-In₂Se₃ were prepared in the solid state laboratory at Qena-Egypt, by means of Bridgman technique. The temperature dependence of the thermal e.m.f. α in the temperature range from 205 K up to 360 K of In₂Se₃ was studied. The δ-phase In₂Se₃ sample appeared to be n-type. The ratio of the electron and hole mobilities are found to be μ_n/μ_p = 1.378. The effective masses of charge carriers are m = 1.3 × 10⁻³⁰, m = 8.27 × 10⁻³¹ kg for holes and electrons, respectively. The diffusion coefficient was estimated to be D_n = 3.37 cm²/s and D_p = 2.45 cm²/s for both electrons and holes, respectively. The mean free time between collision can be deduced to be τ_n = 70 × 10⁻¹⁶ s and τ_p = 8 × 10⁻¹⁴ s for both electrons and holes. The diffusion length of the electrons and holes are found to be L_n = 1.5 × 10⁻⁷ cm and L_p = 4.4 × 10⁻⁷ cm.     

Growth Kinetics of Barium Sulphate in Suspension

The growth rate of barium sulphate seed crystals from stirred solutions was studied conductometrically at 25°C by a stopped-flow technique. The supersaturation ranged from 3 × 10⁻⁷ to 3 × 10⁻⁸ mol BaSO₄/cm³. The seed crystals were grown in the system during the initial (steady-state) period of the experiment. Crystal size distributions were determined by optical microscopy. The growth rate of barium sulphate under the conditions of the experiments can be expressed by a quadratic function of supersaturation. The results, which suggest an interface rate-controlling mechanism, are discussed with respect to published data.