Determination of the electron mobility and density in thin semiconductor films at microwave frequencies using the magnetoplasma resonance

The results of experimental and theoretical investigations of the magnetoplasma resonance at microwave frequencies (ω/2π=8 GHz) in AlGaAs/GaAs heterostructures and n-Cd_xHg_1−x Te films at liquid-nitrogen temperature are reported. To explain the experimental results, an expression is derived for the conductivity σ _xx (ω,B). It is shown that the parameters of the active layer in the samples — the electron mobility and density — can be determined by comparing the computational results with the experimental dependences. Fiz. Tekh. Poluprovodn. 33, 1224–1228 (October 1999)     

Radiation-thermal activation of silicon implanted in gallium arsenide

The layer density, density profile, and mobility of electrons in ²⁸Si-ion-doped layers of semiinsulating GaAs after radiation annealing with electron energy above and below the defect formation threshold and after thermal annealing in the temperature range T _a =590–830 °C are investigated. It is shown that for radiation annealing energy above the defect formation threshold ion-doped layers are formed with much lower annealing temperatures, and the degree of electrical activation of silicon in these layers is high and the density of electron mobility limiting defects is low. Fiz. Tekh. Poluprovodn. 33, 687–690 (June 1999)     

Acoustostimulated activation of bound defects in CdHgTe alloys

This paper describes the results of acoustodynamic studies of the electrical parameters (effective electron concentration n=1/eR _H and Hall mobility μ _H /ρ) of n-Cd_xHg₁₋ x crystals (x≈0.22). It is shown that ultrasonic loading (with intensities up to 0.5×10⁴ W/m²) leads to an increase in the values of n and μ _H in the impurity-conductivity temperature range (T≈100K). The authors explain the effects observed by invoking acoustostimulated liberation (activation) of donor-like bound defects, leading to a corresponding decrease in the scattering potential of alloy nonuniformities. Characteristic parameters of the acoustoelectric interaction are evaluated in the framework of an assumed dislocation model. Fiz. Tekh. Poluprovodn. 33, 410–414 (April 1999)     

Self-organized nanoscale InP islands in an InGaP/GaAs host and InAs islands in an InGaAs/InP host

Arrays of strained nanoscale InP islands in an In_0.49Ga_0.51P host on a GaAs(100) substrate and InAs islands in a In_0.53Ga_0.47As host on an InP(100) substrate are obtained by metalorganic vapor-phase epitaxy (MOVPE). Their structural and photoluminescence properties are investigated. It is shown that the nanoscale islands that are formed measure 80 nm (InP/InGaP) and 25–60 nm (InAs/InGaAs). The photoluminescence spectra of the nanoscale islands display bands in the wavelength ranges 0.66–0.72 and 1.66–1.91 μm at 77 K with maxima whose position does not vary as the effective thickness of InP and InAs increases. The radiation efficiency of the nanoscale InP islands is two orders of magnitude greater than the luminescence intensity of the InAs islands. Fiz. Tekh. Poluprovodn. 33, 858–862 (July 1999)     

Electrical properties of ZnSe/GaAs (100) heterostructures grown by photostimulated vapor-phase epitaxy

Epitaxial layers of ZnSe were grown on GaAs (100) by photostimulated vapor-phase epitaxy, using a He-Cd laser (power P⋍1 mW/cm², hν=2.807 eV) at a substrate temperature of T= (175–300) K. The temperature dependences of the mobility of the majority charge carriers were studied in layers doped during growth, using such sources as AlCl₃, Zn, Al, and Ga. Based on an analysis of the thermally stimulated current and thermally stimulated depolarization curves, parameters were established for seven deep local levels that have a substantial effect on the electrical characteristics of the heterostructures. Fiz. Tekh. Poluprovodn. 31, 11–14 (January 1997)     

Photoconductivity spectral characteristics of semiconductors with exponential fundamental absorption edge

An analysis has been performed of photoconductivity spectral characteristics of semiconductors with an exponential fundamental absorption edge as functions of the surface recombination rate and sample thickness. It is shown, in particular, that in crystals of Cd_xHg_1−x Te (x≈0.2) the spectral position of the photoconductivity maximum over a wide range of values of these parameters can be used, with an error not exceeding 1%, to determine the effective band gap and, consequently, the composition of the material. Fiz. Tekh. Poluprovodn. 33, 1295–1299 (November 1999)     

Temperature anomalies of the work function and relaxation of the surface conductivity of n-type Si in the presence of structural defects

The temperature behavior of the high-frequency conductivity of surface electron channels in Schottky diodes based on high-resistivity p-type Si containing near-surface, oxidation-induced stacking faults is studied. It is shown that the reversible temperature-induced changes in the surface band bending and the work function of Si have a stepwise character in the temperature range 80–300 K. It is concluded that the surface concentration of free electrons increases during cooling from 180 to 80 K at temperatures which are characteristic of the ordering of water dipoles. These effects are associated with structuring of the water adsorbed on the Si-SiO₂ interface and with the ordered orientation of the water dipoles on the surface in response to the loss of their rotational mobility. Fiz. Tekh. Poluprovodn. 32, 82–88 (January 1998)     

Negative dynamic differential conductivity at the cyclotron frequency in Ga1−x AlxAs under conditions of ballistic intervalley electron transfer

It is theoretically shown that under certain conditions a cyclotron resonance maser can be fabricated based on n-Ga_1−x Al_xAs-type materials. Low temperatures and strong crossed fields (E⊥H) are considered. In these fields the electrons in the lower (light) valley of the conduction band dynamically (ballistically) transit the band up to the onset energy of intervalley scattering ɛ ₀. Studies were carried out on solid solutions with composition 0<x<0.39 (ɛ ₀=(2–17)ℏω*, where ℏω* is the intervalley phonon energy). The magnitudes of the E and H fields were varied within the limits E=5–20 kV/cm and H=6–40 kOe. This produced a smooth change in the transit conditions in the passive region (ɛ<ɛ ₀), which makes it possible to obtain the desired frequency dependence of the differential conductivity (DC), σ(ω). As our studies show, previously unknown, interesting peculiarities of the hot electron system appear under these conditions. Fiz. Tekh. Poluprovodn. 32, 164–170 (February 1998)     

Controlling the U −-center density in Se-As chalcogenide-glass semiconductors by doping with metals and halogens

Temperature dependences of the drift mobilities of electrons and holes are investigated in chalcogenide-glass semiconductors with composition Se₉₅As₅, both without impurities and with the impurities Ag and Br. The data obtained indicate that the localized states that control the transport of charge carriers are U ⁻-centers, and that the change in the magnitude of the drift mobility after doping is caused by a change in the concentration of these centers. Estimates of the concentrations of positive and negatively charged intrinsic defects show that their values are similar, equalling ∼10¹⁶ cm⁻³ in impurity-free glasses with the composition Se₉₅As₅ and lying in the range 10¹³–10¹⁷ cm⁻³ when these glasses are doped with Ag, Br, and Cl. It is established that halogen impurities change the concentration of U ⁻-centers most strongly (by two to three orders of magnitude). Analysis of the data obtained shows that the percentage of electrically active Br and Cl impurity atoms is 1%, while for Ag atoms it is 10⁻²%. Fiz. Tekh. Poluprovodn. 33, 866–869 (July 1999)     

Effect of illumination time on the annealing of optically created metastable defects in p-type a-Si:H

The effect of illumination time on the relaxation of the concentration of optically created metastable defects in films of boron-doped a-Si:H in the temperature range 360–400 K is discussed. The concentration relaxes according to a stretched exponential law ~exp[\t-(t/σ _r ) ^β . In the region of temperatures under study and for illumination times of 0.1–7.0 s, the coefficient β is equal to 0.55–0.65; furthermore, the temperature dependence of the effective time τ _r was activated, with an activation energy E _a of 0.97–1.07 eV. As illumination increased, a weak increase in E _a and β is observed. The quantity τ _r increases as the illumination time increases, in accordance with a law that is close to logarithmic. The experimental results obtained are compared with the existing microscopic models for the formation and annealing of metastable defects in a-Si:H films. Fiz. Tekh. Poluprovodn. 31, 347–349 (March 1997)     

Laser-modulated epitaxy of lead telluride

The dependences of the density and mobility of free current carriers in PbTe/KCl(KBr) layers, grown by epitaxy modulated by infrared laser radiation, on the power density W of the laser radiation at the target and the substrate temperature T _s were investigated. It is shown that the free-carrier density in the regions of both electronic and hole conductivity (10¹⁶<N, P<10¹⁹cm⁻³) with mobility at 77 K corresponding to the most perfect crystals can be controlled over wide limits by varying W and T _s. Fiz. Tekh. Poluprovodn. 32, 299–302 (March 1998)     

Longitudinal photoeffect in In0.53Ga0.47As p-n junctions

A longitudinal photoeffect in In_0.53Ga_0.47As p-n junctions was investigated: the dependence of the longitudinal photoemf V _{ph 1} on the coordinates of the light spot, the temperature, and the magnetic field. The dependences on the coordinates of the light spot were found to be linear; the theoretical values of V _{ph 1} agree with the experimental values. The temperature variation of V _{ph 1} in the interval 100–300 K is explained by the variation of the current-carrier mobility as a result of thermal scattering by the lattice. In a magnetic field, V _{ph 1} is observed to increase as a result of the photomagnetic effect. Fiz. Tekh. Poluprovodn. 31, 864–865 (July 1997)     

Optical absorption in PbGa2Se4 single crystals

Optical measurements are performed in a PbGa2Se4 single crystal. The nature of the optical transitions is determined in the interval of photon energies 2.24–2.46 eV in the temperature range 77–300 K. It is shown that indirect and direct optical transitions take place in the energy intervals 2.28–2.35 eV and 2.35–2.46 eV, corresponding to E _gi =2.228 eV and E _gd =2.35 eV, respectively, at 300 K. The temperature coefficients of E _gi and E _gd are equal to −0.6×10⁻⁴ eV/K and −4.75×10⁻⁴ eV/K, respectively. Fiz. Tekh. Poluprovodn. 33, 39–41 (January 1999)     

Electron localization in sound absorption oscillations in the quantum Hall effect regime

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/Al_0.25Ga_0.75As heterostructure (with two-dimensional electron mobility μ=1.3×10⁵ cm²/(V·s) at T=4.2 K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependences of the high-frequency conductivity (in the region 30–210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy “tails” of Landau levels is discussed. Fiz. Tekh. Poluprovodn. 31, 451–458 (April 1997)     

Gadolinium-doped InGaAsSb solid solutions on an InAs substrate for light-emitting diodes operating in the spectral interval λ=3–5 µm

The influence of a gadolinium impurity on the electrical and luminescence characteristics of epitaxial structures made from narrow-gap n-InGaAsSb solid solutions grown by liquid-phase epitaxy on InAs substrates is investigated. The addition of gadolinium to the flux solution in the interval of concentrations 0<X _Gd ^l ⩽0.14 at. % has the effect of lowering the density of electrons in the InGaAsSb layers from (3–6)×10¹⁶ cm⁻³ to (7–8)×10¹⁵ cm⁻³ and increasing the carrier mobility from 32 000 cm²/(V·s) to 61 500 cm²/(V·s) (T=77 K). Also observed are a decrease in the half-width of the photoluminescence spectra from 25 meV to 12 meV and as much as a tenfold increase in their intensity (T=77 K). The electroluminescence intensity of LEDs fabricated from gadolinium-doped n-InGaAsSb/p-InAs epitaxial structures (T=300 K) increases approximately a factor of 2 relative to the undoped samples. Fiz. Tekh. Poluprovodn. 33, 1010–1013 (August 1999)     

Effect of In doping on the kinetic coefficients in solid solutions of the system PbzSn1−z )0.95Ge0.05Te

In the quaternary solid solutions (Pb_zSn_1−z )_0.95Ge_0.05Te (z=0.35 and 0.40) the effect of addition of indium (in amounts of 5–20 at. %) on the temperature dependence of the electrical conductivity σ, Hall coefficient R, Seebeck coefficient S, and Hall mobility u is investigated on samples prepared using powder technology. We found a monotonic dependence of the hole density p on the indium content N _In with a tendency toward saturation at a level p _max≈3×10²¹ cm⁻³, an abrupt drop in the mobility in samples with p≈p _max, and changes in the character of the temperature dependences R(T) and σ(T). We show that these peculiarities in the behavior of the kinetic coefficients can be interpreted in terms of quasilocal indium impurity states against the background of the valence band spectrum (with energy ɛ _In∼0.3 eV) and resonance hole scattering into these states. Fiz. Tekh. Poluprovodn. 32, 1190–1193 (October 1998)     

Transport phenomena in n-MnxHg1−x Te/Cd0.96Zn0.04Te epitaxial films

The results of an experimental study of samples of Mn_xHg_1−x Te films grown by liquid-phase epitaxy on a Cd_0.96Zn_0.04Te substrate are presented. It shows that, as a result of the diffusion of cadmium from the substrate, a Cd_xMn_yHg_1−x−y Te film with a variable band-gap layer is formed close to the 〈epitaxial-film〉-substrate interface. The appearance of this variable band gap is revealed by the transport phenomena. The temperature dependence of the band gap E _g (T) is determined in a linear approximation on T from the results of a theoretical analysis of the temperature dependences of the free-carrier concentration and mobility. It is shown that averaging the semiempirical dependences for the ternary compounds with the extreme compositions, using the virtual-crystal approximation, can produce large errors when determining E _g (T) in a specific semiconductor. Fiz. Tekh. Poluprovodn. 31, 268–272 (March 1997)     

Electron mobility and drift velocity in selectively doped InAlAs/InGaAs/InAlAs heterostructures

An increase in the electron mobility and drift velocity in high electric fields in quantum wells of selectively doped InAlAs/InGaAs/InAsAs heterostructures is obtained experimentally via controlling the composition of semiconductors forming the interface. The electron mobility at the interface in the In_0.8Ga_0.2As/In_0.7Al_0.3As metamorphic structure with a high molar fraction of In (0.7–0.8) is as high as 12.3 × 10³ cm² V⁻¹ s⁻¹ at room temperature. An increase in the electron mobility by a factor of 1.1–1.4 is attained upon the introduction of thin (1–3 nm) InAs layers into a quantum well of selectively doped In_0.53Ga_0.47As/In_0.52Al_0.48As heterostructures. A maximal drift velocity attains 2.5 × 10⁷ cm/s in electric fields of 2–5 kV/cm. The threshold field F _th for the intervalley Γ-L electron transfer (the Gunn effect) in the InGaAs quantum well is higher than in the bulk material by a factor of 2.5–3. The effect of two- to threefold decrease in the threshold field F _th in the InGaAs quantum well is established upon increasing the molar fraction of In in the InAlAs barrier, as well as upon the introduction of thin InAs inserts into the InGaAs quantum well.     

Electrical properties of epitaxial indium arsenide and narrow band solid solutions based on it

The electrical properties of epitaxial InAs and solid solutions based on it (InGaAsSb, InAsSbP, InAsGa, InAsP) have been investigated. It is shown that intentionally undoped crystals have n-type conductivity, which is determined by shallow donor impurities (E ₁=0.002–0.003 eV) and structural defects (E ₂=0.02–0.03 eV and E ₃=0.09–0.10 eV). It is shown that growth of epitaxial InAs using the neutral solvent Pb and also rare-earth elements makes it possible to reduce the electron density by almost an order of magnitude (to levels as low as 3×10¹⁵ cm⁻³) due to due to a decrease in the density of structural defects. Fiz. Tekh. Poluprovodn. 33, 781–788 (July 1999)