Electrical properties of Si:H/<Emphasis Type="Italic">p</Emphasis>-Si structures fabricated by hydrogen implantation

Hydrogenated silicon (Si:H) layers and Si:H/p-Si heterostructures were produced by multiple-energy (3–24 keV) high-dose (5×10¹⁶–3×10¹⁷ cm^?2) hydrogen implantation into p-Si wafers. After implantation, current transport across the structures is controlled by the Poole-Frenkel mechanism, with the energy of the dominating emission center equal to E _c ?0.89 eV. The maximum photosensitivity is observed for structures implanted with 3.2×10¹⁷ cm^?2 of hydrogen and annealed in the temperature range of 250–300°C. The band gap of the Si:H layer E _g ≈2.4 eV, and the dielectric constant ?≈3.2. The density of states near the Fermi level is (1–2)×10¹⁷ cm^?3 eV^?1.     

A 4<Emphasis Type="Italic">H</Emphasis>-SiC<Emphasis Type="Italic">p-i-n</Emphasis> diode fabricated by a combination of sublimation epitaxy and CVD

The possibility of fabricating heavily doped (N _a ?N _d ≥ 1 × 10¹⁹ cm_?3) p⁺-4H-SiC layers on CVD-grown lightly doped n-4H-SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (～2 × 10^?5 Ω cm²) with high thermal stability (up to 700°C), is the optimal contact to p-4H-SiC. The p-n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.     

A study of recombination centers related to As-Sb nanoclusters in low-temperature grown gallium arsenide

Electronic traps in “low-temperature” GaAs (LT-GaAs) grown at 150°C were studied. The As-Sb clusters appearing in this material after annealing were located in a plane that contained a single Sb monolayer formed during growth. The diameter of the clusters was as large as 20 nm. For the purpose of measurement, Au-n-GaAs Schottky barriers were used, in which, for certain bias voltages, the space charge region enclosed the narrow LT-GaAs layer containing the plane of clusters. The bias-voltage dependence of the structure capacitance indicates that the majority of the electrons in this layer are captured by traps, whose energy level lies ～0.5 eV below the bottom of the conduction band. The energy density of states at this energy is 10¹⁴ cm^?2 eV^?1, which sharply decreases towards the midgap. The existence of traps with activation energies of ～0.5 eV for the thermal emission of electrons is confirmed by deep-level transient spectroscopy. The magnitude of the electroncapture cross section determined by this method is in the range 5 × 10^?14?1 × 10^?12 cm². It is assumed that traps of this type are related to large As-Sb clusters.     

Thermoelectric figure of merit in solid solutions with phonon scattering by off-center impurities

The Seebeck coefficient and the electrical and thermal conductivities (S, σ, and κ) of ternary PbTe_1?xSe_x (x=0.1 and 0.3) and quaternary PbTe_1?2xSe_xS_x (x=0.025, 0.05, 0.1, and 0.15) solid solutions have been studied. Polycrystalline samples with an electron density of (0.5–5.0)×10¹⁸ cm^?3 were used; their quality was monitored by comparing the measured and calculated mobility values at 85 K. A considerable decrease in mobility and an anomalous trend in the σ(T) curve near 77 K were revealed in quaternary alloys with x?0.1; for x=0.15, unusual behavior of κ(T) was also found. According to estimates, the lattice thermal conductivity of this material is temperature-independent in the 80-to 300-K temperature range. This means that a reduction in phonon-phonon scattering with an increase in temperature is completely compensated by an increase in the scattering on impurities. The observed anomalies of σ(T) and κ(T) are considered assuming the possible of off-center location of sulfur atoms at the lattice sites. The thermoelectric figure of merit Z of the studied alloys has been determined in the range 80–300 K. In spite of decreasing mobility, the maximum Z was obtained in a quaternary compound with x=0.1: at 300 K, Z_max=2×10^?3 K^?1 with a carrier density of ～3×10¹⁸ cm^?3; at 175 K, Z_max=1.5×10^?3 K^?1 with the density decreasing to 5×10¹⁷ cm^?3. The obtained data indicate that the introduction of off-center impurities rises Z at T?300 K.     

Au-TiB<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-<Emphasis Type="Italic">n</Emphasis>-6<Emphasis Type="Italic">H</Emphasis>-SiC Schottky barrier diodes: Specific features of charge transport in rectifying and nonrectifying contacts

Mechanism of charge transport in a diode of a silicon carbide’s Schottky barrier formed by a quasi-amorphous interstitial phase TiB _x on the surface of n-6H-SiC (0001) single crystals with an uncompensated donor (nitrogen) concentration of ～10¹⁸ cm^?3 and dislocation density of ～(10⁶–10⁸) cm^?2 has been studied. It is demonstrated that, at temperatures T ? 400 K, the charge transport is governed by the tunneling current along dislocations intersecting the space charge region. At T > 400 K, the mechanism of charge transport changes to a thermionic mechanism with a barrier height of ～0.64 eV and ideality factor close to 1.3.     

Diffusion of chromium into epitaxial gallium arsenide

Diffusion of Cr into epitaxial GaAs in an open system in the temperature range of 750–850°C was studied. Temperature dependences of the diffusion coefficient and solubility of Cr in GaAs were determined. Temperature dependences of the diffusion coefficient and solubility of Cr are described by the Arrhenius equation with the parameters D ₀ = 1.9 × 10⁹ cm²/s and E = 4.1 ± 0.2 eV for the diffusion coefficient and N ₀ = 2.3 × 10²⁴ cm^?3 and E ₀ = 1.9 ± 0.4 eV for solubility. The effect of protective SiO₂ filmon the Cr diffusion coefficient and morphology of the GaAs surface after diffusion was studied.     

MOCVD growth and Mg-doping of InAs layers

Epitaxial layers of Mg-doped InAs were grown by MOCVD, and electrical properties of these layers were studied. The doping with magnesium in the course of MOCVD growth allows one to obtain strongly compensated p-InAs with a high hole density (p≈2×10¹⁸ cm^?3) and a low carrier mobility (μ≈50 cm²/(V s)) at T=300 K. When the samples are lightly doped with Mg, neutral impurities are bound with Mg, and n-type InAs layers with a carrier mobility exceeding that in undoped samples are formed.     

Electrical properties of Zinc-Tin diarsenide (ZnSnAs<Subscript>2</Subscript>) irradiated with H<Superscript>+</Superscript> ions

The results of studying the electrical properties and isochronous annealing of p-ZnSnAs₂ irradiated with H⁺ ions (energy E = 5 MeV, dose D = 2 × 10¹⁶ cm^?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R _H (D)_lim ≈ ?4 × 10³ cm³ C^?1, conductivity σ (D)_lim ≈ 2.9 × 10^?2 Ω^?1 cm^?1, and the Fermi level position F _lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs₂ compound is calculated.     

Improvement in Thermoelectric Performance of SnS Due to Electronic Structure Modification Under Biaxial Strain

Ab-initio calculations using the full potential linearized augmented plane-wave technique and the semi-classical Boltzmann theory are used to study thermoelectric properties of unstrained SnS and at 1%, 2% and 3% applied biaxial tensile (BT) strain. The studies are carried out at 800 K for p-type and n-type carriers. For an increase in BT strain, lattice constants of SnS change causing changes in the band structure and increase in the band gap which in turn modifies thermoelectric coefficients. In the case of unstrained SnS, the maximum thermopower (S) obtained is 426 μV/K at carrier concentration 5.40?×?10¹⁸ cm^?3 for p-type carriers and 435 μV/K at carrier concentration 1.68?×?10¹⁸ cm^?3 for n-type carriers. At 3% applied BT strain, S is increased to 696 μV/K at carrier concentration 4.61?×?10¹⁷ cm^?3 for p-type carriers and 624 μV/K at carrier concentration 3.21?×?10¹⁷ cm^?3 for n-type carriers. The power factor (PF) increases?～?2 times at 3% BT strain as compared to unstrained SnS, and it is 6.20 mW K^?2 m^?1 for p-type carriers. For n-type carriers, PF at 3% applied BT is slightly less than the PF for unstrained SnS, which is 6.81 mW K^?2 m^?1. For both types of carriers, the figure of merit (ZT) is found to be?～?1.5 for unstrained SnS. For p-type carriers ZT is enhanced 1.4 times at 3% applied BT strain as compared to that of unstrained SnS. However, for n-type carriers, ZT does not change drastically with increase in BT strain.     

Low-frequency noise in gallium nitride epitaxial layers with different degrees of order of mosaic structure

The correlation between the noise level 1/f and the degree of mosaic-structure order in gallium nitride epitaxial layers was studied for the first time. Samples with a doping level of N _d ?N _a ≈8×10¹⁶ cm^?3 and a relatively high degree of order were characterized by the Hooge parameter α≈1.5×10^?3. This value is unprecedently low for thin GaN epitaxial films. The Hooge parameter was significantly higher for samples with N _d ?N _a ≈1.1×10¹⁸ cm^?3 and a low degree of order despite the fact that α generally decreases with increasing doping level at the same degree of order. Thus, the degree of mosaic-structure order affects not only the optical and electrical characteristics but also the fluctuation parameters of GaN epitaxial layers.     

Optical absorption and chromium diffusion in ZnSe single crystals

ZnSe:Cr single crystals were obtained using diffusion-related doping with chromium. The diffusion of chromium was performed in an atmosphere of saturated zinc vapors, and the metallic Cr layer deposited on the crystal surface was used as the source. Lines corresponding to chromium absorption at 2.766, 2.717, and 2.406 eV were observed in the optical-density spectrum at 77 K. The highest chromium concentration in the crystals was determined from infrared absorptance in the region of 0.72 eV and was found to be equal to 8 × 10¹⁹ cm^?3. It is shown that the diffusion profile of the chromium impurity can be determined by measuring the optical density of the crystals in the visible region of the spectrum. The diffusion coefficients D of chromium in ZnSe crystals at temperatures of 1073–1273 K are calculated. An analysis of the temperature dependence D(T) made it possible to determine the coefficients in the Arrhenius equation: D₀ = 4.7 × 10¹⁰ cm²/s and E = 4.45 eV.     

Capacitance study of electron traps in low-temperature-grown GaAs

Electron traps in GaAs grown by MBE at temperatures of 200–300°C (LT-GaAs) were studied. Capacitance deep level transient spectroscopy (DLTS) was used to study the Schottky barrier on n-GaAs, whose space-charge region contained a built-in LT-GaAs layer ∼0.1 μm thick. The size of arsenic clusters formed in LT-GaAs on annealing at 580°C depended on the growth temperature. Two new types of electron traps were found in LT-GaAs layers grown at 200°C and containing As clusters 6–8 nm in diameter. The activation energy of thermal electron emission from these traps was 0.47 and 0.59 eV, and their concentration was ∼10¹⁷ cm⁻³, which is comparable with the concentration of As clusters determined by transmission electron microscopy. In LT-GaAs samples that were grown at 300°C and contained no arsenic clusters, the activation energy of traps was 0.61 eV. The interrelation between these electron levels and the system of As clusters and point defects in LT-GaAs is discussed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 401–406. Original Russian Text Copyright ? 2004 by Brunkov, Gutkin, Moiseenko, Musikhin, Chaldyshev, Cherkashin, Konnikov, Preobrazhenskii, Putyato, Semyagin.     

DLTS Analysis and Interface Engineering of Solution Route Fabricated Zirconia Based MIS Devices Using Plasma Treatment

In this work, we have fabricated low-temperature sol–gel spin-coated and oxygen (O₂) plasma treated ZrO₂ thin film-based metal–insulator–semiconductor devices. To understand the impact of plasma treatment on the Si/ZrO₂ interface, deep level transient spectroscopy measurements were performed. It is reported that the interface state density (D _it) comes down to 7.1 × 10¹⁰ eV^?1 cm^?2 from 4 × 10¹¹ eV^?1 cm^?2, after plasma treatment. The reduction in D _it is around five times and can be attributed to the passivation of oxygen vacancies near the Si/ZrO₂ interface, as they try to relocate near the interface. The energy level position (E _T) of interfacial traps is estimated to be 0.36 eV below the conduction band edge. The untreated ZrO₂ film displayed poor leakage behavior due to the presence of several traps within the film and at the interface; O₂ plasma treated films show improved leakage current density as they have been reduced from 5.4 × 10^?8 A/cm² to 1.98 × 10^?9 A/cm² for gate injection mode and 6.4 × 10^?8 A/cm² to 6.3 × 10^?10 A/cm² for substrate injection mode at 1 V. Hence, we suggest that plasma treatment might be useful in future device fabrication technology.     

Diffusion of implanted sodium in oxygen-containing silicon

The effect of oxygen on diffusion of sodium implanted into silicon is studied for the first time in the temperature range from 500 to 850°C. A high-resistivity p-Si (ρ > 1 kΩ cm) grown by the Czochralski method in a magnetic field (mCz) with the oxygen concentration ～3 × 10¹⁷ cm^?3 was used. For comparison, we used silicon grown by the crucibleless floating zone method (fz). Temperature dependences of the effective diffusion coefficient of sodium in the mCz-Si and fz-Si crystals were determined and written as D _mCz[cm²/s] = 1.12exp(?1.64 eV/kT) cm²/s and D _fz[cm²/s] = 0.024exp(?1.29 eV/kT) cm²/s, respectively. It is assumed that larger values of diffusion parameters in oxygen-containing silicon are caused by formation of complex aggregates that contain sodium and oxygen atoms.     

The Improvement of Electrical Characteristics of Pt/Ti Ohmic Contacts to Ga-Doped ZnO by Homogenized KrF Pulsed Excimer Laser Treatment

We investigated the effect of KrF excimer laser surface treatment on Pt/Ti ohmic contacts to Ga-doped n-ZnO (N_d = 4.3 × 10¹⁷ cm^?3). The treatment of the n-ZnO surfaces by laser irradiation greatly improved the electrical characteristics of the metal contacts. The Pt/Ti ohmic layer on the laser-irradiated n-ZnO showed specific contact resistances of 2.5 × 10^?4 ～ 4.8 × 10^?4 Ω cm² depending on the laser energy density and gas ambient, which were about two orders of magnitude lower than that of the as-grown sample, 8.4 × 10^?2 Ω cm². X-ray photoelectron spectroscopy and photoluminescence measurements showed that the KrF excimer laser treatments increased the electron concentration near the surface region of the Ga-doped n-ZnO due to the preferential evaporation of oxygen atoms from the ZnO surface by the laser-induced dissociation of Zn-O bonds.     

Traps with near-midgap energies at the bonded Si/SiO<Subscript>2</Subscript> interface in silicon-on-insulator structures

Capture centers (traps) are studied in silicon-on-insulator (SOI) structures obtained by bonding and hydrogen-induced stratification. These centers are located at the Si/SiO₂ interface and in the bulk of the split-off Si layer. The parameters of the centers were determined using charge deep-level transient spectroscopy (Q-DLTS) with scanning over the rate window at fixed temperatures. Such a method allows one to study the traps near the Si midgap at temperatures near 295 K. It is shown that the density of traps with a continuous energy spectrum, which are located at the bonded Si/SiO₂ interface, decreases by more than four orders of magnitude at the mid-gap compared with the peak density observed at the activation energy E _a ≈0.2–0.3 eV. The capture centers are also found in the split-off Si layer of the fabricated SOI structures. Their activation energy at room temperature is E _a =0.53 eV, the capture cross section is 10^?19 cm², and the concentration is (0.7–1.7)×10¹³ cm^?3. It is assumed that these capture centers are related to deep bulk levels induced by electrically active impurities (defects) in the split-off Si layer close to the Si/SiO₂ interface.     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

Special features of annealing of radiation defects in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si single crystals grown by the Czochralski method were studied; the hole concentration in these crystals was p = 6 × 10¹³ cm^?3. The samples were irradiated with 8-MeV electrons at 300 K and were then annealed isochronously in the temperature range T _ann = 100–500°C. The studies were carried out using the Hall method in the temperature range of 77–300 K. It is shown that annealing of divacancies occurs via their transformation into the B _s V ₂ complexes. This complex introduces the energy level located at E _v + 0.22 eV into the band gap and is annealed out in the temperature range of 360–440°C. It is assumed that defects with the level E _v + 0.2 eV that anneal out in the temperature range T _ann = 340–450°C are multicomponent complexes and contain the atoms of the doping and background impurities.     

Low-temperature (77 K) impurity breakdown in <Emphasis Type="Italic">p</Emphasis>-type 4<Emphasis Type="Italic">H</Emphasis>-SiC

The impact ionization of acceptors in aluminum-doped 4H-SiC epitaxial films (Al concentration 2 × 10¹⁵ cm^?3) at a temperature of 77 K is studied. It is found that the impact-ionization coefficient exponentially depends on the reverse electric field: α _p = α*_pexp(?F*/F). The largest ionization coefficient is α* _p = 7.1 × 10⁶ cm^?3 s^?1, and the threshold field is F* = 2.9 × 10⁴ V/cm.     

Electron emission from multilayer ensembles of vertically coupled InAs quantum dots in an <Emphasis Type="Italic">n</Emphasis>-GaAs matrix

Electron emission from multilayer arrays of vertically coupled InAs quantum dots into the n-GaAs matrix in Schottky-barrier structures (electron concentration n ≈ 2 × 10¹⁶ cm^?3) is studied by admittance spectroscopy. It is established that, in the temperature region below ～70 K, electron emission in a rate range of 3 × 10⁴–3 × 10⁶ s^?1 proceeds via thermally activated tunneling through intermediate virtual states. As the number of layers in the quantum dot array increases from three to ten, a decrease in the electron emission rate is observed.