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.     

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.     

Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 10¹⁴ and 2 × 10¹⁵ cm^–2. The diffusion coefficient of interstitial magnesium donor centers (D _i ) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence D _i (T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.     

Diffusion of yittrium in silicon

The diffusion of yttrium in silicon is studied for the first time. The diffusion is performed in air or vacuum in the temperature range of 1100–1250°C. The temperature dependence of the diffusivity of yttrium in silicon is described by the relation D = 8 × 10^?3 exp(?2.9 eV/kT) cm² s^?1. The acceptor nature of yttrium in silicon is revealed.     

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.     

Chromium diffusion in gallium arsenide

Chromium diffusion in GaAs was studied by measuring the thickness of high-resistivity layers formed during diffusion of chromium (a deep acceptor) in n-GaAs. The dependence of the chromium diffusivity in GaAs on the temperature, arsenic-vapor pressure, conductivity type, and carrier density was determined. The temperature dependence of the diffusivity is described by the Arrhenius equation with the parameters D₀=8×10⁹ cm²/s and E=4.9 eV. The dependence of the diffusivity on the arsenic-vapor pressure is described by the expression \(D \propto P_{As_4 }^{ - m} \), where m≈0.4. The experimental data obtained are interpreted in terms of the concept of the dissociative mechanism of migration of Cr atoms in GaAs.     

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.     

Special features of radiation-defect annealing in silicon <Emphasis Type="Italic">p-n</Emphasis> structures: The role of Fe impurity atoms

Deep-level transient spectroscopy is used to study the formation of complexes that consist of a radiation defect and a residual impurity atom in silicon. It is established that heat treatment of the diffused Si p⁺-n junctions irradiated with fast electrons lead to the activation of a residual Fe impurity and the formation of the FeVO (E_0.36 trap) and FeV₂ (H_0.18 trap) complexes. The formation of these traps is accompanied by the early (100–175°C) stage of annealing of the main vacancy-related radiation defects: the A centers (VO) and divacancies (V₂). The observed complexes are electrically active and introduce new electron (E_0.36: E _t ^e =E _c -0.365 eV, σ _n =6.8×10^?15 cm²) and hole (H_0.18: E _t ^h =E _v +0.184 eV, σ _p =3.0×10^?15 cm²) levels into the silicon band gap and have a high thermal stability. It is believed that the complex FeVO corresponds to the previously observed and unidentified defects that have an ionization energy of E _t ^e =E _c ?(0.34–0.37) eV and appear as a result of heat treatment of irradiated diffused Si p⁺-n junctions.     

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.     

Electronic Processes in CdIn<Subscript>2</Subscript>Te<Subscript>4</Subscript> Crystals

The results of investigations of electrical, optical, and photoelectric properties of CdIn₂Te⁴ crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass m_n = 0.44m₀ and the mobility 120–140 cm²/(V s), which weakly depends on temperature. CdIn₂Te₄ behaves as a partially compensated semiconductor with the donor-center ionization energy E_d = 0.38 eV and the compensation level K = N_a/N_d = 0.36. The absorption-coefficient spectra at the energy hν < E_g = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

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.     

Deep Radiation-Induced Defect Centers Created by a Fast Neutron Flux in CdZnTe Single Crystals

The effect of a fast neutron flux (Φ = 10¹⁴–10¹⁵ cm^–2) on the electrical and photoluminescence properties of p-CdZnTe single crystals is studied. Isothermal annealing is performed (T = 400–500 K), and the activation energy of the dissociation of radiation-induced defects is determined at E_D ≈ 0.75 eV.     

Formation kinetics of various types of hydrogen-related donors in proton-implanted silicon

The method of C-V characteristics has been used to study the accumulation kinetics of double and shallow hydrogen-related donors in proton-implanted epitaxial silicon. It is shown that the kinetics corresponds to the first-order reactions. The activation energies ΔE ₁ = 2.3 eV and ΔE ₂ = 1.4 eV and the pre-exponential factors τ₀₁ = 9.1 × 10^?17 s and τ₀₂ = 4.2 × 10^?9 s were determined for both types of the donors, respectively. It was shown that the bistability of the electric properties of silicon is due to the double hydrogen-related donor.     

Raman and infrared spectroscopy of GaN nanocrystals grown by chloride-hydride vapor-phase epitaxy on oxidized silicon

Raman and infrared spectroscopy were applied to study nanocrystalline GaN films grown by chloride-hydride vapor-phase epitaxy on SiO₂/Si(111) substrates at T=520°C. It was ascertained that GaN nanocrystals are formed on the oxidized silicon surface at a rate of 10^?2 nm/s. It was shown that the peaks in the Raman spectra E₂(high)=566 cm^?1 and A₁(LO)=730 cm^?1 correspond to the elastically strained GaN wurtzite structure. It was detected that a peak related to E₁(TO)=558 cm^?1 arises in the infrared spectra, which shows that elastic stresses in the nanocrystals are insignificant.     

Surface texture of single-crystal silicon oxidized under a thin V<Subscript>2</Subscript>O<Subscript>5</Subscript> layer

The process of surface texturing of single-crystal silicon oxidized under a V₂O₅ layer is studied. Intense silicon oxidation at the Si–V₂O₅ interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO₂ inclusions in silicon depth up to 400 nm is formed at the V₂O₅–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10^–15 cm² s^–1). A model of low-temperature silicon oxidation, based on atomic oxygen diffusion from V₂O₅ through the SiO₂ layer to silicon, and SiO _x precipitate formation in silicon is proposed. After removing the V₂O₅ and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.     

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H₂ are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O₂ is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H₂ is added. The values obtained for the activation energy of the silicon diffusion coefficient, E _a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t ^1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.     

Diffusion-Controlled growth of Ge nanocrystals in SiO<Subscript>2</Subscript> films under conditions of ion synthesis at high pressure

The growth of Ge nanocrystals in SiO₂ films is studied in relation to the dose of implanted Ge⁺ ions and the annealing temperature at a pressure of 12 kbar. It is established that the dependences of the nanocrystal dimensions on the content of Ge atoms and the annealing time are described by the corresponding root functions. The nanocrystal radius squared is an exponential function of the inverse temperature. The dependences correspond to the model of the diffusion-controlled mechanism of nanocrystal growth. From the temperature dependence of the nanocrystal dimensions, the diffusion coefficient of Ge in SiO₂ at a pressure of 12 kbar is determined: D = 1.1 × 10^–10 exp(–1.43/kT). An increase in the diffusion coefficient of Ge under pressure is attributed to the change in the activation volume of the formation and migration of point defects. Evidence in favor of the interstitial mechanism of the diffusion of Ge atoms to nanocrystal nuclei in SiO₂ is reported.     

Special features of charge transport in PbGa<Subscript>2</Subscript>Se<Subscript>4</Subscript> crystals

The current-voltage (I-V) characteristics of PbGa₂Se₄ single crystals grown by the Bridgman-Stockbarger method with a resistivity of 10¹⁰–10¹² Ω cm were measured. The value of the majority carrier mobility μ=14 cm² V^?1 s^?1, calculated by the differential method of analysis of I-V characteristics, makes it possible to evaluate a number of parameters: the carrier concentration at the cathode (n_c0=2.48 cm^?3), the width of the contact barrier d_c=5.4×10^?8 cm, the cathode transparency D _c ^* =10^?5–10^?4 eV, and the quasi-Fermi level E_F=0.38 eV. It is found that a high electric field provides the charge transport through PbGa₂Se₄ crystals in accordance with the Pool-Frenkel effect. The value of the dielectric constant calculated from the Frenkel factor is found to be equal to 8.4.     

Simulation of Electronic Center Formation by Irradiation in Silicon Crystals

We present the results of a study on localized electronic centers formed in crystals by external influences (impurity introduction and irradiation). The main aim is to determine the nature of these centers in the forbidden gap of the energy states of the crystal lattice. For the case of semiconductors, silicon (Si) was applied as model material to determine the energy levels and concentration of radiation defects for application to both doped and other materials. This method relies on solving the appropriate equation describing the variation of the charge carrier concentration as a function of temperature n(T) for silicon crystals with two different energy levels and for a large set of N ₁, N ₂ (concentrations of electronic centers at each level), and n values. A total of almost 500 such combinations were found. For silicon, energy level values of ε ₁ = 0.22 eV and ε ₂ = 0.34 eV were used for the forbidden gap (with corresponding slopes determined from experimental temperature-dependent Hall-effect measurements) and compared with photoconductivity spectra. Additionally, it was shown that, for particular correlations among N ₁, N ₂, and n, curve slopes of ε ₁/2 = 0.11 eV, ε ₂/2 = 0.17 eV, and α = 1/2(ε ₁ + ε ₂) = 0.28 eV also apply. Comparison between experimental results for irradiation of silicon crystals by 3.5-MeV energy electrons and Co⁶⁰ γ-quanta revealed that the n(T) curve slopes do not always coincide with the actual energy levels (electronic centers).