Characterization of ohmic contacts to InP

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as ohmic contacts are presented. The layers were heat treated at temperatures up to 550°C and were examined with Auger electron spectroscopy. For contact to n-type InP three thin film systems were investigated: gold, nickel and a composite Ni/Au/Ge layer. Nickel was found to produce ohmic behavior in the Ni/Au/Ge/InP system with a minimum specific contact resistance r_c of 3×10^?5 Ω cm² for a net doping of 3×10¹⁶ cm^?3. For contact to p-type InP a film consisting of Au/Mg was investigated. For heat treatment of the Au/Mg/InP system above 350°C, r_c decreased as the temperature of the heat treatment increased and the surface morphology exhibited increasing signs of alloying at higher temperatures. The smoothest surface was obtained at 446°C for 50 min with r_c≈1×10^?4Ω cm² for a net doping of 6×10¹⁷ cm^?3.     

Effect of deposition conditions on the InP thin films prepared by spray pyrolysis method

InP thin films were prepared by spray pyrolysis technique using aqueous solutions of InCl₃ and Na₂HPO₄, which were atomized with compressed air as carrier gas. The InP thin films were obtained on glass substrates. Thin layers of InP have been grown at various substrate temperatures in the range of 450–525°C. The structural properties have been determined by using X-ray diffraction (XRD). The changes observed in the structural phases during the film formation in dependence of growth temperatures are reported and discussed. Optical properties, such as transmission and the band gap have been analyzed. An analysis of the deduced spectral absorption of the deposited films revealed an optical direct band gap energy of 1.34–1.52 eV for InP thin films. The InP films produced at a substrate temperature 500°C showed a low electrical resistivity of 8.12 × 10³ Ω cm, a carrier concentration of 11.2 × 10²¹ cm⁻³, and a carrier mobility of 51.55 cm²/Vs at room temperature.     

Vapor growth of thin heteroepitaxial InP films on CdS

InP was heteroepitaxially deposited onto CdS single-crystal substrates by chemical vapor deposition using phosphine (PH₃), HCl and indium as reactants. Single-crystalline films were deposited at substrate temperatures as low as 450°C. Scanning Auger microscopy shows that the films are InP and that formation of solid solutions between the CdS and the InP is minimal. The as-grown films are n type with residual donor densities of 4 × 10¹⁶–4 × 10¹⁷ cm^-3.     

The growth and properties of Mn-doped single-crystal InP

Manganese has been studied as a new acceptor impurity in bulk InP. Large single crystals which possess the lowest hole concentrations yet reported, 3 × 10¹⁴ cm^?3, have been grown by the liquid encapsulated Czochralski pulling technique. This low carrier level is due to the low distribution coefficient for the electrically active manganese, k_active = 4 × 10^?3 and the high activation energy, 0.30 eV. In comparison, the acceptor commonly used to produce p-type material in InP, Zn, has a distribution coefficient of ≈1.0 which makes it especially difficult to achieve the low hole concentrations necessary for certain device applications. Optical absorption and photoluminescence data are also reported.     

Activation of p-type conduction in ZnO:N films by annealing in atomic oxygen

ZnO:N epitaxial films have been grown by reactive magnetron sputtering. The effect of annealing in atomic oxygen on the structural and electrical properties of the ZnO:N films has been studied by X-ray diffraction, atomic force microscopy, Hall effect measurements, and X-ray photoelectron spectroscopy. By annealing at temperatures from 500 to 700°C, we have obtained p-type ZnO:N films with a resistivity of ～57 Ω cm, hole mobility of ～2.7 cm²/(V s), and hole concentration of ～6.8 × 10¹⁷ cm^?3. X-ray photoelectron spectroscopy results suggest that the p-type conductivity of the films is due to a decrease in the concentration of (N₂)_O and V _O donors.     

Mixage ionique sur des structures Au/InP

The reactions induced by Zn⁺ implantations near the interface of Au/InP contacts have been studied by using scanning electron microscopy, X-ray diffraction, He⁺ Rutherford backscattering, secondary ion mass spectrometry and current-voltage measurements. A 5 × 10¹⁴ Zn ions cm^-2 dose does not induce compound formation but accelerates the growth of Au₃In and Au₂P₃ patches during post-annealing treatment. After a 5 × 10¹⁵ Zn ions cm^-2 implantation, many compounds, different from those obtained by a thermal anneal, are detected. These compounds, which depend on the implantation temperature (25 or 200°C), have a layered structure. In this case no Au₂P₃ is observed. However, for the range of doses (from 10¹⁴ to 5 × 10¹⁵ Zn ions cm^-2), the temperatures of implantation (25 and 200°C) and the range of annealing temperatures (from 320 to 450°C) that were studied, no contact with a low resistivity is formed. The electrical properties are in fact limited by an InP layer damaged by the ion implantation in which the zinc atoms are trapped in an electrically inactive form.     

Investigation of germanium films and GeSi interface structure by transmission electron microscopy

The structure of germanium films (d≌0.3 μm) evaporated onto a silicon substrate and the GeSi interface have been investigated by transmission electron microscopy (TEM). Ge was evaporated in a vacuum of approximately 10^?6 Torr onto (111) Si. Epitaxial growth was observed at substrate temperatures T_s>500°C. The films grown at T_s = 520°–600°C (low temperature epitaxy) were characterized by a high density of stacking faults (SF), microtwin lamellae and dislocations which lay normal to the film surface. In this case the interface dislocations were regular and the dislocation density was equal to (3–4)×10¹⁰ cm^?2. At T_s = 700°–850°C (high temperature epitaxy) few stacking faults were discovered. Dislocations in the interior of the film formed three-dimensional networks as a result of interactions of different slip systems and dislocation climb. The formation of misfit dislocations was apparent at the interface. The region T_s = 630°–700°C is an intermediate region.     

Properties of polycrystalline silicon films prepared from fluorinated precursors

Polycrystalline silicon films have been prepared at low temperature on glass substrate from fluorinated precursors by PECVD technique varying the hydrogen dilution and gas flow rate. Undoped film with dark-conductivity 1.05×10⁻² S cm⁻¹ has been obtained. For n-type poly-Si film the highest conductivity achieved is 2.8 S cm⁻¹. Grain size observed from SEM varies from 4 to 6 μm for undoped and 2 to 3 μm for phosphorous doped films. The main crystalline peak is 〈111〉 whereas the crystallite size calculated from XRD is 350 Å. The optical absorptions and hydrogen contents in the films deposited under different conditions have been studied. Growth kinetics are dominated by the precursors SiF_nH_m (m+n≤3) and concentrations of F and H on the growth surface.     

Growth of p-type ZnO thin films by using an atomic layer epitaxy technique and NH3 as a doping source

Nitrogen-doped, p-type ZnO thin films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C₂H₅)₂ [Diethylzinc, DEZn], H₂O and NH₃ as a zinc precursor, an oxidant and a doping source gas, respectively. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 210 Ω cm with a hole concentration of 3.41 × 10¹⁶ cm^− 3. Low temperature-photoluminescence analysis results support that the nitrogen ZnO after annealing is a p-type semiconductor. Also a model for change from n-type ZnO to p-type ZnO by annealing is proposed.     

Influence of deposition temperature on the superconductivity of Y1−x HoxBa2Cu3O7 −δfilms produced by dc-magnetron sputtering

Experimental results of research on the influence of deposition temperature (T _s) on crystal structure and superconductivity of Y_1?x HoxBa₂Cu₃O_{7 ?δ} (YHBCO) films deposited by dcmagnetron sputtering are reported. X-ray diffraction analysis showed that the films grew with preferential orientation of thec-axis normal to the substrate surface in the range of temperature 750–820°C. The single-crystal structure of the YHBCO films grown epitaxially at the optimal substrate temperatures of 820, 800, 760, and 750°C, respectively, have been established by rocking curves, Φ-scan, and electron channeling pattern (ECP). Typical values of the critical current density (A · cm^?2) at 77 K and 0.1 T field are 2.1×10⁵, 4×10⁵, 6.2×10⁵, and 3.1×10⁵ for thex=0, 0.2, 0.4, 0.7 films respectively, measured by a Quantum Design magnetrometer (H∥c).     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

The origin of the uniaxial anisotropy in thin films of (YLaPb)3 (FeGa)5O12 and its variation along the growth direction

The uniaxial anisotropy of La, Ga: YIG films grown by liquid phase epitaxy has been measured using spin-wave resonance techniques. The results show that in films produced at growth temperatures above 840°C on [111] Gd₃Ga₅O₁₂ substrates the uniaxial anisotropy is stress induced. At lower growth temperatures the Pb incorporation gives rise to a positive growth-induced anisotropy of 4×10⁴ erg/cm³ per Pb atom per formula unit. Around the growth temperature of 840°C, where the Pb and La effects cancel, homogeneous films can be grown. Variations of anisotropy within the filmsthickness will be shown to be due to variations of local growth rates which in turn cause composition changes.     

Structural, electrical and optical properties of Si doped ZnO films grown by atomic layer deposition

Si doped ZnO (SZO) films with various Si concentrations were deposited by atomic layer deposition at 300 °C using triethyzinc, tris(dimethylamino)silane and H₂O₂ as the precursors. The influences of Si doping concentration on structural, electrical and optical properties of ZnO films have been investigated. All the films exhibited a highly preferential c-axis orientation. A minimum resistivity of 9.2 × 10^?4 Ω cm, with a carrier concentration of 4.3 × 10²⁰ cm^?3 and a Hall mobility of 15.8 cm²/Vs, was obtained for SZO film prepared with the Si concentration of 2.1 at%. The increase of conductivity with Si doping was attributed to the presence of Si in +3 valence state acting as donor in ZnO and the increases of oxygen vacancies with Si concentration as proven by XPS measurements. The optical bandgap of SZO films initially increased from 3.25 to 3.55 eV with increasing of Si concentration to 2.1 at%, then decreased with further increase of Si concentration. The blue shift of band gap of SZO films with increasing carrier concentration can be explained by the Burstein-Moss (B-M) effects.     

Electrical properties and extension mechanism of Ohmic region of sol–gel derived Ba0.7Sr0.3TiO3 thin films by Zn doping

Undoped and 3 mol% Zn-doped barium strontium titanate thin films were deposited on Pt/Ti/SiO₂/Si substrates using a sol–gel method. The microstructure and morphology of the films were characterized by X-ray diffraction and atomic force microscopy. It showed that both films are polycrystalline with a perovskite structure and smaller grains were observed for the Zn-doped thin films. Dielectric measurements showed that the dielectric loss at 500 kHz was reduced from 0.042 to 0.019 by Zn doping, which was accompanied by a slight decrease of the dielectric constant from 303 to 273. At an applied electric field of 60 kV/cm, the leakage current density of the Zn-doped Ba_0.7Sr_0.3TiO₃ thin films was 2.5 × 10⁻⁸ A/cm², which was by two orders of magnitude lower than that of the undoped films. The leakage current characteristics also indicated that the Ohmic conduction region of barium strontium titanate thin films was extended by Zn dopant. The microstructure, electrical properties and extension mechanism of Ohmic conduction region of the Zn-doped barium strontium titanate thin films were discussed in relation to the effect of Zn doping.     

Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds

HfO₂ films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 Å) nearly stoichiometric monoclinic HfO₂. The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO₂ films varied between 2 × 10⁶ and 4.5 × 10⁶ V cm^?1. C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10¹¹ and 6 × 10¹¹ cm^t?2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V_FB values were between ?0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V² over a wide range.     

Nitrogen doping of ZnTe for the preparation of ZnTe/ZnO light-emitting diode

Nitrogen-doped p-type zinc telluride (p-ZnTe) films are prepared by sputtering in a mixture of nitrogen/argon plasma. The effect of doping level N (ratio of N₂ flow rate to that for the mixed gas) in the range 0–10 % on the films properties is investigated. Heterojunction diodes are prepared on stainless steel flexible substrate from the p-ZnTe (doping level, N = 5 %) and solution-grown n-ZnO films. The junction parameters and light-emission properties of diodes are investigated. Doping level beyond N = 1 %, changes the cubic crystal structure of ZnTe to hexagonal and reduces the size of crystallites. At the doping level N = 2–4 %, films with the highest hole density of 2.5 × 10¹⁸ cm^?3 and lowest band gap energy of 1.4 eV are obtained. The diodes junction built-in potential and the donor density in n-ZnO films are found to be in the range 0.4–0.7 V and 1.5 × 10¹⁷–1.4 × 10¹⁸ cm^?3, respectively. Diodes exhibit electroluminescence in the UV and visible regions due to the band edge and defect emissions in ZnO.     

Local structure and electron spin resonance of copper-doped SrTiO3 ceramics

We report X-ray diffraction and electron spin resonance (ESR) measurements of the effect of SrTiO₃ ceramics doping using Cu²⁺ ions. ESR measurements reveal two kinds of Cu²⁺ centers in weakly (0.2–0.5 mol% Cu) doped SrTiO₃. Both kinds of centers have been attributed to Cu²⁺ at octahedral Ti sites and possibly associated either with a nearest-neighboring oxygen vacancy (center #1) or some other positively charged defect (center #2). The ESR spectra of the above centers are described by the following spin Hamiltonian parameters: g _‖ = 2.263(1), g _⊥ = 2.041(1), A _‖ = 170(1) × 10^?4 cm^?1, A _⊥ = 27(1) × 10^?4 cm^?1 (center #1) and g _‖ = 2.334(1), g _⊥ = 2.059(1), A _‖ = 137(1) × 10^?4 cm^?1, A _⊥ ≈ 0(1) × 10^?4 cm^?1 (center #2). For copper concentration larger than 2 mol%, the antiferromagnetic SrCu₃Ti₄O₁₂ (SCTO) phase has been detected by both X-ray diffraction and ESR. Its volume increases with increase of Cu concentration reaching about 17 % at Cu doping of 20 mol%. The composite SrTiO₃–SCTO ceramics exhibits substantial magnetocapacitance effect, which could be enhanced by electrostriction of SrTiO₃.     

Micropore density in a-Si:H and a-Si:H:Cl films

a-Si:H films deposited from various silane-containing gas mixtures have been studied regarding their porosity. Micropore densities of 2.O × 10²cm^-2, 5.0 × 10⁴cm^-2 and 5.0 × 10⁴cm^-2 were determined for a-Si:H:C1, a-Si:H(H₂) and a-Si:H(Ar) films, respectively. It is suggested that these values correlate with the structural properties of the films, so that a-Si:H:Cl films seem to be the most uniform on the microstructural scale.     

Growth and characterization of pulsed-laser-deposited polycrystalline Bi3.33Sm0.67Ti3O12 ferroelectric thin films

Ferroelectric Bi_3.33Sm_0.67Ti₃O₁₂ (BSmT) thin films have been fabricated on Pt/TiO_x/SiO₂/Si substrates by pulsed laser deposition and their structural and ferroelectric properties have been characterized. The structure and morphology of the films were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. About 520-nm-thick BSmT films grown at 700 °C exhibit excellent ferroelectric properties with a remanent polarization (2P_r) of 41.8 μC/cm² and coercive field (E_c) of 91.0 kV/cm, at an applied electric field of 385 kV/cm. The leakage current density was 2.0 × 10^− 6 A/cm² at a dc electric field of 200 kV/cm. The films also demonstrate fatigue-free behavior up to 10⁹ read/write switching cycles with 1 MHz bipolar pulses at an electric field of 192 kV/cm. As a result, Sm-substituted bismuth titanate films with good ferroelectric properties and excellent fatigue resistance are useful candidates for ferroelectric memory applications.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.