CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Hole mobility and trapping in PVK films doped with CdSe/CdS and CdSe quantum dots

Experimental study of the hole mobility in polyvinylcarbazole (PVK) films doped with two kinds of nanocrystals, on bare core CdSe and core-shell CdSe/CdS quantum dots, with concentrations ranging from 3 · 10¹⁰ to 3 · 10¹⁵ cm⁻³, is presented. The quantum dots investigated were made using colloidal chemistry. The hole mobility was measured using the time-of-flight technique as a function of the applied electrical field in the range 10⁵–10⁶ V/cm and for temperatures from 20°C to 50°C. The transient curves, being featureless on a linear plot, show on a double logarithmic scale a sharp inflection point indicating a dispersive carrier drift process. The recovered values of the mobility are in the range 3 · 10⁻⁸–10⁻⁶ cm²·V⁻¹·s⁻¹ and their field and temperature dependences can be analyzed formally within the framework of the Gaussian disorder model proposed by B?ssler. The energetic disorder is, within the experimental accuracy, independent of the concentration and type of quantum dots for the CdSe quantum dots at all concentrations and for the CdS/CdSe quantum dots up to 10¹⁴ cm⁻³. The spatial disorder factors are very large (from 5.3 to 8.7) and do not depend in a systematic way upon the type and concentration of quantum dots (QDs). The experiments show that the apparent mobility does not change considerably with concentration, but it was found that the samples with CdSe/CdS quantum dots at concentrations from 10¹⁵ to 3 · 10¹⁵ cm⁻³ show a decreased photocurrent response. The dependence of the time-integrated transients (corresponding to the full charge value) upon the quantum-dot concentration has been determined. Differences in total photogenerated charge for pure and doped polymer films imply that the quantum dots of that type are the hole traps with capture times much more smaller than the transit time and with emission times a few orders longer than the transit time. CdSe quantum dots without a shell do not seem to exhibit the same properties as core shells and do not produce considerable changes in the charge transfer, even at a density of 10¹⁵ cm⁻³.     

The nonlinear optical property and photoinduced anisotropy of?a?novel azobenzene-containing fluorinated polyimide

A novel azobenzene-containing fluorinated polyimide was synthesized. The nonlinear optical property and photoinduced birefringence of a polyimide thin film were investigated. Large third-order nonlinear refraction (n ₂=−4.49×10⁻¹¹ cm²/W) was observed in the polyimide thin film by carrying out Z-scan measurement. The polyimide thin film exhibited larger nonlinear refraction than that of a mono-azo dye doped PMMA thin film (n ₂=−1.63×10⁻¹² cm²/W). The photoinduced birefringence of the polyimide thin film (▵ n∼10⁻²) under different pump intensities was investigated; it was much larger than that of the mono-azo dye doped PMMA thin film (▵ n∼10⁻³). Moreover, the time constants for birefringence growth and relaxation processes were determined.     

Development of a segmented fast neutron spectrometer

We discuss the development of a spectrometer based on full energy absorption using liquid scintillator doped with enriched ⁶Li. Of specific interest, the spectrometer is expected to have good pulse height resolution, estimated to lie in the range 10–15% for 14-MeV neutrons. It should be sensitive to flux rates from 10⁻⁶ cm⁻² s⁻¹ to 10⁶ cm⁻² s⁻¹ above a threshold of 500 keV in an uncorrelated γ background of up to 10⁴ s⁻¹. We have constructed a pilot version of the detector using undoped liquid scintillator, and we report its present status. The detector’s efficiency is determined by the volume of the scintillator (∼1.21) and is estimated to be 0.2–0.5% for 3-MeV neutrons. The good pulse height resolution is achieved by compensation of the nonlinear light yield of the scintillator due to the use of optically separated segments, which collect scintillations from each recoil proton separately. We demonstrate here the response of the detector to neutrons from a Pu-α-Be source, whose energies range up to 10 MeV. Initial testing indicates a low threshold (≈600 keV) and good spectral response after requiring a multiplicity of three segments. Such a spectrometer has applications for low-background experiments in fundamental physics research, characterizations of neutron flux in space, and the health physics community. The text was submitted by the authors in English.     

Control of acceptor doping in MOCVD HgCdTe epilayers

The acceptor doping of mercury cadmium telluride (HgCdTe) layers grown by MOCVD are investigated. (111)HgCdTe layers were grown on (100)GaAs substrates at 350°C using horizontal reactor and interdiffused multilayer process (IMP). TDMAAs and AsH3 were alternatively used as effective p-type doping precursors. Incorporation and activation rates of arsenic have been studied. Over a wide range of Hg_1−xCd_xTe compositions (0.17 < x < 0.4), arsenic doping concentration in the range from 5×10¹⁵ cm⁻³ to 5×10¹⁷ cm⁻³ was obtained without postgrowth annealing. The electrical and chemical properties of epitaxial layers are specified by measurements of SIMS profiles, Hall effect and minority carrier lifetimes. It is confirmed that the Auger-7 mechanism has decisive influence on carrier lifetime in p-type HgCdTe epilayers.     

Dielectric properties of natural,modified, and irradiated zeolites

The complex permittivity (ɛ = ɛ′ − iɛ″) of natural, modified, and irradiated zeolites as a function of the frequency of a variable electric field is measured. For Ba²⁺-modified (doped) zeolite, the permittivity and dielectric loss tangent (tanδ) as functions of the electric field frequency are found to decrease monotonically. When the irradiation dose rises to 10⁵ cm⁻², the dielectric loss tangent reaches a maximum and then, starting from a dose of 3 × 10¹⁶ cm⁻², sharply drops. Such behavior of tanδ is assumed to be associated with Ba²⁺- and irradiation-induced structural modifications in the unit cell of zeolite.     

Realization of a heavily doped and fully compensated semiconductor state in a crystalline semiconductor with a deep impurity band

We use the data on the pressure (up to P=1.5 GPa) and field (up to H=17 kOe) dependence of the Hall coefficient and the resistivity at 77.6 and 300 K in p-CdSnAs₂〈Cu〉 to calculate the effective kinetic characteristics of the charge carriers, the density and mobility of the conduction electrons and the holes of the deep acceptor and valence bands, in an interval of excess-acceptor densities N _ext ranging from 10¹⁰–10¹⁷ cm⁻³. We establish that in a heavily doped semiconductor with a deep impurity band at the tail of the density of states of the intrinsic band, with unequal donor and acceptor densities, a a heavily doped and fully compensated semiconductor state is realized under hydrostatic compression. The threshold value of the pressure that initiates the transition into such a state, P _c, depends on the extent to which the impurity band is populated. In p-CdSnAs₂〈Cu〉 at N _ext=N _A, where N _A is the density of deep acceptors, and T⩽77.6 K the value of P _c amounts to 10⁻⁴ GPa. As the population of the deep acceptor band grows, P _c increases and in the limit becomes infinite. We discuss the special features of the electrophysical properties of p-CdSnAs₂〈Cu〉 arising from the absence of an energy gap between the states of the conduction band and those of the deep acceptor band. Zh. éksp. Teor. Fiz. 111, 562–574 (February 1997)     

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×10¹⁵ cm⁻² can be obtained for a gallium implantation of 10¹⁶ cm⁻² by laser annealing with an energy density of more than 1.0 J cm⁻². Although the peak carrier concentration was found to be 8.0×10²⁰ cm⁻³, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm⁻². The annealing took place in the solid phase in this energy density range.     

Analysis of trace impurities in semiconductor gas via cavity-enhanced direct frequency comb spectroscopy

Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) has demonstrated powerful potential for trace-gas detection based on its unique combination of high bandwidth, rapid data acquisition, high sensitivity, and high resolution, which is unavailable with conventional systems. However, previous demonstrations have been limited to proof-of-principle experiments or studies of fundamental laboratory science. Here, we present the development of CE-DFCS towards an industrial application—measuring impurities in arsine, an important process gas used in III–V semiconductor compound manufacturing. A strongly absorbing background gas with an extremely complex, congested, and broadband spectrum renders trace detection exceptionally difficult, but the capabilities of CE-DFCS overcome this challenge and make it possible to identify and quantify multiple spectral lines associated with water impurities. Further, frequency combs allow easy access to new spectral regions via efficient nonlinear optical processes. Here, we demonstrate detection of multiple potential impurities across 1.75–1.95 μm (5710–5130 cm⁻¹), with a single-channel detection sensitivity (simultaneously over 2000 channels) of ∼4×10⁻⁸ cm⁻¹ Hz^−1/2 in nitrogen and, specifically, an absorption sensitivity of ∼4×10⁻⁷ cm⁻¹ Hz^−1/2 for trace water doped in arsine.     

Characteristics of p-type ZnO:As thin films prepared by the ampoule-tube method and ZnO p–n homojunction

A p-type ZnO thin film was prepared using arsenic diffusion via the ampoule-tube method. This was followed by fabrication of a ZnO p–n homojunction using n-type ZnO and characterization of the device properties. The ZnO thin film exhibited p-type characteristics, with a resistivity of 2.19×10⁻³ Ω cm, a carrier concentration of 1.73×10²⁰/cm³, and a mobility of 26.7 cm²/V s. Secondary ion mass spectrometer analysis confirmed that in- and out-diffusion occurred simultaneously from the external As source and the GaAs substrate. The device exhibited the rectification characteristics of a typical p–n junction; the forward voltage at 20 mA was approximately 5.5 V. The reverse-bias leakage current was very low—0.1 mA for −10 V; the breakdown voltage was −11 V. The ampoule-tube method for fabricating p-type ZnO thin films may be useful in producing ultraviolet ZnO LEDs and other ZnO-based devices.     

Hf-sputtered indium oxide films doped with tin

Indium oxide films doped with tin (ITO-films) have been hf-sputtered from an 80 at-%In₂O₃/20 at-%SnO₂ target onto glass substrates. The sputter atmosphere contained mainly argon (10⁻²Torr) with addition of oxygen (0≦p _{O 2}≦2·10⁻²Torr). The sputtered films aren-conductors. The conductivity and density of charge carriers depend on the oxygen content of the sputter gas. They could be varied by two orders of magnitude. In air or in oxygen atmosphere the films oxidize at the surface and for a certain depth beneath the surface, thus decreasing the conductivity. The Hall mobility of the sputtered films is smaller (≈10 cm²V⁻¹ s⁻¹) than one observes at ITO films produced by CVD sparaying or other methods. The conductivity of as sputtered films approached maximum values of about 1000Ώ⁻¹cm⁻¹.     

Muonium centers in heavily n‐doped Si under illumination: Evidence for Mu–hole interaction

A small fraction of implanted muons exists as a paramagnetic state (presumably Mu_BC ⁰, muonium at the Si—Si bond center) in heavily Sb‐doped Si (n-type, [Sb]\ \simeq 10¹⁸\ cm^–3). The paramagnetic state is susceptible to illumination both at 10–20 K and 290 K, providing evidence that holes (minority carriers) play an important role in determining the dynamical properties of muonium centers, where change may occur via a process Mu_BC ⁰+ h⁺\to Mu_BC ⁺ followed by charge exchange reaction (or transition Mu⁺ _BC+ e⁻→ Mu⁰ _T). This revised version was published online in August 2006 with corrections to the Cover Date.     

ESR of V4+ in α-RbTiOPO4 single crystals

We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO₄ single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian corresponding to axial symmetry with the parameters g _∥1=1.9305, g _⊥1=1.9565, A _∥1=−168.2×10⁻⁴cm⁻¹, and A _⊥1=−54.3×10⁻⁴cm⁻¹ for V1 centers and g _∥2=1.9340, g _⊥2=1.9523, A _∥2=−169.0×10⁻⁴cm⁻¹, and A _⊥2=−55.2×10⁻⁴cm⁻¹ for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO²⁺ ion forms when α-RbTiOPO₄ crystals and crystals of the KTP group (KTiOPO₄, NaTiOPO₄, α-and β-LiTiOPO₄), studied earlier, are doped with vanadium is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 534–536 (March 1998)     

Spectral components that form UV absorption spectrum of Ce3+ and Ce(IV) valence states in matrix of photothermorefractive glasses

We have measured the UV absorption spectra of photothermorefractive glasses of the system Na₂O-ZnO-Al₂O₃-NaF-SiO₂ doped by cerium oxide in the range of (2.8–5.0) × 10⁴ cm⁻¹ (360–200 nm). The spectra have been processed by the method of dispersion analysis based on the analytical convolution model for the complex dielectric function of glasses. We show that the absorption band centered at 3.3 × 10⁴ cm⁻¹ (∼303 nm) that is attributed to the transition 2F _5/2 → 5d in the Ce³⁺ ion, is an envelope of three spectral components. The broad absorption range (3.5–4.7) × 10⁴ cm⁻¹ (200–270 nm) that is commonly interpreted as a charge transfer band of the Ce(IV) valence state, is an envelope of at least three spectral components.     

Optical properties of Tm,Mg:LiTaO3 laser crystal

A Tm, Mg co-doped LiTaO₃ crystal has been grown by Czochralski method. Room temperature polarized absorption spectra and fluorescence spectrum of the Tm, Mg:LiTaO₃ crystal were measured and analyzed. The maximum absorption cross-section is 6.0791 × 10⁻²⁰ cm² at around 790 nm with full width at half maximum of 5 nm. The emission cross-section of ³ F ₄ manifold was 2.2 × 10⁻²⁰ cm². The spectroscopic parameters of Tm³⁺ ion were calculated by applying the Judd-Ofelt approach, and the intensity parameters Ω₂, Ω₄, and Ω₆ were obtained to be 7.71 × 10⁻²⁰, 1.09 × 10⁻²⁰, and 1.16 × 10⁻²⁰ cm², respectively. The branching ratios and radiative lifetimes were also presented and the radiative lifetime of Tm^{3+ 3} F ₄ → ³ H ₆ transition is 968.3 μs. The results were also analyzed and compared with other Tm³⁺ doped hosts.     

A cobalt-doped transparent glass ceramic saturable absorber Q-switch for a LD pumped Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript> glass microchip laser

We fabricate a transparent glass ceramic contains magnesium-aluminum spinel nanocrystallites doped with Co²⁺ ions. The ground-state and excited-state absorption cross section of this glass ceramic at 1.54 μm are estimated to be (2.8 ± 0.3) × 10⁻¹⁹ cm² and (4.8 ± 0.5) × 10⁻²⁰ cm², respectively. For the first time, the passively Q-swithched operation of LD pumped 1.54 μm microchip Yb³⁺/Er³⁺ glass laser is realized with transparent glass ceramic as saturable absorber. The Q-switched pulses of 3.846 kHz in repetition rate, 6.2 ns in duration and 6.3 μJ in energy are obtained. At last, the dependences of pulse width and repetition rate on pump power are also investigated.     

CEMS study on aluminium implanted iron

Up to now a great deal of investigations in ion beam mixing of iron-aluminium layers are known. However, the easier way to produce such layers by direct implantation of aluminium ions in iron is less studied. In the present work aluminium implanted iron layers are studied. Iron samples were implanted with aluminium ions at 50, 100, and 200 keV, respectively, with doses between 5×10¹⁶ and 5×10¹⁷ cm⁻². Independent of energy, at doses up to 2×10¹⁷ cm⁻², besides alpha iron further magnetic fractions with a Fe₃Al-like structure are formed while at a dose of 5×10¹⁷ cm⁻² amorphous nonmagnetic components are formed.     

Tunable diode laser spectroscopy of ethylene oxide near 1693 nm

We describe the application of the vertical-cavity surface-emitting laser (VCSEL) to absorption spectroscopy of the ethylene oxide (EO) Q-branch near 1693 nm. The VCSEL was electrically scanned over spectral intervals of up to ∼13 cm⁻¹ at a 1 kHz repetition rate. A methane absorption line at 5903.3 cm⁻¹ and Fabry–Pérot etalon with a free spectral range of 0.4 cm⁻¹ were used to calibrate frequency scale. The EO was mixed with ambient air, and total gas pressure and mixing ratios were varied from a few mbar to 1 bar and from ∼10² to 10⁵ parts per million, respectively. A rapid roll off of EO absorbance at 5903.7 cm⁻¹ was observed at gas pressures below ∼0.5 bar. A linear dependence of EO peak absorbance on mixing ratio was found at a total gas pressure of 1 bar. We conclude that monolithic VCSELs operating near 1693 nm could be used in EO sensors with a detection limit in the ppb range.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.     

Infrared angular spectroscopy characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates

Summary In this paper the technique of infrared angular spectroscopy applied to the characterization of epitaxial layers ofn-type silicon grown on N⁺ or P⁺ substrates is illustrated. Some results are reported and discussed concerning films having a free-carrier concentration ranging from 10¹⁴ cm⁻³ to 10¹⁷ cm⁻³ and thickness of the order of 10 μm. A significant comparison with results obtained by other techniques (four-point probe, spreading resistance,C−V plots, etc.) is performed and a few simple conclusions are drawn. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.