Influence of localized states in a semiconducting film of critical thickness on the electrical properties of thinfilm ms' is structures

The current-voltage and high-frequency capacitance-voltage (C-V) characteristics have been used to investigate the electrical properties of thin Ga₂Ses films in Me-Ga₂Se₃-Si structures (n and p type). The features of the high-frequency C-V dependences of the structures based on p-type Si are explained in the framework of a model of the MS' IS structure with donor type centers in the semiconducting S'film (the thickness of the S' film is comparable with the generalized screening length). It is shown that in the investigated structures the charge transport mechanism is due to ionization of volume centers (the activation energy of a deep donor center is 0.72 eV) in the Ga₂Se₃ film, the mechanism being enhanced by an electric field. Analysis of the high-frequency C-V characteristics showed that the majority carriers in the Ga₂Se₃ films are electrons with concentration 10¹² cm^–3; the concentration of the deep donor centers is 5·10¹⁶ cm^–3.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–88, January, 1981.     

Concentrations and velocity distributions of positive ions in laser ablation of copper

It is shown that the generation of secondary electrons by excited neutrals hitting a surface makes the so-called probe method unsuited for measuring the positive ion fraction in laser ablation plumes. Experiments have been performed in a modified set-up, in which the disturbance by secondary electrons is avoided. For a typical case of Cu irradiated in ultra-high vacuum by nanosecond excimer laser pulses of 3 J cm^–2 the ionized fraction is about 10^–8 at a distance of 60 cm. This number is in fair agreement with Saha-Langmuir predictions based on the assumption of local thermal equilibrium at an estimated temperature of about 3000K. Angular-resolved time-of-flight measurements show that there are three different ion velocity distributions. A slow contribution (kinetic energy 2eV) with an angular distribution peaked along the normal, and two fast, isotropic contributions (kinetic energy 20–50 eV). The fast contributions are attributed to ions involved in a Coulomb explosion.     

CdZnTe <Emphasis Type="BoldItalic">γ</Emphasis> detector for deep inelastic neutron scattering on the VESUVIO spectrometer

In this paper it is shown that solid-state cadmium-zinc-telluride (CZT) is a promising photon detector for neutron spectroscopy in a wide energy interval, ranging from thermal (25 meV) to epithermal (70 eV) neutron energies. In the present study two CZT detectors were tested as part of the inverse-geometry neutron spectrometer VESUVIO operating at the ISIS pulsed neutron source. The response of the CZT detector to photon emission from radiative neutron capture in ²³⁸U was determined by biparametric measurements of neutron time of flight and photon energy. The scattering response function F(y) from a Pb sample has been derived using both CZT and conventional ⁶Li-glass scintillator detectors. The former showed both an improved signal to background ratio and higher efficiency as compared to ⁶Li glass, allowing us to measure F(y) up to the fourth ²³⁸U absorption energy (E_r=66.02 eV). Due to the small size of CZT detectors, their use is envisaged in arrays, with high spatial resolution, for neutron-scattering studies at high energy (>1 eV) and low wavevector (q <10 Å^-1) transfers. PACS 29.30.Hs; 29.30.Kv; 29.40.Kw; 61.12.Ek     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Deep bandtail states picosecond intensity-dependent carrier dynamics of GaN epilayer under high excitation

Picosecond carrier dynamics of deep bandtail states (3.1 eV) in an unintentionally n-doped GaN epilayer at room temperature under high excitation densities (i.e., N ₀ = 1.0× 10¹⁹– 1.1× 10²⁰ cm^–3) have been investigated with nondegenerate femtosecond pump–probe (267/400 nm) reflectance ( R/R ₀). All R/R ₀ traces possess a 2 ps buildup time that represents an overall time for the initial non-thermal carrier population to relax towards the continuum extremes and then into the probed tail states. We observe a saturation of R/R ₀ initial (first 10 ps) recovery rate _i at a density of 5– 6×10¹⁹ cm^–3 close to the Mott transition threshold obtained from time-integrated PL measurements. Such a saturation phenomenon has been identified as the trap-bottleneck due to the bandtail states and deep traps. As N ₀ is further increased, _i accelerates due to the onset of Auger recombination as the trap-bottleneck becomes effective. The best fit by the Auger model for N ₀ in the range of the mid-10¹⁹–10²⁰ cm^–3 yields an Auger coefficient of C _a 5.0× 10^–30 cm⁶ s^–1.     

Optical Properties of Nonstoichiometric Tantalum Oxide TaO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> &lt; 5/2) According to Spectral-Ellipsometry and Raman-Scattering Data

Optical properties of amorphous nonstoichiometric tantalum-oxide films of variable composition (TaO_x, x = 1.94–2.51) in the spectral range of 1.12–4.96 eV, obtained by ion-beam sputtering-deposition of metallic tantalum at different partial oxygen pressures (0.53–9.09 × 10^–3 Pa), have been investigated. It is shown by spectral ellipsometry that the character of dispersion of the absorption coefficient and refractive index in TaO_x of variable composition suggests that light-absorbing films with dispersion similar to that in metals are formed at oxygen pressures in the growth chamber below 2.21 × 10^–3 Pa, whereas transparent films with dielectric dispersion are formed at pressures above 2.81 × 10^–3 Pa. According to the data of quantumchemical simulation, the absorption peak at a photon energy of 4.6 eV in TaO_x observed in the absorptioncoefficient dispersion spectrum is due to oxygen vacancy. The peak in the Raman-scattering spectra of TaO_x films with metallic dispersion at frequencies of 200–230 cm^–1 is presumably related to tantalum nanoclusters.     

Thermoluminescence glow curves of CaF2: Dy crystals irradiated by soft X-rays

Applying a deconvolution of the thermoluminescence glow curves, parameters of single glow peaks of CaF₂: Dy TLD 200 dosemeters irradiated by soft X-rays were determined. A dependence of the height ratio of low temperature (T393, 413 and 473 K) single peaks on energy of absorbed photons was measured in a region of 1–22.2 keV. Standard radionuclides¹⁰⁹Cd,²³⁸Pu,⁵⁵Fe and iodine laser produced aluminium plasma (T _e 500 eV) were used as soft X-ray sources. The ratios of the heights of different single peaks are discussed with respect to high local doses. The decreasing ratio of the heights of the first and third and/or second and third peak with increasing photon energy allows to determine reversely a mean photon energy of absorbed soft X-ray radiation.     

Dual excimer and CO2 laser etching studies of polyethylene terephthalate

Polyethylene terephthalate (PET) films preheated with a pulsed CO₂ laser have been ablatively etched with an XeCl laser. The observed reduction in ablation threshold, from 170 to 140 mJ cm^–2, is consistent with a thermal mechanism for XeCl laser ablation of PET. Transient changes in the UV absorption coefficient of PET caused by heating with pulsed CO₂ laser radiation have also been studied and a significant increase in absorption observed at 308 nm. Permanent changes in the ultraviolet absorption of PET following exposure to low fluence XeCl laser radiation are also reported.     

Transverse MIR fast response in PbSe films

Under lightening, anisotropic semiconductor or semimetal films can show large transverse voltage. PbSe and PbS films have a room temperature intense sub nsec response ( V/MW) in the 10µm region due to free carrier photon drag, but the effective direct matched response on a 50 impedance is lower ( 0.1 V/MW for 1 cm² film) because of the high film resistance (> KW). CO₂ 500ps mode locked pulses are easily detected in the scope limit.     

Semiconductor laser crystallization of a-Si:H on conducting tin-oxide-coated glass for solar cell and display applications

Semiconductor laser (=805 nm) crystallization of hydrogenated amorphous silicon (a-Si:H) deposited on a low-cost fluoride-doped tin-oxide-coated glass substrate is demonstrated. X-ray diffraction confirms that the structure of the polycrystalline silicon thus formed shows (111), (220), and (311) peaks. A sharp Raman peak at 520 cm^-1 further confirms the crystallization. Atomic force microscope images of a Secco-etched laser-treated sample reveal the granular structure of the poly-Si. Grains as big as 10 times the film thickness are readily obtained and sample as thick as 5000 Å is easily crystallized. The method can be extended to films with a thickness of several microns. PACS 42.55.Px; 42.62.Cf; 81.05.Gc     

Hydrogen-like recombination X-ray lasers using ps pulse drivers

We propose a scheme for producing high gain recombination X-ray lasers on hydrogen-like Balmer transitions by irradiating fibre targets with a 2 ps Chirped Pulse Amplification CPA beam of a Nd-glass laser facility. Very high gain coefficients for H-like C, N, O, F, Na Balmer transitions are predicted. The optimum electron density and temperature for maximum gain operation scale approximately asN _e 4 × 10¹³ Z ⁷ cm^–3 and T_e 7 × 10^–3 Z ⁴ eV, respectively, at the time when maximum lasing gain appears. Significant improvement in gain performance of recombination X-ray lasers is predicted by using CPA ps pulse drivers.     

Exponential absorption edge in hydrogenated α-Si films

Optical and photoelectric measurements demonstrate that hydrogenated amorphous silicon prepared by glow discharge decomposition of silane has an exponential optical absorption edge, over the photon energy range 1.4–1.8 eV with a slope of 0.05–0.08 eV. Evidence is presented that the photogeneration efficiency is unity at room temperature and independent of electric field (10²?10⁴ V/cm^?1) and photon energy (1.2–2.2 eV).     

Infrared spectroscopy on lead silicate glass

The reflectance spectra of some lead silicate glasses of general formula (PbO)_x(SiO₂)_y have been measured in the infrared frequency range from 50 to 4000 cm^–1. The dispersion and absorption spectra in the range 50–2000 cm^–1 have been calculated from the reflectance data using the Kramers-Kronig relations. The band at 135 cm^–1 is assigned to the stretching vibration of lead-oxygen bonds. The shoulder band of the silicon-oxygen stretching mode at 900 cm^–1 shows a weak coupling of those bonds to the Pb²⁺ modifier. The vibration strength of those bands shows that the number of the Pb²⁺ modifier increases first up approximately to 50 Mol% with the increase of PbO content and then decreases rapidly. It indicates that different PbO content causes different structural forms in lead silicate glasses: The addition of small amounts of PbO to vitreous silica serves to modify the continuous three-dimensional silica network: whereas in those glasses with a high lead content, the influence of the cation, Pb²⁺, appears to lie between that of network former and network modifier. This result is in agreement with the structural model of Worrel and Henshall.     

High resolution photoabsorption spectroscopy at the carbonK-Edge

Using plane grating, ellipsoidal mirror, grazing incidence monochromators at the storage ring BESSY, a resolution of 150meV was achieved for a photon energy of 285 eV. This high energy resolution considerably extends the range of possible studies using core level Spectroscopy. Some of the new opportunities are illustrated at the CK edge by resolving the vibrational fine structure of condensed C₂H₄ multilayers in the (1s^–1, ^*) state by means of photoabsorption spectroscopy. For the sake of comparison with other high resolution instruments, the vibrational fine structure of condensed N₂ multilayers at the NK edge ( 400eV) was also measured, yielding a resolving power of 3000.     

Damage created by high-current-density implants of phosphorus into 〈100〉 and 〈111〉 silicon wafers

The damage left by high-current-density, 9 A/cm², implants of 120 keV phosphorus into 100 and 111 silicon oriented substrates was investigated as a function of the fluence in the range 4×10¹⁵–1.5×10¹⁶/cm². The samples were analyzed by 2 MeV He⁺ channeling and transmission electron microscopy. Initially a buried amorphous layer forms at low fluences until the wafer temperature saturates at 450 °C at a fluence of 4.5×10¹⁵/cm². As the fluence is further increased ion-assisted regrowth of this initial buried amorphous layer takes place and is 2 to 2.5 times faster (with respect to ion fluence) for 100 substrates than for 111 substrates. At higher fluences, most of the residual damage is located at a depth equal to the sum of the projected range and of the straggling. In the regrown layers twins are found in both orientations, and in some cases a hexagonal silicon phase is present at high fluences. The results are compared with the ion assisted regrowth of amorphous layers at well defined temperatures in the 250°–400 °C range.     

Spectroscopic ellipsometric characterization of organic films obtained via organic vapor phase deposition

Thin films of Tris(8-hydroxyquinoline)-aluminum(III) (Alq₃) and N,N-Di-[(1-naphthyl)-N,N-diphenyl]-(1,1-biphenyl)-4,4-diamine (-NPD ) were deposited on large-area silicon substrates by means of the recently developed organic vapor phase deposition (OVPD) method. Variable-angle spectroscopic ellipsometry was used to measure the optical constants of OVPD Alq₃ and -NPD layers in the 0.8–5 eV energy range. The absorption onset which defines the lower limit of the optical band gap was found to be at 2.65 eV and 2.9 eV for Alq₃ and -NPD , respectively. Additionally, the thicknesses of the layers as well as the thickness profiles of the organic thin films were determined along the 8 diameter of the wafers. The thickness analysis revealed large-area uniform deposition of the films. PACS 78.20.Ci; 81.70.Fy; 81.15.-z     

Plasma — Processed obliquely deposited Bi-Ge-Se and Ag/Bi-Ge-Se films as resist materials

Lithographic properties of photoexposed Bi₁₀Ge₂₀Se₇₀ and Ag/Bi₁₀Ge₂₀Se₇₀ films and hydrogen plasma exposed Ag/Bi₁₀Ge₂₀Se₇₀ films have been investigated. The asdeposited films show a positive resist behavior on exposure to photons and the silver overlayered films show a negative resisti behavior on exposure to both photons and hydrogen plasme. The contrast values are 1.25 and 2.3 for photoexposed positive and negative resists, respectively, and 5.0 for plasma-exposed negative resist. The sensitivity is 10²⁰ photons/cm² for the photoexposed positive and negative resists and 10¹⁸ ions/cm² (0.11 C/cm²) for the plasma-exposed negative resist.     

Discretization of the thermal excitation in highly excited matter

In this paper the thermal energy diffusion for quantum particles is described. The quantum heat transport equation is obtained. It is shown that, for a short-time thermal excitation (of the order of the relaxation time), the excited matter response is quantized on the different levels (atomic, nuclear, quark) with quantum thermal energy equalE ^atomic 9 eV,E ^nuclear 7 MeV, andE ^quark 139 MeV.     

立方氮化硼薄膜的光学带隙

用射频溅射法在p型Si(100)衬底上沉积立方氮化硼(c-BN)薄膜,薄膜的成分由傅里叶变换红外谱标识,用紫外-可见分光光度计测量了c-BN薄膜的反射光谱,利用K-K(Kramers-Kroning)关系从反射谱计算出c-BN薄膜的光吸收系数,进而确定c-BN薄膜的光学带隙.对于立方相含量为55.4%的c-BN薄膜,光学带隙为5.38eV. 关键词： 立方氮化硼薄膜 光学带隙 K-K关系