Electron velocity in short samples of Ga0.47In0.53As at 300 K

Velocity-field characteristics of short samples of n-type Ga0.47In0.53As are calculated for 300 K using a Monte Carlo model and recent values of physical constants. The average electron velocity reaches a peak value for a field of about0.5/L(V . cm^-1),Lbeing the sample length in centimeters. The peak value increases to about 8.5 × 10⁷cm . s^-1for a sample length of 0.1 µm. The values are 1.3-1.6 times the values for GaAs.     

Emission frequencies of the CF4laser

104 (nu_{2} + nu_{4}) leftarrow nu_{2}hot-band transitions, some of which correspond to known(nu_{2} + nu_{4}) leftarrow nu_{2}CF4laser lines, have been identified and measured in high-resolution Doppler-limited spectra of¹²CF4near 16 μm, obtained with a tunable diode laser. From an analysis of these frequencies, the rotational and tensor splitting constants for the ν2vibrational level have been determined. These constants, together with thenu_{2} + nu_{4}pump-band spectrum previously obtained, allow the laser emission frequencies for any given CO2pump line to be calculated with an accuracy of 0.01-0.003 cm^-1.     

Microwave properties of traveling-wave electrodes in LiNbO3 electrooptic modulators

The microwave characteristics of a traveling-wave electrode in electrooptic modulators on z-cut LiNbO₃ crystals with buffer layers with various dielectric constants are calculated by a quasi-TEM analysis. The theoretical results are compared with the measured results on z-cut crystals for coplanar waveguide (CPW) electrodes. The agreement between the calculated and the measured results is good     

Elastic and piezoelectric constants of Sr4KLiNb10O30type ferroelectric crystal

Elastic, piezoelectric, and dielectric constants of Sr4KLiNb10O30type ferroelectric crystal were determined mainly by resonant method. The electromechanical coupling constant for the Z-cut thickness vibration is 48 percent.     

Possibility ofNd1.9Ba1.1Cu3O7+δ andPr1.14Ba1.86Cu3O7-δsingle crystals for insulator in high-speed superconductingcircuits

Dielectric properties of both Nd_1.9Ba_1.1Cu ₃O_7+δ (NBCO-213) and Pr_1.14Ba_1.86Cu₃O_7-δ (Pr-rich PBCO) single crystals have been examined at low temperature. These materials have good lattice matching to high-T_c superconductors (HTS), but they are conductive at room temperature. Below 80 K, they are insulators with low dielectric constants, ε _τ below 25, and low dielectric loss tan δ below 0.1 at 100 kHz. The value of ε_τ is suitable for insulators in integrated circuits using strip line widths of 10 μm order, providing short delay time, no excitation of surface wave, and low radiation loss. The value of tan δ is comparable to loss of superconducting surface resistance above 100 GHz. These results indicate the applicability for the insulator layers in multilayer superconducting electronic devices such as Single Flux Quantum (SFQ) circuits operated at high speed     

Frequency measurements of 9- and 10-μm N2O lasertransitions

We have measured frequencies of N₂O transitions by heterodyning sub-Doppler fluorescence-stabilized N₂O laser radiation with that from a reference CO₂ laser. A high-resolution cavity incorporates a ribbed tube and a highly reflective grating, permitting the CW oscillation of both the 10⁰ 0-02⁰0 9-μm and the 10⁰0-00⁰1 10-μm regular bands. This is the first sub-Doppler frequency measurement of the 9-μm band. The accuracy in the determination of the rotational constants for both bands has been improved by an order of magnitude, and calculated transition frequencies are presented     

The photoionization cross sections of the Rg*2[3Σ+u] excimer states for Ne*2, Ar*2, and Kr*2

Based on the recently determined Rydberg series of the³Sigma+_{u}excimer states of Ne*2, Ar*2and Kr*2, the photoionization cross sections of these molecules are calculated using a single-channel quantum defect method. These cross sections are found to differ considerably from those of the asymptotic metastable atomic Rg*(ns^{3}P_{2}) states, but are in good agreement with recently reported experiments at isolated wavelengths. The implications of these results for VUV and XUV lasers are discussed.     

Optically triggeredIn0.53Ga0.47As-transferred-electron devices forrepeater applications

The generation of current pulses in In_0.53Ga_0.47 As-transfer devices by short optical pulses is demonstrated. The triggering conditions for the generation of single domains are determined with respect to optical peak power, doping concentration, and location of irradiation. The sensitivity and gain of a proposed repeater circuit are calculated     

Evaluation of the profile constants of p+-n-n+hyperabrupt junctions

A method for evaluating the profile constants of a p⁺-n-n⁺hyperabrupt junction is given. The method is useful in the design and characterization of hyperabrupt tuning varactors.     

Design and performance of very high-speed In0.53Ga0.47As/In0.52Al0.48As p-i-n photodiodes grown by molecular beam epitaxy

High-speed In0.53Ga0.47As/In0.52Al0.48As photodiodes have been grown by molecular beam epitaxy (MBE) on semi-insulating InP substrates and fabricated. The measured impulse response characteristics are very close to the analytically calculated ones. The temporal response to pulsed optical excitation is characterized by a rise time of 21 ps and a width (FWHM) of 27 ps. The 25 × 20-µm²diodes have a junction capacitance <0.1 pF, a dark current ∼1 nA, and a peak responsivity of 0.35 A/W. These characteristics are comparable or better than most epitaxial InGaAs photodiodes reported to date and make the devices suitable for a host of high-speed applications and monolithic integration.     

Far-infrared CW Raman and laser gain of14NH3

The FIR Raman and laser gain properties of¹⁴NH3optically pumped by the CO29R(30)and the N2O10P(13)laser lines, respectively, have been measured and calculated using the quantum mechanical theory of three-level systems. The laser gain is about two orders of magnitude higher than for usual FIR laser transitions. The Raman gain shows two features characteristic for the two-photon process: extremely high saturation intensity and high pressure maximum. Very satisfactory agreement between theoretically calculated and experimentally measured gain properties is found.     

Pd—SnOxMIS capacitor as a new type of O2gaseous sensor

Device characteristics of a new type of O2gaseous sensor are presented. These sensors are fabricated in the MIS configuration Pd-SnOx-Si3N4-SiO2-Si-Al with highly resistive SnOxas an oxygen adsorptive element. Partial pressures of O2below 0.1 torr can be detected at room temperature by these devices. Steady-state and transient behavior are described as a function of O2partial pressure and temperature. Adsorption and desorption rates and time constants are determined. Activation energy for O2adsorption in SnOxis found to be 1.6 K cal/ mole.     

Anomalous dispersion in Er3+ and Yb3+-dopedfibers

In experimental and theoretical study of anomalous dispersion in Er³⁺and Er³⁺-Yb³⁺-doped fibers has been developed. Anomalous time delay caused by both absorption and emission at 1.535 μm has been theoretically calculated and experimentally measured. A pump power dependence of anomalous time delay in rare-earth-doped fibers has been theoretically calculated and experimentally investigated. It has been shown that pump power fluctuations lead to propagation time jitter in Er³⁺-doped fiber amplifiers. The pulse interaction due to refractive index change caused by gain saturation is predicted. It has been shown that for Er ³⁺-doped fibers with SiO₂-GeO₂ core composition, the anomalous dispersion per 1-dB gain is twice that of fibers with SiO₂-Al₂O₃ core, which is caused by gain curve form difference. A scheme of mutual compensation of intrinsic fiber dispersion and anomalous dispersion caused by Er³⁺ in the region 1.532-1.537 μm has been suggested     

The controlling influence of the Cu2S optical absorption coefficient on the short-circuit currents of Cu2S/CdS solar cells

Cu2S is a p-type defect semiconductor and is the main optical absorber-current generator in the Cu2S/CdS solar cell. This cell undergoes large reversible changes in its short-circuit current depending upon the ambient to which it is exposed. While a large number of mechanisms have been proposed for this effect, we find that it can be accounted for solely on the basis of changes in the absorption coefficient of the Cu2S, as controlled by the position of the Fermi level in the degenerate material. We have calculated the relation between the absorption coefficient and sheet resistance for degenerate Cu2S, and compared the results to existing experimental data on material prepared in the same way as solar cells. We find good agreement between the experimental data and our calculations if Cu2S is acting as a direct-gap semiconductor. Based upon the magnitude of the experimental changes in absorption coefficient with sheet resistance we have calculated the expected change in short-circuit current that would be produced in a typical Cu2S/CdS solar cell. The changes in short-circuit current calculated are on the order of 20-40 percent for ρ/d changing by an order of magaitude. These results are in agreement with the results on actual cells.     

Structure and properties of high efficiencyZnO/CdZnS/CuInGaSe2 solar cells

Thin-film polycrystalline solar cells with the structure ZnO/CdZnS/CuInGaSe₂ fabricated with total area efficiencies of up to 12.5% under AM1.5 equivalent illumination and 10.5% under AM0 equivalent are discussed. These are among the highest total area efficiencies reported for polycrystalline thin-film solar cells. Current-voltage and quantum efficiency data for such a high-efficiency cell are given. Described are the deposition of the CuInGaSe₂ by physical vapor deposition in vacuum, the CdZnS by chemical deposition from solution, and the ZnO by reactive sputtering. The electrical and optical properties of the individual layers have been inferred from measurements on complete devices and on separate witness layers. Optical constants and thicknesses obtained for the device layers from these measurements are presented, and the requirements for optimizing the device efficiency are discussed     

Superfluorescence dynamics in 130Te2

High-resolution analysis results are presented for Te₂ superfluorescence induced by short pulses from a YAG-pumped dye laser pulses, and a comparison is made with CW-laser-induced fluorescence observed by Fourier transform spectroscopy. A complete identification of the transitions involved, based on intensity measurements and supported by calculated Franck-Condon factors, has been achieved. The cooperative emission in Te₂ has been studied by time resolved spectroscopy as a function of density. With increasing density or temperature of the sample, the emission changes continuously from characteristic spontaneous emission to superfluorescence. The evolution of the time characteristics of the signal with the number of partners are presented and compared with the predictions of current theories     

Optoelectronic properties of Zn0.52Se0.48/Si Schottky diodes

Zn_0.52Se_0.48/Si Schottky diodes are fabricated by depositing zinc selenide (Zn_0.52Se_0.48) thin films onto Si(1 0 0) substrates by vacuum evaporation technique. Rutherford backscattering spectrometry (RBS) analysis shows that the deposited films are nearly stoichiometric in nature. X-ray diffractogram of the films reveals the preferential orientation of the films along (1 1 1) direction. Structural parameters such as crystallite size (D), dislocation density (δ), strain (ε), and the lattice parameter are calculated as 29.13 nm, 1.187 × 10⁻¹⁵ lin/m², 1.354 × 10⁻³ lin⁻² m⁻⁴ and 5.676 × 10⁻¹⁰ m respectively. From the I–V measurements on the Zn_0.52Se_0.48/p-Si Schottky diodes, ideality and diode rectification factors are evaluated, as 1.749 (305 K) and 1.04 × 10⁴ (305 K) respectively. The built-in potential, effective carrier concentration (N_A) and barrier height were also evaluated from C–V measurement, which are found to be 1.02 V, 5.907 × 10¹⁵ cm⁻³ and 1.359 eV respectively.     

New direct optical pump schemes for multiatmosphere CO2and N2O lasers

Nine schemes for direct optical pumping of multiatmosphere CO₂ and N₂O lasers at pump wavelengths in the 1.4-3.6-μm region are discussed. Most of these wavelengths can be generated by solid-state lasers, which are more attractive pump sources than the chemical lasers (HBr, HF) used previously to pump high-pressure CO₂ and N₂O lasers. Including previously studied pump schemes, there are altogether 14 possible pump transitions in CO ₂ and N₂O in the 1.4-4.5-μm region. Numerical laser simulations are carried out to compare all of these pump schemes. Assuming 10 J/cm² pump energy in a pulse of 100 ns FWHM, and 5% output coupling as the only resonator loss, the calculated energy conversion efficiencies are in the range of 6-40%. The pump thresholds are in the range of 0.1-3.1 J/cm²     

Relaxation of hot carriers in undoped and n-doped Ga0.47In0.53As generated by subpicosecond pulses

The cooling process of hot carriers in bulk Ga_0.47In_0.53As at 30 K is studied with subpicosecond time resolution. The time-dependence of the sample transmission at a wavelength of 1265 nm is measured after the generation of charge carriers with an excess energy ω-E_g in the order of 200 meV and at densities of up to 7 × 10¹⁷ cm⁻³. In an undoped sample, an almost double-exponential relaxation of the transmission change is found with time constants of about 1 ps and 10 ps, respectively. In contrast, a nearly single-exponential time behavior is observed in a n-doped sample with a time constant of 3 ps. The experimental data agree well with the results of model calculations that do not take into account “hot” phonon reabsorption by the carriers. The model reproduces the approximately double-exponential transmission relaxation of the undoped sample. The two time constants can be attributed to the population change of either the conduction or the heavy hole valence band states that are probed by the light pulses. The experimental data can be explained without assuming different temperatures of the electrons and the holes during the cooling process.