Emissive characteristics of mesa-stripe lasers (λ=3.0–3.6 μm) made from InGaAsSb/InAsSbP double heterostructures

The directional patterns, current-voltage characteristics, and spectral characteristics of mesastripe lasers with InGaAsSb active layers, emitting at λ=3.0–3.6 μm (77 K) and having threshold currents ≥15 mA (j _th≥200 A/cm²), are investigated. The maximum output power is 1.4 mW (λ∼3.3 μm), the differential quantum efficiency ∼3%(τ=5–30 μs, f=500 Hz) for lasing in a longitudinal mode with beam divergences ΔΘ∥∼15° and ΔΘ ⊥ ∼30°. The relationship of the differential quantum efficiency to the order of the spatial mode of the lasing is demonstrated. A single-mode, current-tunable (−30 cm⁻¹/A) laser is used to measure the transmission of methane in the region of the ν ₃ absorption band. Pis’ma Zh. Tekh. Fiz. 24, 40–45 (June 26, 1998)     

Formation of In nanoparticles on InP wafers by laser-assisted etching

Indium nanoparticles were formed by laser etching an InP (100) wafer in a 10% chlorine–helium atmosphere maintained at ~5–8 × 10⁻⁵ Torr. The wafer was irradiated by a homogenized ultraviolet beam with a series of 50–4500 pulses at a fluence of 230 mJ/cm². The surface was also irradiated using fluences from 50 to 340 mJ/cm² with 600 pulses. The irradiated surfaces were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. Raman spectroscopy confirmed that the irradiated surface layer remains crystalline. According to EDS analysis, the surface particles are composed primarily of indium. SEM images show that the number of pulses and the pulse intensity can control the size distribution of the particles.     

Titanium-doped indium oxide films prepared by d.c. magnetron sputtering using ceramic target

Polycrystalline thin films of Ti-doped indium oxide (indium–titanium-oxide, ITiO) were prepared by d.c. magnetron sputtering and their electrical and optical properties were investigated. Doping of Ti was effective in improvement of the electroconductivity of the indium oxide: the electrical resistivity of 1.7 × 10⁻³ Ω cm of non-doping decreased to minimum value of 1.8 × 10⁻⁴ Ω cm at 2.4 at.% Ti-doping when the films were deposited at 300 °C. The polycrystalline ITiO films of 0.8–1.6 at. % Ti-doping showed the high Hall mobilitiy (82–90 cm² V⁻¹ s⁻¹) and the relatively low carrier density (2.4–3.5 × 10²⁰ cm⁻³) resulting in characteristics of both low resistivity (2.1–3.0 × 10⁻⁴ Ω cm) and high transmittance in the near-infrared region (over 80% at 1550 nm), which cannot be shown in the conventional Sn-doped indium oxide (ITO) films.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Field-ion microscopy of deformation effects near the surface in ion-implanted metals (Ir)

Field-ion microscopy is used to determine the deformation due to ion implantation (E=20 keV, D=10¹⁸ ions/cm², j=300 μA/cm²) near the surface in pure iridium. The effect is manifested as a high density of various types of defects in the near-surface volume (∼50 nm from the irradiated surface) of the material. Pis’ma Zh. Tekh. Fiz. 25, 60–64 (March 26, 1999)     

Effect of electron irradiation attenuated by aluminum screens on the electrical parameters of p-n silicon structures

We have studied the influence of irradiation by 6-MeV electrons via flat aluminum screens with thicknesses d = 2−14 mm (mass thicknesses, 0.5–3.8 g/cm²) on the properties of p ⁺-n-n ⁺ silicon structures, including the nonequilibrium charge carrier lifetime (τ), reverse current (I _R), and forward current-voltage (I-U) characteristics. In the case of a screen with d = 14 mm (3.8 g/cm²), the irradiated structures exhibit significantly smaller changes in I _R values and I-U curves compared to those for d = 2–12 mm, whereas a decrease in τ (from 20 to 1.5 μs) is the same.     

Growth and properties of CuInS2 single crystals

CuInS₂ single crystals 14–16 mm in diameter and up to 40 mm in length were grown by the traveling solvent method. The crystals were found to ben-type, with a conductivity of 0.1–10 S/cm, carrier concentration of 10¹⁶–10¹⁷ cm⁻³, and carrier mobility of 150–220 cm²/(V s). The anisotropic thermal expansion of the crystals was measured.     

Characterisation of vacancy-like defects in III–V compound semiconductors using positron annihilation technique

Single crystals of GaP and InSb were irradiated by 3 MeV electrons at 20 K to a total dose of 4 × 10¹⁸ e ⁻/cm². Isochronal annealing in the temperature region 77–650 K followed the irradiation. In GaP, the positron lifetime measurement indicated the presence of irradiation-induced vacancies in the Ga-sublattice. The vacancies disappeared at two stages observed in temperature ranges 200–300 and 450–550 K. In InSb the positron lifetime was found to increase by 8 ps compared to that in as-grown crystals (i.e. 282±2 ps) after irradiation. The increase indicated the presence of irradiation-induced defects; the crystal was found to recover until 350 K with a sharp annealing stage at 250–350 K.     

Investigation of the structure of thin layers of hexadecane on a metal substrate by infrared spectroscopy

Infrared spectroscopy was used to analyze the structure of 0.5–10 μm thick layers of hexadecane on a metal substrate in the range 3000–2800 cm⁻¹. The results suggest that density fluctuations occur in layers between 3 and 10 μm thick, whereas the hexadecane crystallizes in thinner layers. Zh. Tekh. Fiz. 24, 24–28 (May 26, 1998)     

Excimer laser ablation of single crystal 4H-SiC and 6H-SiC wafers

A 248 nm, 23 ns pulsed excimer laser was used to compare the ablation characteristics of single crystal wafers of the polytypes 4H-SiC and 6H-SiC over a wide range of energy fluence (0.8–25 J cm⁻²). Photothermal models based on Beer–Lambert equation using thermal diffusivity and absorption coefficient, energy balance, and heat transfer were presented to predict the ablation mechanisms. Micromachining of trenches was demonstrated at 7 J cm⁻² to demonstrate the potential of UV laser ablation. Results indicate that the ablation process is characterized by two well-defined threshold fluences: (a) decomposition threshold ~1 J cm⁻² and (b) melting threshold ~1.5 J cm⁻² for both polytypes. Contrary to the modeling expectations, the ablation rates were lower and did not increase rapidly with energy fluence. Four types of ablation mechanisms—chemical decomposition, vaporization, explosive boiling, and plasma shielding—either singly or in combination occur as a function of energy fluence. The predictions of photothermal models were not in good agreement with the experimental data implying that a complex interplay among various physical phenomena occurs during ablation. Micromachined trench exhibited ripple patterns, microcracks and recast layers, most of which could be eliminated by a subsequent chemical cleaning process. It is concluded that excimer laser ablation is an effective but slow material removal process for SiC wafers compared to other lasers such as 1064 nm Nd:YAG.     

Photodiodes based on InAs/InAs<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript>/InAsSbP heterostructures for 2.5–4.9 μm spectral range

Photodiodes with a photosensitive area diameter of 0.3 mm operating at room temperature in a middle-IR (2.5–4.9 μm) wavelength range have been created based on InAs/InAs_0.94Sb_0.06/InAsSbP/InAs_0.88Sb_0.12/InAsSbP/InAs heterostructures grown by liquid phase epitaxy. Distinguishing features of the proposed photodiodes are a high monochromatic responsivity, which reaches a maximum of 0.6–0.8 A/W at λ_max = 4.0–4.6 μm, and a low dark current density of (1.3–7.5) × 10⁻² A/cm² at a reverse bias of 0.2 V. The differential resistance at zero bias reaches up to 700–800 Ω. The detection ability of photodiodes in the spectral interval of maximum sensitivity reaches (5–8) × 10⁸ cm Hz^1/2 W⁻¹.     

Silicon metal-dielectric-semiconductor varicaps with an yttrium oxide dielectric

This paper reports an investigation of the electrophysical properties of metal-dielectric-semiconductor varicaps with an yttrium oxide dielectric, prepared by resistive vacuum evaporation of the rare-earth metal with subsequent thermal oxidation of the film in air at 500–550 °C. It is found that the electrical conductivity of the samples follows the Poole-Frenkel law. High-frequency capacitance-voltage characteristics are used to determine the specific capacitance of the dielectric, C ₀=0.027–0.03 μF/cm², the slope of the capacitance-voltage characteristic, dC/dV=35–40 pF/V, the fixed charge in the dielectric, Q _f=(1.7−2.7)×10⁻⁸ C/cm², and the density of surface states at the flat-band potential, N _ss=(1−2)×10¹¹ cm⁻²·eV⁻¹. The capacitance tuning range factor for the metal-dielectric-semiconductor varicaps is 2.5–3. These structures are shown to be applicable as metal-dielectric-semiconductor varicaps with a low control voltage and a high quality factor. Pis’ma Zh. Tekh. Fiz. 23, 50–55 (June 26, 1997)     

Photoelectronic properties of HgI2 crystals for nuclear radiation detection

Photoelectronic properties of red mercuric iodide single crystals, grown from its saturated solution in tetrahydrofuran, have been studied for the wavelength range 450–700 nm at temperatures 80,110, 175, 235 and 300 K. Various aspects of the optical generation of charge carriers have been discussed. The computer simulation of the room temperature photoconductivity has generated the optimized values of the mobility-lifetime products μ_eτ_e = 5.67 × 10⁻⁵ cm²/V, μ_hτ_h = 0.18 × 10⁻⁵ cm²/V), and surface recombination velocities (S_e = 3.2 × 10⁵ cm/s, S_h = 4.5 × 10⁵ cm/s) of the charge carriers in these crystals. The estimated values of the electron and hole drift lengths for typical electric fields suggest that, under the negative electrode illumination, THF α-HgI₂ crystals have high potential as regards to their use as photodetectors in most of the scintillation spectrometers.     

Negative ion formation in laser ion mobility increment spectrometer

A new method is proposed and implemented, according to which small concentrations of organic compounds in the atmosphere are measured by combining the ion mobility increment spectrometer and laser ionization. The experimental setup makes use of the pulsed fourth-harmonic radiation of a YAG:Nd³⁺ laser (λ = 266 nm). At high intensities (q ∼ 10⁷ W/cm²) of laser radiation, ion spectra with reactant peaks are observed, which are identical to the spectra obtained with traditional sources of ionization by corona discharge and β radiation. The ion spectra obtained at low laser radiation intensities (q ∼ 10⁵ W/cm²) are free of background and reactant peaks, which ensures the high selectivity of the analysis. It is concluded that the mechanism of negative ion formation from the molecules of nitro compounds can change depending on the intensity of ionizing laser radiation.     

The effects of temperature gradient and growth rate on the microstructure of directionally solidified Sn–3.5Ag eutectic solder

The mechanical properties (microhardness, tensile strength) of alloys are controlled by their microstructure, which depends strongly on temperature gradient (G) and growth rate (V). Thus, it is important to understand the relationships among G, V and microstructure (rod eutectic) of Sn–Ag solders. The Sn–3.5 wt% Ag eutectic alloy was directionally solidified upward with a constant growth rate, V (16.5 μm/s) at different temperature gradients, G (1.43–4.28 K/mm) and with a constant temperature gradient, G (3.93 K/mm) at different growth rates, V (8.3–500 μm/s) in a Bridgman–type directional solidification furnace. The rod spacings (λ) have been measured from both longitudinal section (parallel to the growth direction, λ _L ) and transverse section (perpendicular to the growth direction, λ _T ) of the samples. The undercooling values (ΔT) were calculated by using V, λ and system parameters (K ₁ and K ₂). It was found that the values of λ (λ _T , λ _L ) decrease while V and G are increasing. The relationships between rod spacing and solidification parameters (G and V) were obtained by linear regression analysis. The dependences of eutectic spacings λ on undercooling (ΔT) are also analyzed. λ² V, λΔT, ΔTV ^−0.5 and ΔTG ^−0.5 values were determined by using λ, ΔT, V and G values. The results obtained in this work are compared with the Jackson–Hunt eutectic theory and the similar experimental works. The experimental l_\textT ² \textV \lambda_{\text{T}}^{ 2} {\text{V}} value (159.3 μm³/s) is slightly lower than the result 174.6 μm³/s calculated from Jackson–Hunt eutectic theory.     

Temperature measurements in the pulsed laser heating of metals

The results of an investigation of the temperature dynamics of certain metals, measured by a photoemission method with a time resolution of 1 μsec, when they are heated in air and in an argon medium by millisecond laser radiation (λ = 1.06 μm) with energy densities of 75–140 J/cm² are presented.     

Spectral parameters of Nd3+ ion in Nd<Superscript>3+</Superscript>:LaCa<Subscript>4</Subscript>O(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystal

The spectral parameters of Nd³⁺ ions in Nd:LaCa₄O(BO₃)₃ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters Ω_λ are Ω₂ =1.98 × 10^–20 cm², Ω₄ =2.39 × 10^–20 cm², Ω₆ =1.38 × 10^–20 cm², the radioactive lifetime is 655 μs, the quantum efficiency is 10%, and the fluorescence branch ratios were calculated: β₁ = 0.51, β₂ = 0.42, β₃ = 0.066, β₄ = 0.003. Electronic Publication     

Controlling the wavelength of InGaAs/GaAs/InGaP lasers by ion implantation

The possibility of controlling the wavelength of emission from an InGaAs/GaAs/InGaP laser heterostructure with strained quantum wells (QWs) using medium-energy proton implantation followed by thermal annealing has been studied. It is established that the optimum proton energy is related to the arrangement of QWs in the structure (e.g., 150 keV for QWs at a depth of ≈1.3 μm). Proton irradiation to a total dose of 6 × 10¹⁴ cm⁻² followed by annealing at 700°C allows the wavelength of emission from the modified region to be decreased by 8–10 nm at minimum losses in the output intensity. The observed effect can be used to obtain two-band emission from the same chip and has good prospects for use in the development of new optoelectronic schemes.     

Use of Nd: YAG laser forin situ growth of thin films of Y1Ba2Cu3O7−δ

As-deposited superconducting films of Y₁Ba₂Cu₃O_7−δ with zero resistance at a temperature of ⋍ 80 K have been successfully grown using a Nd:YAG laser. A substrate temperature in the range 450–550°C was found most appropriate. The use of a Nd:YAG laser instead of an excimer laser is likely to improve the cost effectiveness of the laser ablation technique.     

Superconducting properties of ion beam modified YBCO microbridges

We prepared ion beam modified microbridges based on thin sputtered or laser ablated YBCO films on SrTiO₃ substrates. The microbridges with a width of 10 μm were irradiated through slits in a 700 nm thick double layer resist mask. In our experiments we used O⁺ ions with an ion energy of 30 keV or 100 keV varying the dose between 10¹³ ions·cm⁻² and 10¹⁴ ions·cm⁻². We investigated the influence of film thickness and slit width on the superconducting properties of these junctions. We show the temperature dependence of the junctions properties on microwave radiation or external magnetic fields.