Measurement of the optical constants of crystal quartz at 10 K and 300 K in the far infrared spectral range: 10–600 cm−1

The optical constants of crystal quartz in the far infrared (10 – 600 cm^?1) are reported at room temperature and at 10 K, for both polarizations parallel and perpendicular to the c-axis, respectively extraordinary and ordinary ray. These constants are obtained from the analysis of the transmissivity channeled spectra below 300 cm^?1, and from the analysis of the reflectivity spectra between 300 – 600 cm^?1, measured by using a grating infrared spectrometer. The extrapolated zero frequency refractive indices of quartz obtained in the present work are: n_o(0) = 2.106 and n_e(0) = 2.153 at 300 K; n_o(0) = 2.072 and n_e(0) = 2.130 at 10 K.     

Low-Temperature Midinfrared Absorption in GaSe

We report the measurement of the temperature dependence of the absorption spectra of ε- GaSe over the temperature range 300 K to 5 K. Measurements have been made for both the e-ray (polarized parallel to the crystal’s c-axis) and the o-ray (polarized perpendicular to the c-axis), over the spectral range 4000 to 10 cm^?1. Nine absorption lines at 417, 440, 499, 546, 891, 945, 1015, 1093, 1270 cm^?1 were recorded at 300 K for the e- ray spectra. Some of these lines were identified using the results of a modified single layer, linear chain model of GaSe. The lines at 417, 440 and 499 cm^?1 were assigned to local impurity absorption originating from N, Mg and O, respectively. The weak lines at 945, 1015 and 1093 cm^?1 were assigned to hole transitions from the acceptor levels to the top of the valence band. Two absorption lines at 891 cm^?1 and 1270 cm^?1 were assigned to hole transitions from the quasi-local acceptor levels to the double degenerate valence sub-bands Γ₅ or Γ₆. The origin of lines recorded in the far IR absorption spectra at 20, 37 cm^?1 and 362 cm^?1 were also identified.     

Effect of band inversion on the phonon spectra of the Hg1-x ZnxTe alloys

The narrow-gap II-VI and IV-VI alloys are convenient objects for studying the electron-phonon interaction. However, the concentration of free carriers in the IV-VI alloys is rather high (～10¹⁸ cm^?3), which complicates studying this effect, by the optical reflection method. The concentration of free carriers in the narrow-gap Hg_1-x Zn_xTe alloys is considerably lower (～10¹⁶ cm^?3). Therefore, the plasma component exerts less effect on the lattice reflection spectrum. The reflection spectra of Hg_1-x Zn_xTe crystals with x = 0.1–1 were studied in the far-IR region in the range of 30–700 cm^?1 at 40–300 K. Using the dispersion analysis and the Kramers-Kronig method, the frequencies of the TO phonons of the HgTe-like and ZnTe-like modes were determined depending on the composition. It is shown that the reconstructed phonon spectrum involves two modes. The temperature dependences of the frequencies of the TO phonons and the damping parameter were measured for the narrow-gap alloy with x = 0.1 in the range of 80–200 K. A decrease in the frequency of the TO phonon of the soft mode in the vicinity of the inversion point of the bands at T = 110 K was for the first time found by optical methods. The damping parameter slightly increases in the vicinity of this temperature. The result obtained qualitatively agreed with the theoretical model of Kawamura et al., which makes allowance for the effect of the electron-phonon interaction on the frequency of the soft mode in the IV-VI compounds.     

Analysis of channel noise and threshold voltage in sos-MOS transistors in the temperature range of 77–300 K

A characterization is carried out for MOS transistors on sapphire on the basis of an analysis of the threshold voltage V_T and the channel noise current using the doping of the silicon (2 × 10¹⁵ cm^?3 to 6 × 10¹⁶ cm^?3) and the temperature (77–300 K) as parameters.The experimental values of V_T, as a function of the bulk potential V_BS, show that it is possible to deplete the silicon film fully for doping magnitudes less than 10¹⁶ cm^?3. The modelling of V_T vs. V_BS, using a relation derived for bulk Silicon devices, points to finite volume effects of the silicon.The analysis of the noise shows, at 300 K, an excess noise which follows a 1/f law for the Silicon film not fully depleted and a 1/f² law in the depleted case. On the other hand, at 77 K, this noise always shows a 1/f behaviour. The study of the noise as a function of temperature suggests that the traps of the Silicon-Sapphire interface become more active around room temperature than around 77 K. The thermal level is reached at about 1 MHz at room temperature for all devices, whereas at 77 K it is only observed for the higher doping devices.     

Electrical properties of uncontaminated PbTe films on mica substrates prepared by molecular beam deposition

Uncontaminated PbTe films were prepared by molecular beam deposition under clean conditions in a uhv environment and the film properties were measured in situ. The carrier concentration was found to be determined by source conditions and values between 10¹⁶ cm^?3 (intrinsic level) and n = 5 × 10¹⁸cm^?3 could be obtained in a controllable manner. A low temperature anneal enabled bulk value Hall mobilities (1750 cm² V^?1 sec^?1 at 300 K) to be obtained at room temperature and above which indicated that surface scattering in the films was predominantly specular. The mobility at low temperatures (down to 100 K) was limited by small potential barriers located at the double-positioned grain boundaries which were present in the film. Field effect measurements indicated the potential barriers arose from a continuous distribution of band gap states situated in the grain boundaries. These states had a fairly uniform density (? 10¹²cm^?2 (kT)^?1) but there was some increase towards the conduction band edge. They also limited the field effect mobility (μ_FE) to ?0.5 bulk value, giving μ_FE ? 800cm² (volt sec)^?1 for films with carr concentrations above 5 × 10¹⁷ cm^?3. By exposure to low pressures of oxygen the carrier concentrations in annealed n-type films could be reduced to near intrinsic values with no associated degradation in the electrical properties. This indicated that the films were not compensated with the native p-type defect.     

Optical properties of Ca4Ga2S7:Eu2+

The features of optical transitions in the photon-energy range of 1.85–3.00 eV in single-crystal Ca₄Ga₂S₇:Eu²⁺ were determined from optical measurements in the temperature range of 77–300 K. It was ascertained that indirect and direct optical transitions with band gaps of E _gi=1.889 eV and E _gd=2.455 eV, respectively, occur at 300 K in the photon-energy ranges of 2.2–2.6 and 2.6–3.0 eV. The temperature coefficients of E _gi and E _gd are equal to ?5.15×10^?4 and ?14.86×10^?4 eV/K, respectively.     

The physical properties of CdTe doped with V and Ge

CdTe:(V, Ge) single crystals are grown using the Bridgman-Stockbarger method. The impurity concentrations in the melt are N_V = 1 × 10¹⁹ cm^?3 and N_Ge = 5 × 10¹⁸ and 1 × 10¹⁹ cm^?3. Electrical and galvanomagnetic characteristics are studied in the temperature range 300–400 K. It is found that the equilibrium characteristics are governed by deep levels (ΔE = 0.75–0.95 eV) located close to the midgap. Low-temperature optical absorption spectra indicate that the impurity levels of V and Ge ions in the low-energy region are in different charge states. In addition, the samples are annealed in Cd vapor and then rapidly cooled. This annealing causes the decomposition of various complexes formed during the crystal growth and an increase in both electrical conductivity and charge carrier concentration.     

Extra-drude contribution to the far infrared conductivity oxygen deficient YBCO films

We measured reflectance spectra R(v) of oxygen deficient Y₁Ba₂Cu₃O_7?x (YBCO) films of different thickness, with critical temperatures between 85 and 87 K. Measurements were made at room temperature between 15 and 25000 cm^?1. The measured R(v) have a maximum below 100 cm^?1 and then decrease for v → 0. This low frequency behaviour of R(v) can be accounted for by considering a relevant extra-Drude contribution to the far infrared optical conductivity of YBCO.     

Hall effect in CdTe crystals doped with Sn from the vapor phase

The Hall effect in semiinsulating CdTe crystals doped with a Sn impurity from the vapor phase in a closed volume is studied. It is found that the conductivity is due to a donor center with E _t ≈ 0.7 eV and the concentration of electrons and their mobility at 300 K are (4–8) × 10⁶ cm^?3 and 200–300 cm² V^?1 s^?1, respectively.     

Thermoelectric figure of merit in solid solutions with phonon scattering by off-center impurities

The Seebeck coefficient and the electrical and thermal conductivities (S, σ, and κ) of ternary PbTe_1?xSe_x (x=0.1 and 0.3) and quaternary PbTe_1?2xSe_xS_x (x=0.025, 0.05, 0.1, and 0.15) solid solutions have been studied. Polycrystalline samples with an electron density of (0.5–5.0)×10¹⁸ cm^?3 were used; their quality was monitored by comparing the measured and calculated mobility values at 85 K. A considerable decrease in mobility and an anomalous trend in the σ(T) curve near 77 K were revealed in quaternary alloys with x?0.1; for x=0.15, unusual behavior of κ(T) was also found. According to estimates, the lattice thermal conductivity of this material is temperature-independent in the 80-to 300-K temperature range. This means that a reduction in phonon-phonon scattering with an increase in temperature is completely compensated by an increase in the scattering on impurities. The observed anomalies of σ(T) and κ(T) are considered assuming the possible of off-center location of sulfur atoms at the lattice sites. The thermoelectric figure of merit Z of the studied alloys has been determined in the range 80–300 K. In spite of decreasing mobility, the maximum Z was obtained in a quaternary compound with x=0.1: at 300 K, Z_max=2×10^?3 K^?1 with a carrier density of ～3×10¹⁸ cm^?3; at 175 K, Z_max=1.5×10^?3 K^?1 with the density decreasing to 5×10¹⁷ cm^?3. The obtained data indicate that the introduction of off-center impurities rises Z at T?300 K.     

Preparation and properties of Mn-doped epitaxial gallium arsenide

The preparation of manganese-doped GaAs epitaxial layers growth from the liquid-phase, and Hall effect and resistivity measurements in the temperature range from 60 to 300°K, are described. An anomalous solubility of GaAs in the Ga + GaAs + Mn solution was observed and occurrence of a Mn₂As-phase in solution was identified. From the analysis of the Hall effect measurements the thermal activation energy of the manganese acceptor was determined. The energy decreases from 0·092 to 0·084 eV with the Mn-concentration in the epitaxial layers increasing from 6 × 10¹⁷ cm^?3 to 3 × 10¹⁹ cm^?3. The solubility of Mn in GaAs at the temperature of the preparation (850°C) was found to be about 4 × 10¹⁹ cm^?3.     

InAsSb/InAsSbP double-heterostructure lasers emitting in the 3–4 µm spectral range

Our earlier reports concerning the fabrication by liquid-phase epitaxy and investigation of InAsSbP/InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm are reviewed. The dependences of spectral characteristics and the spatial distribution of the laser emission on temperature and current are discussed. Lasing modes are shifted by 0.5–1.0 cm⁻¹ to longer wavelengths with increasing temperature. The tuning of the lasing modes by means of current is very fast (10⁻⁸–10⁻¹² s). With increasing current, the modes are shifted to shorter wavelengths by 50–60 ? at 77 K. The maximum mode shift of 104 ? (10 cm⁻¹) is observed at 62 K. The spectral line width of the laser is as narrow as 10 MHz. Abnormally narrow directional patterns in the p-n junction plane are observed in some cases in the spatial distribution of laser emission. The current tuning of lasers, due to nonlinear optical effects, has been modeled mathematically in good agreement with the experiment. Transmittance spectra of OCS, NH₃, H₂O, CH₃Cl, and N₂O gases were recorded using current-tuned lasers. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 12, 2001, pp. 1466–1480. Original Russian Text Copyright ? 2001 by Danilova, Imenkov, Kolchanova, Yakovlev. See [1].     

Capture cross sections of the gold donor and acceptor states in n-type Czochralski silicon

The hole and electron capture cross sections of the gold donor and acceptor have been measured directly in n-type silicon. The samples have been grown by the Czochralski technique and have originated from several different suppliers. They have been diffused with gold so that N_T ? 0.1 (N_D-N_A). Measurements have been made on both Schottky diodes and diffused junctions and similar results obtained from all samples. The electron cross section of the acceptor level was found to be (0.85±0.2) × 10^?16cm² and the hole cross section of the donor (3.5±0.8) × 10^?15cm², both were essentially temperature independent. The hole cross section of the acceptor was (0.9±0.2) × 10^?14cm² at 300 K and showed a T^?1.3 temperature dependence. The electron cross section of the donor was (0.9±0.2) × 10^?15cm² at 180 K with a T^?2 dependence.     

Exfoliation and blistering of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te substrates by ion implantation

As part of a series of wafer bonding experiments, the exfoliation/blistering of ion-implanted Cd_0.96Zn_0.04Te substrates was investigated as a function of postimplantation annealing conditions. (211) Cd_0.96Zn_0.04Te samples were implanted either with hydrogen (5×10¹⁶ cm⁻²; 40–200 keV) or co-implanted with boron (1×10¹⁵ cm⁻²; 147 keV) and hydrogen (1–5×10¹⁶ cm⁻²; 40 keV) at intended implant temperatures of 253 K or 77 K. Silicon reference samples were simultaneously co-implanted. The change in the implant profile after annealing at low temperatures (<300°C) was monitored using high-resolution x-ray diffraction, atomic force microscopy (AFM), and optical microscopy. The samples implanted at the higher temperature did not show any evidence of blistering after annealing, although there was evidence of sample heating above 253 K during the implant. The samples implanted at 77 K blistered at temperatures ranging from 150°C to 300°C, depending on the hydrogen implant dose and the presence of the boron co-implant. The production of blisters under different implant and annealing conditions is consistent with nucleation of subsurface defects at lower temperature, followed by blistering/exfoliation at higher temperature. The surface roughness remained comparable to that of the as-implanted sample after the lower temperature anneal sequence, so this defect nucleation step is consistent with a wafer bond annealing step prior to exfoliation. Higher temperature anneals lead to exfoliation of all samples implanted at 77 K, although the blistering temperature (150–300°C) was a strong function of the implant conditions. The exfoliated layer thickness was 330 nm, in good agreement with the projected range. The “optimum” conditions based on our experimental data showed that implanting CdZnTe with H⁺ at 77 K and a dose of 5×10¹⁶/cm² is compatible with developing high interfacial energy at the bonded interface during a low-temperature (150°C) anneal followed by layer exfoliation at higher (300°C) temperature.     

INFRARED MEASUREMENTS OF POSSIBLE IR FILTER MATERIALS

A Fourier Transform Infrared Spectrometer (FTS) was used to obtain the transmission spectra of candidate materials for use as infrared (IR) filters in cryogenic receivers. The data cover the range from 50 cm^?1 (～1.5 THz), well below the peak of the 300 K black body spectrum, to 5000 cm^?1 (～150 THz), Z-cut quartz, Goretex, Zitex G and Zitex A, High Density Polyethylene (HDPE), Teflon (PTFE), Fluorogold and Black Polyethylene were measured. The relative effectiveness of each material as a filter is determined by integrating the transmission spectrum multiplied by the Planck distribution to obtain a normalized attenuation for the mid-IR band. Measurements at both room temperature and 8 K are compared.     

A Far IR Study of NbN in the Normal and Superconductive State

A thin film of NbN (thickness t = 300 Å), has been deposited on an MgO and a Si wafer. Both samples have been studied by transmission from 10 or 20 to 120 cm^?1, and have exhibited one maximum of transmission at a given frequency like the classical superconductors as Pb, Sn or Hg in the superconductive state. From the Far IR experimental data, the characteristic temperature θ_c, and the gap frequency (ν_gap (θ) = 2 Δ (θ), Δ(θ) being the energy gap) are immediately obtained (for instance for the NbN / MgO sample, θ_c = 15.5 K; ν_g (5 K) = 39.7 cm^?1), and it is seen that $\frac{{{\text{2}}\vartriangle (4{\text{K)}}}}{{{\text{k}}_{\text{B}} \theta _c }} \approx 3.5$ as expected from the BCS theory for a weak coupling. To fit the data we had to adjust only two additionnal parameters: collision and plasma frequency, ν_c (θ) and ν_p (including all carriers). At θ = 5 K, thebest fit for the NbN / MgO sample is obtained with ν_c = 371 cm^?1 and ν_p = 12,600cm^?1.     

Thermoelectric Properties of Polycrystalline SrZn2Sb2 Prepared by Spark Plasma Sintering

Compact polycrystalline samples of SrZn₂Sb₂ [space group $ P\overline{3} m1 $ , a = 4.503(1) Å, c = 7.721(1) Å] were prepared by spark plasma sintering. Thermoelectric performance, Hall effect, and magnetic properties were investigated in the temperature range from 2 K to 650 K. The thermoelectric figure of merit ZT was found to increase with temperature up to ZT = 0.15 at 650 K. At this temperature the material showed a high Seebeck coefficient of +230 μV K^?1, low thermal conductivity of 1.3 W m^?1 K^?1, but rather low electrical conductivity of 54 S cm^?1, together with a complex temperature behavior. SrZn₂Sb₂ is a diamagnetic p-type conductor with a carrier concentration of 5 × 10¹⁸ cm^?3 at 300 K. The electronic structure was calculated within the density-functional theory (DFT), revealing a low density of states (DOS) of 0.43 states eV^?1 cell^?1 at the Fermi level.     

Electrical and optical characterization studies of lower dose Si-implanted AlxGa1−xN

Electrical and optical activation studies of lower dose Si-implanted Al_xGa_1?xN (x=0.14 and 0.24) have been made systematically as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 1×10¹⁴ cm^?2 at room temperature. The samples were proximity cap annealed from 1,100°C to 1,350°C with a 500-Å-thick AlN cap in a nitrogen environment. Nearly 100% electrical activation efficiency was obtained for Al_0.24Ga_0.76N implanted with a dose of 1 × 10¹⁴ cm^?2 after annealing at an optimum temperature around 1,300°C, whereas for lower dose (≤5×10¹³ cm^?2) implanted Al_0.24Ga_0.76N samples, the electrical activation efficiencies continue to increase with anneal temperature up through 1,350°C. Seventy-six percent electrical activation efficiency was obtained for Al_0.14Ga_0.86N implanted with a dose of 1 × 10¹⁴ cm^?2 at an optimum anneal temperature of around 1,250°C. The highest mobilities obtained were 89 cm²/Vs and 76 cm²/Vs for the Al_0.14Ga_0.86N and Al_0.24Ga_0.76N, respectively. Consistent with the electrical results, the photoluminescence (PL) intensity of the donor-bound exciton peak increases as the anneal temperature increases from 1,100°C to 1,250°C, indicating an increased implantation damage recovery with anneal temperature.     

Solution-processed field-effect transistors based on polyfluorene –cesium lead halide nanocrystals composite films with small hysteresis of output and transfer characteristics

We have designed and investigated electrical and optical properties of solution-processed organic field-effect transistors (OFETs) based on conjugated polymer PFO and perovskite –cesium lead halide nanocrystals (CsPbI₃) composite films. It was shown that OFETs based on PFO:CsPbI₃ films exhibit current-voltage (I-V) characteristics of OFETs with dominant hole transport and saturation current behavior at temperatures 200–300 K. It was found that PFO:CsPbI₃ OFETs have a negligible hysteresis of output and transfer characteristics especially at temperatures below 250 K. The values of the hole mobility estimated from I-Vs of PFO:CsPbI₃ OFETs were found to be ∼2.4 10⁻¹ cm²/Vs and ∼1.9 10⁻¹ cm²/Vs in saturation and low fields regimes respectively at 300 K; the hole mobility dropped down to ∼6 10⁻³ cm²/Vs and 2.8 10⁻³ cm²/Vs respectively at 200 K, and then down to 5.5 10⁻⁵ cm²/Vs at 100 K (in low field regime), which is characteristic of hopping conduction. The effect of sensitivity to light and light-emitting effect were found under application of negative source-drain and gate pulse voltages to PFO:CsPbI₃ OFETs at 300 K. The mechanism of charge carrier transport in OFETs based on PFO:CsPbI₃ hybrid films is discussed.     

Local vibrational modes of the oxygen-vacancy complex in germanium

Infrared absorption of n-and p-Ge crystals enriched with ¹⁶O and/or ¹⁸O isotopes was studied after irradiation with 6-MeV electrons. Absorption spectra were measured at 10 and 300 K. Along with known bands characteristic of oxygen-containing defects, new lines at 669, 944, and 990 cm^?1 were detected. These bands are annealed at temperatures of 120–140°C; the band at 621 cm^?1, previously related to the vacancy-oxygen complex in Ge, is simultaneously annealed. The bands at 621 and 669 cm^?1 showed identical temperatures (10 → 300 K) and oxygen isotope (¹⁶O → ¹⁸O) shifts. These bands were found to correspond to various charge states of a defect with an energy level near E_v=0.25±0.03 eV. It is assumed that such a defect is the vacancy-oxygen complex (A center). The weak bands at 944 and 990 cm^?1 were identified as combinations of asymmetric stretching modes at 621 and 669 cm^?1 with a symmetric one at 320 cm^?1 for neutral and negative charge states of the A center, respectively.