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.     

The accumulation of radiation defects in gallium arsenide that has been subjected to pulsed and continuous ion implantation

Measurements of electrical conductivity and Rutherford backscattering are used to study the accumulation of defects in GaAs that has been subjected to pulsed (τ_p = 1.3 × 10^?2 s and an off-duty factor of 100) and continuous irradiation with ³²S, ¹²C, and ⁴He ions at room temperature at the ion energies E=100–150 keV, doses Φ = 1 × 10⁹–6 × 10¹⁶ cm^?2, and current densities j = 1 × 10^?9–3 × 10^?6 A cm^?2. It is shown that the defect-accumulation rate during the pulsed implantation is much lower than it is during the continuous implantation.     

Theory and experiment for silicon Schottky barrier diodes at high current density

Metal-silicon Schottky barrier diodes exhibit n values which theoretically vary as a function of doping and applied voltage. The expected variation depends on which theoretical model is used to describe the current transport.Titanium n-type silicon barriers were prepared. At a doping level of 3 × 10¹⁵ cm^?3 the barrier height and n-value measured at 100 mV were 0.485±0.005 V and 1.02±0.01 whereas for a doping level of 2 × 10¹⁴ cm^?3 the corresponding values were 0.500±0.005 V and 1.18±0.05.The experimental variation of the diode n value as a function of semiconductor band bending showed good agreement with the thermionic-diffusion model of Crowell and Beguwala: n values increased rapidly as the band bending β → 2, and n values were highest at a given β for diodes with the lowest doping concentration. Similar results were obtained by measurements on magnesium and aluminium barriers on n-type silicon.An analysis of the results has shown that the variation of the diode saturation current I_s follows the predictions of the thermionic-diffusion theory, although there were some anomalies at high current densities. The anomalies did not result from variation of the width of the undepleted region of the epitaxial silicon layer or from diode self-heating effects.     

Microwave Dielectric Properties of BiCu<Subscript>2</Subscript>PO<Subscript>6</Subscript> Ceramics with Low Sintering Temperature

A BiCu₂PO₆ microwave dielectric ceramic was prepared using a solid-state reaction method. As the sintering temperature increased from 800°C to 880°C, the bulk density of BiCu₂PO₆ ceramic increased from 6.299 g/cm³ to 6.366 g/cm³; the optimal temperature was 860°C. The best microwave dielectric properties [permittivity (? _r ) = ～16, a quality factor (Q × f) = ～39,110 GHz and a temperature coefficient of resonant frequency (τ _f ) = ～?59 ppm/°C] were obtained in the ceramic sintered at 860°C for 2 h. Then, TiO₂ with a positive τ _f (～+400 ppm/°C) was added to compensate the τ _f value. The composite material was found to have a near-zero τ _f (+2.7 ppm/°C) and desirable microwave properties (? _r  = 19.9, Q × f = 24,885 GHz) when synthesized at a sintering temperature of 880°C. This system could potentially be used for low-temperature co-fired ceramics technology applications.     

Pyroelectric properties of the wide-gap semiconductor CdS in the low-temperature region

Spontaneous polarization, thermally stimulated conductivity and depolarization are comprehensively studied in the range from 4.2 to 300 K on nonstoichiometric n-type CdS crystals grown from the gas phase in an argon atmosphere at T = 1450 K. The objects of study are initial samples and samples polarized by a weak electric field at T = 4.2 K. Sample polarization results in a decrease in the conductivity σ₃₃ due to restructurization of the entire energy level spectrum associated with the formation of donor-acceptor pairs. The latter processes also contribute to the temperature dependences of the spontaneous polarization and the pyroelectric effect, characterized by the formation of anomalies below 15 K and the formation of thermoelectret. The role of an uncontrollable oxygen impurity in the formation of CdS cationic conductivity above 270 K, associated with the decay of a fraction of donor-acceptor pairs, is discussed. In the temperature range from 20 to 250 K, the pyroelectric coefficient and spontaneous polarization are independent of external influences within experimental error; at T = 200 K, they are ΔP _s = ?(6.1 ± 0.2) × 10^?4 C/m² and γ _s = ?(4.1 ± 0.3) × 10^?5 C/m² K.     

Device-quality SiO2 films on InP and Si obtained by operating the pyrolytic CVD reactor in the retardation regime

A cold wall atmospheric pressure Chemical Vapor Deposition (CVD) reactor was used to deposit films of SiO₂ at 250°C on n-InP and p-Si substrates. By varying the ratio of oxygen to silane flow rates, the reactor was operated in both the reaction rate controlled and retardation regimes. The insulator-semiconductor interface was evaluated with the aid of high frequency and quasi-static C-V curves. Films deposited on Si in the retardation regime with O₂:SiH₄ = 6 had lowest Q_ss of 5.8 × 10¹¹ cm^?2 and minimum fast surface state density of 1 × 10¹¹cm^?2eV^?1. C-V curves on InP had a hysteresis of 0.5 V, a well defined dip in the quasi-static curve and the accumulation capacitance exhibited no frequency dispersion.     

Electron traps in thin layers of low-temperature-grown gallium arsenide with As-Sb nanoclusters

Electron traps in low-temperature-grown ～40-nm-thick GaAs layers containing nanometer As-Sb clusters have been studied using deep-level transient spectroscopy. Measurements at various bias voltages and small-amplitude filling pulses have allowed the identification of two groups (T1 and T2) of traps with substantially different thermal electron emission rates. It is shown that the density of traps T2 (with an activation energy of 0.56 ± 0.04 eV and electron capture cross section of 2 × 10^?13?10^?12cm²) is ～2 × 10¹²cm_?2, while the density of traps T1 (0.44 ± 0.02 eV and 2 × 10^?14?10^?13 cm², respectively) is ten times lower. It is assumed that, according to the existence of the two cluster groups observed in the layers under study, traps T2 are associated with clusters 4–7 nm in diameter and traps T1, with clusters up to ～20 nm in diameter.     

Effect of high-temperature H2-anneals on the slow-trapping instability of MOS structures

It is shown that the slow-trapping instability upon negative bias-temperature aging of MOS structures (poly-Si and Al-gate) can be significantly reduced by a high temperature (800–900°C) H₂-anneal prior to Al metallization. Additional data are presented on the effects of high (700–900°C) and low temperature (450°C) H₂ annealing of MOS structures containing n-(111) Si, dry HCl oxide and B-doped poly-Si. The midgap N_ss (range: 8×10¹¹ to 1.5×10¹⁰ cm^?2 eV^?1) is reduced by both high and low temperature H₂ anneals whereas the Q_ss (range: 7×10¹¹ to 1×10¹¹ cm^?2 eV^?1) is reduced mainly by the high-temperature H₂-anneals. Presence of B near the interface is believed to cause an abnormal voltage asymmetry of the slow-trapping drift, i.e. ΔV_FB(-BT) < ΔV_FB(+BT). These effects are discussed in the light of Deal's model of the structure of the Si/SiO₂ interface.     

Metal Ion‐Terpyridine‐Functionalized L‐Tyrosinamide Aptamers: Nucleoapzymes for Oxygen Insertion into C?H Bonds and the Transformation of L‐Tyrosinamide into Amidodopachrome

A series of metal ion‐terpyridine‐modified L‐tyrosinamide aptamers (M^{n +} = Cu²⁺ or Fe³⁺) act as enzyme‐mimicking catalysts (nucleoapzymes) for oxygen‐insertion into C? H bonds and the transformation of L‐tyrosinamide into amidodopachrome. The reaction proceeds in the presence of H₂O₂ and coadded L‐ascorbic acid. In one series of experiments, the catalyzed oxidation of L‐tyrosinamide to amidodopachrome by a set of nucleoapzymes consisting of Fe³⁺‐ or Cu²⁺‐terpyridine complexes tethered directly or through a 4 × thymidine (4 × T) bridge, to the 5′‐ or 3′‐end of the 49‐mer L‐tyrosinamide aptamer or to a shorter 23‐mer L‐tyrosinamide aptamer is examined. All nucleoapzymes reveal catalytic Michaelis–Menten enzyme‐like activities and the separated Fe³⁺‐ or Cu²⁺‐terpyridine and L‐tyrosinamide aptamer units show only minute catalytic properties. The catalytic activities of the nucleoapzymes are attributed to the concentration of the L‐tyrosinamide substrate by the aptamer units in proximity to the catalytic sites (K_d = (14 ± 0.1) × 10^?6 m for all 49‐mer catalysts and K_d = (2.5 ± 0.1) × 10^?6 m and K_d = (0.8 ± 0.04) × 10^?6 m for the 23‐mer catalysts). Electron spin resonance experiments reveal that ?OH radicals and ascorbate radicals participate in the transformation of tyrosine derivatives to catechol products. An autocatalytic feedback mechanism for the amplified generation of the two radicals is suggested.     

Humidity dependence of the atmospheric absorption coefficient in the transparency windows centered at 0.88 and 0.73 MM

A dependence is investigated of the absorption coefficient of atmospheric water vapor on absolute air humidity in the spectral intervals ν=11.1+12.0 and 13.2+14.3 cm^?1 by a radiospectrometer with a multipass vacuum cell. Measurements are carried out in the humidity range ??3+23 g/m³ at 140 m length of the optical path. Parts of the absorption coefficient linearly and quadratically depending on ? have been separately defined from the experimental data. In particular, it has been obtained for the centers of transparency windows: Γ (α=0.73mm) [dB/km]=1.68 (±0.08) ?+0.019 (±0.004) ?², Γ (α=0.88 mm) [dB/km]=0.83 (±0.06) ?+0.013 (±0.002) ?². The given values correspond to the temperature of 306 K and the pressure of dry air of 735 Torr. A comparison is made between our results and theoretical calculations and data of other measurements.     

Thermal emission rates and capture cross sections of majority carriers at vanadium centers in silicon

The thermal emission rates and capture cross sections of majority carriers on the vandium associated centers in the depletion region of reverse biased silicon p-n junctions have been measured by the dark capacitance transient method. The three vanduim associated levels observed, two donor levels and a deep acceptor level, belong to the same vandium center. Least square fits of the emission data give the following emission rates; e_nl^t = 1.047 × 10⁶T² exp [?0.179±0.004 eV/kT], e_n0^t = 3.55 × 10⁷T² exp [?0.426±0.004 eV/kT] and e_p-2^t = 1.514 × 10⁶T² exp [?0.450±0.003 eV/kT]. The activation energy of the hole emission rate at the lower donor level is about 0.1 eV larger than the equilibrium thermal activation energy. The capture cross sections are σ_n0 = 3 × 10^?17cm² and σ_p0 = 8 × 10^?16cm² for the electron capture process at the deep acceptor level and the hole capture process at the upper donor level, respectively. The hole capture cross section on the lower donor level (σ_p-1) depends significantly on temperature. The large temperature dependence of the hole capture cross section can be expected due to the nonradiative multiphonon emission process.     

A submillimeter heterodyne receiver for the Kuiper Airborne Observatory and the detection of the 372 μm carbon monoxide line J=7–6 in OMC-1 and W3

A compact heterodyne receiver system used in the Kuiper Airborne Observatory (KAO) is described. Calibration techniques and methods for eliminating standing wave effects are presented. The J=7–6 rotational transition of carbon monoxide was detected in OMC-1 and in W3 with a beam of 5.5′ HPBW. The peak antenna temperature of OMC-1 is 55 K, with the line center at +8±1 kms^?1 and FWHM 6.0±0.3 kms^?1. The total line flux in our beam is 7.8×10^?13 Wm^?2. This relatively high value seems to indicate that OMC-1 might be extended over at least several arcminutes in CO (J=7–6). In W3, the peak antenna temperature is 6±2 K, with line center at ?42±2 kms^?1 and FWHM ～9 kms^?1. The total line flux is 1.5×10^?13 Wm^?2. W3 thus emits about 50 L_⊙ in CO (J=7–6) alone.     

Measurements of 220 GHz atmospheric opacity on Mt. Fuji with a radiometer/radome system

We measured atmospheric opacity at 220 GHz at the summit of Mt. Fuji (alt. 3776 m) about one year in order to explore a feasibility of submillimeter-wave astronomical observations. For this purpose, a 220 GHz radiometer system enclosed in a radome (51×51×62 cm³) has been developed. The 220 GHz opacity was lower than 0.06 for a significant fraction (～ 45 %) of time from November 1994 to March 1995. Diurnal variation of the opacity at the summit of Mt. Fuji is so small that continuous observation at submillimeter-wave is possible through day and night. Yearly variation of the opacity is studied from water vapor pressure data measured at the weather station for the past 3 years. To prevent accumulation of ice and snow on the Gore-Tex membrane in the radome, the outer membrane was supplied with a thermal flux of 0.63 kW m^?2 and the adjacent metal radome surfaces were supplied with a flux of ～0.9 kW m^?2. We evaluate from the 220 GHz transmission data that this heat flux is sufficient to keep the membrane on the radome free of ice and snow during 83 % of the time in 5 winter months. The summit of Mt. Fuji appears to be a promising site for submillimeter-wave observations.     

Thermoelectric Properties of p-Type Mg2Si0.25Sn0.75 Doped with Sodium Acetate and Metallic Sodium

We have investigated the thermoelectric properties of p-type Na-doped Mg₂ Si_0.25Sn_0.75 solid solutions prepared by liquid–solid reaction and hot-pressing methods. Na was introduced into Mg₂Si_0.25Sn_0.75 by using either sodium acetate (CH₃COONa) or metallic sodium (2 N). The samples doped with sodium acetate consisted of phases with antifluorite structure and a small amount of MgO as revealed by x-ray diffraction, whereas the sample doped with metallic sodium contained the Sn, MgO, and Mg₂SiSn phases. The hole concentrations of Mg_1.975Na_0.025Si_0.25Sn_0.75 doped by sodium acetate and metallic sodium were 1.84 × 10²⁵ m^?3 and 1.22 × 10²⁵ m^?3, respectively, resulting in resistivities of 4.96 × 10^?5 Ω m (sodium acetate) and 1.09 × 10^?5 Ω m (metallic sodium). The Seebeck coefficients were 198 μV K^?1 (sodium acetate) and 241 μV K^?1 (metallic sodium). The figures of merit for Mg_1.975Na_0.025Si_0.25Sn_0.75 were 0.40 × 10^?3 K^?1 (sodium acetate) and 0.25 × 10^?3 K^?1 (metallic sodium) at 400 K. Thus, sodium acetate is a suitable Na dopant for Mg₂Si_1?x Sn _x .     

Schottky-barrier capacitance measurements for deep level impurity determination

The time dependence of a Schottky-barrier capacitance due to thermal excitation of trapping centres has been studied. An expression for the junction capacitance is derived which is not restricted to any special range of reverse bias nor to a special relation between shallow and deep impurity concentration. The concentration ratio of shallow to deep centres is calculated from the values of the capacitance at zero and infinite time. From a capacitance vs. time plot the trap emission rate for electrons e_n is obtained. Their energetic level within the forbidden band-gap is determined from the temperature dependence of e_n as well as from the capacitance-time variation. Experimental studies which do confirm the calculations were carried out on gold contacts on oxygen-doped n-type GaAs. Representative results of the investigated samples were: shallow donor density 3 × 10¹⁵ cm^?3, trap density 9·8 × 10¹⁵ cm^?3, electron emission rate 6 × 10^?2 sec^?1, energetic level 0·68 eV and capture cross section 7 × 10^?16 cm².     

Dark-current relaxation in MnGa2Se4 single crystals

The results of investigation of isothermal currents and charge accumulation in In-MnGa₂Se₄-In sandwich structures are presented. The obtained data are analyzed on the basis of the theory of isothermal currents and the relay-race mechanism of charge transport. It is shown that the dark-current relaxation in MnGa₂Se₄ single crystals is associated with charge accumulation at deep levels due to injection from the cathode. The following parameters are determined: the contact capacitance C _k = 2 × 10^?13 F, the charge-accumulation-layer thickness d _k = 4 × 10^?6 cm, and the drift charge-carrier mobility μ_ch = 3 × 10^?8 cm² V^?1 s^?1 in MnGa₂Se₄ single crystals.     

Diffusion of chromium in GaAs under equilibrium arsenic-vapor pressure

The diffusion of chromium in GaAs is studied under equilibrium arsenic-vapor pressure. The temperature dependences of chromium diffusivity and solubility in GaAs are determined. These dependences are described by the Arrhenius equation with the parameters D ₀ = 3.1 × 10⁵ cm²/s and E = 3.2 ± 0.4 eV for the diffusivity and N _S = 2.1 × 10²¹ cm^?3 and E _S = 1.0 ± 0.3 eV for the solubility. The obtained experimental results are compared with our previously published data on the diffusion of chromium under high arsenic-vapor pressure and analyzed in terms of the dissociative mechanism of migration of chromium in GaAs.     

Transient and steady state space-charge-limited current in CdTe

The current response to pulsed and constant external bias is studied on wafers of semi-insulating CdTe crystals which are provided with contacts of aquadag. Space-charge-limited current (sclc) is observed. The magnitude of the large-signal turn-on transient current suggests that electrons are the injected carriers. The time constant of the current decay yields a value of the electron trapping time τ⁺ of ～ 10^?7 sec. Double pulse experiments provide the value of the detrapping time τ_D and its activation energy E_t = 0.65 eV. From these quantities, a trap concentration N_t = 0.85 × 10¹²cm^?3 and a trapping cross-section σ = 3.8 × 10^?13 are deduced. The results are compared with the d.c. characteristic of the devices and with data reported in the literature. Good agreement is obtained, indicating the usefulness of transient and d.c. sclc for characterizing semi-insulating materials and the injecting nature of the contacts.     

Evaluation of mobility gaps and density of localized hole states in p-Ge/Ge1−x Six heterostructures in the quantum Hall effect mode

The temperature (0.1 K?T?20 K) and magnetic field (0 T?B?12 T) dependences of the longitudinal (ρ_xx) and Hall (ρ_xy) resistivities have been studied in detail for p-Ge/Ge_1?x Si_x (x=0.07) multilayer heterostructures with hole density p=(2.4–2.6)×10¹¹ cm^?2 and mobility μ=(1.1–1.7)×10⁴ cm² V^?1 s^?1. The energy spectrum parameters of two-dimensional (2D) hole gas in the quantum Hall effect mode have been determined. The mobility gap W=(2–2.5) meV and the background density of localized states g _c =(5–7)×10¹⁰ cm^?2 meV^?1 for the filling factors ν=1 and 2. The results are discussed in terms of long-range impurity potential models for selectively doped 2D systems.     

Irradiation-Induced Defects in Cd0.9Zn0.1Te:Al

The effects of gamma-irradiation, produced by a ⁶⁰Co source with a dose of 2.7?kGy, on defect levels in a Cd_0.9Zn_0.1Te:Al (CZT:Al) crystal were investigated by thermally stimulated current spectroscopy. Nine observed defect levels were identified, and the irradiation-induced variations of trap signatures for these levels, i.e., the thermal activation energy, concentration, and capture cross-section, have been evaluated using simultaneous multiple peak analysis. In addition, the dark-current spectra dominated by the deep donor (E _DD) level have been certified. By fitting plots of the logarithm of dark current ln(I _DC) versus 1/kT, the E _DD level is determined to be 0.554?±?0.001?eV and 0.792?±?0.004?eV before and after gamma-irradiation, respectively. One month after irradiation, the E _DD level moved slightly to 0.782?±?0.003?eV. This result indicates that the E _DD level is closer to the middle of the bandgap of CZT:Al after irradiation, which should be responsible for Fermi-level pinning near the middle of the bandgap, leading to high resistivity. This is consistent with the resistivity variation of CZT:Al at room temperature from the original value of 7.5?×?10⁹?Ω?cm before irradiation to the irradiated value of 5.6?×?10¹⁰?Ω?cm as determined by current–voltage measurements.