Investigation of the electrical and photoelectric properties of manganese-doped gallium arsenide as a material for photoresistive detectors

An investigation was made into the electrical and photoelectric properties of gallium arsenide with an initial electron density 5×10¹⁵–4×10¹⁷ cm^–3 doped with Mn in different thermodynamic diffusion regimes characterized by diffusion temperatures of 900 and 1000°C and arsenic vapor pressure 10^–2 and 10^–3 atm. The ionization energy and defect concentration were determined by a computer analysis of the equilibrium hole density determined from the Hall effect. Centers with ionization energy 0.08–0.10 eV were found, their concentration varying from 2×10¹⁹ to 2×10²⁰ cm^–3 depending on the diffusion temperature and the doping level of the original crystals. Data obtained by investigating the stationary intrinsic photoconductivity were used to determine a hole lifetime of t_p 10^–9 sec. The photoconductivity spectra were investigated in the range 0.5–2 eV at 77°K, and defects with ionization energy E_v + 0.6 eV were found in all samples. The impurity photoconductivity at wavelength 10.6 m was investigated. It was shown that GaAsMn can be used as a material for impurity photoresistors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 15–19, March, 1981.     

Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas

We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm² into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu₂, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×10⁶ cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu₂A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu₂ is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×10¹³ cm^–3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.     

Electrical characteristics of the rf-excited oxygen plasma-cathodization-grown SiO2/Si interface

The electrical properties of the SiO₂/n-type Si(100) interface, where the silicon-oxide layer was grown by an electrodeless rf oxygen-plasma-cathodization technique, were investigated usingC-V and DLTS methods. Interface traps with high density in the range of 10¹² eV^–1 cm^–2 and a capture cross section as large as 10^–18 cm² were found in the upper region of the silicon forbidden gap. After a post-annealing process, typically at 400°C for 30 min in dry N₂ atmosphere, their densities and capture cross sections were reduced to the range of 1–2 × 10¹¹ eV^–1 cm^–2 and 10^–19 cm^–2, respectively. Apparant differences in DLTS curves before and after thermal annealing were also observed. Results are qualitatively explained by considering the specific oxidation and annealing mechanism of this low-temperature silicon-oxidation technique.     

Relaxation oscillations and damping factors of 1.3 μm In(Ga)As/GaAs quantum-dot lasers

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 10¹⁰ cm^–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm². The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10^–16 cm² and 3.4 × 10 ^–17 cm ³, respectively. Using these parameters, the maximum modulation bandwidth f _{3 dB max} is estimated as 7.9 GHz.     

Absorption of subpicosecond ultraviolet laser pulses in high-density plasma

The absorption of 250 fs KrF laser pulses incident on solid targets of aluminum, copper and gold has been measured for normal incidence as a function of laser intensity in the range of 10¹²–10¹⁴ W cm^–2 and as a function of polarization and angle of incidence for the intensity range of 10¹⁴–2.5×10¹⁵ W cm^–2. As the intensity increases from 10¹² W cm^–2 the reflectivity at normal incidence changes from the low-intensity mirror reflectivity value to values in the range of 0.5–0.61 at 10¹⁴ W cm^–2. For this intensity maximum absorption of 63–80% has been observed for p-polarized radiation at angles of incidence in the range of 54°–57°, increasing with atomic number. The results are compared with the expected Fresnel reflectivity from a sharp vacuum-plasma interface with the refractive index given by the Drude model and also to numerical calculations of reflectivity for various scale length density profiles. Qualitative agreement is found with the Fresnel/Drude model and quantitative agreement is noticed with the numerical calculations of absorption on a steep density profile with normalized collision frequencies, v/, in the range of 0.13–0.15 at critical density and normalized density gradient scale lengths, L/₀, in the range of 0.018–0.053 for a laser intensity of 10¹⁴ W cm^–2.At 2.5×10¹⁵ W cm^–2 a small amount of preplasma is present and maximum absorption of 64–76% has been observed for p-polarized radiation at angles of incidence in the range of 45°–50°.Dedicated to Prof. Dr. Rudolf Wienecke on the occasion of his 65^th birthdayOn leave from: Department of Electrical Engineering, University of Alberta, Edmonton, T6G 2G7, Canada     

Electrical conductivity of Ag/Na ion-exchanged titanosilicate glasses

The Ag₂O–TiO₂–SiO₂ glasses were prepared by Ag⁺/Na⁺ ion-exchange method from Na₂O–TiO₂–SiO₂ glasses at 380–450 °C below their glass transition temperatures (T_g), and their electrical conductivities were investigated as functions of TiO₂ content and the ion-exchange ratio (Ag/(Ag+Na)). In a series of glasses 20R₂O·xTiO₂·(80−x)SiO₂ with x=10, 20, 30 and 40 in mol%, the electrical conductivities at 200 °C of the fully ion-exchanged glasses of R=Ag were in the order of 10⁻⁵ or 10⁻⁴ S cm⁻¹ and were 1 or 2 orders of magnitude higher than those of the initial glasses of R=Na. The glass of x=30 exhibited the highest increase of conductivity from 3.8×10⁻⁷ to 1.3×10⁻⁴ S cm⁻¹ at 200 °C by Ag⁺/Na⁺ ion exchange among them. When the ion-exchange ratio was changed in 20R₂O·30TiO₂·50SiO₂ system, the electrical conductivity at 200 °C exhibited a minimum value of 7.6×10⁻⁸ S cm⁻¹ around Ag/(Ag+Na)=0.3 and increased steeply in the region of Ag/(Ag+Na)=0.5–1.0. When the ion-exchange temperature was changed from 450 to 400 °C, the conductivity of the ion-exchanged glass of x=30 decreased. The infrared spectroscopy measurement revealed that the ion-exchange temperature of 450 °C induced a structural change in the glass of x=30. The T_g of the fully ion-exchanged glass of x=30 was 498 °C. It was suggested that the incorporated silver ions changed the average coordination number of titanium ions to form higher ion-conducting pathway and resulted in high conductivity in the titanosilicate glasses.     

Optical emission diagnostics of laser-induced plasma for diamond-like film deposition

Optical emission from a laser-induced plasma plume is recorded during KrF excimer laser ablation of graphite in a gas mixture of Ar and H₂ (3%) for deposition of diamond-like thin films. At sub-GW/cm² laser intensities the spectrum is dominated by the bands of C₂ and CN. From the band intensities, the vibrational temperatures of both radicals are calculated to be 12–15×10³ K, and their concentrations are estimated to be 5×10¹⁴ cm^–3 and 2×10¹⁴ cm^–3, respectively.     

Effect of deep dislocation levels in silicon on the properties of p-n junctions

We present the results of studies on the influence of deep levels, due to dislocations in electronic-grade silicon, on the lifetime of minority carriers and on the current-voltage and capacitance-voltage characteristics of p-n junctions. The parameters of the deep levels were determined by means of dynamic spectroscopy. The carrier lifetime in the high-resistance region of the p-n junction correlates well with the dislocation density and varies from 10^–7 sec to 3 · 10^–8 sec when the dislocation density N_d varies from 10⁷ cm^–2 to 5 · 10³ cm^–2. The voltage across the p-n junction at a high level of injection varies 1.6 to 6.2 v as a function of N_d. The ionization energy of deep levels associated with dislocation in silicon is 0.44 and 0.57 eV, measured from the bottom of the conduction band.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 81–84, January, 1988.     

High resolution molecular spectroscopy in the submillimeter region

Fourier Transform laboratory measurements have been carried out, for the first time in the 8–85 cm^–1 spectral region, with an unapodized resolution of 3.3. 10^–3 cm^–1 and a frequency accuracy of 2. 10^–4 cm^–1. Samples from spectra of several molecules namely: CO, O₃, H₂O₂, NO, NO₂, HNO₃, SO₂, H₂S, HOCL, NOCL, HNCO, ND₃ and AsH₃ are presented to show both the quality of the measurements and the type of information supplied by high resolution spectroscopy in the submillimeter region.     

Far infrared emission spectra from stratospheric hydrogen peroxide

Synthetic emission spectra from two stratospheric altitude observations have been analyzed for the presence of H₂O₂ in the far infrared region. The calculations are made with a high spectral resolution (10^–3 cm^–1 or 10^–4 cm^–1) greater than those in experimental measurements which are in the region of 3.10^–3 cm^–1. Spectra cover a spectral interval between 40 and 120 cm^–1 showing the best features of H₂O₂ susceptible to observation in a stratospheric spectrum. The optimum conditions for identification have been considered. Using the variations in H₂O₂ abundance in the measurement data and photochemical models, the H₂O₂ features detection limits have been studied.     

Environmental influence on the IR fluorescence of Xe<Subscript>2</Subscript><Superscript>*</Superscript> molecules in electron beam excited Ar–Xe mixture at high density

We report new measurements of the near infrared (NIR) Xe₂^* excimer fluorescence in an electron–beam–excited Ar (90%)–Xe (10 %) mixture at room temperature. Previous measurements up to a density N≈2×10²⁶ m^-3 discovered a broad excimer fluorescence band at ≈7800 cm^-1, whose center is red–shifted by increasing N [A.F. Borghesani, G. Bressi, G. Carugno, E. Conti, D. Iannuzzi, J. Chem. Phys. 115, 6042 (2001)]. The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density–dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to N≈6×10²⁶ m^-3, confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credibility to the validity of the proposed explanation of the experimental findings.     

Trap centers in Au-implanted MOS structures

Trap centers in the Si-SiO₂ interface region of MOS structures doped by ion implantation of gold have been investigated using constant capacitance deep level transient spectroscopy (CC-DLTS). Gold doses of 10¹²–3 × 10¹³ cm^–2 were implanted into the back surface of the wafers and were then redistributed during a diffusion anneal for 30 min at 1100° or 900° C. Three Au-related trap levels have been observed in the interface region, which were attributed to the Au-donor (E _v +0.35 eV), the Au-acceptor (E _v +0.53 eV), and the Au-Fe complex (E _v +0.45 eV). The trap concentration profiles show that the Si-SiO₂ interface affects the Au concentration in a depth range of 1 m from the interface and that gettering of Au occurs at the interface. The interface state density is independent of the Au concentration at the interface even for concentrations of 10¹⁵ cm^–3.     

Shallow acceptor population and free hole concentration in Si: In and Si:Ga with IR-photoexcitation

Hall measurements at low temperaturesT<50 K have been performed on Si:In (N _In10¹⁷ cm^–3) and Si:Ga (N _Ga10¹⁸ cm^–3) with infrared photoexcitation of holes into the valence band. It is shown in quantitative agreement with a theoretical model that the population of shallow acceptors, e.g. B and Al, which are present as impurities in concentrations ofN _B,Al10¹²-10¹⁴ cm^–3 strongly affects the photoexcited hole concentration. Photo-Hall measurements can, therefore, serve as a tool for the determination of low impurity acceptor concentrations in the case of high In- or Ga-doping. Hole capture coefficientsB _In=6×10^–4 (T/K)^–1,8 cm³ s^–1 andB _Ga=2×10^–4 (T/K)^–1 cm³ s^–1 have been determined.     

Far infrared surface electromagnetic waves propagation on A3B5 semiconductors

The real and imaginary parts of surface electromagnetic waves (SEW) refraction index n_ef in n-type InSb, GaAs and InP have been measured in FIR region (=85–142 cm^–1). The n_ef measurements allowed to determine plasma frequency _p and plasmon damping . The obtained nonlinear SEW propagation distance L dependence on Te impurity concentration in GaAs (N=10¹⁷–10¹⁹ cm^–3) was explained taking into account the conduction band nonparabolity as well as the presence of isostructural phase transition at N=2×10¹⁰ cm^–3.     

Dislocation structure of kcl crystals grown with vibration of the melt

Summary The amplitude at all frequencies was 0.04 mm. Three crystals were grown at each frequency, with seeds of dislocation density D = 6 × 10⁴ cm^–2. Figure 1 shows the frequency dependence of the final D. Each point in Figs. 1 and 2 is the mean from 50 measurements (50 fields of view). At all frequencies except 180 Hz, D was 2–4 times less than that without vibration, while at 100 and 160 Hz it was less by nearly an order of magnitude.The effects of amplitude (0.02 to 0.2 mm) were examined at 100 Hz, the minimum D occurring at 0.1 mm (Fig. 2). At 0.04–0.08 mm, D was less by a factor 3–4 than for crystals grown without vibration, while at 0.1 mm it was less by an order of magnitude, being 2 × 10^–4 cm^–2. The size of the etch pits on crystals grown at amplitudes up to 0.1 mm did not differ from that for crystals grown at rest, but above 0.1 mm the size increased, by more than a factor 3 at 0.2 mm. Figure 3 illustrates these effects.Optimal vibration reduces D by improving the growth conditions (reduction of temperature gradients by mixing, more uniform impurity distribution).     

Characteristics of SrBi2Ta2O9 ferroelectric films on Si using LaAlO3 thin film as an insulator

Metal–ferroelectric–insulator–semiconductor structures using LaAlO₃ (LAO) layers as an insulating barrier have been investigated. LAO films were deposited on n-Si substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). SrBi₂Ta₂O₉ (SBT) films were prepared as ferroelectric layers at a low processing temperature of 650 °C by a metalorganic decomposition method. The MOCVD-derived LAO buffer layer shows an amorphous structure, relatively high dielectric constant, and good electrical properties. Au/SBT/LAO/n-Si exhibits a larger counterclockwise C–V memory window of 3.7 V and a lower leakage-current density of 2.5×10^-8 A/cm² at an applied voltage of 10 V. It has been confirmed that the hysteresis loop is caused by ferroelectricity. The Auger electron spectrometry depth profile indicates that the introduction of the LAO buffer layer prevents the interfacial diffusion between SBT and the Si substrate effectively and improves the interface quality. PACS 77.84.Dy; 81.15.Fg     

The magnetic susceptibility of p-type CdSb

The paper gives the measurements of the magnetic susceptibility of p-type CdSb at 77°K on samples crystallographically oriented and cut from single crystals having an acceptor concentration of 2.3×10¹⁵cm^–3, 2.4×10¹⁶ cm^–3 and 1.5×10¹⁷ cm^–3. The anisotropy of the lattice and hole gas contribution was found and the ratio of the hole effective mass obtained from measurement of the transversal magnetoresistivity in p-type CdSb at 77°K [3] was used to determine their absolute values:m _a=0.48m ₀=m _b=0.44m ₀,m _c=0.17m ₀.     

Influence of the noise driving force on the diffusion of copper in aluminium thin films

The diffusion of copper in thin polycrystalline aluminium films subjected to current stressing at 140 C was studied. Experimental aluminium stripes were doped with copper in a limited (source) region and the movement of copper away from this region was investigated by electron probe microanalyser. Samples were stressed both by dc and by superimposed dc and noise current. The dc density (5×10⁵ A/cm²) was equal to that of the effective (r.m.s.) value of superimposed current. The frequency range of the noise signal with the Gaussian distribution of amplitudes was 5 Hz to 20 kHz. Under the described conditions copper diffused due to the concentration gradient as well as the electromigration driving force. The diffusion coefficients of copper at both current stressings were obtained by fitting the measured concentration profiles to those calculated theoretically. The results yield that the diffusion becomes enhanced when the noise is applied. The values of thermal grain boundary-assisted diffusion coefficient obtained in six independent measurements with dc loading vary betweenD _Tb=8×10^–13 cm²/s and 25×10^–13 cm²/s. The corresponding values of total diffusion coefficient (i.e. the sum of the thermal and noise induced component) areD _b=(20÷83)×10^–13 cm²/s. The noise-induced enhancement of the diffusion was predicted theoretically. Thus, the present results confirm the previous theoretical calculations.The authors wish to thank Dr. V. Bezák for stimulating discussions.     

A polarized CARS investigation of the fine structure population inversion of Cl atoms from laser photolysis of ICl and the quenching of Cl(2 P 1/2) by O2

The time resolved polarized CARS technique has been used to detect Cl atoms produced by photolysis of ICl in the presence and absence of O₂. A population inversion was observed between the ground state electronic levels Cl(² P _1/2) and Cl(² P _3/2). The rate constant for Cl(² P _1/2) decay (quenching + reaction) in ICl was determined to be (3.2±0.2)×10^–13 cm³/molecule×s; the rate constant for Cl(² P _3/2) reaction with ICl was determined to be (7.8±0.5)×10^–12 cm³/molecule×s; and the rate constant for Cl(² P _1/2) quenching by O₂ was determined to be (1.9±0.2)×10^–13 cm³/molecule×s.     

Quantitative assessment of solid oxide electrochemical doping

Quantitative analysis of metal cation doping by solid oxide electrochemical doping (SOED) has been performed under galvanostatic doping conditions. A M–β″-Al₂O₃ (M=Ag, Na) microelectrode (contact radius: about 10 μm) was used as cation source to attain a homogeneous solid–solid contact between the β″-Al₂O₃ and doping target. In Ag doping into alkali borate glass, the measured dopant amount closely matched the theoretical value. High Faraday efficiencies of above 90% were obtained. This suggests that the dopant amount can be precisely controlled on a micromole scale by the electric charge during electrolysis. On the other hand, current efficiencies of Na doping into Bi₂Sr₂CaCu₂O_y (BSCCO) ceramics depended on the applied constant current. Efficiencies of above 80% were achieved at a constant current of 10 μA (1.6 A cm⁻²). The relatively low efficiencies were explained by the saturation of BSCCO grain boundaries with Na. By contrast, excess Na was detected on the anodic surface of ceramics at a constant current of 100 μA (16 A cm⁻²). In the present study, we demonstrate that SOED enables micromole-scale control over dopant amount.