Infrared plasma reflectivity minimum in heavily doped n-Si

This paper presents a numerical analysis of infrared (IR) plasma reflectivity minimum in ultra heavily doped (UHD) n-Si (impurity concentration N up to 6 × 10²¹cm⁻³) by using a self-consistent method (SCM) and a complex physical model. The necessity of taking into account the dependence of effective mass on impurity concentration is shown. The scattering on defects (N_def = 5 × 10¹⁷ cm⁻³) and dislocation (N_dis = 5 × 10¹¹ cm⁻²) is included. The approximate relation for the wavelength λ_m(N) of the reflectivity minimum is given. The results obtained are compared with the experimental results for n-Si and satisfactory agreement is found.     

Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy

In this study deep level transient spectroscopy has been performed on boron–nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N_A–N_D)∼3×10¹⁷ cm⁻³. We observed a hole H₁ majority carrier and an electron E₁ minority carrier traps in the device having activation energies E_v+0.24 eV, E_c −0.41 eV, respectively. The capture cross-section and trap concentration of H₁ and E₁ levels were found to be (5×10⁻¹⁹ cm², 2×10¹⁵ cm⁻³) and (1.6×10⁻¹⁶ cm², 3×10¹⁵ cm⁻³), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H₁ defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E₁ defect to a nitrogen donor.     

Substitutional disorder effects on optical spectra of extremely heavily doped Si : P obtained by ion implantation and laser annealing

The optical reflectivity spectrum (2500–5000 Å) of extremely heavily phosphorus (P)-doped Si has been studied. The E₁ and E₂ peaks, which represent the completeness of the Si crystal, are slightly affected when doping concentrations are less than 10²¹ cm^-3 (2% Si : P). However,they appreciably degrade as the doping concentration increases from 10²¹ to 5×10²¹cm^-3 (10% Si : P). As the result of band calculations using a supercell configuration and pseudopotential method, we have been able to ascribe this behavior to the substitutional disorder effect.     

The optical conductivity of free carriers in GaAs

The optical conductivity of free electrons in polar semiconducting compounds has recently been calculated by use of a generalized Boltzmann equation derived from the equation of motion of the quantum density matrix. This reduces to the quasi-classical Boltzmann transport equation in the low frequency limit: the optical conductivity thus obtained spans a spectral range from around 30cm^?1 to 1.2 × 10⁴cm^?1 in GaAs. In this paper, the optical conductivity is calculated for GaAs as a function of carrier concentration in terms of a frequency dependent relaxation time which reduces to the usual relaxation time in the limit of low frequencies and an elastic scattering mechanism. The low frequency limit of the relaxation time is used to estimate the mobility as a function of carrier concentration. The frequency dependent relaxation time is given for GaAs at 298 K over the spectral region from 45 cm^?1 to 2.3 × 10³cm^?1 for carrier concentrations from 3.4 × 10¹⁵cm^?3 to 8.7 × 10¹⁸cm^?3.     

极化诱导实现AlGaN薄膜材料中的超高电子浓度(1020cm-3)掺杂

材料的载流子浓度和迁移率是影响器件性能的关键因素, 变温Hall测试结果证明杂质掺杂AlGaN中的载流子浓度和迁移率随温度 降低而减小.然而极化诱导掺杂的载流子浓度和迁移率不受温度变化的影响.以准绝缘 的GaN体材料作为衬底, 在组分分层渐变的AlGaN中实现的极化诱导掺杂浓度 仅仅在10¹⁷ cm^-3数量级甚至更低. 本研究采用载流子浓度为10¹⁶ cm^-3量级的非有意n型掺杂GaN模板为衬底, 用极化诱导掺杂技术在分子束外延生长的AlGaN薄膜材料中实现了高 达10²⁰ cm^-3 量级的超高电子浓度. 准绝缘的体材GaN半导体作衬底时, 只有表面自由电子作为极化掺杂源, 而非有意掺杂的GaN模板衬底除了提供表面自由电子外,还能为极化电场 提供更多的自由电子"源", 从而实现超高载流子浓度的n型掺杂.     

Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ(T), as well as the temperature and field dependences of the magnetic susceptibility χ(T, B) and magnetoresistance ρ(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ_∥(T)/σ_⊥>50, which disappears in the brominated samples. The χ(T, B) data were used to estimate the carrier concentration n ₀ in the samples: n _0ini ～3×10¹⁰ cm^?2 for the pristine sample, and n _0Br～10¹¹ cm^\t—2 for the brominated sample. Estimation of the total carrier concentration n=n _e+n _p from the data on ρ(B, T) yields n _ini=4×10¹⁷ cm^?3 (or 1.3×10¹⁰ cm^?2) and n _Br=2×10¹⁸ cm^?3 (or 6.7×10¹⁰ cm^?2). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination.     

3 MeV electron irradiation-induced defects in CuInSe2 thin films

3 MeV electron irradiation induced-defects in CuInSe₂ (CIS) thin films have been investigated. Both of the carrier concentration and Hall mobility were decreased as the electron fluence exceeded 1×10¹⁷ cm⁻². The carrier removal rate was estimated to be about 1 cm⁻¹. To evaluate electron irradiation-induced defect, the electrical properties of CIS thin films before and after irradiation were investigated between 80 and 300 K. From the temperature dependence of the carrier concentration in non-irradiated thin films, we obtained N_D=1.8×10¹⁷ cm⁻³, N_A=1.7×10¹⁶ cm⁻³ and E_D=18 meV from the SALS fitting to the experimental data on the basis of the charge balance equation. After irradiation, a new defect level was formed, and N_T0=1.4×10¹⁷ cm⁻³ and E_T=54 meV were also obtained from the same procedure. From the temperature dependence of Hall mobility, the ionized impurity density was discussed before and after the irradiation.     

Absorption edge shift in ZnO thin films at high carrier densities

The optical absorption edge has been measured as a function of carrier concentration for thin films of zinc oxide prepared by organometallic chemical vapour deposition and reactive R.F. magnetron sputtering. Large shifts of the absorption edge have been observed which are only a function of the carrier concentration. Below n = 3 × 10¹⁹ cm^-3 the shifts are well described by the Burstein-Moss model. For carrier concentrations between 3–5 ×10¹⁹cm^-3, the shift decreases very rapidly, finally increasing again with further increases in the carrier density. These effects are consistent with a merging of the donor band with the conduction band following a semiconductor-metal transition.     

Anregung metastabiler Zustände von Barium und Thallium durch Atomstöße im Stoßwellenrohr

It is shown that relaxation times for the excitation of metastable levels of Ba and Tl by collisons of the ground state atoms with carrier gases Ne and Ar can be measured with good accuracy behind reflected shock waves (2700≦T≦3300 °K) by means of two-channel atomic line absorption spectroscopy. Quenching cross-sections, which thus can be derived, cover in principle the range 10^?14 cm²<Q<10^?21 cm². In collisions with Ar one finds for the deactivation of Ba(¹ D ₂)Q=1.2 · 10^?19cm², of Ba(³ D ₁)Q=0.95 · 10^?19 cm² and of Tl(² P _3/2)Q<5 · 10^?21 cm² without noticeable temperature dependence. From this follows a) (on the basis of the Landau-Zener formula) that the pseudo-crossing of the potential energy curves of Ba-Ar takes place within 0.25 eV of the Ba(D) levels and b) that spin-orbit coupling is not rate controlling in the Ba(³ D ₁ →¹ S ₀) transition. The ratio of cross-sections for quenching of Ba(¹ D ₂) by Ar and Ne is about 3, suggesting that the polarizabilities of the noble gas collision partners play a major rôle in the transition probabilities. The mean self-quenching cross-sectionQ=5 · 10^?16 cm² of Tl(² P _3/2) at 3000 °K is about the same as the one reported for 1000 °K and it exceeds the self-quenching cross-section of metastable Ba by at least one order of magnitude.     

Effect of deposition pressure on structural, optical and electrical properties of zinc selenide thin films

ZnSe thin films have been prepared by inert gas condensation method at different gas pressures. The influence of deposition pressure, on structural, optical and electrical properties of polycrystalline ZnSe films have been investigated using X-ray diffraction (XRD), optical transmission and conductivity measurements. The X-ray diffraction study reveals the sphalerite cubic structure of the ZnSe films oriented along the (1 1 1) direction. The structural parameters such as particle size [6.65-22.24 nm], strain [4.01-46.6×10⁻³ lin⁻² m⁻⁴] and dislocation density [4.762-18.57×10¹⁵ lin m⁻²] have been evaluated. Optical transmittance measurements indicate the existence of direct allowed optical transition with a corresponding energy gap in the range 2.60-3.00 eV. The dark conductivity (σ_d) and photoconductivity (σ_ph) measurements, in the temperature range 253-358 K, indicate that the conduction in these materials is through an activated process having two activation energies. σ_d and σ_ph values decrease with the decrease in the crystallite size. The values of carrier life time have been calculated and are found to decrease with the reduction in the particle size. The conduction mechanism in present samples has been explained, and the density of surface states [9.84-21.4×10¹³ cm⁻²] and impurity concentration [4.66-31.80×10¹⁹ cm⁻³] have also been calculated.     

Trap-free lifetime in hopping systems: Neutral traps in PVK

The concentration of deep hole traps in layers of PVK is found to be ≈-10¹⁵cm^?3. The traps are believed to be neutral. An expression of general validity in hopping transport is derived for the free carrier lifetime before capture by neutral traps. In PVK the lifetime depends on field, but the Schubweg ≈-10^?4/T cm²V^?1, does not.     

Untersuchung von Raumladungsschichten an Zinkoxid-Oberflächen mit Hilfe der Elektroreflexion

Using the electroreflectance method space charge layers on crystals of different conductivities have been identified. The space charge layers were formed by adsorption of oxygen or atomic hydrogen. The limit of sensitivity required the irradiation with 5×10¹³ photons/cm²×sec of band gap energy. After exposure to atomic hydrogen all samples showed accumulation layers. With a partial pressure of oxygen above 350 mm Hg crystals of high conductivity (σ=47 ohm^?1 cm^?1) exhibit depletion layers, which change into accumulation layers, if the partial pressure is reduced below the limit. Crystals of a lower conductivity (σ=10^?3–10^?1 ohm^?1 cm^?1) show accumulation layers up to the highest applied oxygen pressure of 760 mm Hg. The phenomena are attributed to a dynamical equilibrium between adsorption and photo-desorption of oxygen. This equilibrium depends on oxygen pressure and free carrier concentration. By comparing a calculated curve with the experimental results the value of 3.31 ev is obtained for the energy gap, light polarized perpendicular to thec-acis.     

Shubnikov-de Haas effects in Bi2Se3 with high carrier concentrations

Shubnikov-de Haas frequencies were measured in highly degenerate n-type Bi₂Se₃ having a higher carrier density (～9 × 10²⁵m^-3) than previously reported. The Fermi surface was found to be elongated along the trigonal axis, fitting a spheroidal model with an axial ratio of 5.0 for angles up to θ = 45°. Comparison of the number of carriers obtained from Hall measurements with that obtained from the Shubnikov-de Haas measurement supports the contention that the lowest conduction band minimum is a single surface located in the center of the Brillouin zone. The higher effective mass (0.25 m₀) found for these carrier concentrations indicates that the band is non-parabolic.     

Abhängigkeit der effektiven Masse von der Ladungsträgerkonzentration im Bi2Se3

High quality Bi₂Se₃ crystals with 50 to 65 At% Se have been produced. As a consequence of a Se-doping, the carrier density varies between 3 · 10¹⁹ to 8 · 10¹⁷ cm^?3. Based on optical reflection and transmission measurements in the near infrared the dispersion of the refractive indexn(λ) has been calculated. The plasma resonance frequencyΝ _Pl lies within the energy region from 0.05 to about 0.1 eV. Fromn(λ) andΝ _Pl the effective mass of the electrons in Bi₂Se₃ has been evaluated. Near the band edge a value ofm _⊥c ^*+0.02m ₀ has been found. It depends on the orientation of the crystals and on the carrier concentration. The results of the electrical and optical investigations give reason to assume an isotropic mean free time of the electrons. The “six-valley-model” ofHashimoto for the energy-surfaces in Bi₂Se₃, is confirmed.     

Microwave excitation of large volumes of plasma at electron cyclotron resonance in multipolar confinement

Very large volume (>2 m³) homogeneous maxwellian plasmas in the 10⁹?10¹⁰cm^?3 density range have been easily obtained by using a microwave electron cyclotron resonance source operating at 2.45 GHz. The magnetic multiple device has proved its efficiency in confining plasmas containing no primary electrons.     

The observation of high concentrations of arsenic anti-site defects in electron irradiated n-type GaAs by X-band EPR

N-type GaAs doped with sulphur (2.8 × 10¹⁸ cm^-3) has been subjected to 2 MeV electron irradiation in stages at room temperature and examined by the EPR technique. When the free carrier absorption is first eliminated no EPR signal is detected. After further irradiation, the spectrum of the As anti-site defect appears, grows and subsequently saturates at a concentration of about 10¹⁸ cm^-3. The saturation concentration is about one third of [n] in most samples. The defects are stable on annealing to 500°C but are not observed in various irradiated p-type samples. It is suggested that grown-in defects such as [V_Ga-As_Ga-V_Ga] capture Ga interstitials during the irradiation and are thereby converted to the simpler anti-site defect.     

Transmutation doping of GaAs by thermal neutrons

The electrical properties of GaAs have been modified by transmutation of about 1 × 10¹⁸ As atoms per cm³ to Se and 0.7 × 10¹⁸ Ga atoms per cm³ to Ge in a flux of thermal neutrons, followed by annealing at temperatures from 625 to 900°C. Enhancement of carrier concentration was not observed in n⁺ samples, although p and n^? material showed changes in carrier concentration of the expected magnitude.     

Features of the radioactive decay of Mössbauer isotopes in the presence of an intrinsic gamma-radiation field

A limit for the concentration of radioactive nuclei (3 × 10¹⁴ 1/cm³) of the Mössbauer emitters ^119m Sn and ^125m Te below which the earlier demonstrated effect of the collective nuclear decay vanishes is experimentally found in the framework of a study aimed at the control of the decay of nuclear levels. A general theoretical concept of the phenomenon is presented. Based on this concept, the parameters of the nonexponential decay are numerically estimated. The notion of the width of the Mössbauer γ photon is introduced.     

Electrical properties of n-type vapor-grown gallium nitride

Hall measurements are reported for undoped and Zn-doped vapor-grown single crystal GaN on (0001) Al₂O₃ layers with 298 K carrier concentrations (n-type) between 1·4×10¹⁷cm^?3 and 9×10¹⁹ cm^?3. Then n～10¹⁷ cm^?3 crystals (undoped) have mobilities up to μ～440 cm²/V sec at 298 K. Their conduction behavior can be described by a two-donor model between 150 and 1225 K and by impurity band transport below 150 K. Crystals with n≥8×10¹⁸ cm^?3 show metallic conduction with no appreciable variation in n or μ between 10 and 298 K.Results of mass spectrographic analyses indicate that the total level of impurities detected is too low to account for the observed electron concentration at the n～10¹⁹ cm^?3 level, and suggest the presence of a high concentration of native donors in these crystals. No significant reduction in carrier concentration was achieved with Zn doping up to concentrations of ～10²⁰ cm^?3 under the growth conditions of the present work, and no evidence was found to indicate that high conductivity p-type behavior may be achieved in GaN. The influence of factors such as growth rate, crystalline perfection and vapor phase composition during growth on the properties of the layers is described.     

Absolute intensities and pressure broadening coefficients measured at different temperatures for the 201II ← 000 band of 12C16O2 at 4978cm-1

Absolute line intensities and self-broadening coefficients have been measured at 197° and 294°K for the 201_II ← 000 band of ¹²C¹⁶O₂ at about 4978cm^-1. The vibration-rotation factor (F_VR), the purely vibrational transition moment (∣R(O)∣), and the integrated band intensity (S_band) are deduced from the measurements. The results are: F_VR(m)=1+(0.24±0.08)x10^-4m+(0.55+0.21)x10^-4m², ∣R(O)∣= (4.340±0.008x10^-3 debye, S_band=96372±190cm^-1km^-1atm^-1_STP. The results for self-broadening coefficients, as well as for individual vibration-rotation lines, are presented in the text.