Effect of Impurities and Structural Defects on the Transport Properties of n-Type GaAs Crystals

The carrier mobility and concentration in n-type GaAs single crystals, undoped, doped during growth (Te, Sn, and Ge), and neutron-transmutation doped (NTD) with Se and Ge, were measured as a function of temperature. Although the donor concentration was the same in all of the doped crystals, the carrier mobility and concentration in the GaAs crystals were found to be lower than those in the GaAs, GaA, and NTD GaAs crystals by about a factor of three and one order of magnitude, respectively. These results are interpreted in terms of the compensation ratio and predominant scattering processes in the crystals. The large compensation ratio in the GaAs crystals is due to the high acceptor concentration. The low carrier mobility in GaAs is associated with the strong scattering of charge carriers by ionized defects, because of their high density, and also, in contrast to the undoped, GaAs, and GaAs, and NTD GaAs crystals, with additional scattering by nonuniformly distributed structural defects. In calculations of the compensation ratio and analysis of the scattering mechanisms, the Brooks–Herring or Cornell–Weisskopf approximation was used, depending on the compensation ratio in the material.     

Impurities in single crystal indium phosphide

The impurity concentrations in present low carrier concentration indium phosphide single crystals (N _D-N _A=2×10¹⁵ to 5×10¹⁵cm^–3) grown by the Czochralski technique have been measured by spark-source mass spectrometry and radio-gamma activation analysis and compared with both the polycrystalline source material and the excess indium produced during compounding and growth. The predominant impurities are shown to be carbon, oxygen and silicon but the segregation of lesser impurities into the excess indium has allowed some nineteen other elements which are likely to be present in indium phosphide to be identified. No consistent correlation is evident between the measured concentration of specific impurities and the ionized donor (N _D) and acceptor (N _A) impurity levels as determined from the free-electron concentration (N _D-N _A) and Hall mobility at 77 K using the Brooks-Herring theory.     

Transport property of Sn-doped In0.5Ga0.5P layers grown by liquid phase epitaxy

The temperature-dependent Hall mobility and carrier concentration of Sn-doped In_0.5Ga_0.5P epilayers grown on (100) semi-insulating GaAs substrates by the liquid phase epitaxy technique have been investigated in the range of 77–300 K. It was found that the Sn-doped In_0.5Ga_0.5P epilayer was heavily compensated with the compensation ratio of 0.4–0.6. It was also found that the Sn shallow donor has an ionization energy 17–12 meV with increasing carrier concentrations through Hall measurements. The model taking into account ionized impurity, alloy and space-charge scattering mechanisms is considered in order to properly portray the observed features of the electron mobility results. The theoretical prediction is in good agreement with the observed results. The electron mobility was limited by ionized scattering up to 120 K and was also limited by alloy, space-charge scattering up to 300 K.     

Effect of plastic bending on electron transport in highly compensatedn-type InSb in the temperature range 1.2–300 K

Measurements of Hall coefficient, dc conductivity, and magnetoresistance have been made on a highly compensatedn-type InSb sample from liquid helium to room temperature, and the effect of plastic bending of this sample on these transport properties has been studied. The measurements show that the extent of the impurity-band conduction depends considerably on the compensation ratio and the effective concentration of the carriers. The effective carrier concentration and compensation ratio are reduced due to deformation, resulting in a slight reduction of the extent of the impurity-band conduction. Two activation energies have been identified in the impurity-band conduction region for both states of the sample. The behavior of the magnetoresistance for the undeformed and deformed states of the sample is explained on the basis of the two activation energies, the effective carrier concentration, and the compensation ratio.     

Electrical transport parameters of heavily-doped zinc oxide and zinc magnesium oxide single and multilayer films heteroepitaxially grown on oxide single crystals

Heavily doped epitaxial ZnO:Al and Zn_1−xMg_xO:Al films were grown by radio frequency magnetron sputtering onto single crystalline substrates (sapphire, MgO, silicon) and characterized by structural and electrical measurements. It is the aim of this investigation to better understand the carrier transport and the doping mechanisms in heavily doped transparent conducting oxide (TCO) films. It was found that the crystallographic film quality determines only partly the mobilities and the carrier concentrations: ZnO:Al films on a-plane (110) sapphire and on MgO (100) exhibit the highest mobilities. The oxygen partial pressure during the deposition from ceramic targets is more important influencing especially the carrier concentration N of the films. Though the films grew epitaxially grain boundaries are still existent, which reduce the mobility due to electrical grain boundary barriers for N < 3 · 10²⁰ cm^− 3. From annealing experiments the role of point defects and dislocations for the carrier transport could be estimated. For carrier concentrations above 3 · 10²⁰ cm^− 3 ionized impurity scattering limits the mobility, which is in agreement with our earlier review [K. Ellmer, J. Phys. D: Appl. Phys. 34 (2001) 3097].     

Codoping of Ge with Al and Sb

Ge single crystals were doped with Al or Sb to various concentrations and codoped with Al and Sb in the ratios 3:1, 1:1, and 1 : 3. Using Hall effect measurements, the electron and hole concentrations in the doped crystals were determined. A relationship between the dopant-solubility limits and the maximum carrier concentration was found. The data obtained were shown to be consistent with the processes Al ↔ Al^- + h and Sb ↔ Sb⁺ + e in Ge doped with Al or Sb up to the solubility limit. In the material codoped with Al and Sb in the atomic ratio 3 : 1, the hole concentration is equal to the difference in the Al and Sb concentrations. At an Al : Sb ratio of 1 : 3, the electron concentration in Ge(Al, Sb) is higher than that in Ge<Sb> because of the increase in Sb solubility in the presence of Al. The crystals doped with equal concentrations of Al and Sb aren-type. The results are interpreted in terms of donor-acceptor interaction and compensation effect.     

Temperature-dependent Hall analysis of carbon-doped GaAs

The temperature dependence of the electrical properties, such as hole concentration, Hall mobility and resistivity of carbon-doped GaAs epilayers over a wide range of doping levels has been investigated. The carbon-doped GaAs epilayers have been grown by low pressure metalorganic chemical vapor deposition. The electrical properties have been obtained by Hall measurements. Experimental data on the carrier mobility, Hall effect, and resistivity over a wide temperature range have been analyzed and possible scattering mechanisms have been explained. Our experimental data show that the ionized impurity scattering tend to be dominant at temperatures below 100 K, while the lattice scattering as well as the ionized impurity scattering plays an important role at temperatures above 100 K. The dependence of the electrical on the doping levels has also been studied. In the case of heavily C-doped GaAs, the mobility curves are nearly flat at temperatures below 100 K and the mobility decreases as temperature increases above 100 K. The reason is that the degenerate conduction occurs at high doping level. The degenerate conduction begins at the hole concentration of about 2 × 10¹⁸ cm⁻³ at 77 K and at room temperature.     

Constriction and Corner Permeances for Finite Domains

The known formulas for two-dimensional "corner" and "constriction" permeances, which were derived by using conformal mappings for infinite domains, can be applied only for large enough domains. In this paper, we analytically solve the problem for finite domains and propose new exact and approximate formulas. We show that, for finite domains, the corner and constriction permeances can be much smaller than for infinite dimensions, and we determine the limits of applicability of simple exact formulas. This offers the possibility to make more accurate analytical calculations of magnetic devices and better evaluate acting magnetic forces     

Theoretical Electron Mobility Analysis in Thin-Body FETs: Dependence on Substrate Orientation and Biaxial Strain

Results of recent mobility measurements in ultrathin-body FETs are analyzed theoretically for different substrate orientations. A Monte Carlo method incorporating the degenerate statistics exactly is used for calculations of the mobility. Due to volume inversion, the mobility in double-gate ultrathin-body (110) FETs is enhanced in comparison with the mobility of single-gate structures, in the whole range carrier concentrations. In contrast, the mobility in a double-gate (100) 3 nm thick structure plotted as a function of the carrier concentration per channel sinks below the single-gate mobility value for high effective fields. It is shown that degeneracy effects play a crucial role in mobility degradation for (100) double-gate FETs, as they lead to the opening of additional intersubband scattering channels. Biaxial strain has little influence on the mobility of ultrathin-body FETs. Simulation results are in good agreement with recent mobility measurements     

Influence of ion-induced interfacial chemical reactivity on contact resistance

Contact resistance measurements of chromium contacts deposited by partially ionized beam deposition on transparent conducting indium tin oxide (ITO) were performed. These provide a direct experimental evidence of the influence of interfacial chemical interaction on the contact resistance. The interfacial reactivity is controlled by modifying the energy and flux of ionized chromium atoms deposited on ITO employing a specially designed partially ionized deposition system with very high ionization efficiency. The true contact resistivityρ _c is obtained by iteratively correcting the experimentally measured values for the finite sheet resistance of the ITO layer.ρ _c decreases linearly with the energy of the ionized chromium. Auger sputter profiling shows no structural modifications at the interface due to a change in the energy of the chromium atoms, confirming that the observed change in the contact resistivity is directly related to interfacial chemical bonding of the atoms with the oxygen atoms in the ITO leading to a local increase of carrier concentration and lower interfacial resistance.     

Anisotropic Quantum Transport through a Single Spin Channel in the Magnetic Semiconductor EuTiO3

Magnetic semiconductors are a vital component in the understanding of quantum transport phenomena. To explore such delicate, yet fundamentally important, effects, it is crucial to maintain a high carrier mobility in the presence of magnetic moments. In practice, however, magnetization often diminishes the carrier mobility. Here, it is shown that EuTiO₃ is a rare example of a magnetic semiconductor that can be desirably grown using the molecular beam epitaxy to possess a high carrier mobility exceeding 3000 cm² V⁻¹ s⁻¹ at 2 K, while intrinsically hosting a large magnetization value, 7 μ_B per formula unit. This is demonstrated by measuring the Shubnikov–de Haas (SdH) oscillations in the ferromagnetic state of EuTiO₃ films with various carrier densities. Using first-principles calculations, it is shown that the observed SdH oscillations originate genuinely from Ti 3d-t_2g states which are fully spin-polarized due to their energetical proximity to the in-gap Eu 4f bands. Such an exchange coupling is further shown to have a profound effect on the effective mass and fermiology of the Ti 3d-t_2g electrons, manifested by a directional anisotropy in the SdH oscillations. These findings suggest that EuTiO₃ film is an ideal magnetic semiconductor, offering a fertile field to explore quantum phenomena suitable for spintronic applications.     

Carrier properties of B atomic-layer-doped Si films grown by ECR Ar plasma-enhanced CVD without substrate heating

Abstract

The atomic-layer (AL) doping technique in epitaxy has attracted attention as a low-resistive ultrathin semiconductor film as well as a two-dimensional (2-D) carrier transport system. In this paper, we report carrier properties for B AL-doped Si films with suppressed thermal diffusion. B AL-doped Si films were formed on Si(100) by B AL formation followed by Si cap layer deposition in low-energy Ar plasma-enhanced chemical-vapor deposition without substrate heating. After fabrication of Hall-effect devices with the B AL-doped Si films on unstrained and 0.8%-tensile-strained Si(100)-on-insulator substrates (maximum process temperature 350°C), carrier properties were electrically measured at room temperature. Typically for the initial B amount of 2?×?10¹⁴ cm^?2 and 7?×?10¹⁴ cm^?2, B concentration depth profiles showed a clear decay slope as steep as 1.3 nm/decade. Dominant carrier was a hole and the maximum sheet carrier densities as high as 4?×?10¹³ cm^?2 and 2?×?10¹³ cm^?2 (electrical activity ratio of about 7% and 3.5%) were measured respectively for the unstrained and 0.8%-tensile-strained Si with Hall mobility around 10–13 cm² V^?1 s^?1. Moreover, mobility degradation was not observed even when sheet carrier density was increased by heat treatment at 500–700 °C. There is a possibility that the local carrier (ionized B atom) concentration around the B AL in Si reaches around 10²¹ cm^?3 and 2-D impurity-band formation with strong Coulomb interaction is expected. The behavior of carrier properties for heat treatment at 500–700 °C implies that thermal diffusion causes broadening of the B AL in Si and decrease of local B concentration.     

Thickness dependence of the electrical and structural properties of In2O3:Sn films

Films of In₂O₃:Sn (10 wt.% Sn) of various thicknesses were deposited onto heated glass substrates (450 °C) by spray pyrolysis. The electrical and structural properties were studied for different thicknesses, and the scattering mechanism is discussed. Hall measurements showed that thicker films (about 500 mm) have relatively higher Hall mobilities compared with those of thinner films. The electrical resistivity of a film about 600 nm thick was found to be about 2.66 x 10^-6 ωm at room temperature, and the average transmission in the visible range was found to be 86%. The high carrier concentration (6.49 × 10²⁶ m^-3) and the negligible dependence of the electrical properties on temperature show that the films are degenerate. The relationship between carrier concentration and Hall mobility revealed that the ionized impurity scattering centres were the dominant cause of scattering.     

Effects of quantum confinement on the doping limit of semiconductor nanowires

We have calculated the effects of quantum confinement on maximum achievable free carrier concentrations in semiconductor nanowires. Our calculations are based on the amphoteric defect model, which describes the thermodynamic doping limit in semiconductors in terms of the compensation of external dopants by native defects. We find that the generation of amphoteric native defects strongly limits maximum achievable carrier concentrations for nanowires with small widths where quantum confinement is appreciable. The magnitude of this effect in a given material is found to be determined by two material properties: the effective mass of the free carriers, and the position of the conduction (n-type) or valence band (p-type) edge on the absolute energy scale. These results offer a simple, predictive guideline for designing nanostructure devices and contacts where high doping levels are needed.     

Heat exchange in laminar flow through planar and quasiplanar channels of variable cross section

Formulas are derived for both the local and averaged over the surface Nusselt number. Experimental results are presented and the limits of applicability of the calculated formulas are indicated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 2, pp. 208–216, August, 1976.     

Reconstruction of the temperature field in a solid from a limited number of measurements

We have obtained extrapolation formulas for calculating the temperatures, temperature gradients, and heat fluxes in a solid heated by a varying thermal flux from the results of temperature measurements at two points. The applicability limits and errors of the proposed formulas have been investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 3, pp. 553–558, September, 1969.     

Liquid phase epitaxy growth of GaAs: Si by temperature difference method

The LPE growth of a horizontal sliding system by temperature difference method is used to grow single and multiple layers of GaAs compounds from dilute solution. The weight ratio of Si to Ga solvent is 10⁻⁴ wt%. The growth rate, surface morphology, carrier concentration and Hall mobility are studied. Relationship between the above properties and the growth temperature and temperature different (ΔT) is also discussed. In general, the present results appear quite consistent with the diffusion limited model. The growth rate can be precisely controlled. The stability of the solid-liquid interface can be obtained in the epilayer growth at a constant temperature of the system which can avoid the effect of constitutional supercooling. Under proper control, a perfect epilayer and multiple smooth layers can be obtained.     

透明导电膜ZnO:Al(ZAO)的组织结构与特性

ZnO:Al(ZAO)是一种简单并半导体氧化物薄膜材料，具有高的载流子浓度和光学禁带宽度，因而具有优异的电学和光学性能，极具应用价值，对于其能级高度简并的ZAO半导体薄膜材料，在较低的温度下，离化杂质散射占主导地位，在较高的温度下，晶格振动散射将成为主要的散射机制；晶界散射仅当晶粒尺寸较小（与电子的平均自由程相当）时才起作用，本文分析了ZAO薄膜的制备方法，晶体结构特性，电子和光学性能以及载流子的散射机制。     

Thermopower Modulation Clarification of the Operating Mechanism in Wide Bandgap BaSnO3–SrSnO3 Solid‐Solution Based Thin Film Transistors

The transparent oxide semiconductor (TOS) with large bandgap (E_g ≈ 4 eV) based thin‐film transistors (TFTs) showing both high carrier mobility and UV–visible transparency has attracted increasing attention as a promising component for next generation optoelectronics. Among TOSs, BaSnO₃–SrSnO₃ solid‐solutions (E_g = 3.5–4.2 eV) are good candidates because the single crystal shows very high mobility. However, the TFT performance has not been optimized due to the lack of fundamental knowledge especially the effective thickness (t_eff) and the carrier effective mass (m*). Here, it is demonstrated that the electric field thermopower (S) modulation method addresses this problem by combining with the standard volume carrier concentration (n_3D) dependence of S measurements. By comparing the electric field accumulated sheet carrier concentration (n_2D) and n_3D at same S, it is clarified that the t_eff (?n_2D/n_3D) of the conducting channel becomes thicker with increasing Sr concentration, whereas the m* becomes lighter. The former would be due to the increase of E_g and latter would be due to the enhancement of overlap population of neighboring Sn 5s orbitals. The present analyses technique is useful to experimentally clarify the t_eff and m*, and essentially important to realize advanced TOS‐based TFTs showing both high optical transparency and high mobility.