Donor Activation Energy Research Articles

Electrical properties of pure CdS

Electrical measurements on single-crystal CdS are used to evaluate the various material parameters of vapor-grown material. Hall measurement data is used to obtain a computer fit to a single donor level partially compensated model for the purpose of determining the donor density, acceptor density, and activation energy. Hall mobility data is fitted to a scattering model which includes lattice, neutral impurity, and ionized impurity scattering. The donor level in the low density doping limit is found to be approximately 32 meV below the conduction band. Over a temperature range of 100 k–300 K lattice scattering is predominate and the mobility variations have little impact on the electrical properties; the major variations are due to ionized donor variations and the band-gap variations with donor densities. At low temperatures, impurity densities and the type of impurity scattering have a significant impact on the mobility. Pure CdS displays a very high mobility, i.e., μ>10 000 cm2/V sec at low temperatures in the absence of ionized vacancy scattering. The absence of ionized vacancy scattering at low temperatures is found to be the result of vacancy pairing which results in a neutral scattering center. Low mobilities at low temperatures are found to result from a relatively high density of netural impurity scattering centers.

Pressure dependence of oxygen-related defect levels in silicon

The activation energies of thermal donors and of the A center in silicon, the oxygen vacancy complex, are measured as a function of hydrostatic pressure by Hall effect and by deep level transient spectroscopy. The A center is classified as a deep level because the strong pressure dependence of its activation energy indicates a short-range potential. In contrast, thermal donors are true shallow levels associated with a long-range coulomb potential because of the low pressure dependence of their activation energy. Based on these results, an atomic model for thermal donors is suggested, consistent with results of investigations concerning pressure dependence of energy levels, formation kinetics, IR absorption, electrical activity, and electron paramagnetic resonance.

The effect of aluminum composition on silicon donor behavior in AlxGa1−xAs

The behavior of Si in AlxGa1−xAs grown by molecular beam epitaxy (MBE) has been studied. Temperature-dependent Hall measurements were made to investigate the doping behavior of Si in MBE grown AlxGa1−xAs across the composition range 0.2<x<0.8. Aluminum composition was determined using photoluminescence. Doped AlxGa1−xAs layers were separated from underlying semi-insulating GaAs substrates by an unintentionally doped AlxGa1−xAs spacer layer and a 0.2 μm GaAs buffer layer. Low-temperature mobility of the structures proved that no two-dimensional electron gas was formed at the GaAs/AlxGa1−xAs interface. Therefore, the data obtained are characteristic of bulk AlxGa1−xAs. Si donor activation energy increased from ∼6 meV for GaAs to ∼200 meV for x=0.33 and decreased for x>0.6. Net electron concentration and mobility were also strongly dependent on aluminum composition.

Electrical properties of CdS x Se1−x single crystals

Electrical conductivity and Hall effect were studied on vapour phase grown CdS x Se1−x single crystals in the entire range of composition in the temperature range 90–300 K. The conductivities of the as-grown crystals varied significantly. High conducting samples were obtained by annealing either in vacuum or in cadmium vapour. Hall mobilities, carrier concentration and donor activation energies were calculated. No definite variation in mobility with composition was observed. Donor activation energy showed an increasing trend with increase of CdS content.

The Activation Energy of Phosphorus Donors in Silicon‐Rich Silicon–Germanium Alloys

AbstractThe activation energy of phosphorus substituted into Si1−xGex alloys (0 ≦ x ≦ 0.27) is investigated by IR absorption. A weak shift of the activation energy with germanium content is found: E(A1) = (45.5 − 26x) meV. This can be explained by multivalley effective mass theory with a phenomenological central cell potential which does not depend on alloy composition within the investigated range. The experiments show that P atoms are distributed at random in the alloy and that their positions are uncorrelated to those of the Ge atoms.

Electrical Properties of Black Phosphorus Single Crystals

Large single crystals of black phosphorus have been grown under high pressure, and by using the crystals, the Hall measurements have been done in a range from 4.2 K to 550 K. All the undoped samples have exhibited p -type conduction, while we have succeeded in obtaining n -type crystals by doping Te impurity. The effective acceptor concentrations N A -N D of the p -type samples and those of donor in n -type samples N D -N A have been in the range of 2∼5×10 15 cm -3 and 2∼3×10 16 cm -3 , respectively. From the intrinsic range of the conductivity, the energy gap has been estimated to be 0.335 eV, The acceptor and donor activation energies have been determined to be ∼18 meV and ∼39 meV, respectively. The Hall mobility of the hole reaches its maximum of 6.5×10 4 cm 2 /V·sec around 20 K. The anisotropies of the conductivity and the mobility along the three crystal axes have been investigated.

Properties of silicon-doped AlxGa1-xAs grown by molecular beam epitaxy

The incorporation of silicon in AlxGa1-xAs grown by molecular beam epitaxy was investigated. In Al0.25Ga0.75As and Al0.35Ga0.65As doping levels were proportional to the incident silicon flux for effusion cell temperatures below 1125°C. At 1125°C the electron concentration saturated at about 2×1018 cm-3 and then decreased slightly. For cell temperatures above 1150°C silicon precipitation observable with an optical microscope took place. Silicon incorporation decreased with increasing growth temperature above 650°C with an activation energy of 2.1 eV. Electron mobilities in excess of 1000 cm2V-1 s-1 were obtained for doping levels above 1×1018 cm-3. Donor activation energies were typically between 5 and 20 meV and increased slightly as the silicon flux was increased.

Tellurium and iodine in silicon part II: Hall effect and resistivity measurements on ion implanted silicon

Abstract The fraction of substitutional Te atoms in silicon deduced from temperature dependent Hall measurements is comparable to that derived from channeling experiments. The donor activation energy of these atoms is found to be about 0.19 eV. Approximately 10% of the Te-atoms give rise to a shallow donor level at Ec -0.06 eV and is probably associated with a defect. Substitutional iodine is not electrically active in Si up to 450 K. From this a lower limit of the donor activation energy of 0.30 eV is estimated.

Si incorporation in AlxGa1−xAs grown by molecular beam epitaxy

The incorporation of Si in Al0.25Ga0.75As was studied as a function of Si cell temperature and substrate growth temperature. Within experimental error, the measured electron concentration was equal to the Si atomic concentration as determined by secondary ion mass spectroscopy. For substrate growth temperatures much above 650 °C, the Si concentration decreased with increasing substrate temperature. This is attributed to a possible decrease in the effective group V/III ratio and evaporation of Si. For Si cell temperatures above 1150 °C, stacking faults in the surface morphology indicated the initiation of Si precipitation. Electron mobilities at room temperature were between 1300 and 600 cm2/Vs, decreasing at higher doping levels. The donor activation energy was observed to increase as a function of both Si cell temperature and substrate growth temperature.

An explanation for anomalous donor activation energies in Al0.35Ga0.65As

Transport properties of Si-doped Al0.35Ga0.65 As epitaxial layers grown by molecular beam epitaxy were studied and the activation energy of the Si donors determined. Previously reported values for the Si-donor activation energy for x = 0.35 have varied considerably and values as high as 100 meV have been suggested. For x values above and below x = 0.35, the activation energies reported are much lower, and show better consistency. Anomalously high activation energies for Se (300 meV) and Te (150 meV) doped AlxGa1−x As near the direct-indirect transition have also been reported. In this letter, a possible explanation for these anomalies in previous results based on the modulation doping effect is described. Results obtained for layers grown so as to avoid modulation doping indicate the activation energy of Si in Al0.35Ga0.65 As is less than 14 meV. When modulation doping effects were not suppressed, apparent activation energies as high as 125 meV were obtained. Finally, electron mobilities in samples not displaying modulation doping effects for an electron concentration of 6.5×1017 cm−3 were approximately 1 100 cm2/Vs.

Chemical vapour deposition of tin oxide films and their electrical properties

Transparent electrically conducting SnO2 films were prepared by chemical vapour deposition technique. The films were obtained at various deposition temperature ranging from 350 to 500 degrees C by stannous chloride oxidation. The SnO2 films thus produced have a conductivity of 50-700 (ohm cm)-1, an n-type carrier concentration of 1*1019-6*1020 cm-3 and a Hall mobility of 7.8-31.2 V-1 s-1 depending on the deposition conditions. The studies on the variation of conductivity with temperature indicated two donor activation energies for the films.

Electron concentration and mobility in cds single crystals

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An introduction to principles of the solid state. Extrinsic semiconductors

Includes a previous analogy is extended to cover n- and p-type semiconductors and discussions of the concepts of donors and acceptors, donor and acceptor activation energies and the corresponding charge carrier production at various temperatures, and the effects of the presence of both donors and acceptors.

Magnetic freeze-out in n type indium antimonide

The transverse components of the conductivity tensor of a number of specimens of n type indium antimonide in a magnetic field large enough to cause appreciable freeze-out are analyzed to give the electron concentration remaining in the conduction band. For magnetic fields greater than 5kG, the two-band model used by Miyazawa and Ikoma (1967) gives the same results as is obtained by assuming the contribution to the component of the conductivity sigma xy of electrons frozen out is negligible. The donor activation energy ED deduced from these measurements is compared with the values obtained from the longitudinal component of the conductivity sigma zz.

Electrical Properties of Gallium Phosphide

Hall coefficient and conductivity of GaP crystals produced by the solution-growth method were measured at temperatures between 4.2°K and 300°K. Activation energies of donors in undoped, Si-doped and S-doped samples are almost the same indicating about 0.10 eV. In Zn-doped Gap, the level of Zn lies 0.031 eV above the valence band. Electron mobility in undoped samples and hole mobility in Zn-doped samples are 140–180 cm2/volt·sec and about 50 cm2/volt·sec respectively at room temperature. These samples exhibited impurity conduction at considerably high temperature, for example, at 50°K for undoped samples, and its characteristics are similar to those of germanium in the metallic and the transition region.

Optical Properties due to Donor Electrons in Semiconductors

The free carrier-like absorptions observed at low temperatures have been interpreted, in the previous theory, as due to excitations of donor electrons into the lowest conduction band. This theory is modified by making use of the hydrogen-like wave function for the continuous spectrum of a donor electron. According to the present theory, the maximal value of the absorption coefficient appears at the photon energy of about 2.2 times the donor activation energy. And the qualitative behavior is similar to that by the previous theory. The theory is compared with experiments for n-type GaP and Si, and gives a better agreement with experiments for GaP with respect to the wavelength dependence. The Faraday rotation due to donor electrons is calculated considering the presences of the excited donor states and the lowest conduction band. The result is found to be similar to that due to free carriers with respect to the magnitude and the wavelength dependence, for the photon energy larger than about three times the donor activation energy.

Electrical Conduction inn-Type Germanium at Low Temperatures

A thorough study has been made of the electrical conductivity (including Hall effect) of high-purity $n$-type Ge in the temperature range 4-25\ifmmode^\circ\else\textdegree\fi{}K. Both the Ohmic region and non-Ohmic or "hot electron" region were studied, the latter by both dc and high-speed pulse techniques. From measurements in the Ohmic region, accurate values for the impurity concentrations, in particular the compensating impurities, and for the donor activation energies are obtained; these must be known in order to convert the pulse data to cross sections for certain elementary processes that were investigated. As a subsidiary result, it is confirmed that for P and As donors there is a difference between the thermal and optical activation energies which is proportional to the singlet-triplet splitting of the ground state. By comparing experimental results for the electric field dependence of the drift mobility with the (hot electron) theory for acoustic phonon scattering including anisotropy, it is shown that the electrons appear to be hotter at lower temperatures than the theory would predict. One must conjecture a "forward scattering effect" that reduces the average collision rate for hot electrons moving in the heavy-mass direction, i. e., they can scatter only through small angles at low temperatures because of a death of the appropriate phonons. The conjecture is confirmed by a measurement of the mobility anisotropy parameter $K$ (=4.2 for phonon scattering), obtained from data on the magnetic field dependence of the breakdown field. The major aim of the work was to determine values for the (velocity-and temperature-dependent) cross sections for two recombination processes: the recombination of a single electron with an ionized donor (the inverse of thermal ionization) and the Auger recombination of an electron with an ionized donor (the inverse of ionization of a donor by collision). Cross sections have been determined for these processes, and for the inverse processes as well. Criticisms made of some of our early work by Ascarelli and Brown are shown to be invalid. In particular the ad hoc assumption by Ascarelli and Brown that Auger processes do not exist is what led them to false conclusions; their data, reinterpreted, give values for the Auger recombination probability in agreement with ours. Both the direct and Auger recombination cross sections are very large (\ensuremath{\sim}${10}^{\ensuremath{-}12}$ ${\mathrm{cm}}^{2}$ and \ensuremath{\sim}${10}^{\ensuremath{-}24}$ n ${\mathrm{cm}}^{2}$, respectively); they agree well, as regards absolute magnitude, and temperature and energy dependence, with the "giant trap" cascade mechanism proposed first by M. Lax. Moreover, the inverse of the giant-trap mechanism would be a mechanism for impact ionization of neutral impurities that would have a rapid dependence on lattice temperature and would have no threshold for the energy of the colliding electron. This has been observed. Lastly, the hot electron behavior for orientations of the applied electric field other than along a $〈100〉$ direction have been studied; the electrons in different valleys then have different "temperatures" and densities. It is shown that, though this is the case, no net transfer of carriers from one valley to the other occurs. A simple theoretical treatment for the breakdown field in terms of impurity content and for the variation of the breakdown field with crystallographic orientation and with magnetic field has been formulated, using as a basis Price's criterion for breakdown, which is in excellent agreement with the data.

Electrical and optical properties of natural stannic oxide crystals

A survey has been made of the electrical conductivity and optical transmission properties of a number of stannic oxide crystals cut from Bolivian cassiterite. A fundamental optical energy gap, E G ⩾ 3.54 eV with a thermal shift of −6 × 10 −4 V °K has been determined from the short wavelength cutoff. A sharp absorption at 3.07 μ has been attributed to the presence of O-H groups oriented in a plane perpendicular to the c-axis of the crystal. A simple single-level, wide bandgap analysis was applied to the conductivity and Hall data in the temperature range 100° to 500°K yielding a major donor activation energy of approximately 0.7 eV for samples containing 10 14–10 15 carriers/cm 3 at room temperature. Hall mobilities vary from 10 to 300 cm 2 V sec with effective masses and donor densities estimated near 0.8 m and 10 20 cm −3, respectively. Note is made of comparable parameter values observed by other investigators in film and powder specimens. No p-type conduction has been observed. It is concluded that stannic oxide is a broad-band semiconductor unlike the structurally similar material, rutile, which exhibits narrow 3 d-band conduction.

A Dielectric Approach to Impurity Conduction

Impurity conduction is formulated on a dielectric basis. It is assumed here that the condition for the transition from insulator to metal is provided by the dielectric catastrophe which occurs through the polarizability of the neutral particle. On the basis of the Onsager formula, the contribution to the permittivity arising from the hydrogenic donor atoms is calculated assuming all catastrophic excited states merge with the continuum. The upper temperature limit of the phase transition from N discrete levels to N - 1 discrete levels can then be estimated and in this way the donor activation energy is found to be a stepwise decreasing function of both temperature and donor concentration. The dielectric theory is next extended to include screening by the conduction electrons. With an appreciable number of carriers present the hydrogen model breaks down and there is no polar contribution to the dielectric constant. Furthermore, the donor activation energy decreases smoothly and more rapidly with increasing temperature and donor concentration than it would do had only the unscreened catastrophe been operative in producing the band model.