J. O. Dimmock

Hall coefficient factor for polar mode scattering in n-type GaAs

Abstract The temperature and magnetic field dependence of the Hall coefficient factor for polar mode scattering in n -type GaAs is examined in the temperature range from 300 to 77°K. The experimental results are in qualitative agreement with the theory of Lewis and Sondheimer. In practice, although the variation of r H with temperature is small, it can lead to a higher calculated carrier concentration at 77 than at 300°K and mask real changes in the actual carrier concentration.

Ionized Impurity Density in n‐Type GaAs

Total ionized impurity densities (ND+NA) from 7×1013 to 3×1017 cm−3 are determined for epitaxial samples of n‐type GaAs by analyzing mobility and carrier concentration data as a function of temperature with the Brooks‐Herring formula for ionized impurity scattering. This procedure results in the determination of a temperature range within which the effects of other scattering mechanisms are minimal and gives values of ND and NA which are in good agreement with impurity densities obtained from analyses of the temperature variation of the Hall constant. These results are then used to determine empirical curves relating the impurity density to the 77°K Hall mobility. With these data a good estimate of the total ionized impurity concentration in a sample can be determined from Hall constant and resistivity measurements at 77°K.

Identification of exciton-neutral donor complexes in the photoluminescence of high purity GaAs

Abstract Several near band edge photoluminescence transitions at 4.2°K in high purity GaAs are shown to be associated with excitons bound to centers in the vacinity of a neutral donor. Using a magnetic field, the presence of two-electron transitions (recombination involving terminal excited states) is also demonstrated.

Multiplet Structure in the Reflectance Spectra of Europium Chalcogenides

The ferromagnetic semiconducting europium chlacogenides exhibit two strong reflectance peaks arising from 4f–5d transitions of the Eu+ + ion which are split by a strong crystal field. The lower peak corresponds to transitions from the 4f7(8S7/2) ground state to the 4f6(7FJ)5d(T2g) configuration, whereas the higher energy peak corresponds to transitions to the 4f6(7FJ)5d(Eg) configuration. The structure and polarizations of the peaks in a magnetic field are analyzed in terms of the transition probabilities for right and left circularly polarized radiation taking into account (i) the multiplet structure of the 4f6(7FJ) configuration, (ii) the spin‐orbit splitting of the 5d level, (iii) a phenomenological exchange field which acts on the 5d electron spin in the ordered phase, and (iv) the Zeeman splitting due to the domain orienting magnetic field.

Electronic Band Structure, Fermi Surface, and Magnetic Properties of Palladium Metal

The electronic energy bands of Pd metal have been determined using the nonrelativistic A.P.W. method. The Fermi surface, which consists of two hole surfaces and a compensating electron surface, agrees very well with the de Haas‐van Alphen data of Vuillemin and Priestly. The electron surface is centered at Γ and contains approximately 0.3 electrons per Pd atom. One hole surface consists of a small pocket centered at X. The other hole surface is open along the [100] directions in agreement with galvanomagnetic measurements. The Fermi energy lies slightly above a maximum in the calculated density of states N (E) as expected from studies of dilute alloys. Using the computed N (EF) we obtain an electronic contribution to the specific heat which is only about half the observed value, indicating an electron‐phonon enhancement typical for d‐band metals. The computed paramagnetic susceptibility χ(T) is much smaller than the experimental value, emphasizing the importance of exchange in markedly enhancing χ(T), part...

Effects of Light on the Charge State of InSb–MOS Devices

We have made a detailed study of the effects of photon radiation in the energy range between 0.5 and 5.0 eV on InSb metal‐oxide‐semiconductor (MOS) devices. Measurements of the photocurrent through the MOS structures made at several temperatures showed that even at 300°K a photovoltage is developed for photon energies greater than about 1.3 eV. For photon energies above 3 eV the indium‐antimony oxide layer became photoconductive. The charging and discharging characteristics of the InSb‐oxide interface were investigated by measuring the response of the InSb–MOS structure to modulated long wavelength (3.9 μ) radiation. This radiation acts as a probe for examining the band bending in the InSb at the InSb‐oxide interface, which in turn depends on the amount of charge trapped in the oxide or at the interface. When the MOS structure is irradiated with 1.3‐ to 4‐eV photons, the oxide and/or the interface becomes negatively charged. At photon energies above 3.5 eV there is a competition between the mechanism which induces negative charge in the oxide and/or interface region and the mechanism which releases this charge. This competition can be influenced by applied bias, and by properly biasing the device and irradiating with photons having energies greater than 4 eV the charges can be released.

BAND STRUCTURE OF GADOLINIUM METAL

The heavy rare‐earth metals have been viewed traditionally as consisting of trivalent atomic cores plus three conduction electrons per atom. Previous theoretical work1‐3 has attempted to explain the available experimental data by assuming that the three conduction electrons occupy essentially free electron‐like bands. We have obtained approximate nonrelativistic energy bands for Gd metal using the augmented plane wave method.4 The calculated bands differ markedly from the free electron model due to the fact that the bands originating from atomic 5d and 6s states overlap and are strongly mixed. The bands, in fact, show a close resemblance to those of the transition metals. This resemblance also appears in the calculated density‐of‐states curve. The density of states at the Fermi energy is large, about three times that of the free electron model. This density of states is about one half that given for Sc, Y, and La by specific heat measurements.A detailed version of this paper will be submitted to the Physi...

Magnetic Ordering Effects in the Reflectance of EuO, EuS, EuSe, and EuTe

In the reflectance spectra of the ferromagnetic semiconductors EuO,1 EuS,2,3 and EuSe2,3 and antiferromagnetic EuTe,4 there are two prominent peaks, E1 and E2, which involve 4f7→4f65d(t2g) and 4f7→4f65d(eg) transitions respectively. Measurements of E1 and E2 in the ferromagnetic compounds as a function of temperature and polarization in a magnetic field show changes with magnetic ordering which indicate exchange splittings of the 5d states of about 0.25 eV. In antiferromagnetic EuTe above 40 kOe applied field, the spectrum becomes characteristic of the ferromagnetic chalcogenides suggesting a transition to parallel spin alignment which saturates at H∼80 kOe. The observed effects also indicate confirmation of the prediction that there are superlattice splittings in the band structure of an antiferromagnetic crystals.