ABS1RACT / I;· I.Strong negative electron affinity effects have been observed on the surface of as-grown chemical vapor deposited diamond using Secondary Electron Emission. The test samples were randomly oriented and the surface was tenninated with hydrogen. The effect appears as an intensive peak in the low energy part of the spectrum of the electron energy distribution and may be described in the model of effective negative electron affinity.One of the remarkable features of diamond ~s the negative electron affinity (NEA) that may be observed on its surface under specific conditions. llO For NEA the vacuwn energy level lies below the conduction band minimum which allows electrons to escape easily from the surface.11 Semiconductors with NEA are widely used as photo-and cold-cathode emitters.NEA from diamond has been shown to correspond with the presence of hydrogen bounded to the surface.
Electron emission observations from asgrown and vacuumcoated chemical vapor deposited diamondStable secondary electron emission from chemical vapor deposited diamond films coated with alkalihalides
PACS 71.55. Eq, 75.50.Pp This article describes progress towards producing prototype magnetoelectronic structures based on III -N semiconductor materials. We focus on the materials properties connected with the key physical phenomena underlying potential spintronic devices: producing, injecting, transporting, manipulating and detecting spin-polarized electron populations. Our experiments have shown that the maximum magnetic moment is realized for a composition of Ga 0.97 Cr 0.03 N and a substrate growth temperature of ~1050 K. Ion channeling experiments show that ~90% of Cr sits substitutionally on the cation site. The highest measured magnetization was 1.8µ B /Cr atom (~60% of the expected moment from band theory for ideal material) with the Curie temperature over ~900 K. This strongly suggests a link between the Cr Ga impurity band and ferromagnetism and suggests that a double-exchange-like mechanism is responsible for the ferromagnetic ordering. The transport properties of spin-polarized charge carriers were modeled theoretically taking into account both the Elliott -Yafet and the D'yakonov -Perel' scattering mechanisms. We include the spinorbit interaction in the unperturbed Hamiltonian and treat scattering by ionized impurities and phonons as a perturbation. Our numerical calculations predict two orders of magnitude longer electron spin relaxation times and an order of magnitude shorter hole spin relaxation times in GaN than in GaAs. First-principles electronic structure calculations predict that efficient spin injection can be achieved using a ferromagnetic GaN : Cr electrode in conjunction with an AlN tunnel barrier. In this structure, the electrode is found to be half-metallic up to the interface and is thus a candidate for high-efficiency magnetoelectronic devices.
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