Room-temperature drift mobilities of 4500 square centimeters per volt second for electrons and 3800 square centimeters per volt second for holes have been measured in high-purity single-crystal diamond grown using a chemical vapor deposition process. The low-field drift mobility values were determined by using the time-of-flight technique on thick, intrinsic, freestanding diamond plates and were verified by current-voltage measurements on p-i junction diodes. The improvement of the electronic properties of single-crystal diamond and the reproducibility of those properties are encouraging for research on, and development of, high-performance diamond electronics.

Standard electronic devices encode bits of information by controlling the amount of electric charge in the circuits. Alternatively, it is possible to make devices that rely on other properties of electrons than their charge. For example, spintronic devices make use of the electron spin angular momentum as a carrier of information. A new concept is valleytronics in which information is encoded by the valley quantum number of the electron. The analogy between the valley and spin degrees of freedom also implies the possibility of valley-based quantum computing. In this Article, we demonstrate for the first time generation, transport (across macroscopic distances) and detection of valley-polarized electrons in bulk diamond with a relaxation time of 300 ns at 77 K. We anticipate that these results will form the basis for the development of integrated valleytronic devices.

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Strain states in buried lattice-mismatched quantum wires are studied by polarization analysis with high magnetic fields. Remarkably large in-plane polarization anisotropy is observed, which remains even in very high fields. These results cannot be explained by the isotropic biaxial strain picture, and theoretical calculations show that it is attributed to nonbiaxial (anisotropic triaxial) strain, the symmetry of which is broken. Circular polarization experiments show that Zeeman splitting is highly nonlinear to the field, which is also theoretically explained by the nonbiaxial nature of strain. [S0031-9007(98)05721-4] PACS numbers: 73.20.Dx, 71.70.Ej, 78.20.Ls, After the invention of a quantum-well structure, further essential steps towards advanced semiconductor architecture were achieved by the introduction of strained-layer systems and quantum wire/dot structures. The former have a drastic impact on controlling band structure and have been applied to various devices. The latter are expected to exhibit a peculiar nature of lowdimensional electron systems due to 2D/3D quantum confinement (QC). Both have been extensively studied in the last decade. However, it has been only very recently that the combined effects of strain and 2D/3D QC have started to attract attention. Several types of latticemismatched quantum wires and dots have been fabricated and studied, but, in most cases, their strain has been considered to be the same as that in strained films. The strain in films has usually been characterized as biaxial, which means that constraints exist only in two axes and the remaining axis is free. This biaxial strain in conventional heterostructures is usually very simple: It is uniform and in-plane symmetric (if we ignore small crystal anisotropy), and there is no strain in surrounding layers. In contrast, such features are impossible in buried strained wires, as they have an added constraint in the remaining direction and do not have in-plane translation symmetry. Strain in wires is essentially nonbiaxial; nonuniform and anisotropic as shown in Fig. 1. We hereafter refer to this strain distribution in wires as anisotropic "triaxial" because constraints exist in three axes and the in-plane translation symmetry is broken. From another viewpoint, this change can be regarded as a dimensionality effect (dimensional crossover) on strain since this strain distribution is essentially a 2D mathematical elastic problem in wires although it is 1D in films.The quantitative analysis of this effect in latticemismatched quantum wires/dots has only just begun. Both realistic strain calculations [1,2] and high-resolution x-ray diffraction experiments [3] indeed report a nonbiaxial character of strain in these structures. This nonbiaxial nature of strain is expected to imply even more interesting physics since it should essentially affect the electronic/ optical properties. The major experimental problem in observing such effects of triaxial strain is that these effects are often mixed with the QC effects, and it is generally ha...

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