Recent progress in the area of hyperbolic metamaterials (HMMs) has sparked interest in transparent conducting oxides (TCOs) that behave as plasmonic media in the near-IR and at optical frequencies for imaging and sensing applications. It has been shown that by depositing alternating layers of negative-epsilon/positive-epsilon materials, a medium can be created with unusual index values such as near zero. HMMs support high-k waves corresponding to a diverging photonic density of states (PDOS), the quantity determining phenomena such as spontaneous and thermal emission. Also, modeling such structures allows evanescent fields containing sub-wavelength information to be coupled to propagating radiation. We investigate the optical, electronic, and physical properties of radio frequency plasma-assisted molecular beam epitaxial (RF-MBE) growth of alternating layers of ZnO and TCO of uniform thickness for HMM applications. Preliminary work creating HMMs with ZnO and Al-doped ZnO (AZO) has shown a negative real part of the permittivity at near-IR whose modulus is proportional to the number density of Al dopant. However, increasing the Al content of the AZO increases the transmission losses to unacceptable levels for device applications at industry standard wavelengths. A TCO with conductivity and physical structure superior to that of AZO is gallium-doped ZnO (GZO). Uniformly grown GZO has been demonstrated to possess improved crystal quality over AZO due to the higher diffusivity of Al in the ZnO. AZO and GZO HMM structures grown by RF-MBE are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Hall effect, four-point probing, deeplevel transient spectroscopy (DLTS), ellipsometry, visible and ultraviolet spectroscopy (UV-VIS) and in-situ reflection high energy electron diffraction (RHEED).
Modern Nano electronics involves the use of heterojunctions in forming energy steps
based on band-edge alignments in effecting quantum confinements. When the electron meanfree-
path exceeds couple of periods, man-made quantum states appeared, mimicking natural
solids with sharpness determined by the degree of coherence dictated by a relatively long meanfree-
path. When a single quantum well is involved, the structure is represented by resonant
tunneling. This process can further be extended to 3D (3-dimension), known as QD, for quantum
dot, however, thus far only few systems have been found possible, mostly involving InAs, or
InN. However, the real problem lies in I/O, making contact to a single quantum dot, seems to be
impractical on account of difficulties in making contacts in Nano scale regime. The issue with
impedance matching, is the most important aspect for efficient devices, whether as detectors, or
as generator in frequencies between THz to visible light. As size shrinks to Nano-regime, even
the wavelength of IR is too large for effective coupling to the quantum dots without some sort of
coupling such as the use of Fabry-Perrot mirrors, which is in fact unsuited for quantum dots,
unless these dots are arranged in an array mimicking a solid with translational symmetry, which
in fact defeating the purpose of going to quantum dots, except when the distribution of these
quantum dots are arranged either representable by some distribution functions suitable for
arriving at a meaningful average, or periodically mimicking a solid, such as the man-made
superlattice, SL, originally proposed by Esaki and Tsu. [1, 2]. Interestingly Esaki and Tsu were
asked to remove the reference on doping in the barrier region for increased mobility by the
reviewer for the IBM’s own J. of Research and Development. We did protest to the Editor-in-
Chief of the Journal to no avail! Because of this experience, it did occur to me of requiring
something beyond the regular reviewing process in technical journals. Some ten years ago, I
proposed to M. Henini the need to have a journal with two outlets for publications, one ‘regular’,
and another as ‘special’: rejected by reviewer, but accepted by the editorial staff. For some
reason, we did not get enough support then.
Floatation or levitation, as well as free suspension are intriguing phenomenon. Both require minimum in
energy. However, as Lord Kelvin observed only composite systems of diamagnets with permanent and induced magnets
can achieve stable equilibrium. Permanent magnets, in contrast to electromagnets retain their ability to attract and hold
magnetic objects without any external energy expenditure. This persistent property similar to superconductors is entirely
quantum mechanical. Recently M.V. Berry, A.K. Geim and others have re-instigated interest in the stability criteria of
these systems. In this work, stability in the horizontal plane is guaranteed by the localization of the holding field. Smart
response gives rise to vertical stability. Smartness causes the net force to be repulsive when the object is too close and
attractive when far. Here we report for the first time, the production of smart response in a system with diamagnetic and
ferromagnetic constituents. The restoring force, F is strongly asymmetric and non-linear with displacement (z); F(z) is
non-harmonic, does not follow hook's law. Two types of diamagnetic materials bismuth and pyrolytic graphite were
investigated. Consistent with the higher susceptibility, the later provides a factor of two stronger repulsive forces under
ambient conditions. Also, for the first time we show that this smart system is extremely un- harmonic. For stable
equilibrium, restoring force is essential and sufficient however harmonic behavior is not essential.
We report a strong and extremely stable electroluminescence (EL) from silicon based EL device. The active layer of the device utilizes a crystalline Si/O superlattice, grown by molecular beam epitaxy with in-situ oxygen exposure. Oxygen exposure is used to limit the growth of oxides to a monolayer in order to continue the silicon epitaxial growth and to create a highly localized interaction between the oxygen and silicon atoms. The visible EL is peaked at 1.8 - 2 eV, showing no degradation in a six month life-test under continuous operation, longer than other silicon based schemes in the literature. The efficacy of both photoluminescence and electroluminescence is similar to better than that from porous silicon. The robustness and stability of the c-Si/O superlattice opens the door for a silicon chip combining IC with integrated optics.
Data from a series of experiments on porous silicon are presented, which provide important information about the luminescence processes in this promising new material. Raman spectra were correlated with PL spectra to clarify the significance of the silicon microcrystallites sizes on the photoluminescence (PL). The temperature dependence of the PL intensity, time constants, and peak PL energies was determined to reveal the role of more highly localized states such as defects and impurities. The dielectric constant was measured using angel resolved ellipsometry to relate quantum size effects to possible excitonic levels in the microcrystallites. The excitation power dependence of the PL was determined to be linear, indicating a one photon-one electron process is responsible for the excitation of the PL. The excitation spectrum of the PL was measured to provide information about the PL excitation process and the critical energy levels.
STRACT Resonant tunneling in threedimensionally quantum confined (3DQC) microcrystalline silicon surrounded by amorphousSi02(aSiO barriers is experimentally observed. Unlike quantum confinement in lower dimenstons charge accumulation in 3DQC silicon box results in large shifts of the discrete energy states with conductancegate voltage measurements.
The optical response of conduction electrons in a superlattice is presented. The time response of electron tunneling through a double barrier is examined with the time dependent Schroedinger''s equation. The energy states of a silicon quantuirt box are calculated with the use of a variational procedure for a spherical box. The regions of applicability of the band-model and the hoppingmodel for negative differential conductivity are discussed. And finally sonie problems involv ing phase rardoraization and inelastic scatterings with the presence of attractive o repulsive elastic scattering centers in a confined re gion are discussed.