김현성 교수

Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple mo

We report the direct measurement of spin transport characteristics in a GaN spin valve, with a relatively defect-free single GaN nanowire (NW) as the channel and FeCo/MgO as the tunnel barrier spin contact. Hanle spin precession and non-local transport measurements are made in an unintentionally doped nanowire spin valves. Spin diffusion length and spin lifetime values of 260 nm and 100 ps, respectively, are derived. Appropriate control measurements have been made to verify spin injection, trans

Abstract Complex-oxide materials are gaining a tremendous amount of interest in the semiconductor materials and device community as they hold many useful intrinsic physical properties such as ferro/piezoelectricity, pyroelectricity, ferromagnetism, as well as magnetostriction and other properties suitable for energy storage elements. Complex-oxides can also be complemented with conventional semiconductor-based devices or used by themselves to realize state-of-the-art electronic/photonic/quantum

We present a method of epitaxially growing thermodynamically stable gallium nitride (GaN) nanorods via metal-organic chemical vapor deposition (MOCVD) by invoking a two-step self-limited growth (TSSLG) mechanism. This allows for growth of nanorods with excellent geometrical uniformity with no visible extended defects over a 100 mm sapphire (Al₂O₃) wafer. An ex-situ study of the growth morphology as a function of growth time for the two self-limiting steps elucidate the grow

Intermediate band solar cells promise improved efficiencies beyond the Shockley-Queisser limit by utilizing an intermediate band formed within the bandgap of a single junction solar cell. InP quantum dots (QDs) in an In0.49Ga0.51P host are a promising material system for this application, but two-step photon absorption has not yet been demonstrated. InP QDs were grown via metalorganic chemical vapor deposition, and a density, a diameter, and a height of 0.7 × 1010 cm−2, 56 ± 10 nm, and 18 ± 2.8

The control of magnetoresistance of a lateral spin valve with bias applied to a gate placed outside the channel region is demonstrated. The spin valve channel consists of an InAs/In0.53Ga0.47As/In0.52Al0.48As two-dimensional electron gas lattice matched to (001) InP. The polarizer and analyzer contacts are made with 35 nm type B MnAs/In0.52Al0.48As Schottky tunnel barriers. The magnetoresistance changes from 0.14% to 4% at 10 K in a device in which the spin transport is in the direction of magne

Gate control and amplification of magnetoresistance are demonstrated at room temperature in a fully epitaxial three-terminal GaAs-based device. In addition to the two ferromagnetic spin injector and detector electrodes of a MnAs/AlAs/GaAs:Mn/AlAs/MnAs vertical spin valve, a third non-magnetic gate electrode (Ti/Au) is placed directly on top of the heavily p-doped GaAs channel layer. The magnetoresistance of the device can be amplified to reach values as high as 500% at room temperature with the

The reverse bias leakage characteristics of InGaN/GaN light emitting diodes (LEDs) grown on Si (111) were investigated as a function of two factors: (1) bulk depletion width and (2) V-pit size. The reverse leakage current showed a decreasing trend with an increase in V-pit size, given a fixed depletion width. Atomic probe tomography was used to verify that a reduction in electric field near the vicinity of threading dislocations suppresses field-assisted carrier emission, reducing reverse leakag