Shung-Yi Wu

Room-temperature operation type-II GaSb/GaAs quantum-dot infrared light-emitting diode

A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED.

High-quality thin single-crystal γ-Al2O3 films grown on Si (111)

Single-crystal Al2O3 films have been epitaxially grown on Si (111) substrates despite a lattice mismatch of more than 30%. The oxide was electron-beam evaporated from a high-purity sapphire source. The structural and morphological studies carried out by x-ray diffraction, x-ray reflectivity, atomic force microscopy, and transmission electron microscopy, with the initial epitaxial growth observed by in situ reflection high-energy electron diffraction show that the oxide films as thin as 3.8 nm have the cubic γ-phase with a very uniform thickness and a high structural perfection. The film surface is very smooth with a roughness of 0.12 nm and the oxide∕Si interface is atomically sharp. The γ-Al2O3 films are well aligned with Si substrate with an orientation relationship of Si(111)∕∕Al2O3(222), Si[220]∕∕Al2O3[440].

Room-Temperature Electro-Luminescence of Type-II GaSb/GaAs Quantum Rings

The influence of Sb/background As flux ratios on GaSb nano-structures is investigated in this letter. With decreasing Sb/background As flux ratios under high Sb irradiation during the post soaking procedure, ring formation, photoluminescence (PL) intensity enhancement, and PL peak red shift are observed. With further reduced Sb flux and Sb/background As ratios, the observed more intense PL intensities of the quantum-ring (QR) samples compared with quantum dots suggest that more electron-hole wave function overlapping is obtained. The observation of room-temperature electro-luminescence of a QR PIN diode has revealed the potential of the nano-structure in light-emitting device application.

Influence of as on the Morphologies and Optical Characteristics of GaSb/GaAs Quantum Dots

The influence of As atoms on the morphologies of GaSb quantum dots (QDs) is investigated. Without any special treatment, GaSb quantum rings (QRs) are observed in the embedded GaSb layer even when the uncapped layer reveals QD like morphologies. With intentional As supply after the uncapped GaSb QD deposition, a QD to QR transition is observed. The phenomenon suggests that insufficient Sb atoms on the GaSb QDs would lead to the QD to QR transition as in the case of embedded GaSb layers. With extended Sb soaking time following GaSb deposition, QD structures could be well maintained for the embedded GaSb layers. A light-emitting diode operated at room temperature is fabricated based on the GaSb/GaAs QD structure. Identical peak positions in photoluminescence and electroluminescence (EL) spectra of the device show that type-II GaSb QDs are responsible for the observed EL.

Lattice strain and in situ chemical depth profiling of nanometer-thick molecular beam epitaxy grown Y2O3 epitaxial films on Si (111)

The strain/relaxation behavior of nanometer thick Y2O3 (111) epitaxially grown on Si (111) has been investigated with x-ray diffraction using synchrotron radiation. The authors systematically measured a series of Bragg reflections to determine the lattice parameters of Y2O3 films with thickness ranging from 1.6 to 9.5 nm. The strain state of the oxide lattice along surface normal and lateral directions is analyzed as a function of the oxide thickness. The spectra of Si 2p and Y 3d, obtained with in situ angle-resolved x-ray photoelectron spectroscopy on Y2O3 5 nm thick, showed no Y silicide but a very small incorporation of Si into the Y2O3 films at the interface.