Pae Wu

Characteristics of InN grown on SiC under the in-rich regime by molecular beam heteroepitaxy

InN epitaxial films were grown by N2 plasma-assisted molecular beam epitaxy on 4H- and 6H-SiC substrates using low-temperature InN nucleation layers. InN films grown at various In fluxes under the In-rich regime show improved crystal quality, surface morphology, and optical properties, without sizable metallic In incorporation. Photoluminescence measurements show emission up to room temperature, band gap values as low as 0.64eV at T=10K, and carrier concentrations of the order of 8×1017cm−3.

Band bending and adsorption/desorption kinetics on N-polar GaN surfaces

Highly reactive N-polar [000−1] GaN surfaces were analyzed using spectroscopic ellipsometry. Following exposure to air, observed changes in the pseudodielectric function near the GaN band edge indicate that surface contamination reduces the band bending. A subsequent Ga adsorption/desorption experiment on pristine N-polar GaN indicates that it contains a mixture of Ga-terminated and N-terminated surfaces. During deposition, Ga adatoms preferentially bond to the dangling bonds on the N-terminated surface: the measured 3.19 eV desorption activation energy equals the Ga–N decomposition energy. Further deposition forms a 1 ML Ga wetting layer whose 2.78 eV desorption activation energy is comparable to the Ga sublimation energy.

Spin-dependent resonant tunneling through 6μm diameter double barrier resonant tunneling diode

A vertical resonant tunneling diode based on the paramagnetic Zn1−x−yMnyCdxSe system has been fabricated with a pillar diameter down to ∼6μm. The diode exhibits high quality resonant tunneling characteristics through the electron subband of the quantum well at a temperature of 4.2K, where a clear phonon replica was observable in addition to the primary peak. Both peaks show a giant Zeeman splitting in an applied magnetic field. Employing a self-consistent real-time Green’s function method, the current-voltage characteristic was simulated, showing good agreement with the measured result.

Real time optical monitoring of molecular beam epitaxy of InN on SiC substrates

Spectroscopic ellipsometry has been used to monitor in real time and in situ the molecular beam epitaxial growth of InN on SiC substrates. A three-step growth process consisting of (i) low-temperature (200°C) nitridation of the SiC surface, (ii) low-temperature (350°C) nucleation of a thin InN buffer layer, and (iii) growth of the InN epitaxial layer at 450°C has been applied. The impact of the In flux on the growth kinetics, morphology, and structural and optical properties of InN has been investigated. It is found that independent of the In flux the low-temperature buffer shows In surface accumulation. This In surface accumulation increases during InN growth under In-rich conditions and is depleted during growth under intermediate and N-rich conditions. Better structural, morphological, and optical properties are obtained when the films are grown under In-rich conditions.

Impact of unintentional and intentional nitridation of the 6H-SiC(0001)Si substrate on GaN epitaxy

We report the impact of both unintentional and intentional nitridation of 6H-SiC(0001)Si substrates on the epitaxial growth of GaN by molecular-beam epitaxy. The unintentional nitridation is dependent upon the details of the pregrowth Ga flash-off process used to remove surface oxides and to achieve a specific pregrowth surface reconstruction. The nucleation process and structural and morphological properties of GaN epitaxial layers are strongly influenced by the modifications of the SiC surface induced by the pregrowth preparation process. We found that residual oxygen at the SiC surface, unintentional SiC nitridation, and the formation of cubic GaN grains at the initial nucleation stage strongly decrease as the concentration of Ga used is increased during the flash cleaning. In addition, recent work has shown that the use of a SiN interlayer for GaN epitaxy on various substrates reduces dislocation density. We observe an improvement in the heteroepitaxy of GaN when the SiC surface is intentionally nitri...

Modification of InN properties by interactions with hydrogen and nitrogen

The interaction of InN epitaxial films grown by r.f. plasma assisted molecular beam epitaxy with atomic hydrogen and nitrogen, produced by remote r.f. H2 and N2 plasmas, is investigated. InN strongly reacts with both atomic hydrogen and nitrogen yielding depletion of nitrogen and concurrent formation of In clusters. The impact of hydrogen treatments on the optical properties of InN is assessed using photoluminescence (PL). It is found that hydrogen suppresses the intense PL band peaked at approximately 0.7eV for the as-grown InN epitaxial layers, and results in the appearance of a new PL band whose peak energy and intensity increase with H-dose. The effect of exposure to atomic hydrogen and nitrogen on electrical properties of InN is investigated using Hall effect measurements. Atomic force microscopy is also used for studying the morphological changes of InN upon interaction with atomic hydrogen and nitrogen.