Comparatively, we present and analyze the structural and electrical parameters of GaN metal-oxide-semiconductor capacitor structures based on a series of the transition metal oxide films, including HfO2, ZrO2, Ta2O5, TiO2, Nb2O5, and Y2O3, along with Al2O3 and SiO2 for reference. We fabricated the GaN metal-oxide-semiconductor capacitor structures using atomic layer deposition, depositing the oxide films onto the GaN substrate at two temperature ranges, 100-125 degrees C and 250-300 degrees C, using either water or ozone as the oxidant. A selective crystallization process was observed in both as-deposited and post-deposition annealed films, with annealing temperatures reaching up to 1200 degrees C, depending on the oxide material and deposition conditions. Enhanced crystallization revealed films composed of either a single phase or two phases, which remained stable without phase transformation under varying deposition or annealing temperature. For the crystallized films, we extracted nanocrystallite sizes (5-30 nm) and strain from grazing incidence X-ray diffraction scans and evaluated the surface roughness from atomic force microscopy images. We analyzed the surface morphology dynamics in relation to the oxide type, oxidant, and deposition and annealing temperatures. From C-V measurements, we extracted the interface trap density and trapped charge density for as- deposited ALD oxide/GaN interfaces, reporting new interface trap density data for Ta2O5/GaN and Y2O3/GaN interfaces. Additionally, we performed GaN band-edge photoluminescence investigations on atomic layer deposition oxide/GaN interface and correlated the results with the morphological and electrical observations. Through this systematic analysis, we demonstrate the competitiveness of the high-k ALD oxides compared to the traditional Al2O3 and SiO2 for GaN metal-oxide-semiconductor capacitor applications.

Herein, the optical properties of aluminum nitride (AlN) epitaxial layers grown on sapphire substrates by metal‐organic chemical vapor deposition (MOCVD) are reported. The structures investigated in this study are grown at highly different degrees of supersaturation in the MOCVD process. In addition, both pulsed and continuous growth conditions are employed and AlN is deposited on nucleation layers favoring different polarities. The samples are investigated by photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy and are found to vary significantly in absorption and emission characteristics. Two distinct absorption bands in the UV‐C spectral range are observed and examined in greater detail, with either giving rise to a significant absorption coefficient of around 1000 cm−1. The corresponding defect transitions are identified by PL spectroscopy. Combined with secondary‐ion mass spectrometry (SIMS) measurements, these absorption bands are allocated to the incorporation of carbon and oxygen impurities, depending on the applied growth conditions. Furthermore, similarities with other epitaxial growth techniques serving as basis for UV‐C applications are highlighted. These results are highly relevant for a better understanding of absorption issues in AlN templates grown by various deposition techniques. In addition, consequences for the growth of efficient UV‐C devices by MOCVD on sapphire substrates are outlined.

We have deposited a series of ALD oxides HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 , SiO 2 , Al 2 O 3 within same reactor and prepared as GaN-MOS structure. A comprehensible diverse distribution of flat-band voltage depending on two different deposition temperatures 100-125°C and 250-300°C, and oxidant H 2 O or O 3 was obtained. At zero gate voltage and under unstressed condition we have observed a qualitative feature demonstrating different dependence of the net fixed charge in the oxide or/and at the interface with the deposition temperature, namely, an increase of positive charge for oxidant water oxide and an increase of negative charge for oxidant ozone oxide. Best interface quality, least charge only slightly influenced by the deposition temperature, we have observed for the ZrO 2 /H 2 O (oxide/oxidant). Instead, highest deposition temperature dependence we have observed for the Al 2 O 3 /H 2 O.

Atomic layer deposited aluminum oxide (ALD-Al2O3) is a dielectric material, which is widely used in organic light emitting diodes in order to prevent their organic layers from humidity related degradation. Unfortunately, there are strong hints that in some cases, ALD-Al2O3 itself is suffering from humidity related degradation. Especially, high temperature and high humidity seem to enhance ALD-Al2O3 degradation strongly. For this reason, the degradation behavior of ALD-Al2O3 films at high temperature and high humidity was investigated in detail and a way to prevent it from degradation was searched. The degradation behavior is analyzed in the first part of this paper. Using infrared absorbance measurements and X-ray diffraction, boehmite (γ-AlOOH) was identified as a degradation product. In the second part of the paper, it is shown that ALD-Al2O3 films can be effectively protected from degradation using a silicon oxide capping. The deposition of very small amounts of silicon in a molecular beam epitaxy system and an X-ray photoelectron spectroscopy investigation of the chemical bonding between the silicon and the ALD-Al2O3 surface led to the conclusion that a silicon termination of the ALD-Al2O3 surface (Al*-O-SiOx) is able to stop humidity related degradation of the underlying ALD-Al2O3 films. The third part of the paper shows that the protection mechanism of the silicon termination is probably due to the strong tendency of silicic acid to resilificate exposed ALD-Al2O3 surfaces. The protective effect of a simple silicon source on an ALD-Al2O3 surface is shown exemplary and the related chemical reactions are presented.

The degradation of atomic layer deposited aluminum oxide (ALD-Al2O3) at high temperature and high humidity was investigated. The intrinsic hydroxyl concentration of as-deposited ALD-Al2O3 was evaluated using a temperature dependent deposition study and its impact on degradation behavior was analyzed. In addition, the degradation of ALD-Al2O3 was monitored in situ using a plate capacitor with ALD-Al2O3 as dielectric. A model for the ALD-Al2O3 degradation mechanism was proposed based on the penetration of water molecules into the ALD-Al2O3 and on the formation of aluminum hydroxide. Two parameters, delay-time (time till a change in capacitance occurs) and wetting speed (speed of molecular water penetration into the ALD-Al2O3), were extracted from the capacitance measurements in order to evaluate the dependence of ALD-Al2O3 degradation on temperature and humidity.

Summary form only given. GaN nanorods and related high aspect ratio 3D GaN nanostructures recently attracted a lot of attention since they are expected to be an exciting new route towards extending the freedom for device design in GaN technology. Such structures offer large surfaces, defect free high quality material, as well as non-polar surface orientations, including the possibility to use very large area foreign substrates without implementing large area strain. All of these aspects are difficult or impossible to achieve when planar substrate approaches are used. Meanwhile, such 3D high aspect ratio GaN based nanostructures can reproducibly be fabricated with high aspect ratios and good homogeneity, and more and more device and application aspects are under investigation.Details on the MOCVD growth of such high aspect ratio structures will be given, and the influence of growth parameters (and particularly the silicon doping) on the properties of the quantum wells will be discussed. Silicon is shown to lead to passivation effects at m-plane sidewall surfaces, which hinder the high quality growth of InGaN quantum wells. Strategies to circumvent this problem will be discussed, leading to InGaN quantum wells with PL-IQE values of 60% at room temperature. This talk will give an overview on the state of the art of our 3D GaN research, pointing out the necessity for further epitaxy related research, but also describing the increasingly interesting demonstration of 3D devices and their substantial potential for solid state lighting.

A uniform array of gallium nitride core‐shell microrod (MR) light‐emitting diode (LED) structures was grown by metalorganic vapor phase epitaxy. Defects and the quantum well (QW) luminescence in an individual rod were investigated by scanning tunneling electron microscopy (STEM) and STEM cathodoluminescence. Luminescence with different wavelength was detected from the quantum wells on the semipolar tip facets and the nonpolar sidewalls of the MRs. Furthermore, the MR array is processed into LED chips. The electro‐optical characteristics of the devices are analyzed. Two separate emission bands are distinguished, which are attributed to the QWs on the semipolar tip facets and the nonpolar sidewalls, respectively. To obtain white LEDs, micrograin phosphors were developed which fit in between individual MRs. By using electrophoretic particle deposition, these phosphors are deposited onto the MR LED chips. Color coordinates, color temperature, and device efficiency are evaluated.Blue (top) and phosphor‐converted white (bottom) microrod LEDs on 4″ wafer.

The growth mechanisms of selective area growth of GaN microcolumns by metal organic vapor phase epitaxy on patterned SiOx/sapphire templates, are investigated. Both Ga‐ and N‐polar domains within a GaN column are detected. The growth system of mixed polar GaN columns is near reaction limitation, which is quantitatively determined by the Damköhler number. The major part of the mixed polar GaN columns is N‐polar. However, the Ga‐polar domains increase the vertical growth rate of the whole column. The strain status of the columns is almost totally relaxed. Core–shell LED structures were realized on the mixed polar GaN columns. The optical properties of the core–shell LEDs were characterized.

Transmission and scanning electron microscopy have been used to characterise GaN/InGaN 3D nanostructures grown on patterned GaN/sapphire substrates by metal organic vapour phase epitaxy (MOVPE). It has been found that the growth of well ordered arrays of such nanostructures, containing multiple quantum wells on non-polar side-facets, can be achieved with a low density of defects. Growth changes and surface morphology play a major role in the nucleation of any defects present. The nanostructure morphology has been investigated and differing growth rates on adjacent facets studied. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Green (λ~540 nm) - and red-emitting (λ~610 nm) InGaN/GaN disks-in-nanowires have been grown by RF plasma-assisted molecular beam epitaxy on (001) Silicon substrates. The growth of disks-in-nanowires heterostructures has been optimized and the nanowires have been passivated to achieve radiative efficiencies of 54% and 52% in the green and red InGaN disks, respectively. Radiative efficiency increases significantly (by ~10%) when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. Light emitting diodes on silicon, incorporating InGaN/GaN quantum disks as the active medium have been fabricated and the devices have been characterized. Quantum Confined Stark Effect (QCSE) blue-shift of 7nm and 15nm have been observed in the measured electroluminescence peak of the green and red LEDs respectively, from which polarization fields have been calculated in the disks to be 605kV/cm for green and 1.26MV/cm for red. For green and red LEDs, external quantum efficiency peaks at current densities of ~25A/cm2 and 12A/cm2, respectively. To improve light extraction efficiency, LED heterostructures have been transferred to Ag mirrors from the silicon growth substrate and preliminary device results have been demonstrated.

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

Columnar structures of III–V semiconductors recently attract considerable attention because of their potential applications in novel optoelectronic and electronic devices. In the present study, the mechanisms for the growth of catalyst-free self-organized GaN columns on sapphire substrate by metal organic vapor phase epitaxy have been thoroughly investigated. The growth behaviours are strongly affected by the choice of carrier gas. If pure nitrogen is used, Ga droplets are able to accumulate on the top of columns during growth, and they are converted into a high quality GaN layer during the cool down phase due to nitridation. Hydrogen as the carrier gas can improve the optical quality of the overall GaN columns substantially, and in addition increase the vertical growth rate. In this case, no indication of Ga droplets could be detected. Furthermore, silane doping during the growth promotes the vertical growth in both cases either pure nitrogen or pure hydrogen as the carrier gas.

We have investigated the radiative properties of InGaN disks in GaN nanowires grown by plasma enhanced molecular beam epitaxy on (001) silicon substrates. The growth of the nanowire heterostructures has been optimized to maximize the radiative efficiency, or internal quantum efficiency (IQE), for photoluminescence emission at λ = 650 nm. It is found that the IQE increases significantly (by ∼10%) to 52%, when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. The increase in efficiency is supported by radiative- and nonradiative lifetimes derived from data obtained from temperature dependent- and time-resolved photoluminescence measurements. Light emitting diodes with p-i-n disk-in-nanowire heterostructures passivated with parylene have been fabricated and characterized.