Growth Of InGaN Films Research Articles

Growth of InGaN films on hardness-controlled bulk GaN substrates

We carried out an evaluation of the crystalline quality of bulk GaN substrates and the properties of InGaN films grown on them. The Urbach energy estimated by photothermal deflection spectroscopy and the tail states near the valence band maximum determined by hard x-ray photoemission spectroscopy were larger for hardness-controlled bulk GaN (hard GaN) than those for conventional bulk GaN (conventional GaN). However, InGaN on hard GaN grows in a step-flow-like mode, while InGaN grown on conventional GaN exhibits spiral-like growth. The photoluminescence decay at room temperature for InGaN grown on the hard GaN was 470 ps, compared with 50 ps for that grown on the conventional GaN. This can be attributed to the suppression of spiral-like growth due to the resistance to deformation of the hard GaN. These results indicate that substrate hardness is one of the most important factors for III–V nitride growth on the bulk GaN substrate.

Impact of Molecular Dynamics Simulations on Research and Development of Semiconductor Materials

ABSTRACTAtomic scale defects critically limit performance of semiconductor materials. To improve materials, defect effects and defect formation mechanisms must be understood. In this paper, we demonstrate multiple examples where molecular dynamics simulations have effectively addressed these issues that were not well addressed in prior experiments. In the first case, we report our recent progress on modelling graphene growth, where we found that defects in graphene are created around periphery of islands throughout graphene growth, not just in regions where graphene islands impinge as believed previously. In the second case, we report our recent progress on modelling TlBr, where we discovered that under an electric field, edge dislocations in TlBr migrate in both slip and climb directions. The climb motion ejects extensive vacancies that can cause the rapid aging of the material seen in experiments. In the third case, we discovered that the growth of InGaN films on (0001) surfaces suffers from a serious polymorphism problem that creates enormous amounts of defects. Growth on ($11\bar{2}0$) surfaces, on the other hand, results in single crystalline wurtzite films without any of these defects. In the fourth case, we first used simulations to derive dislocation energies that do not possess any noticeable statistical errors, and then used these error-free methods to discover possible misuse of misfit dislocation theory in past thin film studies. Finally, we highlight the significance of molecular dynamics simulations in reducing defects in the design space of nanostructures.

Fabrication of InGaN thin-film transistors using pulsed sputtering deposition.

We report the first demonstration of operational InGaN-based thin-film transistors (TFTs) on glass substrates. The key to our success was coating the glass substrate with a thin amorphous layer of HfO2, which enabled a highly c-axis-oriented growth of InGaN films using pulsed sputtering deposition. The electrical characteristics of the thin films were controlled easily by varying their In content. The optimized InGaN-TFTs exhibited a high on/off ratio of ~108, a field-effect mobility of ~22 cm2 V−1 s−1, and a maximum current density of ~30 mA/mm. These results lay the foundation for developing high-performance electronic devices on glass substrates using group III nitride semiconductors.

Nonuniformity of electron density in In-rich InGaN films deduced from electrolyte capacitance-voltage profiling

In x Ga 1 − x N films with 0.4≤x≤1 are analyzed using electrolyte-based capacitance-voltage technique. In-rich InxGa1−xN for x>0.4 samples exhibit a strong surface electron accumulation. At x=0.4, the Fermi level at the surface is pinned to the conduction band edge indicating a crossover from surface accumulation to depletion. The measured Mott–Schottky plots are fitted using a model based on a Schrödinger–Poisson solver. By comparing the measured data to the fitting results, we conclude that a subsurface layer of ∼15 nm thickness with remarkably lower donor defect concentration is formed during the growth of InGaN films.

Growth and characterizations of InGaN on N- and Ga-polarity GaN grown by plasma-assisted molecular-beam epitaxy

Plasma-assisted molecular-beam epitaxial (RF-MBE) growth of InGaN films on both N- and Ga-polarity GaN underlayers was carried out. Clear evidence was obtained for the difference in the film quality between InGaN grown on the N- and Ga-polarity GaN underlayers, to which the Ga-polarity GaN is preferred. Based on this point, high-quality InGaN films were obtained on the Ga-polarity GaN underlayers with an In composition up to 0.36. Intense photoluminescence (PL) emissions from the InGaN films were observed. Comparing the PL peak energy and the In composition determined by X-ray diffraction, it was found that the band-gap bowing parameter of InGaN films depends on the In composition.

InGaN Double-Heterostructures and Dh-Leds on Hvpe Gan-on-Sapphire Substrates

AbstractWe report on the growth of InGaN films, and the fabrication and characterization of GaN homojunction LEDs and InGaN double heterostructure (DH) LEDs on HVPE GaNon- sapphire substrates. The use of these substrates facilitates the III-nitrides growth process, as it avoids the use of complicated buffer layers. We have achieved InGaN films with strong and sharp band-to-band photoluminescence (PL) from 370 to 540 nm. Typical In 0.o9Ga0. g9N/GaN DH films had double-crystal XRD FWHM ∼ 300 arcsec, and 400 nm peak PL emission with FWHM ∼ 100 meV. DH-LEDs were fabricated with InGaN layers with various compositions, and produced strong electroluminescence (EL) in the blue and blue/green regions.

A Model for Indium Incorporation in the Growth of InGaN Films

ABSTRACTThe development of high quality indium based III-nitride compounds is lagging behind the corresponding aluminum and gallium based compounds. Potential problems confronting the growth of epitaxial and double heterostructure InGaN will be discussed. A mass balance model is presented describing the competing reaction pathways occurring during the growth of indium containing compounds. Atomic layer epitaxy and metalorganic chemical vapor deposition grown InGaN films will be used to explain this model. Also, the growth parameters leading to the attainment of high InN percentages, reduced indium metal formation, and improved structural and optical properties of indium containing nitrides will be discussed.

Growth of InGaN Films by MBE at the Growth Temperature of GaN

ABSTRACTWe report the growth of InGaN alloys over practically the entire composition range at the growth temperature of GaN (700–800 °C) by MBE. We found that when the grown films are thick (> 0.3 μm), incorporation of more than about 30% indium results in phase separation of InN, which is consistent with spinodal decomposition. On the other hand we discovered that such phase separation is absent in thin InGaN films ( < 600Å) grown as GaN/InGaN/GaN heterostructures. In such configurations we were able to incorporate up to 81% In, which is the highest yet reported.