Growth Mode Of GaN Research Articles

Investigation of the Dislocation Behavior of 6- and 8-Inch AlGaN/GaN HEMT Structures with a Thin AlGaN Buffer Layer Grown on Si Substrates

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = <0001>) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3<112¯0>) and (a+c)-type (b = 1/3<112¯3>) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content.

Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth

Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth

Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth

Study on Nucleation and Growth Mode of GaN on Patterned Graphene by Epitaxial Lateral Overgrowth

Influence of InGaN interlayer thickness on GaN layers grown by metal organic chemical vapour deposition

InGaN interlayer was grown between GaN layers on sapphire substrate using metal organic chemical vapour deposition. The crystalline quality of the sample was investigated using high-resolution X-ray diffraction. The indium composition and InGaN thickness were determined to be 10–15% and 5–10 nm, respectively. Transmission electron microscopy image revealed the interfacial characteristics of the InGaN and GaN layers. Raman spectroscopy revealed prominent GaN peak positions with InGaN shoulder peaks. The growth mode of InGaN and GaN was determined as nanoislands with helical-like morphology by atomic force microscopy. Hall measurement showcased improvement in the mobility and bulk concentration for the GaN/InGaN (5 nm)/GaN structures.

The influence of V/III ratio on GaN grown on patterned sapphire substrate with low temperature AlN buffer layer by hydride vapor phase epitaxy

In this paper, 2–4 in. GaN wafers with high crystal quality were obtained with optimized V/III ratio of source gases on the patterned sapphire substrate (PSS) covered by a sputtered thin AlN buffer layer by using hydride vapor phase epitaxy (HVPE) growth technology. It was found that the morphology and crystal quality of the top GaN layer were significantly different with the variation of V/III ratio of source gases in initial nucleation growth step. Transparent single crystalline GaN layer could be obtained under relatively low V/III ratio of source gases, while it transferred to yellow and polycrystalline structure with increasing of V/III ratio of source gases. This is mainly attributed to the significant transition of GaN nucleation process with different crystallographic plane of AlN buffer layer, and corresponding variation of GaN growth mode at different V/III ratio of source gases, supported by surface, lateral SEM characterization, high-resolution X-ray diffraction (XRD) measurement, and detailed growth mechanism analysis. Moreover, the crystal quality of GaN grown under optimized condition can be further improved by increasing the thickness of GaN. It would offer a simple way to obtain GaN templates with high crystal quality at relatively low cost.

Control of dislocation morphology and lattice distortion in Na-flux GaN crystals

The dislocation morphology and lattice distortion, including the tilting and twisting of lattice planes, at the Na-flux GaN/seed-GaN interface were investigated using transmission electron microscopy (TEM) and position-dependent nanobeam X-ray diffraction (nanoXRD). The results revealed that the dislocation morphology and lattice distortion in Na-flux GaN at the initial growth stage are strongly influenced by the seed-GaN surface morphology and the growth mode of Na-flux GaN. From the TEM results, one can observe that the formation of dislocation-related etch pits (DREPs) on the seed-GaN surface and the three-dimensional (3D) growth mode for Na-flux GaN give rise to the bending and lateral propagation of dislocations penetrating from the seed-GaN to the Na-flux GaN. This simultaneously results in homogenization of the GaN crystal domain structure as confirmed by nanoXRD. The mechanism responsible for the bending and lateral propagation of dislocations by the formation of DREPs and the 3D growth mode for the Na-flux GaN and the correlation between the dislocation morphology and the lattice distortion are discussed on the basis of TEM and nanoXRD results.

Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces.

The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal space analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. Island nucleation spacing obeys a power-law dependence on growth rate, with exponents of -0.24 and -0.29 for the m- and c-plane, respectively.

Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500–700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20–30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

Highly Mg-doped GaN dots and films grown by VLS transport at low temperature

In this study, a new approach toward localized p-type doping of GaN was explored by implementing vapor–liquid–solid (VLS) transport for both reducing the growth temperature and reaching very high Mg incorporation levels. The starting seeds are GaN(0001) epilayers grown on Si(111). The growth cycle includes three steps. At first, Ga is deposited by MOCVD onto the GaN surface, resulting in a network of Ga droplets with sub-micrometer diameters. Then, Mg is incorporated into the droplets, from the gas phase, using (MeCP)2Mg precursor. Finally, droplets are nitridated at 600–700 °C in flowing NH3. Performing one complete growth cycle leads to a network of well-separated dots and/or ring-shaped GaN features. It is demonstrated that the Mg content in the droplets drastically influences the GaN growth mode. Increasing Mg incorporation promotes growth at the liquid/solid interface versus growth at the triple line. To improve the seed coverage, several successive cycles have been performed leading to GaN films with thickness up to ∼250 nm. SIMS analyses demonstrate the very high incorporation of Mg in the VLS-grown material, with concentrations from 3 × 1019 to 8 × 1021 cm−3. Nevertheless, pronounced O incorporation (a few 1020 cm−3) is also found.

Effect of pressure on the semipolar GaN (10-11) growth mode on patterned Si substrates**Project support by the National High Technology Research and Development Program of China (Green Laser).

In this paper, we investigate the effect of pressure on the growth mode of high quality (10-11) GaN using an epitaxial lateral over growth (ELO) technique by metal organic chemical vapor deposition (MOCVD). Two pressure growth conditions, high pressure (HP) 1013 mbar and low pressure growth (LP) 500 mbar, are employed during growth. In the high pressure growth conditions, the crystal quality is improved by decreasing the dislocation and stack fault density in the strip connection locations. The room temperature photoluminescence measurement also shows that the light emission intensity increases three times using the HP growth condition compared with that using the LP growth conditions. In the low temperature (77 K) photoluminescence, the defects-related peaks are very obvious in the low pressure growth samples. This result also indicates that the crystal quality is improved using the high pressure growth conditions.

Effects of initial GaN growth mode on the material and electrical properties of AlGaN/GaN high-electron-mobility transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) with different initial GaN growth modes were prepared on AlN/sapphire substrates. Secondary ion mass spectroscopy and Hall effect measurements confirmed that a highly conductive n-type region was generated at the GaN/AlN buffer interface during the three-dimensional to two-dimensional (3D–2D) growth mode transition. This n-type region was created by oxygen impurity incorporation during the 3D–2D growth mode transition, and its thickness increased with the transition time. The existence of this n-type conduction path not only changed the material properties but also degraded the device performance of HEMTs.

Control of growth mode in Mg-doped GaN/AlN heterostructure

We investigated the effect of carrier gas on the growth mode of Mg-doped GaN on AlN layers. The growth mode of Mg-doped GaN strongly depends on the type of carrier gas used. In H2 carrier gas, Mg-doped GaN on AlN layers is grown in the shape of an island. In contrast, in N2 carrier gas, Mg-doped GaN on AlN layers shows a two-dimensional growth different from the initial growth mode. We observed that the type of carrier gas used has a significant impact on the electrical conductivity of Mg-doped GaN owing to the difference in surface flatness.

Growth techniques to reduce V‐defect density in GaN and AlGaN layers grown on 200 mm Si (111) substrate

AbstractV‐defects can be very detrimental to the functionality of GaN based light emitting diodes (LEDs) and high power transistors grown on 200 mm Si (111) substrates. This work focuses on reducing these detrimental defects in the GaN/AlGaN/AlN stacks grown in a Veeco Turbodisc Maxbright MOCVD system. The origins of V‐defects in GaN/AlGaN/AlN material were studied by cross‐sectional transmission electron microscope (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM). It was found that V‐defects were associated with inversion domain boundary (IDB) like defects, which started from the interface between the AlN nucleation layers and the Si (111) substrates. These IDB‐like defects were terminated by generating V‐defects in the upper layers. Encouraging the 2‐D GaN growth mode helped to close these V‐defects in the GaN layers, but relaxed the built‐in compressive stress faster and resulted in excessive wafer bow. Optimizing the V/III ratio during the AlN nucleation step improved AlN crystal quality and surface morphology, and close V‐defects in GaN without degrading wafers stress condition.

Growth and Characterization of GaN Nanostructures toward Electron Field Emitter Application

We have investigated the growth of GaN nanostructures on three different Si substrates [Si(001) covered with native oxides, Si(001)(2×1), and Si(111)(7×7)] under N-rich conditions by using plasma-assisted molecular beam epitaxy (PA-MBE). For Si native oxides, hexagonal GaN (h-GaN) nanorods with a c-axis fiber texture are formed, i.e., the c-axis is aligned along the substrate normal without any preferential in-plane orientations. For the clean Si(001)(2×1) substrates, c-axis-orientated nanorods are also grown with the epitaxial relationship of <112̄0>hGaN∥<110>Si or <123̄0>hGaN∥<110>Si. On the other hand, mesh-like structures of h-GaN are formed on the clean Si(111)(7 ×7) substrates with the epitaxial relationship of {0001}hGaN∥{111}Si and <112̄0>hGaN∥<110>Si. The difference in the growth mode of GaN will be discussed in terms of the nitridation process during the initial stages of GaN growth, the chemical states of the substrate surfaces, and the substrate orientations. On the basis of the present findings, toward the fabrication of excellent electron field emitters by utilizing the GaN nanorods grown on the Si(001) with native oxides, we have shown the electron field-emission characteristics with a turn-on electric field as low as 1.25 V/µm at a current density of 0.1 µA/cm2 and a field-emission current density as high as 2.5 mA/cm2 at an applied electric field of 2.5 V/µm. We will demonstrate the fabrication of electron field emitter arrays of GaN nanorods on patterned W/SiO2/Si substrates in a selective-area growth mode by PA-MBE.

Pulsed laser deposition of hexagonal GaN-on-Si(100) template for MOCVD applications

Growth of hexagonal GaN on Si(100) templates via pulsed laser deposition (PLD) was investigated for the further development of GaN-on-Si technology. The evolution of the GaN growth mechanism at various growth times was monitored by SEM and TEM, which indicated that the GaN growth mode changes gradually from island growth to layer growth as the growth time increases up to 2 hours. Moreover, the high-temperature operation (1000 °C) of the PLD meant no significant GaN meltback occurred on the GaN template surface. The completed GaN templates were subjected to MOCVD treatment to regrow a GaN layer. The results of X-ray diffraction analysis and photoluminescence measurements show not only the reliability of the GaN template, but also the promise of the PLD technique for the development of GaN-on-Si technology.

Effects of Initial GaN Growth Mode on Patterned Sapphire on the Opto-Electrical Characteristics of GaN-Based Light-Emitting Diodes

We have studied the initial growth modes of GaN on patterned sapphire substrate (PSS) with different initial TMGa flow rates. The FWHM of the (102) XRD spectrum of GaN on PSS increased from 470 to 580 arcsec when the initial TMGa flow rate was increased from 80 to 200 sccm. A low TMGa flow rate sufficiently suppresses GaN island growth on the top of the pattern and hence improves GaN crystal quality. The electrical and optical characteristics of GaN-based LEDs on PSS with low initial TMGa were also improved. More than 90% of the GaN LED chips with low initial GaN growth rate can hold the 1-kV machine-mode electrostatic discharge level.

Improvement of the quality of GaN epilayer by combining a SiNx interlayer and changed GaN growth mode

GaN epilayers with porous SiNx interlayer and changed growth modes were grown by metal–organic chemical vapor deposition on c-plane sapphire substrates. Comparing with GaN epilayer grown by ordinary method, the crystalline qualities were significantly improved. The improvement was attributed to the reduction of the density of threading dislocations causing by over-growth process combining with delayed coalescence of individual GaN islands. The influence of the deposition and annealing of nucleation layer on the GaN regrowth was also discussed.

Ultra-violet GaN/Al0.5Ga0.5N quantum dot based light emitting diodes

Taking advantage of the strain-induced 2-dimensional (2D)–3D “Stransky–Krastanov type” growth mode of GaN on AlxGa1−xN, we report on the fabrication of ultraviolet (UV) light emitting diodes (LEDs) using GaN quantum dots (QDs) as emitters. The structures have been grown by molecular beam epitaxy on sapphire (0001) substrates. GaN QDs, with density ∼8×1010cm−2, are formed on Al0.5Ga0.5N layers. The electroluminescence (EL) spectrum is dominated by a blue–violet emission (400–430nm) at very low injection currents (≤2A/cm2). At currents above 10A/cm2, a UV emission (<390nm) is observed. An additional peak, at wavelength ∼314nm, originates from the EL emission from the GaN wetting layer. For increasing current, we observe a large shift (∼300meV) towards higher energies and a reduction by one third of the full width at half maximum of the EL peak. Furthermore, the appearance of an additional peak on the EL high energy side is observed. These properties are governed by the quantum confined Stark effect and band-filling in the QDs. AlxGa1−xN-based QD-LED performances (optical power, external quantum efficiency) are presented and discussed in correlation to the specific 3D localization of excitons in the QDs.

Improvement of the Quality of a GaN Epilayer by Employing a SiNx Interlayer

GaN epilayers with a porous SiNx interlayer were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. It is found that the crystalline qualities are significantly improved with SiNx growth. The improvement is attributed to the reduction of the density of threading dislocations (TDs) by an over-growth process of GaN grown on a SiNx interlayer. The influence mechanism of SiNx interlayers on GaN growth mode is also discussed.

Epitaxial growth of GaN films on Si(110) substrates by rf‐MBE

AbstractGaN films grown by rf‐MBE on Si(110) substrates using AlN buffer layers are investigated. Single crystalline AlN films are obtained by Al pre‐deposition during the buffer layer growth. 2‐dimensional epitaxial growth mode of GaN is confirmed by in‐situ RHEED observations. HRXRD results show that the FWHM values of diffraction peaks decrease with the increase of the film thickness. Atomically flat GaN surface morphology with mono‐layer steps is obtained and crack‐free GaN films until 2 μm are successfully achieved. Micro‐Raman measurements show that the tensile strain in the GaN films on Si(110) substrates is reduced compared to those on conventional Si(111) substrates. It is expectable that high‐quality III‐nitrides can be grown by rf‐MBE technique for device applications. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)