A new method to fabricate InGaN quantum dots by metalorganic chemical vapor deposition

A new method to form nanoscale InGaN quantum dots using MOCVD is reported, This method is much different from a method. which uses surfactant or the Stranski-Krastannow growth mode. The dots were formed by increasing the energy barrier for adatoms, which are hopping by surface passivation, and by decreasing the growth temperature. Thus, the new method can be called as a passivation-low-temperature method. Regular high-temperature GaN films were grown first and were passivated. A low-temperature thin layer of GaN dot was then deposited on the surface that acted as the adjusting layer. At last the high-density InGaN dots could be fabricated on the adjusting layer. Atomic force microscopy measurement revealed that InGaN dots were small enough to expect zero-dimensional quantum effects: The islands were typically 80 nm wide and 5 nm high. Their density was about 6 x 10(10) cm(-2). Strong photoluminescence emission from the dots is observed at room temperature, which is much stronger than that of the homogeneous InGaN film with the same growth time. Furthermore, the PL emission of the GaN adjusting layer shows 21 meV blueshift compared with the band edge emission of the GaN due to quantum confine effect. (C) 2002 Elsevier Science B.V. All rights reserved.

Cubic InGaN grown by MOCVD

We report on the growth of high-quality cubic phase InGaN on GaAs by MOCVD. The cubic InGaN layers are grown on cubic GaN buffer layers on GaAs (001) substrates. The surface morphology of the films are mirror-like. The cubic nature of the InGaN films is obtained by Xray diffraction (XRD) measurements. The InGaN layers show strong photoluminescence (PL) at room temperature. Neither emission peak from wurtzite GaN nor yellow luminescence is observed in our films. The highest In content as determined by XRD is about 17% with an PL emission wavelength of 450 nm. The FWHM of the cubic InGaN PL peak are 153 meV and 216 meV for 427 nm and 450 nm emissions, respectively. It is found that the In compositions determined from XRD are not in agreement with those estimated from PL measurements. The reasons for this disagreement are discussed.

Metal-organic Vapor Phase Epitaxy Growth and Characterization of InAlGaN Epilayers

In order to improve crystal quality for growth of quaternary InAlGaN, a series of InAlGaN films were grown on GaN buffer layer under different growth temperatures and carrier gases by low-pressure metal-organic vapor phase epitaxy. Energy dispersive spectroscopy (EDS) was employed to measure the chemical composition of the quaternary, high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) technique were used to characterize structural and optical properties of the epilayers, respectively. The PL spectra of InAlGaN show with and without the broad-deep level emission when only N2 and a N2+H2 mixture were used as carrier gas, respectively. At pressure of 1.01×104 Pa and with mixed gases of nitrogen and hydrogen as carrier gas, different alloy compositions of the films were obtained by changing the growth temperature while keeping the fluxes of precursors of indium (In), aluminum (Al), gallium (Ga) and nitrogen (N2) constant. A combination of HRXRD and PL measurements enable us to explore the relative optimum growth parameters-growth temperature between 850℃ and 870℃,using mixed gas of N2+H2 as carrier gas.

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si3N4 (Si4+) but also in the intermediate nitridation states with one (Si1+) or three (Si3+) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si1+, Si3+, and Si4+ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si4+ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si3N4 by molecular beam epitaxy (MBE). (C) 2010 Elsevier B.V. All rights reserved.

Curvature Management in Buffer Layer for Device Quality GaN Growth on Si (111)

An efficient buffer layer scheme has been designed to address the issue of curvature management during metalorganic chemical vapour deposition growth of GaN on Si (111) substrate. This is necessary to prevent cracking of the grown layer during post-growth cooling down from growth temperature to room temperature and to achieve an allowable bow (<40 m) in the wafer for carrying out lithographic processes. To meet both these ends simultaneously, the stress evolution in the buffer layers was observed carefully. The reduction in precursor flow during the buffer layer growth provided better control over curvature evolution in the growing buffer layers. This has enabled the growth of a suitable high electron mobility transistor (HEMT) stack on 2'' Si (111) substrate of 300 m thickness with a bow as low as 11.4 m, having a two-dimensional electron gas (2DEG) of mobility, carrier concentration, and sheet resistance values 1510 cm(2)/V-s, 0.96 x 10(13)/cm(2), and 444 /, respectively. Another variation of similar technique resulted in a bow of 23.4 m with 2DEG mobility, carrier concentration, and sheet resistance values 1960 cm(2)/V-s, 0.98 x 10(13)/cm(2), and 325 /, respectively.

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

Influence of AlN Buffer Thickness on GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia

Hexagonal GaN is grown on a Si(111) substrate with AlN as a buffer layer by gas source molecular beam epitaxy (GSMBE) with ammonia. The thickness of AlN buffer is changed from 9 to 72 nm. When the thickness of AlN buffer is 36 nm, the surface morphology and crystal quality of GaN is optimal. The in-situ reflection high energy electron diffraction (RHEED) reveals that the transition to a two-dimensional growth mode of AlN is the key to the quality of GaN. However, the thickness of AlN buffer is not so critical to the residual in-plane tensile stress in GaN grown on Si(111) by GSMBE for AlN thickness between 9 to 72 nm.

Influence of AlN buffer layer thickness on the properties of GaN epilayer on Si(111) by MOCVD

The effect of thickness of the high-temperature (HT) AlN buffer layer on the properties of GaN grown on Si(111) has been investigated. Optical microscopy (OM), atomic force microscopy (AFM) and X-ray diffraction (XRD) are employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness of HT AlN buffer layer, and the optimized thickness of the HT AlN buffer layer is about 110 nm. Together with the low-temperature (LT) AlN interlayer, high-quality GaN epilayer with low crack density can be obtained. (C) 2008 Elsevier Ltd. All rights reserved.

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 mum thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 mum thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously. (C) 2004 American Institute of Physics.

Surface morphology of AlN buffer layer and its effect on GaN growth by metalorganic chemical vapor deposition

The in situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above low-temperature AlN buffer layer on c-plane sapphire substrate by metalorganic chemical vapor deposition. It is found that the lateral growth of GaN islands and their coalescence is promoted in the initial growth stage if the AlN buffer layer is treated with a long annealing time and has an optimal thickness: As confirmed by atomic force microscopy observations, the quality of GaN epilayers is closely dependent on the surface morphology of AlN buffer layer, especially the grain size and nuclei density after the annealing treatment. (C) 2004 American Institute of Physics.

The influence of AlN buffer layer thickness on the properties of GaN epilayer

The influence of low-temperature AlN buffer layer thickness on GaN epilayer was investigated by triple-axis X-ray diffraction (XRD) and photoluminescence measurements. A method was proposed to measure the screw and edge dislocation densities by XRD. It was found that the buffer layer thickness was a key parameter to affect the quality of GaN epilayer and an appropriate thickness resulted in the best structural and optical properties except the lateral grain size. After the thickness exceeding the appropriate value, the compressive stress in the epilayer decreased as the thickness increased, which led to the redshift of the near-band edge luminescence. The experimental results showed the buffer layer thickness had more influence on edge dislocation than screw type and the former was perhaps the main source of the yellow band. (C) 2004 Elsevier B.V. All rights reserved.

Low-frequency noise properties of GaN Schottky barriers deposited on intermediate temperature buffer layers

Metal-semiconductor-metal (MSM) structures were fabricated by RF-plasma-assisted MBE using different buffer layer structures. One type of buffer structure consists of an AlN high-temperature buffer layer (HTBL) and a GaN intermediate temperature buffer layer (ITBL), another buffer structure consists of just a single A IN HTBL. Systematic measurements in the flicker noise and deep level transient Fourier spectroscopy (DLTFS) measurements were used to characterize the defect properties in the films. Both the noise and DLTFS measurements indicate improved properties for devices fabricated with the use of ITBL and is attributed to the relaxation of residue strain in the epitaxial layer during growth process. (C) 2003 Elsevier Ltd. All rights reserved.

Influence of the growth temperature of the high-temperature AlN buffer on the properties of GaN grown on Si(111) substrate

We have studied the influence of the growth temperature of the high-temperature (HT) AIN buffer layer on the properties of the GaN epilayer which was grown on Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). It was found that the crystal quality of the GaN epilayer strongly depends on the growth temperature of the HT-AIN buffer. The growth temperature of the AIN buffer to obtain high-quality GaN epilayers lies in a narrow window of several tens of degrees. When the temperature is lower than a certain temperature range, the appearance of AIN polycrystals results in the deterioration of the crystal quality of the AIN buffer layer, which is greatly disadvantageous to the coalescence of the GaN epilayer. Although the AIN buffer's crystal quality is improved as the growth temperature increases, the Si outdiffusion from the substrate is also enhanced when the temperature is higher than a certain temperature range, which will demolish the subsequent growth of the GaN epilayer. Therefore, there exists an optimum growth temperature range of the AIN buffer around 1080degreesC for the growth of high-quality GaN epilayers. (C) 2003 Elsevier B.V. All rights reserved.

Effect of the N/Al ratio of AlN buffer on the crystal properties and stress state of GaN film grown on Si(111) substrate

The effect of the N/Al ratio of AlN buffers on the optical and crystal quality of GaN films, grown by metalorganic chemical vapor deposition on Si(111) substrates, has been investigated. By optimizing the N/Al ratio during the AlN buffer, the threading dislocation density and the tensile stress have been decreased. High-resolution X-ray diffraction exhibited a (0002) full-width at half-maximum as low as 396 acrsec. The variations of the tensile stress existing in the GaN films were approved by the redshifts of the donor bound exiton peaks in the low-temperature photoluminescence measurement at 77 K. (C) 2003 Elsevier B.V. All rights reserved.

Growth and properties of GaN on Si (111) substrates with AlGaN/AlN buffer layer by NH3-GSMBE

We describe the growth of GaN on Si (111) substrates with a AlGaN/AlN buffer layer by NH3-GSMBE. The influence of the AlN and AlGaN buffer layer thickness on the crack density of GaN has been investigated. It is found that the optimum thickness is 120 nm and 250 nm for AlN and AlGaN layers, respectively. The full width at half maximum of the GaN (0002) peak in the triple-crystal x-ray rocking curve measurement is about 15 arcmin.