Metalorganic Chemical Vapor Phase Deposition Research Articles

Lateral NiO/AlN Heterojunction Rectifiers with Breakdown Voltage >11 kV

Lateral NiO/AIN heterojunction diodes (HJDs) with breakdown voltage up to 11.6 kV and Ni/Au/AlN Schottky barrier diodes (SBDs) with VB of 8.6 kV were fabricated on layers grown on sapphire substrates by metalorganic chemical vapor phase deposition. The power figure-of-merits VB 2/RON where RON is the on-resistance were 0.31 MW·cm−2 for HJD and 0.16 MW·cm−2 for SBD. The lowest turn-on voltages were ∼2.03 and 1.91 V for HJDs and SBDs, respectively, with ON/OFF ratios up to 102. The maximum field before breakdown was 0.45 MV·cm−1 in HJDs and 0.31 MV·cm−1 in SBDs. These correspond to <3% of the critical field in AlN of ∼15 MV·cm−1. This work demonstrates there is still significant optimization to be done in the overall quality of the AlN, including purity, crystal perfection, and defect density to realize the potential of this material as an ultra-wide bandgap semiconductor for efficient multi-kV power switching applications. Our results also demonstrate the promise of NiO as a p-type conducting oxide for forming heterojunctions with AlN.

High-voltage AlN Schottky barrier diodes on bulk AlN substrates by MOCVD

This letter reports the demonstration of Aluminum nitride (AIN) Schottky barrier diodes on bulk AlN substrates by metalorganic chemical vapor phase deposition with breakdown voltages exceeding 3 kV. The devices exhibited good rectifying characteristics with ON/OFF ratios of 106–108 and excellent thermal stability from 298 to 623 K. The device Schottky barrier height increased from 0.89 to 1.85 eV, and the ideality factor decreased from 4.29 to 1.95 with increasing temperature, ascribed to the inhomogeneous metal/AlN interface. This work demonstrates the potential of AlN as an ultra-wide bandgap semiconductor for developing multi-kV AlN high-voltage and high-power devices.

Ferroelectric-like behavior in HfO2/Al2O3/AlN metal-insulator-semiconductor capacitor through AlN thermal stress

By modulating the thermal stress during film growth, the strained aluminum nitride (AlN) thin films with ferroelectric-like behavior were successfully grown by metal organic chemical vapor phase deposition (MOCVD) on silicon (Si) (111) substrate. The capacitors with strained AlN were fabricated and experimentally demonstrated, the linear to ferroelectric-like behavior on the fabricated AlN capacitors was observed, and the behavior was explained in terms of residual strains in the film. This work reports the ferroelectric-like properties of AlN film grown under specific deposition conditions for the first time.

Growth of ultrathin barrier InAlGaN/GaN heterostructures with superior properties using sputtered AlN/sapphire templates and optimized group-III injection rate by metalorganic chemical vapor phase deposition

In this paper, we investigate the influence of group-III precursor injection rate on the material and electrical properties of InAlGaN/GaN heterostructures grown by Metalorganic Chemical Vapor Phase Deposition. It is demonstrated that high-quality GaN layers can be achieved by using the sputtered AlN/sapphire templates. During the barrier layer growth, the injection rate of the Trimethylindium plays an important role in the amount of Ga incorporation into the InAlGaN layer, while the variation of Trimethylaluminum has less impact. High mobility of 1800 cm2/(V·s) and high carrier electron density with an ultrathin of 3 nm thickness InAlGaN barrier layer simultaneously maintaining high crystallinity and smooth surface of InAlGaN barrier layer is achieved with sputtered AlN/sapphire templates and optimized group-III injection rate.

Investigation of Composition Uniformity in Thickness of GaInAsP Layers Grown on InP Substrates by Vapor-Phase Epitaxy

GaInPAs/InP heterostructures grown by metalorganic chemical vapor-phase deposition at a temperature of 600°C and pressure of 0.1 bar are investigated. The thicknesses of the grown GaInAsP layers amount to about 1 μm. For Ga1 –xInxP1 –yAsy solid solutions with average compositions of x = 0.77–0.87 and y = 0.07–0.42, the variation in the content y of V-group atoms over the epitaxial-layer thickness by a value of Δy up to 0.1 atomic fractions in the sublattice of the V-group elements is revealed by secondary ion mass spectrometry. In most cases, a change in y occurs in the GaInAsP layer over a length to 200 nm from the InP heterointerface. In certain cases, y varies throughout the entire GaInPAs-layer thickness. For the epitaxial layers with satisfactory crystalline perfection, the value of Δy is less in the case of better lattice-matching between the GaInPAs epitaxial layer and the substrate. For GaInPAs layers strongly lattice-mismatched with the substrate and characterized by a low degree of crystalline perfection, the value of Δy is close to zero. All these facts enable us to assume that it is elastic deformations arising in the forming monolayer lattice-mismatched with the growing surface that affect the incorporation of V-group atoms into the forming crystalline lattice.

Исследование однородности состава по толщине слоев GaInAsP, полученных на подложках InP методом газофазной эпитаксии

GaInPAs/InP heterostructures grown by low pressure (0.1 bar, 600 oC) metal-organic chemical vapor phase deposition were investigated. The thicknesses of grown GaInAsP layers were about 1 µm. For the epitaxial layers Ga&lt;sub&gt;1-x&lt;/sub&gt;In&lt;sub&gt;x&lt;/sub&gt;P&lt;sub&gt;1-y&lt;/sub&gt;As&lt;sub&gt;y)&lt;/sub&gt; with average compositions of x = 0.77 – 0.87 and y = 0.07 – 0.42 the variation of V group elements content y with the epilayer depth were revealed, weher the compositions of V-group elements were changed up to Δy = 0.1 atomic fractions in V group elements sublattice. In most cases, y change occurs in a GaInAsP region up to 200 nm thick adjacent to the InP. In some cases, y changes throughout the whole GaInPAs layer thickness. Fo the epitaxial layers with a satisfactory crystal perfection the less was the mismatch between the substrate and the GaInPAs epitaxial layer, the smaller was the value of Δy. For GaInPAs layers characterized by a low degree of crystal perfection and a high lattice mismatch between GaInAsP and InP layers, the value of Δy was about zero. These data let us suggest that the incorporation of atoms of the V group in the epitaxial layer strongly depends on elastic deformation of the growing monolayer, that is mismatched with the underlying crystal surface.

RF Dielectric Loss Due to MOCVD Aluminum Nitride on High Resistivity Silicon

The contribution of high-frequency losses from an aluminum nitride (AlN) layer on high resistivity silicon (Si) is reported. The AlN, deposited on silicon via metalorganic chemical vapor phase deposition as a nucleation layer for subsequent gallium nitride growth, is analyzed for its contribution to the dielectric losses from 6–20 GHz and differentiated from the loss due to the p-type layer formed in the silicon substrate. It is found that AlN is a stronger contributor to overall dielectric loss in comparison with the silicon substrate.

Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

Developments in understanding the nucleation of AlN on silicon by MOCVD and its effects on defects

We have studied the process of AlN nucleation on silicon by metal-organic chemical vapor phase deposition. We have shown that for our reactor, which incorporates a chlorine-based chamber clean, we require similar growth conditions to those shown to be optimum by molecular beam epitaxy, that is to say a small amount of NH3 followed by tri-methyl aluminum (TMAl). When TMAl was introduced first, the resulting layers were low quality and cracked. Furthermore, we have shown that for the highest quality layers, with longer TMAl injection, we have an increased density of “inverted pyramid” defects in the layer which can impact electrical device performance. As we have shown that wafer bow becomes increasingly concave with reduced crystalline quality of the GaN layers, a compromise should be achieved between layer quality and morphology to produce wafers which can be processed into large area, high power transistors. We have been able to produce wafers with a low vertical leakage current density 900 V for test structures up to 12 mm2, with a total nitride structure of 3.6 μm on silicon, resulting in a bow less than <50 μm on the 200 mm wafer.

Characterization of MOCVD Thin-Film CdTe Photovoltaics on Space-Qualified Cover Glass

This paper details the AM0 conversion efficiency of a metal–organic chemical vapor phase deposition thin-film cadmium telluride (CdTe) solar cell deposited onto a cerium-doped cover glass (100 μm). An AM0 best cell conversion efficiency of 12.4% (0.25-cm2 contact area) is reported. An AM0 mean efficiency of 12.1% over eight cells demonstrated good spatial uniformity. Excellent adhesion of the cell structure to the cover glass was observed with an adhesive strength of 38 MPa being measured before cohesive failure of the test adhesive. The device structure on cover glass was also subject to severe thermal shock cycling of +80 °C to −196 °C, showing no signs of delamination and no deterioration of the photovoltaic (PV) performance.

Formation and characteristics of AlGaN-based three-dimensional hexagonal nanopyramid semi-polar multiple quantum wells.

We demonstrated for the first time the formation and study of semi-polar AlGaN multiple-quantum-wells (MQWs) grown on highly regular hexagonal AlN nanopyramids. The AlN nanopyramids were obtained by a metal-organic chemical vapor phase deposition regrowth method on a well-ordered AlN nanorod array prepared by a top-down etching process. The growth mechanism of the AlN nanopyramids was ascribed to the slow growth of the (101[combining macron]1) semi-polar plane, which resulted from hydrogen passivation. Beneath the semi-polar facets, air voids were formed. This was attributed to the insufficient delivery of gas reactants to the bottom of the nanorods during the growth process. The polarization effect in semi-polar AlGaN MQWs was numerically calculated. The results showed that the internal electric field (IEF) in the semi-polar MQWs was remarkably reduced by 80% in comparison with c-plane MQWs. Power dependent photoluminescence indicated that the semi-polar AlGaN MQWs had negligible wavelength shifts that resulted from the reduced IEF, which was in accordance with theoretical predictions. In addition, epitaxial strain was greatly relieved in the AlN regrowth layer, which was revealed from the peak shift of the E2(high) phonon using micro-Raman spectroscopy. The advantages of AlGaN-based hexagonal nanopyramid semi-polar three dimensional nanostructures would lead to a large improvement of output power in UV-LEDs.

Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

AlGaN合金中局域态和极化电场的竞争机制

Three AlxGa1-xN samples were grown by metal organic chemical vapor phase deposition(MOCVD),and their optical properties were analyzed by the steady-state and time-resolved photoluminescence(PL) techniques.In view of the fact that the experimental phenomena can't be fully explained by a single mechanism of polarization electric field or that of local state,which remarkably influence luminescent properties of nitrids,the competition mechanism between local state and internal polarization electric field was proposed.By analyzing the experimental data,two crucial conclusions are drawn.First,the temperature starting point of PL peak blue-shift basically corresponds to the shift point between the effect of local state and the effect of polarization electric field.The temperature starting point of PL peak blue-shift is well consistent with the temperature point where the slope of illuminant intensity-temperature curve changes significantly.Then,there is non-uniform polarization electric field distribution in the sample if the PL peak has two blue-shifts with the temperature increasing in AlGaN alloy.

Characteristics of AlN crystal growth depending on m‐ and a‐axis oriented off‐angle of c‐sapphire substrate

AbstractFor the achievement of high‐efficiency AlGaN‐based deep‐ultraviolet (DUV) light‐emitting diodes (LEDs), we investigated the characteristics of AlN crystal growth depending on m‐ and a‐axis oriented off‐angle of c‐sapphire substrate. In order to reduce threading dislocation density (TDD) in AlN crystal growth, we used ammonia (NH3) pulse‐flow multilayer (ML) growth technique in the metal‐organic chemical vapor phase deposition (MOCVD). We found that a macrostep geometry (large step‐bunching) is generated on the surface of AlN template grown on m‐axis oriented (0001) sapphire substrate. On the other hand, macrostep‐free surface can be obtained for AlN grown on a‐axis oriented sapphire. We also found that cracks are easier generated in AlN grown on a‐axis oriented sapphire. It is considered that step‐flow growth is easily obtained for the growth of a‐axis oriented case due to that the atom site of the step edge in the growth is more stable. On the other hand, for m‐axis oriented case, step‐bunching is considered to occur because atoms are easily drifted during the growth due to that the atom site of the edge steps are more unstable. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth of epitaxial sodium-bismuth-titanate films by metal-organic chemical vapor phase deposition

The liquid-delivery spin metal-organic chemical vapor phase deposition method was used to grow epitaxial sodium-bismuth-titanate films of the system Bi 4Ti 3O 12 + xNa 0.5Bi 0.5TiO 3 on SrTiO 3(001) substrates. Na(thd), Ti(O iPr) 2(thd) 2 and Bi(thd) 3, solved in toluene, were applied as source materials. Depending on the substrate temperature and the Na/Bi ratio in the gas phase several structural phases of sodium-bismuth-titanate were detected. With increasing temperature and/or Na/Bi ratio, phase transitions from an Aurivillius phase with m = 3 to m = 4 via an interleaved state with m = 3.5, and, finally, to Na 0.5Bi 0.5TiO 3 with perovskite structure ( m = ∞) were established. These phase transitions proceed at remarkably lower temperatures than in ceramics or bulk crystals for which they had been exclusively observed so far.

Investigation of Oxygen Vacancies in Micro-Patterned PZT Thin Films Using Raman Spectroscopy

Micro-patterned Pb(Zr,Ti)O3 (PZT) films with dot-pattern were grown by metal organic chemical vapor phase deposition (MOCVD). Micro-patterned Pb(Zr,Ti)O3 (PZT) films were formed on dot-patterned SrRuO3 (SRO) buffer layer that was prepared by MOCVD through the metal mask on (111)Pt/Ti/SiO2/Si substrate. The orientation of dot-patterned PZT films was ascertained by the micro-beam x-ray diffraction (XRD) and their crystallinity was characterized by Raman spectroscopy. It was found that PZT films were oriented to (111) on dot-pattern, while (100)/(001) out of dot-pattern and the amount of oxygen vacancies at the circumference of the dot-pattern were larger than that of center of dot-pattern.

Orientation controlled deposition of Pb(Zr,Ti)O3 films using a micron-size patterned SrRuO3 buffer layer

Orientation controlled, micron-sized dot-patterned PZT films were grown by metal organic chemical vapor phase deposition (MOCVD), and their crystal structure was evaluated. A micron-size dot-patterned SrRuO3 (SRO) buffer layer was initially prepared by MOCVD through a metal mask on the (111) Pt/Ti/SiO2/Si substrate. Then, a PZT film was deposited over the entire substrate. Micron-beam X-ray diffraction and Raman spectroscopy indicated that (111)-orientated PZT was prepared on the SRO covered area, while the (100)/(001)-orientated one was directly grown on Pt-covered substrates. The PZT film grown on SRO was thinner than that on the Pt-covered substrate. The estimated ferroelectric property on the center of the dot pattern was larger than that at the circumference by Raman spectroscopy because the strain is accelerated at the center of the dot.

Novel Quantum Dot Gate FETs and Nonvolatile Memories Using Lattice-Matched II–VI Gate Insulators

This paper presents the successful use of ZnS/ZnMgS and other II-VI layers (lattice-matched or pseudomorphic) as high-k gate dielectrics in the fabrication of quantum dot (QD) gate Si field-effect transistors (FETs) and nonvolatile memory structures. Quantum dot gate FETs and nonvolatile memories have been fabricated in two basic configurations: (1) monodispersed cladded Ge nanocrystals (e.g., GeO x -cladded-Ge quantum dots) site-specifically self-assembled over the lattice-matched ZnMgS gate insulator in the channel region, and (2) ZnTe-ZnMgTe quantum dots formed by self-organization, using metalorganic chemical vapor-phase deposition (MOCVD), on ZnS-ZnMgS gate insulator layers grown epitaxially on Si substrates. Self-assembled GeO x -cladded Ge QD gate FETs, exhibiting three-state behavior, are also described. Preliminary results on InGaAs-on-InP FETs, using ZnMgSeTe/ZnSe gate insulator layers, are presented.

The effect of SixNy interlayer on the quality of GaN epitaxial layers grown on Si(111) substrates by MOCVD

Abstract In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(1 1 1) substrates by metal–organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(1 1 1) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(1 1 1) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 μm. Secondly, the effect of in situ substrate nitridation and the insertion of an Si x N y intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the Si x N y layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without Si x N y layer) and B (with Si x N y layer on Si(1 1 1)). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0 0 0 2) diffraction from the GaN epilayer of the sample B in ω -scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a Si x N y intermediate layer significantly improved the optical and structural properties. In sample C (with Si x N y layer on Al 0.11 Ga 0.89 N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.

MOVPE growth of GaN on Si(1 1 1) substrates

Metalorganic chemical vapor phase deposition of thick, crack-free GaN on Si can be performed either by patterning of the substrate and selective growth or by low-temperature (LT) AlN interlayers enabling very thick GaN layers. A reduction in dislocation density from 10 10 to 10 9 cm −2 is observed for LT-AlN interlayers which can be further improved using monolayer thick Si x N y in situ masking and subsequent lateral overgrowth. Crack-free AlGaN/GaN transistor structures show high room temperature mobilities of 1590 cm 2/V s at 6.7×10 12 cm −2 sheet carrier concentration. Thick crack-free light emitters have a maximum output power of 0.42 mW at 498 nm and 20 mA.