Metalorganic Vapor Phase Epitaxy Growth Research Articles

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520°C at atmospheric pressure. Trimethylindium was added in the case of Ga1−xInxSb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga1−xInxSb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga1−xInxSb vapour composition and solid composition has been studied at a V/III ratio of 0.78.

X-ray characterization of GaN and related materials at growth temperatures–system design and measurements

To investigate the phenomena that occur at the growth temperatures, an MOVPE (metalorganic vapor phase epitaxy) growth system was installed in the X-ray diffractometer of the laboratory level. The present MOVPE system is capable of growing GaN and related materials that are advanced in the device applications but very little is known, especially experimentally, what is going on at the growth front and in the environment. Since MOVPE growth is conducted at an atmospheric pressure or at a low pressure, very limited tools can be used to probe the growing surface. It is demonstrated that the X-ray diffraction, X-ray CTR (crystal truncation rod) scattering, and X-ray reflectivity can be used even at 1000°C that is a normal growth temperature for GaN and related materials.

Mechanisms of impurity incorporation during MOVPE growth of m‐plane GaN layers on LiAlO2

AbstractWe study the oxygen incorporation during growth of m‐plane GaN films on LiAlO2 substrates by metal organic vapour phase epitaxy (MOVPE). A broad peak at ∼550 nm in photoluminescence spectra is probably caused by oxygen impurities. Secondary ion mass spectroscopy (SIMS) confirms this finding and reveals a concentration in the order of 1019 cm‐3 which is consistent to the measured n‐type doping level. A general slow decrease of the oxygen concentration in growth direction is observed. A c‐plane GaN film grown on sapphire co‐loaded together with a piece of LiAlO2 shows a slightly increased doping concentration compared to a c‐plane GaN reference. However, the achieved concentration of ∼1017 cm‐3 is much lower compared to m‐plane GaN films. Growth of GaN on a backside‐coated GaN/LiAlO2 template does neither suppress the impurity incorporation. This implies that oxygen incorporation via the gas phase is not the dominant factor. The SIMS oxygen profile of this GaN film on the template shows a strong peak at the position of growth interruption indicating the formation of a surface oxide. We assume that the m‐plane GaN surface has a large affinity for oxygen at the deposition temperature which leads to the high oxygen impurity level. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stability of hydrogen on nonpolar and semipolar nitride surfaces: Role of surface orientation

The stability of hydrogen on nonpolar and semipolar orientations during the metal-organic vapor-phase epitaxy growth is systematically investigated on the basis of density-functional total-energy calculations. The calculated surface energies demonstrate that there are several reconstructions depending on the growth conditions. Using surface phase diagrams which are obtained by comparing the calculated adsorption energy with vapor-phase chemical potentials, we find semipolar GaN(112¯2) surface forms N–H and Ga–NH2 bonds beyond ∼1000K while nonpolar GaN surface without hydrogen is stabilized ranging 1200–1400K. The stabilization of hydrogen free surfaces in the nonpolar orientation can be interpreted in terms of the electron counting rule, in which surface dangling bonds of Ga and N are empty and filled by electrons, respectively. For InN, on the other hand, the surfaces with hydrogen are stabilized over the wide range of growth conditions regardless of surface orientation. This is because the growth temperatures of InN are much lower than those of GaN. These results thus suggest that the growth kinetics and its orientation dependence could be different between GaN and InN surfaces.

Selective MOVPE growth of InAs QDs using double-cap procedure

Broadband spectrum emission was obtained for self-assembled Stranski–Krastanov (S–K) InAs/InP quantum dots (QDs) grown by selective area low pressure metalorganic vapor phase epitaxy (MOVPE) using the double-cap procedure. Selective area growth using a SiO2 narrow stripe mask array pattern was carried out to control and widen the emission wavelength range of the QDs in 16 stripe mask array waveguides. The height of the QDs in the multi stacked QD layers was changed using the double-cap procedure, and the strain was controlled by changing the composition of the GaInAs buffer layer under the QDs, which resulted in the broadband spectrum emission of this structure.

N-face GaN nanorods: Continuous-flux MOVPE growth and morphological properties

We demonstrate the morphological properties of height, diameter and shape controlled N-face GaN nanorods (NRs) by adjusting conventional growth parameters of a standard metalorganic vapour phase epitaxy (MOVPE) growth process. Particularly the hydrogen fraction within the carrier gas was shown to be an important shaping tool for the grown nanostructures. Additionally, the aspect ratio of the NRs was successfully tuned by increasing the pitch of the nanoimprint lithography (NIL) pattern, while maintaining the hole-diameter constant. An optimum aspect ratio could be found at pitches between 400 and 800 nm, whereas larger pitches are counter-productive. The major conclusion drawn from our experiments is that the whole amount of growth material available over the masked surface contributes to the growth of the NRs.

Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods andembedded InGaN quantum wells

We demonstrate the fabrication of N-face GaN nanorods by metal organic vapourphase epitaxy (MOVPE), using continuous-flux conditions. This is in contrastto other approaches reported so far, which have been based on growth modesfar off the conventional growth regimes. For position control of nanorods anSiO2 masking layer with a dense hole pattern on ac-plane sapphire substrate was used. Nanorods with InGaN/GaNheterostructures have been grown catalyst-free. High growth rates up to25 µm h − 1 were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogenenabled homogeneous nanorod diameters down to 220 nm with aspect ratios ofapproximately 8:1. The structural quality and defect progression within nanorods weredetermined by transmission electron microscopy (TEM). Different emission energies forInGaN quantum wells (QWs) could be assigned to different side facets by roomtemperature cathodoluminescence (CL) measurements.

MOVPE growth and characterization of a ‐plane AlGaN over the entire composition range

AbstractWe report the metal organic vapor phase epitaxy (MOVPE) growth and characterization of non‐polar (11$ \bar 2 $0) a ‐plane Alx Ga1–xN on (1$ \bar 1 $02) r ‐plane sapphire substrates over the entire composition range. Alx Ga1–xN samples with ∼0.8 μm thick layers and with x = 0, 0.18, 0.38, 0.46, 0.66, and 1.0 have been grown on r ‐plane sapphire substrates. The layer quality can be improved by using a 3‐stage AlN nucleation layer and appropriate V/III ratio switching following nucleation. All a ‐plane AlGaN epilayers show an anisotropic in‐plane mosaicity, strongly influenced by Al incorporation and growth conditions. Careful lattice parameter measurements show anisotropic in‐plane strain that results in an orthorhombic distortion of the hexagonal unit cell, making Al composition determination from X‐ray diffraction difficult. In general lower Al incorporation is seen in a ‐plane epilayers compared to c ‐plane samples grown under the same conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

MOVPE growth and optical characterization of InGaAsN T‐shaped quantum wires lattice‐matched to GaAs

AbstractInGaAsN T‐shaped quantum wire (T‐QWR) lattice‐matched to GaAs was grown by metal organic vapour‐phase epitaxy (MOVPE) and its optical property was investigated. The InGaAsN T‐QWR was observed at the intersection of two InGaAsN quantum wells (QWs) on (001) and (110) surfaces, namely QW1 and QW2, respectively. In, N contents and well‐thickness in QW1 and QW2 were determined by high resolution X‐ray diffraction (HRXRD). Photoluminescence (PL) was taken to obtain excitonic states in the one‐dimensional T‐QWR as well as QW1 and QW2. High PL intensity reveals an achievement of high quality T‐QWR. At low‐temperature, InGaAsN T‐QWR exhibits an emission at around 1.141 eV with a large lateral confinement of about 61 and 99 meV for QW1 and QW2, respectively. This method for producing InGaAsN T‐QWR may be useful for optical or electronic device applications.

GaAs nanowires grown by MOVPE

AbstractGaAs nanowire (NW) growth was studied by metal‐organic vapour phase epitaxy (MOVPE). The vapour–liquid–solid (VLS) mechanism with gold‐based alloy particles and the selective‐area growth (SAG) mechanism on electron beam lithographically prepared SiNx/GaAs mask structures were applied. A special focus is set on thermodynamic aspects of the VLS process. The alloy particle formation and the influence of MOVPE growth parameters on the growth rate and the GaAs NW morphology are examined. Furthermore, the improvement of the real structure with particular interest on the twin formation is studied. Besides the commonly used continuous VLS growth mode also a pulsed VLS growth mode with alternating precursor supply is reported. Based on photoluminescence measurements the effect of strain in core/shell NW structures is confirmed. For the SAG mechanism the MOVPE growth parameters are determined and the real structure is described. magnified image

MOVPE growth and study of ZnO, ZnMgO epilayers and ZnO/ZnMgO MQW structures

AbstractDue to large exciton binding energy, ZnO/ZnMgO heterostructures are promising for modern optoelectronic devices in UV range. We report on the metal‐organic vapor phase epitaxy (MOVPE) growth of ZnO, ZnMgO layers and periodic ZnO/ZnMgO MQW structures at atmospheric pressure of hydrogen using diethylzinc (DEZ), bismethyl‐cyclopentadienil‐magnesium ((MeCp)2Mg) and tertiary‐butanol (t‐BuOH) as precursors. Wurtzite‐type layers and MQW structures were grown below 450°C on Al2O3(0001) substrates. The growth rate is constant in the temperature interval from 170 to 430°C and decreases abruptly above 430°C as a result of decomposition in hydrogen. X‐ray measurement confirms the wurtzite structure of ZnMgO films with the Mg content of up to 35%. The as‐grown films show good optical quality and near band edge emission in the photoluminescence (PL) and cathodoluminescence (CL). Periodic ZnO/ZnMgO MQW structures with strong ZnO QWs emission at room temperature were grown. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Lattice-Latching Effect in Metalorganic Vapor Phase Epitaxy Growth of InGaAsN Film Lattice-Matched to Bulk InGaAs Substrate

The effects of lattice mismatch between an InzGa1-zAs bulk substrate and an InxGa1-xAs1-yNy epilayer on the incorporation kinetics of N (y) and In (x) were investigated. Compositions (x,y) were revealed to be pinned by the substrate to those satisfying lattice-matching conditions. With decreasing In (z) content in the substrate, the incorporation of N is spontaneously enhanced. On the other hand, the In content of the layer is reduced to decrese the deformation energy due to the lattice mismatch. On the basis of our results, thick InxGa1-xAs1-yNy (0.289 < x < 0.312 and 0.009 < y < 0.014) layers exhibiting photoluminescence in the wavelength range of 1.3–1.55 µm were observed to grow owing to the “lattice-latching” effect.

Development of m-plane GaN anisotropic film properties during MOVPE growth on LiAlO 2 substrates

The anisotropic film properties of m-plane GaN deposited by metal organic vapour phase epitaxy (MOVPE) on LiAlO 2 substrates are investigated. To study the development of layer properties during epitaxy, the total film thickness is varied between 0.2 and 1.7 μm. A surface roughening is observed caused by the increased size of hillock-like features. Additionally, small steps which are perfectly aligned in (1 1 −2 0) planes appear for samples with a thickness of ∼0.5 μm and above. Simultaneously, the X-ray rocking curve (XRC) full width at half maximum (FWHM) values become strongly dependent on incident X-ray beam direction beyond this critical thickness. Anisotropic in-plane compressive strain is initially present and gradually relaxes mainly in the [1 1 −2 0] direction when growing thicker films. Low-temperature photoluminescence (PL) spectra are dominated by the GaN near-band-edge peak and show only weak signal related to basal plane stacking faults (BSF). The measured background electron concentration is reduced from ∼10 20 to ∼10 19 cm −3 for film thicknesses of 0.2 μm and ∼1 μm while the electron mobilities rise from ∼20 to ∼130 cm 2/V s. The mobilities are significantly higher in [0 0 0 1] direction which we explain by the presence of extended planar defects in the prismatic plane. Such defects are assumed to be also the cause for the observed surface steps and anisotropic XRC broadening.

MOVPE growth and study of ZnO, ZnMgO epilayers and ZnO/ZnMgO MQW structures

Due to large exciton binding energy, ZnO/ZnMgO heterostructures are promising for modern optoelectronic devices in the UV range. We report on the metal-organic vapor phase epitaxy (MOVPE) of ZnO, ZnMgO layers and periodic ZnO/ZnMgO MQW structures at atmospheric hydrogen pressure using diethylzinc (DEZ), bismethyl-cyclopentadienil-magnesium ((MeCp)2Mg) and tertiary-butanol (t-BuOH) as precursors. Wurtzite-type layers and MQW structures were grown below 450°C on Al2O3(0001) substrates. The growth rate is constant in the temperature interval from 170 to 430°, and decreases abruptly above 430° as a result of ZnO decomposition in hydrogen. PL and X-ray measurements confirm a wurtzite structure f ZnMgO films with a Mg content of up to 35 at%. The as-grown films show good optical quality and near band edge emission in the photoluminescence (PL) and cathodoluminescence (CL). Periodic ZnO/ZnMgO MQW structures with strong ZnO QWs emission were grown at room temperature.

GaN grown on AlN/sapphire templates

Properties of unintentionally-doped GaN re-grown on molecular beam epitaxy grown AlN/Sapphire templates by metal organic vapor phase epitaxy (MOVPE) are studied in this article. X-ray diffraction (XRD), transmission electron microscope (TEM), and atomic force microscope are used to investigate the influence of the crystal quality and surface morphology of AlN on the GaN. It is found that when surface roughness of AlN is small, the GaN has a full width at half maximum (FWHM) values of XRD rocking curves (200—300 and 400—500 arcsec for (002) and (102) plane ω-scan, respectively) and surface roughness (0.1—0.2 nm), which are comparable to those grown on sapphire substrates by using "two-step" method, although the FWHMs of (102) plane XRD ω-scan curves of AlN are 900—1500 arcsec. The reason for dislocation reduction in GaN shown by TEM image is that a part of dislocations in AlN are eliminated in the interface between AlN and GaN. This is probably due to the lattice restoration from Ga atoms for their large size. On the other hand, when surface roughness of AlN is large, the surface migration of Ga atoms is nestricted during the MOVPE growth, which results in a poor GaN quality. Moreover, the resistivity of GaN confirmed with Van der Pauw method is between 105 and 106 Ω ·cm, which is about six orders of magnitude higher than that in GaN grown on sapphire substrates. This is attributed to the replacement of low temperature GaN buffer layer by the AlN.

Recent advances in the MOVPE growth of indium nitride

AbstractSince a few years, indium nitride promising properties for device applications have attracted much attention worldwide. Huge efforts are dedicated to optimize indium nitride growth. However, this growth is extremely challenging, in particular using the metal organic vapor phase epitaxy (MOVPE) technique which exhibits very low growth rates. This may explain why most of the samples available in the scientific community, which also present the best electrical properties, were grown by molecular beam epitaxy (MBE). However, up to date, no intrinsic indium nitride layer was obtained. InN epilayer crystalline quality suffers from the lack of lattice matched substrates, leading to the use of double‐step growth process. In this paper, we show that InN low lateral growth rate is a limiting parameter for efficient double‐step growth process. But, we also report that the use of CBrCl3 during InN growth enhances the lateral growth rate. To improve the growth rate along the c‐axis, we investigate alternative precursors for both nitrogen and indium species. We show that ammonia remains the best precursor, but combined with triethylindium, the growth rate increases with optimum crystalline quality. Finally, we compare MOVPE‐grown and MBE‐grown InN layers in order to understand the difference observed on the electrical properties. We show how thermal annealing can improve the MOVPE‐grown InN layers leading to similar electrical properties than reported in MBE‐grown samples. The role of ammonia as source of hydrogen is also discussed.

High material efficiency MOVPE growth with in situ monitoring

The possibility of growing a GaAs single-junction solar cell structure with high growth rate and low partial pressure of tertiary-butylarsine (TBAs) has been explored in order to minimize the cost and material consumption in metal-organic vapor phase epitaxy (MOVPE). In situ surface reflectance anisotropy measurements suggested that we can grow reasonable quality GaAs layers at a growth rate of 3.3 μm/h and a V/III ratio of 2.5. Dark current–voltage characteristics of the pn junction that was grown at this condition yielded an ideality factor of 1.3, which was equivalent to the value obtained with a lower growth rate and higher V/III ratio, suggesting a possibility that we can grow GaAs with reasonable crystal quality at a high material efficiency. However, there seemed to exist spots of accumulated defects with a spacing of hundreds of micrometers at such a growth condition with a high material efficiency. If they are situated in the vicinity of the pn junction, the efficiency of the PV cell was significantly degraded, which suggests the necessity of tuning the growth conditions according to the impact of a layer on the electrical properties of a PV cell.

Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

This paper reports on the optical and structural properties of strained type-I Ga1−xInxSb quantum wells embedded in GaSb from a metal-organic vapour phase epitaxial growth perspective. Photoluminescence measurements and transmission electron microscopy were used to evaluate the effect of the growth temperature on the quality of Ga1−xInxSb strained layers with varied alloy compositions and thicknesses. Although the various factors contributing to the overall quality of the strained layers are difficult to separate, the quantum well characteristics are significantly altered by the growth temperature. Despite the high growth rates (∼2 nm/s), quantum wells grown at 607 °C display photoluminescence emissions with full-width at half-maximum of 3.5–5.0 meV for an indium solid content (x) up to 0.15.

Metalorganic Vapor Phase Epitaxy of III-Nitride Light-Emitting Diodes on Nanopatterned AGOG Sapphire Substrate by Abbreviated Growth Mode

Metalorganic vapor phase epitaxial (MOVPE) growth of GaN on nanopatterned AGOG sapphire substrates was performed, and characteristics of the light-emitting diode (LED) devices grown on patterned sapphire and planar substrates were compared. The nanopatterned sapphire substrates were fabricated by a novel process (AGOG) whereby aluminum nanomesas were epitaxially converted into crystalline Al2O3 via a two-stage annealing process. The GaN template grown on the nanopatterned sapphire substrate was done via an abbreviated growth mode, where a 15-nm thick, low-temperature GaN buffer layer was used, without the use of an etch-back and recovery process during the epitaxy. InGaN quantum wells (QWs) LEDs were grown on the GaN template on the nanopatterned sapphire, employing the abbreviated growth mode. The optimized InGaN QW LEDs grown on the patterned AGOG sapphire substrate exhibited a 24% improvement in output power as compared to LEDs on GaN templates grown using the conventional method. The increase in output power of the LEDs is attributed to improved internal quantum efficiency of the LEDs.

Suspended aluminum nitride structures grown via metal organic vapor phase epitaxy

The development of III-Nitride suspended structures for Micro-Electro Mechanical Systems (MEMS) and Nano-Electro Mechanical Systems (NEMS) is challenging due to lack of selective etching techniques. Recent efforts have focused on the removal of sacrificial layers based on material properties, such as crystalline quality, bandgap, polarity, doping, etc. These techniques require several processing steps in addition to precise control over the sacrificial and functional layer properties. In this work, conditions have been identified for the growth of etch-resistant polycrystalline AlN films via Metal Organic Vapor Phase Epitaxy (MOVPE) on silicon oxide surfaces, thus allowing silicon oxide to be used as a sacrificial layer in a surface micro-machining process. The MOVPE growth conditions reported result in a well oriented crystal with superior mechanical strength demonstrated by the fabrication of unsupported AlN structures with widths from 5 μm to 110 μm and air gaps ranging from 200 nm to 800 nm. This technique simplifies the fabrication process of AlN suspended structures and is well suited for achieving group III-Nitride heteroepitaxial MEMS/NEMS systems.