Low-pressure Metalorganic Vapor Research Articles

On the electrical properties of Si-doped InGaP layers grown by low pressure‐metalorganic vapor phase epitaxy

The electrical properties of undoped and silicon doped InGaP layers grown lattice matched on GaAs by low pressure metal–organic vapor phase epitaxy were investigated under different growth conditions. The possible presence of superlattice ordering was excluded by photoluminescence analysis. Undoped layers exhibited a background p-type contamination of the order of 1016cm−3; the role of possible carbon contamination is discussed. Capacitance–voltage and Hall investigation of Si-doped n-type layers evidenced a room temperature free electron density linearly increasing from 3.6×1016 to 6×1018cm−3 as a function of the Si precursor flow. The corresponding electron mobilities decreased from 1800 to 483cm2/Vs. At lower temperatures, the conductivity and mobility of the n-doped samples showed a metallic like behavior, in some cases with values not consistent with a simple electronic transport into the conduction band, suggesting the presence of an additional parallel transport channel. Five main electron traps were identified by deep level transient spectroscopy and among them, two traps resulted to be dominant, one turned out to play a major role in the bulk, probably associated to the Si doping, and the other was active near the InGaP surface, ascribable to P-related defects.

Reflection absorption infrared spectroscopy analysis of the evolution of ErSb on InSb

We discuss an ex-situ monitoring technique based on glancing-angle infrared-absorption used to determine small amounts of erbium antimonide (ErSb) deposited on an indium antimonide (InSb) layer epitaxially grown on an InSb (100) substrate by low pressure metal organic chemical vapor deposition (MOCVD). Infrared absorption from the indium–hydrogen (InH) stretching mode at 1754.5cm−1 associated with a top most surface of an epitaxial InSb layer was used to compare varying levels of surface coverage with ErSb. Among four samples of varying coverage of ErSb deposition (7.2 to 21.5 monolayers), detected infrared absorption peaks distinct to InH weakened as ErSb surface coverage increased. In the early stage of ErSb deposition, our study suggests that outermost indium atoms in the InSb buffer layer are replaced by Er resulting in increase in absorption associated with the InH mode. Using this simple ex-situ technique, we show that it is possible to calibrate the amount of ErSb deposited atop each individual InSb substrate for depositions of few to tens of monolayers.

Influence of the GaN capping thickness on the strain and photoluminescence properties of InN/GaN quantum dots

InN quantum dots (QDs) were grown on 1μm thick GaN/(0001) sapphire substrates by low pressure metal organic chemical vapor deposition. A single crystalline 10-nm thick GaN capping layer was achieved on the InN QDs by the flow-rate modulation epitaxy method at 650°C. The (002) ω/2θ scans of the X-ray diffraction measurements show that the reduction of the lattice constant with a capping thickness indicate that the GaN capping process exerts a compressive strain on the InN QDs. The residual strain was reduced from 0.245% to −0.245% as the GaN cap thickness increases from 0 to 20nm. In addition, the analysis of the photoluminescence peak energy estimated that the free electron concentration (i.e. density of indium (In) vacancy) decreased from 1.62×1018cm−3 to 1.24×1018cm−3. The suggestion here is that the increase of the compressive strain on InN QDs due to the increased GaN capping layer thickness provides the high driving force for the interdiffusion of the In atom and gallium (Ga) atoms between the interface of InN QDs and the GaN capping layer. Thus, we believe that more Ga atoms can diffuse from the GaN capping layer and substitute the high density of In vacancy in the InN QDs, resulting in a decrease of the free electron concentration in the InN QDs with the increase in the GaN capping layer thickness.

Monolithically integrated dual-wavelength photodetector based on a step-shaped Fabry-Perot filter

A novel long wavelength photodetector with dual-wavelength spectral response is designed and fabricated using a step-shaped Fabry-P′erot (F-P) filter structure. The step-shaped GaAs/AlGaAs distributed Bragg reflectors and the InP PIN photodetector are grown on a GaAs substrate using low pressure metal organic chemical vapor deposition. High quality GaAs/InP heteroepitaxy is realized by employing a thin low temperature buffer layer. The photodetector structure is optimized by theoretical simulation. This device has a dual-peak distance of 19 nm (1 558 and 1 577 nm). The 3-dB bandwidth of 16 GHz is simultaneously obtained with peak quantum efficiencies of 8.5% and 8.6% around 1 558 and 1 577 nm, respectively.

The effect of combined processes for advanced oxidation of organic dye using CVD TiO2 film photo-catalysts

The preparation of TiO2 photo-catalyst films on alumina balls via low pressure metal organic chemical vapor deposition using titanium tetraisopropoxide and their photo-catalytic activity in bromothymol blue (BTB) decomposition using a microwave/UV/TiO2 photo-catalyst combined process system were investigated. The results indicate that the film structure strongly depended on the reaction temperature. Among the grown TiO2 films, anatase and rutile showed high photo-catalytic activities, whereas amorphous TiO2 films showed lower activities. The BTB decomposition rate increased with the microwave intensity and ozone injection rate. A significant synergistic effect was observed when hydrogen peroxide addition was combined with other elemental techniques.

The effect of ammonia flow in the AlN spacer on the electrical properties of InAlN/AlN/GaN HEMT structures

AbstractDuring the past few years it has been reported that a thin AlN spacer of few nanometers needs to be inserted in InAlN/GaN high electron mobility transistors (HEMTs) to obtain high 2DEG carrier mobility. This work presents a systematic study of the effects of varying the ammonia flow in the AlN spacer of InAlN/AlN/GaN HEMTs grown by low pressure metalorganic vapour phase epitaxy (LP‐MOVPE). The strain state, the surface roughness and the growth rate of AlN were found to be dependent on the V/III ratio. In addition the ammonia flow in the interlayer has a strong impact on the structural properties of the subsequent InAlN barrier layer and on the electrical properties of the structure. A sheet resistance as low as 327 Ω/□ with a sheet carrier density of 1.5 × 1013 cm−2 has been obtained at room temperature.

Stress and morphology of a nonpolar a-plane GaN layer on r-plane sapphire substrate

The anisotropic strain of a nonpolar (112̄0) a-plane GaN epilayer on an r-plane (11̄02) sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.

Growth of High-Quality Si-Doped AlGaN by Low-Pressure Metalorganic Vapor Phase Epitaxy

In this paper we report the growth of Si-doped AlGaN on an AlN/sapphire substrate by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) with an in situ monitoring system to fabricate a high-quality film with controlled thickness. The AlN mole fraction in AlGaN can be controlled by adjusting the growth temperature. We also discuss the quality and growth mechanism of AlGaN on AlN. GaN and AlGaN with an AlN mole fraction of 0.28 were free from stress because of the occurrence of three-dimensional (3D) growth. The lattice constant a of AlGaN with an AlN mole fraction of 0.40 was larger than that at an AlN mole fraction of 0.28 despite the two-dimensional (2D) growth mode. This indicates that the lattice mismatch between AlGaN and the underlying AlN adversely affects the crystal quality. AlGaN with an AlN mole fraction of over 0.60 was coherently grown on AlN owing to the fact that the AlN/sapphire template used in this work was subjected to compression. For this reason, in the samples with an AlN mole fraction of over 0.6, the crystal quality was high because of the coherent growth on the underlying AlN. Moreover, Si doping was performed for AlGaN. The carrier concentration increased linearly up to a Si concentration of 2 ×1018 cm-3, indicating that the activation rate was approximately 1.

Growth of High-Quality Si-Doped AlGaN by Low-Pressure Metalorganic Vapor Phase Epitaxy

In this paper we report the growth of Si-doped AlGaN on an AlN/sapphire substrate by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) with an in situ monitoring system to fabricate a high-quality film with controlled thickness. The AlN mole fraction in AlGaN can be controlled by adjusting the growth temperature. We also discuss the quality and growth mechanism of AlGaN on AlN. GaN and AlGaN with an AlN mole fraction of 0.28 were free from stress because of the occurrence of three-dimensional (3D) growth. The lattice constant a of AlGaN with an AlN mole fraction of 0.40 was larger than that at an AlN mole fraction of 0.28 despite the two-dimensional (2D) growth mode. This indicates that the lattice mismatch between AlGaN and the underlying AlN adversely affects the crystal quality. AlGaN with an AlN mole fraction of over 0.60 was coherently grown on AlN owing to the fact that the AlN/sapphire template used in this work was subjected to compression. For this reason, in the samples with an AlN mole fraction of over 0.6, the crystal quality was high because of the coherent growth on the underlying AlN. Moreover, Si doping was performed for AlGaN. The carrier concentration increased linearly up to a Si concentration of 2 ×1018 cm-3, indicating that the activation rate was approximately 1.

InAs/GaSb superlattices grown by LP-MOCVD for ∼10 μm wavelength infrared range

A type-II InAs/GaSb superlattice (SL) was grown on Te-doped (1 0 0) GaSb substrate by low pressure metal organic chemical vapor deposition (LP-MOCVD). The samples were obtained at different growth temperatures and with different interface layers. By introducing an InAsSb interface layer between InAs and GaSb, a good surface morphology of the superlattice was achieved when the sample growth temperature was around 500–520 °C. The photoluminescence (PL) peak wavelength of the sample was 10.7 μm at 77 K, with FWHM of ∼30 meV.

Textured surface boron-doped ZnO transparent conductive oxides on polyethylene terephthalate substrates for Si-based thin film solar cells

Textured surface boron-doped zinc oxide (ZnO:B) thin films were directly grown via low pressure metal organic chemical vapor deposition (LP-MOCVD) on polyethylene terephthalate (PET) flexible substrates at low temperatures and high-efficiency flexible polymer silicon (Si) based thin film solar cells were obtained. High purity diethylzinc and water vapors were used as source materials, and diborane was used as an n-type dopant gas. P-i-n silicon layers were fabricated at ~ 398 K by plasma enhanced chemical vapor deposition. These textured surface ZnO:B thin films on PET substrates (PET/ZnO:B) exhibit rough pyramid-like morphology with high transparencies ( T ~ 80%) and excellent electrical properties ( Rs ~ 10 Ω at d ~ 1500 nm). Finally, the PET/ZnO:B thin films were applied in flexible p-i-n type silicon thin film solar cells (device structure: PET/ZnO:B/p-i-n a-Si:H/Al) with a high conversion efficiency of 6.32% (short-circuit current density J SC = 10.62 mA/cm 2, open-circuit voltage V OC = 0.93 V and fill factor = 64%).

Magnetism in GaN layers implanted by La, Gd, Dy and Lu

We present a complex study of rare earth elements implanted GaN layers grown by low pressure metal-organic vapor phase epitaxy on c-plane sapphire substrates. Gd, Dy, La and Lu ions were implanted with energies of 200 keV and doses ranging from 5 × 10 13 to 4 × 10 17 atoms.cm − 2 . The chemical composition and concentration profiles of ion-implanted layers were studied by secondary ion mass spectrometry and Rutherford back scattering. The structural properties of the layers were characterized by Rutherford back scattering/channeling and X-ray diffraction reciprocal space mapping. Gd implanted layers exhibit ferromagnetic behavior persisting up to ~ 720 K. Since the ferromagnetic behavior was not observed in the case of La and Lu implanted layers, it cannot be attributed to the structural damage of the layer. Based on the fact that the samples are electrically conducting we conclude that the ferromagnetism can be associated with doped electrons mediating the ferromagnetic interaction between local moments on Gd and Dy.

Anomalies in the Temperature Dependence of the Photoelectrical Response of GaAs/InGaP Superlattices

Photoelectrical measurements were taken on InGaP (p+)-GaAs/InGaP-InGaP (n+) multilayers structures, formed by a sequence of nominally undoped InGaP/GaAs quantum wells, interposed between two p+ and n+ InGaP cladding layers. The heterostructures were grown through Low Pressure Metal Organic Vapour Phase Epitaxy, with liquid precursors for the III–V elements and growth conditions optimized for obtaining sharp interfaces and negligible ordering effects in InGaP. The experimental temperature dependence of the photoelectrical signal intensity exhibited peculiarities and anomalies which could lead to erroneous analysis of the perpendicular transport mechanisms, so that they are here critically discussed in the light of a partial depletion of the nominally intrinsic superlattice region of the p–i–n structure.

Structural, optical and electrical study of undoped GaN layers obtained by metalorganic chemical vapor deposition on sapphire substrates

We investigate optical, structural and electrical properties of undoped GaN grown on sapphire. The layers were prepared in a horizontal reactor by low pressure metal organic chemical vapor deposition at temperatures of 900 °C and 950 °C on a low temperature grown (520 °C) GaN buffer layer on (0001) sapphire substrate. The growth pressure was kept at 10,132 Pa. The photoluminescence study of such layers revealed a band-to-band emission around 366 nm and a yellow band around 550 nm. The yellow band intensity decreases with increasing deposition temperature. X-ray diffraction, atomic force microscopy and scanning electron microscopy studies show the formation of hexagonal GaN layers with a thickness of around 1 μm. The electrical study was performed using temperature dependent Hall measurements between 35 and 373 K. Two activation energies are obtained from the temperature dependent conductivity, one smaller than 1 meV and the other one around 20 meV. For the samples grown at 900 °C the mobilities are constant around 10 and 20 cm 2 V −1 s − 1 , while for the sample grown at 950 °C the mobility shows a thermally activated behavior with an activation energy of 2.15 meV.

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.

Role of growth mode in the formation of magnetic properties of InMnAs grown by MOVPE

The magnetic and structural properties of InMnAs self-assembled dots and epitaxial layers prepared from the identical composition of the gas phase were investigated. All structures under study were grown by low pressure metal organic vapor phase epitaxy at the growth temperature of 500°C. Magnetization measurements indicated that the Curie temperature of InMnAs dots prepared under the Stranski–Krastanov growth mode varied from 7 to 235K in relation to the material composition. The Curie temperature of epitaxial layers prepared under layer by layer growth mode was found to be independent from the material composition. Transmission electron microscopy and microstructure analysis revealed that the dots have a zinc blende structure and they are plastically relaxed.

The etching of a-plane GaN epilayers grown by metal-organic chemical vapour deposition

Morphology of nonpolar a-plane GaN epilayers on r-plane sapphire substrate grown by low-pressure metal-organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.

Effect of growth pressure on coalescence thickness and crystal quality of GaN deposited on 4H–SiC

The influence of growth pressure on the coalescence thickness and the crystal quality of GaN deposited on 4H–SiC by low pressure metalorganic vapor phase epitaxy was studied. It was shown that growth pressure has an impact on the surface roughness of epilayers and their crystal quality. GaN coalescence thicknesses were determined for the investigated growth pressures. The GaN layers were characterized by AFM and HRXRD measurements. HEMT structures were also fabricated and characterized. Among the growth pressures studied, 50, 125 and 200 mbar, 200 mbar was found to be most suitable for GaN/SiC epitaxy.

A study of the photocatalytic destruction of propylene using microwave discharge electrodeless lamp

A microwave discharge electrodeless lamp (MDEL) was used as the light source for microwave-assisted TiO 2 photo-catalysis to degrade propylene. A MDEL filled with low pressure mercury gas has been developed for the photocatalytic treatment of air pollutants over TiO 2 balls. TiO 2 balls used were produced by the low pressure metal organic chemical vapor deposition method. With increasing microwave power, the degradation efficiency of propylene increased resulting in increased production of CO 2, H 2O, and CO. It is proposed that propylene is degraded by MDEL and photocatalysts into CH 4 and C 2H 6, which are then mineralized into CO 2, H 2O, and CO. C 2H 2 is suggested to be produced from CH 4 or C 2H 6 by microwave.

Optimization of low density InP/GaInP quantum dots for single-dot studies

We achieve well-controlled and reproducible growth by low-pressure metalorganic vapor phase epitaxy (MOVPE) of low density InP/GaInP quantum dots optimized for single-dot physics and applications. We overcome the common occurrence of multi-modal distributions of quantum dot sizes by optimizing the growth on (100) GaAs substrates with a 3° misorientation towards ⟨111⟩. In contrast to other epitaxial techniques for quantum dot growth, very controllable dependence of the quantum dot sizes and densities on the nominal thickness of the InP layer is observed, enabling highly reproducible growth.