Metalorganic Vapor Deposition Research Articles

Grain Boundaries in Barium Strontium Titanate Thin Films: Structure, Chemistry and Influence on Electronic Properties

In this paper, we investigate the role of grain boundaries in polycrystalline (BaxSr1−x)Ti1+yO3+z films, grown by metal organic vapor deposition, in the accommodation of nonstoichiometry, as well as their role in the strong composition dependence of the electric and dielectric behavior observed in these films. High-spatial resolution electron energy-loss spectroscopy is used for the analysis of composition and structural changes at grain boundaries, as a function of film composition. The existence of amorphous, titanium rich, TiO2-like phases at the grain boundaries of films with large amounts of excess Ti (y ≥ 0.08) may explain the non-monotonic resistance degradation behavior of the films as a function of Ti content. However, we show that a grain boundary phase model fails to explain the strong composition dependence of the dielectric behavior. Electron energy-loss spectra indicate a distortion of the Ti–O octahedra in the grain interiors in samples with increasing Ti excess. The decrease of the dielectric constant with increasing amounts of excess Ti is therefore more likely due to Ti accommodation in the grain interiors.

Cu(In,Ga)Se2 solar cells with a ZnSe buffer layer: interface characterization by quantum efficiency measurements

We investigate Cu(In,Ga)Se 2 -based solar cells with a new ZnSe buffer layer deposited by metal-organic vapour deposition and compare their electronic properties to reference cells using a standard CdS buffer layer. The best solar cell with a ZnSe buffer layer achieves an efficiency of 11.6%. We further investigate a large series of solar cells with varied thickness of both types of buffer layers by means of quantum efficiency measurements in equilibrium and under light and voltage bias. The characterization of the devices concentrates on the analysis of the collection of photogenerated holes from the buffer layer. We introduce a new method to determine the recombination probability of holes at the buffer/absorber interface. We find a similar interface recombination probability of about 40% for both devices, those with a ZnSe buffer layer and those with a CdS buffer layer. An anomalous enhancement of the quantum efficiency measured under current bias is ascribed to a barrier modulation effect which is caused by light absorbed in the buffer layer.

Observation of ordering and phase separation in In xGa 1− xN layers

A series of InGaN layers grown by metalorganic vapour deposition and molecular beam epitaxy have been investigated by transmission electron microscopy (TEM). It is shown that for In concentrations lower than 15%, the InGaN layers has a crystalline quality comparable to that of the underlying thick GaN buffer layer. Both ordering inside the InGaN films and phase separation have been observed when the In concentration was brought over 20%; they are found to depend on the growth conditions as well.

Influence of structural defects on lattice parameter and measured composition of Hg 1− xCd xTe epilayers

Structural and compositional parameters of the Hg 1− x Cd x Te layers grown by metal-organic vapor deposition on (2 1 1)-oriented CdTe substrates were investigated by high-resolution X-ray diffraction, high-resolution scanning electron microscopy, energy dispersive spectroscopy in scanning electron microscopy and Fourier transform infra-red spectroscopy in a transmission mode. Divergence in Cd concentrations, obtained by different methods, is explained in terms of extended defects which cause lattice swelling of the Hg 1− x Cd x Te matrix. Strong correlation between defect density and lattice swelling was established by absolute measurements of lattice parameters (Bond method) and by direct defect imaging. It is proposed to use high-resolution Bond technique for nondestructive monitoring of the layer quality.

X-Ray Diffraction Measurements on c-Axis Oriented YBaCuO Thin Films Deposited by Metalorganic Vapour Deposition

X-Ray Diffraction Measurements on c-Axis Oriented YBaCuO Thin Films Deposited by Metalorganic Vapour Deposition

Growth of Copper Films by Metal Organic Vapor Deposition Using (Pyrazolylborate)copper(I) Compounds

AbstractCuCl reacts with Na[HB(R3R5pz)3] and phosphine (PR3) or isonitrile (CNR) to yield volatile (pyrazolylborate)copper(I) complexes. These compounds were evaluated as MOCVD precursors. Using [{HB(pz)3}Cu(PEt3)] and [{HB(pz)3}Cu(PMe3)], thin copper films were grown by thermal metal organic chemical vapor deposition in a low pressure reactor in the temperature range 150–350°C. Polycrystalline Cu‐phases were obtained at temperatures as low as 150°C. The metallic films were characterized by four‐point‐probe resistivity measurements, AES, and XPS, as well as AFM and SEM. Selective deposition on metal‐seeded surface sites was observed on Pt, Au, Al, and W versus SiO2. Anti‐selective deposition was found to occur on Pd‐seeded samples.

Photoluminescence analysis of InGaP top cells for high-efficiency multi-junction solar cells

A way of evaluate the minority-carrier lifetime by using photoluminescence (PL) measurement is proposed which includes self-absorption. The room-temperature PL intensity is analyzed theoretically for bulk crystals and a device with n +-p junction configuration, based on a one-dimensional model. Photoluminescence analysis of In 0.5Ga 0.5P solar cells grown on GaAs and Si substrates by MOCVD (metal organic vapor deposition) have been carried out and compared with the properties of the In 0.5Ga 0.5P solar cells. By improving minority-carrier lifetime, high-efficiency In 0.5Ga 0.5P cells on GaAs substrates with an efficiency of 18.5% have been made.

Inversion domains in GaN grown on sapphire

Planar defects observed in GaN films grown on (0001) sapphire have been identified as inversion domain boundaries (IDBs) by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all were found to contain IDBs. The IDBs in the MBE and HVPE films extended from the interface to the film surface and formed columnar domains that ranged in width from 3 to 20 nm in the MBE films and up to 100 nm in the HVPE films. For the films investigated, the MBE films had the highest density, and the MOCVD films had the lowest density of IDBs. The nucleation of inversion domains (IDs) may result from step-related inhomogeneities of the GaN/sapphire interface.

Metalorganic vapor deposition growth of AlGaAs on a ridged GaAs(100) substrate for a low threshold current laser

We have investigated the epitaxial growth of AlGaAs on a non-planar GaAs(100) substrate, which has ridged stripes aligned in the [011] direction. The morphology of the (100) plane depended on the Al content of the AlGaAs layers — a high Al content meant a rough surface. The roughness of the surface was independent of the V/III ratio, but depended on the growth rate of the epitaxial layers. The morphology of the (100) plane was improved using a growth rate of less than 0.16 nm/s.

Photoluminescence study of InAsSb/InAsSbP heterostructures grown by low-pressure metalorganic chemical vapor deposition

Photoluminescence has been measured for double- and separate-confinement InAsSb/InAsSbP heterostructures grown by low-pressure metalorganic vapor deposition. A measurement of the integrated luminescence intensity at the temperature range of 77–300 K shows that over a wide range of excitation level (1–5×102 W/cm2) the radiative transitions are the dominant mechanism below T∼170 K. Auger recombination coefficient C=C0 exp(−Ea/kT) with C0≊5×10−27 cm6/s and Ea≊40 meV has been estimated.

Formation of Thin Oxide Films by Metal-Organic Chemical Vapour Deposition

A summary is given of the metal-organic vapour deposition, performed during the last eight years at the University of Twente (The Netherlands), of thin alumina, silica, and titania films at atmospheric and at low pressure on stainless steels. Alumina films were produced from aluminium-tri-sec-butoxide (ATSB) and aluminium-tri-iso-propoxide (ATI), silica films from di-acetoxy-di-t-butoxy-silane (DADBS), and titania films from titanium-tetra-iso-propoxide (TTIP). These investigations can be separated into a number of projects: 1) mechanistic aspects of the decomposition chemistry of the precursors, 2) kinetics of the deposition processes, 3) chemical properties, and 4) mechanical properties of the thin oxide films.

Evolution of Ti Schottky Barrier Heights on n-Type GaN with Annealing

ABSTRACTWe report the effect of mild annealing on Ti Schottky diodes on n-type GaN. The Ti films were deposited by electron beam evaporation on n-type GaN grown by metal organic vapor deposition. We determine the effective barrier height Ф60 by current-voltage measurements as a function of temperature. The as-deposited Ti contacts show rectifying behavior with low barrier heights Ф60 ≤ 200meV. At annealing temperatures as low as 60°C we observe an increase of the barrier height to values of 250meV. After annealing at 230°C and above a stable barrier height of 450meV is measured. The increase in barrier height is not due to any macroscopic interfacial reaction. The origin of the observed changes are discussed in terms of the Schottky-Mott model and possible microscopic interfacial reactions.

Inversion Domain Boundaries in GaN Grown on Sapphire

ABSTRACTInversion domain boundaries (IDBs) in GaN grown on sapphire (0001) were studied by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam diffraction. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all found to contain IDBs. Inversion domains (IDs) that extended from the surface to the interface were found to be columnar with facets on the {10–10} and {11–20} planes. Other domains ended within the film that formed IDBs on the (0001) and {1–102} planes. The domains were found to grow in clusters and connect at points along the boundary.

Nitrogen Plasma Pretreatment of Sapphire Substrates for the GaN Buffer Growth by Remote Plasma Enhanced MOCVD

ABSTRACTLow-temperature GaN buffer layers with smooth surfaces and high crystallinity could be prepared by a remote plasma enhanced metalorganic vapor deposition after the pretreatment of substrates with rf nitrogen plasma. Smooth AIN thin layer was formed on the (0001) sapphire substrate by the nitrogen plasma pretreatment for an hour. The AIN layer provided the nucleation sites for the subsequent buffer layer growth, thus highly preferred (0001) GaN buffer layers could be grown on the pretreated substrate. Formation of the AIN layer on sapphire and the surface smoothness were affected by pretreatment parameters such as exposure time, temperature, and rf power.

Room Temperature Fabrication of Thin Oxide Films by Laser Induced Metalorganic Chemical Vapor Deposition.

Fabrication mechanisms of thin oxide films have been investigated by using the excimer laser induced metalorganic vapor deposition (Laser-MOCVD) method without heating substrates. TiO2 and PbO films are successfully obtained on (100) Si substrates from their parent metalorganics, Ti (O-iC3H7) 4 and (C2H5) 3PbOCH2C (CH3) 3, respectively. A ZrO2 film is notf ormed from Zr (O-tC4H9) 4. The laser wavelength and irradiation angle dependence measurements indicate that film formation proceeds via light absorption of the metalorganic species adsorbed on the substrates. The existence of one-photon process in the TiO2 film formation is assured by laser fluence dependence measurements. The maximum growth rate, 0.05 Å per laser pulse, of TiO2 film obtained in the experiments is compared with a rough estimation by a surface reaction model. The model can essentially explain the slow growth rate from the small absorption cross section of the metalorganics and the mild fluence of laser irradiation.

The chemistry of rhodium on TiO 2(110) deposited by MOCVD of [Rh(CO) 2Cl] 2 and MVD

The deposition of rhodium through metal-organic vapour deposition (MOCVD) of [Rh(CO) 2Cl] 2 and direct metal vapour deposition has been investigated on TiO 2(110). The nature and chemistry of the surface rhodium phase has been characterised by TPD, XPS and FT-RAIRS, using CO as a probe adsorbate molecule. The thermal stability and adsorbate induced inter-conversion of the rhodium phases is also investigated. The rhodium geminal dicarbonyl species (Rh(CO) 2) is formed by the dissociative adsorption of [Rh(CO) 2Cl] 2 at 150 K. At this temperature the physisorption of the parent molecule subsequently takes place at higher exposures. The gem-dicarbonyl is observed exclusively during adsorption at 300 K, and is characterised by v sym(C-O) at 2112 cm −1, and v asym(C-O) at 2028 cm −1. These are observed in p-polarised FT-RAIRS by a coupling of v sym(C-O) to the normal component of the field yielding an increased reflectivity (transmission band), and the coupling of v asym(C-O) to the tangential component, yielding a decreased reflectivity (absorption band). The Rh(3d 5 2 ) binding energy of 309.1 eV is close to that of the parent molecule, while the Cl(2p 3 2 ) binding energy of 198.3 eV is clearly shifted from that found for the parent molecule (199.1 eV), and is associated with the adsorption of the chlorine onto the TiO 2(110) substrate. The frequencies of the bands of the gem-dicarbonyl shift only ca. 9 cm −1 with coverage which saturates at 0.35 ML. The physisorbed layers are characterised in FT-RAIRS by a complex series of transmission and absorption bands when using p-polarised radiation which arise from the coupling of the radiation to four normal modes of an isotropic layer of the parent molecule. The four normal modes give rise to absorption bands in the p-polarised spectrum, and transmission bands in the s-polarised spectrum, at 2102, 2087, 2039 and 2027 cm −1 correspond closely to values observed in the crystalline solid state. The gem-dicarbonyl is stable to 450 K at which temperature CO is cleanly desorbed, and highly dispersed metal particles are produced. For surfaces heated to 500 K, the gem-dicarbonyl can be partly regenerated by exposure of the surface to CO at 300 K, with additional adsorption of linear CO taking place on the remaining metallic particles, characterised by a strong absorption band with v linear(C-O) in the range 2064–2071 cm −1. For surfaces heated to 800 K, a narrower distribution of larger metallic particles is produced from which the regeneration of the gem-dicarbonyl is not facilitated by exposure to CO. The adsorption of CO on the metallic particles is characterised by a very low sticking probability, and a small coverage dependent, red frequency shift. This we suggest is associated with the migration of oxygen from the substrate over the surface of the rhodium during heating, and CO adsorption is only possible after sites are made available by the reaction of CO with adsorbed oxygen to produce CO 2. Exposure of the gem-dicarbonyl to hydrogen at 300 K leads to partial dccarbonylation, and partial disproportionation of the CO resulting in adsorbed carbon. Re-exposure to CO again results in the partial regeneration of the gem-dicarbonyl species. Rhodium deposition by MVD at 300 K leads initially to layer-by-layer growth of metallic rhodium, and exposure of such layers to CO during or following deposition did not result in the formation of the gem-dicarbonyl species. A facile adsorption of linearly bound CO on these films is observed, with v linear(C-O) in the range 2024–2090 cm −1 for both submonolayer and multilayer films. The p-polarised FT-RAIRS spectra produced transmission bands for films below ca. 7 ML, and absorption bands above ca. 20 ML. CO desorbs from the films at 420–550 K, and the TiO 2(110) substrate appears not to influence the CO adsorption behaviour expected for metallic rhodium, even for the first atomic layer. Heating the rhodium layers to 500 K and above produced rhodium particles which on exposure to CO produced the same characteristics of the large particles of rhodium resulting from the decomposition of the gem-dicarbonyl.

Cathodoluminescence and photoluminescence studies of dislocations in GaAs/AlGaAs quantum wells

The optical properties of low pressure metal organic vapor deposition grown GaAs/AlxGa1−xAs (x=0.5) single quantum well structures (SQW) with grown-in dislocations (GD) were studied by low temperature cathodoluminescence (CL) and photoluminescence (PL). High luminescence efficiency around the GD was observed and attributed to impurity decoration. CL spectra show a region surrounding the GD that consists of Si impurities and native defects in the SQW and barrier layers. The diameter of this region was found to be in the order of 1 μm using spectrally resolved CL micrographs.

Growth of GaSb and InSb by low-pressure plasma MOVPE

High-quality InSb and GaSb epitaxial layers were grown by low-pressure plasma metalorganic vapor deposition ( p tot=20 hPa). Studies were made on the effect of growth temperature, V/III ratio and precracking the Sb-precursor TESb in a DC hydrogen plasma on the growth kinetics and material quality. For GaSb growth, a comparative study with TMGa and TEGa as Ga precursors revealed the combination of TEGa and TESb to be more convenient with respect to growth efficiency and suitable V/III ratios. An additional TESb precracking did not exhibit any further improvement of the layer quality (on GaAs substrates: μ 300K=600 cm 2/V·s, P 300K=5×10 16 cm −3, μ 77K=2700 cm 2/V· s, p 77K=9×10 15 cm −3). For the temperature dependence of the growth rate of InSb (TMIn, TESb) on GaAs we observed a shift of the kinetic branch towards lower temperatures with TESb precracking. Additionally, the strong enhancement of the growth efficiency points to the reduction in the kinetic barrier due to plasma precracking of TESb. At 750 K, the best electrical material quality was achieved with TESb precracking (μ 300K=35,000 cm 2/V· s, n 300K=2×10 16 cm −3; without TESb plasma: μ 300K=2000 cm 2/V· s, n 300K=7×10 17 cm -3).

Characterization of high quality c axis oriented ZnO thin films grown by metal organic chemical vapor deposition using zinc acetate as source material

High quality c axis oriented zinc oxide (ZnO) thin films have been deposited on glass substrates by low pressure, metal organic vapor deposition, using zinc acetate (Zn(CH 3COO) 2) and H 2O as source materials. Films have been characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy.

Dependence of the growth direction of CdTe layers on the orientation of GaAs substrates

CdTe layers have been grown by metalorganic vapor deposition on GaAs substrates of different crystallographic orientations. The dependence of the layer direction on the substrate orientation, surface preparation, and growth conditions was investigated. For each substrate direction studied, we have found that two layer orientations can exist. Experimental conditions under which only one layer orientation dominates the growth process, have been found. We propose a model, in terms of twin conjugated directions, explaining our as well as other results appearing in this paper.