Organometallic Chemical Vapor Deposition Research Articles

High-yield processing and single-mode operation of passive antiguide region vertical-cavity lasers

We report the first continuous-wave (CW) operation single-mode, low-threshold, passive antiguide region (PAR) vertical-cavity surface-emitting laser (VCSEL) using organometallic chemical vapor deposition (OMCVD) for the regrowth of the PAR structure. With improved laser wafer design, fabrication process and regrowth design, a stable single fundamental mode at high currents has been achieved experimentally for laser aperture as large as 16 /spl mu/m diameter. Single-mode power of 1.7 mW is achieved with more than 20-dB high-order mode suppression. The lasers show a more than 99% yield with high uniformity. Isolation etch and wet-thermal oxidation are used to study and eliminate the finite-leakage current in the PAR VCSEL's. Using multimode rate equations in conjunction with beam propagation method, single-mode lasing criteria is derived for PAR VCSEL. PAR VCSEL is shown to be a very efficient structure to meet the single-mode lasing condition.

STM investigation of a Cu organometallic complex adsorbed on Si(111)-(7 × 7)

The initial stages of adsorption and decomposition of the organometallic chemical vapour deposition precursor bis(hexafluoroacetylacetonato)copper(II) on Si(111)-(7 × 7) have been investigated using scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and Rutherford backscattering (RBS) spectroscopy. This combination of techniques has allowed the chemical identification and quantification of the features observed in the STM images. Even though each precursor molecule releases a single Cu atom, the Cu atoms form clusters which contain on average 10 ± 2 atoms over a wide range of total coverage (below one monolayer) on a room temperature substrate. The Cu clusters are physically separated from the organic ligands which are themselves adsorbed in clusters on the surface. Possible mechanisms for this surprising behaviour are postulated.

Molecular layer epitaxy by real-time optical process monitoring

In this paper we consider modern methods of optical process monitoring and control in the context of atomic layer epitaxy. One specific method, p-polarized reflectance spectroscopy (PRS), is chosen to assess details of layer-by-layer growth. We show that PRS monitoring under conditions of steady-state growth by pulsed chemical beam epitaxy (PCBE) can achieve the deposition of molecular layers of GaP on silicon (100) deposited with a precision of 5%, which can be improved by reducing the growth rate and increasing the period of time averaging of the reflectance data. Since in the nucleation period prior to formation of a contiguous heteroepitaxial film inhomogeneous surface chemistry and roughening complicates the modeling of the overgrowth process, advances in both experimental methods and theory are required for extending the control to non-steady-state growth conditions. Results of simultaneous single-wavelength PR monitoring and laser light scattering measurements in conjunction with atomic force microscopy studies of short period heteroepitaxial overgrowth processes are presented. The extension of PRS to the monitoring of organometallic chemical vapor deposition at higher pressures is also discussed.

Quantum wire self-ordered growth seeded by electron-beam lithography

We developed new quantum wire (QWR) structures, using organometallic chemical-vapor deposition (OMCVD) growth in V-grooves made by electron-beam lithography (EBL). Our method combines the flexibility and precision of EBL with the clean, defect-free interfaces and small QWR size obtained by OMCVD self-ordered growth. Using EBL, we prepared QWR arrays of different pitches and angles which show high optical quality and can be used in more complex QWR structures. In particular, we demonstrate V-groove wires in which the channel width or orientation varies along the wire axis, which would be useful for the realization of QWR Y-branch or coupled wire-dot structures.

Relaxation of interfacial stress and improved quality of heteroepitaxial 3C–SiC films on (100)Si deposited by organometallic chemical vapor deposition at 1200 °C

We were able to significantly improve the quality of the heteroepitaxial films of the cubic modification of silicon carbide, 3C–SiC, by the use of organosilicon precursors and a careful control of the initial stage of the growth. The films were prepared by chemical vapor deposition from an organometallic precursor, methyltrichlorosilane. It is shown that the interfacial stress, which originates from the large lattice mismatch between the silicon substrate and the SiC film, efficiently relaxes with increasing distance between the interface yielding thick films of high quality for a thickness of ⩾20 μm.

Selection, Growth, and Characterization of Gate Insulators on Mocvd Gallium Nitride for the Use in High Power Field Effect Devices

AbstractMetal-insulator-semiconductor (MIS) capacitors have been fabricated on n-type GaN (0001) films using thermally grown Ga2O3, remote plasma enhanced chemical vapor deposited (RPECVD) SiO2, and molecular beam epitaxy (MBE) AIN as the gate insulator and Al as the gate electrode. Each GaN epitaxial layer was grown by organometallic chemical vapor deposition (OMCVD) on a 6H-SiC(0001) substrate on which was previously deposited a 1000Å buffer layer of AIN. Nitrogen-free polycrystalline films of Ga2O3 were grown on the GaN. Capacitancevoltage measurements of capacitors fabricated from this oxide showed distinct depletion and accumulation regions with significant leakage. The AIN and SiO2 capacitors demonstrated better electrical characteristics than the Ga2O3 because of lower leakage. The RPECVD SiO2/GaN heterostructures, in particular, showed good agreement with the curves calculated for an ideal oxide and a small amount of hysteresis.

Low-pressure OMCVD growth of AlGaAs vertical quantum wells on non-planar substrates

AlGaAs vertical quantum well structure were formed by low-pressure (20 mbar) organometallic chemical vapor deposition on V-grooved substrates. Ga segregation in the wells of these structures was evidenced by means of atomic force microscopy and photoluminescence experiments. Transmission electron microscopy cross sections resolve different branches in the well. This substructure, whose definition is enhanced in low-pressure growth, is associated with the formation of specific facets at the bottom of the grooves. The dependence of the growth rate on the crystallographic facet and the Al mole fraction is the key mechanism for the establishment of the self-limiting profile in the V-grooves.

Low Pressure CVD Growth of AlxTi1-xN Films with Tetrakis- (Dimethylamido)Titanium (Tdmat) and Dimethyl Aluminum Hydride (DMAH) Precursors

ABSTRACTAlxTi1-xN film growth has been studied by a organometallic chemical vapor deposition andin-situX-ray photoelectron spectroscopy. Terakis(dimethylamido)titanium (TDMAT) and dimethyl aluminum hydride (DMAH) were used as the Ti, N and Al precursors. AlTiN film growth was observed on SiO2/Si(100) with substrate temperatures between 200 and 400 °C. The Al content in the film is controlled by the ratio of partial pressures of the two precursors in the gas phase. The metal to C to N ratio is approximately constant at 1:1:1 for most conditions studied. The chemical states of Ti, C, and N in AlxTi1-xN and titanium-carbo-nitride (TiCN) films are identical, while the Al chemical state is nitride at low, but increasingly carbidic at high Al concentration. The initial growth rate on SiO2was significantly suppressed by the presence of DMAH. At lower growth temperatures, the DMAH effect is more severe. Good step coverage was observed for AlxTi1-xN on 0.3 μm vias with a 3:1 aspect ratio.

Step ordering during OMCVD growth on non-planar substrates

We used atomic force microscopy (AFM) in air to investigate the structure of atomically smooth terraces separated by monoatomic steps which are formed during organometallic chemical vapor deposition (OMCVD) on non-planar substrates. We found that grooves along the [011̄]-direction can orient the steps on the (100) ridge between them in the [011]-direction. This orientation effect is sustained for a distance of about 500 nm from each groove. The distance between the oriented steps is determined by the initial misorientation angles of the substrate, and their width is nearly constant. We explain these step orientation phenomena as coming from the interplay between {311}A and (100) growth on the non-planar substrate. The step orientation control could be useful for preparation of improved nanostructures, such as quantum wells, quantum wires and fractional monolayer superlattices.

Fabrication of Micron Scale Magnetic Nickel Features by Selective Area Organometallic Chemical Vapor Deposition

AbstractWe demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted and electron radiation induced selective area organometallic chemical vapor deposition. Large arrays of identical micron to nano scale Ni features were deposited by these methods. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features.

Structure and formation mechanisms of AlGaAs V-groove vertical quantum wells grown by low pressure organometallic chemical vapor deposition

The structure of AlGaAs vertical quantum well (VQW) structures grown by low-pressure organometallic chemical vapor deposition on V-grooved GaAs substrates was analyzed as a function of growth temperature and Al mole fraction using transmission electron microscopy and atomic force microscopy (AFM). The low-pressure growth yields several, extremely narrow (a few nm wide) branches of Ga-enriched VQWs at the bottom of the grooves. The variation in Al content across the VQW was evaluated by measuring the AlGaAs oxide thickness on a cleaved edge of the structure using AFM in air. The transmission electron microscopy analysis demonstrates that the different VQW branches originate from distinct nanofacets that self-order at the bottom of the V-groove, probably due to facet-induced segregation of group III species.

Atomic force microscopy of III–V nanostructures in air

Atomic force microscopy (AFM) in air was used to study the ( 1 10) and (001) surfaces of III–V-heterostructures, grown by organometallic chemical vapor deposition (OMCVD) on planer or patterned (001) substrates. Topographies of the grown (001) surfaces as well as of ( 1 10) cleaved cross-sections were examined. Although contamination and oxidation processes in air are expected to modify the structure of the surfaces in both cases, the AFM height profile, taken at constant force, yields structural information down to the monolayer level. On a cleaved surface of a III–V-heterostructure exposed to air, a natural oxide layer starts to grow immediately after cleaving. The growth rate of the oxide depends on the material composition and thus the topography can be used to map the composition within the scanned area. We used the AFM to characterize the growth of oxide on Al x Ga 1− x As- and GaAs-layers, and performed imaging of Al x Ga 1−x As GaAs heterostructures utilizing the topography for composition identification. On the (001) surface of GaAs and InP, exposed to air, we observed terraces, separated by steps of monolayer height, and exhibiting a staircase-like morphology. Average terrace size and direction depend on the misorientation of the substrate. Formation of isolated growth islands, probably due to spontaneous nucleation, was also observed.

Raman and infrared spectroscopy and transport properties of aged organometallic precursors used for the deposition of high-Tc superconducting films

Raman and infrared (IR) spectra of Ba, Sr and Ca 2,2,6,6-tetramethyl-3,5-heptanedionates (THD), volatile precursors used for organometallic chemical vapor deposition (OMCVD) of high-Tc superconducting (HTCS) thin films, have been studied for freshly supplied commercial materials or those prepared in our laboratory and aged for several months in vacuum and in air. Some of the spectral lines present in freshly prepared material disappeared in precursors aged in air but were unchanged if aged in vacuum. Only freshly prepared or vacuum-stored Ba(THD)2 could be 100% transported by sublimating at 210°C. Air aged material transported only 60% under the same conditions of evaporation. Mixing 20% aged Ba(THD)2 with 80% naphthalene achieved 100% transport of Ba(THD)2.

Fabrication of large arrays of micron-scale magnetic features by selective area organometallic chemical vapor deposition

We demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted selective area organometallic chemical vapor deposition. Large arrays of identical micron-scale Ni features were deposited on a Si(111) wafer by this method. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features. This method can be adapted to the fabrication of smaller-scale magnetic and electronic devices.

Photodetection at 3.65 in the atmospheric window using heteroepitaxy

The photoconductive properties of layers deposited by organo metallic chemical vapour deposition (OMCVD) on GaAs substrates have been investigated through the characterization of a test photoconductor device. The spectral responses at 300 K and 77 K show that this material allows detection in the best region of transparency of the atmospheric window, around . The large increase of the response with decreasing temperature is attributed to the variation of the recombination time. Noise measurements between Hz and Hz indicate the presence of two types of fluctuations: the low-frequency one is inversely proportional to the frequency f and is partly due to non-optimized contacts; the higher-frequency one is due to a generation - recombination process. At , an estimated limit to detection of is deduced at 80 K in the ideal case of pure thermal noise.

Influence of surface morphology on ordered GaInP structures

Ga0.51In0.49P layers, grown by organometallic chemical vapor deposition on differently misoriented (001) GaAs substrates exhibit CuPtB-type domains. The increase in structural homogeneity of the ordered domains, with increasing substrate misorientation, results in a very sharp distribution of the degree of ordering. The correlation between cathodoluminescence emission from ordered regions and changes in surface step distribution direction confirm the influence of the surface morphology on the distribution of ordered regions and their antiphase boundaries.

Wavelength conversion by difference frequency generation in AlGaAs waveguides with periodic domain inversion achieved by wafer bonding

Wavelength conversion by difference-frequency generation is achieved in a periodically domain reversed AlGaAs waveguide. The AlGaAs waveguide is epitaxially grown on a template substrate where a periodic crystal domain inversion is achieved using wafer bonding, selective etching, and organometallic chemical vapor deposition. Wavelength conversion experiments on a fabricated buried heterowaveguide showed a 90 nm conversion bandwidth, polarization diversified operation, and polarization independent conversion efficiency. The experimental results also showed linearity and spectral inversion, which imply transparency to signal formats including analog and frequency modulation. Simultaneous conversion of multiple input wavelengths with no measurable cross talk is also demonstrated.

Selective deposition of amorphous germanium on Si with respect to SiO 2 by organometallic CVD

Low temperature (180 to 300°C) organometallic chemical vapor deposition (CVD) from a novel precursor yields pure films of amorphous germanium at deposition rates up to 13 Å/s. The films were characterized by X-ray diffraction (XRD), infrared absorption spectroscopy, photo electron spectroscopy (XPS) and scanning electron microscopy (SEM). Selective deposition of amorphous germanium on Si with respect to SiO 2 is shown on a structured wafer.

Reactivity and molecular structure of silicon-oxygen-carbon-containing films derived from organometallic chemical vapor deposition (OMCVD)

The organometallic chemical vapor deposition (OMCVD) of non-crystalline solids is an attractive method to provide surface protection. The drawback of large scale processing is the difficulty in depositing films reproducibly with long-term reliability. Hence, there is continuing research for the preparation of ceramic films, such as metal carbides, which are reliable with respect to composition and performance. The purpose of the present study was to produce films inside tubes by decomposing an organometallic precursor down a heated tube length and to study the compositional variability of the film as a function of position in the tube. Additionally, the goal was to study the behavior of the film in an oxidizing atmosphere. X-ray photoelectron spectroscopy (XPS) characterization was used before and after heat treatment in air to study surface and subsurface compositions.

InP/GaAsSb/InP and InP/GaAsSb/InGaAsP double heterojunction bipolar transistors with a carbon-doped base grown by organometallic chemical vapor deposition

InP/GaAsSb double heterojunction bipolar transistors (DHBTs) may be an attractive alternative to InP/InGaAs DHBTs, since estimates of the band alignment indicate that it is ideal for fabricating n-p-n DHBTs. We have demonstrated the first organometallic chemical vapor deposition grown InP/GaAsSb DHBTs, with carbon-doped bases having an ft and fmax of 30 and 45 GHz, respectively.