Trimethylgallium Flow Rate Research Articles

Properties of GaN epitaxial layers grown at high growth rates by metalorganic chemical vapor deposition

GaN epitaxial layers were grown at high growth rates by increasing the input trimethylgallium (TMG) flow rate while keeping the NH3 flow rate constant in metalorganic chemical vapor deposition. The electrical and optical properties of the grown layers have been investigated. With the increasing TMG flow rate, the electron concentration tends to decrease gradually and the Hall mobility decreases significantly. Considering the temperature dependence of the Hall mobility and the correlation between the Hall mobility and the electron concentration, it has been indicated that the more acceptors are incorporated and consequently the compensation ratio becomes higher with increasing the TMG flow rate. Photoluminescence measurements have revealed that the intensity ratio of the bound exciton emission to the 2.2 eV band emission, which is assumed to correlate to carbon or Ga vacancies, was decreased with increasing the TMG flow rate. It might be reasonable to take a lot of acceptor incorporation to explain the degradation of the electrical and optical properties in the samples grown at high growth rates by increasing the TMG flow rate.

Effect of TMG Addition on the Epitaxial Growth of 3C-SiC on Si(100) and Si(111) Using Hexamethyldisilane

ABSTRACTEpitaxial and crack-free 3C-SiC film was successfully grown on Si(100)/(111) by a one step process without separate nucleation or carbonization steps at a low temperature of 1200°C by MOVPE. The growth was achieved by using hexamethyldisilane (HMDS) with the addition of a small amount of trimethylgallium (TMG) (0.5 sccm) with dilute hydrogen (12% H2 + Ar) as a carrier gas. Without the addition of TMG during growth, epitaxial growth of SiC on Si was only possible at temperatures above 1300°C following a nucleation step at 1200∼1250°C. After growth, all the films were analyzed by using cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Nomarski differential interference microscopy (NDIM). It was observed by XPS that the SiC film contained only a small amount of Ga, which means the Ga component of TMG does not much accumulate in SiC, in spite of a relatively high ratio of TMG/HMDS. To investigate the effect of TMG flow rate, various amounts of TMG (0.5 - 5sccm) were added during SiC deposition. Below 0.5 sccm of TMG flow rate, the SiC film showed epitaxial growth, observed by TEM and XRD. However, with an increasing flow rate of TMG above 1 sccm, the XRD peak of 3C-SiC becomes smaller and slightly shifted. At 5 sccm, the film was polycrystalline possibly implying that the SiC lattice is being strained gradually with TMG addition. It is also observed by AFM that, at the initial stages of growth, nucleation is much facilitated with the addition of TMG. The deposition rate with the addition of TMG at 1200°C is about 650 nm/hr, which is much faster than the rate without TMG addition (480 nm/hr). Thus, it is believed that TMG addition has a positive effect on the nucleation and HMDS decomposition during deposition. Also, with the addition of a small amount of Ar+10%HCl during growth, one-step deposition was possible helped by stress release due to void formation at the SiC/Si interface.

Wide Gan Stripes by Lateral Growth in Metalorganic Vapor Phase Epitaxy

AbstractWe investigated the growth conditions for enhancing epitaxial lateral overgrowth (ELO) of GaN stripes selectively grown by low-pressure metalorganic vapor phase epitaxy. The ELO was enhanced for GaN <1100> stripes and with a small trimethylgallium flow-rate. This tendency did not depend on mask materials. The cross-sectional shape of the GaN <1100> stripes was trapezoidal for SiO2 masks, and rectangular for silicon nitride (SiN2) masks in a certain growth condition. A low dislocation density in the ELO region was obtained not only for the SiO2 masks but also for the SiN2 masks.

Growth mechanisms in excimer laser photolytic deposition of gallium nitride at 500°C

The mechanisms of controlling laser-induced chemical vapour deposition of GaN at substrate temperatures between 350 and 650°C have been investigated. Ultraviolet (193 nm) photolytic decomposition of trimethylgallium (TMGa) and ammonia (NH 3) precursors was examined in this range. Laser-induced fluorescence studies support the view that the dissociated intermediate fragments GaCH 3 and NH are the reacting species in GaN film formation, irrespective of substrate temperature. It was found that two crystal phases coexist in films grown at substrate temperatures below 500°C, wurtzite crystal structure with (0002) orientation forms at substrate temperatures above 500°C. The growth rate increases with both NH 3 TMGa ratio, and TMGa flow rate, while the temperature dependence shows a thermal activation energy of 0.2 eV which is smaller by a factor of five than that of films prepared by conventional thermal CVD. The large NH 3 TMGa ratios needed to achieve stoichiometry are interpreted in terms of the two-photon dissociation cross section of NH 3.

AlGaAs/GaAs light-emitting diode on a Si substrate with a self-formed GaAs islands active region grown by droplet epitaxy

We report the preliminary results on self-formed GaAs islands grown on the GaAs/Si substrate by metalorganic chemical vapor deposition using droplet epitaxy. Atomic force microscope observation shows that the GaAs islands exhibit a conical shape with heights of 90–170 nm, diameters of 600–750 nm, and densities of 107 cm−2, which are controlled by the trimethylgallium flow rate. In addition, an AlGaAs/GaAs light-emitting diode (LED) on Si with a self-formed GaAs island active region was fabricated by the use of this technique. The LED was operated up to 27 μW at 190 mA under direct current conditions at room temperature.

Lateral Growth Process of GaAs over Tungsten Gratings by Metalorganic Chemical Vapor Deposition

Lateral epitaxial growth of over tungsten gratings with 5 μm wide lines and spaces on (001) substrates is performed using metalorganic chemical vapor deposition. A study is made of the dependence of facet shapes and growth rates of the overgrown layers on grating direction, growth temperature, and arsine and trimethylgallium (TMG) flow rates. From the perspective of crystallography, all the facets observed in the overgrown layers were found to be classified into four individual groups: {110}, {111}As, {1̅12}As, and {113}Ga faces. The opening direction on the (001) substrate surface is found to be the most essential parameter for determining the crystallographic planes of the facets. Other important controlling parameters for the facet formation are the growth temperature and partial pressure of. The partial pressure of TMG has no influence on the faceting growth. On the other hand, the overall growth rate of the overgrown layer is limited only by the TMG flow rate. These results can be qualitatively explained by the Langmuir‐Rideal model.

GaAs Growth Using TMG and AsCl3

A new vapor‐phase epitaxial (VPE) technique using trimethylgallium (TMG) and arsenic trichloride has been developed. This VPE is free from the source instability in chloride VPE and fatally toxic arsine in hydride and metalorganic VPE. The growth reaction is based on the gallium chloride transport method. Growth rates of 300–4000 Å/min were obtained at growth temperatures between 650° and 780°C. At III/V ratios below 2.3, the growth rate increased as the TMG flow rate increased and the flow rate decreased. The growth rate was independent of the temperature in the gas mixing region of the reactor. High purity with a 77 K mobility of 36,000 cm2/Vs was obtained.

Low Temperature Plasma‐Enhanced Epitaxy of GaAs

Low temperature (⩽450°C) deposition of single‐crystal using a new plasma‐enhanced MO‐CVD technique is reported. In this technique, plasma is created by a dc potential and the substrate is not directly exposed to the plasma. Deposition of was achieved at extremely low plasma power (0.3–0.5 W/cm2) using trimethylgallium (TMGa) and arsine (or trimethylarsenic) reactants. The resulting epitaxial films show excellent surface morphology and thickness uniformity over a large area substrate. A linear dependence of growth rate upon TMGa concentration was observed with a typical growth rate of 0.1 μm/min for a TMGa flow rate of 15 ml/min. Undoped films were found to be n‐type with a room temperature mobility in the range of 5200 cm2 V−1 · s−1. Measurements on Schottky barrier devices fabricated on n/n+ layers show uniform impurity doping profiles. Temperature dependence of the diode capacitance indicates a density of deep trapping centers as low as .