Sun Transactions Semiconductor Manufacturing 25 494 (original) (raw)
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Direct formation of large-area carbon thin films on gallium nitride by chemical vapor deposition without metallic catalysts is demonstrated. A high flow of ammonia is used to stabilize the surface of the GaN (0001)/sapphire substrate during the deposition at 950°C. Various characterization methods verify that the synthesized thin films are largely sp 2 bonded, macroscopically uniform, and electrically conducting. The carbon thin films possess optical transparencies comparable to that of exfoliated graphene. This paper offers a viable route toward the use of carbon-based materials for future transparent electrodes in III-nitride optoelectronics, such as GaN-based light emitting diodes and laser diodes. . His major is semiconductor materials and devices, particularly, in low-dimensional structure growth and nanodevice fabrication/characterization. He is the Coordinator of this paper. He specialized in GaAs-, InP-, and Si-based semiconductors, and in oxide-based dielectrics (SiO 2 , Al 2 O 3 , and HfO 2 ). He has designed and studied ballistic and quantum devices, as well as analog and digital nanoelectronic circuitry. He has published about 60 articles with a Hirsch index of 10. He is the first author or corresponding author of 21 papers that are published in journals covered by the scientific citation index, such as the IEEE Electron Device Letters, Applied Physics Letters, Nanotechnology, and others. Currently, he is with the
One-step graphene coating of heteroepitaxial GaN films
Nanotechnology, 2012
Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ∼0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.
Carbon doping of cubic GaN under gallium‐rich growth conditions
physica status solidi (c), 2003
Successful p-type doping of cubic GaN by carbon grown under Ga-rich conditions is reported with maximum hole concentration of 6 × 10 18 cm-3 and hole mobility of 19 cm 2 /Vs at room temperature, respectively. Cubic GaN : C was grown by rf-plasma assisted molecular beam epitaxy (MBE) on a semiinsulating GaAs (001) substrate (3 inches wafer). C-doping of the c-GaN was achieved by e-beam evaporation of a graphite rode with an C-flux of 1 × 10 12 cm-2 s-1. Optical microscopy, Hall-effect measurements and room temperature photoluminescence were used for the investigation of the morphological, electrical and optical properties of cubic GaN : C. Under Ga-rich growth conditions most part of the carbon atoms were incorporated substitutially on N-site giving p-type conductivity. Our results verify that effective p-type doping of c-GaN can be achieved under Ga-rich growth conditions.
Optical and x-ray diffraction studies on the incorporation of carbon as a dopant in cubic GaN
2003
We performed optical and x-ray diffraction experiments on carbon doped cubic-GaN samples, deposited by plasma-assisted molecular beam epitaxy on ͑001͒ GaAs substrates, for various carbon concentrations. The samples were studied by Raman, photoluminescence, and photoluminescence excitation spectroscopies. These techniques give some insight into the mechanism of carbon incorporation in the material. Detailed analysis of these spectra leads to a picture in which carbon initially enters into N vacancies producing a marked improvement in the crystalline properties of the material. At higher concentrations it also begins to enter interstitially and form C complexes, with a consequent decrease of crystalline quality. This increase and later decrease of crystalline quality of our samples with the addition of C were also detectable in x-ray diffraction scans. A model calculation of the localized vibrations of the C atom in the GaN lattice allows for the interpretation of a feature in the Raman spectrum of some samples, which reinforces this view.
Growth and characterization of gallium nitride nanocrystals on carbon nanotubes
Journal of Crystal Growth, 2008
Gallium nitride (GaN) nanocrystals have been grown on the tip of aligned carbon nanotubes (CNTs) substrate by chemical vapour transport method. It was found that GaN nanocrystals were formed on the tip and outermost shells of CNT bundles in the form of nanorods. X-ray diffraction (XRD) pattern shows that the GaN nanocrystals are of wurtzite structure. Scanning electron microscopy (SEM) images show the nanocrystals ranging from 10 to 100 nm has been realized under different experimental conditions exhibiting different shapes. Heterojunctions between CNTs and GaN nanocrystals, depending on their unique property, can be utilized for nanosized optical and optoelectronic devices. UV-optical absorption spectrum show the band edge at 360 nm, which is related to the bandgap energy of GaN. r
Metal-Free Graphene as Transparent Electrode for GaN-Based Light-Emitters
Japanese Journal of Applied Physics, 2013
Graphene contacts to p-GaN are considered as an alternative to indium-tin-oxide transparent electrodes in GaN based verticalcavity surface-emitting lasers (VCSELs). Contact properties were investigated on light-emitting diode and p-GaN test structures, where dielectric apertures were used to eliminate the influence of the metal pads used to bias the contacts. Using single layer graphene we were able to operate light emitting diodes with current densities of 300 A/cm 2. Addition of a second layer of graphene increased the maximum bias current to 1 kA/cm 2. However, the contacts are non-linear and cannot withstand high current densities for a long time. The results are promising but further investigation and improvement is needed for graphene to be a viable alternative to indium-tin-oxide for blue VCSELs.
Near band-edge optical properties of cubic GaN with and without carbon doping
Microelectronics Journal, 2004
We report the results of studying the optical properties of cubic GaN thin films with photoluminescence and photoluminescence excitation spectroscopies. The films are deposited by plasma-assisted molecular beam epitaxy on GaAs (001) substrates, with and without intentional doping with carbon atoms (p-type doping). The evolution of the optical spectra of the C-doped samples is consistent with a picture in which carbon enters into N-vacancies at low concentrations, producing a marked improvement in the crystalline properties of the material. At higher concentrations it begins to form complexes, possibly due to interstitial occupation. The temperature dependence on the absorption edge of the doped material is also measured and is analyzed with standard theoretical models.