Optimization of ion-atomic beam source for deposition of GaN ultrathin films

Abstract

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Low temperature selective growth of GaN single crystals on pre-patterned Si substrates

“…On the other hand, at lower (or zero) fluxes of hyperthermal nitrogen ions, surplus Ga adatoms diffuse along the surface and form Ga droplets at energetically favorable sites, e.g. at terrace edges of the Si(111)7 × 7 surface as reported in [23] and shown in Fig. 2c.…”

“…The substrates were exposed to a gallium atom beam from an effusion cell -(Omicron) and to a ultra-low energy nitrogen ion beam (50 eV) produced from nitrogen gas (99.9999%) by a home-made ion-atomic beam source being a combination of an effusion cell and electron impact ion-beam source being 13 cm away from the sample. The detailed design of the source was described elsewhere [22,23] ). The experimental setup is schematically shown in Fig.…”

“…To synthesize GaN films at lower temperatures (≈300°C), a combination of Ga atomic beam evaporation (in principle an identical method to molecular beam epitaxy -MBE) and direct ion beam deposi tion have been successfully used in our group [22]. In this method, similarly to [23], nitrogen ion beams of hyperthermal energies (below 100 eV) provide activation energy needed for synthesis of GaN and so lower substrate temperatures can be used. An important advantage of the combination of the direct Ion beam deposition and "classical" MBE technique over MOCVD is the mutual independence of both processes and compatibility with UHV conditions enabling application of a wider spectrum of in-situ analytical methods.…”

Mechanism and Suppression of Physisorbed-Water-Caused Hysteresis in Graphene FET Sensors

“…A large-area polycrystalline graphene layer was grown by a standard low-pressure chemical vapor deposition (CVD) method . To get a high-quality graphene layer, an ultrasmooth copper foil was used for graphene growth. − The growth procedure consisted of three technology steps: (1) copper annealing at a hydrogen flow (4 sccm, 10 Pa, 1000 °C, 30 min) to remove air adsorbates, (2) methane introduction (40 sccm, 70 Pa, 1000 °C, 30 min) to grow graphene in a H 2 /CH 4 mixture, and (3) bottom-side copper cleaning in oxygen–argon plasma (20% O 2 , 80% Ar, 2 min) to remove graphene from this side, while that one from the top side was protected from plasma etching by a spin-coated poly­(methyl methacrylate) (PMMA) layer.…”

Low temperature 2D GaN growth on Si(111) 7 × 7 assisted by hyperthermal nitrogen ions

“…On top of that, the precise control of the deposition rate enables us to achieve the required nanostructure size. We propose to adopt DE for low-temperature synthesis of GaN by using a special ion-atom beam source developed in our group and capable of working under UHV conditions [18] [19]. In this way, a low-temperature droplet epitaxy (LTDE) method under the welldefined conditions was utilized for fabrication of planar GaN triangular nanocrystals with a crystal structure different from wurtzite GaN and qualitatively and quantitatively corresponding to 2D GaN nanocrystals.…”