Self-organized growth of zero-, one-, and two-dimensional nanoscale SiC structures by oxygen-enhanced hydrogen plasma sputtering

Lee J., Ren H., Sugou S., Masumoto Y.

Our study of GaAs growth over self-assembled In0.5Ga0.5As quantum dots grown by metalorganic vapor-phase epitaxy showed that GaAs capping layer surface morphology at the onset strongly depended on temperature. Incompletely capped In0.5Ga0.5As islands were elongated toward [110], indicating anisotropy in intermixing. During higher-temperature growth interruption, islands show craters in quantum dot centers. Craters become hexagonal holes whose depth matches GaAs capping layer thickness. Postannealing photoluminescence spectra show no peak corresponding to overly large quantum dot radiation, indicating that growth interruption after capping layer formation at a certain thickness eliminates overly large quantum dots.

Sun Y., Miyasato T., Sonoda N.

The excess of C atoms diffused into the (111) Si substrate during the growth of the cubic SiC films are detected by Auger electron spectroscopy, infrared absorption, and x-ray photoelectron spectroscopy. The diffusion coefficient of the C atoms into the Si substrate at 820 °C is 8.4×10−15 cm2 s−1, which is close to the value of the diffusion of the C atoms into Si crystal using solid source. The C atoms mainly occupy substitutional sites in the Si substrate when the substrate temperature is below 750 °C, and both substitutional and nonsubstitutional sites when it is above 820 °C.

Nabetani Y., Sawada K., Furukawa Y., Wakahara A., Noda S., Sasaki A.

InP islands are grown on a GaP substrate by organometallic vapor-phase epitaxy using tertiarybutylphosphine and characterized by atomic force microscopy and transmission electron microscopy. InP grows two-dimensionally at first and then begins to grow three-dimensionally at 1.2 ML. The island sizes are 400 nm in lateral dimension and 100 nm in height at 1.8 ML with the growth temperature of 550°C. The island density increases with increasing InP layer thickness while the island size remains the same. Misfit dislocations are observed in the islands at 1.8 ML growth. By lowering growth temperature to 420°C, the island size becomes as small as 40 nm in the lateral direction, moreover smaller islands without dislocations are obtained. The formation mechanism of large islands is discussed.

Wankerl A., Schremer A.T., Shealy J.R.

We report on the selective area growth of InAs quantum dots on GaAs by ultraviolet (UV) laser stimulated organometallic vapor phase epitaxy. At the low substrate temperature of 435 °C, exposure to a 248.2 nm continuous wave laser beam enhances the InAs growth rate by approximately 30%, causing the transition from two-dimensional (2D) to 3D growth mode to occur in the laser stimulated region only. Photoluminescence spectra from the UV laser stimulated growth region show both wetting layer and quantum dot luminescence, whereas only the wetting layer peak is present in the spectra from the dark grown regions. A photoluminescence map shows good spatial agreement between the region exhibiting quantum dot luminescence and the UV stimulated spot size. Since no quantum dot peak shifts are detected, but the luminescence intensity increases towards the center of the region stimulated with the Gaussian UV beam, we conclude that the island density rather than island size distribution is influenced by the UV intensity.

Widmann F., Daudin B., Feuillet G., Samson Y., Rouvière J.L., Pelekanos N.

Self-organized GaN islands of nanometric scale were fabricated by controlling the Stranski–Krastanov growth mode of GaN deposited by molecular beam epitaxy on AlN. Evidence for ripening of dots under vacuum has been observed, resulting in changes in dot size distribution. We also show that in superlattice samples, consisting of multiple layers of GaN islands separated by AlN, the GaN islands are vertically correlated provided that the AlN layer thickness remains small enough. The luminescence peak of GaN dots is blueshifted with respect to bulk emission and its intensity does not vary with temperature, both effects demonstrating the strongly zero-dimensional character of these nanostructures.

Shklyaev A.A., Shibata M., Ichikawa M.

Three-dimensional Ge islands between 15 and 200 nm in size were found to grow only on Si(111) surface windows in ultrathin SiO2 film after Ge deposition and subsequent SiO2 decomposition. The size of Ge islands gradually decreased as the Ge thickness decreased. Pseudomorphic two-dimensional Ge layers with the 5×5 structure formed in surrounding areas of the windows. The windows were produced by selective thermal SiO2 decomposition induced by focused electron beam irradiation. These results suggest a new technique for nanometer-scale Ge island fabrication at given points on Si surfaces.

Fissel A., Pfennighaus K., Richter W.

The growth kinetics of Si dots grown on 6H-SiC(0001) by molecular beam epitaxy were studied in real time by reflection high-energy electron diffraction. The critical thickness for the Stranski–Krastanov growth mode transition was found to be kinetically delayed leading to a gradual decrease of this thickness with increasing temperature (T). At T<625 °C and coverages below the critical thickness, a post-deposition evolution of dots is clearly established. The dot growth process is, under these conditions, mainly determined by the mass transfer out of the two-dimensional layer towards the Si dots. The dots grown on top of a 1 monolayer (ML) thick wetting layer are quantum sized with typical dimensions of 5–6 nm in height and 20–30 nm in diameter after a long post-deposition evolution times at 2–3 ML coverages. Above 625 °C and coverages above the critical thickness, the dot growth is only determined by surface-diffusion kinetics resulting in the growth of larger dots.

Han Y., Kim Y., Lee J.

In order to investigate the effects of argon and oxygen on diamond synthesis, the behaviors of diamond deposition using microwave plasma chemical vapor deposition method have been studied by varying the concentrations of argon and oxygen in the methane-hydrogen gas mixture. Diamond films were deposited on silicon wafer under the conditions of substrate temperatures: 1073 ∼ 1173 K, total reaction pressure: 5333 Pa (40 Torr), methane concentrations: 0.5 ∼ 5.0%, and they were characterized by scanning electron microscopy, Raman spectroscopy and optical emission spectroscopy. The deposition rates of diamond films were enhanced by adding argon into the methane-hydrogen system, but nondiamond carbon phases in the films also increased. It resulted from the increase of hydrocarbon radicals in the plasma. As oxygen was added, the quality of deposited diamond films was improved due to the decrease of C2 radicals and increase of OH radicals in the plasma. Simultaneous addition of 0.3% oxygen and 20% argon has been able to effectively suppress the formation of nondiamond carbon components and increase the deposition rate of diamond films. It appears that the ionized argon (Ar+) and excited argon atoms (Ar*) may activate the various chemical species and promote the reactions between the gas phase species and oxygen in the plasma.

Hasegawa H., Fujikura H.

In view of applications to next-generation electronics based on quantum devices, this paper presents and discusses the results of a systematic study recently done by the authors' group on the growth conditions, characterization and device application of InP-based In0.52Al0.48As/In0.53Ga0.47As quantum wires and dots formed by selective M13E growth on mesa-patterned (001) InP substrates. First, selective MBE growth experiments of InAlAs/InGaAs wire and dot structures on patterned (001) InP substrates are discussed generally. Then, particular attention is paid to successful growth conditions and properties of (110) oriented InAlAs/InGaAs ridge quantum wires (QWRs), including the effect of misorientation of mesa stripes. Finally, device related issues such as successful surface passivation by a technique using a silicon interface control layer (Si ICL) and electronic transport characterization by QWR transistors are discussed. The QWR transistor exhibited excellent gate-controlled one-dimensional transport with the appearance of clear conductance oscillations near pinch-off, visible up to about 50K.

Sun Y., Miyasato T., Wigmore J.K., Sonoda N., Watari Y.

Detailed characterization using x-ray diffractometry, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and Auger infrared and focused ion-beam spectroscopy, was carried out on cubic SiC films grown on single-crystal (100) Si substrates by reactive hydrogen plasma sputtering over a range of growth temperatures between 700 and 1000 °C. It was found that the first few deposited atomic layers were always amorphous. The subsequent SiC films showed well-defined (111) growth at the lowest temperatures, becoming randomly oriented by 1000 °C. The measured C:Si ratio was always >1, and varied with depth inside a film and also with temperature. At higher temperatures, the presence of “hollow voids” was observed, our data being consistent with their formation by outdiffusion of Si atoms from the substrate through the SiC layer. Associated with the hollow voids we observed the presence of a porous, highly C-rich region at the Si–SiC interface. We propose that this was due to diffusion of C from the SiC film into the voids themselves.

Gölz A.

The initial stages of SiC–SiO2 interface formation by low temperature (300 °C) remote plasma assisted oxidation (RPAO) on flat and vicinal 6H SiC(0001) wafers with Si faces have been studied by on-line Auger electron spectroscopy (AES). Changes in AES spectral features associated with Si–C and Si–O bonds are readily evident as oxidation progresses; however, there are no detectable AES features that can be attributed to C–O bonds. Initial oxidation rates as determined from AES data are greater for vicinal wafers than for flat wafers paralleling results for RPAO oxidation of Si. Devices fabricated on vicinal SiC wafers require an 1150 °C anneal in an H2 containing ambient to reduce defect densities from the 1013 to 1011 cm−2 range, consistent with termination of C atom step edge dangling bonds by H atoms. Devices prepared by thermal oxidation also require a 1150 °C anneal in H2 even though silicon oxycarbide regions with C–O bonds are formed in a transition region at the SiC–SiO2 interfaces.

Ledentsov N.N.

Nobuo Sonoda N.S., Yong Sun Y.S., Tatsuro Miyasato T.M.

Highly oriented β-SiC film is prepared on (100) Si substrate at 800°C by reactive hydrogen plasma sputtering of a ceramic SiC target. The highly oriented β-SiC film can be grown on (100) Si substrate without void formation at the SiC film/Si interface. Hydrogen plasma etching of the growing film plays an important role in the growth of the oriented β-SiC films. Voids at the SiC film/Si interface are formed at a temperature of about 800°C due to the reaction of SiC film with Si substrate. Also, a thin amorphous buffer layer of 5 nm thickness is formed at the SiC film/Si interface. The results of this study indicate that the buffer layer can be eliminated by a suitable surface treatment of Si substrate before film growth.

Miyata K., Kobashi K.

Air oxidation of undoped and B-doped polycrystalline diamond films was investigated at temperatures between 500 and 700 °C. Diamond (111) facets were etched for both undoped and B-doped films after 1 h at 700 °C. The etching rate of (111) facet due to oxidation was approximately 50% lower by B-doping of 1 × 1019 cm−3, presumably because of the decrease of sp 2 bands and lattice defects that were identified by Raman and photoluminescence spectroscopy. X-ray photoelectron and electron energy loss spectroscopy revealed that by the high temperature treatment, the diamond surface was initially converted into graphite and successively etched by oxygen.

Petroff P.M., DenBaars S.P.

Abstract In this paper, we review our latest developments on the growth and properties of self-assembling quantum dot structures. The self-assembling growth technique which was initially developed using molecular beam epitaxy (MBE), has now been extended to metalorganic chemical vapor deposition (MOCVD). The paper first presents structural results based on atomic force and transmission electron microscopy studies of the quantum dot arrays which were obtained by MBE and MOCVD growth. From the detailed structural analysis we have observed that the formation of coherently strained dots of InAs, InAlAs, and InP dots on various cladding layer surfaces. MBE growth of InAs self-assembled dots has achieved the smallest size distribution, with dots as small as 12nm in diameter. For the MOCVD growth of InP dots we have found that the surface morphology and growth temperature of lower cladding layer growth has a profound influence on island size and density. Recent results on the optical and transport properties of the MBE grown self-assembling dot (SAD) arrays are also presented.

Medvid’ A., Mychko A., Onufrievs P.

Experimentally observed self-organization of a 2D lattice on the surface of Ge single crystal after irradiation by pulsed Nd:YAG laser is reported. The 2D lattice consists of nano-size hills arranged in a pattern of C6i point group symmetry and is characterized by translational symmetry with the period of [email protected] Calculations of time-dependent distribution of temperature in the bulk of the Ge sample are presented to explain the phenomenon. The calculations show that overheating of the crystal lattice occurs at laser radiation intensities exceeding 30MW/cm^2. According to synergetic ideas, the presence of the non-equilibrium liquid phase of Ge and a huge gradient of temperature (~3x10^8K/m) can lead to self-organization of the 2D lattice similar to Benard cells.

Cheng Q.J., Long J.D., Xu S.

Self-assembled SiC quantum dots (QDs) are grown on Si substrates at a low substrate temperature of 400°C by means of low-frequency, inductively coupled plasma assisted rf magnetron sputtering from a sintered SiC target in a reactive Ar+H2 gas mixture. Effects of SiC target power and working gas pressure on the surface morphology and structural properties of SiC QDs are investigated. The growth dynamics of the QDs obeys cubic root-law behavior. With the increase of SiC target power, the growth rate increases greatly, resulting in nonuniform surface morphology and higher intensity of Si–C transmittance band. Scanning electron microscopy shows that (i) at pressure below 1Pa, SiC quantum dots are highly uniform and the average size of quantum dots increases with the increase of pressure; (ii) at pressure above 1Pa, SiC quantum dots are nonuniform, and the size of quantum dots decreases with the increase of pressure. These behaviors are explained by the scattering effects and the surface mobility of the sputtered atoms. X-ray photoelectron and Fourier transform infrared spectroscopic results show that the predominant bonds are Si–C and the elemental composition of Si and C atoms is near stoichiometric.

Cheng Q., Xu S., Long J., Ostrikov K.(.

Despite major advances in the fabrication and characterization of SiC and related materials, there has been no convincing evidence of the synthesis of nanodevice-quality nanoislanded SiC films at low, ultralarge scale integration technology–compatible process temperatures. The authors report on a low-temperature (400°C) plasma-assisted rf magnetron sputtering deposition of high-quality nanocrystalline SiC films made of uniform-size nanoislands that almost completely cover the Si(100) surface. These nanoislands are chemically pure, highly stoichiometric, have a typical size of 20–35nm, and contain small (∼5nm) nanocrystalline inclusions. The properties of nanocrystalline SiC films can be effectively controlled by the plasma parameters.

He-Lin W., Xi-Xiang Z., Han-Chen H.

Uniformly distributed indium hillocks are grown on silicon substrates by dc magnetron sputtering. The morphologies and the microstructures have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). From the TEM and SEM images, we find that, at the earlier stage, the grain coalescent process dominates. This coalescent process induces a larger compressive stress. We believe that the drive force for hillock growth comes from this compressive stress. Under this compressive stress, the grain locating in the middle of several grains are extruded from these grains, and then a hillock forms with the increasing deposition time. For low melting point and high diffusion coefficient metal, such as bismuth and indium, this spontaneous-hillock growth mechanism can be used to fabricate well aligned nanostructures.

Medvid A., Fedorenko L., Lytvyn P.M., Yusupov N.

Medvid’ A., Fedorenko L., Berzina B., Yusupov N., Lytvyn P.

Formation of nanostructures on a surface of 6H–SiC:N, B under irradiation by the N2 pulsed laser was found and studied. The nanostructures have a shape of a hill, and arise along the circular line around the focussed spot. We propose the following model for the explanation of the formation of nano-hills. The laser irradiation creates a liquid phase in the bulk under a thin solid state layer. The pressure of laser radiation (LR) together with the pressure of the liquid phase result in a bulging of the material on the surface. The results of experimental studies of the irradiated surface by Atomic Force Microscope (AFM) and Friction Force Microscope (FFM) allow us to conclude that the concentration of nitrogen in nano-hills is bigger compared with that of the unirradiated crystal. The increase of the nitrogen concentration in the hills can be explained by presence of the temperature gradient field. The 6H–SiC samples contain both N and B atoms with strongly different covalent radii, in the temperature gradient field atoms of N move towards the irradiated surface, while atoms of B—into the bulk of the crystal. The obtained results are explained by presence of the Thermogradient effect (TGE).

Liu J.W., Zhong D.Y., Xie F.Q., Sun M., Wang E.G., Liu W.X.

SiC nanofibers were synthesized using carbon nanotubes as templates by depositing silicon on the templates of carbon nanotubers and then annealing the as-deposited specimen at 1200 °C for 15 min with a dc self-heating method. The analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering and scanning electron microscopy (SEM) were performed for the as-annealed specimen. The measurement results show that the SiC phase (SiC nanofibers) and the graphite phase (carbon nanotubers) coexist in the specimen, so the coaxial structure of the SiC nanofibers and the carbon nanotubes is considered to exist.

Yong Sun Y.S., Kenta Kirimoto K.K., Tatsuro Miyasato T.M.

Nanoscale cubic SiC particle film is grown on Si substrate by hydrogen plasma sputtering of a SiC target. Before the film growth an amorphous SiC buffer layer of about 100 nm thickness is prepared on the Si substrate. By annealing the buffer layer in hydrogen atmosphere, the nanoscale cubic SiC particle film can be grown on the buffer layer on Si. Particle size, composition and crystallinity of the film depend on the composition, the crystallinity and the surface morphology of the buffer layer.