Sb Surfactant Research Articles

Sb segregation in Si and SiGe: effect on the growth of self-organised Ge dots

The segregation and incorporation coefficients of antimony (Sb) in Si 1− x Ge x buried doped layers were investigated simultaneously using specific temperature sequences. We first showed an exponential kinetic evolution of Sb surface segregation in Si. In contrast such an evolution could not be observed in Si 1− x Ge x because of the Sb thermal desorption, at growth temperatures of 550°C. We also showed an increased surface segregation increasing with the partial Ge concentration in Si 1− x Ge x alloys, which was explained by a decrease of the kinetic barrier for Sb atoms mobility. It was, therefore, possible to determine the growth conditions to obtain a Si 1− x Ge x doped layer with a controlled incorporation level and a negligible surface segregation obtained by the thermal desorption of the Sb surface coverage. Finally, using Sb surfactant mediated growth, we found Ge dots with lateral sizes reduced by a factor of 2.8 and density multiplied by a factor of four as compared to dots directly deposited on Si(001).

Sb-mediated Ge growth on singular and vicinal Si(001) surfaces: A surface optical characterization study

In this work, we apply Raman spectroscopy (RS) and spectroscopic ellipsometry (SE) to surfactant mediated growth (SMG) of Ge on Si(001) surfaces. Under molecular-beam epitaxy conditions, a growth temperature of $400\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and in the absence of a predeposited surfactant (Sb) monolayer, we show that SE can be used to determine the Stranski-Krastanov critical thickness for island formation. In the presence of a predeposited Sb monolayer, SE predicts that layer-by-layer growth is possible up to a Ge coverage of 20 monolayers (MLs). However, no evidence of relaxation through dislocation formation, known to exist in this coverage regime, could be detected. With RS, we present one of the first studies of Sb mediated growth on a vicinal Si(001) substrate. Two Sb surface related phonon peaks are identified, one associated with Sb dimers bonded to the Si(001) substrate $(130.5 {\mathrm{cm}}^{\ensuremath{-}1}),$ the other with Sb dimers on the grown Ge epilayer $(141 {\mathrm{cm}}^{\ensuremath{-}1}).$ The former disappears and the latter appears gradually with increased Ge coverage up to 3.5 MLs. This indicates that surfactant exchange occurs differently on vicinal Si(001) than on singular Si(001), where exchange has been shown to be complete by deposition of between 0.5--1.0 monolayer (ML). To explain this difference, step bunching must occur during the initial stages of growth on vicinal Si (001), leading to areas of preferred growth on the surface. At a higher Ge coverage of 20 MLs, theoretical predictions of the Raman shift for a strained pseudomorphically grown Ge layer show good agreement with the Raman data presented. This demonstrates that even at 20 ML coverage, some areas of unrelaxed Ge must still exist, pointing to inhomogeneities within the Ge epilayer, as predicted by our model for SMG on a step bunched Si(001) substrate.

Experimental study of a surfactant-assisted SiGe graded layer and a symmetrically strained Si/Ge superlattice for thermoelectric applications

A method to grow high-quality SiGe graded buffer layer is presented. The main concept of the method is to use Sb as a surfactant when growing SiGe graded layers. Compared with a Si0.5Ge0.5 graded sample without Sb surfactant, the Sb-assisted Si0.5Ge0.5 graded layer has much smoother surface and a significantly lower threading dislocation density. Thermal conductivity of a symmetrically strained Si/Ge superlattice grown on Sb-assisted Si0.5Ge0.5 graded layer is also presented.

Composition and morphology of SiGe alloys grown on Si(1 0 0) using an Sb surfactant

The effect of using a surfactant during SiGe alloy growth was investigated. Previous studies of surfactant-assisted growth have focused on the properties of pure Ge films grown on Si or on pure Si grown after Ge. Using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), we have studied the Ge compositional profile and morphology of SiGe alloys grown by molecular-beam epitaxy on Si (1 0 0) with an Sb surfactant. Using XPS, we have found that Ge segregation occurs at the start of alloy growth in the presence of up to 1 monolayer (ML) of Sb surface coverage but that the amount of Ge segregation is less than without Sb. We did find, however, that 0.75 ML of Sb after alloy growth can completely suppresses Ge segregation into a subsequent Si capping layer. Using XRD and TEM, we have found that SiGe films grown with 0.8 ML of Sb did not relax appreciably but did produce a non-planar surface morphology having an abrupt chemical interface between the alloy layer and the capping layer. We also found that the use of 0.8 ML of Sb resulted in compositional fluctuations within the alloy. We propose that the use of the Sb surfactant resulted in a separation of Si and Ge during the growth of the alloy layer producing the observed Ge segregation, surface morphology and compositional fluctuations.

Surfactant controlled growth of GaInP by organometallic vapor phase epitaxy

The effect of the surfactant Sb has been studied for GaInP semiconductor alloys grown by organometallic vapor phase epitaxy. Dramatic changes in the optical and electrical properties of GaInP with CuPt ordering have been observed. A small concentration of triethylantimony (TESb) in the vapor is found to cause Sb to accumulate at the surface. In situ surface photoabsorption analysis indicates that Sb changes the surface bonding by replacing the [1̄10] P dimers that are responsible for the formation of the CuPt structure during growth with [1̄10] Sb dimers. As a result, the degree of order for the GaInP layers is decreased, as shown by transmission electron diffraction studies. The 20 K photoluminescence spectra show a 131 meV peak energy increase for GaInP layers grown on vicinal substrates when a small amount of Sb [Sb/P(v)=4×10−4] is added to the system during growth. The use of surfactants to control specific properties of materials is expected to be a powerful tool for producing complex structures. In this article, the growth of heterostructures by modulating the Sb concentration in the vapor is demonstrated.

The use of a surfactant (Sb) to induce triple period ordering in GaInP

A surfactant is used to induce an ordered structure in an epitaxial layer. The addition of small amounts of triethylantimony during the organometallic vapor phase epitaxy growth of GaInP on (001) GaAs substrates is shown to remove CuPt ordering with a resultant increase in band gap energy. Increasing the concentration of Sb in the vapor beyond a critical Sb to P ratio [Sb/P(v)] of 4×10−4 gives a reversal of this behavior. The band gap energy is observed to decrease by 50 meV at a concentration of Sb/P(v)=1.6×10−3, coincident with the formation of an ordered phase with a period triple the normal lattice spacing along the [111] and [1̄1̄1] directions. The formation of this new ordered structure is believed to be related to high concentrations of Sb on the surface, which leads to a change in the surface reconstruction from (2×4)-like to (2×3)-like, as indicated by surface photoabsorption performed in situ.

Ｓｉ基板上に製作したＡｕ／ｎ‐Ｇｅショットキー障壁ダイオードの電気的特性

We have grown a Ge layer on Si (100) substrate and fabricated Au/n-Ge Schottky barrier diode. The Ge layer was grown by solid source molecular beam epitaxy (MBE). The growth procedure consisted of epitaxial growth of Ge layer using Sb as a surface-active-agent (surfactant) and high temperature (620°C) post growth annealing. The crystal structure was evaluated by reflection high-energy electron diffraction (RHEED) and the surface morphology was evaluated by atomic force microscopy (AFM). The RHEED pattern indicated the epitaxial growth of the Ge layer. Examination by AFM revealed some pits on the surface which were considered to be related to dislocation within the sample. The Sb surfactant worked as the donor in the epitaxial layer after the high temperature post growth annealing. The Sb concentration at the surface of the sample was 3 × 1017 cm-3. The fabricated device showed the diode characteristics. The leakage current under the reverse bias condition was high and the ideal factor was large. It would seem that the reasons for the high leakage current and the large ideal factor were related to the pits on the surface of the sample.

Growing high-quality C 60 films by using Sb buffer layer

The structure and growth morphologies of C 60 films, prepared by pre-depositing a layer of surfactant Sb over NaCl(0 0 1) substrates with vacuum vapor deposition method, were studied by a transmission electron microscope. It was found that the structure and growth behavior of C 60 films is significantly affected by Sb and the substrate temperatures. The thickness of pre-deposited Sb film has a great effect on the quality of C 60 films, and the optimal thickness for high-quality C 60 film growth is about 0.5 nm. (1 1 1) oriented C 60 single-crystal films with large C 60 crystal grains were obtained when the substrate temperatures were kept at 170 and 185°C, respectively. Possible growth mechanisms of the Sb-buffered C 60 films are proposed.

Sb mediated C60 film growth on mica, Si, and glass substrates

The structure and growth morphology of Sb mediated C60 films, prepared by predepositing a layer of surfactant Sb over mica(001), Si(111), and glass substrates with the vacuum vapor deposition method, were studied along with pristine C60 films by an atomic force microscope. It was found that the growth behavior of C60 films was greatly affected by the substrate temperature. On the mica substrate, the average size of C60 crystal grains in Sb mediated C60 films was about two times larger than that in pristine C60 films. On Si and glass substrates, the predeposited Sb had no significant effect on the size of the C60 crystal grains, but made C60 films grow more easily especially at high substrate temperatures. Possible growth mechanisms of the Sb mediated C60 films are proposed.

A surfactant-mediated relaxed Si0.5Ge0.5 graded layer with a very low threading dislocation density and smooth surface

A method to grow a relaxed Si0.5Ge0.5 graded layer with a very smooth surface and a very low threading dislocation density using solid-source molecular-beam epitaxy is reported. This method included the use of Sb as a surfactant for the growth of a 2 μm compositionally graded SiGe buffer with the Ge concentration linearly graded from 0% to 50% followed by a 0.3 μm constant Si0.5Ge0.5 layer. The substrate temperature was kept at 510 °C during the growth. Both Raman scattering and x-ray diffraction were used to determine the Ge mole fraction and the degree of strain relaxation. Both x-ray reflectivity and atomic force microscopy measurements show a surface root mean square roughness of only 20 Å. The threading dislocation density was determined to be as low as 1.5×104 cm−2 as obtained by the Schimmel etch method. This study shows that the use of a Sb surfactant and low temperature growth is an effective method to fabricate high-quality graded buffer layers.

Strained Ge/Si(001) interface in the presence of Bi and Sb surfactants

Abstract The adsorption of Ge on the Bi/Si(001)2×5 surface (Bi saturation coverage of 0.7 ML) and on Sb/Si(001)2×1 (Sb saturation coverage of 0.9 ML), was investigated by core level photoemission spectroscopy. For the Bi/Si(001)2×5 interface, at submonolayer Ge coverage, the presence of a bulk component largely dominating the Ge 3d core level, demonstrates that the favorite adsorption sites are the Bi-terminated terraces, where the Ge–Bi site exchange takes place. At larger Ge coverage, in addition to the previous process, the occurrence of a pure Ge epitaxy on the bare fraction of the substrate is indicated by the presence of the 2×1 surface components in the Ge 3d core level. In the case of Sb/Si(001)2×1 interface, the Ge 3d shows a complete lack of surface components, which indicates the absence of dimerized Ge atoms at the top layer, and demonstrates that the Ge–Sb site exchange process has taken place on the whole Si(001) surface.

Low threshold InGaAsN/GaAs single quantum well lasers grown by molecular beam epitaxy using Sb surfactant

Long wavelength InGaAsN/GaAs single quantum well (SQW) laser diodes have been grown by solid source molecular beam epitaxy (MBE) using Sb as a surfactant. A record low threshold current density of 1.47 kA/cm2 and a quantum efficiency of 0.11 W/A are reported for broad area laser diodes (LDs) operating at a wavelength of 1.275 µm under pulsed operation at room temperature.

Surfactant-mediated epitaxy of Ge on Si: progress in growth and electrical characterization

Smooth, continuous, relaxed, and high quality Ge films have been grown on Si(111) using surfactant-mediated epitaxy (SME). Using high temperature SME we have reduced the Sb surfactant doping level by more than three orders of magnitude below the solid solubility. This enhanced surfactant segregation is attributed to the formation of an ordered (2×1)-Sb reconstruction on the Ge(111) growthfront. With increasing growth temperature the Sb incorporation decreases to 1×10 16cm −3 at 700°C. This low Sb doping concentration has been determined by electrical characterization. The electron Hall mobility varies strongly with the doping concentration. Record values of 3159 cm 2/Vs at 300 K suggest interesting potential of SME grown Ge films for future device applications. Capacitance voltage measurements on vertical p +n diodes show a uniform doping profile and are in good agreement with Hall measurements.

Sb mediated C60 thin film growth on mica

We studied the growth of C60 thin films on a layer of surfactant Sb which was predeposited on mica substrates with vacuum vapor deposition method. It was found that the growth behaviors of C60 films are significantly affected by the surfactant Sb and the substrate temperature. (112)- and (111)-oriented C60 single-crystal films with large C60 single crystals were obtained when the substrate temperatures were 200 and 215 °C, respectively. The growth mechanisms of the Sb mediated C60 films were attributed to the reduced surface diffusion rate of adsorbed C60 molecules and the lowered boundary potential energy of C60 islands by surfactant Sb.

Sb induced compact-fractal-compact growth transition of C 60 films

The growth morphology of C 60 films grown on a NaCl (0 0 1) substrate is significantly affected by the substrate temperature and the predepositing of surfactant Sb. With increasing substrate temperature from 130°C to 185°C, a compact-fractal-cornpact growth transition occurred in the Sb-mediated C 60 film. Possible growth mechanisms are discussed.

Improvement of Ge self-organized quantum dots by use of Sb surfactant

A Sb-mediated growth technique is developed to deposit Ge quantum dots (QDs) of small size, high density, and free of dislocations. These QDs were grown at low growth temperature by molecular beam epitaxy. The photoluminescence and absorption properties of these Ge QDs suggest an indirect-to-direct conversion, which is in good agreement with a theoretical calculation.

Effect of Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate

Cross-sectional transmission electron microscopy and Raman spectra are used to investigate the effect of monolayer Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate. Without Sb, inner diffusion of the epilayer Ge atoms into the Si substrate occurs, resulting in a severe intermixing of atoms at the Ge–Si interface. With the presence of Sb as a surfactant, the inner diffusion of epitaxial Ge atoms into the Si substrate is greatly suppressed. This result is explained in terms of the strain relief in the Si substrate by the Sb surfactant.

Surfactant-grown low-doped germanium layers on silicon with high electron mobilities

We present the first investigation of the electrical properties (electron Hall mobilities and concentrations) of 1- μm thick relaxed Ge layers grown by surfactant-mediated epitaxy (SME) with the surfactant Sb on Si(111) substrates at growth temperatures between 640°C and 720°C. We found that with rising growth temperatures the Ge layer quality improves as is demonstrated by the mobility increases at 300 K and 77 K. A record high electron mobility of 3100 cm 2/Vs at 300 K (12 300 cm 2/Vs at 77 K) which is close to the Ge lattice mobility was measured in the 720°C layer together with an electron concentration of 1.1×10 16 cm −3. This was derived from a differential Hall analysis and is identical to an interpolation value obtained from a comparison with high-quality bulk Ge mobility data. A secondary ion mass spectroscopy (SIMS) analysis yielded a concentration below the detection limit of 2×10 17 cm −3 Sb. Our results demonstrate an Sb background doping reduction of three orders of magnitude in SME-grown Ge/Si layers compared to earlier reports. We interpret this as being due to an enhanced surfactant segregation without kinetic limitations at high growth temperatures. The high quality, low doping and high mobility of these Ge layers suggests an exciting potential for future device applications.

Surfactant mediated heteroepitaxial growth of Ge/Si(111) probed by X-ray photoelectron diffraction

X-ray photoelectron diffraction (XPD) is used as a tool to investigate the growth of Ge on Si(111) with and without surfactant (Sb) mediation. Structural information is extracted directly from the forward scattering maxima of recorded photoelectron diffraction patterns. The result of a quantitative analysis of the patterns taken for Ge layers of different coverage are used for a structural growth model of Ge on Si(111). Without Sb, a compression of the top Si and the first Ge double layers is found followed by a relaxation of the Ge structure. Under the presence of Sb an intermixed interface is formed followed by compressed Ge double layers and relaxed distances between double layers.

Enhanced Sb segregation in surfactant-mediated-heteroepitaxy: High-mobility, low-doped Ge on Si

Surfactant-mediated epitaxy (SME) allows the growth of smooth, continuous, relaxed, and principally defect free Ge films directly on Si(111); however, the very high surfactant doping level in the range of the solid solubility limit made them unacceptable for most device applications. By using high temperature SME we have reduced the Sb surfactant background doping level by more than three orders of magnitude. This is attributed to an enhanced surfactant segregation without kinetic limitations. The low Sb incorporation has been determined by an electrical characterization: An electron concentration of 1.1×1016 cm−3 and a very high electron Hall mobility of 3100 cm2/V s at 300 K (12 300 cm2/V s at 77 K) suggest an interesting potential of SME grown Ge films for future device applications.