SiGe Epitaxial Layers Research Articles

Reduction of Interfacial Carbon and Boron Contamination as Sources for Degradation of Epitaxial SiGe Layers Grown by MBE

Reduction of Interfacial Carbon and Boron Contamination as Sources for Degradation of Epitaxial SiGe Layers Grown by MBE

In-situ dual-wavelength and ex-situ spectroscopic ellipsometry studies of strained SiGe epitaxial layers and multi-quantum well structures

In-situ dual-wavelength ellipsometry and ex-situ spectroscopic ellipsometry have been used to study strained Si 1−x Ge x Si multilayers. Reference dielectric function spectra of strained Si 1− x Ge x with 0.06 < x < 0.29 have been obtained for the first time and an interpolation procedure based on the strain dependence of the dominant critical point energies developed. Good agreement with composition and thickness values from corroborative techniques was obtained when the effects of strain were taken into account.

Effect of compressive and tensile strain on misfit dislocation injection in SiGe epitaxial layers

The relaxation behavior of short-period Si/Ge superlattices and SixGe1−x alloy layers under compressive and tensile strain field is compared experimentally by means of transmission electron microscopy as well as theoretically on the basis of a half-loop dislocation nucleation model. It was found that misfit dislocations in tensily strained layers grown on Ge(001) substrates are imperfect and of the 90° Shockley type provided some critical misfit fc is exceeded. Subsequent nucleation and glide of these partial dislocations on adjacent {111} glide planes leads to the formation of stacking faults and microtwins. In the low misfit regime (f&amp;lt;fc), the nucleation of 60° perfect dislocations is energetically favorable. In contrast, misfit dislocations in layers which experience a compressive strain field within the (001) growth plane are generally of the 60° type. In this case the critical thickness for coherent growth is found to be substantially enlarged with respect to the inverse strain situation where microtwin formation occurs.

A Novel Approach for The Production of Low Dislocation Relaxed Sige Material.

AbstractIn this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin Silicon On Insulator, SOl, substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced into the upper SiGe material, which appeared dislocation free to the limit of the cross sectional Transmission Electron Microscopy (TEM) analysis. We thus have a method for producing very low dislocation, relaxed SiGe films with the additional benefit of an SO substrate. This buffer structure is significantly less than a micrometer in thickness and offers distinct advantages over the thick SiGe buffer layers presently in use.

Wet oxidation of amorphous Si-Ge layer deposited on Si(001) at 800 and 900 °C

Amorphous Si0.56G0.44 films were deposited on (001)Si by electron beam evaporation in a vacuum having a base pressure of 10−7 Torr. They were then wet oxidized at 800 and 900 °C in an open tube furnace for various times. Cross (x)-sectional and plan view transmission electron microscope techniques were employed to characterize the samples. At 800 °C, 30 min of wet oxidation produced a continuous polycrystalline Si-Ge layer, whereas 60 min of wet oxidation produced a discontinuous polycrystalline layer. After 100 min of wet oxidation at 800 °C, the Si-Ge layer was almost completely oxidized and no observable evidence of the epitaxial Si-Ge layer was found. Wet oxidation at 900 °C for 10 min produced a bilayer structure; one epitaxial and one polycrystalline layer separated by a contamination layer initially present on the substrate prior to deposition. A mostly epitaxial Si-Ge layer was obtained after 30 min of wet oxidation at 900 °C. These results will be discussed in terms of a previously suggested epitaxial growth model. The failure to obtain an observable epitaxial Si-Ge layer by wet oxidation at 800 °C will be discussed by consideration of changes in the kinetics and the stability of both SiO2 and GeO2 at this temperature.

Refractive index determination of SiGe using reactive ion etching/ellipsometry: Application of the depth profiling of the GE concentration

The complex refractive index at a wavelength of 632.8 nm of strained epitaxial SiGe layers on silicon substrates has been determined as a function of the germanium content using in situ ellipsometry during reactive ion etching. The germanium concentration was obtained from Rutherford backscattering. These index values are used to invert the ellipsometry equations. Using this principle, the Ge concentration depth profile of an unknown SiGe structure can be determined from an in situ ellipsometry measurement sequence that is taken while the unknown sample is being etched

X-Ray Characterisation of Boron Delta Layers in Si and SiGe

ABSTRACTWe demonstrate the growth, by MBE, of high sheet density B delta layers in both Si and SiGe epitaxial layers. Double Crystal X-Ray Diffraction is shown to be a non-destructive method of characterising the width of very narrow (0.3 nm) delta layers and the sheet density of the activated B. The ability of delta layers to withstand high temperature anneals is considered and it is found that a 750 °C anneal for 1 hour broadens the delta layer to beyond the width required for carrier confinement.

Aspects of “High Minority-Carrier Lifetime” GaAs on Si Using A Novel SiGe/Ge Buffer

Heteroepitaxial GaAs-on-Si utilizing a Si 0.4 Ge 0.96 /Ge buffer, with a hole minority-carrier lifetime as long as ∼ 2.5 nsec is described. This is the longest minority-carrier lifetime in GaAs grown on Si reported to date by any approach. Here we discuss the microstructural aspects of this heteroepitaxial system, including a crossectional transmission electron microscopy (XTEM) study of the interface of the SiGe/Ge buffer and the role of the SiGe layer. An x-ray double crystal diffraction (DCD) study of the GaAs layers is also presented. The SiGe/Ge buffer approach to heteroepitaxial GaAs on Si is a result of two observations: (1) SiGe epitaxial layers grown on Ge are under biaxial compressive stress (from DCD) and (2) dislocations tend to bend over into the Ge substrate (from TEM). These data and a description of the heteroepitaxy of SiGe layers on Ge are presented.

Solid phase epitaxy of a Ge-Si alloy on [111] Si through a Pd2Si layer

Solid phase epitaxy of a Ge70Si30 alloy on [111]Si substrates was achieved in the amorphous Ge/Pd2Si/[111]Si system. Upon annealing at temperatures above 600 °C,the Ge transported through the silicide layer and formed a Ge-rich, Si-Ge epitaxial layer on top of the Si substrate. At the same time the Pd silicide layer exchanged positions with the Ge, leading to the final configuration of Pd2Si/Si-Ge/[111]Si. The crystallinity of Pd2Si had a major effect on the epitaxy of the Ge-Si alloy. On [100]Si where the Pd2Si was polycrystalline, epitaxial Ge-Si growth was not observed.

Formation of epitaxial Si1−xGex films produced by wet oxidation of amorphous SiGe layers deposited on Si(100)

Epitaxial SiGe/Si structures have been formed by wet oxidation of amorphous SiGe films. Amorphous, 1000-Å-thick Si0.86Ge0.14 films were electron beam evaporated onto RCA cleaned Si(100) substrates at a background pressure of 1×10−7 Torr. They were then wet oxidized in an open tube furnace, at 900 °C for various times. They have been examined by reflective high-energy electron diffraction and Rutherford backscattering. Results indicate the formation of an epitaxial SiGe layer following the oxidation, whereas a polycrystalline layer forms following a vacuum or nitrogen ambient anneal. It is suggested that the oxide contamination at the amorphous SiGe/Si interface is too high to allow solid phase epitaxial growth to occur in an oxygen-free ambient, but during the oxidation process, some native oxide is dissolved due to a gradient of silicon from the substrate to the growing SiO2 on the surface. This allows grains of the SiGe alloy to orient with respect to the substrate, and secondary grain growth occurs during the oxidation process.

The properties of Si/Si1-xGex films grown on Si substrates by chemical vapor deposition

A growth parameter study was made to determine the proper of a SiGe superlattice-type configuration grown on Si substrates by chemical vapor deposition (CVD). The study included such variables as growth temperature, layer composition, layer thickness, total film thickness, doping concentrations, and film orientation. Si and SiGe layers were grown using SiH4 as the Si source and GeH4 as the Ge source. When intentional doping was desired, diluted diborane for p-type films and phosphine for n-type films were used. The study led to films grown at ∼1000°C with mobilities from ∼20 to 40 percent higher than that of epitaxial Si layers and ∼100 percent higher than that of epitaxial SiGe layers grown on (100) Si in the same deposition system for net carrier concentrations of ∼8x1015 cm-3 to ∼2x1017 cm-3. Enhanced mobilities were found in multilayer (100)-oriented Si/Si1-xGex films for layer thicknesses ≥400A, for film thicknesses >2μm, and for layers with x = 0.15. No enhanced mobility was found for (111)-oriented films and for B-doped multilayered (100)-orlented films.

Electron mobility enhancement in epitaxial multilayer Si-Si1−xGex alloy films on (100) Si

Enhanced Hall-effect mobilities have been measured in epitaxial (100)-oriented multilayer n-type Si/Si1−xGex films grown on single-crystal Si substrates by chemical vapor deposition. Mobilities from ∼20 to 40% higher than that of epitaxial Si layers and ∼100% higher than that of epitaxial SiGe layers on Si were measured for the doping range ∼8×1015–∼1017 cm−3. The mobilities of multilayer Si/SiGe films approach that of single-crystal Si films at ∼2×1017 cm−3. No mobility enhancement was observed in multilayer p-type (100) films and n-type (111)-oriented films. Experimental studies included the effects upon film properties of layer composition, total film thickness, doping concentrations, layer thicknesses, and growth temperature.