Ge Predeposition Research Articles

Understanding of the Growth Mechanism Leading to Twin Boundary Elimination during 3C-SiC Heteroepitaxy on α-SiC Substrate by CVD

Starting from the previously demonstrated twin-free 3C-SiC growth on 4H-SiC when using Ge pre-deposition treatment, this work focuses on the understanding of the growth mechanism that stands behind this result. Toward this end, short growth experiments were performed to allow the investigation of the nucleation stage. Based on the experimental observations, a mechanism is proposed which involves a Ge-induced transient homoepitaxial growth step followed by 3C nucleation when large terraces are formed by step faceting. Lateral expansion of the 3C islands leads to orientation selection and twin boundary elimination. Similar results can be obtained when applying a Si-based pre-deposition treatment so that the crucial transient homoepitaxial step is promoted in fact by the presence of a liquid phase itself, no by its chemical nature.

Effect of different Ge predeposition amounts on SiC grown on Si (1 1 1)

The SiC films were grown by solid source molecular beam epitaxy (SSMBE) on Si (1 1 1) with different amounts of Ge predeposited on Si prior to the epitaxial growth of SiC. The samples were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results indicate that there is an optimized Ge predeposition amount of 0.2 nm. The optimized Ge predeposition suppress the Si outdiffusion and reduce the formation of voids. For the sample without Ge predeposition, the Si outdiffusion can be observed in RHEED and the results of XRD show the worse quality of SiC film. For the sample with excess amount of Ge predeposition, the excess Ge can increase the roughness of the surface which induces the poor quality of the SiC film.

Surface morphology of Ge‐modified 3C‐SiC/Si films

AbstractThe influence of Ge deposition prior to carbon interaction with 3° off‐axis Si(111) substrates on the structural and morphological properties of the formed silicon carbide (SiC) layer is studied. In situ reflection high‐energy electron diffraction (RHEED) and X‐ray diffraction (XRD) revealed the formation of the cubic silicon carbide (3C‐SiC) modification. In situ spectroscopic ellipsometry measurements revealed a decreasing 3C‐SiC thickness with increasing Ge predeposition. Atomic force microscopy (AFM) studies revealed that the surface overlayer morphology is mainly formed by periodic step arrangements whose relevant geometric parameters, i.e. lateral separation, height and terrace width, depend on the Ge content. Besides the changes of the step morphology, the surface roughness and the grain size and the strain of the formed 3C‐SiC decreases with increasing germanium precoverage. Copyright © 2008 John Wiley & Sons, Ltd.

SiC polytypes process affected by Ge predeposition on Si(111) substrates

Structural and optical measurements were performed on silicon carbide (SiC) samples containing several polytypes. The SiC samples investigated were grown on (111) Si substrates by solid source molecular beam epitaxy (SSMBE). Several quantities of Ge were predeposited before the growth procedure. The influence of Ge on the SiC polytypes formation was studied by X-Ray, FTIR and μ -Raman characterizations methods. The spectra of the samples with less than one Ge monolayer exhibit a mixture of 2H, 15R and 3C–SiC polytypes. This mixture is due to the mismatch between the heterostructure layers. We propose that the Ge predeposition in the heterostructure can be used to stabilize and unify the polytypes formation.

Spectroscopic investigations of the role of Ge in modifying the Si to SiC conversion process

AbstractThe influence of Ge on the conversion process of Si to SiC was studied by depositing Ge and C on Si(111) followed by a stepwise annealing procedure. After the annealing step, the carbon deposited on the surface was completely converted into SiC. In the case of Ge predeposition, the SiC amount detected by XPS, AES and ellipsometry was lower compared to the reference sample in which no Ge was predeposited on the Si(111) surface. Therefore, Ge lowers the probability of SiC formation in the early stages. During the conversion process, Ge diffuses into the Si substrate and is mainly located near the SiCSi interface with a concentration of around 2.5–3%. As a result of a complex alloying process promoted by interdiffusion of C and Ge as well as SiC nucleation, a thin 3C‐SiC layer is formed on top of a Si1−xGex buffer layer. Copyright © 2008 John Wiley & Sons, Ltd.

Effect of Predeposited Ge on the Growth of SiC Films on Si(111) by SSMBE

SiC films were grown at substrate temperature of 900 ℃ by solid source molecular beam epitaxy (SSMBE) on Si(111) with different thicknesses (0, 0.2, 1 nm ) of Ge predeposited on Si prior to the epitaxy of SiC. The films were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR). The results indicated that the quality of the film with Ge predeposition of 0.2 nm was the best. The surface of the sample was even and there were no voids observed. The Ge prdeposition of 0.2 nm suppressed the Si diffusion and decreased the void formation. For the sample without Ge predeposition, the roughness of the surface was larger and there were some voids and Si grains on the surface. For the sample with the Ge prdeposition of 1 nm, island growth mode of Ge caused the surface of SiC films rougher and the crystalline quality of SiC film worse and even induced the formation of the polycrystalline SiC film.

Determination of strain and composition in SiC/Si and AlN/Si heterostructures by FTIR-ellipsometry

Abstract Heteroepitaxially grown 3C-SiC and 2H-AlN layers on Ge modified Si(111) substrates were investigated by Fourier transform infrared spectroscopic ellipsometry. The obtained phonon frequencies increase with increasing Ge pre-deposition indicating a decrease of the residual stress in both wide band gap materials. Additionally, it is shown that infrared ellipsometry allows the analysis of the polytype content of the grown epitaxial layers.

The role of Ge predeposition temperature in the MBE epitaxy of SiC on Ssilicon

An alternative method for stress relaxation in the SiC/Si heteroepitaxial system based on the incorporation of a group-IV element (germanium) into the interface between SiC and Si is presented. We have investigated the effect of the temperature during the predeposition of 1 ML of Ge on a silicon (111) surface, prior to the MBE carbonization. The resulting structures were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR). The crystalline quality of the 3C-SiC layer was improved by the Ge predeposition, as shown by XRD measurements and by the smaller damping constants of the TO and LO phonons in the FTIR analysis. As the temperature of Ge predeposition increases, the SiC layer exhibits lower residual strain and larger grain size. Furthermore, the incorporation of Ge at the interface suppresses the outdiffusion of Si from the substrate to the surface of the growing SiC layer and, therefore, impedes the formation of voids at the SiC/Si interface. TEM and SIMS results revealed a strong segregation of Ge at the interface leading to an increased stress relaxation, in agreement with theoretical predictions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical characterization of SiC/Si heterostructures with Ge-modified interfaces

The electrical properties of the n-3C–SiC/p-Si heterojunction grown by solid source molecular beam epitaxy on germanium-modified Si(1 1 1) substrates have been investigated. The current flow in the forward direction is determined by diffusion and recombination currents. The interface state density was determined to be not larger than 10 11 cm −2. The obtained interface state density is lower than in the case of 3C–SiC grown on Si(1 1 1) by chemical vapour deposition. Ge predeposition on silicon prior to silicon carbide is able to improve the ideality factor of the diode and decreases currents of the reverse biassed n-3C–SiC/p-Si heterojunction diode.

The Influence of Surface Preparation on the Properties of SiC on Si(111)

The silicon (111) surface was converted into silicon carbide by using: 1. propane diluted in hydrogen and rapid thermal processing, 2. elemental carbon deposited onto the silicon surface by solid source molecular beam epitaxy and subsequent annealing, i.e. conversion in a hydrogen poor environment, 3. modification of the silicon surface by Ge predeposition prior to elemental carbon deposition. These methods were compared according to their influence on the structure, morphology and electronic properties of the SiC/Si(111) heteroepitaxial system. It was found that the conversion in a hydrogen rich environment leads to the formation of a carbon () silicon carbide face, whereas a silicon (111) silicon carbide face was formed under hydrogen poor conditions. Germanium predeposition led to an improvement of the structural morphological and electrical properties of the silicon carbide–silicon heteroepitaxial system.

Silicon etching with oxygen molecular beam assisted by predeposited germanium

Si was etched using an O2 molecular beam according to the chemical reaction 2Si+O2→2SiO↑. The minimum etching temperature was decreased by 25 °C when a Ge layer had been deposited on a clean Si surface before etching. At 800 °C, the Ge-coated Si surface was etched while the clean Si surface was not. The O2 partial pressure during etching was 2×10−5 Torr; the etching rate was about 80 Å/min at 800 °C. Auger electron spectroscopy showed that the number of Ge atoms slightly decreased during Si etching. Ge atoms on the surface are thought to weaken Si back bonds by forming a thin Ge-Si alloy layer on the surface. Undercutting at the SiO2 mask edge was suppressed by this Ge predeposition technique at 800 °C because the sidewall without Ge was not etched at this temperature.