Controlling the surface roughness of epitaxial SiC on silicon

The surface of cubic silicon carbide (3C-SiC) hetero-epitaxial films grown on the (111) surface of silicon is a promising template for the subsequent epitaxial growth of III-V semiconductor layers and graphene. We investigate growth and post-growth approaches for controlling the surface roughness of epitaxial SiC to produce an optimal template. We first explore 3C-SiC growth on various degrees of offcut Si(111) substrates, although we observe that the SiC roughness tends to worsen as the degree of offcut increases. Hence we focus on post-growth approaches available on full wafers, comparing chemical mechanical polishing (CMP) and a novel plasma smoothening process. The CMP leads to a dramatic improvement, bringing the SiC surface roughness down to sub-nanometer level, though removing about 200 nm of the SiC layer. On the other hand, our proposed HCl plasma process appears very effective in smoothening selectively the sharpest surface topography, leading up to 30% improvement in SiC roughness with only about 50 nm thickness loss. We propose a simple physical model explaining the action of the plasma smoothening

RF Sputtering, Post-Annealing Treatment and Characterizations of ZnO (002) Thin Films on 3C-SiC (111)/Si (111) Substrates

We report on the radio frequency (RF) sputtering of c-axis oriented ZnO thin films on top of epitaxial 3C-SiC-on-Si (111) substrates, which were then subjected to post-annealing treatment at 400, 600 and 800 °C. Grazing incident X-ray Diffraction (XRD) data show that the Full Width Half Maximum (FWHM) values for O2/Ar ratios between 30% and 60% are consistent, with a mean of 0.325° and a standard deviation of 0.03°. This is largely attributed to the smaller lattice mismatch of 5% between the ZnO (002) and SiC (111) films. The quality of the ZnO films deteriorated at the post-annealing treatment of 800 °C, as demonstrated by the increasing value of FWHM diffraction peaks, the reducing value of the peak intensity, the reducing percentage of (002) oriented area under the curve, and the increasing value of biaxial stress. We propose a simple growth model to explain the result

A large pseudo-Hall effect in n-type 3C-SiC(1 0 0) and its dependence on crystallographic orientation for stress sensing applications

The pseudo-Hall effect in n-type single crystal 3C-SiC(1 0 0) with low carrier concentration has been investigated. Low pressure chemical vapor deposition was used to grow the single crystal n-type 3C-SiC(1 0 0) and Hall devices were fabricated by photolithography and dry etch processes. A large pseudo-Hall effect was observed in the grown thin films which showed a strong dependence on the crystallographic orientation. N-type 3C-SiC(1 0 0) with low carrier concentration shows a completely different behavior of pseudo-Hall measurements as compared to the p-type 3C-SiC(1 0 0). Contrary to p-type, the effect is maximum along [1 0 0] crystallographic orientation and minimum along [1 1 0] orientation. Moreover, the observed pseudo-Hall effect is 50% larger than p-type with higher carrier concentration grown by the same process which makes n-type 3C-SiC(1 0 0) with low carrier concentration more suitable material for designing highly sensitive micro-mechanical sensors

Pseudo-Hall Effect in Single Crystal n-Type 3C-SiC(100) Thin Film

This article reports the first results on stress induced pseudo-Hall effect in single crystal n-type 3C-SiC(100) grown by LPCVD process. After the growth process, Hall devices were fabricated by standard photolithography and dry etching processes. The bending beam method was employed to study the stress induced changes in the electrical response of the fabricated Hall devices. It has been observed that when stress is applied to the 3C-SiC(100) Hall devices, the offset voltage of the Hall devices varies linearly with the applied compressive and tensile stresses which is called, the pseudo-Hall effect. The variation of the offset voltage of these Hall devices is also proportional to the applied input current. This variation of the offset voltage with the applied compressive and tensile stresses shows that single crystal n-type 3C-SiC(100) can be used for stress sensing applications

Piezo-Hall effect and fundamental piezo-Hall coefficients of single crystal n-type 3C-SiC(100) with low carrier concentration

This article reports the results on the piezo-Hall effect in single crystal n-type 3C-SiC(100) having a low carrier concentration. The effect of the crystallographic orientation on the piezo-Hall effect has been investigated by applying stress to the Hall devices fabricated in different crystallographic directions. Single crystal n-type 3C-SiC(100) and 3C-SiC(111) were grown by low pressure chemical vapor deposition at 1250 °C. Fundamental piezo-Hall coefficients were obtained using the piezo-Hall effect measurements as P11 = (–29 ± 1.3) × 10−11 Pa−1, P12 = (11.06 ± 0.5)× 10−11 Pa−1, and P44 = (–3.4 ± 0.7) × 10−11 Pa−1. It has been observed that the piezo-Hall coefficients of n-type 3C-SiC(100) show a completely different behavior as compared to that of p-type 3C-SiC

Growth mechanism for alternating supply epitaxy

Low-cost large-diameter cubic silicon carbide (3C-SiC) film grown on silicon (Si) has been demonstrated to have a wide range of applications in photonics, electronics, photoelectrochemistry and micro-electro-mechanical system technologies. In this paper, the epitaxial growth of SiC on Si by low-pressure chemical vapour deposition is investigated. Two modes were employed to supply the precursors: the alternating supply and the simultaneous supply. Compared with SiC films grown at the same temperature by simultaneous supply epitaxy method, the SiC grown by alternating supply epitaxy (ASE) method has better crystallinity, smoother surface, and better thickness uniformity as confirmed by X-ray diffraction and atomic force microscopy characterisation. We propose the growth mechanism for ASE growth of 3C-SiC and validate it in detail experimentally. It is found that, Si deposition on SiC follows either Stranski–Krastanov mode or island growth mode, while SiC formation proceeds in two possible reaction paths: redistributing of the formed Si islands or smoothing of the formed SiC islands by decomposition migration process. Both reaction paths are driven by minimizing the surface free energy and reducing dangling bonds density. In summary, the key features of ASE are: (1) Si has a longer diffusion length and thus higher probability to adhere to a crystallographically favourable position; (2) undesirable gas phase reactions can be avoided. The obtained results indicate that ASE is a unique and economically viable method to prepare uniform 3C-SiC on multiple large-diameter Si wafers.Queensland Government, AustraliaAustralian Research Counci

Excellent Rectifying Properties of the n-3C-SiC/p-Si Heterojunction Subjected to High Temperature Annealing for Electronics, MEMS, and LED Applications

Abstract This work examines the stability of epitaxial 3C-SiC/Si heterojunctions subjected to heat treatments between 1000 °C and 1300 °C. Because of the potential for silicon carbide in high temperature and harsh environment applications, and the economic advantages of growing the 3C-SiC polytype on large diameter silicon wafers, its stability after high temperature processing is an important consideration. Yet recently, this has been thrown into question by claims that the heterojunction suffers catastrophic degradation at temperatures above 1000 °C. Here we present results showing that the heterojunction maintains excellent diode characteristics following heat treatment up to 1100 °C and while some changes were observed between 1100 °C and 1300 °C, diodes maintained their rectifying characteristics, enabling compatibility with a large range of device fabrication. The parameters of as-grown diodes were J0 = 1 × 10−11 A/mm2, n = 1.02, and +/−2V rectification ratio of 9 × 106. Capacitance and thermal current-voltage analysis was used to characterize the excess current leakage mechanism. The change in diode characteristics depends on diode area, with larger areas (1 mm2) having reduced rectification ratio while smaller areas (0.04 mm2) maintained excellent characteristics of J0 = 2 × 10−10 A/mm2, n = 1.28, and +/−2V ratio of 3 × 106. This points to localized defect regions degrading after heat treatment rather than a fundamental issue of the heterojunction

Robust free-standing nano-thin SiC membranes enable direct photolithography for MEMS sensing applications

This work presents fabrication of micro structures on sub–100 nm SiC membranes with a large aspect ratio up to 1:3200. Unlike conventional processes, this approach starts with Si wet etching to form suspended SiC membranes, followed by micro‐machined processes to pattern free‐standing microstructures such as cantilevers and micro bridges. This technique eliminates the sticking or the under‐etching effects on free‐standing structures, enhancing mechanical performance which is favorable for MEMS applications. In addition, post‐Si‐etching photography also enables the formation of metal electrodes on free standing SiC membranes to develop electrically‐measurable devices. To proof this concept, the authors demonstrate a SiC pressure sensor by applying lithography and plasma etching on released ultrathin SiC films. The sensors exhibit excellent linear response to the applied pressure, as well as good repeatability. The proposed method opens a pathway for the development of self‐sensing free‐standing SiC sensors

Ultra-thin LPCVD silicon carbide membrane: A promising platform for bio-cell culturing

This work presents the fabrication, mechanical strength characterization, and cell culture demonstration of a high aspect ratio silicon carbide (SiC) membrane. Optimizations in the deposition and fabrication make an ultra-high aspect ratio up to 20,000 SiC membranes with high fracture strength possible. Utilizing the superior properties of SiC material, the ultra-thin SiC membrane is a promising for cell culture/stretching devices, enabling very short optical accesses. The biocompatibility of the SiC membrane was confirmed with the 3T3 fibroblasts cell viability rate of 92.7%, in which the cells flattened and elongated their morphology while maintaining a strong adhesion to the SiC surface