Synthesis and Characterization of Silicon Carbide Layers Grown on Silicon Substrates by Low Pressure Chemical Vapor Deposition Technique

Abstract

Wide bandgap semiconductor materials have gained considerable attention for fabrication of electronic devices that can operate at high power, high frequency and high temperature for various applications where conventional semiconductor cannot work satisfactorily. These materials have potential applications in optoelectronics, such as light emitting diodes (LEDs), in the blue and ultraviolet (UV) wavelengths regions. It is widely recognized that the performance, yield, reliability and degradation behavior of devices are adversely affected due to presence of defects. In this study synthesis and characterization of most common polytypes 3C, 4H and 6H-SiC are performed. 3C-SiC layers grown on low cost p-type silicon (100 and/or 111) substrates maintained at constant temperature (1050 - 1350 0C) in a low pressure chemical vapor deposition (LPCVD) reactor. Typical Fourier transform infrared (FTIR) spectrum revealed a dominant peak at 800 cm -1 due to Si-C bond excitation. Large area x-ray diffraction spectra showed single crystalline cubic structure of 3C-SiC (111) and 3C-SiC (200) at 2θ angles of 28.280 and 34.080 on Si (111) and Si (100) substrates, respectively. Cross-sectional viewed revealed by scanning electron microscopy (SEM) display up to 104 μm thick SiC layer. Energy dispersive spectroscopy (EDS) of the grown layers demonstrated a stoichiometric growth of SiC. Surface roughness and morphology of the films were studied using atomic force microscopy (AFM). It was observed that resistivity of the as-grown layers increased with increasing substrate temperature due to decrease of isolated intrinsic defects such as silicon and/or carbon vacancies having activation energy 0.59 ± 0.02 eV. The p-type 6H- SiC were grown by fast sublimation method. The epilayer is co-doped with boron– nitrogen with free carrier concentration 3 × 1017 cm-3 (NA–ND). The detail investigations of electrical properties of deep level defects in the grown sample were carried out by deep level transient spectroscopy (DLTS). A hole H1 majority carriers and electron E1 minority carriers trap were observed in the device having activation energies Ev + 0.24 eV and Ec - 0.41 eV, respectively. The capture cross-section (trap concentration) of H1 and E1 deep levels were found to be 5 × 10-19 cm2 and 2 × 1 015 cm-3 (1.6 × 10-16 cm2 and 3 × 1015 cm-3) respectively. Considering the background involvement of aluminum in growth reactor and comparison of the obtained data with the available literature, the H1 defect was identified as aluminum acceptor and a sound justification was given to correlate the E1 defect to a nitrogen donor. The n-type 6H-SiC layers were also grown by sublimation method. To study the deep level defects in n-type 6H-SiC, as-grown, nitrogen doped and nitrogen- boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having free carrier concentration (ND–NA) 2.0 × 1012, 2× 1016 and 9× 1015 cm-3, respectively, DLTS was performed. The DLTS measurement of ELS-1 and ELS-11 samples revealed three electron trap A, B and C having activation energies EC – 0.39, Ec – 0.67 and Ec – 0.91 eV, respectively. The isochronal annealing study of the samples demonstrated that the observed electron traps were stable up to 750 oC. While DLTS spectra of sample ELS-131 showed only single ‘A’ level. This observation indicated that levels B and C in ELS-131 were compensated by boron and/or nitrogen–boron complex. A comparison with the published data revealed that A, B and C were related to E1/E2, Z1/Z2 and R levels, respectively in n-type 6H-SiC. The 4H-SiC layers were grown on p-type Si (100) substrate by simple evaporation method. The chamber was evacuated using mechanical and diffusion pump with base pressure of 5 × 10-7 torr. A mixture of Si and C60 powder of high purity (99.99%) with weight ratio of 1:1 was used as source material and was evaporated by Mo boat. A high current of 210A was used to increase the temperature of boat in the vicinity of 1100 0C. The temperature of substrate was fixed at 300 0C. The distance between substrate and boat was kept 10 cm and total evaporation time was 3 hours. To study the crystalline quality of as-grown material, x-ray diffraction, FTIR and photoluminescence (PL) were performed. The x- ray spectrum consist of six peaks at 2Θ angles 25.50, 28.5, 30.70, 32.70, 36.10 and 59.00 and four of them were related to 4H-SiC. Typical Fourier transform infrared (FTIR) spectrum revealed a dominant peak at 790 cm-1 due to Si-C bond excitation. The PL spectrum of grown samples showed strong band to band emission at 3.22 eV seemed an evident of 4H-SiC.