dc.description.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. |
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