Optoelectronic and structural properties of amorphous silicon–carbon alloys deposited by low-power electron-cyclotron resonance plasma-enhanced chemical-vapor deposition

Abstract

The optoelectronic and structural properties of hydrogenated amorphous silicon-carbon alloys ͑a-SiC:H͒ are studied over the entire compositional range of carbon content. The films are prepared using low-power electron-cyclotron resonance ͑ECR͒ plasma-enhanced chemical vapor deposition. The carbon content was varied by using different methane ͑or ethylene-͒-to-silane gas phase ratios and by introducing the methane ͑or ethylene͒ either remotely into the plasma stream or directly through the ECR source, together with the excitation gas ͑hydrogen͒. Regardless of the deposition conditions and source gases used, the optical, structural and transport properties of the a-SiC:H alloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The deep defect density from photothermal deflection spectroscopy, the ESR spin density, the steady state and the transient photoluminescence, the dark and photoconductivity, the temperature of the hydrogen evolution peaks and the bonding from infrared spectroscopy are correlated to the Urbach tail energy, the B factor of the Tauc plot and E 04 ͑defined as the energy at which the absorption coefficient is equal to 10 4 cm Ϫ1 ͒. Silicon-rich and carbon-rich regions with very different properties, corresponding approximately to carbon fractions below and above 0.5, respectively, can be distinguished. The properties of the ECR a-SiC:H alloys are compared with those of alloys deposited by rf glow discharge.

Time-resolved study of photoluminescence polarization in a-C:H films

“…The subnanosecond decay times (s I ), due to both radiative and non-radiative recombination mechanisms, are in quantitative agreement with previous studies of amorphous carbon ®lms [11]. A similar dependence of intrinsic decay times on E em has been reported in C-rich silicon carbon alloys [10].…”

“…Intensity decays have been ®tted using a convolution between the laser excitation and an intrinsic decay function made of the sum of three exponentials (six parameter ®t) [9]. This empirical analytic function is found to describe accurately the PL decays in a-C:H ®lms and silicon±carbon alloys [10]. The intrinsic decay times s I ) of PL intensity, obtained from a weighted average of the ®tted decay times, decrease from 965 to 39 ps as a function of increasing E em ( Table 1).…”

FTIR analysis of a-SiC:H films grown by plasma enhanced CVD

“…The peak near 1000 cm À1 represents the wagging mode C-H 2 bond within SiCH 2 , and its integrated intensity increases with increasing plasma power density and with decreasing substrate temperature. The weak peaks near 1250, 2000-2200, 2890, 2960 cm À1 correspond to bending mode Si-CH 3 , stretching mode Si-H n (n ¼ 1; 2), and stretching mode C-H 2 and C-H 3 , respectively [14,[17][18][19][20]. All include hydrogen, and the intensity of the peaks decreases with increasing substrate temperature.…”

“…Infrared spectroscopy can be used to determine the content of chemical bonds, including hydrogen bonds [11][12][13][14][15][16], based on the integrated absorption intensity of stretching mode bonds. Si-H n (n ¼ 1; 2), C-H 2, C-H 3 and Si-C bonds are observed as peaks at 2000-2200, 2890, 2960 and 790 cm À1 , respectively [14,[17][18][19][20]. The absorption cross-section and film thickness are also required for this calculation, obtained from Ref.…”

Self-organized colloidal quantum dots and metal nanoparticles for plasmon-enhanced intermediate-band solar cells

“…polymer foil). (2) The bandgap of the material can be controlled by doping it with carbon (a-Sii_^C^:H) [46]. Increasing concentration of carbon (x) in the alloy widens the bandgap, allowing it to be tuned from a minimum value of about 1.75 eV (x = 0) to 3 eV (x = 1).…”