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The thickness of the thin semiconductor film, the refractive index (n), the absorption coefficient (α) and the energy band gap (Eg) can be determined by the analysis of the optical transmittance spectra.
Here, two frequently encountered methods for the analysis of the transmittance, one by Swanepoel and the other by Manifacier,et all., are reexamined and compared. These methods use the interference maxima and minima for the evaluation of the refractive index and its dependence on the wavelength n(λ). As an alternative, we examine the determination of the n(λ) from the pace of the interference patterns. Further, we inspect the use of the substrate’s transmittance for the base line (Io). This is useful for samples grown on substrates with the unpolished backside as well as for the spectral range where the transmission of the substrate is not constant.
In the experimental part, several thin GaN films grown on the sapphire substrate are studied. The transmittance spectra are measured in the range 300-1100 nm. Derived expressions, as well as the equations known from literature, are applied for the determination of the thickness, the optical parameters (n, α) and the energy band gap (Eg). |