OpticCal is a software for calculating optical properties of mostly semiconductor and insulator. With OpticCal, the complex dielectric function and other optical properties can be obtained by using the calculated density functional theory’s (DFT) result(e.g. from Nanodcal). In semiconductor or insulator, the optical properties is mainly determined by the intraband transition of the charge carrier while for metal, it is mainly due to the interband transition. In OpticCal, we mainly consider the first case.
In a lot of photonic research and the area of device fabrication technology, the dielectric function (or the relative permittivity) is one of the key fundamental parameters. In designing an integrated circuit, materials with a high dielectric constant is implemented to reduce the leakage current of the gate; materials with a low dielectric constant is adopted to reduce the capacitive effect around the interconnected metal layers. Indeed, the knowledge of dielectric function allows further calculation of many interesting optical aspects such as the refractive index, extinction coefficients, absorption coefficient, etc. These in turns allow further investigation into many application areas such as photonic waveguides, lasers, etc.
By considering the linear response under the influence of a transverse pertubational field, OpticCal can obtain transverse dielectric function ( or relative permittivity function) in the homogeneous medium. By using long-wavelength approximation, both longitudinal and transverse dielectric function can be obtained.
In order to calculate the optical properties, the procedure of using OpticCal (with Nanodcal) is as follows:
- Obtain the self-consistent calculation from Nanodcal (e. NanodcalObject.mat)
- Calculate the momentum matrix (in Momentum.mat) using the output from step 1.
- Use OpticCal to calculate the optical properties using by using the results from previous steps.
As an example, the complex dielectric function of silicon can be calculated using OpticCal as shown in the figure below.