gives the carrier concentration (in cm^-3)

        Returns
            a dictionary {temp:[]} with an array of carrier concentration
            (in cm^-3) at each temperature
            The array relates to each step of electron chemical potential

def get_carrier_concentration(self):
        """
        gives the carrier concentration (in cm^-3)

        Returns
            a dictionary {temp:[]} with an array of carrier concentration
            (in cm^-3) at each temperature
            The array relates to each step of electron chemical potential
        """

        return {temp: [1e24 * i / self.vol for i in self._carrier_conc[temp]]
                for temp in self._carrier_conc}