Studies on aluminum-doped ZnO films for transparent electrode and antireflection coating of β-FeSi2 optoelectronic devices

β-FeSi2 can be used for various optoelectronic devices owing to its superior material features including high optical absorption coefficient and direct band gap of about 0.8 eV. Due to its high refractive index (>5.6), however, suitable antireflection coating (ARC) is necessary for practical device applications. In order to increase the effective areas of optoelectronic devices, transparent electrodes should be also developed. In this work, Al-doped ZnO (AZO) films were fabricated by sputtering on β-FeSi2 thin films and were found suitable for both transparent electrodes and ARC films. Choosing optimum substrate temperature and sputtering rate, high quality AZO films were formed. The conductivity of AZO films was as high as 3×103 S/cm and ohmic contact was easily achieved between AZO and β-FeSi2 films, indicating AZO film as an ideal transparent electrode for β-FeSi2. The transmittance of 400-nm-thick AZO films was >80% and >70% in the wavelength ranges 400-1400 and 1400-1600 nm, respectively. By changing the thickness of AZO film, the central wavelength of minimum reflectance was adjusted to 1550 nm where the total reflectance of AZO/β-FeSi2/Si structure was reduced below 2%.