Temperature Dependence of Optical Properties and Minority Carrier Diffusion Length in a-SiGe:H,F

We report the temperature dependence of several optical parameters of thin films of hydrogenated and fluorinated amorphous silicon alloys (a-SiGe:H,F) between 5 and 95 °C. The absorption coefficient near the optical band gap Eg increases with temperature. From this increase we calculate a temperature coefficient for Eg of −4.5×10−4 eV/K, which is essentially independent of band gap The concomittant change of index of refraction n was determined in the near infrared region from the interference pattern in the reflection spectra. The temperature coefficient dn/n/dT is 0.9×10−4 K−1 for un-alloyed a-Si:H,F and increases with increasing Ge atomic fraction. The changes of Eg and n with temperature are consistent with a simple quantummechanical description of the complex dielectric constant. We also report the temperature dependence of the minority carrier diffusion length in a-SiGe:H,F.