Structural and electrical analysis of poly-Ge films fabricated by e-beam evaporation for optoelectronic applications

We have investigated the relationship between structural and electrical properties of Ge thin films deposited on single crystal silicon (100) substrates by electron beam evaporation at room temperature. Post-thermal annealing was applied to obtain poly-crystalline Ge thin films. The structural effects of the annealing temperature and annealing time on the crystallization of Ge films were analyzed using Raman and X-ray diffraction measurements. Raman and X-ray diffraction spectra revealed a structural evolution from amorphous to crystalline phase with increasing annealing temperature and annealing time. It was found that high quality poly-crystalline Ge films were obtained with crystallization ratio of 90% at an annealing temperarure of 500 °C following the crystallization threshold of 450 °C. Effects of structural ordering on the electrical properties were investigated through current-voltage characteristics of fabricated heterostructure devices (Ge/p-Si). Smooth cathode-anode interchange in the diode behavior has been clearly observed following the structural ordering as a function of annealing temperature in a systematic way. These outcomes could be exploited for engineering of low-cost Ge based novel electronic and opto-electronic devices.