Slow Relaxation of Amorphous Germanium: Stretching Beyond the Stretched Exponential
Unlike their crystalline counterparts, the electronic transport properties of highly disordered (amorphous) semiconductors exhibit novel temperature and time dependencies. For example, following a high-temperature anneal and rapid cooling to a lower temperature (but above room temperature), the current in hydrogenated amorphous Germanium (a-Ge:H) increases as a function of time at a fixed voltage and temperature. This time dependence in amorphous semiconductors has been observed before, with time dependencies described as a stretched exponential relaxation. However, our results indicate that a stretched exponential function is insufficient to account for current relaxation in a-Ge:H. In particular, at 405K, the sample undergoes a transition. Initially, its conductivity follows a stretched exponential trend similar to that observed at 410K, before relatively rapidly changing to one resembling 400K after approximately 100,000 seconds of relaxation time. The mechanism underlying this jump is not well understood.