Examination of the temperature dependent electronic behavior of GeTe for switching applications

The DC and RF electronic behaviors of GeTe-based phase change material switches as a function of temperature, from 25K to 375K, have been examined. In its polycrystalline (ON) state, GeTe behaved as a degenerate p-type semiconductor, exhibiting metal-like temperature dependence in the DC regime. This was consistent with the polycrystalline (ON) state RF performance of the switch, which exhibited low resistance S-parameter characteristics. In its amorphous (OFF) state, the GeTe presented significantly greater DC resistance that varied considerably with bias and temperature. At low biases (<1 V) and temperatures (<200 K), the amorphous GeTe low -field resistance dramatically increased, resulting in exceptionally high amorphous -polycrystalline (OFF-ON) resistance ratios, exceeding 109 at cryogenic temperatures. At higher biases and temperatures, the amorphous GeTe exhibited nonlinear cutTent-voltage characteristics that were best fit by a space charge limited conduction model that incorporates the effect of a defect band. The observed conduction behavior suggests the presence of two regions of localized traps within the bandgap of the amorphous GeTe, located at approximately 0.26-0.27 eV and 0.56-0.57 eV from the valence hand. Unlike the polycrystalline state, the high resistance DC behavior of amorphous GeTe does not translate to the RF switch performance; instead, a parasitic capacitance associated with the RF switch geometry dominates OFF state RF transmission. Published by AIP Publishing.