The Effect of Carbon Doping on the Crystal Structure and Electrical Properties of SbTe.

As a new generation of non-volatile memory, phase change random access memory (PCRAM) has the potential to fill the hierarchical gap between DRAM and NAND FLASH in computer storage. SbTe, one of the candidate materials for high-speed PCRAM, has high crystallization speed and poor thermal stability. In this work, we investigated the effect of carbon doping on SbTe. It was found that the FCC phase of C-doped SbTe appeared at 200 °C and began to transform into the HEX phase at 25 °C, which is different from the previous reports where no FCC phase was observed in C-SbTe. Based on the experimental observation and first-principles density functional theory calculation, it is found that the formation energy of FCC-SbTe structure decreases gradually with the increase in C doping concentration. Moreover, doped C atoms tend to form C molecular clusters in sp hybridization at the grain boundary of SbTe, which is similar to the layered structure of graphite. And after doping C atoms, the thermal stability of SbTe is improved. We have fabricated the PCRAM device cell array of a C-SbTe alloy, which has an operating speed of 5 ns, a high thermal stability (10-year data retention temperature 138.1 °C), a low device power consumption (0.57 pJ), a continuously adjustable resistance value, and a very low resistance drift coefficient.