Ge-Sb-Te相变纳米线的掺杂改性及其相变机理研究

Chalcogenides nanowires (NWs) have great potential for nonvolatile memory applications due to fast phase transitions, good thermal stability and long-term endurance. However, several key constrains, which concerned with large programing currents, slow crystallization speed and the instability between the phase-change materials and the contact electrodes, are urgent to be solved. A selective doping technology has nationally and internationally been considered as a focus to solve the above restraints. This project proposes to study the key challenges in this field including controllable synthesis, phase-change properties and mechanism of doped Ge-Sb-Te (GST) NWs by combining the experimental and theoretical approaches. In order to achieve these goals, we will explore controllable fabrication of GST NWs with different doping concentrations by the chemical vapor deposition (CVD) method and clarify the relationship between the electrical property and doping behavior of GST NWs. Meanwhile, we will construct doping models and adjust doping concentrations of GST NWs to investigate reversible phase transitions，carrier mutations and transport properties during the phase transition，which revealing the phase transformation mechanism and subsequently resolving the key issues restricting the performance of GST NWs. We will further fabricate a device structure based on a single NW to observe its phase-change property by the doping modification. Additionally, we will devote ourselves to indicate the influence factors on phase-change performances and explore their applications on phase-change memory (PCM), which will thus provide significant experimental and theoretical references on the design of new-type and high-performance PCM prototype chips.

硫系化合物纳米线以其相变速度快、热稳定性好、疲劳特性好等特点在非易失性存储领域具有巨大应用潜力；但目前仍存在编程电流较大、结晶速度较慢以及材料-电极接触稳定性等关键制约问题亟待解决，选择性的掺杂被国内外认为是解决上述制约的前沿热点。本项目采用实验和理论相结合研究掺杂Ge-Sb-Te（GST）纳米线可控制备、相变特性及其机理。利用化学气相沉积法探索生长掺杂剂量可控的纳米线，弄清GST纳米线的电学性能与掺杂的关系；构建纳米线掺杂模型并调节掺杂剂量，研究其可逆相变、相变过程中载流子的突变与输运特性，揭示掺杂纳米线的相变机理，解决制约GST纳米线性能的关键问题。进一步制作单纳米线的相变器件结构，测量其掺杂改性后的相变特性，揭示掺杂GST纳米线相变性能的受控因素与规律，探讨其在相变存储器件（PCM）中的应用，为获得新型、高性能PCM提供重要的实验参考与理论依据。

硫系化合物纳米线以其相变速度快、热稳定性好、疲劳特性好等特点在相变存储领域具有巨大应用潜力；但目前仍存在编程电流较大等关键制约问题亟待解决，选择性的掺杂被国内外认为是解决上述制约的前沿热点。本项目采用实验和理论相结合研究了Sn掺杂GeTe（SGT）纳米线的可控制备、电学性质及其相变特性。我们利用化学气相沉积法生长出不同组分的SGT纳米线，观察到随着Sn含量的提升，SGT纳米线的结构从菱方向立方转变。为了弄清GST纳米线的电学性能与掺杂的关系，我们构建了不同样品的结构模型，采用从头计算研究其电学特性，揭示出适量的掺杂会引起费米面附件的态密度降低，电导率减小，从而SGT_3.0纳米线较SGT_25.0更适合PCM应用，这是由于Sn原子引入造成的结构变化导致了其电学性质上的差异。实验上，我们制作了单纳米线的器件结构来研究其掺杂改性后的相变特性。SGT_3.0纳米线有两个显著的阈值转换效应和理想的高低电阻比率（~105）。和未掺杂GeTe相比，掺杂后其晶态电阻值得到了提升，这与我们的理论计算结果一致，并且完全满足了PCM低编程电流的需求。因此，本项目为获得新型、高性能PCM提供重要的实验参考与理论依据。