INVESTIGATION ON ELECTRONIC CHARACTERISTICS OF SiGe MULTI-QUANTUM WELL CHANNEL MOSFETs ON A SOI SUBSTRATE

我们研制了一种基于超清洁技术的异质外延化学气相沉积装置，并利用该装置在硅或SOI(Silicon On Insulator)衬底上生长了SiGe量子阱。我们通过透射电子显微镜、SIMS和光致发光测量验证了该结构的物理性质，发现该结构是无缺陷的，并且Si/SiGe界面非常尖锐。量子阱的能级与理论能级一致。我们在SOI衬底(这里使用的是SIMOX晶片)上以550℃的速度生长了40 nm的硅，并用5.9 nm厚的栅氧化硅制作了PMOSFET。该器件的I-V特性几乎与直接在SIMOX晶片上形成的PMOSFET相同。结果表明，外延工艺和器件工艺具有良好的精密度和准确度。我们在SIMOX衬底上制作了SiGe量子阱PMOSFET(栅氧化硅：5.9 nm，硅帽层：7 nm，SiGe合金的Ge含量：0.2，势垒宽度：13 nm，SOI厚度：280 nm，SOI衬底上的Si缓冲层：40 nm)。我们通过饱和区和亚阈值区域的I-V特性确定了限制在SiGe势垒中的空穴电流。用0.266 m0作为SiGe层中重空穴的有效质量，12.6m0作为层的介电常数，对硅势垒高度为145 meV的单层和三层量子阱中重空穴的能级和电荷密度进行了数值计算。假设井内孔洞密度在10~10 cm~(-3)以下。阐明了单量子阱的能级与势垒宽度的关系，论证了三量子阱的能级或电荷密度与硅势垒宽度的关系。

We had developed a heteroepitaxial chemical vapor deposition apparatus on the basis of ultra-clean technology and grew SiGe quantum wells on a silicon or SOI (Silicon On Insulator) substrate by the apparatus. We verified the physical quality of the wells through TEM, SIMS and photoluminescence measurements and found that the wells were defect-free and the Si/SiGe interfaces were very sharp. The energy levels of the quantum wells agreed with those of the theoretical ones. We grew the 40-nm Si at 550℃ on a SOI substrate (a SIMOX wafer was here used) and fabricated a PMOSFET with the 5.9-nm-thick gate silicon oxide. The I-V characteristics of the device were almost all equal to those for the PMOSFET directly formed on a SIMOX wafer. The results indicated the good precision and accuracy of the epitaxial and device processes. We made SiGe-quantum-well-channel PMOSFETs on a SIMOX wafer (gate Si oxide : 5.9 nm, Si cap layer : 7 nm, Ge fraction of SiGe alloy : 0.2, well width : 13 nm, SOI thickness : 280 nm, Si buffer layer on a SOI wafer : 40 nm). We confirmed the current of holes confined to the SiGe well through the I-V characteristics in the saturation and subthreshold regions. Numerical calculation was carried out for the energy levels and charge densities of heavy holes in single and triple SiGe quantum wells with the Si barrier height of 145 meV.We used 0.266 m_0 as the effective mass of heavy holes in the SiGe layers and 12.6 as the permittivity of the layers. A low hole density below 10^<10> cm^<-3> in the wells was assumed. We clarified the energy levels of the single quantum wells related to the well width and demonstrated the relationship between the energy level or charge density and the Si Barrier width of the triple quantum wells.