Collaborative Research: Quantum-Cascade-Laser Active Materials Based on Silicon-Germanium Nanomembranes

技术.本计画系以矽锗量子威尔斯（QWs）为基础，探讨量子级联（QC）中、远红外线发光材料之合成/制程/制造研究。由于QC激光器是基于子带间（ISB）跃迁的半导体光源（即，相同能带内的量子化状态之间的电子跃迁），它们的操作基本上不受下面材料的能带隙的性质的影响。因此，这样的考虑提供了一种方法，用于演示激光在硅中的作用？一个由（Si）（Ge）的间接带隙复杂化的目标。然而，与Si/SiGe量子阱相关的应变似乎是进步的一个重大挑战。该项目采用了一种新的方法，其中弹性弛豫的SiGe纳米膜被用作生长衬底和/或活性材料。这种纳米膜将在绝缘体上的Si（Ge）衬底上外延生长，然后通过经由湿法蚀刻去除下面的氧化物层而从处理晶片释放。期望的结果将是一个独立的异质结构，其中通过组成外延层之间的弹性应变共享发生应变松弛，而不会形成缺陷，因此实际上没有位错。然后可以将释放的纳米膜转移到其他基底上。硅基QC激光器的演示复杂化的进一步挑战是由特定于SiGe QW材料系统的设计问题提供的，这些问题也在该项目中得到解决。基于Ge/SiGe量子阱L谷的电子ISB跃迁的方法将被探索。最近的计算表明，这种方法可能比迄今为止研究的p型结构具有更大的优势，包括更长的非辐射寿命、更大的振子强度和更有效的隧穿输运。该项目涉及电子/光子材料科学领域的基础研究问题，具有技术相关性。所提出的使用纳米膜技术来制造复杂半导体量子结构具有超出上述SiGe材料系统和QC激光器件应用的广泛技术影响的潜力。此外，项目活动将通过培训跨学科的学生来促进教育，从半导体外延生长到纳米膜合成和加工、带隙工程和太赫兹光子学。为了提高该方案的有效性和范围，将强调本科生和高中实习生的参与，利用现有的方案，重点关注代表性不足的少数民族。

Technical. This project addresses synthesis/processing/fabrication research to explore quantum-cascade (QC) mid- and far-infrared light-emitting materials based on SiGe quantum wells (QWs). Since QC lasers are semiconductor light sources based on intersubband (ISB) transitions (i.e., electronic transitions between quantized states within the same energy band), their operation is essentially unaffected by the nature of the energy band gap of the underlying materials. Hence such considerations provide an approach for the demonstration of laser action in silicon ? a goal complicated by the indirect band gap of (Si)(Ge). Strain, however, associated with Si/SiGe QWs appears as a significant challenge to progress. This project takes a new approach, in which elasti-cally relaxed SiGe nanomembranes are used as the growth substrates and/or the active material. Such nanomembranes will be grown epitaxially on Si(Ge)-on-insulator substrates and then re-leased from the handle wafer by removing the underlying oxide layer via wet etching. The de-sired result would be a free-standing heterostructure where strain relaxation occurs via elastic strain sharing among the constituent epilayers without the formation of defects, and thus be vir-tually free of dislocations. The released nanomembranes could then be transferred onto other substrates. Further challenges complicating the demonstration of silicon-based QC lasers are provided by design issues specific to the SiGe QW materials system, which are also being ad-dressed on this project. An approach based on electronic ISB transitions in the L valleys of Ge/SiGe QWs will be explored. Recent calculations indicate that this approach may have advan-tages over the p-type structures that have been investigated so far, including longer nonradiative lifetimes, larger oscillator strengths, and more efficient tunneling transport.Non-Technical. The project addresses fundamental research issues in a topical area of elec-tronic/photonic materials science having technological relevance. The proposed use of nanomembrane technology for the fabrication of complex semiconductor quantum structures has the potential for broad technological impact beyond the SiGe materials system and the QC-laser device application described above. Moreover, the project activities will promote education through the training of students across disciplines, ranging from semiconductor epitaxial growth to nanomembrane synthesis and processing, bandgap engineering, and THz (terahertz) photonics. To increase the effectiveness and scope of the program, the involvement of undergraduates and high-school interns will be emphasized, by leveraging existing programs with a strong focus on under-represented minorities.