Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, USA.
ACS Nano. 2013 Jan 22;7(1):100-7. doi: 10.1021/nn3028166. Epub 2012 Dec 20.
The heterogeneous integration of III-V optoelectronic devices with Si electronic circuits is highly desirable because it will enable many otherwise unattainable capabilities. However, direct growth of III-V thin film on silicon substrates has been very challenging because of large mismatches in lattice constants and thermal coefficients. Furthermore, the high epitaxial growth temperature is detrimental to transistor performance. Here, we present a detailed studies on a novel growth mode which yields a catalyst-free (Al,In)GaAs nanopillar laser on a silicon substrate by metal-organic chemical vapor deposition at the low temperature of 400 °C. We study the growth and misfit stress relaxation mechanism by cutting through the center of the InGaAs/GaAs nanopillars using focused ion beam and inspecting with high-resolution transmission electron microscopy. The bulk material of the nanopillar is in pure wurtzite crystal phase, despite the 6% lattice mismatch with the substrate, with all stacking disorders well confined in the bottom-most transition region and terminated horizontally. Furthermore, InGaAs was found to be in direct contact with silicon, in agreement with the observed crystal orientation alignment and good electrical conduction across the interface. This is in sharp contrast to many III-V nanowires on silicon which are observed to stem from thin SiN(x), SiO(2), or SiO(2)/Si openings. In addition, GaAs was found to grow perfectly as a shell layer on In(0.2)Ga(0.8)As with an extraordinary thickness, which is 15 times greater than the theoretical thin-film critical thickness for a 1.5% lattice mismatch. This is attributed to the core-shell radial geometry allowing the outer layers to expand and release the strain due to lattice mismatch. The findings in this study redefine the rules for lattice-mismatched growth on heterogeneous substrates and device structure design.
III-V 族光电器件与 Si 电子电路的异质集成是非常理想的，因为它将实现许多原本无法实现的功能。然而，由于晶格常数和热膨胀系数的巨大不匹配，直接在硅衬底上生长 III-V 薄膜一直极具挑战性。此外，高的外延生长温度对晶体管性能有害。在这里，我们通过金属有机化学气相沉积（MOCVD）在 400°C 的低温下，在硅衬底上生长出一种无催化剂（Al，In）GaAs 纳米柱激光器，对这一新型生长模式进行了详细研究。我们通过聚焦离子束（FIB）切割穿过 InGaAs/GaAs 纳米柱的中心，并通过高分辨率透射电子显微镜（HRTEM）进行检查，研究了生长和失配应力松弛机制。尽管与衬底存在 6%的晶格失配，但纳米柱的体材料仍处于纯纤锌矿晶体相，所有的层错都很好地局限在最底层的过渡区，并沿水平方向终止。此外，发现 InGaAs 与硅直接接触，这与观察到的晶体取向一致，并且在界面处具有良好的电导率。这与许多在硅上的 III-V 纳米线形成鲜明对比，这些纳米线通常是从薄的 SiN(x)、SiO(2)或 SiO(2)/Si 开口中生长出来的。此外，GaAs 被发现作为 In(0.2)Ga(0.8)As 的壳层完美生长，其厚度是晶格失配理论薄膜临界厚度的 15 倍。这归因于核壳径向几何形状允许外层扩展并释放由于晶格失配而产生的应变。本研究的结果重新定义了异质衬底上晶格失配生长和器件结构设计的规则。
