Karthikeyan Sengunthar, Johnston Steven W, Gayakwad Dhammapriy, Mahapatra Suddhasatta, Bodnar Robert J, Zhao Jing, Joshi Rutwik, Hudait Mantu K
Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA.
National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
Nanoscale. 2024 Apr 4;16(14):7225-7236. doi: 10.1039/d3nr05904a.
Group IV GeSn quantum material finds application in electronics and silicon-compatible photonics. Synthesizing these materials with low defect density and high carrier lifetime is a potential challenge due to lattice mismatch induced defects and tin segregation at higher growth temperature. Recent advancements in the growth of these GeSn materials on Si, Ge, GaAs, and with substrate orientations, demonstrated different properties using epitaxial and chemical deposition methods. This article addresses the effect of GaAs substrate orientation and misorientation on the materials' properties and carrier lifetimes in epitaxial GeSn layers. With starting GaAs substrates of (100)/2°, (100)/6°, (110) and (111)A orientations, GeSn epitaxial layers were grown with an intermediate Ge buffer layer by molecular beam epitaxy and analyzed by several analytical tools. X-ray analysis displayed good crystalline quality, and Raman spectroscopy measurements showed blue shifts in phonon wavenumber due to biaxial compressive strain in GeSn epilayers. Cross-sectional transmission electron microscopy analysis confirmed the defect-free heterointerface of GeSn/Ge/GaAs heterostructure. Minority carrier lifetimes of the unintentionally doped n-type GeSn epilayers displayed photoconductive carrier lifetimes of >400 ns on (100)/6°, 319 ns on (100)/2°, and 434 ns on (110) GaAs substrate at 1500 nm excitation wavelength. On the other hand, GeSn layer showed poor carrier lifetime on (111)A GaAs substrate. The observed differences in carrier lifetimes were correlated with the formation energy of the Ge on (100)/6° and (100)/2° GaAs heterointerface using Stillinger-Weber interatomic potential model-based atomistic simulation with different heterointerfacial bonding by Synopsys QuantumATK tool. Total energy computation of 6280-atom Ge/GaAs supercell on (100)/6° leads to lower formation energy than (100)/2°, making it more thermodynamically stable. Hence, the growth of the GeSn/III-V material system using misoriented (100) substrates that are more thermodynamically stable will enhance the performances of optoelectronic devices.
IV族GeSn量子材料在电子学和硅兼容光子学中有着应用。由于晶格失配引起的缺陷以及在较高生长温度下的锡偏析，合成具有低缺陷密度和高载流子寿命的这些材料是一个潜在挑战。近期在Si、Ge、GaAs上以及不同衬底取向生长这些GeSn材料方面取得的进展，使用外延和化学沉积方法展现了不同的特性。本文探讨了GaAs衬底取向和错取向对外延GeSn层中材料特性和载流子寿命的影响。以(100)/2°、(100)/6°、(110)和(111)A取向的起始GaAs衬底，通过分子束外延生长带有中间Ge缓冲层的GeSn外延层，并使用多种分析工具进行分析。X射线分析显示出良好的晶体质量，拉曼光谱测量表明由于GeSn外延层中的双轴压缩应变，声子波数发生蓝移。截面透射电子显微镜分析证实了GeSn/Ge/GaAs异质结构无缺陷的异质界面。在1500 nm激发波长下，非故意掺杂的n型GeSn外延层的少数载流子寿命在(100)/6°衬底上显示出大于400 ns的光导载流子寿命，在(100)/2°衬底上为319 ns，在(110) GaAs衬底上为434 ns。另一方面，GeSn层在(111)A GaAs衬底上显示出较差的载流子寿命。利用Synopsys QuantumATK工具基于Stillinger-Weber原子间势模型进行原子模拟，通过不同的异质界面键合，观察到的载流子寿命差异与(100)/6°和(100)/2° GaAs异质界面上Ge的形成能相关。(100)/6°上6280原子的Ge/GaAs超胞的总能量计算得出其形成能低于(100)/2°，使其在热力学上更稳定。因此，使用热力学上更稳定的错取向(100)衬底生长GeSn/III-V材料系统将提高光电器件的性能。
