Lattice matched GeSn/InAlAs heterostructure: role of Sn in energy band alignment, atomic layer diffusion and photoluminescence
Lattice matched GeSn/InAlAs heterostructure: role of Sn in energy band alignment, atomic layer diffusion and photoluminescence
复制标题
DOI：
10.1039/d3tc01018j
复制
发表时间：
2023-06-21
影响因子：
6.4
通讯作者：
Hudait，Mantu K.
中科院分区：
文献类型：
--
作者：
Karthikeyan，Sengunthar;Joshi，Rutwik;Hudait，Mantu K.
锗与α-锡合金（GeSn）转变为直接带隙半导体，对光电子学具有重要意义。为了提高GeSn基激光器的量子效率，必须将载流子局域化。在这项工作中，外延GeSn异质结构材料系统进行了分析，以确定载流子限制的带偏移：（i）0.53%的压缩应变Ge 0.97Sn 0.03/AlAs;（ii）0.81%的压缩应变Ge 0.94Sn 0.06/Ge;和（iii）晶格匹配的Ge 0.94Sn 0.06/In 0.12Al 0.88As。利用拉曼光谱研究了GeSn合金中声子模随Sn组分的变化，发现Sn引起Ge-Ge纵向光学声子模峰的波数发生红移。表示对Ge 0.94 Sn 0.06合金的拉曼位移的应变贡献的材料参数B被确定为B = 314.81 ± 14 cm-1。在79 K下进行低温光致发光测量，以确定对于0.81%压缩应变的Ge 0.94Sn 0.06的直接和间接能带隙Eg，Γ = 0.72 eV和Eg，L = 0.66 eV，以及对于晶格匹配的Ge 0.94Sn 0.06外延层的直接和间接能带隙Eg，Γ = 0.73 eV和Eg，L = 0.68 eV。使用X射线光电子能谱（XPS）分析了Sn原子种类的化学效应，揭示了Ge 3d芯能级（CL）谱向影响键合环境的较低结合能的偏移。用XPS测量的CL谱确定了Ge_（0.94）Sn_（0.06）/In_（0.12）Al_（0.88）As异质结构的大的价带偏移ΔEV = 0.91 ± 0.1 eV，导带偏移ΔEC = 0.64 ± 0.1 eV。评估的频带偏移被认为是I型配置，需要在激光器中的载流子限制。此外，这些带偏移值进行了比较与基于第一性原理计算的Ge/InAlAs带对齐，它被发现有砷向上扩散限制到1单层的外延GeSn覆盖层，排除了缺陷引起的带对齐的修改的可能性。此外，这种晶格匹配的GeSn/InAlAs异质结构带偏移值显着高于GeSn生长在IV族缓冲/衬底上。因此，晶格匹配的GeSn/InAlAs材料系统具有大的带偏移，提供上级载流子限制以实现高效的基于GeSn的光子器件。
Germanium alloyed with α-tin (GeSn) transitions to a direct bandgap semiconductor of significance for optoelectronics. It is essential to localize the carriers within the active region for improving the quantum efficiency in a GeSn based laser. In this work, epitaxial GeSn heterostructure material systems were analyzed to determine the band offsets for carrier confinement: (i) a 0.53% compressively strained Ge0.97Sn0.03/AlAs; (ii) a 0.81% compressively strained Ge0.94Sn0.06/Ge; and (iii) a lattice matched Ge0.94Sn0.06/In0.12Al0.88As. The phonon modes in GeSn alloys were studied using Raman spectroscopy as a function of Sn composition, that showed Sn induced red shifts in wavenumbers of the Ge–Ge longitudinal optical phonon mode peaks. The material parameter b representing strain contribution to Raman shifts of a Ge0.94Sn0.06 alloy was determined as b = 314.81 ± 14 cm−1. Low temperature photoluminescence measurements were performed at 79 K to determine direct and indirect energy bandgaps of Eg,Γ = 0.72 eV and Eg,L = 0.66 eV for 0.81% compressively strained Ge0.94Sn0.06, and Eg,Γ = 0.73 eV and Eg,L = 0.68 eV for lattice matched Ge0.94Sn0.06 epilayers. Chemical effects of Sn atomic species were analyzed using X-ray photoelectron spectroscopy (XPS), revealing a shift in Ge 3d core level (CL) spectra towards the lower binding energy affecting the bonding environment. Large valence band offset of ΔEV = 0.91 ± 0.1 eV and conduction band offset of ΔEC,Γ–X = 0.64 ± 0.1 eV were determined from the Ge0.94Sn0.06/In0.12Al0.88As heterostructure using CL spectra by XPS measurements. The evaluated band offset was found to be of type-I configuration, needed for carrier confinement in a laser. In addition, these band offset values were compared with the first-principles-based calculated Ge/InAlAs band alignment, and it was found to have arsenic up-diffusion limited to 1 monolayer of epitaxial GeSn overlayer, ruling out the possibility of defects induced modification of band alignment. Furthermore, this lattice matched GeSn/InAlAs heterostructure band offset values were significantly higher than GeSn grown on group IV buffer/substrates. Therefore, a lattice matched GeSn/InAlAs material system has large band offsets offering superior carrier confinement to realize a highly efficient GeSn based photonic device.