Structural and Optical Behavior of Germanium Quantum Dots
Structural and Optical Behavior of Germanium Quantum Dots
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DOI：
10.1088/0256-307x/29/11/118101
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发表时间：
2012-11
影响因子：
3.5
通讯作者：
A. Samavati;Z. Othaman;Shyam Sundar Ghoshal;M. Dousti;R. J. Amjad
中科院分区：
文献类型：
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作者：
A. Samavati;Z. Othaman;Shyam Sundar Ghoshal;M. Dousti;R. J. Amjad
通过简单的制备方法控制高密度、大尺寸Ge纳米结构的生长、合成和表征是光电子器件的关键问题。在不同的热处理下，通过射频磁控溅射在Si（100）衬底上生长密度为1011 cm-2且尺寸小至108 nm的Ge量子点（QD）。使用原子力显微镜、X射线衍射、场发射扫描电子显微镜、能谱、光致发光（PL）和拉曼光谱测量了与退火温度相关的结构和光学性质。退火的效果被发现粗糙的Ge量子点从金字塔圆顶形的结构，因为它们长大，并将纳米岛到相对稳定和稳态配置。因此，退火允许Si混合到Ge QD中，从而降低了增强较大纳米岛形成的应变能。室温下的PL谱在2.87 eV和3.21 eV处有两个强峰，这归因于Ge和GeOx之间的相互作用以及量子点核壳结构的存在。量子限域效应导致的最强PL峰红移达<$0.05 eV，目前尚无报道。此外，预退火量子点的拉曼光谱由在大约305.25 cm-1、409.19 cm-1和515.25 cm-1处的三个峰组成，分别归因于Ge-Ge、Ge-Si和Si-Si振动模式。与退火样品相关的Ge-Ge光学声子频移（Δ 3.27 cm-1）被归因于不同量子点中形状、尺寸分布和Ge成分的变化。退火依赖的表面粗糙度和数密度的变化范围分别为0.83 ~ 0.24 nm和0.41 ~ 0.24 × 1011 cm−2。
Controlled growth, synthesis, and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic devices. Ge quantum dots (QDs) having a density of ∼1011 cm−2 and a size as small as ∼8 nm are grown by radio frequency magnetron sputtering on Si (100) substrates under different heat treatments. The annealing temperature dependent structural and optical properties are measured using AFM, XRD, FESEM, EDX, photoluminescence (PL) and Raman spectroscopy. The effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state configurations. Consequently, the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger nanoislands. The room temperature PL spectra exhibits two strong peaks at ∼2.87 eV and ∼3.21 eV attributed to the interaction between Ge, GeOx and the possibility of the presence of QDs core-shell structure. No reports so far exist on the red shift ∼0.05 eV of the strongest PL peak that results from the effect of quantum confinement. Furthermore, the Raman spectra for the pre-annealed QDs that consist of three peaks at around ∼305.25 cm−1, 409.19 cm−1 and 515.25 cm−1 are attributed to Ge-Ge, Ge-Si, and Si-Si vibration modes, respectively. The Ge-Ge optical phonon frequency shift (∼3.27 cm−1) associated with the annealed samples is assigned to the variation of shape, size distribution, and Ge composition in different QDs. The variation in the annealing dependent surface roughness and the number density is found to be in the range of ∼0.83 to ∼2.24 nm and ∼4.41 to ∼2.14 × 1011 cm−2, respectively.