Epitaxial Growth of Germanium on Silicon for Light Emitters

National Basic Research Program of China [2007CB613404, 2012CB933503]; National Natural Science Foundation of China [61036003, 60837001, 61176092]; Fundamental Research Funds for the Central Universities [2010121056]This paper describes the role of Ge as an enabler for light emitters on a Si platform. In spite of the large lattice mismatch of similar to 4.2% between Ge and Si, high-quality Ge layers can be epitaxially grown on Si by ultrahigh-vacuum chemical vapor deposition. Applications of the Ge layers to near-infrared light emitters with various structures are reviewed, including the tensile-strained Ge epilayer, the Ge epilayer with a delta-doping SiGe layer, and the Ge/SiGe multiple quantum wells on Si. The fundamentals of photoluminescence physics in the different Ge structures are discussed briefly

Fire dynamics and driving mechanisms on the Eastern Coast of China since the Late Pleistocene: evidence from charcoal records on Shengshan Island

Fires play a significant role in ecosystems, exerting a profound influence on climate, vegetation, and geochemical cycles, while being reciprocally affected by these factors. The reconstruction of past fire events serves as a valuable window into understanding environmental changes over time. To investigate the history of ancient fires on the Eastern Coast of China, we conducted the first charcoal analysis on a loess profile of Shengshan Island (East China Sea). Along with other biological and geochemical proxies, we successfully reconstructed the ancient fire dynamics and elucidated their driving mechanisms in this region since the Late Pleistocene. Our initial findings revealed a peak in charcoal concentration during the 60-50 ka period, but after calibrating for sedimentation rate, the concentration significantly decreased. Fire activities remained weak during 50-30 ka, likely due to the scarcity of combustible materials. Between 30-12 ka, fires were frequent in the early period, while gradually diminishing during the later stage. Dry climate and dense vegetation likely attributed to frequent fires in early period, while some extreme events (e.g., sudden change in temperature) may have decreased the fire frequency in later period. The Holocene (began ~12 ka) evidenced the most frequent fire events as a high charcoal concentration was recorded, likely caused by human activities. After comparing our findings with other paleoecological records from surrounding areas, we confirmed the accuracy of our reconstruction of ancient fires. This reconstruction captures not only local shifts but also broader regional changes. Overall, our study highlights the importance of calibrating sedimentation rate in charcoal profiles, while also contributing to an enhanced understanding of environmental changes along the Eastern Coast of China since the Late Pleistocene

Physical and electrical properties of thermally oxidized dielectrics on Si-capped Ge-on-Si substrate

National Basic Research Program of China [2012CB933503]; National Natural Science Foundation of China [61036003, 61176092]; Fundamental Research Funds for the Central Universities [2010121056]Thermal oxidation of silicon (Si)-capped germanium (Ge) epilayer on Si substrate is performed to study the effect of the physical interface on the electrical properties of Ge metaloxide-semiconductor capacitors. During the growth and oxidation of the Si cap layer, Ge atoms diffuse through the Si cap layer, and they are oxidized to GeO2. Once the Si cap layer is consumed, more Ge suboxides are generated, resulting in the serious degradation of the capacitance-voltage characteristics. Both the positive fixed charges generated by the evaporation of GeO and the negative fixed charges induced by the formation of Si-O-dangling bonds are proposed to affect the flat-band voltage shifts. These results suggest that the deposition of a thin Si cap layer on Ge is effective in suppressing the generation of Ge sub-oxides during thermal oxidation, thereby improving the performance of Ge capacitors. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3668115

Physical and electrical properties of thermally oxidized dielectrics on Si-capped Ge-on-Si substrate

National Basic Research Program of China [2012CB933503]; National Natural Science Foundation of China [61036003, 61176092]; Fundamental Research Funds for the Central Universities [2010121056]Thermal oxidation of silicon (Si)-capped germanium (Ge) epilayer on Si substrate is performed to study the effect of the physical interface on the electrical properties of Ge metaloxide-semiconductor capacitors. During the growth and oxidation of the Si cap layer, Ge atoms diffuse through the Si cap layer, and they are oxidized to GeO2. Once the Si cap layer is consumed, more Ge suboxides are generated, resulting in the serious degradation of the capacitance-voltage characteristics. Both the positive fixed charges generated by the evaporation of GeO and the negative fixed charges induced by the formation of Si-O-dangling bonds are proposed to affect the flat-band voltage shifts. These results suggest that the deposition of a thin Si cap layer on Ge is effective in suppressing the generation of Ge sub-oxides during thermal oxidation, thereby improving the performance of Ge capacitors. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3668115

Epitaxial Growth of Germanium on Silicon for Light Emitters

National Basic Research Program of China [2007CB613404, 2012CB933503]; National Natural Science Foundation of China [61036003, 60837001, 61176092]; Fundamental Research Funds for the Central Universities [2010121056]This paper describes the role of Ge as an enabler for light emitters on a Si platform. In spite of the large lattice mismatch of similar to 4.2% between Ge and Si, high-quality Ge layers can be epitaxially grown on Si by ultrahigh-vacuum chemical vapor deposition. Applications of the Ge layers to near-infrared light emitters with various structures are reviewed, including the tensile-strained Ge epilayer, the Ge epilayer with a delta-doping SiGe layer, and the Ge/SiGe multiple quantum wells on Si. The fundamentals of photoluminescence physics in the different Ge structures are discussed briefly

A Review on Analytical Modeling for Collapse Mode Capacitive Micromachined Ultrasonic Transducer of the Collapse Voltage and the Static Membrane Deflections

Analytical modeling of capacitive micromachined ultrasonic transducer (CMUT) is one of the commonly used modeling methods and has the advantages of intuitive understanding of the physics of CMUTs and convergent when modeling of collapse mode CMUT. This review article summarizes analytical modeling of the collapse voltage and shows that the collapse voltage of a CMUT correlates with the effective gap height and the electrode area. There are analytical expressions for the collapse voltage. Modeling of the membrane deflections are characterized by governing equations from Timoshenko, von Kármán equations and the 2D plate equation, and solved by various methods such as Galerkin’s method and perturbation method. Analytical expressions from Timoshenko’s equation can be used for small deflections, while analytical expression from von Kármán equations can be used for both small and large deflections

Depth-dependent etch pit density in Ge epilayer on Si substrate with a self-patterned Ge coalescence island template

National Basic Research Program of China [2012CB933503]; National Natural Science Foundation of China [61036003, 61176092, 60837001]; Fundamental Research Funds for the Central Universities [2010121056]; State Key Laboratory of Functional Materials for InformaticsGe epilayer with low dislocation density is prepared on a low temperature self-patterned Ge coalescence island template on Si substrate by ultra-high vacuum chemical vapor deposition. The depth profile of dislocation density in the Ge epilayer measured by etch-pit counting indicates that the dislocation density decreases drastically when the thickness of Ge layer is larger than 270 nm, and then depends weakly on the further increase of Ge thickness. The reduction of dislocations is ascribed to the Ge islands coalescence and lateral growth during deposition of Ge at higher temperature. 1.05-mu m-thick Ge epilayer on Si with a dislocation density of the order of 10(6)cm(-2) and root-mean-square surface roughness of 0.45 nm are achieved without any additional thermal treatments. (C) 2011 Elsevier B.V. All rights reserved

Depth-dependent etch pit density in Ge epilayer on Si substrate with a self-patterned Ge coalescence island template

National Basic Research Program of China [2012CB933503]; National Natural Science Foundation of China [61036003, 61176092, 60837001]; Fundamental Research Funds for the Central Universities [2010121056]; State Key Laboratory of Functional Materials for InformaticsGe epilayer with low dislocation density is prepared on a low temperature self-patterned Ge coalescence island template on Si substrate by ultra-high vacuum chemical vapor deposition. The depth profile of dislocation density in the Ge epilayer measured by etch-pit counting indicates that the dislocation density decreases drastically when the thickness of Ge layer is larger than 270 nm, and then depends weakly on the further increase of Ge thickness. The reduction of dislocations is ascribed to the Ge islands coalescence and lateral growth during deposition of Ge at higher temperature. 1.05-mu m-thick Ge epilayer on Si with a dislocation density of the order of 10(6)cm(-2) and root-mean-square surface roughness of 0.45 nm are achieved without any additional thermal treatments. (C) 2011 Elsevier B.V. All rights reserved