Comparative Studies of the Growth and Characterization of Germanium Epitaxial Film on Silicon (001) with 0° and 6° Offcut

The quality of germanium (Ge) epitaxial films grown directly on silicon (Si) (001) with 0° and 6° offcut orientation using a reduced-pressure chemical vapor deposition system is studied and compared. Ge film grown on Si (001) with 6° offcut presents ～65% higher threading dislocation density and higher root-mean-square (RMS) surface roughness (1.92 nm versus 0.98 nm) than Ge film grown on Si (001) with 0° offcut. Plan-view transmission electron microscopy also reveals that threading dislocations are more severe (in terms of contrast and density) for the 6° offcut. In addition, both high-resolution x-ray diffraction and Raman spectroscopy analyses show that the Ge epilayer on 6° offcut wafer presents higher tensile strain. The poorer quality of the Ge film on Si (001) with 6° offcut is a result of an imbalance in Burgers vectors that favors dislocation nucleation over annihilation.     

Si基外延Ge薄膜及退火对其特性的影响研究

采用超高真空化学气相沉积(UHV-CVD)系统,用低温Ge缓冲层技术在Si衬底上外延了张应变Ge薄膜.扫描电镜(TEM)图表明Si基外延Ge薄膜拥有低的位错密度,原子力显微镜(AFM)测试Ge层表面粗糙度仅为1.2 nm.对Si基外延Ge薄膜进行了不同温度下的退火,并用双晶X射线衍射(DCXRD)曲线和Raman谱进行...     

UHV/CVD法生长硅基低位错密度厚锗外延层

采用超高真空化学气相淀积系统,以高纯Si2 H6和GeH4作为生长气源,用低温缓冲层技术在Si(001)衬底上成功生长出厚的纯Ge外延层.对Si衬底上外延的纯Ge层用反射式高能电子衍射仪、原子力显微镜、X射线双晶衍射曲线和Ra-man谱进行了表征.结果表明在Si基上生长的约550nm厚的Ge外延层,表面粗糙度小于1nm,XRD双晶衍射曲线和Ra-man谱Ge-Ge模半高宽分别为530'和5.5cm-1,具有良好的结晶质量.位错腐蚀结果显示线位错密度小于5×105cm-2可用于制备Si基长波长集成光电探测器和Si基高速电子器件.     

Observation and nucleation control of Ge nanoislands on Si(111) surfaces using scanning reflection electron microscopy

Using a high-resolution scanning reflection electron microscope with multifunctions, we investigate Ge nucleation processes on clean Si(111) surfaces and form Ge islands on them by controlling step arrangements of Si(111) surfaces and by using focused electron beam (EB)-induced surface reactions. It is found that three-dimensional (3D) Ge islands grow selectively at step band areas on the surfaces without growth of the islands at terrace areas. Three-dimensional Ge nanoislands are formed at given points by stimulating the Ge wetting layer using focused electron beams and scanning tunnelling microscopy. Ge nanoislands are also formed by depositing Ge on Si windows in ultrathin SiO2 films and subsequent annealing of the sample. The islands are formed only at the window positions. These results imply new methods for forming Ge quantum dots or nanostructures at given areas.     

硅缓冲层提高选区外延生长硅基锗薄膜质量

研究了Si缓冲层对选区外延Si基Ge薄膜的晶体质量的影响。利用超高真空化学气相沉积系统,结合低温Ge缓冲层和选区外延技术,通过插入Si缓冲层,在Si/SiO_2图形衬底上选择性外延生长Ge薄膜。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)表征了Ge薄膜的晶体质量和表面形貌。测试结果表明,选区外延Ge薄膜的晶体质量比无图形衬底外延得到薄膜的晶体质量要高;选区外延Ge薄膜前插入Si缓冲层得到Ge薄膜具有较低的XRD曲线半高宽以及表面粗糙度,位错密度低至5.9×10~5/cm^2,且薄膜经过高低温循环退火后,XRD曲线半高宽和位错密度进一步降低。通过插入Si缓冲层可提高选区外延Si基Ge薄膜的晶体质量,该技术有望应用于Si基光电集成。     

Resonant cavity enhanced photoluminescence of tensile strained Ge/SiGe quantum wells on silicon-on-insulator substrate

The tensile strained Ge/SiGe multiple quantum wells （MQWs） grown on a silicon-on-insulator （SOI） substrate were fabricated successfully by ultra-high chemical vapor deposition. Room temperature direct band photoluminescence from Ge quantum wells on SOI substrate is strongly modulated by Fabry-Perot cavity formed between the surface of Ge and the interface of buried SiO2. The photoluminescence peak intensity at 1.58 μm is enhanced by about 21 times compared with that from the Ge/SiGe quantum wells on Si substrate, and the full width at half maximum （FWHM） is significantly reduced. It is suggested that tensile strained Ge/SiGe multiple quantum wells are one of the promising materials for Si-based microcavity lijzht emitting devices.     

Deposition,post-deposition annealing,and characterization of epitaxial Ge films grown on Si(100) by pyrolysis of GeH4

As a first step towards developing heterostructures such as GaAs/Ge/Si entirely by chemical vapor deposition, Ge films have been deposited on (100) Si by the pyrolysis of GeH₄. The best films are grown at 700° C and are planar and specular, with RBS minimum channeling yields of ≈4.0% (near the theoretical value) and defect densities of 1.3 x 10⁸ cm⁻². Variations of in-situ cleaning conditions, which affect the nature of the Si substrate surface, greatly affect the ability to get good epitaxial growth at 700° C. The majority of the defects found in the Ge films are extrinsic stacking faults, formed by dissociation of misfit and thermal expansion accommodation dislocations. The stacking fault density is not significantly reduced by post-deposition annealing, as is the case for the dislocations observed in MBE Ge films. It is suggested that lowering the CVD growth temperature through the use of high vacuum deposition equipment would result in dislocation defects like those of MBE films which could then be annealed more effectively than stacking faults. Films with defect densities equivalent to MBE Ge films (~2 x 10⁷ cm⁻²) could then probably be produced.     

Mechanism of hemispherical-grained Si formation for dynamic random access memory cells by rapid thermal chemical vapor deposition

An uneven coating made of hemispherical-grained Si (HSG) was formed on an amorphous Si layer by a rapid thermal chemical vapor deposition (CVD) (RTCVD) process. The uneven coating increases the effective surface area of a capacitor electrode in dynamic random access memory (DRAM) cells. The formation of the HSG consists of “seeding” and subsequent isothermal annealing stages. During the seeding stage, nanometer size Si single crystals are formed on the surface of the amorphous Si layer. During rapid thermal annealing at 665°C, under high vacuum, the Si grains grow linearly with increasing temperature and reach an average size of 95 nm after 20 sec. The nucleation and growth of the HSG occurs within a narrow range of temperature and time, which is sufficient for a short diffusion path of Si atoms on the surface of the amorphous Si layer, but insufficient for crystallization of the amorphous Si layer: The HSG coating increases the capacitance of a memory cell by a factor of 2.     

Comparison of time-to-failure of GeSi and Si bipolar transistors

The effects of Ge in the epitaxial-base on the reliability of Si/Ge_xSi_1-x/Si heterojunction bipolar transistors were investigated. The ten-year time-to-failure under emitter-base junction reverse-bias stress was measured at the designed operation voltage by the current-acceleration method and compared to that of Si bipolar junction transistors with no Ge (x=0). The investigation shows that the Ge incorporated by the reduced pressure chemical vapor deposition epitaxial technology to give the ramp-type Ge profile has no adverse effects on the transistor reliability     

Pure germanium epitaxial growth on thin strained silicon-germanium graded layers on bulk silicon substrate for high-mobility channel metal-oxide-semiconductor field-effect transistors

We demonstrate epitaxially grown high-quality pure germanium (Ge) on bulk silicon (Si) substrates by ultra-high-vacuum chemical vapor deposition (UHVCVD) without involving growth of thick relaxed SiGe buffer layers. The Ge layer is grown on thin compressively strained SiGe layers with rapidly varying Ge mole fraction on Si substrates resulting in several SiGe interfaces between the Si substrate and the pure Ge layer at the surface. The presence of such interfaces between the Si substrate and the Ge layer results in blocking threading dislocation defects, leading to a defect-free pure Ge epitaxial layer on the top. Results from various material characterization techniques on these grown films are shown. In addition, capacitance-voltage (CV) measurements of metal-oxide-semiconductor (MOS) capacitors fabricated on this structure are also presented, showing that the grown structure is ideal for high-mobility metal-oxide-semiconductor field-effect transistor applications.     

用减压化学气相沉积技术制备应变硅材料

利用减压化学气相沉积技术，制备出应变Si/弛豫Si0.9Ge0.1/渐变组分弛豫SiGe/Si衬底. 通过控制组分渐变SiGe过渡层的组分梯度和适当优化弛豫SiGe层的外延生长工艺，有效地降低了表面粗糙度和位错密度.与Ge组分突变相比，采用线性渐变组分后，应变硅材料表面粗糙度从3.07nm减小到0.75nm，位错密度约为5E4cm-2，表面应变硅层应变度约为0.45%.     

Integration of InGaP/GaAs/Ge triple‐junction solar cells on deeply patterned silicon substrates

We report preliminary results on InGaP/InGaAs/Ge photovoltaic cells for concentrated terrestrial applications, monolithically integrated on engineered Si(001) substrates. Cells deposited on planar Ge/Si(001) epilayers, grown by plasma‐enhanced chemical vapor deposition, provide good efficiency and spectral response, despite the small thickness of the Ge epilayers and a threading dislocation density as large as 10⁷/cm². The presence of microcracks generated by the thermal misfit is compensated by a dense collection grid that avoids insulated areas. In order to avoid the excessive shadowing introduced by the use of a dense grid, the crack density needs to be lowered. Here, we show that deep patterning of the Si substrate in blocks can be an option, provided that a continuous Ge layer is formed at the top, and it is suitably planarized before the metalorganic chemical vapor deposition. The crack density is effectively decreased, despite that the efficiency is also lowered with respect to unpatterned devices. The reasons of this efficiency reduction are discussed, and a strategy for improvement is proposed and explored. Full morphological analysis of the coalesced Ge blocks is reported, and the final devices are tested under concentrated AM1.5D spectrum. Copyright © 2016 John Wiley & Sons, Ltd.     

Growth of a Ge layer on 8 in. Si (100) substrates by rapid thermal chemical vapor deposition

We have made the successful growth of Ge layer on 8 in. Si (100) substrates by rapid thermal chemical vapor deposition (RTCVD). In order to overcome the large lattice mismatch between Ge and Si, we used a two-step growth method. Our method shows the uniformity of the thickness and good quality Ge layer with a homogeneous distribution of tensile strain and a lower etch pit density (EPD) in order of 10⁵ cm⁻². The surface morphology is very smooth and the root mean square (RMS) of the surface roughness was 0.27 nm. The photocurrent spectra were dominated by the Ge layer related transition that corresponding to the transitions of the Si and Ge. The roll-off in photocurrent spectra beyond 1600 nm is expected due to the decreased absorption of Ge.     

The nucleation of coherent semiconductor islands during the Stranski-Krastanov growth induced by elastic strains

The Ge island growth on the Si(100) and Si(111) surfaces was investigated through spectral ellipsometry in real time. It is found that both cases correspond to Stranski-Krastanov growth; i.e., a Ge wetting layer is initially formed, and only then do the islands of the new phase grow on the surface of this layer. However, the island nucleation on the (100) surface is accompanied by a substantial decrease in the wetting layer thickness, whereas, on the (111) surface, the islands nucleate and grow on the wetting layer of constant thickness. The Ge atoms on the (100) surface transfer from the wetting layer to islands, thus substantially decreasing the elastic energy of the system, but increasing the surface energy. For this reason, it is concluded that, in this case, it is the elastic energy which represents the fundamental driving force of the island nucleation. Thermodynamic and kinetic theories of island nucleation from the wetting layer under the effect of elastic energy are developed. A new notion of overstress is introduced by analogy with supersaturation and overcooling. The time evolution of the wetting layer thickness, the nucleation rate, and the island surface density of the new phase is described. The theoretical results are compared to experimental data obtained through ellipsometric simulation, and it is found that the theory and experiment are in good agreement.     

采用低温缓冲层技术在Si衬底上生长高质量Ge薄膜

采用低温缓冲层技术,在Si衬底上生长了质量优良的Ge薄膜。利用原子力显微镜（AFM）、双晶X射线衍射（XRD）和拉曼散射等研究了薄膜的晶体质量。结果表明,由于无法抑制三维岛状生长,低温Ge缓冲层的表面是起伏的。然而,Ge与Si间的压应变几乎完全弛豫。当缓冲层足够厚时,后续高温Ge外延层的生长能够使粗糙的表面变得平整。在...     

Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD

Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 °C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 °C. Root mean square of roughness (RMS) of ∼0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. ∼4 × 10⁸ cm⁻² for a 4.7 μm thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 °C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as ∼7 × 10⁵ cm⁻² is achieved for 4.7 μm Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of ∼0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated.     

Interaction of self-assembled Ge islands and adjacent Si layers grown on unpatterned and patterned Si(001) substrates

For use in electronic devices, self-assembled Ge islands formed on Si(001) must be covered with an additional Si layer. Chemically vapor deposited Si layers initially grow very rapidly over Ge islands because of the catalytic effect of Ge on the reaction of the Si-containing gas. The edges of the Si features covering Ge “pyramids” are rotated by 45° with respect to the edges of the Ge pyramids because of the different mechanisms orienting the Ge islands and the Si features. When multiple layers of islands are formed, the in-plane ordering of the Ge islands depends on the thickness of the Si interlayer separating the island layers. When selective Si is grown on a patterned Si wafer to form the underlying structure for the Ge islands, the position of the islands is influenced by the detailed shape of the Si near the edges, which in turn depends on the thickness of the selectively deposited Si, the pattern size, and the amount of surrounding oxide.     

GaN在Si(001)上的ECR等离子体增强MOCVD直接生长研究

研究了用电子回旋共振(ECR)等离子体增强金属有机物化学气相沉积(PEMOCVD)技术在Si(001)衬底上,低温(620～720℃)下GaN薄膜的直接外延生长及晶相结构.高分辨透射电镜(HRTEM)和X射线衍射(XRD)结果表明:在Si(001)衬底上外延出了高度c轴取向纤锌矿结构的GaN膜,但在GaN/Si(001)界面处自然形成了一层非晶层,其两个表面平坦而陡峭,厚度均匀(≈2nm).分析认为,在初始成核阶段N与Si之间反应所产生的这层SixNy非晶层使GaN的β相没有形成.XRD和原子力显微镜(AFM)结果表明,衬底表面的原位氢等离子体清洗,GaN初始成核及后续生长条件对GaN膜的晶体质量非常重要.     

GaN在Si(001)上的ECR等离子体增强MOCVD直接生长研究

研究了用电子回旋共振(ECR)等离子体增强金属有机物化学气相沉积(PEMOCVD)技术在Si(001)衬底上,低温(620～720℃)下GaN薄膜的直接外延生长及晶相结构.高分辨透射电镜(HRTEM)和X射线衍射(XRD)结果表明:在Si(001)衬底上外延出了高度c轴取向纤锌矿结构的GaN膜,但在GaN/Si(001)界面处自然形成了一层非晶层,其两个表面平坦而陡峭,厚度均匀(≈2nm).分析认为,在初始成核阶段N与Si之间反应所产生的这层SixNy非晶层使GaN的β相没有形成.XRD和原子力显微镜(AFM)结果表明,衬底表面的原位氢等离子体清洗,GaN初始成核及后续生长条件对GaN膜的晶体质量非常重要.     

RPCVD生长SiGe薄膜及其性能研究

利用应用材料公司外延设备,在Si(001)衬底上,通过RPCVD方式生长出完全应变、无位错的SiGe外延层.通过X射线衍射和原子力显微镜测试技术,得到了外延层Ge摩尔分数、外延层厚度、生长速率以及表面粗糙度等参数,研究了运用RPCVD方法制备的应变SiGe外延层的生长特性以及薄膜特性.结果表明,在660℃所生长的薄膜,其XRD图像均出现了Pendelossung条纹,表明薄膜质量较好.Ge摩尔分数高达16.5%.薄膜表面粗糙度RMS在0.3～0.6nm.