Author: Yan Cai (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 197
Get Book Here
Book Description
Germanium (Ge) is an optically active material with the advantages of Si-CMOS compatibility and monolithic integration. It has great potential to be used as the light emitter for Si photonics. Tensile strain and n-type doping are two key properties in Ge to achieve optical gain. This thesis mainly focuses on: (1) physical understandings of the threshold behavior of Ge-on-Si bulk laser and the temperature dependent performance; (2) process developments to grow and planarize the epitaxial Ge on Si in oxide trenches and corners; (3) introduction of n-type dopant into Ge-on-Si thin films while studying the threading dislocation behavior in n-Ge during annealing; (4) Design an external cavity Ge laser integrated with Si waveguides for a low threshold current and single mode operation. Heavy n-type doping was observed to change the Ge electronic band structure by band gap narrowing effect. We also found a failure of using a simple Drude model to explain free carrier absorption in n-Ge. We modified the optical gain simulation based on the above two observations in Ge. We found a broad gain bandwidth of ~ 200 nm from 1550 nm to 1750 nm and a higher net materials gain. We predicted a theoretical lasing threshold current density of 5~10 kA/cm2 in the bulk Ge laser device with the n-type doping of mid-1019 cm-3 at room temperature. We also predicted the Ge laser device would have better temperature stability regarding the threshold current compared to the III-V laser. Single crystalline Ge was epitaxial grown on Si in oxide trenches using ultra high vacuum chemical vapor deposition. The selective growth lead to the faceting in Ge because of the different growth rates of crystal orientations. We developed a suitable photolithography and oxide etch process to get the vertical oxide sidewall for Ge trench filling. We also tested the Ge growth in the T-shape corners to improve the reflectivity at the waveguide end. The T-shape structure was also useful for the Ge/Si waveguide coupling in the external cavity laser. Furthermore, we developed a chemical mechanical polishing (CMP) process for the over-grown Ge waveguides. The Ge CMP process was selective to oxide, flexible to change in the CMP rate by DI water dilution and controllable for a minimum dishing of Ge in the oxide trenches. N-type doping helped to increase the direct band transition in Ge for light emission. We developed a delta-doping method to grow a dopant source called "delta doping layer" on the single crystalline Ge layer without introducing extra defects. We then used rapid thermal annealing to drive the dopant into the underlying Ge layer. The dopant enhanced diffusion was discovered to speed up the drive-in process. The active n-type concentration in Ge could reach up to 5×1019 cm-3 using the delta doping source and annealing process. Since the dopant source layer had a disrupted Ge growth, we used the developed CMP process to remove it after the dopant drive-in. A comprehensive dopant diffusion simulation was developed to predict the annealing temperature and time to achieve high n-type doping and uniform distribution. We used plan-view transmission electron microscopy to examine the threading dislocation density (TDD) in n-Ge for both blanket films and trench grown waveguides. We found a high TDD of ~ 1×108cm-2 in 1 [mu]m thick blanket Ge with doping of 3×1018 cm-3 after high temperature annealing at 850 °C for 40 min. The TDD is 1×109 cm-2 in the 300 nm thick and 1 [mu]m wide Ge waveguide. We examined the effects of annealing temperature, Ge thickness, Si/Ge inter-diffusion and trench width on the threading dislocation behavior. However, we have not found the exact reason causing the high TDD and therefore, further study is required on the TDD reduction for the Ge waveguide. Finally, we designed an external cavity Ge laser using distributed Bragg reflector (DBR) gratings on Si waveguides. A detailed discussion on the cross section design was presented to mitigate the internal optical loss from claddings and metal layers and to improve the current injection uniformity across the Ge waveguide. The aim of the DBR grating design was to achieve a single mode operation by controlling the full width half maximum of the grating reflectance spectrum. We also discussed the coupling between Ge and Si waveguides and different designs were presented to increase the coupling efficiency.
Author: Kazumi Wada
Publisher: John Wiley & Sons
ISBN: 3527650237
Category : Science
Languages : en
Pages : 336
Get Book Here
Book Description
Representing a further step towards enabling the convergence of computing and communication, this handbook and reference treats germanium electronics and optics on an equal footing. Renowned experts paint the big picture, combining both introductory material and the latest results. The first part of the book introduces readers to the fundamental properties of germanium, such as band offsets, impurities, defects and surface structures, which determine the performance of germanium-based devices in conjunction with conventional silicon technology. The second part covers methods of preparing and processing germanium structures, including chemical and physical vapor deposition, condensation approaches and chemical etching. The third and largest part gives a broad overview of the applications of integrated germanium technology: waveguides, photodetectors, modulators, ring resonators, transistors and, prominently, light-emitting devices. An invaluable one-stop resource for both researchers and developers.
Author: Laurent Vivien
Publisher: Taylor & Francis
ISBN: 1439836116
Category : Science
Languages : en
Pages : 831
Get Book Here
Book Description
The development of integrated silicon photonic circuits has recently been driven by the Internet and the push for high bandwidth as well as the need to reduce power dissipation induced by high data-rate signal transmission. To reach these goals, efficient passive and active silicon photonic devices, including waveguide, modulators, photodetectors,
Author: R. Szweda
Publisher: Elsevier
ISBN: 0080541216
Category : Business & Economics
Languages : en
Pages : 419
Get Book Here
Book Description
The first edition of Silicon Germanium Materials & Devices - A Market & Technology Overview to 2006 examines the development of the silicon germanium business over a six-year period 2001 to 2006. It analyses the trends in markets, technologies and industry structure and profiles all the major players. It is specifically aimed at users and manufacturers of substrates, epiwafers, equipment and devices. The analysis includes a competitive assessment of the market of silicon germanium vs. gallium arsenide, indium phosphide vs. other forms of silicon. Silicon Germanium Materials & Devices - A Market & Technology Overview to 2006 is designed to assist with business plans, R&D and manufacturing strategies. It will be an indispensable aid for managers responsible for business development, technology assessment and market research. The report examines the rapid development of silicon germanium from an R&D curiosity to production status. An extensive treatment from materials through processes to devices and applications it encapsulates the entire silicon germanium business of today and assesses future directions. For a PDF version of the report please call Tina Enright on +44 (0) 1865 843008 for price details.
Author: Gudrun Kissinger
Publisher: CRC Press
ISBN: 1466586648
Category : Science
Languages : en
Pages : 436
Get Book Here
Book Description
Despite the vast knowledge accumulated on silicon, germanium, and their alloys, these materials still demand research, eminently in view of the improvement of knowledge on silicon–germanium alloys and the potentialities of silicon as a substrate for high-efficiency solar cells and for compound semiconductors and the ongoing development of nanodevices based on nanowires and nanodots. Silicon, Germanium, and Their Alloys: Growth, Defects, Impurities, and Nanocrystals covers the entire spectrum of R&D activities in silicon, germanium, and their alloys, presenting the latest achievements in the field of crystal growth, point defects, extended defects, and impurities of silicon and germanium nanocrystals. World-recognized experts are the authors of the book’s chapters, which span bulk, thin film, and nanostructured materials growth and characterization problems, theoretical modeling, crystal defects, diffusion, and issues of key applicative value, including chemical etching as a defect delineation technique, the spectroscopic analysis of impurities, and the use of devices as tools for the measurement of materials quality.
Author: Abdelrahman Al-Attili
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Author: Szu-Lin Cheng
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
A silicon (Si) compatible laser for applications in telecommunication and optical interconnect systems has been an interesting topic for several years now, but has yet to be practically demonstrated. The main problem is finding an appropriate lasing material at 1550 nm which can be monolithically integrated on silicon with conventional CMOS processes. Germanium (Ge) is compatible with Si and has a direct band gap of 0.8 eV, corresponding to the required optical communication wavelength of 1550 nm. The small difference of 0.134 eV between the direct and indirect band gaps of Ge suggests the possibility of a radiative direct band gap transition. Strategies to improve the luminescence properties of germanium have included large tensile strain, tin alloying, and electron band filling. In this talk, we focus on the last approach since the emission wavelength from such a method stays near the desired 1550 nm. We first show how Ge direct band emission can be improved by using electron band filling of the conduction band. To achieve high electron band filling, an in-situ doping technique was applied during the growth of epitaxial Ge on Si. A strong enhancement from direct band photoluminescence (PL) was observed from highly-doped (1E19 cm^-3) n-type epi-Ge, demonstrating that electron band filling improves the direct band emission strength. We then successfully demonstrate room temperature direct band electroluminescence (EL) from Ge n+/p light emitting diodes (LED) on a Si substrate, which is a key step towards a CMOS-compatible laser. The contribution of electron band filling and the temperature dependence to the device efficiency will also be discussed. Additionally, we fabricate and optically characterize epitaxial Ge microdisks on Si. These microdisk resonators are successfully coupled to fiber tapers and display clear whispering gallery modes (WGM) in transmission as well as photoluminescence. Finally, we combined the LED structure and the microdisk cavity to demonstrate an electrically-pumped Ge resonator diode. Both our optical and electrical resonators are currently limited by the Ge doping concentration, which prevents sufficient electron band filling to allow material gain or lasing. Possible solutions to this problem will also be discussed.
Author: Erich Kasper
Publisher: Inst of Engineering & Technology
ISBN: 9780863415579
Category : Technology & Engineering
Languages : en
Pages : 372
Get Book Here
Book Description
The industrial relevance of SiGe has increased dramatically in the last few years with the manufacture of heterojunction bipolar circuits for the commercial wireless and datacomms markets by IBM and TEMIC, with over 20 companies planning manufacture in the near future. Major high technology companies see the development and use of SiGe as an important part of their strategy, so that there is a strong impetus to improve its characterization and exploitation. This liberally illustrated and fully indexed volume distils in a homogeneous, structured way the expertise of some 40 invited authors to comprehensively review the whole range of properties as well as SiGe: C, self-assembled nanostructures, quantum effects and device trends. The book contains 75% more text than Prof. Kasper's earlier book Properties of strained and relaxed SiGe (INSPEC, IEE, 1995), thoroughly updates its content and adds many new topics.
Author: Brian Ross Albert
Publisher:
ISBN:
Category :
Languages : en
Pages : 171
Get Book Here
Book Description
Optoelectronic devices based on III-V direct gap semiconductors enable ecient energy conversion for photovoltaic cells, light emission for LEDs, and on-chip communication via various microphotonic components. However, widespread adoption of III-V solar cells is limited by the expensive Germanium and III-V standard substrates required, while monolithic integration of III-V devices with Silicon CMOS circuitry is not yet well established. III-V solar cell cost reduction and direct Si/III-V integration can both be realized by depositing a thin layer (e.g. 1 [mu]m) of high quality Ge on relatively inexpensive Si substrates for which the decreased cost is due to Si's greater material abundance and larger possible wafer diameters. Efficient device performance will be retained if the Ge layer maintains a sufficiently low threading dislocation density (TDD) that does not adversely elect carrier lifetimes in epitaxially deposited III-V layers that inherit the Ge film's TDD. Assuming recombination at dislocations is carrier diffusion limited, an acceptable limit for most applications is below 106 cm-2 due to typical minority carrier diffusion lengths of ~ 10 [mu}m in III-V materials. However, direct deposition of Ge on Si will initially generate a TDD as high as 1012 cm-2 to plastically relax the 4.2% lattice mismatch between the two materials. State of the art approaches can reduce the TDD in large-area films to 106 cm-2 by including a 10+ m thick SiGe compositionally graded buffer, while TDD reduction in thinner films (e.g. 1 [mu]m) is limited to 107 cm-2 after cyclic annealing which enhances dislocation fusion and annihilation reactions. By introducing Ge film edges spaced approximately 10 [mu]m apart to serve as dislocation sinks during dislocation glide, the TDD has been reported to further decrease to 2:3106 cm-2 in 1 m thick patterned Ge. However, these films are limited to areas too small for photovoltaic cells, and the sinks appear ineffective for thread reduction at the edges of faceted, selectively grown Ge. Thus, no solution has previously existed for a thin Ge-on-Si film grown over large areas that achieves a TDD of 106 cm-2 or below. This thesis first explores the limitations to dislocation reduction by sinks in selectively-grown Ge and provides structure and fabrication modifications to enable patterned Ge films with a TDD below 106 cm-2 throughout the patterned region. To use these films for large-area applications, overgrowth and coalescence of patterned Ge films are then evaluated in different pattern designs to determine the structures that optimize coalescence in terms of throughput as well as simultaneously avoid generation of additional defects as a result of coalescence. TDD reduction in patterned Ge films by glide to film edges requires uniform resolved shear stresses and minimum dislocation pinning during cyclic annealing. Because film facets allow for elastic relaxation of the applied thermal strain, the process of selective growth must be reversed: blanket Ge is to be grown instead to avoid faceting, followed by sidewall etching and filling before the cyclic anneal. Thermal expansion mismatch between Ge and the sidewall causes undesirable shear stress components while repulsive image forces are created if the sidewall surface's shear modulus is greater than that of Ge. Therefore, the ideal sidewall is primarily composed of Ge, separated from the primary Ge film by a thin SiO2 layer. Monte Carlo simulations of dislocation glide were developed to estimate the limitations of glide due to the pinning elect of orthogonal dislocations. For small mesa widths w (or more generally, the spacing between adjacent dislocation sinks), TDD was found to scale with wa with a~ 4. The threshold of the small width regime and the value of a both increase for greater applied thermal stresses and thicker Ge films. Due to the high surface energy of the Ge/SiO2 interface, lateral overgrowth and film coalescence do not readily occur. The rate was observed to strongly correlate with the Ge film perimeter concavity, delayed at convex mesa corners while relatively promoted at the ends of isolated SiO2 lines surrounded by a concave Ge film perimeter. Ge mesa arrays were staggered to eliminate regions entirely dependent on overgrowth from mesa corners, decreasing the growth time until complete coalescence by at least 50% as compared to a regular gridded array. The faster overgrowth rates over isolated SiO2 lines was observed to further increase for lines of reduced widths. Due to the facets that develop, orientation of SiO2 lines relative to intersections of {111} planes with the substrate surface further affected overgrowth rates which maximized for slight offsets below 15°. Etch pit studies of coalesced, selectively-grown Ge films around SiO2 sidewalls indicated a maximum TDD above the SiO2 (6X107 cm-2 for staggered grids) while decreasing to 107 cm-2 further away in the film. As predicted by modeling, the dislocation pile-up near SiO2 walls was due to inverted resolved shear stress and the reduced thickness at the Ge film edge. Significant improvement in TDD reduction is expected by these models if blanket Ge is instead grown, followed by etch and fill of sidewalls with additional Ge separated by a thin layer of SiO2. While fabrication is more involved compared to the selective growth process, the structure will be successful at threading dislocation removal. With isolated line film edges of minimal width, oriented 5 from {111} surface intersection directions, the coalescence rate will be maximized. Coalescence-induced defects resulting from lattice misregistry over the SiO2-coated Ge lines will be prevented as the Ge film is continuous at the line ends prior to overgrowth initiation. Assuming a pinning probability of 50%, a Ge film 1 [mu]m thick with a maximum distance between dislocation sinks
Author: Erich Kasper
Publisher: Inst of Engineering & Technology
ISBN: 9780852967836
Category : Technology & Engineering
Languages : en
Pages : 358
Get Book Here
Book Description
The industrial relevance of SiGe has increased dramatically in the last few years with the manufacture of heterojunction bipolar circuits for the commercial wireless and datacomms markets by IBM and TEMIC. Major high technology companies see the development and use of SiGe as an important part of their strategy, so that there is a strong impetus to improve its characterization and exploitation. This liberally illustrated and fully indexed volume distills in a homogeneous, structured way the expertise of some 40 invited authors to comprehensively review the whole range of properties as well as SiGe; C, self-assembled nanostructures, quantum effects and device trends.
