Refine
Document Type
- Doctoral thesis (4)
Has Fulltext
- yes (4)
Is part of the Bibliography
- no (4)
Language
- English (4)
Keywords
- Heterostruktur (4) (remove)
Institute
Annealing-induced solid phase crystallization of In₂O₃:H leads to a significantly improved electron mobility, which is confirmed by Hall measurements. Indium hydroxide dehydroxylation occurs in In₂O₃:H during annealing, which is well responsible for the structural transformation and a high electron mobility with a decreased carrier concentration in crystallized In₂O₃:H. A significant decrease in the intensity of occupied gap states is observed in crystallized In₂O₃:H, possibly due to a decrease in carrier concentration. Doped In₂O₃ variants have been found to have a quite deeper allowed transition level below the valence-band edge than undoped In₂O₃, which in particular applies to crystallized In₂O₃:H, but most likely attributed to a change of the crystal structure upon annealing and/or a different O 2p-In 4d coupling near the VBM compared to amorphous In₂O₃:H.
To well understand the interface properties of Ag/In₂O₃:H upon annealing, a thin Ag film was grown on the In₂O₃:H substrate and annealed in vacuum up to 300 °C. During annealing, the potential Ag diffusion into the bulk In₂O₃:H and/or a change of an annealing-induced Ag topography (i.e., cluster formation) occurs, with a small Ag oxidation (i.e., Ag₂O and AgO). With Ag deposition, an initial downward band bending of (0.11±0.05) eV was present in In₂O₃:H, attributed to a Schottky contact formed at the Ag/In₂O₃:H interface. Upon annealing, the downward band bending reduces gradually, and the Schottky-barrier height at the Ag/In₂O₃:H interface also decreases.
A thickness series of the individual materials on the respective “substrate” (i.e., MnS/Si, GaN/MnS, and ZnO/GaN) was epitaxially grown on Si (100) wafer, and the interfacial chemistry and energy-level alignment at the respective interfaces are examined using photoelectron spectroscopy. At the MnS/Si interface, an interface-induced band bending (IIBB) appears in Si, which of values are found to be (0.15±0.07) and (0.23±0.07) eV for 4 and 15 nm MnS/Si stacks, respectively. The MnS/Si heterointerface shows a type-II (staggered) band lineup with a VBO of (-0.37±0.10) eV and the corresponding CBO of (2.27±0.10) eV. For the GaN/MnS interface, a significant diffusion of Mn into the GaN layer takes place during GaN deposition. In addition, an interface-induced band bending (IIBB) by ~0.30 eV is observed in MnS. The GaN/MnS interface shows a type-II (staggered) band lineup with a VBO of (1.46±0.10) eV and the corresponding CBO of (-1.09±0.10) eV. At the ZnO/GaN interface, a significant N diffusion from GaN into ZsnO takes place, i.e., Zn-N bonds, when ZnO is grown on the GaN layer. Also, an interfacial oxide (GaOx) layer was formed during ZnO deposited on GaN films. The ZnO/GaN heterointerface shows a type-II (staggered) band lineup with a VBO of (2.48±0.10) eV and the corresponding CBO of (-2.50±0.10) eV, respectively.
We consider semiconductor devices at very low temperatures, composed of a mesoscopic quantum structure (QS) constituting the active region contacted by ideal probes with infinite conductivity. The coherent transport through the QS is described in the Landauer-Büttiker formalism. We perform self-consistent calculations for the electron density in the QS. We present a capacitance model that takes into account the openness of the QS and the existence of finite contacts embedding the system. For single-barrier tunnelling structures, we present the implicit connection between the capacitance and the conductance. For a field induced two-dimensional electron gas in a special GaAs/AlxGa1-xAs heterostructure we present a detailed analysis of the coupling to the contact reservoir. Excellent quantitative agreement in the C-V characteristic is obtained. It is also analized the conductivity of systems with confinement in more dimensions.
The complexity of today´s microelectronic circuitry is not only driven by complementary metal oxide semiconductor (CMOS) scaling, but also by integration of high performance modules for various applications (e.g. wireless and broadband communication systems). These mixed signal circuitries are build up by combining digital CMOS technology with analog SiGe:C hetero-bipolar transistors (HBT) known as SiGe:C BiCMOS technology. State-of-the-art SiGe:C BiCMOS technologies achieve up to the 500 GHz. Nevertheless, Si as semiconductor material is approaching more and more its physical limits, whereby novel approaches have to be found to ensure the future development of SiGe:C HBT BiCMOS technology in order to push the maximum frequency further into the Terahertz regime. Based on this task, two novel material science strategies are investigated in this Ph.D. thesis in terms of material growth and defect studies: A.) Solid-phase epitaxy (SPE) for emitter and base resistivity: This technique has been investigated for local engineering of crystallinity in emitter and base layer of already established SiGe:C HBT technology in order to improve the speed performance. By introducing disilane as new gas source with respect to standard used silane, it is possible to reduce the CVD growth temperature for Si, enabling the differential growth of epitaxial-Si (epi-Si) on Si and amorphous Si (a-Si) on the SiO2 and Si3N4 masks. The so produced requirement for SPE treatments is evaluated for two possible areas of application: A1.) Emitter region and A2.) Base region. In both cases, SPE techniques are applied to change the standard polycrystalline-Si (poly-Si) emitter and base link area on the SiO2 and Si3N4 masks to a fully epi-Si area in order to lower emitter and base resistivity, respectively. B.) III-V/SiGe hybrid device: The ternary compound semiconductor In1-xGaxP [x=0–1] is introduced as potential new collector material as part of an III-V/SiGe hybrid HBT device. With InP having a three times higher saturation velocity, and GaP having a two times bigger bandgap than Si, this approach offers the possibility to adjust speed and power performance of HBTs in a flexible way as a function of the In1-xGaxP collector chemical composition x. The material growth and defect studies in this Ph.D. thesis produced insights, which lead to the following results for future device application: A1.) SPE for emitter region: After investigating the temperature, time and doping concentration dependence on lateral SPE length of in-situ annealed As-doped epi-Si/a-Si test structures, it was possible to crystallize up to 500 nm of a-Si on SiO2 and Si3N4 masks to epi-Si with low defect densities by a combination of 575 °C and 1000 °C postannealing. A2.) SPE for base region: After studying the dependence of time, temperature, thickness, SiO2-capping and Ge incorporation on lateral SPE length of in-situ annealed undoped epi-Si/a-Si test structures, it was possible to crystallize up to 450 nm of SiO2-capped undoped a-Si on SiO2 mask to low-defective epi-Si by 570 °C postannealing. Finally, this technique is applied in a SiGe:C base model structure in order to show the possibility to widen the monocrystalline region around the bipolar window, which results in a possibly improved base resistivity. B.) GaP/Si0.8Ge0.2/Si(001) heterostructure: For pseudomorphic GaP/Si0.8Ge0.2/Si(001) heterostructure growth, the critical thickness of GaP on Si and maximum thermal budget for GaP deposition is evaluated. A detailed structure and defect characterization study by XRD, AFM, and TEM is reported on single crystalline 170 nm GaP/20 nm Si0.8Ge0.2/Si(001) heterostructure. Results show that 20 nm Si0.8Ge0.2 on Si(001) can be overgrown by 170 nm GaP without affecting the pseudomorphism of the Si0.8Ge0.2/Si(001) systems. The GaP layer grows however partially relaxed, mainly due to defect nucleation at the GaP/Si0.8Ge0.2 interface during initial island coalescence. The achievement of 2D GaP growth conditions on Si0.8Ge0.2/Si(001) systems is thus a crucial step for achieving fully pseudomorphic heterostructures. Anti-phase domain-free GaP growth is observed for film thicknesses beyond 70 nm. In addition, no detrimental impurity diffusion could be found in the GaP/Si0.8Ge0.2/Si(001) heterostructure. Finally, it is to mention that further investigation and efforts are still needed to push these new approaches to full integration into SiGe:C HBT BiCMOS technology concepts: A.) For SPE application: Electrical studies are needed in frame of full processed devices to evaluate the value and required modifications for process integration. B.) For III-V/SiGe hybrid device: Future work has to focus on improved 2D GaP layer conditions (before introducing InP) in order to prepare truly pseudomorphic GaP/Si0.8Ge0.2/Si(001) heterostructures with low defect densities. For this purpose, selective GaP growth studies in local HBT Si0.8Ge0.2/Si(001) mesa structures are the next step.
We analyze here some electron properties and lattice dynamics in semiconductor heterostructures, pointing out the dramatic changes relative to the bulk properties due to the existence of the interfaces in these systems. The first part of the study is devoted to the electron scattering phenomena in noninteracting open systems and to the transport properties described in the Landauer-Büttiker formalism. We develop a resonant theory of transport and apply it first to the conductance through a quantum dot embedded in a quantum wire and second to the capacitance of a two dimensional electron gas formed in a MIS-type semiconductor heterostructure. In the second part of the study we illustrate the four major new features of the optical phonon spectra in a strained semiconductor heterostructure in contrast to an unstrained one. The results are particularized for double heterostructures InP/GaAs/InP grown on the faces (001) and (111) of the substrate.