Thomas Hannappel

Thomas Hannappel
Technische Universität Ilmenau | TUI · Institute of Physics

Univ.-Prof. Dr. habil.

About

208
Publications
16,979
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
4,616
Citations
Additional affiliations
August 2011 - present
Technische Universität Ilmenau
Position
  • Head of Department
August 2011 - December 2013
CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbH
Position
  • Research Director
January 2003 - January 2004

Publications

Publications (208)
Preprint
Full-text available
The epitaxial growth of the polar GaP(100) on the nonpolar Si(100) substrate suffers from inevitable defects at the antiphase domain boundaries, resulting from mono-atomic steps on the Si(100) surface. Stabilization of Si(100) substrate surfaces with arsenic is a promising technological step enabling the preparation of Si substrates with double ato...
Article
Full-text available
Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit,...
Article
Full-text available
Photoelectrochemical (PEC) water splitting can be an efficient and economically feasible alternative for hydrogen production if easily processed photoelectrodes made of inexpensive and abundant materials are employed. Here, we present the preparation of porous Cu 2 O photocathodes with good PEC performance using solely inexpensive electrodeposition...
Article
Full-text available
GaP is a preferred candidate for the transition between Si and heterogeneous III-V epilayers as it is nearly lattice-matched to Si. Here, we scrutinize the atomic structure and electronic properties of GaP/Si(0 0 1) heterointerfaces utilizing hard X-ray photoelectron spectroscopy (HAXPES). GaP(0 0 1) epitaxial films with thicknesses between 4 and 5...
Article
Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge...
Article
Epitaxial integration of direct-bandgap III–V compound semiconductors with silicon requires overcoming a significant lattice mismatch. To this end, GaAsP step-graded buffer layers are commonly applied. The thickness and composition of the individual layers are decisive for the envisaged strain relaxation. We study GaAsP growth by metalorganic vapor...
Article
Controlling the surface formation of the group-V face of (111)-oriented III-V semiconductors is crucial for subsequent successful growth of III-V nanowires for electronic and optoelectronic applications. With a view to preparing GaP/Si(111) virtual substrates, we investigate the atomic structure of the MOVPE (metalorganic vapor phase epitaxy)-prepa...
Article
Full-text available
We present a study of buried GaP/Si(001) heterointerfaces by hard X‐ray photoelectron spectroscopy. Well‐defined thin (4–50 nm) GaP films were grown on Si(001) substrates with 2° miscut orientations by metalorganic vapor phase epitaxy. Core level photoelectron intensities and valence band spectra were measured on heterostructures as well as on the...
Article
Full-text available
This article addresses the challenges presented by photoelectrochemical solar fuels technology in a discussion that begins with a functioning device and proceeds to the more fundamental science of its component parts. In this flow of discussion issues are addressed that frame the discussion for the next, increasingly more fundamental topic. The ana...
Article
The efficiency of novel opto-electronic devices e.g. solar cells crucially depends on controlling the doping levels in the device. Decreasing the size of the structure by employing nanowires is attractive for several reasons, for instance reduced material costs, but makes the characterization more challenging. There is still a lack of a precise and...
Article
Full-text available
In this work we report on the characterization of n‐doped MOVPE‐grown InGaP:Si shells in coaxial nid‐GaAs/n‐InGaP as well as npn core‐multishell nanowires. The multi‐tip scanning tunneling microscopy technique is used for contact‐independent resistance profiling along tapered nid‐GaAs/n‐InGaP core‐shell nanowires to estimate the established emitter...
Article
Full-text available
The initial interaction of water with semiconductors determines the electronic structure of the solid–liquid interface. The exact nature of this interaction is, however, often unknown. Here, we study gallium phosphide-based surfaces exposed to H _22 O by means of in situ reflection anisotropy spectroscopy. We show that the introduction of typical i...
Article
Time‐resolved two‐photon photoemission spectroscopy (tr‐2PPE) directly probes the kinetic energy and dynamics of photoemitted electrons. At the same time, the electronic structure and temporal occupation of surface‐near states can be accessed, which allows to unravel the fundamental processes governing electron dynamics and energetics in semiconduc...
Article
The combination of time-resolved (TR) and power-dependent relative (PDR) photoluminescence (PL) measurements reveals the possibility of separating the radiative and non-radiative minority carrier lifetimes and measuring the sample-dependent effective radiative recombination coefficient in direct bandgap semiconductors. To demonstrate the method, me...
Preprint
Full-text available
The initial interaction of water with semiconductors determines the electronic structure of the solid-liquid interface. The exact nature of this interaction is, however, often unknown. Here, we study gallium phosphide-based surfaces exposed to H2O by means of in situ reflection anisotropy spectroscopy. We show that the introduction of typical imper...
Article
Catalysis-assisted vapor–liquid–solid nanowire (NW) growth offers opportunities to prepare versatile, axial, and radial III–V homo- and hetero-structures, which combine multiple scientific and economic benefits including applications in innovative solar energy conversion. For an essential and suitable optoelectronic analysis of NW heterocontacts, w...
Article
GaP/Si(001) virtual substrates are highly interesting for solar cells and optoelectronic device applications. While antiphase disorder at the resulting surface of the virtual substrate—after a few tens of nm GaP—can be suppressed, the structural and electronic properties of the actual GaP-to-Si interface and of the antiphase domains within the GaP...
Article
Dilute nitride III-V nanowires (NWs) possess great potential as building blocks in future optoelectronical and electrochemical devices. Here, we provide evidence for the growth of GaP/GaPN core-shell NWs via metalorganic vapor phase epitaxy, both on GaP(111)B and on GaP/Si(111) hetero-substrates. The NW morphology meets the common needs for use in...
Article
Rotational twins are fundamental defects in III-V epitaxy, in particular for the growth on nonpolar (111) surfaces. Based on density functional theory (DFT) calculations, we develop a general model for III-V nucleation on vicinal nonpolar (111)-oriented substrates and focus on the important differences in the atomic step configuration of different...
Article
Full-text available
Abstract III–V nanowires (NWs) possess great potential for use in future semiconductor technology. Alloying with dilute amounts of nitrogen provides further flexibility in tuning their material properties. In this study, we report on successful in situ nitrogen incorporation into GaP(N) NWs during growth via the Au-catalyzed vapor-liquid-solid (VLS...
Article
The charge transport through GaAs nanowires, partially p-doped and partially intrinsic, is analyzed by four-point resistance profiling along freestanding nanowires using a multip-STM. The charge transport channel in the undoped segment is assigned to the surface conductivity, while the interior of the nanowire is the conductance channel in the p-do...
Article
The integration of III–V semiconductors with Si has been pursued for more than 25 years since it is strongly desired in various high-efficiency applications ranging from microelectronics to energy conversion. In the last decade, there have been tremendous advances in Si preparation in hydrogen-based metalorganic vapor phase epitaxy (MOVPE) environm...
Article
Monolithic multi-junction solar cells made on active silicon substrates are a promising pathway for low-cost high-efficiency devices. We present results of GaInP/GaAs/Si triple-junction solar cells, fabricated by direct growth on silicon in a metal–organic vapor phase epitaxy reactor using a GaAs $_{y}$ P $_{1-}$ $_{y}$ buffer structure to overc...
Article
We report the room-temperature dielectric function (DF) of GaPN grown lattice-matched on Si(100). Data were derived from spectroscopic ellipsometry measurements on a series of films prepared by metalorganic vapor phase epitaxy. The Kramers-Kronig analysis reveals good self-consistency between the real and the imaginary parts of the determined DF. T...
Article
Low-defect III-V integration on Si(1 0 0) requires atomically well-ordered heterointerfaces. To this end, we study the interaction of As with Si(1 0 0) surfaces and the formation of dimerized Si(1 0 0):As surfaces in situ with reflection anisotropy spectroscopy during metalorganic chemical vapor deposition (MOCVD). Control of surface processes allo...
Article
Efficient unassisted solar water splitting, a pathway to storable renewable energy in the form of chemical bonds, requires optimization of a photoelectrochemical device based on photovoltaic tandem heterojunctions. We report a monolithic photocathode device architecture that exhibits significantly reduced surface reflectivity, minimizing parasitic...
Article
Profiling of the electrical properties of nanowires (NWs) and NW heterocontacts with high spatial resolution is a challenge for any application and advanced NW device development. For appropriate NW analysis, we have established a four-point prober, which is combined in vacuo with a state-of-the-art vapor-liquid-solid preparation, enabling contamin...
Article
In chemical vapor ambient, Si(100) surfaces and hydrogen can strongly interact with each other. As a result, energetic considerations cannot solely describe step and terrace formation sufficiently, as the formation of the equilibrium surface reconstruction can be counteracted by surface kinetics, in particular induced by hydrogen and driven by temp...
Article
Efficient photovoltaic tandem cells made of III-V semiconductors open a promising way for the realization of direct solar water splitting devices (artificial leaf) with real economic impact. The growth of an interfacial oxide separating the semiconductor from the metal catalyst brings about chemical stability and an enhancement of the charge transf...
Article
In chemical vapor ambience, Si(100) surfaces and hydrogen are strongly interacting with each other at relevant process temperatures. Energetic considerations cannot solely describe step and terrace formation sufficiently, as the formation of equilibrium surface reconstructions can be counteracted by surface kinetics. In recent years, the combinatio...
Article
Solar energy conversion and photoinduced bioactive sensors are representing topical scientific fields, where interfaces play a decisive role for efficient applications. The key to specifically tune these interfaces is a precise knowledge of interfacial structures and their formation on the microscopic, preferably atomic scale. Gaining thorough insi...
Article
Full-text available
Solar energy conversion and photoinduced bioactive sensors are representing topical scientific fields, where interfaces play a decisive role for efficient applications. The key to specifically tune these interfaces is a precise knowledge of interfacial structures and their formation on the microscopic, preferably atomic scale. Gaining thorough insi...
Article
Minority carrier diffusion lengths and lifetimes were determined for p-type Ga(1-x)InxAs with an In-content of 0 ≤ x ≤ 0.53 by cathodoluminescence and time-resolved photoluminescence measurements respectively under low injection conditions; the resulting minority carrier mobilities are also reported. Highly p-doped samples (3 × 10¹⁸ cm⁻³) demonstra...
Article
Pseudomorphic planar III-V transition layers greatly facilitate the epitaxial integration of vapor-liquid-solid grown III-V nanowires (NW) on Si(111) substrates. Heteroepitaxial (111) layer growth, however, is commonly accompanied by the formation of rotational twins. We find that rotational twin boundaries (RTBs), which intersect the surface of Ga...
Article
Realization of high efficiency III-V-on-Si solar cells requires preparation of an oxygen free Si substrate surface, which allows for subsequent antiphase domain free III-V epitaxy. For GaAsP/Si tandem cells, the impact of As on established Si processing in metal organic vapor phase epitaxy (MOVPE) is essential. Here, we study the interaction of As...
Article
The detection of doping dependent values like contact- and path resistances along nanowires (NWs) still proves to be rather challenging compared to planar structures. Unfortunately, the usually used and well established TLM (transmission line measurement) setup exhibits some drawbacks. Complex preliminary preparation steps and the necessity of ohmi...
Article
The combination of tunable direct bandgap III-V absorbers with active Si substrates promises high-efficiency tandem solar cells. To yield the ideal III-V bandgaps between 1.6 and 1.8 eV which is considered to achieve current matching with the Si bottom-cell, however, either a big lattice-mismatch or dilute nitrides had to be considered so far. Here...
Article
Full-text available
Photoelectrochemical solar fuel generation is evolving quickly towards devices mature for applications, driven by the development of efficient multi-junction devices. The crucial characteristics deciding over feasibility of an application are efficiency and stability. Benchmarking and reporting routines for these characteristics are, however, not y...
Article
Full-text available
Photoelectrochemical solar fuel generation is evolving steadily towards devices mature for applications, driven by the development of efficient multi-junction devices. The crucial characteristics deciding over feasibility of an application are efficiency and stability. Benchmarking and reporting routines for these characteristics are, however, not...
Article
III-V integration on active Si-bottom cells promises not only high-efficiency multi-junction solar cells but also lower production costs. In situ preparation of an adequate Si p-n junction in metalorganic chemical vapor deposition ambient is challenging, particularly since the final Si surface should be atomically well-ordered to enable low-defect...
Article
The atomic and electronic band structures of GaP/Si(001) heterointerfaces were investigated by ab initio density functional theory calculations. Relative total energies of abrupt interfaces and mixed interfaces with Si substitutional sites within a few GaP layers were derived. It was found that Si diffusion into GaP layers above the first interface...
Article
Full-text available
The atomic and electronic band structures of GaP/Si(001) heterointerfaces were investigated by ab initio density functional theory calculations. Relative total energies of abrupt interfaces and mixed interfaces with Si substitutional sites within a few GaP layers were derived. It was found that Si diffusion into GaP layers above the first interface...
Article
GaP/Si(100) is considered as pseudomporphic virtual substrate for III/V-on-Si integration in order to reduce defects related to polar-on-nonpolar heteroepitaxy. The atomic structure of the GaP/Si(100) heterointerface is decisive to yield low defect densities and its dependence on nucleation conditions is still under debate. Recently, Beyer et al. s...
Article
Planar GaP epilayers on Si(111) are considered as virtual substrates for III-V-related optoelectronic devices such as high-efficiency nanowire-based tandem absorber structures for solar energy conversion, next generation LEDs, and fast photodetectors. Rotational twin domains in such heteroepitaxial epilayers are found to strongly impede vertical na...
Article
For well-defined heteroepitaxial growth of III-V epilayers on Si(111) substrates the atomic structure of the silicon surface is an essential element. Here, we study the preparation of the Si(111) surface in H2-based chemical vapor ambient as well as its atomic structure after contamination-free transfer to ultrahigh vacuum (UHV). Applying complemen...
Conference Paper
We report on a cross-sectional scanning tunneling microscopy (XSTM) investigation of anti-phase boundaries on epitaxial grown GaP layers on a Si(001) substrate. The growth conditions of the GaP layer was chosen to produce a significant anti-phase disorder, to favor the XSTM experiment. A different image contrast for the main phase and the anti-phas...
Article
In a fundamental cross-sectional scanning tunneling microscopy investigation on epitaxially grownGaP layers on a Si(001) substrate, differently oriented antiphase boundaries are studied. They can be identified by a specific contrast and by surface step edges starting/ending at the position of an antiphase boundary. Moreover, a change in the atomic...
Article
We have realized a tandem solar cell design that combines a pin-junction with a photovoltaic intersubband absorber. This concept allows harvesting light in the visible range and the near- and mid-infrared at the same time, and theoretically, energy conversion efficiencies beyond the Shockley-Queisser-limit could be achieved. A test structure was gr...
Conference Paper
Full-text available
The Institute of Micro-and Nanotechnology MacroNano® at Technische Universitat Ilmenau was founded in 2005 to provide a structural base for interdisciplinary research ranging from basic to applied and application-oriented research with a strong focus on nano- and microsystems. It comprises the competences of several engineering and natural science...
Article
Full-text available
Metalorganic vapor phase epitaxy of III-V compounds commonly involves arsenic. We study the formation of atomically well-ordered, As-modified Si(100) surfaces and subsequent growth of GaP/Si(100) quasisubstrates in situ with reflection anisotropyspectroscopy.Surface symmetry and chemical composition are measured by low energy electron diffraction a...
Article
We investigate the Ga0.47In0.53As to InP interface with respect to their charge carrier lifetimes, interface recombination velocity and lateral interface homogeneity by using a time- and spatially resolved photoluminescence technique. Different preparation routes, such as group-III- and group-V-rich variations for the upper Ga0.47In0.53As to InP in...
Article
Full-text available
Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoe...
Article
http://www.compoundsemiconductor.net/pdf/magazines/2015/36874_Compound%20Semi_July_DE_OPTcompressed.pdf
Article
Nanowire growth on heteroepitaxial GaP/Si(111) by metalorganic vapor phase epitaxy requires the [-1-1-1] face, i.e., GaP(1