Matthias Steidl

Technische Universität Ilmenau

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Peter Kleinschmidt

Technische Universität Ilmenau

Thomas Hannappel

Technische Universität Ilmenau

Oliver Supplie

Technische Universität Ilmenau

Andreas Nägelein

Technische Universität Ilmenau

Agnieszka Paszuk

Technische Universität Ilmenau

W. Prost

University of Duisburg-Essen

Anja Dobrich

Technische Universität Ilmenau

Christian Koppka

Technische Universität Ilmenau

Ning Li

Henan University

Stefan Korte

Chemnitz University of Technology

Cooperative Institutions

Friedrich-Alexander-Universität Erlangen-Nürnberg

Technische Universität Ilmenau

Helmholtz-Zentrum Berlin für Materialien und Energie

Kirchhoff (Germany)

Forschungszentrum Jülich

Centre for Materials for Electronics Technology

Pontifical Catholic University of Peru

Clausthal University of Technology

University of Duisburg-Essen

Helmholtz Institute Erlangen-Nürnberg

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Charge transport in GaAs nanowires: interplay between conductivity through the interior and surface conductivity

Journal of Physics Condensed Matter (2018)

Stefan Korte Andreas Nägelein Matthias Steidl W. Prost Vasily Cherepanov

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-doped segment. The convoluted interplay between conduction through the interior of the nanowire and surface state conduction is studied in detail. Measurements of the I-V curves along the nanowires provide the experimental basis for the proposed charge transport model for the transition of the conduction from the interior to the surface of the nanowire. A voltage drop along the surface state conduction channel leads to an upward shift of the band edges at the surface. This results, for higher applied voltages, in the removal of the depletion layer and an opening of a conductance channel between the interior of the nanowire and the surface states.

Surface conductivity

Surface charge

Surface States

Voltage drop

10.1088/1361-648x/aaf515

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Integration von nanoskaligen III-V Halbleiterstrukturen auf Silizium für die solare Energiekonversion

Matthias Steidl

Tandem-Absorberstrukturen bestehend aus ternaren III-V-Halbleiter-Nanodrahten (ND) als obere Teilzellen und Si als untere Teilzelle besitzen ein hohes Potential fur kostengunstige, hocheffiziente Photovoltaik und solare Wasserspaltung. Ziel dieser Arbeit ist es den Weg zu einem solchem Tandem zu ebnen, wobei GaP als Pufferschicht zum Si(111)-Substrat und die metallorganische Gasphasenepitaxie (MOVPE) als Praparationsmethode dient. Dafur soll ein detailliertes Verstandnis hierbei erforderlicher Prozessschritte auf moglichst atomarer Skala geschaffen werden, um somit die Kontrolle uber jeden einzelnen dieser Praparationsschritte zu erlangen. Es zeigte sich, dass die Si(111)-Oberflache sich in der H2-Atmosphare des MOVPE-Reaktors wesentlich anders verhalt als wahrend der etablierten Praparation in Ultrahochvakuum: So ist diese nach thermischer Deoxidation (1×1)-rekonstruiert und Monohydrid-terminiert. Reflexionsanisotropie-Spektroskopie erweist sich als geeignet die thermische Deoxidation fehlorientierter Substrate in-situ zu beobachten. Senkrechtes, geradliniges Wachstum von ND erfordert B-polare GaP(111) Pufferschichten auf Si. Epitaxie von GaP auf H-terminiertem Si(111) resultierte jedoch in A-Typ Polaritat. Mit Hilfe einer vorangehenden As-Terminierung der Si(111)-Oberflache gelingt es, die Polaritat zu GaP(111)B umzukehren. Die Verwendung geeigneter Si-Substrate und Nukleationsbedingungen erlaubte es die Dichte an Rotationszwillingengrenzen (RZGs) deutlich zu reduzieren und somit den Anteil senkrechter ND auf uber 97% zu steigern. Denn wie sich zeigte, wirken sich RZGs nachteilig auf anschliesendes ND-Wachstum aus, indem sie es entweder vollstandig unterdrucken, diagonal zur Substratoberflache oder horizontal entlang der RZG verlaufen lassen. Verlasst ein horizontaler ND die RZG, entscheidet die Gitterfehlanpassung uber die weitere Wachstumsrichtung: homoepitaktische ND setzen ihre Wachstum in die Senkrechte fort, wahrend heteroepitaktische ND horizontal bleiben. Zum Verstandnis dieser Phanomenologie wird ein quantitatives, kinetisches Nukleationsmodell entwickelt. Unabhangig vom Auftreten von RZGs vermag dieses Modell, das horizontale ND-Wachstum in gitterfehlangepassten Systemen zu erklaren. Auserdem gelingt es erstmals verdunnt-Stickstoff-haltige ND-Strukturen via MOVPE zu praparieren. Zwei Ansatze sind erfolgreich: N-Einbau wahrend des vapor-liquid-solid-Wachstums; und N-Einbau in eine Hulle. Daruber hinaus wird die Dotierung von Nanodrahten mittels eines Vierspitzen-Rastertunnelmikroskops untersucht. Hiermit werden Widerstandsprofile freistehender ND bestimmt, was eine anschliesende Anpassung der Wachstumsparameter an gewunschte Dotierprofile erlaubt.

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Multi-Probe Electrical Characterization of Nanowires for Solar Energy Conversion

IEEE Journal of Photovoltaics (2019)

Andreas Nägelein Cornelia Timm Matthias Steidl Peter Kleinschmidt Thomas Hannappel

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, we have established a sophisticated multi-tip scanning tunneling microscope (STM) used as a four-point prober, which is in vacuo combined with state-of-the-art preparation, enabling an individual characterization of free-standing NWs with no contamination after preparation and with highest spatial resolution. We apply the superior capabilities of the ultra-high-vacuum-based multi-tip STM to perform an indepth study of gallium arsenide NW structures, incorporating an axial p-n junction. Two- and four-point I-V characteristics of the diode are recorded non-destructively, enabling the determination of a local ideality factor. Four-point-probe measurements at different NW positions result in an axial resistance profile, allowing the calculation of the doping concentration of p- and n-doped parts. Around the p-n junction, a 500-nm-width region of low conductance was detected, indicating a compensation effect of dopants during growth. By recording electron-beam-induced current images, the position of the charge separating contact was confirmed.

Characterization

10.1109/jphotov.2019.2894065

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Suppression of Rotational Twin Formation in Virtual GaP/Si(111) Substrates for III–V Nanowire Growth

Crystal Growth & Design (2016)

Christian Koppka Agnieszka Paszuk Matthias Steidl Oliver Supplie Peter Kleinschmidt

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 nanowire growth. We investigate the twin-induced defect density and surface morphology of B-type GaP/Si(111) virtual substrates in dependence on the GaP nucleation process by metalorganic chemical vapor deposition. By employing quantitative high-resolution X-ray diffraction (HR-XRD)), scanning electron and atomic force microscopy (SEM and AFM), we reveal the significant influence of nucleation temperature and substrate miscut direction on the formation of rotational twin domains during a two-step GaP growth approach. The epilayer defect density is drastically decreased by low temperature GaP nucleation on Si(111) misoriented 3° toward [1̅1̅2], where rotational twin domains are suppressed below 5% and the layers exhibit a smooth surface morphology. We demonstrate that these virtual substrates are highly suitable for vertical GaP nanowire growth.

10.1021/acs.cgd.6b00541

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Impact of N Incorporation on VLS Growth of GaP(N) Nanowires Utilizing UDMH

Nanoscale Research Letters (2018)

Matthias Steidl Mingjian Wu Katharina Peh Peter Kleinschmidt Erdmann Spiecker

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) mechanism. The impact of the nitrogen precursur unsymmetrical dimethyl hydrazine (UDMH) on morphology was found to be overall beneficial as it strongly reduces tapering. Analysis of the crystal structure of NWs with and without N reveals zinc blende structure with an intermediate amount of stacking faults (SF). Interestingly, N incorporation leads to segments completely free of SFs, which are related to dislocations transverse to the growth direction.

Nanochemistry

Vapor–liquid–solid method

10.1186/s11671-018-2833-6

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Atomic surface structure of MOVPE-prepared GaP(1 1 1)B

Applied Surface Science (2020)

Peter Kleinschmidt Pingo Mutombo Theresa Berthold Agnieszka Paszuk Matthias Steidl

Dangling bond

Auger electron spectroscopy

10.1016/j.apsusc.2020.147346

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Controlling the polarity of metalorganic vapor phase epitaxy-grown GaP on Si(111) for subsequent III-V nanowire growth

Applied Physics Letters (2015)

Agnieszka Paszuk Sebastian Brückner Matthias Steidl Weian Zhao Anja Dobrich

Nanowire growth on heteroepitaxial GaP/Si(111) by metalorganic vapor phase epitaxy requires the [-1-1-1] face, i.e., GaP(111) material with B-type polarity. Low-energy electron diffraction (LEED) allows us to identify the polarity of GaP grown on Si(111), since (2×2) and (1×1) surface reconstructions are associated with GaP(111)A and GaP(111)B, respectively. In dependence on the pre-growth treatment of the Si(111) substrates, we were able to control the polarity of the GaP buffers. GaP films grown on the H-terminated Si(111) surface exhibited A-type polarity, while GaP grown on Si surfaces terminated with arsenic exhibited a (1×1) LEED pattern, indicating B-type polarity. We obtained vertical GaAs nanowire growth on heteroepitaxial GaP with (1×1) surface reconstruction only, in agreement with growth experiments on homoepitaxially grown GaP(111).

Vapor phase

Polarity (international relations)

10.1063/1.4922275

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Impact of Rotational Twin Boundaries and Lattice Mismatch on III–V Nanowire Growth

ACS Nano (2017)

Matthias Steidl Christian Koppka Lars Winterfeld Katharina Peh B. Galiana

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 GaP/Si(111) heterosubstrates, generally cause horizontal NW growth and may even suppress NW growth entirely. Away from RTBs, the NW growth direction switches from horizontal to vertical in the case of homoepitaxial GaP NWs, whereas heteroepitaxial GaAs NWs continue growing horizontally. To understand this rich phenomenology, we develop a model based on classical nucleation theory. Independent of the occurrence of RTBs and specific transition layers, our model can generally explain the prevalent observation of horizontal III–V NW growth in lattice mismatched systems and the high crystal quality of horizontal nanowires.

Lattice (music)

10.1021/acsnano.7b01228

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Citations (9)

Low-temperature solution-processed metal oxide buffer layers fulfilling large area production requirements

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2012)

Tobias Stubhan Ivan Litzov Ning Li H. Q. Wang Justin Krantz

This paper is a review of our previous work on the field of low temperature, solution processed metal oxide buffer layers published in various journals. Our work focuses on zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) as n-type and molybdenum oxide (MoO₃) as p-type solution processed buffer layer. In addition to that, we investigate the surface modification of AZO using phosphonic acid-anchored aliphatic and fullerene self assembled monolayers (SAMs).

Buffer (optical fiber)

Buffer solution

10.1117/12.945866

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High fill factor polymer solar cells comprising a transparent, low temperature solution processed doped metal oxide/metal nanowire composite electrode

Solar Energy Materials and Solar Cells (2012)

Tobias Stubhan Johannes Krantz Ning Li Fei Guo Ivan Litzov

Photoactive layer

Open-circuit voltage

Buffer (optical fiber)

Solution process

10.1016/j.solmat.2012.06.039

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Citations (80)