Rainer Timm

• Professor (Associate) at Lund University

Nanoscale optoelectronic components achieve functionality via spatial variation in electronic structure induced by composition, defects, and dopants. To dynamically change the local band alignment and influence defect states, a scanning gate electrode is highly useful. However, this technique is rarely combined with photoexcitation by a controlled...

Metal-halide perovskites (MHPs) have gained substantial interest in the energy and optoelectronics field. MHPs in nanostructure forms, such as nanocrystals and nanowires (NWs), have further expanded the horizons for perovskite nanodevices in geometry and properties. A partial anion exchange within the nanostructure, creating axial heterojunctions,...

Nonvolatile memory devices based on ferroelectric HfxZr1–xO2 (HZO) show great promise for back-end integrable storage and for neuromorphic accelerators, but their adoption is held back by the inability to scale down the HZO thickness without violating the strict thermal restrictions of the Si CMOS back end of line. In this work, we overcome this ch...

The two-dimensional electron gas (2DEG) that forms on a semiconductor surface can be used to explore a variety of phenomena in quantum physics and plays an important role in nanoscale electronics, such as transistors. Controlling its formation is, thus, relevant. Using angle-resolved photoemission spectroscopy (ARPES) and accumulating the signal ov...

The chemical bonding at the interface between compound semiconductors and metals is central in determining electronic and optical properties. In this study, new opportunities for controlling this are presented for nanostructures. We investigate Bi adsorption on 2D wurtzite InAs (112̄0) nanosheets and find that temperature-controlled Bi incorporatio...

Understanding the reaction mechanisms involved during the early stage of atomic layer deposition (ALD) of HfO2 on InAs is a key requirement for improving interfaces in III-V semiconductor-based devices. InAs is an excellent candidate to outperform silicon regarding speed and power consumption, and combined with HfO2, it gives promise for a new gene...

Recent work showing a strong quality improvement of the Si/SiO2 material system by low temperature atomic hydrogen annealing (AHA), and the fact that III–V semiconductors outperform Si in many applications makes the investigation of AHA on III–V/high-k interfaces to a very interesting topic. In this work, the potential of AHA as a low temperature a...

Two-dimensional (2D) topological insulators have fascinating physical properties which are promising for applications within spintronics. In order to realize spintronic devices working at room temperature, materials with a large nontrivial gap are needed. Bismuthene, a 2D layer of Bi atoms in a honeycomb structure, has recently attracted strong att...

We demonstrate a significant improvement in the optical performance of GaAs nanowires achieved using a mixed nitrogen-hydrogen plasma which passivates surface states and reduces the rate of nonradiative recombination. This has been confirmed by time-resolved photoluminescence measurements. At room temperature, the intensity and lifetime of radiativ...

The surface chemistry of the initial growth during the first or first few precursor cycles in atomic layer deposition is decisive for how the growth proceeds later on and thus for the quality of the thin films grown. Yet, although general schemes of the surface chemistry of atomic layer deposition have been developed for many processes and precurso...

Mismatch between adjacent atomic layers in low-dimensional materials, generating moiré patterns, has recently emerged as a suitable method to tune electronic properties by inducing strong electron correlations and generating novel phenomena. Beyond graphene, van der Waals structures such as three-dimensional (3D) topological insulators (TIs) appear...

Improved Endurance of Ferroelectric HfxZr1‐xO2 Integrated on InAs The benefits of using a milliseconds flash lamp annealer to crystallize HfxZr1‐xO2 into the ferroelectric orthorhombic crystal phase are highlighted in article number 2201038 by Robin Athle, Mattias Borg, and co‐workers. By annealing 1000x faster than traditional rapid thermal proces...

Ferroelectric HfxZr1–xO2 (HZO) is typically achieved by crystallization of an amorphous thin film via rapid thermal processing (RTP) at time scales of seconds to minutes. For integration on III–V semiconductors, this approach can severely degrade the sensitive HZO/III–V interface. To evaluate whether a reduced thermal budget can improve the interfa...

Atomic layer deposition (ALD) is one of the backbones for today's electronic device fabrication. A critical property of ALD is the layer-by-layer growth, which gives rise to the atomic-scale accuracy. However, the growth rate - or growth per cycle - can differ significantly depending on the type of system, molecules used, and several other experime...

Due to its high hole-mobility, GaSb is a highly promising candidate for high-speed p-channels in electronic devices. However, GaSb exhibits a comparably thick native oxide causing detrimental interface defects, which has been proven difficult to remove. Here we present full oxide removal from GaSb surfaces using effective hydrogen plasma cleaning,...

Correction for 'Strain mapping inside an individual processed vertical nanowire transistor using scanning X-ray nanodiffraction' by Dmitry Dzhigaev et al., Nanoscale, 2020, 12, 14487-14493, DOI: 10.1039/D0NR02260H.

Sb-based semiconductors are critical p-channel materials for III–V complementary metal oxide semiconductor (CMOS) technology, while the performance of Sb-based metal-oxide-semiconductor field-effect transistors (MOSFETs) is typically inhibited by the low quality of the channel to gate dielectric interface, which leads to poor gate modulation. In th...

In-memory computing can be used to overcome the von Neumann bottleneck—the need to shuffle data between separate memory and computational units—and help improve computing performance. Co-integrated vertical transistor selectors (1T) and resistive memory elements (1R) in a 1T1R configuration offer advantages of scalability, speed and energy efficien...

Scaling down material synthesis to crystalline structures only few atoms in size and precisely positioned in device configurations remains highly challenging, but is crucial for new applications e.g., in quantum computing. We propose to use the sidewall facets of larger III–V semiconductor nanowires (NWs), with controllable axial stacking of differ...

To improve the performance and efficiency of Al containing III-Nitride-based devices, a number of issues must be addressed, especially the presence and generation of dislocations and other structural defects. The main sources of the dislocations are growth on non-native substrates and heteroepitaxial growth of lattice-mismatched layers. We demonstr...

Ferroelectric and ferroelastic domains have been predicted to enhance metal halide perovskite (MHP) solar cell performance. While the formation of such domains can be modified by temperature, pressure, or strain, established methods lack spatial control at the level of single domains. Here, we induce the formation of ferroelastic domains in CsPbBr3...

Supplemental Material for the 'Inducing ferroelastic domains in single-crystal CsPbBr 3 perovskite nanowires using atomic force microscopy' paper.

We investigate the impact of electrical current on the structure of single free-standing Be-doped GaAs nanowires grown on a Si 111 substrate. Single nanowires have been structurally analyzed by X-ray nano-diffraction using synchrotron radiation before and after the application of an electrical current. The conductivity measurements on single nanowi...

Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUTs) are presented. The LUTs were derived from the topography of a polished and a lapped surface of a CsI(Tl) crystal measured with atomic force microscopy. Simulations with different combinations of polished and lapped surfaces were performed, to extract...

Resistive random access memory (RRAM) technologies based on non-volatile resistive filament redox switching oxides have the potential of drastically improving the performance of future mass-storage solutions. However, the physico-chemical properties of the TiN bottom metal electrode (BME) can significantly alter the resistive switching (RS) behavio...

Ferroelectric memories based on hafnium oxide are an attractive alternative to conventional memory technologies due to their scalability and energy efficiency. However, there are still many open questions regarding the optimal material stack and processing conditions for reliable device performance. Here, we report on the impact of the sputtering p...

The physical and chemical properties of semiconductor nanowires are significantly influenced by their surface structure and morphology. This can be understood in that surfaces make out a much larger part of the total structure as compared to macroscale objects. An immediate consequence is that the lack of surface control can result in poor performa...

III–V semiconductors, such as InAs, with an ultrathin high-κ oxide layer have attracted a lot of interests in recent years as potential next-generation metal–oxide–semiconductor field-effect transistors, with increased speed and reduced power consumption. The deposition of the high-κ oxides is nowadays based on atomic layer deposition (ALD), which...

Laterally grown InxGa1xAs nanowires (NWs) are promising candidates for radio frequency and quantum computing applications, which, however, can require atomic scale surface and interface control. This is challenging to obtain, not least due to ambient air exposure between fabrication steps, which induces surface oxidation. The geometric and electron...

Understanding formation and distribution of defects in GaN substrates and device layers is needed to improve device performance in rf and power electronics. Here we utilize conductive atomic force microscopy (c-AFM) for studying defect-related leakage paths in an unintentionally doped GaN film formed by nanowire reformation. A nanoscopic Schottky c...

III‐nitrides are considered the material of choice for light‐emitting diodes (LEDs) and lasers in the visible to ultraviolet spectral range. The development is hampered by lattice and thermal mismatch between the nitride layers and the growth substrate leading to high dislocation densities. In order to overcome the issue, efforts have gone into sel...

Semiconductor nanowires in wrapped, gate-all-around transistor geometry are highly favorable for future electronics. The advanced nanodevice processing results in strain due to the deposited dielectric and metal layers surrounding the nanowires, significantly affecting their performance. Therefore, non-destructive nanoscale characterization of comp...

In this work, arrays of predominantly relaxed InGaN platelets with indium contents of up to 18%, free from dislocations and offering a smooth top c-plane, are presented. The InGaN platelets are grown by metal-organic vapor phase epitaxy on a dome-like InGaN surface formed by chemical mechanical polishing of InGaN pyramids defined by six equivalent...

We present an in-depth analysis of the surface band alignment and local potential distribution of InP nanowires containing a p-n junction using scanning probe and photoelectron microscopy techniques. The depletion region is localized to a 15 nm thin surface region by scanning tunneling spectroscopy and an electronic shift of up to 0.5 eV between th...

GaN nanowires are potential candidates for use in scanning probe microscopy due to their well-defined, reproducible, geometric shapes, their hardness, and their light guiding properties. We have developed and investigated probes for high resolution atomic force microscopy and scanning tunneling microscopy utilizing GaN nanowires as probes. The nano...

In this paper we present a process of forming monolithic GaN surface from an ordered nanowire array by means of material redistribution. This process, referred to as reformation, is performed in a conventional MOVPE crystal growth system with the gallium supply turned off and allows a crystal nanostructure to change shape according to differences i...

In this work, we present a method to synthesize arrays of hexagonal InGaN sub-micron-platelets with a top c-plane area having an extension of a few hundred nanometers by selective area metal organic vapor phase epitaxy. The InGaN platelets were made by in-situ annealing of InGaN pyramids, whereby InGaN from the pyramid apex was thermally etched awa...

In this study, a surface plasmon resonance biosensor was developed for the detection and quantification of a secreted bacterial factor (RoxP) from skin. Molecular imprinting method was used for the preparation of sensor chips and five different monomer-cross linker compositions were evaluated for sensitivity, selectivity, affinity and kinetic measu...

Aerotaxy, a recently invented aerosol-based growth method for nanostructures, has been shown to hold great promise in making III-V nanowires more accessible for cheap mass-production. Aerotaxy nanowire surface structure and chemistry, however, remains unexplored, which is unfortunate since this can influence (opto)electronic properties. We investig...

Defects at the interface between InAs and a native or high permittivity oxide layer are one of the main challenges for realizing III-V semiconductor based metal oxide semiconductor structures with superior device performance. Here we passivate the InAs(100) substrate by removing the native oxide via annealing in ultra-high vacuum (UHV) under a flux...

The interplay among spin, lattice, charge and orbit is of central importance for several rich and fascinating properties of oxides, and is the subject of intense research at present. Here, we present an approach to manipulate this interplay by Sn doping to effectively apply uniaxial strain on the TiO2 lattice. The evolution of this interplay in pse...

The properties of semiconductors can be controlled using doping, making it essential for electronic and optoelectronic devices. However, with shrinking device sizes it becomes increasingly difficult to quantify doping with sufficient sensitivity and spatial resolution. Here, we demonstrate how X-ray fluorescence mapping with a nanofocused beam, nan...

Heusler compounds are a ripe platform for discovery and manipulation of emergent properties in topological and magnetic heterostructures. In these applications, the surfaces and interfaces are critical to performance; however, little is known about the atomic-scale structure of Heusler surfaces and interfaces or why they reconstruct. Using a combin...

Self-assembled, atomic diffusion controlled growth of InN quantum dots was realized on the side facets of dislocation-free and c-oriented GaN nanowires having a hexagonal cross-section. The nanowires were synthesized by selective area metal organic vapor phase epitaxy. A 3 Å thick InN wetting layer was observed after growth, on top of which the InN...

Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor-oxide interface....

As semiconductor electronics keep shrinking, functionality depends on individual atomic scale surface and interface features that may change as voltages are applied. In this work we demonstrate a novel device platform that allows scanning tunneling microscopy (STM) imaging with atomic scale resolution across a device simultaneously with full electr...

The perfect switching between crystal phases with different electronic structure in III-V nanowires allows for the design of superstructures with quantum wells only a single atomic layer wide. However, it has only been indirectly inferred how the electronic structure will vary down to the smallest possible crystal segments. We use low-temperature s...

We have developed a novel method to study the influence of surface nanotopography on human fibrinogen adsorption at a given surface chemistry. Well-ordered arrays of nanoholes with different diameters down to 45 nm and a depth of 50 nm were fabricated in silicon by electron beam lithography and reactive ion etching. The nanostructured chip was used...

We study the surface diffusion and alloying of Sb into GaAs nanowires (NWs) with controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal phases. Using atomically resolved scanning tunneling microscopy, we find that Sb preferentially incorporates into the surface layer of the {110}-terminated Zb segments rather than the {112 ̅0}-term...

Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowir...

In this paper, we correlate the growth of InAs nanowires with the detailed interface trap density (Dit) profile of the vertical wrap-gated InAs/high-k nanowire semiconductor-dielectric gate stack. We also perform the first detailed characterization and optimization of the influence of the in-situ doping supplied during the nanowire epitaxial growth...

We present a study of InAs/InSb heterostructured nanowires by x-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM) and in-vacuum electrical measurements. Starting with pristine nanowires covered only by the native oxide formed through exposure to ambient air, we investigate the effect of atomic hydrogen cleaning on the surfac...

Using scanning tunneling microscopy, we evaluate the surface structure and morphology down to the atomic scale for micrometers along Au-free grown InAs nanowires (NWs) free from native oxide. We find that removal of the native oxide (which covers the NWs upon exposure to the ambient air) using atomic hydrogen does not alter the underlying step stru...

Using a scanning tunneling and atomic force microscope (STM/AFM) combined with in-vacuum atomic hydrogen cleaning, we demonstrate stable scanning tunneling spectroscopy (STS) with nanoscale resolution on electrically active nanowire devices in the common lateral configuration. We use this method to map out the surface density of states on both the...

Using in-situ surface sensitive electron microscopy performed in real time, we show that the dynamics of micron sized Ga droplets on GaP(111) can be manipulated locally using Au nanoparticles. Detailed measurements of structure and dynamics of the surface from microns to atomic scale are done using both surface electron and scanning probe microscop...

While shell growth engineering to the atomic scale is important for tailoring semiconductor nanowires with superior properties, a precise knowledge of the surface structure and morphology at different stages of this type of overgrowth has been lacking. We present a systematic scanning tunneling microscopy (STM) study of homoepitaxial shell growth o...

We determine the detailed differences in geometry and band structure between wurtzite (Wz) and zinc blende (Zb) InAs nanowire (NW) surfaces using scanning tunneling microscopy/spectroscopy and photoemission electron microscopy. By establishing unreconstructed and defect-free surface facets for both Wz and Zb, we can reliably measure differences bet...

Gated transport measurements are the backbone of electrical characterization of nanoscale electronic devices. Scanning gate microscopy (SGM) is one such gating technique that adds crucial spatial information, accessing the localized properties of semiconductor devices. Nanowires represent a central device concept due to the potential to combine ver...

Nanoscale contacts between metals and semiconductors are critical for further downscaling of electronic and optoelectronic devices. However, realizing nanocontacts poses significant challenges since conventional approaches to achieve ohmic contacts through Schottky barrier suppression are often inadequate. Here we report the realization and charact...

Utilizing semiconductor nanowires for (opto)electronics requires exact knowledge of their current–voltage properties. We report accurate on-top imaging and I–V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile applica...

Using Scanning Tunneling Microscopy and Spectroscopy (STM/S) we study the atomic scale geometry and electronic structure of GaAs nanowires exhibiting controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal segments. We find that the nonpolar low-index surfaces: {110}, {10-10}, and {11-20} are unreconstructed, unpinned, and without s...

MOS devices based on III-V semiconductors and thin high-k dielectric layers offer possibilities for improved transport properties. Here, we have studied the interface structure and chemical composition of realistic MOS gate stacks, consisting of a W or Pd metal film and a 6- or 12-nm-thick HfO2 layer deposited on InAs, with Hard X-ray Photoemission...

The Half Heuslers are currently an attractive family of compounds for high temperature thermoelectrics research, and recently, there has been renewed interest since some of these compounds are proposed to be topological insulators. NiTiSn belongs to the family of 18 valence electron Half Heuslers that are predicted to be semiconducting, despite bei...

We report transport and electronic band structure measurements on epitaxial films of the Half Heusler compound CoTiSb. CoTiSb belongs to the family of Half Heuslers with 18 valence electrons per formula unit that are predicted to be semiconducting despite being composed of all metallic components. Here the CoTiSb films were grown by molecular beam...

Using both synchrotron-based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy, we obtain a complete picture of the surface composition, morphology, and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfa...

The atomic and electronic structures of ErAs nanoparticles embedded within a GaAs matrix are examined via cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS). The local density of states (LDOS) exhibits a finite minimum at the Fermi level demonstrating that the nanoparticles remain semimetallic despite the predictions of prev...

The influence of InAs orientations and high-k oxide deposition conditions on the electrical and structural quality of Au/W/Al2O3/InAs metal-oxide-semiconductor capacitors was investigated using capacitance-voltage (C-V) and x-ray photoemission spectroscopy techniques. The results suggest that the interface traps around the conduction band edge are...

InP nanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as w...

Self-assembled InAs/InGaAsP/InP(001) nanostructures are investigated using cross-sectional scanning tunneling microscopy. Atomically resolved images show elongated nanostructures with binary composition and a truncated pyramidal shape. The investigation of the InGaAsP/InP interface shows a tendency of the quaternary matrix material towards decompos...

Vertical InAs nanowires (NWs) wrapped by a thin high-kappa dielectric layer may be a key to the next generation of high-speed metal-oxide-semiconductor devices. Here, we have investigated the structure and chemical composition of the interface between InAs NWs and 2 nm thick Al2O3 and HfO2 films. The native oxide on the NWs is significantly reduced...

The atomic and electronic structures of ErAs nanoparticles embedded within a GaAs matrix are examined via cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS). The local density of states (LDOS) exhibits a finite minimum at the Fermi level demonstrating that the nanoparticles remain semimetallic despite the predictions of prev...

We present a synchrotron-based XPS investigation on the interface between InAs and Al2O3 or HfO2 layers, deposited by ALD at different temperatures, for InAs substrates with different surface orientations as well as for InAs nanowires. We reveal the composition of the native Oxide and how the high-kappa layer deposition reduces Oxide components. We...

The atomic and electronic structure of molecular beam epitaxy (MBE)-grown rare earth-monopnictide nanostructures embedded within a III-V semiconductor matrix are examined via scanning tunneling microscopy (STM) and spectroscopy (STS). We examine several systems, including ErSb nanoparticles embedded in GaSb, ScAs nanoparticles embedded in GaAs, and...

The growth and atomic/electronic structure of molecular beam epitaxy (MBE)-grown ErAs nanoparticles and nanorods embedded within a GaAs matrix are examined for the first time via cross-sectional scanning tunneling microscopy (XSTM) and spectroscopy (XSTS). Cross sections enable the interrogation of the internal structure and are well suited for stu...

We studied the influence of nitrogen incorporation on the InAsN/GaAs quantum dot formation using cross-sectional scanning tunneling microscopy. Upon nitrogen exposure during InAs growth, rather strong dissolution effects occur, leading to the formation of extended almost spherical InGaAs quantum dots with a low indium content and almost free of nit...

We show that the principally two-dimensional (2D) scanning tunneling microscope (STM) can be used for imaging of 1D micrometer high free-standing nanowires. We can then determine nanowire megahertz resonance frequencies, image their top-view 2D resonance shapes, and investigate axial stress on the nanoscale. Importantly, we demonstrate the extreme...

Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. A...

We use scanning tunneling spectroscopy to show directly that the conduction band density of states (DOS) of GaAs1−xNx with low nitrogen (N) content x is enhanced about 0.5 eV above the band edge, followed by a decrease at higher energy. The structure of the measured DOS is in excellent agreement with calculations based on a Green’s-function formali...

Thin high-κ oxide films on InAs, formed by atomic layer deposition, are the key to achieve high-speed metal-oxide-semiconductor devices. We have studied the native oxide and the interface between InAs and 2 nm thick Al2O3 or HfO2 layers using synchrotron x-ray photoemission spectroscopy. Both films lead to a strong oxide reduction, obtaining less t...

Cross-sectional scanning tunneling microscopy is used to study the spatial structure and composition of self-assembled InAs nanostructures grown on InGaAsP lattice matched to the InP substrate. Images of the (110) and ( 1 10) cleavage surfaces reveal InAs quantum dashes of different lateral extensions. They are found to be about 60 nm long, about 1...