Harri Kalevi Lipsanen

Aalto University · Department of Electronics and Nanoengineering

Anti-ambipolar transistors (AATs) are the leading platform for the paradigm shift from binary to multi-valued logic (MVL) circuits, increasing circuit integration density and data processing capacity. However, most AATs with p–n heterojunctions present limited controllability of the transconductance peak, which is key to MVL operation. Here, we rep...

Understanding the growth mechanisms of a newly discovered polymorphic material and achieving large-scale selective growth is critical for accurate material characterization and application. Post-transition metal monochalcogenides, including Ge chalcogenides, are...

Gallium arsenide (GaAs) semiconductor wires have emerged as potent candidates for nonlinear optical devices, necessitating bandgap engineering for an expanded operational wavelength range. We report the successful growth of strain-mediated GaAs microwires (MWs) with an average diameter of 1.1 μm. The axial tensile strain in these wires, as measured...

Layered two-dimensional (2D) materials have gained popularity thanks to their ultimate thin physique and strong coupling with light. Here, we investigate a comparatively wide band gap (≥2 eV) 2D material,...

Miniaturized spectrometers are of immense interest for various on-chip and implantable photonic and optoelectronic applications. State-of-the-art conventional spectrometer designs rely heavily on bulky dispersive components (such as gratings, photodetector arrays, and interferometric optics) to capture different input spectral components that incre...

In this work, we demonstrated a kind of flexibly monolithic saturable absorber (SA) with GaAs nanowires (NWs) on polyimide (PI) plastic substrate for broadband optical modulation at 1.0 and 1.5 µm, separately. The monolithic SA sample was prepared by the metalorganic vapor phase epitaxy (MOVPE) method. The crystal structure and element analysis wer...

Molybdenum ditelluride (MoTe2) exhibits immense potential in post‐silicon electronics due to its bandgap comparable to silicon. Unlike other 2D materials, MoTe2 allows easy phase modulation and efficient carrier type control in electrical transport. However, its unstable nature and low‐carrier mobility limit practical implementation in devices. Her...

Understanding phonon transport and thermal conductivity of layered materials is not only critical for thermal management and thermoelectric energy conversion but also essential for developing future optoelectronic devices. Optothermal Raman characterization has been a key method to identify the properties of layered materials, especially transition...

Abstract The large‐scale synthesis of high‐purity semiconducting single‐walled carbon nanotubes (s‐SWCNTs) plays a crucial role in fabricating high‐performance and multiapplication‐scenario electronics. This work develops a straightforward, continuous, and scalable method to synthesize high‐purity and individual s‐SWCNTs with small‐diameters distri...

We report ultra-miniaturized (~10×20 µm ² ) spectrometers with electrically modulated van der Waals junctions in conjunction with a reconstruction algorithm, achieving spectral reconstruction with a spectral resolution of ~3-nm over a broad operation bandwidth for spectral imaging.

Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic...

Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of li...

Control over the doping at the nanoscale during the growth of nanostructures is one of the key challenges of device fabrication. In this work we study p (Zn)- and n (Sn)- doping distributions and a formation of 3D p–n junctions in planar GaAs nanowires grown on doped GaAs substrates. We employ a combination of scanning electron microscopy, transmis...

We demonstrate highly-doped Er ³⁺ and Yb ³⁺ doped gain media on SiN waveguides by plasma-enhanced atomic layer deposition, showing great potential for integrated lasers and amplifiers.

Various nanophotonic devices based on semiconductor wires with a diameter of several ten nanometers have been studied. Nevertheless, studying the optoelectronics properties and performance of such devices based on large-diameter wires is interesting and meaningful. Here, we successfully grew the micronsized indium antimonide (InSb) wires, and exami...

In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause per...

With the development of microscale and standalone electronic devices the demand for microscale energy storage is increasing. Micro-supercapacitors are emerging as the candidate for microscale energy storage, especially when combined with energy harvesters. In this work, we enhance the capacitance of porous silicon (PS) supercapacitor electrodes up...

Miniaturized computational spectrometers, which can obtain incident spectra using a combination of device spectral responses and reconstruction algorithms, are essential for on-chip and implantable applications. Highly sensitive spectral measurement using a single detector allows the footprints of such spectrometers to be scaled down while achievin...

Mixed-dimensional van der Waals heterostructures are promising for research and technological advances in photonics and optoelectronics. Here we report vapor−liquid−solid (VLS) method-based van der Waals epitaxy of one-dimensional InP nanowires (NWs) directly on two-dimensional MoS 2. With optimized growth parameters (V/III ratio, flow rates of pre...

Nanowire Assemblies In article number 2201968, Harish Bhaskaran and co‐workers develop a universal and deterministic way of assembling single nanowires with a placement precision below 1 micron. They further demonstrate first‐of‐its‐kind devices in the nanowire realm, heralding new opportunities and large‐scale nanowire integration.

With the introduction of techniques to grow highly functional nanowires of exotic materials and demonstrations of their potential in new applications, techniques for depositing nanowires on functional platforms have been an area of active interest. However, difficulties in handling individual nanowires with high accuracy and reliability have so far...

Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, we probe various relevant electronic states in monolayer MoS2, such as multiple excitonic Rydberg states and free-particle energy bands, with a high relative contrast of up to >200 via broadband (from ~1.79 to 3.10 eV) static third-...

Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high...

We demonstrate dipole-based modeling for designing nanostructured emitters in a stratified surrounding medium in the presence of parasitic absorption, while giving equivalent information about far-field emission as Lorentz reciprocity. We consider the challenging modeling case of a single nanowire with a parasitically absorbing planar top contact l...

WITio is a free script-based MATLAB data evaluation toolbox for the files generated by thousand WITec microscopes operated globally by thousands of academic and industrial users. These modular microscopes excel at advanced imaging techniques and correlative studies, but also easily yield unwieldy big data. Though the shipped WITec software can batc...

Engineering of the dipole and the symmetry of materials plays an important role in fundamental research and technical applications. Here, a novel morphological manipulation strategy to engineer the dipole orientation and symmetry of 2D layered materials by integrating them with 1D nanowires (NWs) is reported. This 2D InSe –1D AlGaAs NW heterostruct...

The growth of self-catalyzed GaAs nanowires (NWs) and monolithic light-emitting diode (LED) directly on flexible plastic substrates is reported. Dense GaAs NW forest is attained in self-catalyzed mode using metalorganic vapor phase epitaxy. The NWs are shown to be crystalline with a zinc-blende phase. The optical properties of the GaAs NWs are foun...

In this paper, indium phosphide (InP) nanowires (NWs) are fabricated by Au-nanoparticle assisted vapor-liquid-solid method and applied as a saturable absorber (SA) for continuous-wave (CW) mode-locked femtosecond Yb:KYW bulk laser. I-scan method was used to characterize the saturable absorption properties of the prepared InP NWs SA. Pulses as short...

We report direct growth of InSb nanowires (NWs) and monolithic device fabrication on flexible plastic substrates. The nanowires were grown using metal–organic vapor-phase epitaxy (MOVPE) in self-catalyzed mode. The InSb NWs are shown to form in the zinc-blende crystal structure and to exhibit strong photoluminescence at room temperature. The NW arr...

We report tunable tunneling van der Waals heterointerfaces with two strategies (oxidation layer and bandgap engineering) for broadband photodetection covering from the ultra-violet to the mid-infrared ranges.

The development of powerful terahertz (THz) emitters is the cornerstone for future THz applications, such as communication, medical biology, non-destructive inspection, and scientific research. Here, we report the THz emission properties and mechanisms of mushroom-shaped InAs nanowire (NW) network using linearly polarized laser excitation. By inves...

Graphene-based van der Waals heterostructures are promising building blocks for broadband photodetection because of the gapless nature of graphene. However, their performance is mostly limited by the inevitable trade-off between low dark current and photocurrent generation. Here, we demonstrate a hybrid photodetection mode based on the photogating...

III-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire...

Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, we probe various relevant electronic states in monolayer MoS2, such as multiple excitonic Rydberg states and free-particle energy bands, with a high relative contrast of up to 200 via broadband (from ∼1.79 to 3.10 eV) static third-h...

Packaged photodiodes suffer from Fresnel reflection from the package window glass, especially at high angles of incidence. This has a notable impact particularly on black silicon (b-Si) photodiodes, which have extreme sensitivity. In this work, we show that by adding a simple grass-like alumina antireflection (AR) coating on the window glass, excel...

Nanoplasmonics is a potential game-changer in the development of next-generation on-chip photonic devices and computers, owing to the geometrically controlled and amplified linear and nonlinear optical processes. For instance, it resolves the limited light-matter interaction of the unique two-dimensional (2D) crystalline materials like semiconducti...

Functional 2D material‐based devices are likely subjected to high ambient temperatures when integrated into miniaturized circuits for practical applications, which may induce irreversible structural changes in materials and impact the device performance. However, majority of 2D devices’ studies focus on room temperature or low‐temperature operation...

Atomic layer deposition (ALD) technology has unlocked new ways of manipulating the growth of inorganic materials. The fine control at the atomic level allowed by ALD technology creates the perfect conditions for the inclusion of new cationic or anionic elements of the already-known materials. Consequently, novel material characteristics may arise w...

All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elus...

Indium arsenide phosphide (InAsP) nanowires (NWs), a member of the III–V semiconductor family, have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap. In this work, we synthesize InAsP NWs and further explore their nonlinear op...

Young's modulus of tapered mixed composition (zinc-blende with a high density of twins and wurtzite with a high density of stacking faults) Gallium Phosphide (GaP) nanowires (NWs) was investigated by atomic force microscopy (AFM). Experimental measurements were performed by obtaining bending profiles of as-grown inclined GaP NWs deformed by applyin...

In article number 2002119, Mika Pettersson, Zhipei Sun, and co‐workers demonstrate an optical modification process that simultaneously creates topographical structures and alters the optical properties of MoS2 monolayer. This local and controllable optical modification method shows great promise for applications in electronics, photonics, and mecha...

The use of thin-films made by atomic layer deposition (ALD) is rapidly growing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require pl...

Numerical optics modeling is an invaluable tool in the design of nanostructures for nanophotonics applications where diffraction effects often lead to complex dependency between the nanostructure geometry and its optical properties and response. In order to analyze, design, and optimize such nanostructures, computationally efficient numerical optic...

Nanophotonics—the science and technology of confining, guiding, and making photons interact with matter at the nanoscale—is an active research field. By varying the geometry and constituent materials, nanostructures allow precise control of the scattering of incident light and tailoring of emitted light. In this Tutorial, we outline the use of the...

Transition metal dichalcogenide monolayers have demonstrated a number of exquisite optical and electrical properties. Here, the authors report the optical modification of topographical and optical properties of monolayer MoS2 with femtosecond pulses under an inert atmosphere. A formation of three‐dimensional structures on monolayer MoS2 with tunabl...

Graphene is an ideal candidate as a component of flexible/wearable electronics due to its two-dimensional nature and low gate bias requirements for high quality devices. However, the proven methods for fabrication of graphene thin film transistors (TFTs) on fixed substrates involve using a sacrificial polymer layer to transfer graphene to a desired...

Van der Waals heterostructures are the fundamental building block of electronic and optoelectronic devices. Here we report that, through a single-step chemical vapour deposition (CVD) process, high-quality vertical bilayer MoS2/WS2 heterostructures with the size of ∼50 μm can be synthesized from molten salts precursors, Na2MoO4 and Na2WO4. Instead...

Several passivation techniques are developed and compared in terms of their ability to preserve the optical properties of close-to-surface InAs/GaAs quantum dots (QDs). In particular, the influence of N-passivation by hydrazine chemical treatment, N-passivation by hydrazine followed by atomic layer deposition (ALD) of AlOx and use of AlNx deposited...

Successful deployment of carbon nanomaterials in many applications, such as sensing, energy storage, and catalysis, relies on the selection, synthesis, and tailoring of the surface properties. Predictive analysis of the behavior is difficult without detailed knowledge of the differences between various carbon nanomaterials and their surface functio...

For the design of nanostructured semiconductor solar cells and photodetectors, optics modelling can be a useful tool that reduces the need of time-consuming and costly prototyping. We compare the performance of three of the most popular numerical simulation methods for nanostructure arrays: the Fourier modal method (FMM), the finite element method...

Semiconductor nanowires offer a promising route of realizing nanolasers for the next generation of chip-scale optoelectronics and photonics applications. Established fabrication methods can produce vertical semiconductor nanowires which can themselves act both as a gain medium and as a Fabry–Pérot cavity for feedback. The lasing threshold in such n...

This work presents a superhydrophobic antireflective (AR) coating on glass. The coating consists of a grass-like alumina layer capped with plasma-deposited fluoropolymer. The grass-like alumina is formed by hot water treatment of atomic layer-deposited alumina on glass, and the fluoropolymer is plasma-deposited from CHF3. Excellent broadband AR per...

Recently, erbium-doped integrated waveguide devices have been extensively studied as a CMOS-compatible and stable solution for optical amplification and lasing on the silicon photonic platform. However, erbium-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon...

We report an indium phosphide nanowire (NW)-induced cavity in a silicon planar photonic crystal (PPC) waveguide to improve the light–NW coupling. The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide, which gives rise to a microcavity located on the NW section. Resonant modes with Q factors...