Sami Suihkonen

Sami Suihkonen
Aalto University · Department of Electronics and Nanoengineering

About

105
Publications
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1,403
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Publications

Publications (105)
Article
Full-text available
We report on impurity diffusion in ion implanted AlN layers after thermal annealing. Silicon, tin, germanium, and magnesium ions were implanted into single-crystal AlN layers grown on sapphire substrates. By annealing at 1600 o C, silicon and magnesium atoms were diffused in the AlN layer, while less change was observed in the distribution of germa...
Article
In this work, we demonstrate the potential of a gallium nitride (GaN)-based visible-blind ultraviolet (UV) photodetector (PD) on a commercially viable 150-mm Si wafer. The influence of thermionic field emission (TFE) and Poole–Frenkel (PF) mechanisms on the current transport of the PD has been analyzed. Conduction due to the TFE mechanism dominates...
Article
In this article, we report the temperature-dependent transistor characteristic of Epi-Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlGaN/GaN metal oxide semiconductor high electron mo...
Conference Paper
Due to the functional limitations of SiO2 for SOI applications, alternative dielectric materials have been investigated. Alternative SOI materials in this work include, AlN and AlGaN. The dielectrics were deposited using MOCVD, and with the aid of PECVD deposited SiO2, and the SiO2 was directly bonded to a handle Si wafer. Tensile tests were perfor...
Article
Full-text available
We demonstrate that thicker layers can be achieved in gallium nitride (GaN) epitaxy by using a patterned silicon (Si) substrate compared to a planar Si substrate. GaN films were grown by metalorganic vapour-phase epitaxy on 6-inch Si (111) substrates patterned with arrays of squares with various corner shapes, height and lateral dimensions. Stress...
Article
Full-text available
We report on studies of electrically excited non-equilibrium 2D electrons and 2D plasmons in an AlGaN/GaN nanostructure. Optical access to 2D plasmons is provided by means of a metal grating fabricated at the nanostructure surface, while the properties of 2D electrons are examined in the samples without metal grating. The paper focuses on the creat...
Article
Terahertz radiation emission from an electrically excited AlGaN/GaN heterostructure with a surface metal grating was studied under conditions of two-dimensional (2D) electron heating by the lateral electric field. Intensive peaks related to nonequilibrium 2D plasmons were revealed in the terahertz emission spectra with up to 4 times selective ampli...
Article
Metalorganic chemical vapor deposited (MOCVD) aluminum nitride (AlN) on vertical sidewalls can be used to implement piezoelectric in-plane actuation and sensing in microelectromechanical system (MEMS) sensors. The AlN films should optimally cover conformally the sidewalls and have good crystal quality with c-axis oriented microstructure for optimal...
Article
In this letter, we report the impact of epitaxial Gd2O3 on the electrical properties of an AlGaN/GaN high electron mobility transistor (HEMT) grown on a 150 mm diameter Si (111) substrate. Incorporation of epitaxial Gd2O3 grown by the molecular beam epitaxy technique under a metal gate (metal/Gd2O3/AlGaN/GaN) causes six orders of magnitude reductio...
Article
This letter reports the demonstration of N-polar Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N/AlN continuously-graded-channel polarization-doped field-effect transistors (PolFET...
Article
Full-text available
In this work, we demonstrate a recessed-gate p-channel MISFET using a p-GaN (70 nm)/Al0.2Ga0.8N (15 nm)/GaN heterostructure grown by Metal-Organic Chemical Vapor Deposition (MOCVD) on Si substrate. A major benefit of such epi-structure is that it contains both a 2-dimensional electron gas (2-DEG) and a 2-dimensional hole gas (2-DHG), hence making i...
Article
Atomic-layer-deposited Al 2 O 3 films can be used for passivation, protective, and functional purposes in electronic devices. However, as-deposited, amorphous alumina is susceptible to chemical attack and corrosion during manufacturing and field-use. On the contrary, crystalline Al 2 O 3 is resistant against aggressive chemical treatments and corro...
Article
Full-text available
We report the studies on optical properties of a GaN/AlGaN heterostructure with a surface metal grating. The fabricated structures were optimized for the observation of 2D plasmon resonances in the spectral range of 2–5 THz. The spectra of the equilibrium optical transmission were experimentally investigated and the 2D plasmon resonance was found....
Article
We present the electrical characterization of N-polar AlN layers grown by metal-organic vapor phase epitaxy and the demonstration of N-polar AlN-channel metal-semiconductor field-effect transistors (MESFETs). A high concentration of silicon is unintentionally incorporated during the high-temperature growth of N-polar AlN, causing a high buffer leak...
Article
We report on the electrical characterization of Si-ion implanted AlN layers and the first demonstration of metal–semiconductor field-effect transistors (MESFETs) with an ion-implanted AlN channel. The ion-implanted AlN layers with Si dose of 5 × 10¹⁴ cm⁻² exhibit n-type characteristics after thermal annealing at 1230 °C. The ion-implanted AlN MESFE...
Article
We present the effect of miscut angle of SiC substrates on N-polar AlN growth. The N-polar AlN layers were grown on C-face 4H-SiC substrates with a miscut towards 〈1¯100〉 by metal-organic vapor phase epitaxy (MOVPE). The optimal V/III ratios for high-quality AlN growth on 1° and 4° miscut substrates were found to be 20,000 and 1000, respectively. M...
Article
Full-text available
We present a comprehensive study on metal-organic vapor phase epitaxy growth of N-polar and Al -polar AlN on 4H-SiC with 4° miscut using constant growth parameters. At a high temperature of 1165 °C, N-polar AlN layers had high crystalline quality whereas the Al-polar AlN surfaces had a high density of etch pits. For N-polar AlN, the V/III ratio bel...
Article
Full-text available
Almost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general lighting, the convent...
Preprint
Almost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general lighting, the convent...
Article
In this work, atomic layer etching (ALE) of thin film Ga-polar GaN(0001) is reported in detail using sequential surface modification by Cl2 adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a standard reactive ion etching system. The feasibility and reproducibility of the process are demonstrated by patterning...
Article
Full-text available
We report on the studies of the surface plasmon polaritons in n-GaN epitaxial layers. The grating etched on the surface of the epitaxial layer is used to excite surface plasmon polaritons by means of terahertz photons. The experimental reflectivity spectrum for p-polarized radiation demonstrates a set of resonances associated with excitation of dif...
Article
Native bulk gallium nitride (GaN) has emerged as an alternative for sapphire and silicon as a substrate material for III-N devices. While quasi-bulk GaN substrates are currently commercially available, single crystal GaN substrates are considered essential for future high performance light emitters and power devices. The ammonothermal method is cur...
Article
Full-text available
We studied theoretically and experimentally plasmon-phonon polaritons and longitudinal plasmon-phonon oscillations in n-GaN epitaxial layers. The studies were carried out on the epitaxial layers with various doping levels. Simulation of the reflectivity spectra and dispersion relations of plasmon-phonon polaritons was performed in a wide frequency...
Article
We demonstrate that higher crystalline quality, lower strain and improved electrical characteristics can be achieved in gallium nitride (GaN) epitaxy by using a silicon-on-insulator (SOI) substrate compared to a bulk silicon (Si) substrate. GaN layers were grown by metal-organic vapor phase epitaxy on 6-inch bulk Si and SOI wafers using the standar...
Article
Ammonothermally grown GaN is a promising substrate for high-power optoelectronics and electronics thanks to its scalability and high structural perfection. Despite extensive research, ammonothermal GaN still suffers from significant concentrations of impurities. This article discusses the evolution of impurity incorporation during growth of basic a...
Article
The ammonothermal method is one of the most promising candidates for large-scale bulk GaN growth due to its scalability and high crystalline quality. However, emphasis needs to be put on understanding the incorporation and effects of impurities during growth. This article discusses how impurities are incorporated in different growth zones in basic...
Article
Full-text available
Variation of absorption of terahertz radiation in lateral electric field was investigated in GaN epitaxial layers. Different behaviour of the absorption modulation in electric field was observed for radiation polarized along electric field and perpendicular to it. Joint analysis of optical and transport measurements let us obtain field dependencies...
Article
Though several methods exist to produce bulk crystals of gallium nitride (GaN), none have been commercialized on a large scale. The sodium flux method, which involves precipitation of GaN from a sodium-gallium melt supersaturated with nitrogen, offers potentially lower cost production due to relatively mild process conditions while maintaining high...
Article
Polarization controlled Fourier transform infrared (FTIR) absorption measurements were performed on a high quality m-plane ammonothermal GaN crystal grown using basic chemistry. The polarization dependence of characteristic absorption peaks of hydrogen-related defects at 3000–3500 cm−1 was used to identify and determine the bond orientation of hyd...
Poster
Ammonothermal GaN is a promising substrate for high-power optoelectronics and electronics. Despite its high structural quality, ammonothermal GaN still suffers from high concentrations of impurities which may affect substrate transparency (defect states, free carrier absorption), device epitaxy (lattice constant mismatch) and electrical properties...
Article
We present the results of experimental and theoretical studies of the surface plasmon polariton excitations in heavily doped GaNepitaxial layers. Reflection and emission of radiation in the frequency range of 2–20 THz including the Reststrahlen band were investigated for samples with grating etched on the sample surface, as well as for samples with...
Article
We demonstrate a technique for fabricating position-controlled, large-area arrays of vertical semiconductor nanowires (NWs) with adjustable periods and NW diameters. In our approach, a Au-covered GaAs substrate is first coated with a thin film of photoresponsive azopolymer, which is exposed twice to a laser interference pattern forming a 2D surface...
Article
Full-text available
We study theoretically and experimentally transverse and longitudinal electromagnetic waves in n-GaN epitaxial layers. The studies are carried out on the epitaxial layers with various doping levels. Simulation of the reflectivity and absorptivity spectra is performed in a wide frequency range. Additionally, the radiation emission spectra are simula...
Conference Paper
Diffusion-driven current transport (DDCT) has recently been proposed as a new way to organize the current injection in nanoscale optoelectronic devices. The very recent first proof-of-principle experiments have also shown that DDCT works as predicted theoretically. In this work we perform simulations on DDCT-based III-Nitride devices and demonstrat...
Article
Charge injection to the prevailing and emerging light-emitting devices is almost exclusively based on the double heterojunction (DHJ) structures that have remained essentially unchanged for decades. In this letter, we report the excitation of a near surface indium gallium nitride (InGaN) quantum well (QW) by bipolar carrier diffusion from a nearby...
Article
The optical and electrical properties of silicon-doped epitaxial gallium nitride layers grown on sapphire have been studied. The studies have been performed over a wide range of silicon concentrations on each side of the Mott transition. The critical concentrations of Si atoms corresponding to the formation of an impurity band in gallium nitride (∼...
Article
Due to their potential to improve the performance of light-emitting diodes (LEDs), novel device structures based on nanowires, surface plasmons, and large-area high-power devices have received increasing amount of interest. These structures are almost exclusively based on the double hetero junction (DHJ) structure, that has remained essentially unc...
Article
Full-text available
Surface plasmon polaritons are investigated in heavily doped n-GaN epitaxial layers. The grating etched on the surface of the epitaxial layer is used to convert photons into the surface plasmon polaritons and vice versa. The spectral study of reflection demonstrates the possibility of nonequilibrium surface plasmon polaritons excitation due to tera...
Conference Paper
Surface plasmon polaritons at the n-GaN/vacuum interface are investigated. Experimental studies of terahertz radiation reflection and emission are performed on heavily silicon-doped GaN epitaxial layers grown on sapphire substrates. To provide interaction of THz radiation with the surface plasmon polaritons, a regular grating was fabricated on the...
Article
The large-area defect structure of high-quality ammonothermal GaN was studied by synchrotron radiation X-ray topography (SR-XRT) and high-resolution X-ray diffraction (XRD). The threading dislocation densities of mixed and screw dislocations were determined separately by SR-XRT and were 3.2 × 104 and 3.1 × 103 cm−2, respectively. Threading edge dis...
Article
The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid an...
Article
We report on the epitaxial growth of ZnO on GaN template by atomic layer deposition (ALD). Diethylzinc (DEZn) and water vapour (H2O) were used as precursors. The structure and the quality of the grown ZnO layers were studied with scanning electron microscope (SEM), X-ray diffraction (XRD), photoluminescence (PL) measurements and positron annihilati...
Article
The attention towards light-emitting diode (LED) structures based on nanowires, surface plasmon coupled LEDs, and large-area high-power LEDs has been increasing for their potential in increasing the optical output power and efficiency of LEDs. In this work we demonstrate an alternative way to inject charge carriers into the active region of an LED,...
Article
In this paper, we present out studies on low energy electron beam induced optical degradation and defect activation of indium gallium nitride quantum wells. A clear reduction in band-to-band photoluminescence of metal organic vapor phase epitaxy grown III-nitride films and quantum well structures treated with low energy electron beam has been found...
Article
Nanostructured CdS microspheres were prepared by hydrothermal synthesis and used as photocatalyst in the degradation of dyes under near UV and blue LED radiation. Nearly complete degradation of methylene blue, phenol red and methyl red was achieved in 3 h. Catalytic performance of the microspheres remained unchanged during five recycling steps. Dif...
Article
The processing and characterization of optical components often requires the use of low energy electron beam (e-beam) techniques, such as scanning electron microscopy or electron beam lithography. The e-beam irradiation has been shown to produce band-edge luminescence degradation in GaN films grown by metal-organic vapor phase epitaxy (MOVPE), down...
Article
Full-text available
Migration kinetics of ion-implanted beryllium in ZnO and GaN has been studied using the modified radiotracer technique utilizing 7Be tracers. For ZnO the studies were carried out in the temperature range 650–750 °C. Clear Be migration following Arrhenius type behaviour was noted. The process is suggested to be limited due to formation of the BeZnO...
Article
High-resolution Raman mapping of the stress distribution in an etched GaN micro-pillar template and a 5 μm thick GaN layer grown on a micro-pillar patterned GaN template is investigated. Raman mapping of the E2 (high) phonon shows differences in stress between the coalescing boundary, the top surface of the pillar region and around the GaN micro-pi...
Article
Full-text available
In this paper, we demonstrate self-alignment of mi-crochips on a simple-to-fabricate hybrid template with both wa-ter and UV-curing adhesive (EPO-TEK UVO-114). The hybrid template contains receptor sites with solid edges for droplet con-finement and large wetting contrast between the receptor sites and the substrate for microchip manipulation. Nano...
Article
GaP0.98N0.02 layers having a thickness from 75 nm to 600 nm are grown on GaP substrates by metalorganic vapor phase epitaxy. Back-reflection X-ray topographs made with a synchrotron radiation of the thick GaP0.98N0.02 layers reveal images of misfit dislocations. The critical thickness of the grown GaP0.98N0.02 layer on GaP substrate is evaluated fr...
Article
In this paper we report on the MOCVD growth and characterization of GaN structures and InGaN single quantum wells grown on pillar patterned GaN/sapphire templates. During the regrowth a network of voids was intentionally formed at the interface of sapphire substrate and GaN epitaxial layer. The regrowth process was found to decrease the threading d...
Article
Although conventional III-V compound semiconductors are often considered not to exhibit an efficiency droop, a pronounced low temperature droop was recently measured in AlGaInP/GaAs multi-quantum well structures. In this work, we investigate the efficiency droop in simple optically pumped lattice matched InGaAs/InP single well heterostructures to e...
Article
Carrier lifetimes of the recombination processes in light emitting diodes (LEDs) depend strongly on the operating point. We measure the carrier lifetimes of InGaN/GaN LEDs at low current densities by applying the differential carrier lifetime analysis. In the measurement setup the LED is driven with constant current modulated with small amplitude a...
Article
In this paper, we present our studies on thermally assisted recovery of low energy electron beam induced optical degradation of gallium nitride. A clear reduction in MOVPE grown GaN band-to-band photoluminescence intensity induced by low energy electron beam irradiation has been found before. Partial recovery of the band-to-band emission was observ...
Article
Full-text available
We demonstrate that an extraction enhancement by a factor of 2.8 can be obtained for a GaN quantum well structure using metallic nanostructures, compared to a flat semiconductor. The InGaN/GaN quantum well is inserted into a dielectric waveguide, naturally formed in the structure, and a silver grating is deposited on the surface and covered with a...
Article
Optical spectra and electrical conductivity of silicon-doped epitaxial gallium nitride layers with uncompensated donor concentrations N D — N A up to 4.8 × 1019 cm−3 at T ≈ 5 K have been studied. As follows from the current-voltage characteristics, at a doping level of ∼3 × 1018 cm−3 an impurity band is formed and an increase of donor concentration...
Article
We present cathodoluminescence (CL) studies on low energy e-beam irradiated (LEEBI) metal-organic vapor phase epitaxy (MOVPE) grown GaN films. High intensity LEEBI has been reported to reduce the band-edge photoluminescence intensity of MOVPE grown GaN films. Here we observe similar reduction of band-edge CL intensity with increasing LEEBI dose. Th...
Article
We report on patterning and subsequent metal-organic vapor phase epitaxy overgrowth of GaN films on patterned GaN/sapphire templates. Templates with a hexagonal hole pattern were prepared by photolithography and dry etching. After GaN overgrowth voids were formed at the GaN/sapphire interface. Threading dislocations were found to bend and terminate...
Article
Full-text available
We present near-UV GaN light-emitting diodes (LEDs) grown on patterned GaN/sapphire templates with improved material quality and light extraction efficiency. Enhancement of light extraction efficiency is attributed to voids generated at the GaN/sapphire interface. The sidewall inclination angle of the voids can be controlled from nearly vertical (s...
Article
We propose a direct electrical measurement method for determining the extraction efficiency (EXE) and internal quantum efficiency (IQE) of III-Nitride light-emitting diodes (LEDs). The method is based on measuring the optical output power as a function of injection current at current densities near the external quantum efficiency (EQE) maximum and...
Conference Paper
In this study, homoepitaxial GaN grown on ammonothermal GaN substrates is non-destructively investigated by synchrotron radiation X-ray topography (SR-XRT) and X-ray diffraction (XRD). The homoepitaxial GaN layer was found to be of excellent crystal quality with individual dislocations clearly visible in the SR-XRT images. SR-XRT images and XRD roc...
Conference Paper
We report a study of the structural and optical properties of near-surface InGaN/GaN single quantum wells, grown by metalorganic chemical vapour deposition, as a function of underneath layer structure and GaN capping thickness. Special attention is paid to characterize properties which are important for non-radiative coupling applications, such as...
Article
We present our studies on low energy electron beam induced damage to gallium nitride semiconductor material. We have observed a clear reduction in InGaN single quantum well and bulk GaN band-to-band emission intensity induced by low energy electron beam irradiation. The dose and energy of the e-beam were 0 - 500 μC/cm2 and of 5 - 20 keV, respective...
Article
In this article, we analyze the behavior of threading dislocations in GaN layers re-grown on hexagonally patterned mask-less GaN. The growth mode of the material with patterned hexagonal morphology changes with the diameter and the periodicity of the hexagonal patterns. The growth mode directly affects the shape of the voids that are formed in this...
Article
Full-text available
Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5–20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degrad...
Article
We have studied optical properties of single In0.1Ga0.9N quantum wells with GaN barriers in close proximity to the wafer surface (<10 nm). We have found that at room temperature a balance of radiative, non-radiative recombination and complex surface states effects results in an optimum cap thickness of 3nm for achieving highest brightness emitters....
Article
We present results on optical degradation of gallium nitride based materials under low energy electron beam irradiation (LEEBI). GaN thin film and GaN/InGaN quantum well samples, grown by metal-organic vapor phase epitaxy (MOVPE), were exposed to a tightly focused (ø = 2 nm, J = 0-130 kA/cm2), rapidly scanning electron beam (e-beam) with energy of...
Article
doi: 10.1557/opl.2012.782, Published by Cambridge University Press, 13 April 2012. The acknowledgment that follows should have been included in the published article: THE CORRECTION This article was originally published on June 2012 with a mistake. The name of the third author was incorrect. The correct name of the third author is “Lukasz Kilanski...