Showing papers in "Semiconductor Science and Technology in 2015"

Indium oxide—a transparent, wide-band gap semiconductor for (opto)electronic applications

Abstract: The present review takes a semiconductor physics perspective to summarize the state-of-the art of In2O3 in relation to applications. After discussing conventional and novel applications, the crystal structure, synthesis of single-crystalline material, band-structure and optical transparency are briefly introduced before focussing on the charge carrier transport properties. The issues of unintentional n-type conductivity and its likely causes, the surface electron accumulation, and the lack of p-type conductivity will be presented. Intentional doping will be demonstrated to control the electron concentration and resistivity over a wide range, but is also subject to compensation. The control of the surface accumulation in relation to Schottky and ohmic contacts will be demonstrated. In the context of scattering mechanisms, the electron mobility and its limits will be discussed. Finally, the Seebeck coefficient and its significance will be shown, and ferromagnetic doping of In2O3 will be critically discussed. With this overview most if not all ingredients for the use of In2O3 as semiconductor material in novel or improved conventional devices will be given.

Recent progress in high performance and reliable n-type transition metal oxide-based thin film transistors

Abstract: This review gives an overview of the recent progress in vacuum-based n-type transition metal oxide (TMO) thin film transistors (TFTs). Several excellent review papers regarding metal oxide TFTs in terms of fundamental electron structure, device process and reliability have been published. In particular, the required field-effect mobility of TMO TFTs has been increasing rapidly to meet the demands of the ultra-high-resolution, large panel size and three dimensional visual effects as a megatrend of flat panel displays, such as liquid crystal displays, organic light emitting diodes and flexible displays. In this regard, the effects of the TMO composition on the performance of the resulting oxide TFTs has been reviewed, and classified into binary, ternary and quaternary composition systems. In addition, the new strategic approaches including zinc oxynitride materials, double channel structures, and composite structures have been proposed recently, and were not covered in detail in previous review papers. Special attention is given to the advanced device architecture of TMO TFTs, such as back-channel-etch and self-aligned coplanar structure, which is a key technology because of their advantages including low cost fabrication, high driving speed and unwanted visual artifact-free high quality imaging. The integration process and related issues, such as etching, post treatment, low ohmic contact and Cu interconnection, required for realizing these advanced architectures are also discussed.

Ion beam irradiation of nanostructures: sputtering, dopant incorporation, and dynamic annealing

Abstract: Nanostructured materials are today subject to intense research, as their mesoscopic properties will enable a variety of new applications in the future. They can be grown with specific properties under equilibrium conditions by a variety of different top-down and bottom-up synthesis techniques. Subsequent modification, including doping or alloying using the highly non-equilibrium process of ion irradiation, significantly expands the potpourri of functionality of what is today an important material class. Important and newly discovered effects must be considered compared to ion irradiation of bulk or thin film counterparts, as the ion range becomes comparable to the size of the nanotructure. Here, we will review recent high fluence irradiation studies reporting on non-linear incorporation of implanted species, enhanced sputtering yields, morphological changes induced by the high thermal impact, as well as strongly enhanced dynamic annealing for such confined nanostructures. Our review will also include the concurrent and recent progress in developing new simulation tools in order to describe and quantify those newly observed effects.

Single-walled carbon nanotube networks for flexible and printed electronics

Abstract: Networks of single-walled carbon nanotubes (SWNTs) can be processed from solution and have excellent mechanical properties. They are highly flexible and stretchable. Depending on the type of nanotubes (semiconducting or metallic) they can be used as replacements for metal or transparent conductive oxide electrodes or as semiconducting layers for field-effect transistors (FETs) with high carrier mobilities. They are thus competitive alternatives to other solutionprocessable materials for flexible and printed electronics. This review introduces the basic properties of SWNTs, current methods for dispersion and separation of metallic and semiconducting SWNTs and techniques to deposit and pattern dense networks from dispersion. Recent examples of applications of carbon nanotubes as conductors and semiconductors in (opto-)electronic devices and integrated circuits will be discussed.

First-principles calculations of bismuth induced changes in the band structure of dilute Ga-V-Bi and In-V-Bi alloys: chemical trends versus experimental data

Abstract: Bi-induced changes in the band structure of Ga–V–Bi and In–V–Bi alloys are calculated within the density functional theory (DFT) for alloys with Bi ≤3.7% and the observed chemical trends are discussed in the context of the virtual crystal approximation (VCA) and the valence band anticrossing (VBAC) model. It is clearly shown that the incorporation of Bi atoms into III–V host modifies both the conduction band (CB) and the valence band (VB). The obtained shifts of bands in GaP1−xBix, GaAs1−xBix, GaSb1−xBix, InP1−xBix, InAs1−xBix, and InSb1−xBix are respectively, 15, −29, −16, −27, −15, and −10 meV/%Bi for CB, 82, 62, 16, 79, 45, and 16 meV/%Bi for VB, and −17, −3, −2, −8, −6, and 14 meV/%Bi for spin–orbit split off band. The Bi-induced reduction of the band gap is very consistent with the available experimental data. The chemical trends observed in our calculations as well as in experimental data are very clear: in a sequence of alloys from III–P–Bi to III–Sb–Bi the Bi-induced changes in the band structure weaken. For dilute GaSb1−xBix and InSb1−xBix alloys the band structure modification, in the first approximation, can be described within the VCA, while for Ga–V–Bi and In–V–Bi alloys with V = As or P another phenomenological approach is needed to predict the Bi-induced changes in their band structure. We have found that a combination of the VCA with the VBAC model, which is widely applied for highly mismatched alloys, is suitable for this purpose. The chemical trends for III–V–Bi alloys observed in our DFT calculations are also exhibited by the coupling parameter which describes the magnitude of interaction between Bi-induced levels and VB states in the VBAC model. This coupling parameter monotonously decreases along the sequence of alloys from III–P–Bi to III–Sb–Bi.

A review on the recent developments of solution processes for oxide thin film transistors

Abstract: This review article introduces the recent advances in the development of oxide semiconductor materials based on solution processes and their potential applications In the early stage, thin film transistors based on oxide semiconductors fabricated by solution processes used to face critical problems such as high annealing temperatures (>400 °C) required to obtain reasonable film quality, and the relatively low field effect mobility (<5 cm2 V−1 s−1) compared to devices fabricated by conventional vacuum-based techniques In order to overcome such hurdles, the proper selection of high mobility amorphous oxide semiconductor materials is addressed first The latter involves the combination of high mobility compounds and multilayered active stacks Ensuing overviews are provided on the selection of optimum precursors and alternative annealing methods that enable the growth of high quality films at relatively low process temperatures (<200 °C) Reasonably high field effect mobility values (~10 cm2 V−1 s−1) could thus be obtained by optimizing the above process parameters Finally, potential applications of solution processed oxide semiconductor devices are summarized, involving, for instance, flexible displays, biosensors, and non-volatile memory devices As such, further innovations in the solution process methods of oxide semiconductor devices are anticipated to allow the realization of cost effective, large area electronics in the near future

Copper(I) thiocyanate (CuSCN) as a hole-transport material for large-area opto/electronics

Abstract: Recent advances in large-area optoelectronics research have demonstrated the tremendous potential of copper(I) thiocyanate (CuSCN) as a universal hole-transport interlayer material for numerous applications, including transparent thin-film transistors, high-efficiency organic and hybrid organic-inorganic photovoltaic cells, and organic light-emitting diodes. CuSCN combines intrinsic hole-transport (p-type) characteristics with a large bandgap (>3.5 eV) which facilitates optical transparency across the visible to near infrared part of the electromagnetic spectrum. Furthermore, CuSCN is readily available from commercial sources while it is inexpensive and can be processed at low-temperatures using solution-based techniques. This unique combination of desirable characteristics makes CuSCN a promising material for application in emerging large-area optoelectronics. In this review article, we outline some important properties of CuSCN and examine its use in the fabrication of potentially low-cost optoelectronic devices. The merits of using CuSCN in numerous emerging applications as an alternative to conventional hole-transport materials are also discussed.

The role of printing techniques for large-area dye sensitized solar cells

Abstract: The versatility of printing technologies and their intrinsic ability to outperform other techniques in large-area deposition gives scope to revolutionize the photovoltaic (PV) manufacturing field. Printing methods are commonly used in conventional silicon-based PVs to cover part of the production process. Screen printing techniques, for example, are applied to deposit electrical contacts on the silicon wafer. However, it is with the advent of third generation PVs that printing/coating techniques have been extensively used in almost all of the manufacturing processes. Among all the third generation PVs, dye sensitized solar cell (DSSC) technology has been developed up to commercialization levels. DSSCs and modules can be fabricated by adopting all of the main printing techniques on both rigid and flexible substrates. This allows an easy tuning of cell/module characteristics to the desired application. Transparency, colour, shape, layout and other DSSC's features can be easily varied by changing the printing parameters and paste/ink formulations used in the printing process. This review focuses on large-area printing/coating technologies for the fabrication of DSSCs devices. The most used and promising techniques are presented underlining the process parameters and applications.

Temperature-dependent thermal conductivity in Mg-doped and undoped β-Ga 2 O 3 bulk-crystals

Abstract: For - only little information exists concerning the thermal properties, especially the thermal conductivity λ. Here, the thermal conductivity is measured by applying the electrical 3ω-method on Czochralski-grown - bulk crystals, which have a thickness of and . At room temperature (RT), the thermal conductivity along the [100]-direction in Mg-doped electrical insulating and undoped semiconducting - is confirmed as for both crystals. The thermal conductivity increases for decreasing temperature down from 25 K to . The phonon contribution of λ dominates over the electron contribution below RT. The observed function is in accord with phonon–phonon–Umklapp scattering and the Debye model for the specific heat at which is about 0.1 times the Debye temperature . Here, a detailed discussion of the phonon–phonon–Umklapp scattering for is carried out. The influence of point defect scattering is considered for .

Towards printed perovskite solar cells with cuprous oxide hole transporting layers: a theoretical design

Abstract: Solution-processed p-type metal oxide materials have shown great promise in improving the stability of perovskite-based solar cells and offering the feasibility for a low cost printing fabrication process. Herein, we performed a device modeling study on planar perovskite solar cells with cuprous oxide (Cu2O) hole transporting layers (HTLs) by using a solar cell simulation program, wxAMPS. The performance of a Cu2O/perovskite solar cell was correlated to the material properties of the Cu2O HTL, such as thickness, carrier mobility, mid-gap defect, and doping concentrations. The effect of interfacial defect densities on the solar cell performance was also investigated. Our simulation indicates that, with an optimized Cu2O HTL, high performance perovskite solar cells with efficiencies above 13% could be achieved, which shows the potential of using Cu2O as an alternative HTL over other inorganic materials, such as NiOx and MoOx. This study provides theoretical guidance for developing perovskite solar cells with inorganic hole transporting materials via a printing process.

Understanding the gradual reset in Pt/Al2O3/Ni RRAM for synaptic applications

Abstract: In this work, a study has been performed to understand the gradual reset in Al2O3 resistive random-access memory (RRAM). Concentration of vacancies created during the forming or set operation is found to play a major role in the reset mechanism. The reset was observed to be gradual when a significantly higher number of vacancies are created in the dielectric during the set event. The vacancy concentration inside the dielectric was increased using a multi-step forming method which resulted in a diffusion-dominated gradual filament dissolution during the reset in Al2O3 RRAM. The gradual dissolution of the filament allows one to control the conductance of the dielectric during the reset. RRAM devices with gradual reset show excellent endurance and retention for multi-bit storage. Finally, the conductance modulation characteristics realizing synaptic learning are also confirmed in the RRAM.

Controlling the diameter distribution and density of InAs nanowires grown by Au-assisted methods

Abstract: III-V semiconductor nanowires have attracted intensive research interest because of their promising optical and electronic properties that can be manipulated by tailoring nanowire composition and morphology. Therefore, it is crucial to measure and control the diameter distribution of the grown nanowires. In this study, we analyze the diameter distribution of Au-catalyzed InAs nanowires. Au colloidal nanoparticles dispersed on InAs (111) B substrates and nanoparticles obtained by the thermal annealing of Au films were used as catalysts for InAs nanowire growth. The annealing time and temperature, the thickness of the Au film and the colloid sizes were systematically varied not only to understand their influence on nanowire diameter distribution, but also to find the optimal parameters for realizing samples with uniform and controlled diameter distribution. Morphological characterization was performed by scanning electron microscopy measurements and the image analysis was carried out using in-house-developed automated image analysis software to accurately determine the diameter distribution of the nanowires. A description of the image analysis software is also presented. The thermal annealing of films turned out to be the most suitable method for uniformity and density control, while the colloidal nanoparticles yielded narrow and more reproducible diameter distributions.

Structural and optical properties of (In,Ga)2O3 thin films and characteristics of Schottky contacts thereon

Abstract: We report on structural and optical properties of a (InxGa)2O3 thin film having a monotonic lateral variation of the indium content x (). The growth condition for each In content is similar allowing precise determination of the dependence of material properties on x. For low In content () the thin film has monoclinic crystal structure; for highest In contents () the cubic bixbyite phase is predominant. For intermediate alloying we observe additionally the rhombohedral InGaO3(II) crystallographic phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (InxGa)2O3 and photo response measurements for

A memristor emulator as a replacement of a real memristor

Abstract: In this paper, we propose a memristor emulator that embraces most of features of a real memristor. The important features that a memristor emulator should include are a sufficiently wide range of memristance, bimodal operability of pulse and continuous signal inputs, a long period of nonvolatility, floating operation, operability with other devices, and the ability to be implemented with off-the-shelf devices. The proposed memristor emulator circuit contains all of these features. Specifically, the small variation range of memristance and the nonfloating operation that limit conventional memristor emulators are improved significantly. It is designed to be built with off-the-shelf electronics devices.

Bandgap-engineered GaAsSb alloy nanowires for near-infrared photodetection at 1.31 μm

Abstract: Single-nanowire photodetectors have potential applications in integrated optoelectronic devices and systems. Here, bandgap-engineered GaAs0.26Sb0.74 alloy nanowires were synthesized via a chemical vapor deposition method. The synthesized nanowires are single crystals grown along the [111]B direction with length up to 50 μm and diameter ranging from 40 to 500 nm. Photodetectors are built based on these single-alloy nanowires, which show a wide response in the near-infrared region with a high response peak located in the optical communication region (1.31 μm), as well as an external quantum efficiency of 1.62 × 105%, a responsivity of 1.7 × 103 A W−1 and a short response time of 60 ms. These novel near-infrared photodetectors may find promising potential applications in integrated infrared photodetection, thermal imaging, information communication and processing.

Requirements for a GaAsBi 1 eV sub-cell in a GaAs-based multi-junction solar cell

Abstract: Multi-junction solar cells achieve high efficiency by stacking sub-cells of different bandgaps (typically GaInP/GaAs/Ge) resulting in efficiencies in excess of 40%. The efficiency can be improved by introducing a 1 eV absorber into the stack, either replacing Ge in a triple-junction configuration or on top of Ge in a quad-junction configuration. GaAs0.94Bi0.06 yields a direct-gap at 1 eV with only 0.7% strain on GaAs and the feasibility of the material has been demonstrated from GaAsBi photodetector devices. The relatively high absorption coefficient of GaAsBi suggests sufficient current can be generated to match the sub-cell photocurrent from the other sub-cells of a standard multi-junction solar cell. However, minority carrier transport and background doping levels place constraints on both p/n and p-i-n diode configurations. In the possible case of short minority carrier diffusion lengths we recommend the use of a p-i-n diode, and predict the material parameters that are necessary to achieve high efficiencies in a GaInP/GaAs/GaAsBi/Ge quad-junction cell.

Thermoelectric performance of classical topological insulator nanowires

Abstract: There is currently substantial effort being invested into creating efficient thermoelectric (TE) nanowires based on topological insulator (TI) chalcogenide-type materials. A key premise of these efforts is the assumption that the generally good TE properties that these materials exhibit in bulk form will translate into similarly good or even better TE performance of the same materials in nanowire form. Here, we calculate TE performance of TI nanowires based on Bi2Te3, Sb2Te3 and Bi2Se3 as a function of diameter and Fermi level. We show that the TE performance of TI nanowires does not derive from the properties of the bulk material in a straightforward way. For all investigated systems the competition between surface states and bulk channel causes a significant modification of the TE transport coefficients if the diameter is reduced into the sub 10 ?m range. Key aspects are that the surface and bulk states are optimized at different Fermi levels or have different polarity as well as the high surface to volume ratio of the nanowires. This limits the maximum TE performance of TI nanowires and thus their application in efficient TE devices.

Towards environmental friendly solution- based ZTO/AlO x TFTs

Abstract: Solution based deposition has been recently considered as a viable option for low-cost flexible electronics. In this context research efforts have been increasingly centred on the development of suitable solution-processed materials for oxide based transistors. Nevertheless, the majority of synthetic routes reported require the use of toxic organic solvents. In this work we report on a new environmental friendly solution combustion synthesis route, using ethanol as solvent, for the preparation of indium/gallium free amorphous zinc-tin oxide (ZTO) thin film transistors (TFTs) including AlOx gate dielectric. The decomposition of ZTO and AlOx precursor solutions, electrical characterization and stability of solution processed ZTO/AlOx TFTs under gate-bias stress, in both air and vacuum atmosphere, were investigated. The devices demonstrated low hysteresis (ΔV = 0.23 V), close to zero turn on voltage, low threshold voltage (VT = 0.36 V) and a saturation mobility of 0.8 cm2 V−1 s−1 at low operation voltages. Ethanol based ZTO/AlOx TFTs are a promising alternative for applications in disposable, low cost and environmental friendly electronics.

Development of n-type polymer semiconductors for organic field-effect transistors

Abstract: We review herein the development of unipolar n-type polymer semiconductors in organic field-effect transistors, which would enable large-scale deployment of printed electronics in combination with a fast-growing area of p-type counterparts. After discussing general features of electron transport in organic semiconductors, various π-conjugated polymers that are capable of transporting electrons are selected and summarized to outline the design principles for enhancing electron mobility and stability in air. The n-type polymer semiconductors with high electron mobility and good stability in air share common features of low-lying frontier molecular orbital energy levels achieved by design. In this review, materials are listed in roughly chronological order of the appearance of the key building blocks, such as various arylene diimides, or structural characteristics, including nitrile and fluorinated groups, in order to present the progress in the area of n-type polymers.

Dislocation filters in GaAs on Si

Abstract: Cross section transmission electron microscopy has been used to analyse dislocation filter layers (DFLs) in five similar structures of GaAs on Si that had different amounts of strain in the DFLs or different annealing regimes. By counting threading dislocation (TD) numbers through the structure we are able to measure relative changes, even though the absolute density is not known. The DFLs remove more than 90% of TDs in all samples. We find that the TD density in material without DFLs decays as the inverse of the square root of the layer thickness, and that DFLs at the top of the structure are considerably more efficient than those at the bottom. This indicates that the interaction radius, the distance that TDs must approach to meet and annihilate, is dependent upon the TD density.

Synthesis of polyaniline-based inks for inkjet printed devices: electrical characterization highlighting the effect of primary and secondary doping

Abstract: Engineering applications for printed electronics demand solution processable electrically conductive materials, in the form of inks, to realize interconnections, piezoresistive pressure sensors, thermoresistive temperature sensors, and many other devices. Polyaniline is an intrinsically conductive polymer with modest electrical properties but clear advantages in terms of solubility and stability with temperature and in time. A comprehensive study, starting from its synthesis, primary doping, inkjet printing and secondary doping is presented, with the aim of elucidating the doping agent effects on its morphology, printability and electronic performance.

The effects of the intense laser and homogeneous electric fields on the electronic and intraband optical properties of a GaAs/Ga0.7 Al0.3As quantum ring

Abstract: The simultaneous influences of an intense laser field and static electric field on one-electron states and intraband optical absorption coefficient are investigated in two-dimensional GaAs/GaAl0.3 As quantum ring. An analytical expression of the effective confining potential in the presence of the external fields is obtained. The one-electron energy levels and wave functions are calculated using the effective mass approximation and an exact diagonalization technique. We show that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that blueshift and redshift are induced by the simultaneous influences of an intense laser and lateral electric fields. The obtained theoretical results indicate a novel opportunity to tune the performance of quantum rings and to control their specific properties by means of intense laser and homogeneous electric fields.

Effect of indium as a surfactant in (Ga1−xInx)2O3 epitaxial growth on β-Ga2O3 by metal organic vapour phase epitaxy

Abstract: (Ga1−xInx)2O3 epitaxial layers have been grown on (100) β-Ga2O3 substrates by metal organic vapour phase epitaxy (MOVPE). The process parameters were tuned in order to obtain an In-poor (Ga1−xInx)2O3 alloy, limiting the In incorporation below 3%. In this way it was possible to study the effect of In on the growth dynamics of Ga2O3. By varying the flow of the carrier gas (Ar) through the In precursor (trimethylindium) in a wide range, it was observed that for Ar/TMIn flows higher than a minimum threshold value, In was essential to obtain layers with very high crystal quality. The concentration of structural defects, such as stacking faults and twins, decreased dramatically and step-flow growth mode was achieved. These results have been explained by the tendency of In to float on the growing Ga2O3 surface, delivering an effective surfactant effect.

Switching characteristics of W/Zr/HfO2/TiN ReRAM devices for multi-level cell non-volatile memory applications

Abstract: In this paper, we report multi-level cell (MLC) switching characteristics of resistive random access memory devices with a W/Zr/HfO2/TiN stack. A multi-step forming technique was implemented in this work which efficiently suppressed the forming current overshoot and allowed device switching at a low set/reset voltage and current. Four distinct resistance states, achieved by controlling the reset stop voltages, showed excellent endurance. Write/read/erase energy values for different states were also calculated. Amongst four MLC states, it was found that the lowest resistance state of three distinct high-resistance states was prone to failing over time under constant voltage stress.

Determination of type-I band offsets in GaBixAs1–x quantum wells using polarisation-resolved photovoltage spectroscopy and 12-band k.p calculations

Abstract: Using photovoltage (PV) spectroscopy we analyse the electronic structure of a series of GaBixAs/(Al)GaAs dilute bismide quantum well (QW) laser structures. The use of polarisation-resolved PV measurements allows us to separately identify transitions involving bound light- and heavy-hole states in the QWs, as well as bound-to-continuum transitions from the QWs to the barriers. Analysis of these transitions enables us to probe the GaBixAs/(Al)GaAs conduction and valence band offsets, thereby quantifying the band offsets. Using a 12-band Hamiltonian, we extract the band offsets in the QWs explicitly by constraining the Bi-related parameters of the model against the experimentally measured transition energies. The PV measurements and calculations we present provide the first explicit confirmation of a type-I band offset at the GaBixAs/GaAs heterointerface near x = 2%. This result, combined with the theory we present for calculating the band offsets at GaBixAs/(Al)GaAs heterointerfaces, can be used to determine the band offsets at arbitrary Bi composition x.

Relaxed c-plane InGaN layers for the growth of strain-reduced InGaN quantum wells

Abstract: A fully relaxed In0.1Ga0.9N layer was grown by plasma-assisted molecular beam epitaxy on c-plane GaN using a grading technique. The growth of the graded InGaN layer in the intermediate regime enabled a smooth surface without the accumulation of In droplets. Transmission electron microscopy images show that the relaxation occurs through the formation of a high density of threading dislocations (TDs). Despite the presence of these TDs, relaxed InGaN films were then successfully used as a pseudo-substrate for the growth of InGaN/GaN quantum wells which luminesced at room temperature.

Flexible organic light emitting diodes fabricated on biocompatible silk fibroin substrate

Abstract: Flexible and biodegradable electronics are currently under extensive investigation for biocompatible and environmentally-friendly applications. Synthetic plastic foils are widely used as substrates for flexible electronics. But typical plastic substrates such as polyethylene naphthalate (PEN) could not be degraded in a natural bio-environment. A great demand still exists for a next-generation biocompatible and biodegradable substrate for future application. For example, electronic devices can be potentially integrated into the human body. In this work, we demonstrate that the biocompatible and biodegradable natural silk fibroin (SF) films embedded with silver nanowires (AgNWs) mesh could be employed as conductive transparent substrates to fabricate flexible organic light emitting diodes (OLEDs). Compared with commercial PEN substrates coated with indium tin oxide, the AgNWs/SF composite substrates exhibit a similar sheet resistance of 12 Ω sq−1, a lower surface roughness, as well as a broader light transmission range. Flexible OLEDs based on AgNWs/SF substrates achieve a current efficiency of 19 cd A−1, demonstrating the potential of the flexible AgNWs/SF films as conductive and transparent substrates for next-generation biodegradable devices.

Properties of hybrid MOVPE/MBE grown GaAsBi/GaAs based near-infrared emitting quantum well lasers

Abstract: A combined growth approach involving both molecular-beam epitaxy and metal-organic vapor phase epitaxy has been developed to fabricate GaAsBi/GaAs-based quantum well (QW) laser structures with a Bi composition up to 8%. Lasing operation has been demonstrated at room temperature at 1.06 μm in laser diodes containing 3QWs that in turn contain approximately 6% Bi. A 5QW device demonstrated lasing at 1.09 μm at 80 K. Using temperature- and pressure-dependent measurements of stimulated emission as well as pure spontaneous emission measurements, we show that the threshold current of the devices is limited by non-radiative defect-related recombination and an inhomogeneous carrier distribution. This is suspected to be due to inhomogeneity of the QW width as well as non-uniform Bi composition in the active region.

Ultra high voltage MOS controlled 4H-SiC power switching devices

Abstract: Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.