Table of contents

A free-standing GaN layer was produced by combining electrochemical (EC) etching from the front surface, photo-electrochemical (PEC) etching from the back surface, and subsequent regrowth of GaN on the porous template thus produced. The EC etching resulted in the formation of etch channels on the surface portion of the starting film, whereas the back-side PEC etching gave rise to a columnar structure supporting the entire film. When the n-GaN layer was regrown on such template, the underlying columnar structure provided weak places for easy separation and transfer of the film by mechanical bonding.

The a- and a+c-type threading dislocation (TD) inclinations were observed in Mg-doped tensile-strained GaN/Al_0.15Ga_0.85N superlattice (SL) with a high-temperature (HT) AlN interlayer (IL). Most of the inclined dislocations are a-type, toward the equivalent [100] line direction, following dislocation climb model, while a+c-type dislocations gliding on (101) second slip plane inclined toward the [110] line direction. The analysis by comparing samples gave no evidence of Mg dopants to affect the TD inclination. The stress evolution, specifically, the stress transformation of the tensile-stress-relieved AlGaN barrier to the compressive-strain-enhanced GaN well caused by the HT-AlN IL, dominantly affected the a- and a+c-type TD inclinations.

Epitaxial GaN films were grown by metal organic chemical vapor deposition (MOCVD) on functionalized epitaxial graphene (EG) using a thin (∼11 nm) conformal AlN nucleation layer. Raman measurements show a graphene 2D peak at 2719 cm^-1 after GaN growth. X-ray diffraction analysis reveals [0001]-oriented hexagonal GaN with (0002) peak rocking curve full width at the half maximum (FWHM) of 544 arcsec. The FWHM values are similar to reported values for GaN grown by MOCVD on sapphire. The GaN layer has a strong room-temperature photoluminescence band edge emission. Successful demonstration of GaN growth on EG opens up the possibility of III–nitride/graphene heterostructure-based electronic devices and promises improved performance.

The luminescence of stacking faults (SFs) in m-plane ZnO epilayers grown by metal organic chemical vapor deposition is analyzed using spatially resolved cathodoluminescence (CL) spectroscopy. Complementary features observed in CL images for detection energies of 3.379 (near-band-edge) and 3.324 eV confirm the latter to be a typical SF-associated luminescence. A clear blue shift of the SF-associated luminescence is observed when the electron beam approaches the SF. This experimental result proves the existence of a polarization field in the SFs along the c-axis of the ZnO film. Furthermore, we clearly identify the SF-related transition at low temperatures and at room temperature.

The performances of ZnSnP₂, CdSnP₂, and Zn_1-xCd_xSnP₂ alloys as solar cell photoabsorbers are assessed using photovoltaic conversion efficiency simulations in conjunction with first-principles calculations based on hybrid density functional theory. The band gap of Zn_1-xCd_xSnP₂ decreases with increasing Cd content x and shows a small bowing. The electronic structure and optical absorption spectrum depend weakly on the composition, aside from the band gap and spectral threshold. The conversion efficiency is almost converged to the Shockley–Queisser limit at a photoabsorber thickness of a few micrometers for any composition of Zn_1-xCd_xSnP₂, similarly to the cases of GaAs, CdTe, CuInSe₂, and CuGaSe₂.

From the Fowler–Nordheim (FN) current–voltage (I–V) characteristic and X-ray photoelectron spectroscopy (XPS) analysis, the conduction band offset of 2.73±0.1 eV and the valence band offset of 3.76±0.1 eV have been extracted for the atomic-layer-deposition (ALD) Al₂O₃/InSb structure. By these analyses, the parameters of an Al₂O₃ film including bandgap, electron affinity, and electron effective mass are also deduced. The capacitance–voltage and I–V characteristics of ALD Al₂O₃/InSb at different deposition temperatures indicate the modification of the Fermi level in InSb to 0.09 eV lower than that in metal side of the sample deposited at 250 °C as compared to the samples deposited at lower temperatures.

By controlling quantum fluctuations within SrTiO₃ with light, we were able to study photovariations in the localized Ti 3d electronic structure exploiting X-ray Raman features to analyze the photoinduced local symmetry breaking, which is the origin of an electric dipole moment. Crystal field photomodifications observed in these electronic structures give valuable theoretical identification of the photoinduced T_1u local atomic displacement. Furthermore, the strengthening of the T_1u displacement is clarified by photoinduced covalency enhancements in Ti 3d–O 2p bonds.

A light-driven bistable device was fabricated using nematic liquid crystal (NLC) cells with bare glass and perfluoro-polymer (CYTOP) surfaces. The CYTOP surface induces a discontinuous anchoring transition, when a particular NLC (CCN-47) is introduced into the cells. By doping CCN-47 with a small amount of photoisomerizable azo-dendrimer molecules, the bare glass surface serves as a command surface, since the azo-dendrimer is spontaneously adsorbed on the surface. Using hybrid cells with such different surfaces, a homeotropic orientation was successfully converted to a hybrid orientation by very weak ultraviolet-light irradiation. Because of the bistability at a CYTOP surface, the hybrid orientation is retained.

High-quality planar alignment was achieved in the hexagonal columnar phase of 2,3,6,7,10,11-hexahexyloxytriphenylene by applying an oscillating shear using a piezoelectric actuator. Discotic liquid crystals with thicknesses up to 38 µm could be aligned using this technique, with the molecular columns aligning parallel to the direction of the shear. The quality of the alignment was also found to be higher in this technique than in previously proposed alignment methods, since a higher retardation and a higher dichroic ratio were obtained.

We fabricated tunable photonic crystals (PCs) advanced using the electro-optic (EO) effect. These PCs are composed of transparent Al-doped ZnO (AZO) layers as internal/external electrodes and centered (Pb,La)(Zr,Ti)O₃ (PLZT) layers as EO material to use the longitudinal EO effect enabling a large refractive index variations at low voltage to be obtained. The PCs consisting of four periods of AZO/PLZT multilayer were prepared by RF magnetron sputtering. The PCs exhibited a large refractive index change of 2.9×10^-2 at 8 V, resulting in a high photonic band gap tunability of ∼1 nm/V.

Zr_0.05Ti_0.95O₂ solid solution nanowires were synthesized directly on a SnO₂:F-coated glass via a low-temperature hydrothermal method, and a high-sensitivity self-powered ultraviolet detector based on SnO₂:F/Zr_0.05Ti_0.95O₂ heterojunction was fabricated subsequently. Zr doping not only improves the detector's photoresponse but also adjusts the response range to the short-wavelength direction. At 0 V bias, a highly responsivity of 1.03 A/W and an internal gain of 3.6 were obtained, together with favorable visible-blind characteristics and short response time. This high-sensitivity self-powered ultraviolet detector provides potential applications in wireless environmental monitoring, biological detection, and ultraviolet astronomy.

Light extraction efficiency (LEE) in AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) is investigated using finite-difference time-domain simulations. For flip-chip and vertical LED structures, LEE is obtained to be <10% due to strong DUV light absorption in the p-GaN layer. In flip-chip LEDs, LEE of transverse-magnetic (TM) modes is found to be more than ten times smaller than that of transverse-electric (TE) modes, which explains the decreasing behavior of external quantum efficiency of DUV LEDs with decreasing wavelength. It is also found that vertical LED structures can have advantages over flip-chip structures for increasing LEE in the TM mode.

We study the optical spectral properties for green semipolar (20) and (201) light-emitting diode (LED) with same indium compositions. Compared to (201) devices, the fabricated (20) micro-LED (∼0.005 mm²) showed negligible blue shift and smaller full width at half maximum (FWHM) up to extremely high current densities (10,000 A/cm²). Theoretical simulation indicates that the (20) InGaN quantum well (QW) has reduced polarization-related effects due to combined effects of electric field cancelling and Coulomb screening effect. In addition, the packaged device performance for small-area (∼0.144 mm²) semipolar green (20) and (201) LEDs were also discussed. The green (20) LED showed smaller wavelength shift and narrower FWHM than green LEDs fabricated on other planes.

In this report, we investigated the rod size dependence of photoluminescence (PL) from vertically aligned indium nitride (InN) nanorod arrays grown on Si(111) substrates. Abnormal temperature dependence of the PL peak energy and the PL bandwidth was observed for InN nanorods with a critical diameter, which is of the same order of the surface electron accumulation layer (∼20 nm). Exceptionally large activation energy of the nanorods with the critical diameter implies that holes within these narrow nanorods need to surpass the band bending energy near the surface in order to recombine with electrons accumulated in the surface layer.

In this research, we investigate the interaction between colliding photorefractive spatial solitons. The energy transfer from a vector soliton to a scalar soliton is quantitatively investigated. The energy exchange efficiency increases as the input intensity ratio of the vector soliton increases, while it decreases as the collision angle increases. It is also found that the spatial solitons interact with each other like particles, and the energy of each soliton is conserved after the collision. This observation provides preliminary data for optical computation applications via photorefractive spatial solitons.

We present a module for directly applying a hold-off time to a 1 GHz sinusoidally gated InGaAs avalanche photodiode (APD). With this module, a detection efficiency of 21.3% at 1550 nm was achieved with an afterpulse probability of 3.7% and a dark count probability per gate of 2.1×10^-6. Furthermore, the simple but robust hold-off module was suitable not only for the periodical gating APDs but also for free-running APDs.

This paper reports a quantitative investigation of the nonlinear phase noise (NLPN) in dispersion-shifted and single-mode optical fibers, which is induced by amplified spontaneous emission (ASE) noise through cross-phase modulation. The phase noise power spectral density (PN-PSD) of a probe light, which is transmitted through the fibers and is affected by the copropagating ASE, is precisely measured with the delayed self-heterodyne method. The observed PN-PSDs agree well with the theory that takes account of the group velocity dispersion of the fiber and the polarization states of the propagating lights.

To enhance the conversion efficiency of Cu₂ZnSnS₄ (CZTS) thin film solar cells prepared by the sulfurization method, we investigated the formation process of the CZTS thin film. The holding temperature of the sulfurization was 580 °C. This study showed that the spreading resistance (SR) of the CZTS layer strongly depends on the holding time of the sulfurization. At the intermediate holding time (∼30 min), the SR of the CZTS layer came to a minimum, and the efficiency of the CZTS solar cell came to a maximum. A 7.6% efficiency CZTS solar cell without a high-resistance buffer layer and an antireflection coating was fabricated.

The origin of the fast scintillation component of Ce-doped LiCaAlF₆ crystal excited by gamma ray irradiation was studied with X-ray and vacuum ultraviolet (VUV) irradiation. A fast luminescence component was observed under VUV irradiation and was ascribed to luminescence at defects in the host matrix on the basis of VUV spectroscopy. No fast scintillation component was observed in the scintillation time profile under X-ray irradiation. The fast scintillation component under gamma ray irradiation can be concluded to be the result of Cherenkov radiation from energetic secondary electrons.

We show that a spectroscopic function can be achieved by an artificial combination of very thin metallic plates with modulated cut-through slit arrays by simulation using the finite-difference time-domain method. The novel function is based on the remarkable frequency dependences of optical phased array effects, i.e., the phase variations of optical waves threading through the slit arrays in multi-stacked metallic plates. We also present methods to enhance the phase shift.

The electro-optic properties of cholesteric blue phase (BP) liquid crystals is investigated by two-beam interference microscopy. The technique can facilitate the evaluation of BP materials, since only a single measurement is required to determine the two important electro-optic coefficients, i.e., the Kerr and electrostriction coefficients, of BPs. Moreover, field-induced symmetry transitions can be observed microscopically, making this a powerful tool to investigate the structure–property relationship in BPs. Herein, we observe field-induced transitions from cubic BPs I and II to the centered tetragonal BP X, and investigate the influence of this transition on the Kerr coefficient.

The optical properties of wurtzite AlN under large compressive strain are investigated by photoluminescence and optical reflectivity measurements with two different geometries. The AlN layer was coherently grown on 6H-SiC(0001), resulting in strains of ε_xx=ε_yy=-9.6×10^-3 and ε_zz=5.12×10^-3, as confirmed by high-resolution X-ray diffraction. Free exciton transitions were clearly observed. The transition energy of A free exciton (with Γ₁ symmetry) was estimated to be 6.246 eV at 10 K. The large energy shift of the free exciton transition with respect to the transition in unstrained AlN was well explained by the reported deformation potentials of AlN.

We demonstrate a new wavelength-swept laser based on fiber Raman amplification (FRA), achieved by multiplexing three different pump lasers at wavelengths of 1455, 1475, and 1509 nm. The obtained sweeping bandwidth was from 1526.1 to 1637.9 nm, which was as wide as 111.8 nm. It is the widest hitherto demonstrated based on FRA. We also present the use of this swept laser in the application scenario of optical coherence tomography (OCT). This scheme paves the way for fiber Raman amplification to be employed as a promising source for generating a wideband swept source for OCT application.

We designed and fabricated a double-core-slab-waveguide semiconductor laser for end optical pumping, and demonstrated its laser operations. We developed a method of characterization and analysis to evaluate the pumping profile and efficiency, and showed that 10% of the input power entered through a facet edge was used for uniform pumping over the 500 µm cavity and 9% for local pumping within 40 µm near the edge.

We have fabricated silver microcolumnar photon reflectors to enhance the photon extraction efficiency from a quantum dot. The mechanically robust planar structure is favorable to couple to optical fibers for stable and efficient single-photon sources. A high photon extraction efficiency of up to 18% is achieved. Furthermore, strong suppression of multiphoton generation is confirmed. The proposed structure is quite promising toward the implementation of practical quantum key distribution systems with dot-fiber-coupled photon sources.

Spin-wave logic operation in a ferromagnetic thin film was investigated by using a three-antenna device. Binary output 1/0 signals were realized with the constructive and destructive spin-wave interference signals. It was found that the configuration of the RF antenna determines the phase of the input spin wave, which provides a control method of logic operation in spin-wave devices.

The junction diameter D dependence of effective magnetic fields in a recording layer of CoFeB–MgO magnetic tunnel junctions with perpendicular magnetic easy axis is evaluated by ferromagnetic resonance measurements using the homodyne detection technique. The effective perpendicular magnetic field increases with decreasing D, which reflects mainly the reduction of the demagnetizing factor normal to the film plane. The stray field from a reference layer also increases with reducing D, which is in agreement with the D dependence of the shift field of the center of minor resistance versus perpendicular magnetic field curves with respect to zero magnetic field.

The textured MgO(001) tunnel barrier grown on CoFeB is a fundamental building block for spintronic devices such as magnetic tunnel junctions. Although the insertion of an ultrathin Fe–Co layer between an MgO layer and a bottom CoFeB layer is a common technique for improving the magnetoresistance effect, the characteristics of this technique remain unclear. We systematically investigated the as-grown structure of Fe–Co by reflective high-energy electron diffraction and found that a highly textured MgO(001) is formed only on an amorphous Fe–Co surface. The diffusion of B atoms from underlying CoFeB into Fe–Co is what makes the as-grown Fe–Co layer amorphous.

A DC electric voltage was generated on a Pt-capped Fe₄N bilayer film (Fe₄N/Pt) by inverse spin-Hall effect (ISHE) under ferromagnetic resonance (FMR) conditions at room temperature. Sign reversal of the electric voltage was observed with the application of an external DC field with opposite direction, and the magnitude of the voltage was proportional to the applied microwave power. The spin current was pumped out of the Fe₄N film into the Pt capping film. The real part of the spin mixing conductance (g_r^↑↓) was quantified for Fe₄N/Pt and Ni₇₈Fe₂₂/Pt bilayer films to investigate the spin pumping efficiency at the interface. The g_r^↑↓ value was larger for the Fe₄N/Pt film than for the Ni₇₈Fe₂₂/Pt film. Such a large g_r^↑↓ could reflect the large population of conduction electrons with minority spins in the Fe₄N film compared with that with majority spins.

We report a simple approach to synthesize ZnO–Ag composite nanocrystals with different ZnO/Ag ratios via a nanoemulsion process. The morphology and structure of the nanocrystals are investigated by X-ray diffraction and transmission electron microscopy, showing the high crystallinity of the nanocrystals with narrow size distributions. The corresponding optical and magnetic properties are analyzed with photoluminescence spectroscopy, ultraviolet–visible spectrometry and physical property measurement system in detail. The ensuing magnetism is interpreted in terms of nanosizing and other effects. Such ZnO–Ag nanocrystals may be further explored for biomedical applications and spintronic devices with interesting optical and magnetic properties.

We have demonstrated the extremely wide frequency tunable operation of a continuous terahertz (THz) wave emitter based on a uni-traveling-carrier photodiode (UTC-PD). A novel compact planar antenna was integrated with an InP/InGaAs UTC-PD, and assembled in a quasi-optical package. The fabricated module had a responsivity of 0.21 A/W, and was operated at frequencies from 30 GHz to 1.6 THz. The detected output powers were 120 µW at 200 GHz, 17 µW at 500 GHz, and 2.9 µW at 1 THz for a photocurrent of 10 mA with a bias voltage of only -0.6 V.

Oscillations from 1.02 to 1.40 THz were observed at room temperature from resonant-tunneling-diode (RTD)-based oscillators with integrated patch antennas by improving the mesa structure and tuning the length of the antenna and the feed point location of the RTD. A two-step post structure realized a reduction of series resistance of the RTD, and the oscillation frequency significantly increased with the feed point closer to the center of patch antenna at around 1 THz. Experimental results agreed well with the analysis.

We propose a microwave kinetic inductance detector consisting of an NbN rewound spiral resonator (spiral-MKID) as a possible broadband terahertz detector operating with a conventional cryogen-free ⁴He refrigerator. The spiral-MKIDs fabricated with NbN films reveal high-Q microwave resonation with loaded Q factors on the order of 10⁴ at 3 K, and the temperature dependence of the microwave resonance frequency is well fitted by the Mattis–Bardeen theory. The optical response was confirmed in the terahertz range below 2.4 THz. We also discuss the expected noise equivalent power of the NbN-based MKIDs.

The influence of quantum transport effects in ultrashort-channel InP metal–oxide–semiconductor field-effect transistors (MOSFETs) was investigated using a Wigner Monte Carlo method, in which both quantum transport and carrier scattering effects can be fully incorporated. It was found that source–drain (SD) direct tunneling becomes evident for channel lengths of less than about 20 nm. Since this critical channel length is approximately three times larger than that in Si-MOSFETs, countermeasures should be taken to suppress SD direct tunneling in order to aggressively downscale III–V channel MOSFETs. In contrast, quantum reflection effects were found to have a negligible influence on the on-state drain current.

We demonstrate the separation of high-purity, long semiconducting single-wall carbon nanotubes (s-SWCNTs) by single-stage gel filtration. Semiconducting SWCNTs are preferentially adsorbed on an allyl dextran-based gel column and then eluted with surfactant solution at a rate that depends on nanotube length as well as electronic type of nanotubes. These differences allow the separation of length-sorted and purity-enhanced s-SWCNTs by fractionated collection of the eluate, which provides the desired nanotubes for electronic device applications.

Strain effect on guided modes and electron transmission through the strained graphene waveguide with oscillating potential are explored theoretically. It is found that the guided mode in the waveguide can be controlled by zigzag or armchair direction strain. The transmission spectrum obtained displays a sharply asymmetric tunneling peak, where the energy difference between the tunneling peak and guided mode is equal to the photon induced by the oscillating potential. In view of the quantitative relationship, we propose the photon-assisted tunneling to probe the strain-tunable guided modes.

We prepared string like assemblies of aligned single-wall carbon nanotubes (SWCNTs) in a (6,5) nearly single-chiral state. We observed that by simply adjusting the temperature and incubation time of SWCNT monodispersed solutions, string-like assemblies of aligned SWCNTs could be generated. Polarized Raman and scanning electron microscopy measurements clearly indicated that the SWCNTs were aligned parallel to the string axis. These assemblies exhibited good field-effect performances, exhibiting an on/off ratio of 6.8×10³ and a maximum mobility of 106.5 cm² V^-1 s^-1.

Classical and quantum dynamics are important limits for the understanding of the transport characteristics of interacting electrons in nanodevices. Here, we apply an intermediate semiclassical approach to investigate the dynamics of two interacting electrons in a planar nanochannel as a function of Coulomb repulsion and electric field. We find that charge is mostly redistributed to the channel edges and that an electric field enhances the particle-like character of electrons. These results may have significant implications for the design and study of future nanodevices.

We show that a simple confocal laser scanning system can be used to couple light through grating couplers into nanophotonic circuits. The coupling efficiency is better than 15% per coupler. Our technique avoids using multi-axis fibre stages and is especially advantageous when the nanophotonic circuit is kept in vacuum, e.g., for nanomechanical resonator displacement transduction. This was demonstrated by recording the resonant response of a nanomechanical doubly clamped beam embedded in a race-track optical cavity. The nanophotonic transduction offers an increase of two orders of magnitude in transduction responsivity compared with conventional free-space optical interferometry.

Fiber-based bidirectional photon detection from nanoscale emitters and photon antibunching behavior between two outputs of two single-mode fibers (SMFs) are experimentally demonstrated. Flakes containing the epitaxially grown quantum dots (QDs) are mechanically fixed by both sides with the edge faces of the SMF patch cables. The emitting photons from a single QD are directly taken out of both sides through the SMFs. Single-photon emission between two SMF outputs is confirmed by detecting nonclassical antibunching in second-order photon correlation measurements. This simple optomechanical alignment-free single-photon emitter is advantageous because of its robust stability of more than three months and low-cost fabrication.

The effect of soft X-ray irradiation on the crystallization of a Si_1-xGe_x multilayer was investigated for the realization of low-temperature crystallization. This method is influenced by the Ge concentration and photon flux density by adjusting the photon energy to the optimum value related with the Ge 3d electron orbital. The Ge atom was a trigger for the crystallization because the atomic migration of Ge atoms was enhanced by electron excitation during soft X-ray irradiation. For the Si_1-xGe_x multilayer, the crystallization region can be controlled by varying the Ge concentration. The present crystallization technique can be applied to the fabrication of solar cells with high conversion efficiency.

In_0.3Ga_0.7As layers were grown by metal–organic chemical vapor deposition utilizing compositionally step-graded (Al)GaInP buffers on different misorientated GaAs substrates. The substrate miscut toward the [110] direction promotes α dislocation glide along the [110] direction while it exerts an adverse effect on β dislocations in the perpendicular direction with increasing the miscut degree. In comparison with the 2° and 7° samples, a better surface morphology with a RMS roughness of 5.77 nm and a lower density of threading dislocations indicated by the photoluminescence and transmission electron microscopy results were obtained in the 15° sample.

Through atomization and ionization, we could completely alter the composition of a nonconductive material, aluminum nitride, by femtosecond laser ablation. Preferential production of pure aluminum cluster cations Al_n⁺ (n≤32) reflects not only their higher energetic stability compared with mixed clusters Al_nN_m⁺ but also completion of thermal relaxation in ablation plasma. Observation of metastable dissociation of Al_n⁺ indicates that cluster cations have still enough internal energy for dissociation to occur, although the process is much slower than the cluster formation. Almost no cluster formation has been observed after nanosecond laser ablation of aluminum nitride, which highlights the distinct nature of ablation plasma produced by femtosecond laser ablation.

We propose a method to direct writing of a shape-controlled nanodot array by two-photon nanolithography (TPNL). An elliptical nanodot with a minor axis diameter of 50 nm was realized using an AR-N 4340 photoresist by employing a slit to achieve the elliptical beam. Theoretical simulations were carried out to estimate the feature size of nanostructures. The adjustments of the ellipticity and orientation of nanodot were investigated. Furthermore, we fabricated elliptical and rectangular nanodot arrays on a large scale. This study would provide evidence for fabricating shape-varied nanodot arrays in the fields of plasmonics and photonics by the TPNL.

This study examined the dimensional effects on the channel strain in transistor structures with epitaxial Si_1-xC_x stressors embedded in the source/drain region using both nanobeam diffraction and finite element simulations. The sizes of the gate and source/drain exerted a strong influence on the channel strain but in opposite directions: While declining linearly with decreasing source/drain length, the channel strain increases at an escalating rate with decreasing gate length. For source/drain elevation, its effects on the channel strain were found to be quite limited to the top surface region; however, this elevation method could be more effective for short-channel transistors.

Although characterization of hydrogen (H) in silicon (Si) is of interest from a device physics viewpoint, this is difficult using conventional analytical methods. In this study, deuterium (D) was used as a proxy for H, and the distribution of implanted D-ions in Si(100) was investigated using atom probe tomography (APT). D can be distinguished from the residual H gas in the APT chamber. The APT results indicated that D tended to form clusters, whose distribution was similar to that of 311 defects identified using transmission electron microscopy, suggesting that the D ions segregate in the vicinity of these defects.

The p-type channel of a nanoparticle organic memory field effect transistor (NOMFET) was fabricated by evaporating a thin Au layer, curing at 700 °C, and evaporating pentacene. The resulting NOMFET showed a facilitating ac-pulse drain current after programming and a depressing ac-pulse drain current after erasing that mimicked the behavior of biological synapses. The facilitating and depressing current ratio could be adjusted by using the program or erase voltage; i.e., the facilitating current increased with the program voltage, and the depressing current ratio increased with the erase voltage.