Bottom-Gate Gallium Indium Zinc Oxide Thin-Film Transistor Array for High-Resolution AMOLED Display

The fabrication process and the characteristics of bottom-gate $ hbox{Ga}_{2}hbox{O}_{3}{-}hbox{In}_{2}hbox{O}_{3}{-}hbox{ZnO}$ (GIZO) thin-film transistors (TFTs) are reported in detail. Experimental results show that oxygen supply during the deposition of GIZO active layer and silicon oxide passivation layer controls the threshold voltage of the TFT. The field-effect mobility and the threshold voltage of the GIZO TFT fabricated under the optimum process conditions are 2.6 $hbox{cm}^{2}/hbox{V} cdot hbox{s}$ and 3.8 V, respectively. A 4-in QVGA active-matrix organic light-emitting diode display driven by the GIZO TFTs without any compensation circuit in the pixel is successfully demonstrated.      

Voltage Tunability of Quantum Cascade Lasers

The voltage tunability of three types of quantum cascade laser designs is investigated. The tuning coefficients and tuning ranges of electroluminescence and laser emission from all designs are measured and compared with the calculated results. A reduced tunability was observed in all lasers above threshold. This is attributed to the decrease of resistance across the laser active region (AR) as the photon density increases. A resumed tunability high above threshold occurs in all lasers with anticrossed injector ground and upper laser states. Lasers based on the anticrossed diagonal transition are tunable above threshold, with a tuning range of about 30 ${hbox {cm}}^{-1}$ ($sim$ 3% of the laser emission wavenumber), i.e., a tuning rate of 750 ${hbox {cm}}^{-1} hbox{V}^{-1}cdot hbox{period}^{-1}$ of the AR and the injector.      

Bandgap-Engineered Ga-Rich GaZnO Thin Films for UV Transparent Electronics

Ga-rich GaZnO thin films were prepared by metal–organic chemical vapor deposition. The optical bandgap of GaZnO films can be engineered from 3.3 to 4.9 eV by varying the Ga content. The film is amorphortized and the resistivity increases with an increase of Ga content. The Ga-rich GaZnO alloy with lower resistivity is investigated as a UV transparent conductor, while the semi-insulating Ga-rich GaZnO film with high transparency at 280–900 nm is employed as the channel layer to fabricate deep UV transparent thin-film transistor. The transistor shows a typical n-channel field-effect characteristic with a current on/off ratio of $hbox{10}^{4}$–$ hbox{10}^{5}$, a threshold voltage of $sim$42 V, a saturated field-effect mobility of $sim!hbox{0.06} hbox{cm}^{2} cdot hbox{V}^{-1} cdot hbox{s}^{-1}$, and a subthreshold swing of $ sim!hbox{7.7} hbox{V} cdot hbox{decade}^{-1}$.      

Low-Voltage Organic Field-Effect Transistor With PMMA/$ hbox{ZrO}_{2}$ Bilayer Dielectric

This paper reports on the application of a bilayer polymethylmethacrylate (PMMA)/ $hbox{ZrO}_{2}$ dielectric in copper phthalocyanine (CuPc) organic field-effect transistors (OFETs). By depositing a PMMA layer on $hbox{ZrO}_{2}$, the leakage of the dielectric is reduced by one order of magnitude compared to single-layer $hbox{ZrO}_{2}$. A high-quality interface is obtained between the organic semiconductor and the combined insulators. By integrating the advantages of polymer and high- $k$ dielectrics, the device achieves both high mobility and low threshold voltage. The typical field-effect mobility, threshold voltage, on/off current ratio, and subthreshold slope of OFETs with bilayer dielectric are $hbox{5.6}timeshbox{10}^{-2} hbox{cm}^{2}/hbox{V} cdot hbox{s}$, 0.8 V, $hbox{1.2} times hbox{10}^{3}$, and 2.1 V/dec, respectively. By using the bilayer dielectrics, the hysteresis observed in the devices with single-layer $hbox{ZrO}_{2}$ is no longer present.      

Effect of Growth Temperature on InP QD Lasers

We describe the effect of growth temperature on the optical absorption, gain, and threshold current density of 730-nm emitting, metal–organic vapor phase epitaxy (MOVPE) grown, InP–AlGaInP quantum-dot lasers. Decreasing the growth temperature from 750 $^{circ}hbox{C}$ to 690 $^{circ}hbox{C}$ leads to an increase in ground state absorption, while sufficient optical gain and low 300 K threshold current density is obtained in the growth temperature window between 710 $^{circ}hbox{C}$ and 730 $^{circ}hbox{C}$ . Wider (16 nm compared to 8 nm) interlayer barriers lead to lower threshold current density with 300 K values as low as 165 $hbox{Acm}^{-2}$ for 2-mm-long lasers with uncoated facets.      

Doubly resonant four-photon interactions in Cesium vapor

Four-photon interactions involving both a two-photon resonance with the9d^{2}D_{3/2}level and a one-photon resonance with an np²P level (n = 7-10) are investigated in detail. Gain, gain saturation, gain threshold, and forward-to-backward generation ratios are measured. Comparison with numerical estimates indicates that9d^{2}D_{3/2}tonp^{2}Plasing is the dominant gain mechanism but that a doubly resonant four-photon parametric oscillation makes a significant contribution. Gain saturation is dominated by population of np²P levels. Ionization is important, especially at higher pump powers.     

A simple analysis of the stable field profile in the supercritical TEA

An analytical investigation supported by numerical calculations has been performed of the stable field profile in a supercritical diffusion-stabilized n-GaAs transferred electron amplifier (TEA) with ohmic contacts. In the numerical analysis, the field profile is determined by solving the steady-state continuity and Poisson equations. The diffusion-induced short-circuit stability is checked by performing time-domain computer simulations under constant voltage conditions. The analytical analysis based on simplifying assumptions gives the following results in good agreement with the numerical results. 1) A minimum doping level required for stability exists, which is inversely proportional to the field-independent diffusion coefficient assumed in the simple analysis. 2) The dc current is bias independent and below the threshold value, and the current drop ratio increases slowly and almost linearly with the doping level. 3) The domain width normalized to the diode lengthLvaries almost linearly with(V_{B}/V_{T}-1)^{frac{1}{2}}/(n_{0}L)^{frac{1}{2}}where VBis the bias voltage VTis the threshold voltage, and no is the doping level. 4) The peak domain field varies almost linearly with (V_{B}/V_{T}-1)^{frac{1}{2}} (n_{0}L)^{frac{1}{2}}. Those results contribute to the understanding of the highn_{0}L-product switch and the stability of the supercritical TEA.     

Threshold of the optical backward-wave parametric oscillator

We present a discussion of the threshold condition for the optical backward-wave parametric oscillator, taking into account diffraction due to the finite transverse extent of the fields, and using three transverse modes of both the forward- and backward-wave fields. The coupled differential equations are solved numerically, and the threshold is obtained by minimizing the pump field with respect to the parameters of the forward- and backward-wave fields. Denoting the confocal parameters byb_{1}, b_{2}, and b3for the backward, forward, and pump waves, respectively, and if the length of the crystal is 1, we find that for1/b_{3} geq 2, we may setb_{1} = b_{2} =b_{3}. For most purposes, the phase-matching condition may be taken ask_{2} = k_{1} + k_{3}. Also, when calculating the threshold, it is adequate to consider only the two lowest order transverse modes of the forward-and backward-wave fields.     

Short-channel MOSFET VT-VDScharacteristics model based on a point charge and its mirror images

Short-channel MOS transistordV_{T}/dV_{DS}characteristics are expressed by an analytic function of fundamental device parameters. The expression is derived from a simple model of short-channel MOS transistors in threshold condition, which is based on a point charge and its mirror images. With this expression,dV_{T}/dV_{DS}is found to be proportional to1/L^{2}-1/L^{4}, whereLis channel length. Following factors are also found, wherein the source and drain junction depth effect is only logarithmic ondV_{T}/dV_{DS}characteristics,dV_{T}/dV_{SUB}anddV_{T}/dV_{DS}are closely related in short-channel MOS transistors, and short-channel effects are expected to be smaller in MOS transistors on SOS than on bulk silicon, due to a large number of Si/sapphire interface states. This model is simple, and it can be applied to short-channel MOS transistor designing and circuit simulations.     

New n-Type $hbox{TiO}_{2}$ Transparent Active Channel TFTs Fabricated With a Solution Process

New metal–oxide thin-film transistors (MOxTFTs) with a solution-processed $hbox{TiO}_{2}$ transparent active channel are fabricated with a novel doping process that consists of a deposition of an ultrathin Ti layer on $hbox{TiO}_{2}$ films and a brief rapid thermal annealing. Contrary to an as-prepared device which does not show any appreciable TFT actions, devices with the proposed process exhibit a clear n-type TFT behavior with a saturation mobility of 0.12 $hbox{cm}^{2}cdothbox{V}^{-1}cdothbox{s}^{-1}$ and a threshold voltage of 11 V. A solution processibility and a low-cost manufacturability of $hbox{TiO}_{2}$ make the presented TFTs potentially attractive for cost-sensitive applications.      

The Electrical and Interfacial Properties of Metal-High-$kappa$ Oxide-Semiconductor Field-Effect Transistors With $hbox{LaAlO}_{3}$ Gate Dielectric

$hbox{LaAlO}_{3}$ is a promising candidate for gate dielectric of future VLSI devices. In this letter, n-channel metal–oxide–semiconductor field-effect transistors with $hbox{LaAlO}_{3}$ gate dielectric were fabricated, and the electron mobility degradation mechanisms were studied. The leakage current density is $hbox{7.6} times hbox{10}^{-5} hbox{A/cm}^{2}$ at $-!$ 1 V. The dielectric constant is 17.5. The surface-recombination velocity, the minority-carrier lifetime, and the effective capture cross section of surface states were extracted from gated-diode measurement. The rate of threshold voltage change with temperature $(Delta V_{T} / Delta T)$ from 11 K to 400 K is $-!$ 1.51 mV/K, and the electron mobility limited by surface roughness is proportional to $E_{rm eff}^{-0.66}$.      

Optical losses and efficiency in GaAs laser diodes

Optical gain and losses of GaAs laser diodes were deduced from the length dependence of the threshold current density and the differential external quantum efficiency at 77 and 300°K. It has been confirmed that the optical gain is proportional to the threshold current density Jt; and the optical losses are given by the sum of current independent termalpha_{0}', and current dependent termbeta"J_{t}, which is proportional to the threshold current density. The termbeta"J_{t}depends on the laser wavelength because the threshold current density depends on the laser wavelength. It is believed thatbeta"J_{t}is caused by the penetration of the laser oscillations into the noninverted regions surrounding the inverted population region of thep-njunction.     

Gunn effect in CdTe

We have been examining the response of n-type CdTe to pulsed electric fields. In our best units, prepared to have a uniform cross section, the current remains ohmic, to good approximation, almost to threshold. Above the threshold field of (13±2) kV/cm well-defined Gunn oscillations are observed with a spike amplitude 35-50 percent of the total current. We estimate a domain drift velocityv_{dd}=7times10^{6}cm/s, a field outside the domainE_{1} = 7kV/cm, and a domain fieldE_{2}gsim37kV/cm. After a few nanoseconds of operation, however, current runaway occurs in units showing the spiking mode of oscillation, presumably because of carrier ionization induced by the moving high-field domains.     

AlGaN/GaN MOSHEMTs With Liquid-Phase-Deposited $ hbox{TiO}_{2}$ as Gate Dielectric

$hbox{TiO}_{2}$ films deposited on GaN layers at room temperature through a simple and low-cost liquid-phase deposition (LPD) method are investigated and served as gate dielectrics in AlGaN/GaN MOSHEMTs. The electrical characteristics of the MOS structure on n-doped GaN show that the leakage current is about $hbox{1.01} times hbox{10}^{-7} hbox{A/cm}^{2}$ at 1 MV/cm and that the breakdown field is more than 6.5 MV/cm. The maximum drain current density of MOSHEMTs is higher than that of conventional HEMTs, and a wider gate voltage swing can also be observed. The maximum transconductance and threshold voltage almost maintain the same characteristics, even after inserting a dielectric layer between the gate metal and the 2DEG channel by using $ hbox{TiO}_{2}$ as a gate dielectric. The gate leakage current density is significantly improved, and the bias stress measurement shows that current collapse is much suppressed for MOSHEMTs.      

Conjugated Polymer Films for Piezoresistive Stress Sensing

The changes in the electrical conductivity of an indium-tin-oxide/poly [2-methoxy-5-( $hbox{2}^{prime}$-ethylhexyloxy)-1, 4-phyenylenevinylene] (MEH-PPV)/Al structure under compressive stresses were measured. The current recorded at 3 V showed a nearly linear characteristic response between 0.25 and 1.1 MPa with a sensitivity of 5.0 $mu hbox{A/KPa}$ and a maximal piezoresisitance coefficient of $sim !hbox{1.1} times hbox{10}^{-4} hbox{Pa}^{-1}$. The devices under compression exhibited resistive switching above a threshold voltage with a resistance ratio of five, suggesting that the formation of nanofilamentary chains may be another mechanism in addition to increased intermolecular electron hopping contributing to the stress-induced current changes. The single-layer MEH-PPV sensors also exemplified good stability and repeatability, and appear to be promising for tactile sensing applications.      

Analyses of mode-hopping phenomena in an AlGaAs laser

Intensity fluctuations of the longitudinal modes of a 0.8 μm AlGaAs laser were precisely measured during the occurrence of hopping between two modes. It was found from this result that mode hopping follows the stochastics of a Poisson process. The frequency of mode hopping was measured asf_{c} = [exp [-95(I/I_{th} - 1)]] times 10^{7}(Hz). whereI/I_{th}is the injection current normalized to its threshold value. Results of analog computer simulations showed that spontaneous emission worked as a triggering force for mode hopping. Results of the analysis based on the Fokker-Planck equation were compared to the experimental results, from which the root-mean-square value of the fluctuating electric field of spontaneous emission was estimated as2.3 times 10^{2)(V/m)leqlanglesim{E}_{N} leq 3.2 times 10^{2}(V/m). It is concluded that an effective reduction of mode hopping is achieved if the laser is operated at a higher bias or if the coupling constant between the two modes is increased.     

Flexible Full-Color AMOLED on Ultrathin Metal Foil

Full-color active-matrix organic light-emitting diode panels, driven by poly-Si thin-film transistors (poly-Si TFTs), were successfully fabricated on thin metal foil substrates. The p-channel poly-Si TFTs on metal foil showed a field-effect mobility of 82.9 $hbox{cm}^{2}/hbox{V}cdothbox{s}$ , subthreshold slope of 0.34 V/dec, threshold voltage of $-$ 1.67 V, and off-current of $ hbox{6.6} times hbox{10}^{-14} hbox{A}/muhbox{m}$. The 5.6-in panel had 160 $times$ RGB $times$ 350 pixels, each of which had a pixel circuit of two TFTs and one capacitor.      

Gain spectra in GaInAsP/InP proton-bombarded stripe-geometry DH lasers

We have measured gain spectra for TE polarization in a GaInAsP/InP laser as a function of dc bias current below laser threshold. The measurements were made on a low-threshold device with a stripe geometry defined by proton bombardment. A number of other characteristics of this and similar devices from the same wafer are also reported. These data permit the maximum gain coefficient of the active layer gmaxto be evaluated as a function of nominal current density Jnom. We obtain the linear relationshipg_{max} = (3.1 times 10^{-2}/eta_{r})(J_{nom} - eta_{r} 5.4 times 10^{3}), where ηris the radiative quantum efficiency. Our data apply only for large gain (g gsim 150cm^-1) and large Jnombecause the active layer of the test device is thin (0.1 μm).     

Pentacene-Based Low-Voltage Strain Sensors With PVP/$ hbox{Ta}_{2}hbox{O}_{5}$ Hybrid Gate Dielectrics

Field-controllable pentacene-semiconductor-based strain sensors were fabricated with hybrid gate dielectrics using polyvinyl phenol (PVP) and high-$k$ inorganic tantalum pentoxide $(hbox{Ta}_{2}hbox{O}_{5})$ onto polyethylene naphthalate films. The $hbox{Ta}_{2}hbox{O}_{5}$ gate-dielectric layer combined with a thin PVP layer to form very smooth and hydrophobic surfaces turns out to improve the molecular structures of pentacene films significantly. The PVP– $hbox{Ta}_{2}hbox{O}_{5}$ hybrid-gate-dielectric films exhibit a high dielectric constant of 19.27 and a leakage-current density of as low as 100 $hbox{nA/cm}^{2}$ . The sensors employing a thin-film-transistor-like Wheatstone bridge configuration able to operate at reduced voltage ($sim$4 V) show good device characteristics with a field-effect mobility of 1.89 $hbox{cm}^{2}/hbox{V} cdot hbox{s}$ and a threshold voltage of $-$0.5 V. The strain sensor characterized with bending at 45$^{circ}$ with respect to the bridge bias direction with different bending radii of 50-, 40-, 30-, 20-, and 8-mm displays output signals improved in linearity in a low range of operating voltages.      

AlGaN/GaN Recessed MIS-Gate HFET With High-Threshold-Voltage Normally-Off Operation for Power Electronics Applications

This letter reports normally-off operation of an AlGaN/GaN recessed MIS-gate heterostructure field-effect transistor with a high threshold voltage. The GaN-based recessed MIS-gate structure in conjunction with negative polarization charges under the gate allows us to achieve the high threshold voltage, whereas the low on-state resistance is maintained by the 2-D electron gas remaining in the channel except for the recessed MIS-gate region. The fabricated device exhibits a threshold voltage as high as 5.2 V with a maximum field-effect mobility of 120 $hbox{cm}^{2}/hbox{V}cdot hbox{s}$, a maximum drain current of over 200 mA/mm, and a breakdown voltage of 400 V.