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Forward gate-bias stress experiments are performed to investigate the variation of trap states under Schottky contact in GaN-based high electron mobility transistors. Traps with activation energy ET ranging from 0.22 eV to 0.31 eV are detected at the gate-semiconductor interface by dynamic conductance technique. Trap density decreases prominently after stressing, particularly for traps with ET>0.24 eV. X-ray photoelectron spectroscopy measurements reveal a weaker Ga-O peak on the stressed semiconductor surface. It is postulated that oxygen is stripped by Ni to form NiO upon electrical stress, contributing to the decrease in ON donor sates under the gate contact. [ABSTRACT FROM AUTHOR]

Ambipolar integrated circuits were prepared with poly(diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm2/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date. [ABSTRACT FROM AUTHOR]

A hygroscopic insulator transistor (HIFET) operating at 1 V was manufactured using roll-to-roll techniques on a rough, low-cost plastic substrate. The effects of the substrate roughness on the active channel were studied by using two different plastic substrates and comparing HIFETs and organic field-effect transistors (OFETs). We found that the HIFET, as opposed to OFETs, is rather insensitive to changes in the roughness of plastic substrates. Hence, a robust feature of ion modulated transistors is shown. [ABSTRACT FROM AUTHOR]

The authors investigate the spectral tuning of the exciton resonance of a surface quantum well saturable absorber mirror for the generation of subpicosecond pulses, employing an optically pumped semiconductor disk laser in the 1 μm spectral range. The all-semiconductor laser generates transform-limited pulses as short as 590 fs at a 3 GHz repetition rate and an output power of 30 mW. The pulse duration of the mode-locked laser was supported by the fast relaxation time of the saturable absorber of 1.0 ps. [ABSTRACT FROM AUTHOR]

Self-stabilized passive mode-locking of a diode-pumped Yb:yttrium aluminum garnet laser with a semiconductor saturable absorber was achieved using an off-phase-matching second-harmonic crystal. According to the numerical model, such a condition is accomplished by self-defocusing in the nonlinear crystal in the presence of positive intracavity dispersion. Robust mode locking with Fourier-limited 1.0-ps pulses was obtained, whereas mode locking, unassisted by the nonlinear crystal, yielded 2.2-ps pulses, with the laser operating near the edge of the stability region in order to minimize the saturation energy of the semiconductor device. [ABSTRACT FROM AUTHOR]

We present a 10 GHz passively mode-locked vertical external-cavity surface-emitting semiconductor laser (VECSEL) with 1.4 W average output power in 6.1 ps pulses. The output features a very good pulse quality with a time–bandwidth product of 0.42 in a nearly diffraction-limited beam. This demonstrates that passively mode-locked VECSELs are suitable for generating high powers in high-repetition-rate pulse trains. [ABSTRACT FROM AUTHOR]

We have demonstrated stable self-starting passive mode-locking in a diode-end-pumped Nd:YVO4 laser using a semiconductor saturable absorber mirror (SESAM). An In0.25Ga0.75As single quantum-well SESAM, which was grown by the metalorganic chemical-vapor deposition technique at low temperature, acts as a passive mode-locking device and an output coupler at the same time. Continuous-wave mode-locked transform-limited pulses were obtained at 1064 nm with a pulse duration of 2.1 ps and an average output power of 1.28 W at a repetition rate of 96.5 MHz. [ABSTRACT FROM AUTHOR]

We report on spectral interferometry for measuring the spectrally resolved nonlinear phase and amplitude response in a pump–probe experiment. Using nJ pulses from a femtosecond oscillator, we demonstrate the method by measuring the nonlinear response of a GaAs/AlGaAs single-quantum-well saturable absorber mirror. The demonstrated sub-mrad phase sensitivity constitutes a two-order-of-magnitude improvement of phase resolution, compared to earlier demonstrations. Dynamic spectral interferometry proves to be a powerful tool for evaluating the phase response on nonlinear optical semiconductor devices for mode locking of lasers, optical switching, and other photonic applications. [ABSTRACT FROM AUTHOR]

We have demonstrated stable self-starting passive cw mode locking of a solid-state laser at about 1.3 µm using a GaInNAs semiconductor saturable absorber mirror (SESAM). GaInNAs SESAMs show negligible nonsaturable losses, low saturation fluences (11 µJ/cm²) and picosecond decay times which make them well-suited for self-starting and stable cw mode locking. Sub-10-ps pulses were produced with a Nd:YLF laser at 1314 nm. The incorporation of about 2% nitrogen into InGaAs redshifts the absorption edge above 1330 nm and reduces the strain in the saturable absorber grown on a GaAs/AlAs Bragg mirror. Final absorption edge adjustments have been made with thermal annealing which blueshifts the absorption edge. [ABSTRACT FROM AUTHOR]

We present a semiconductor saturable absorber mirror (SESAM), which also acts as an output coupler at the same time. The influence of the output coupler transmission onto the absorber parameters is investigated theoretically, as well as experimentally. A passively Q-switched Nd:YVO[sub 4] microchip laser is built using such a nonlinear output coupler, yielding clean pulses of 143 ps duration, 48 nJ energy, and 572 W peak power. This result is compared with the traditional approach, where the SESAM is not used as an output coupler. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The output modal content of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) crucially depends upon the thickness of the low-index oxide aperture, its position with respect to the standing waves of the transverse-longitudinal modes and the separation from the cavity. Three-dimensional cold-cavity optical modes of typical AlGaAs/GaAs VCSELs at 850 nm were simulated to study these dependencies quantitatively taking into account the field diffraction and the material dispersion. Modification of one or two periods of the distributed Bragg reflector by positioning the thin oxidized aperture layers in the mode nodes allows single-mode regime to extend to the aperture diameters as large as 10 μm. [ABSTRACT FROM AUTHOR]

We present very compact Nd:YVO[sub 4] lasers which are passively mode-locked with a semiconductor saturable absorber mirror at very high repetition rates between 39 and 59 GHz. We achieved between 30 and 80 mW of average output power and pulse durations of 4.8-5.5 ps. As the pulse-to-pulse spacing is only 17 ps at 59 GHz, we are approaching the limit in repetition rate which is set by the pulse duration. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate that the differential transmission (DT) response of bulk semiconductors excited well above the band edge can be manipulated by chirping of the broadband excitation and readout pulses. In particular, the maximum transmission change in spectrally integrated DT experiments can be modified on the 20 fs time scale. Spectrally resolved DT studies explain this chirp dependence. Depending on the sign of the chirp, positive or negative DT contributions at low or high photon energies are probed with varying efficiency around zero time delay. These results demonstrate that chirp can become an additional degree of freedom for the optimization of device performance in ultrafast all-optical switching. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We passively Q-switched a diode-pumped Er/Yb:glass microchip laser at a 1.535 μm wavelength using semiconductor saturable absorber mirrors and demonstrated pulses as short as 1.2 ns. By varying the design parameters of the saturable absorber, the pump power, and the pump spot size, we achieved repetition rates from 300 Hz to 100 kHz with pulse energies up to 4 μJ. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]