Browsing by Author "Stanley, C. R."
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- Coherent approach to transport and noise in double-barrier resonant diodesPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.We implement a quantum approach which includes long range Coulomb interaction and investigate current voltage characteristics and shot noise in double-barrier resonant diodes. The theory applies to the region of low applied voltages up to the region of the current peak and considers the wide temperature range from zero to room temperature. The shape of the current voltage characteristic is well reproduced and we confirm that even in the presence of Coulomb interaction the shot noise can be suppressed with a Fano factor well below the value of 0.5. This feature can be an indication of coherent tunneling since the standard sequential tunneling predicts in general a Fano factor equal to or greater than the value 0.5. This giant suppression is a consequence of Pauli principle as well as long range Coulomb interaction. The theory generalizes previous findings and is compared with experiments.
- Electric field switching in a resonant tunneling diode electroabsorption modulatorPublication . Figueiredo, J. M. L.; Ironside, C. N.; Stanley, C. R.The basic mechanism underlying electric field switching produced by a resonant tunneling diode (RTD) is analyzed and the theory compared with experimental results; agreement to within 12% is achieved. The electroabsorption modulator (EAM) device potential of this effect is explored in an optical waveguide configuration. It is shown that a RTD-EAM can provide significant absorption coefficient change, via the Franz– Keldysh effect, at appropriate optical communication wavelengths around 1550 nm and can achieve up to 28-dB optical modulation in a 200- m active length device. The advantage of the RTD-EAM over the conventional reverse-biased p–n junction EAM, is that the RTD-EAM has, in essence, an integrated electronic amplifier and, therefore, requires considerably less switching power.
- Giant suppression of shot noise as signature of coherent transport in double barrier resonant diodesPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of the coherent transport regime and can occur near zero temperature as a consequence of the Pauli principle or above about 77 K as a consequence of long range Coulomb interaction. These predictions are validated by experimental data.
- Giant suppression of shot noise in double barrier resonant diode: a signature of coherent transportPublication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of coherent transport regime and can occur at zero temperature as a consequence of the Pauli principle or at sufficiently high temperatures above 77 K as a consequence of a long-range Coulomb interaction. These predictions are in agreement with experimental data.
- Integration of a RTD with an optical waveguide to form a high speed electroabsorption modulatorPublication . Figueiredo, J. M. L.; Ironside, C. N.; Leite, A. M. P.; Stanley, C. R.High speed Optoelectronic modulation using the resonant tunnelling characteristics by interaction of a resonant tunnelling diode (RTD) in the middle of an unipolar ridge optical waveguide based on the GaAs/AlGaAs system is investigated. This interaction of an RTD within an optical waveguide introduces high non-linearities into the electrical characteristics of the waveguide by inducing large electric field changes on the collector region which give rise to a band-edge shift via the Franz-Keldysh effect that can be used for electroabsorption modulation up to millimeter-wave frequencies of light at photon energies close to the bandgap energy of the semiconductor, in this case around 900 nm. The device allows efficient high speed intensity modulation requiring a few hundreds of mV as drive voltage. Streak camera studies have shown around 4 dB modulation depth at 14 GHz for an applied voltage at 1 GHz of around 0.4 V, implying a bandwidth-to-voltage ratio of 33 GHz/V.
- Optical modulation at around 1550 nm in an InGaAlAs optical waveguide containing an InGaAs/AlAs resonant tunneling diodePublication . Figueiredo, J. M. L.; Boyd, A. R.; Stanley, C. R.; Ironside, C. N.; McMeekin, S. G.; Leite, A. M. P.We report electroabsorption modulation of light at around 1550 nm in a unipolar InGaAlAs optical waveguide containing an InGaAs/AlAs double-barrier resonant tunneling diode ~RTD!. The RTD peak-to-valley transition increases the electric field across the waveguide, which shifts the core material absorption band edge to longer wavelengths via the Franz–Keldysh effect, thus changing the light-guiding characteristics of the waveguide. Low-frequency characterization of a device shows modulation up to 28 dB at 1565 nm. When dc biased close to the negative differential conductance region, the RTD optical waveguide behaves as an electroabsorption modulator integrated with a wide bandwidth electrical amplifier, offering a potential advantage over conventional pn modulators.
- Optical modulation in a resonant tunneling relaxation oscillatorPublication . Figueiredo, J. M. L.; Stanley, C. R.; Boyd, A. R.; Ironside, C. N.; McMeekin, S. G.; Leite, A. M. P.We report high-speed optical modulation in a resonant tunneling relaxation oscillator consisting of a resonant tunneling diode (RTD) integrated with a unipolar optical waveguide and incorporated in a package with a coplanar waveguide transmission line. When appropriately biased, the RTD can provide wide-bandwidth electrical gain. For wavelengths near the material band edge, small changes of the applied voltage give rise to large, high-speed electroabsorption modulation of the light. We have observed optical modulation at frequencies up to 14 GHz, associated with subharmonic injection locking of the RTD oscillation at the fundamental mode of the coplanar transmission line, as well as generation of 33 ps optical pulses due to relaxation oscillation.
- Reply to comment on 'Giant suppression of shot-noise in double barrier resonant diode: a signature of coherent transport'Publication . Aleshkin, V. Ya; Reggiani, L.; Alkeev, N. V.; Lyubchenko, V. E.; Ironside, C. N.; Figueiredo, J. M. L.; Stanley, C. R.Shot noise suppression below 1/2 of the full Poisson value in double barrier resonant diodes is confirmed to be a signature of coherent rather than sequential tunnelling transport. We reply to the arguments of the previous comment which dispute the above claim. We anticipate the development of a rigorous theory that improves previous approaches without contradicting the essential findings we recently reported (Aleshkin et al 2003 Semicond. Sci. Technol. 18 L35).
- Superhigh-frequency characteristics of optical modulators on the basis of InGaAlAs resonance-tunnel heterostructuresPublication . Aleshkin, V. Ya; Lyubchenko, V. E.; Figueiredo, J. M. L.; Ironside, C. N.; Stanley, C. R.The impedance of InGaAlAs resonance-tunnel heterostructures used for modulation of optical radiation is experimentally studied in the frequency range from 45 to 18 MHz. The dependence of their equivalent circuit on the bias voltage is determined. The spectrum of the harmonics of the current in the resistive frequency multiplication in such structures is calculated. The results confirm that these structures are promising as applied to the frequency multiplication. The effect of frequency multiplication is demonstrated experimentally at low frequencies.
- Ultralow voltage resonant tunnelling diode electroabsorption modulatorPublication . Figueiredo, J. M. L.; Ironside, C. N.; Stanley, C. R.Embedding a double barrier resonant tunnelling diode (RTD) in a unipolar InGaAlAs optical waveguide gives rise to a very low driving voltage electroabsorption modulator (EAM) at optical wavelengths around 1550 nm. The presence of the RTD within the waveguide core introduces high non- linearity and negative di erential resistance in the current±voltage (I±V) characteristic of the waveguide. This makes the electric ®eld distribution across the waveguide core strongly dependent on the bias voltage: when the current decreases from the peak to the valley, there is an increase of the electric ®eld across the depleted core. The electric ®eld enhancement in the core-depleted layer causes the Franz±Keldysh absorption band-edge to red shift, which is responsible for the electroabsorption e ect. High-frequency ac signals as low as 100mV can induce electric ®eld high-speed switching, producing substantial light modulation (up to 15 dB) at photon energies slightly lower than the waveguide core band-gap energy. The key di erence between this device and conventional p-i-n EAMs is that the tunnelling characteristics of the RTD are employed to switch the electric ®eld across the core-depleted region; the RTD- EAM has in essence an integrated electronic ampli®er and, therefore, requires considerably less switching power.