Monolithically-integrated optoelectronic circuit for ultrafast sampling of a dual-gate field-effect transistor

McIntosh

et al. 1999

The response time of photoconductive submillimeter-wave emitters based on low-temperature-grown (LTG) GaAs is known to increase at high applied bias, which limits the output power of these devices at frequencies near 1 THz. We performed measurements of an LTG GaAs photoconductor embedded in a coplanar waveguide with both static and dynamic illumination to investigate the increase in response time and an increase in direct-current photoconductance that occurs at the same bias voltages. We attribute both phenomena to a reduction of the electron capture cross section of donor states due to electron heating and Coulomb-barrier lowering. We discuss why the phenomena cannot be explained by space-charge-limited current or other injection-limited currents, or by impact ionization.

Section: ͓S0003-6951͑99͒02041-0͔mentioning

confidence: 99%

Increase in response time of low-temperature-grown GaAs photoconductive switches at high voltage bias

McIntosh

et al. 1999

“…1,2 Signals traveling on CPWs are less susceptible to distortion by freely propagating radiation than signals on coplanar strips, because a CPW's signalcarrying center conductor is shielded on both sides by its ground planes, while coplanar strips are unshielded. 3 The main disadvantage of CPWs is that they allow two quasi-transverse-electromagnetic ͑TEM͒ propagating modes, compared to the single quasi-TEM propagating mode of coplanar strips. The modes are called even and odd according to the symmetry of each mode's electric field with respect to the CPW's center conductor.…”

mentioning

confidence: 99%

“…Airbridges have been used to connect the two ground planes of a CPW and suppress the even mode. 3,5 Several authors have optoelectronically sensed the electric field on either side of the center conductor and thereby discriminated between the odd and even modes, allowing the meaningful and spurious parts of signals to be distinguished. 3,6 We propose a simple single-layer CPW circuit that makes airbridges unnecessary and allows mode discrimination and selective mode generation without requiring optoelectronic sampling.…”

mentioning

confidence: 99%

Mode-discriminating photoconductor and coplanar waveguide circuit for picosecond sampling

Verghese

et al. 1999

We introduce a circuit for ultrafast measurements with coplanar waveguide transmission lines. The circuit contains photoconductive switches that allow tunable generation and reception of a coplanar waveguide’s two propagating modes. The circuit has fewer discontinuities than other circuits with similar capabilities and does not require airbridges. We show how the photoconductive switch can be biased to compensate for pump laser beam misalignment, and that a circuit composed of two chips making up a hybrid has only 4% broader temporal resolution than a circuit integrated on a single chip. We measured a minimum temporal resolution of 2.4 ps.

“…We neglect dispersion and assume v p to be the frequencyindependent value 0.37c, or 1.1ϫ10 8 m/s. 10 We use standard microwave circuit analysis to calculate I o1 , the -dependent dc current generated at the probe. We assume that only the horizontal CPWs of Fig.…”

Section: ͑1͒mentioning

confidence: 99%

On-chip frequency-domain submillimeter-wave transceiver

McIntosh

et al. 1999

We demonstrate and model an on-chip frequency-domain transceiver which uses low-temperature-grown GaAs photoconductors to emit and detect continuous waves in the frequency range from 20 to 700 GHz propagating in a coplanar waveguide circuit. Our device has a possible frequency resolution (ϳ1 MHz) that is about 10 3 times better than similar devices used for time-domain spectroscopy, and is therefore appropriate for high-resolution spectroscopy with a ''lab-on-a-chip''-type integrated circuit. © 1999 American Institute of Physics. ͓S0003-6951͑99͒01650-2͔Photoconductive emitters and receivers are attractive as components of submillimeter-wave spectroscopy systems because of their tunability, compactness, and ability to be monolithically integrated with antennas, transmission lines, and microelectronic devices. Such systems can be classified in either of two ways: as time-domain or frequency-domain systems, or as systems involving free-space or on-chip submillimeter-wave propagation. Time-domain systems, which contain a photoconductive pulse emitter and sampler excited by a mode-locked laser, are the most investigated. They have been used for free-space characterization of semiconductor materials, 1 and on-chip characterization of ultrafast devices and circuits with 2.7 ps time resolution. 2 The frequency resolution is the inverse of the time span over which the propagating pulse is sampled. This span is determined by the length of an optical delay line, which usually results in a frequency resolution greater than 1 GHz. 2 A frequency-domain spectrometer was recently introduced 3 with a frequency resolution of better than 1 MHz, 4 which is adequate for molecular line spectroscopy. 4,5