Millimeter wave sources at 60 GHz have been demonstrated using optically driven heterojunction bipolar transistors configured as photodetectors. Two techniques were used to optically generate the millimeter waves; the mixing of two cw lasers and the mode locking of a semiconductor laser. The millimeter wave power generated from these two configurations was radiated into free space using integrated planar twin‐dipole antennas and heterodyne detected with signal‐to‐noise ratios ≳40 dB. As part of these experiments, the dc optical gains and quantum efficiencies of the heterojunction bipolar transistor photodetectors were determined.

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60 GHz sources using optically driven heterojunction bipolar transistors

Monolithic integration of photonic devices such as lasers, modulators, and photodetectors, along with their associated electronic circuitry, has recently made significant advances such that high performance is now being achieved in devices using both the GaAs and InP materials systems. The advances in these optoelectronic integrated circuits, or OEICs, are being driven by the needs of second-generation photonic systems including optical interconnects, optical computing and signal processing, and communications. Furthermore, the pace of the technology is being set by the improvements made in semiconductor materials growth using such methods as molecular beam and vapor phase epitaxies. In this paper we discuss the needs of several generic photonic systems for advanced optoelectronic chips. These needs are now being met by the fabrication of high-performance and highly functional integrated transmitters, receivers, modulators, and arrays of such devices. We discuss examples of these and other archetype integrated circuits which serve to illustrate the advances in, and challenges to this new device technology. Finally, a brief description is given of the materials growth techniques which are used in OEIC structures.

Optoelectronic integrated circuits

Theoretical and experimental work for the DC and RF performance of depletion mode Al/sub 0.3/Ga/sub 0.7/As/GaAs HEMTs under optical illumination is presented. The photoconductive effect increasing the 2-DEG channel electron concentration and photovoltaic effect in the gate junction are considered. Optical tuning of a 2 GHz HEMT oscillator and optical control of the gain of a 2 to 6 GHz HEMT amplifier are presented and potential applications are described. >

Al/sub 0.3/Ga/sub 0.7/As/GaAs HEMT's under optical illumination

We calculate the sensitivity of In 0.53 Ga 0.47 As photoconductor receivers for use in moderate to high bit-rate lightwave transmission applications. It is found that the noise of photoconductive receivers is dominated at all bit rates B Gbit/s by Johnson noise in the conductive channel. Nevertheless, the total noise current decreases approximately linearly with photoconductive gain, and therefore the sensitivity of photoconductive receivers can be comparable to high-sensitivity p-i-n photodiode receivers. The sensitivity of practical photoconductive receivers compares most favorably with p-i-n receivers in the bit-rate range of 500-2 Gbit/s. However, receivers employing high-speed In 0.53 Ga 0.47 As/InP avalanche photodiodes are expected to be more sensitive than photoconductive receivers over the entire bit-rate range considered. In this analysis, we consider the effects of slow photoconductor response on receiver sensitivity, and find that the limited gain-bandwidth product of practical photoconductors increases the complexity of the receiver circuit by necessitating equalization, resulting in a decrease in receiver sensitivity and dynamic range.

The sensitivity of photoconductor receivers for long-wavelength optical communications

Photoluminescence studies of Ga1-xInxAs/Al1-yInyAs quantum wells nominally lattice matched to InP are reported. The photoluminescence from two samples each having six quantum wells of thicknesses ranging from about 6 to 122 AA is studied in detail. The main emission peak associated with each quantum well is attributed to excitonic recombination. The emission from the 6 AA quantum well at 897.3 nm is found to have a peak width of only 18 meV at 4.2 K. Temperature dependence studies show that at 4.2 K the excitons are localised at potential fluctuations in the quantum wells. Impurity-related emission is also observed from some of the quantum wells.

A photoluminescence study of Ga1-xInxAs/Al1-yInyAs quantum wells grown by MBE

We report a high performance interdigitated Al0.48In0.52As/Ga0.47In0.53As heterostructure photoconductive detector for high bit‐rate, single‐mode telecommunication applications. The detector shows a rise time of 80 ps, a fall time of 1.2 ns, and a peak responsivity seven times better than that of a pin photodiode. Our study shows that the long fall time is due to a slow minority‐carrier (hole) drift velocity coupled with a two‐dimensional effect. We have also tested the demodulation characteristics of the detector at frequencies as high as 2.7 GHz. Furthermore, we have investigated the noise properties of the detector in the frequency band of 100 MHz–1.1 GHz.

Interdigitated Al0.48In0.52As/Ga0.47In0.53As photoconductive detectors

We demonstrate a Ga0.47In0.53As/Al0.48In0.52As modulation‐doped photoconductive detector. The detector has a built‐in electric field to separate photogenerated electron‐hole pairs. This allows the electron lifetime to be precisely determined by electrode spacings. When tested by a 200‐ps, λ=1.3  μm laser pulse, the detector shows an internal gain of 18, a peak external quantum efficiency of 300%, a rise time of 80 ps, a full width at half‐maximum of 250 ps, and an internal gain‐bandwidth product of 72 GHz. Typical devices have 4‐μm spacings between electrodes and 94‐μm widths. The detector has a spectral response between 0.6 and 1.65  μm with a dip at 0.86  μm. We also measured the noise power of the detector at room temperature. With its capability to be integrated with a modulation‐doped field‐effect transistor, this detector can be useful in a monolithic integrated photoreceiver.

Modulation‐doped Ga0.47In0.53As/Al0.48In0.52As planar photoconductive detectors for 1.0–1.55‐μm applications

We report a single‐period modulation‐doped Ga0.47In0.53As/Al0.48In0.52As photoconductive detector for long wavelength applications. This detector shows a high equivalent external quantum efficiency. Furthermore, we have also measured the receiver sensitivity of this detector. At 1 Gbits/s, 1.3 μm, and BER=10−9, the receiver sensitivity is −25 dBm. These results suggest that, through further developments, this detector should find applications in monolithic integrated photoreceivers.

C. Y. Chen

Papers

Interdigitated Al0.48In0.52As/Ga0.47In0.53As photoconductive detectors

Modulation‐doped Ga0.47In0.53As/Al0.48In0.52As planar photoconductive detectors for 1.0–1.55‐μm applications

Modulation‐doped Al0.48In0.52As/Ga0.47In0.53As photodetector prepared by molecular beam epitaxy