Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Patent
1992-12-11
1995-01-31
Jackson, Jerome
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
257184, 257190, 257200, 257459, H01L 2714, H01L 3100
Patent
active
053861370
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electro-optic device and a method of fabricating the device.
A demand exists for increased computing power and processing speed in a wide range of applications, however, this is particularly evident for exchanges of broadband telecommunications networks. Perhaps, the only way to meet the demand is by employing massive parallelism in computer architectures, which gives rise to the problem of supplying the requisite interconnections to and between elements of architectures employed. The interconnection problem, however, can be overcome using optical interconnect technology, which involves the use of light sources, detectors and, for a number of particular applications. modulators. Rather than employ a large number of light sources, it is more efficient for a number of reasons, including power consumption and heat sinking, to use a single light source and a number of modulator/detector devices associated therewith.
For example, if a large array of optical fiber terminals in an exchange requires a source of light for each terminal, it is more efficient to provide the sources from a corresponding array of modulators, where each modulator receives a beam of light which has been split from a single light source using an appropriate optical grating. The array of modulators, the grating and the single light source obviate the need to provide an array of light sources for the optical terminals.
According to the above, a modulator/detector structure is required which can be simply and relatively inexpensively fabricated and can be arranged so as to form an array of modulator/detector elements on any substrate. In particular, the array structure should be able to be fabricated on Si or GaAs VLSI circuits or circuit substrates.
One form of modulator/detector comprises an asymmetric Fabry-Perot resonator structure. The structure includes a semiconductor stack having alternating layers of GaAs and AlAs as a first mirror and either the air GaAs interface or another GaAs and AlAs stack as a second mirror. A series of quantum well absorption layers are disposed between the mirrors and the entire structure is doped so as to form a pin diode. Light received by the structure is absorbed by the quantum wells according to the voltage applied across the structure. The absorption is modified according to the voltage by virtue of the quantum confined Stark effect. The effect changes the resonance of the Fabry-Perot cavity and hence the extent to which the structure reflects light received thereby can be modulated in accordance with the voltage applied across the structure. Similarly, the effect can be used to enable the structure to operate as a detector as the voltage which appears across the structure is dependent on the intensity of the light received and absorbed, by the structure. The modulator/detector structure is described in detail in a paper entitled "Low-voltage Multiple Quantum Well Reflection Modulator with On:Off Ratio>100:1, Electronics Letters, 20 July 1989, Vol 25, No 15, which is herein incorporated by way of reference.
The above modulator/detector structure, however, has a number of deficiencies and gives rise to a number of problems, particularly in fabrication on Si substrates. Most electronic control circuitry for optical modulator/detector devices is provided in Si VLSI circuits and therefore it is particularly desirable to be able to place the devices directly onto a Si substrate. To grow a GaAs structure on Si, however, is a time consuming and particularly inefficient process for the following reasons. Firstly, the Si electronic circuits need to be protected by placing a protective layer over the circuits prior to growth of the GaAs structure and the protective layer has to be removed afterwards. The GaAs structure once grown on the Si substrate also tends to be relatively large, particularly with the reflector GaAs. AlAs stack and occupies at least a 10-20 .mu.m island on the Si substrate. The GaAs structure can be up to four times larger than the same structure grown
Dell John M.
Yoffe Gideon W.
Australian & Overseas Telecommunications Corp. Ltd.
Jackson Jerome
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