12-12-2012, 05:10 PM
Recent Developments in Monolithic Integration of InGaAsPAnP Optoelectronic Devices
[attachment=43604]
Abstract
Monolithicdy integrated optoelectronic circuits combine
optical devices such as light sources (injection lasers and light emitting
diodes) and optical detectors with solid-state semiconductor devices
such as field effect transistors, bipolar transistors, and others on asi ngle
semiconductor crystal. Here we review some of the integrated circuits
that have been realized and discuss the laser structures suited for integration
with emphasis on the InGaAsP/InP material system. Some
results of high frequency modulation and performance of integrated
devices are discussed.
INTRODUCTION
HE monolithic integration of optoelectronic devices
composed of the 111-V compounds GaAlAs/GaAs and
InGaAsP/InP has been a topic of considerable interest in
recent years as materials and device technology has advanced.
In particular, the quaternary InP/InGaAsP material system has
been a subject of intense study since devices made of these
materials operate in the 1.1-1.6 pm spectral region, which
coincides with the optimal region for fiber optics communication
systems. As progress is being made in fiber optic technology
and low loss single-mode fibers become available, there
is also a strong interest in developing semiconductor devices
capable of launching, receiving, and processing optical signals
at the extremely high data rates that are possible with fiber
optic transmission systems. The monolithic integration of
optoelectronic devices on a single semiconductor crystal [l] ,
[2] offers the potential advantages of improved reliability,
low cost, and small size and also makes possible very fast
operation by reducing the circuit parasitic reactances
LASERS ON SEMI-INSULATING SUBSTRATES
The use of SI substrates for monolithic integration of optoelectronic
devices is desirable because it facilitates the electrical
isolation of the integrated components and because it is
compatible with FET technology. For high frequency applications,
the use of a SI substrate is important because the parasitic
capacitance of interconnections can be minimized. The
first demonstration of an injection laser on SI GaAs [3] was
done using the crowding effect confinement structure. Since
then, several other laser structures on SI substrates have been
reported, including the buried heterostructure (BH), the transverse
junction stripe (TJS) structure, and groove type laser
structure.
The BH laser on conductive GaAs and InP substrates has
been studied intensively since it can achieve very low threshold
currents and stable transverse mode operation. These
excellent properties have also been obtained with SI substrates
of GaAs [4] and InP [SI, The structure of a BH laser on SI
InP reported by Matsuoka et al. [SI is shown in Fig. 1. This
structure is obtained with two liquid phase epitaxial (LPE)
growths. The process isimilar to the fabrication of BH
lasers on conductive n-type substrates except for the method
of forming the n-type electrode. Here the first growth is of a
thick (7 pm) n-type InP confining layer, an InGaAsP active
layer, a p-type InP confining layer, and an InGaAsP cap layer.
Then, the expitaxial layers are mesa-etched down to the first
n-type I& layer and the sidewalls of the mesa are buried by
the second LPE growth.
INTEGRATION OF OPTICAL AND BIPOLAR DEVICES
Heterojunction bipolar transistors possess the advantages of
high emitter injection efficiency and compatibility with the
double heterostructure of the laser diode. Since the emitter
is made of the high bandgap material, the injection efficiency
is practically independent of the emitter and base doping and
thus, the base doping can be increased [20]. Increasing the
base doping level results in minimized base spreading resistance,
while a decrease of the emitter doping reduces the junction
capacitance. Both effects improve the frequency response
of the device. Bipolar heterojunction transistors can also be
used as high gain photodetectors. The incoming light is absorbed
in the low bandgap base and in the depleted part of the
collector. Several structures of heterojunction phototransistors
(HPT's) in InGaAsP have been reported [21] -1241. The
structure of the device reported by Sasaki et al. [22] is shown
in Fig. 13.
INTEGRATEMDI RRORS
The cavity of a semiconductor injection laser is normally
obtained by cleaving a semiconductor wafer along one of the
crystal cleavage planes. The two parallel planes confining the
wafer provide the optical mirrors of the laser. This technique,
although very useful, is not ideally suited for complex integrated
circuits since it imposes severe limitations on the size
and geometry of the semiconductor wafer. The fabrication of
the mirrors by alternative processes removes these limitations
and permits the integration of the laser cavity with much
more flexibility in a complex integrated device. Injection
lasers with chemically etched mirrors have been reported in
the InGaAsP/InP system. A recent paper describing these
works is given by Wright et al. [26]. The mirrors’ fabrication
processes include both wet chemical techniques and the socalled
dry processes such as plasma, reactive ion, and sputter
etching techniques. Using a wet chemical etching technique,
Wright et al. [26] demonstrated the integration of lasers and
photodiodes (using the same double heterostructure for both
devices) on a single n-type InP substrate.
[attachment=43604]
Abstract
Monolithicdy integrated optoelectronic circuits combine
optical devices such as light sources (injection lasers and light emitting
diodes) and optical detectors with solid-state semiconductor devices
such as field effect transistors, bipolar transistors, and others on asi ngle
semiconductor crystal. Here we review some of the integrated circuits
that have been realized and discuss the laser structures suited for integration
with emphasis on the InGaAsP/InP material system. Some
results of high frequency modulation and performance of integrated
devices are discussed.
INTRODUCTION
HE monolithic integration of optoelectronic devices
composed of the 111-V compounds GaAlAs/GaAs and
InGaAsP/InP has been a topic of considerable interest in
recent years as materials and device technology has advanced.
In particular, the quaternary InP/InGaAsP material system has
been a subject of intense study since devices made of these
materials operate in the 1.1-1.6 pm spectral region, which
coincides with the optimal region for fiber optics communication
systems. As progress is being made in fiber optic technology
and low loss single-mode fibers become available, there
is also a strong interest in developing semiconductor devices
capable of launching, receiving, and processing optical signals
at the extremely high data rates that are possible with fiber
optic transmission systems. The monolithic integration of
optoelectronic devices on a single semiconductor crystal [l] ,
[2] offers the potential advantages of improved reliability,
low cost, and small size and also makes possible very fast
operation by reducing the circuit parasitic reactances
LASERS ON SEMI-INSULATING SUBSTRATES
The use of SI substrates for monolithic integration of optoelectronic
devices is desirable because it facilitates the electrical
isolation of the integrated components and because it is
compatible with FET technology. For high frequency applications,
the use of a SI substrate is important because the parasitic
capacitance of interconnections can be minimized. The
first demonstration of an injection laser on SI GaAs [3] was
done using the crowding effect confinement structure. Since
then, several other laser structures on SI substrates have been
reported, including the buried heterostructure (BH), the transverse
junction stripe (TJS) structure, and groove type laser
structure.
The BH laser on conductive GaAs and InP substrates has
been studied intensively since it can achieve very low threshold
currents and stable transverse mode operation. These
excellent properties have also been obtained with SI substrates
of GaAs [4] and InP [SI, The structure of a BH laser on SI
InP reported by Matsuoka et al. [SI is shown in Fig. 1. This
structure is obtained with two liquid phase epitaxial (LPE)
growths. The process isimilar to the fabrication of BH
lasers on conductive n-type substrates except for the method
of forming the n-type electrode. Here the first growth is of a
thick (7 pm) n-type InP confining layer, an InGaAsP active
layer, a p-type InP confining layer, and an InGaAsP cap layer.
Then, the expitaxial layers are mesa-etched down to the first
n-type I& layer and the sidewalls of the mesa are buried by
the second LPE growth.
INTEGRATION OF OPTICAL AND BIPOLAR DEVICES
Heterojunction bipolar transistors possess the advantages of
high emitter injection efficiency and compatibility with the
double heterostructure of the laser diode. Since the emitter
is made of the high bandgap material, the injection efficiency
is practically independent of the emitter and base doping and
thus, the base doping can be increased [20]. Increasing the
base doping level results in minimized base spreading resistance,
while a decrease of the emitter doping reduces the junction
capacitance. Both effects improve the frequency response
of the device. Bipolar heterojunction transistors can also be
used as high gain photodetectors. The incoming light is absorbed
in the low bandgap base and in the depleted part of the
collector. Several structures of heterojunction phototransistors
(HPT's) in InGaAsP have been reported [21] -1241. The
structure of the device reported by Sasaki et al. [22] is shown
in Fig. 13.
INTEGRATEMDI RRORS
The cavity of a semiconductor injection laser is normally
obtained by cleaving a semiconductor wafer along one of the
crystal cleavage planes. The two parallel planes confining the
wafer provide the optical mirrors of the laser. This technique,
although very useful, is not ideally suited for complex integrated
circuits since it imposes severe limitations on the size
and geometry of the semiconductor wafer. The fabrication of
the mirrors by alternative processes removes these limitations
and permits the integration of the laser cavity with much
more flexibility in a complex integrated device. Injection
lasers with chemically etched mirrors have been reported in
the InGaAsP/InP system. A recent paper describing these
works is given by Wright et al. [26]. The mirrors’ fabrication
processes include both wet chemical techniques and the socalled
dry processes such as plasma, reactive ion, and sputter
etching techniques. Using a wet chemical etching technique,
Wright et al. [26] demonstrated the integration of lasers and
photodiodes (using the same double heterostructure for both
devices) on a single n-type InP substrate.