Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Having diverse electrical device
Reexamination Certificate
1999-09-21
2002-09-24
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Having diverse electrical device
C438S029000, C438S031000, C438S032000
Reexamination Certificate
active
06455338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an integrated semiconductor laser-modulator device and a manufacturing process of the same. More particularly, it relates to the modulator-integrated semiconductor laser device in which frequency-characteristics have been improved by suppressing an influence of the fluctuation of the electric field due to the modulating signals applied to the modulator, and a manufacturing process thereof.
2. Description of Related Art
In order to popularize the public communication web with optical fibers, it is important to improve the performance of such semiconductor laser devices and the productivity for inexpensively manufacturing the same.
Especially for improving the performance of semiconductor laser devices, it is essential to the laser beam thereof at high frequency in order to transmit an increasing amount of information. Since the fluctuation of wavelength modulation should be minimized to transmit the laser beam a long distance, an external modulation system is generally adapted for modulating the laser beam. A modulator device switches on and off beam transmittance, thereby modulating the laser beam at high frequency, while the semiconductor laser device keeps emitting at a constant level.
Since the external modulation system has difficulties in coupling the modulator with the semiconductor laser beam device and in requiring a lot of components, an integrated semiconductor laser-modulator devices, which are a semiconductor laser device monolithically integrated with a modulator, have been developed to overcome such difficulties.
According to such integrated modulator semiconductor laser device, while is common electrode are connected to a ground, the forward biased current is injected into the semiconductor laser and a reverse biased modulating signals are applied to the modulator. Therefore the structure of a separator region provided between the semiconductor laser and the modulator becomes quite important.
Since a high extinction ratio (i.e. a ratio of beam transmittances between ON-state and OFF-state) can be achieved with a low operating voltage when the semiconductor modulator has a beam absorbing multi quantum well (referred to as MQW hereinafter) structure layer, the MQW beam absorption layer is typically adapted in high rate communicating.
FIG. 27
shows a partially sectional perspective view of a conventional modulator-integrated semiconductor laser device (referred to as a modulator-integrated laser device).
FIG. 28
shows a sectional view taken along lines XXVIII—XXVIII of FIG.
27
.
In FIG.
27
and
FIG. 28
, numeral
201
denotes a modulator-integrated laser device, the D region represents a separator/modulator region consisting of a separator region and a modulator region, and the C region represents a laser region.
In FIG.
27
and
FIG. 28
, numeral
202
denotes a substrate of InP, numeral
204
denotes a laser n-side beam confinement layer of InGaAsP,
206
denotes a MQW active layer of InGaAsP,
208
denotes a laser p-side beam confinement layer of InGaAsP. And a laser waveguide
207
is comprised with the laser n-side beam confinement layer
204
, the active layer
206
, and the laser p-side beam confinement layer
208
.
Numeral
210
denotes a first clad layer of p-InP, numeral
212
denotes a diffractive grating, numeral
214
denotes a second clad layer of p-InP, numeral
216
denotes a contact layer of p
+
-InGaAs. “n-” is referred to “n-type”, and “p-” is referred to “p-type” hereinafter.
Numeral
218
denotes an n-side laser beam confinement layer of n-InGaAsP in the separator/modulator region, numeral
220
denotes a MQW beam absorption layer of InGaAsP in the separator/modulator region consisting of a beam absorption layer
220
a
in the modulator region and a beam absorption layer
220
b
in the separator region. Numeral
222
denotes a p-side beam confinement layer of InGaAsP in the separator/modulator region. A waveguide
221
in the separator/modulator region is composed with the n-side beam confinement layer
218
in the separator/modulator region, the beam absorption layer
220
, and the p-side beam confinement layer
221
in the separator/modulator region.
Numeral
224
denotes a first embedded layer of InP doped with Fe, numeral
226
denotes a Hall-trap layer of n-InP, and numeral
228
denotes a second embedded layer of InP doped with Fe. The ridge-shaped laser waveguide
207
and the ridge-shaped separator/modulator waveguide
221
have both side surfaces along the laser emitting direction on which the first embedded layer
224
, the Hall-trap layer
226
, and the second embedded layer
228
are composed to form a current block layer. A window structure
229
is formed at the emitting end surface of the current block layer.
Numeral
230
denotes an insulator layer of SiO
2
, numeral
231
denotes a separator groove separating the laser region C from the modulator region. Numeral
232
denotes a surface evaporated electrode of Ti/Au. Numeral
234
denotes a p-side laser Au-coated electrode. Numeral
236
denotes a p-side modulator Au-coated electrode. Numeral
232
denotes a surface evaporated electrode. Numeral
240
denotes a common electrode. And numeral
242
denotes an arrow showing the direction of the emitting laser beam.
A conventional modulator-integrated laser device is manufactured as described below.
First by using a MOCVD method, formed on the substrate
12
of n-InP are in sequence, an n-InGaAsP layer of the n-side laser beam confinement layer
204
, an InGaAsP MQW layer of the active layer
206
, a p-InGaAsP layer of the p-side laser beam confinement layer
208
, a p-InP layer of the first clad layer
210
, and P-InGaAsP layer for forming the diffractive grating
212
.
Next, by using an interference exposing method, the P-InGaAsP layer is etched with a grating shape to form the diffractive grating
212
. Thereafter a P-InP layer of the first clad layer
210
is disposed entirely to embed the diffractive grating
212
.
A dielectric layer of material such as SiO
2
and SiN is formed on the p-InP layer of the first clad layer
210
, and etched to form a stripe-shaped dielectric layer that includes the diffractive gratings
212
and forms the laser waveguide. Then layers disposed in the region including the separator/modulator region D are etched with using the dielectric layer as a mask until the substrate
202
is exposed.
Next, while retaining the stripe-shaped dielectric layer, by using a MOCVD method, subsequently formed are, the n-InGaAsP of the n-side laser beam confinement layer
218
in the separator/modulator region, the MQW layer of InGaAsP of the beam absorption layer
220
in the separator/modulator region D, and the InGaAsP layer of the p-side beam absorption layer
222
in the separator/modulator region.
Next, after the stripe-shaped dielectric layer is removed, again an another dielectric layer of material such as SiO
2
and SiN is deposited to form the waveguide in the separator/modulator region D and the laser region C, and etched to make the stripe-shaped dielectric layer with stripe-shaped which overlaps over the separator/modulator region D and the laser region C. Then the entire layers are wet-etched with HBr (hydrogen bromide) using a mask of this dielectric layer until the substrate
202
is exposed so that the waveguide is shaped as a ridge. When the window structure
229
is formed, the stripe-shaped dielectric layer is such that the layers at the emitting end surface can be also etched away.
Next, while retaining the stripe-shaped dielectric layer, the InP layer doped with Fe of the first embedded layer
224
, the n-InP layer of the Hall-trap layer
226
, and the InP layer doped with Fe of the second embedded layer
228
are grown by using the MOCVD method.
After removing the stripe-shaped dielectric layer, a p-InP layer of a second clad layer
214
and a p
+
-InGaAs of a contact layer
216
are grown entirely by using the MOCVD method.
Next, the contact layer
216
and the second clad layer
214
in a region co
Tada Hitoshi
Takagi Kazuhisa
Takiguchi Tohru
Leydig , Voit & Mayer, Ltd.
Mulpuri Savitri
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