Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-06-26
2003-10-21
Jackson, Jerome (Department: 2815)
Coherent light generators
Particular active media
Semiconductor
C257S079000, C257S619000, C257S643000, C257S792000
Reexamination Certificate
active
06636543
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a semiconductor device and a surface emitting semiconductor laser device, and more in particular to the semiconductor device and the surface emitting semiconductor laser device having a higher long-term reliability.
(b) Description of the Related Art
A surface emitting semiconductor laser device emitting light in a direction perpendicular to a substrate attracts public attention in the data communication field because of the possible arrangement of a plurality of the laser devices in a two-dimensional array on a single substrate, different from a conventional Fabry-Perot semiconductor laser device.
The surface emitting semiconductor laser device includes a pair of DBRs (Distributed Bragg Reflectors) (for example, Al(Ga)As/Ga(Al)As in the GaAs-based reflector) and an active layer acting as an emitting region sandwiched between the reflectors overlying a GaAs or InP substrate.
In order to increase the current injection efficiency and to reduce the threshold current, a surface emitting semiconductor laser device has been proposed having the current confinement structure made of an Al oxide layer.
As shown in
FIG. 1
, a conventional 850 nm-range surface emitting semiconductor laser device
10
includes a layer structure, overlying an n-GaAs substrate
12
, having a bottom DBR mirror
14
having 35 pairs of n-Al
0.9
GaAs
-Al
0.2
GaAs each having a thickness of &lgr;/4n (“&lgr;” is a lasing wavelength and “n” is a refractivity), a bottom cladding layer
16
, a quantum well active layer
18
, a top cladding layer
20
and a top DBR mirror
22
having 25 pairs of p-Al
0.9
GaAs/p-Al
0.2
GaAs each having a thickness of &lgr;/4n.
In the top DBR mirror
22
, one of the layers close to the active layer
18
is formed as an AlAs layer
24
in place of the Al
0.9
GaAs layer, and Al of the AlAs layer
24
in the area other than a current injection area is selectively oxidized to form a current confinement area made of an Al oxide area
25
which surrounds the current injection area.
The top DBR mirror
22
in the layer structure is configured to be a circular mesa post
23
having a diameter of 30 &mgr;m from the top to the layer near to the active layer
18
made of the photolithographic and etching process.
The current confinement area made of the Al oxide area
25
is formed around the mesa post
23
by selectively oxidizing the Al in the AlAs layer
24
inwardly from the outer periphery of the mesa post
23
by means of the oxidation treatment of the layer structure at about 400° C. in a water vapor ambient.
When, for example, the Al oxide area
25
includes an annular ring having a width of 10 &mgr;m, the surface area of the central AlAs area
24
or the surface area for the current injection (aperture) is about 802 &mgr;m
2
having a circular shape (diameter is 10 &mgr;m).
The mesa post
23
is surrounded by, for example, a polyimide section
26
, and a ring-shaped electrode acting as a p-side electrode
28
is mounted in contact with the periphery of the top surface of the mesa post
23
by the width from 5 &mgr;m to 10 &mgr;m. After the thickness of the n-GaAs substrate
12
is adjusted to about 200 &mgr;m by polishing the bottom surface thereof, an n-side electrode
30
is formed thereon.
An electrode pad
32
for connection with an external terminal is mounted on the polyimide section
26
and in contact with the ring-shaped electrode
28
.
In the surface emitting semiconductor laser device having the narrowed oxide area different from the current confinement structure for ion implantation, the formation of the mesa post
23
having the exposed periphery is required for the oxidation of the AlAs area in the p-type DBR mirror.
The height of the mesa post
23
or the etching depth of the top DBR mirror depends on the thickness of the top DBR mirror
22
because the periphery of the AlAs area
24
should be exposed for the oxidation.
For increasing the refractivity of the DBR mirror
22
, 20 pairs or more of the compound semiconductor layers are necessary. Accordingly, the thickness of the top DBR mirror
22
amounts to about 4 &mgr;m to 5 &mgr;m.
As described earlier, the mesa post
23
is surrounded by the resin such as polyimide to flatten the step of the mesa post
23
. As shown in
FIGS. 2A
to
2
C, the mesa post
23
is entirely surrounded by the polyimide section
26
.
The electrode pad
32
on the polyimide section
26
reduces the parasitic capacitance generated under the electrode pad more significantly than the electrode pad on the compound semiconductor layer, thereby providing the higher speed operation.
The surface emitting semiconductor laser device with the narrowed oxide area is frequently used for higher speed operation (modulation) because of the lower threshold current.
When the surface emitting semiconductor laser device having the mesa post surrounded by the polyimide is thermally treated at 300 to 400° C. in the device manufacturing step (wafer process) or the mounting step (package), the stress is generated between the compound semiconductor layer and the polyimide section due to the difference between the thermal expansion coefficients thereof and is applied to the mesa post, thereby exerting ill effects on the active region. This is not preferable with respect to the initial characteristics and the reliability of the surface emitting semiconductor laser device.
Also in the actual operation circumstance in which the device operates in the temperature range between 0 and 85° C., the stress generated between the polyimide section and the DBR mirror may exert ill effects on the long-term reliability of the surface emitting semiconductor laser device. Accordingly, the reduction of the stress generated between the polyimide section and the mesa post is requested.
A similar problem may arise in the surface emitting semiconductor laser device having the mesa post surrounded by the polyimide in addition to the above device having the narrowed oxide layer. Further, a similar problem may arise in a general semiconductor device including a light emitting device, a light receiving device and a transistor other than the surface emitting semiconductor laser device.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device and a surface emitting semiconductor laser device having a longer time of life which are obtained by reducing stress applied to a mesa post.
In a first aspect of the present invention, a semiconductor device is provided which includes a substrate, a mesa post overlying the substrate and having a substantially cylindrical shape, a resin member surrounding the mesa post and a stress moderating member received in the mesa post for moderating stress between the mesa post and the resin member.
In a second aspect of the present invention, a surface emitting semiconductor laser device is provided which includes a substrate and a layer structure formed thereon, the layer structure including a mesa post surrounded by a resin member having a stress moderating member for moderating stress between the mesa post and the resin member.
In accordance with the present invention, the stress applied to the mesa post of the semiconductor device or the surface emitting semiconductor laser device is reduced because the entire volume of the resin member is divided by the stress moderating member and each of the divided resin members reduces the stress.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.
REFERENCES:
patent: 6298551 (2001-10-01), Wojnarowski et al.
Iwai Norihiro
Shinagawa Tatsuyuki
Yokouchi Noriyuki
Jackson Jerome
Knobbe Martens Olson & Bear LLP
LandOfFree
Semiconductor device and surface emitting semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor device and surface emitting semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device and surface emitting semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3167766