Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-08-30
2003-11-25
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S036000
Reexamination Certificate
active
06654397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device mounted on a heat sink and a manufacturing method thereof.
2. Description of the Background Art
A high power semiconductor laser device is indispensable as a light source for a recordable optical disc system and must have high reliability. One of the reasons why increase in the power of the semiconductor laser device has been restricted is COD (Catastrophic Optical Damage). The COD is believed to occur in the following cycle.
When current is injected to a facet of a cavity having a surface state in a high density, non-radiative recombination is caused through the surface state, and heat is generated. The generated heat reduces the energy gap at the facet portion, so that light is absorbed, which increases the heat generation. As this cycle is repeated, the temperature at the facet increases, and the crystal melts.
As a method of restricting the COD, the use of a current blocking region near the facet and a window structure by Zn diffusion are disclosed in ELECTRONICS LETTERS, Vol. 33, No. 12, pp. 1084-1086, 1997 and IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol. 29, No. 6, pp. 1874-1879, 1993.
FIG. 10
is a partly cut away, perspective view of a conventional semiconductor laser device having a current blocking region near the facet.
FIG. 11
is a partly cut away, perspective view of a conventional semiconductor laser device having a window structure.
In
FIGS. 10 and 11
, an n-GaInP buffer layer
32
, an n-AlGaInP cladding layer
33
, a quantum well active layer
34
and a p-AlGaInP first cladding layer
35
are formed in this order on an n-GaAs substrate
31
.
In a stripe-shaped region on the p-AlGaIn first cladding layer
35
, a p-AlGaInP second cladding layer
36
and a p-GaInP contact layer
37
are formed in this order. These p-AlGaInP second cladding layer
36
and p-GaInP contact layer
37
form a ridge portion R.
An n-GaAs current blocking layer
38
is formed on the p-AlGaInP first cladding layer
35
and both sides of the ridge portion R. The n-GaAs current blocking layer
38
is also formed on regions at the upper surface of the ridge portion R in the vicinity of both facets.
A p-GaAs cap layer
39
is formed on the n-GaAs current blocking layer
38
and the ridge portion R.
Thus, a laser structure
60
of the plurality of layers
32
to
39
is formed on the n-GaAs substrate
31
. On the back surface of the n-GaAs substrate
31
, an n-electrode
42
is formed. On the upper surface of the laser structure
60
, a p electrode (not shown) is formed.
As described above, since the n-GaAs current blocking layer
38
is formed in the regions at the upper surface of the ridge portion R in the vicinity of the facets of the cavity, current is not injected into the regions in the vicinity of the facets. Therefore, the COD is restrained.
Particularly in the semiconductor laser device in
FIG. 11
, a Zn diffusion region
43
by Zn diffusion is provided in the region in the vicinity of a facet of the quantum well active layer
34
. Thus, a window structure allowing a wide band gap is formed in the region of the quantum well active layer
34
in the vicinity of a facet. As a result, there is no light absorption in the vicinity of the facet, and the COD is more restrained.
FIG. 12
is a schematic perspective overview of a conventional high power semiconductor laser device having the laser structure in
FIG. 10
or
11
.
FIG. 13
is a schematic plan view of the semiconductor laser device in FIG.
12
.
FIG. 14
is a schematic sectional view of the semiconductor laser device in
FIG. 12
taken along the length of the cavity.
In the laser structure
60
shown in
FIGS. 10 and 11
, the n-GaAs current blocking layer
38
is formed only in the regions in the vicinity of the facets on the upper surface of the ridge portion R, and raised portions
50
are formed at the p-GaAs cap layer
39
in the regions in the vicinity of the facets.
Furthermore, as shown in
FIGS. 12
to
14
, a p-electrode
41
is formed on the upper surface of the semiconductor laser structure
60
. Raised regions
51
are formed at the p-electrode
41
because of the raised portions
50
. The emitting point
53
of a laser beam is positioned at a facet of the quantum well active layer
34
under the raised portion
50
and the raised region
51
.
FIG. 15
is a schematic sectional view of the semiconductor laser device in
FIG. 12
provided on a sub-mount taken along the length of a cavity.
FIG. 16
is a schematic front view of the semiconductor laser device in
FIG. 12
provided on a sub-mount.
As shown in
FIGS. 15 and 16
, when the semiconductor laser device
300
is mounted junction down on the upper surface of the sub-mount
400
as the p-electrode
41
faces downward, only the raised portions
51
of the p-electrode
41
are in contact with the upper surface of the sub-mount
400
. Therefore, at the time of die-bonding or wire-bonding, great stress is locally applied to the portions in the vicinity of the facets of the semiconductor laser device
300
. Since the area of contact between the p-electrode
41
and the sub-mount
400
is limited, good heat-radiation characteristic does not result and the adhesion intensity is low. The semiconductor laser device
300
could be mounted tilted on the sub-mount
400
. As a result, the reliability of the semiconductor laser device
300
is lowered.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a highly reliable, high power semiconductor laser device having a raised portion on its upper surface and a method of manufacturing thereof.
A semiconductor laser device according to one aspect of the present invention comprises a substrate, a laser structure formed on the substrate and including an active layer forming a cavity, and an electrode layer formed on the laser structure, the laser structure has a raised portion on its upper surface, the electrode layer has a first film thickness of zero or more in a region on the raised portion and a second film thickness larger than the first film thickness in the region excluding the raised portion.
Here, the first thickness may be zero, in other words, an electrode layer does not have to be formed at the raised portion.
In the semiconductor laser device, a laser structure including an active layer is formed on the substrate, and an electrode layer is formed on the laser structure. The electrode layer has a thickness larger than that in the raised portion in the region excluding the raised portion of the laser structure. Therefore, when the semiconductor laser device is mounted junction down on the upper surface of the heat sink as the electrode layer faces downward, the electrode layer is in contact with the heat sink in a large area. As a result, stress is not applied upon a particular part of the semiconductor laser device, but scattered in the whole of the semiconductor laser device and reduced. The contacting area between the electrode layer and the heat sink increases, so that the heat-radiation characteristic is improved, and the adhesion intensity is improved as well. In addition, the semiconductor laser device can be mounted stably almost without being tilted on the heat sink. As a result, the semiconductor laser device has higher reliability.
The second film thickness is preferably at least the sum of the height of the raised portion and the first film thickness. Thus, when the semiconductor laser device is provided on the upper surface of the heat sink as the electrode layer faces downward, the entire upper surface of the electrode layer is in contact with the upper surface of the heat sink. Therefore, stress is not applied upon a particular part of the semiconductor laser device, but sufficiently scattered in the whole of the semiconductor laser device and reduced. The contacting area between the second electrode and the heat sink sufficiently increases, so that the heat-radiation characteristic is more improved, and the adhesion intensity is more improved as well. In addition, th
Hiroyama Ryoji
Inoue Daijiro
Nomura Yasuhiko
Okamoto Shigeyuki
Takeuchi Kunio
Armstrong Westerman & Hattori, LLP
Leung Quyen
Sanyo Electric Co,. Ltd.
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