Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-05-05
2003-12-30
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06671301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device, and a method for producing the same. In particular, the present invention relates to a semiconductor laser device having a window structure for providing an improved production yield, and a method for producing the same.
2. Description of the Related Art
In recent years, semiconductor laser devices for use as light sources for information processing apparatuses (e.g., optical disk apparatuses) have been expected to provide higher and higher output power in order to attain higher recording speeds. One method for satisfying such needs involves the use of a window structure at an end face of a laser cavity, which improves the catastrophic optical damage (hereinafter “COD”) level at the end face.
COD is an instantaneous degradation phenomenon which occurs as the optical output of a semiconductor laser is increased to or above a certain limit value. A COD phenomenon occurs in the case where the vicinity of an end face of a semiconductor laser becomes an absorption region with respect to the light which occurs within the laser.
Specifically, a COD phenomenon may occur when dangling bonds are formed due to oxygen adsorption or surface oxidation on the semiconductor surface of the end face of the laser cavity, generating a peculiar deep level on the semiconductor surface, thereby substantially narrowing the forbidden band width in the vicinity of the end face. Since any non-radiative recombination due to a surface level present on the semiconductor surface introduces an increase in temperature, the occurrence of a COD phenomenon results in further reduction of the forbidden band width in the vicinity of the end faces of the laser cavity and further increases light absorption. Thus, there is a positive feedback with respect to the COD phenomenon. As a result, the end faces may be destroyed due to melting or the like, which leads to a decrease in the optical output as well as irreversible degradation of the device.
Some semiconductor laser devices employ a window structure so as to enhance the band gap energy in a portion of an active layer near a laser cavity end face, thereby preventing COD destruction at the cavity end face. For example, a window structure can be realized by diffusing an impurity in the vicinity of a laser cavity end face so as to disorder the super-lattice structure in the active layer.
Hereinafter, a method for producing a conventional window structure semiconductor laser device will be described.
FIGS. 6A
to
6
D are diagrams illustrating respective steps of a manufacturing process for a conventional window structure semiconductor laser device.
First, as shown in
FIG. 6A
, the following semiconductor multilayer structure is formed on an n-GaAs substrate
601
by using an MOVPE (metal organic vapor phase epitaxy) method, where the respective layers are sequentially grown into crystals in this order: an n-AlGaInP cladding layer
602
, an AlGaInP/GaInP super-lattice active layer
603
, a p-AlGaInP first cladding layer
604
, a p-GaInP etching stop layer
605
, a p-AlGaInP second cladding layer
606
, a p-GaInP band graded layer
607
, and a p-GaAs capping layer
608
.
Next, as shown in
FIG. 6B
, by using a plasma CVD (chemical vapor deposition) technique, an SiN film
609
is formed on the aforementioned semiconductor multilayer structure. Furthermore, the SiN film
609
is patterned by dry etching so as to form two parallel openings whose planar forms appear as two stripes having a width of several dozen &mgr;m. A wet etching step removes the portions of the GaAs capping layer
608
where these openings are formed. Thereafter, a ZnO film
610
and an SiO
2
film
611
are formed by sputtering so as to cover the semiconductor multilayer structure (including the openings). Furthermore, an annealing is performed so as to diffuse Zn from the ZnO film
610
through the portions of the p-GaInP layer
607
which are exposed in the openings of the SiN film
609
, and the openings in the GaAs capping layer
608
. Through such solid-phase diffusion of Zn, impurity diffusion regions
612
having stripe-like planar forms are formed, and the portions of the AlGaInP/GaInP super-lattice active layer
603
which lie within the impurity diffusion regions
612
are converted into a mixed crystal. The regions of the active layer
603
which have been converted into the mixed crystal define window structures. The window structures have a higher band gap energy than that of the regions which have not formed a mixed crystal.
Referring to
FIG. 6C
, the SiO
2
film
611
, the ZnO film
610
, the SiN film
609
, and the GaAs film
608
are removed. Thereafter, by using a known technique, a stripe pattern of SiO
2
film
613
is formed on the exposed p-GaInP band graded layer
607
so as to extend along a plane which is perpendicular to the longitudinal direction of the impurity diffusion regions
612
. By using the stripe pattern of SiO
2
film
613
as a mask, the p-GaInP band graded layer
607
is etched into a ridge shape by using an acetic acid-type etchant. Then, switching to a sulfuric acid-type etchant, the p-AlGaInP second cladding layer
606
is etched away until reaching the p-GaInP etching stop layer
605
. As a result, a ridge structure composed of the p-GaInP band graded layer
607
and the p-AlGaInP second cladding layer
606
is formed as shown in FIG.
6
C. Since the sulfuric acid-type etchant has a greater etching rate for the p-AlGaInP second cladding layer
606
than for the p-GaInP etching stop layer
605
, the etching process can be successfully stopped at the etching stop layer
605
.
Thereafter, an n-type current blocking layer
614
is grown so as to bury the side of the ridge structure by a selective growth technique using an MOVPE method. After removing the SiO
2
film
613
serving as a stripe mask, a p-GaAs contact layer
615
is grown over the n-type current blocking layer
614
and the p-GaInP band graded layer
607
. By using a known technique, p-side and n-side ohmic electrodes are formed (not shown).
The resultant semiconductor multilayer structure is cleaved in the impurity diffusion regions
612
along a plane perpendicular to the longitudinal direction of the ridge structure, thereby forming laser cavity end faces. As a result, a semiconductor laser device having window structures as shown in
FIG. 6D
is accomplished.
Conventional semiconductor laser devices with window structures are formed by the above-described manufacturing process. However, in accordance with the above-described manufacturing process, not only the active layer
603
but also the p-GaInP etching stop layer
605
are converted into a mixed crystal together with the surrounding AlGaInP layers during the step of Zn diffusion. That is, in accordance with above-described conventional manufacturing process, Zn is directly diffused from the Zn source, i.e., the ZnO film
610
, into the AlGaInP layers, which have a relatively large diffusion coefficient. Therefore, it is difficult to control the impurity dose amount. As a result, as shown in
FIG. 1
, for example, a high concentration of impurity is diffused in the AlGaInP crystal, allowing for a rapid development of the mixed crystal. In particular, the thin etching stop layer
605
may eventually be destroyed by the etching. In that case, since the etching selection ratio of the sulfuric acid-type etchant is extremely decreased, the etching cannot be stopped by the etching stop layer
605
, allowing the p-AlGaInP first cladding layer
604
and the active layer
603
to be etched. Thus, the ridge shape may not be controlled properly.
Moreover, in accordance with the above-described conventional manufacturing process, the current blocking layer
614
may be formed so as to be nearer the active layer
603
due to overetching. As a result, the angle of expanse of light exiting the active layer
603
cannot be effectively controlled. In a loss-guide type semiconductor laser device, in particular, the propagation loss is inc
Adachi Hideto
Mannou Masaya
Onishi Toshikazu
Takamori Akira
Ip Paul
Matsushita Electronics Corporation
Menefee James
RatnerPrestia
LandOfFree
Semiconductor device and method for producing the same 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 method for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device and method for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3132742