Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Reexamination Certificate
2002-12-26
2004-03-23
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
C257S088000, C257S021000
Reexamination Certificate
active
06710375
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device, a manufacturing method thereof, and a laser bar locking apparatus.
As is in many cases of semiconductor laser devices, a GaAs laser chip
101
is provided with protective films
103
,
104
having a same reflectance on light emitting end surfaces
101
a
,
101
b
of the GaAs laser chip
101
, as shown in FIG.
10
. The reference numeral
102
in
FIG. 10
denotes an active layer of the GaAs laser chip
101
. When the protective films
103
,
104
have the same reflectance as stated above, both optical outputs from the light emitting end surface
101
a
and the light emitting end surface
101
b
are Po.
In the case where the protective films
103
,
104
are structured from Al
2
O
3
and given a refractive index of 1.60, when the GaAs laser chip
101
is given a refractive index of 3.50, a reflectance of the protective films
103
,
104
is changed by changing the film thickness thereof as shown in
FIG. 11
(a laser emission wavelength &lgr;=7800 Å).
Regardless of thickness of the protective films
103
,
104
, the protective films
103
,
104
has a reflectance smaller than that of the GaAs laser chip
101
. In the above case, when the optical film thickness of the protective films
103
,
104
is odd multiples of &lgr;/4, the reflectance of the protective films
103
,
104
becomes the smallest. On the other hand, when the optical film thickness of the protective films
103
,
104
is integral multiples of &lgr;/2, the reflectance of the protective films
103
,
104
becomes the largest and approximates most to the reflectance of the GaAs laser chip
101
. This is because the refractive index of the protective films
103
,
104
is smaller than the refractive index of the GaAs laser chip
101
. It should be noted that the optical film thickness is defined as a film thickness multiplied by a reflectance.
In the case where the refractive index of the protective films
103
,
104
is larger than the refractive index of the GaAs laser chip
1
, for example, where Si film is used as the protective film, the reflectance of the Si film becomes larger than that of the GaAs laser chip
101
regardless of the thickness of the Si film. In the above case, when the optical film thickness of the Si film is odd multiples of &lgr;/4, the reflectance of the Si film becomes the largest. On the other hand, when the optical film thickness of the Si film is integral multiples of &lgr;/2, the reflectance of the Si film becomes the smallest and approximates most to the reflectance of the GaAs laser chip
101
.
In the case of a semiconductor laser device having a high output laser with an optical output of 20 mW or more for example, as shown in
FIG. 12
, there is provided a protective film
113
with a reflectance smaller than the reflectance of a laser chip
111
on a front-side light emitting end surface (main emitting face)
111
a
. Also, there is provided a protective film
114
with a reflectance larger than the reflectance of the laser chip
111
on a rear-side light emitting end surface
111
b
. Consequently, optical output Pf from the front-side light emitting end surface
111
a
of the laser chip
111
becomes higher than optical output Pr from the rear-side light emitting end surface
111
b
of the laser chip
111
. For example, the protective film
113
on the light emitting end surface
111
a
is formed from Al
2
O
3
so as to have a film thickness of approximately 700 to 1,600 Å, and the reflectance thereof is set to be approximately 15% or less. Here, a reference numeral
112
in
FIG. 12
denotes an active layer of the laser chip
111
.
Also, the protective film
114
on the light emitting end surface
111
b
, if composed of one layer, cannot attain a sufficiently high reflectance even if the refractive index thereof is larger than that of the laser chip
111
. Therefore, the protective film
114
is composed of a plurality of layers. Specifically, the protective film
114
is composed of a first layer
114
a
to a fifth layer
114
e
. The first layer
114
a
and the third layer
114
c
are Al
2
O
3
films with a thickness of &lgr;/4 (&lgr;: laser emission wavelength). The second layer
114
b
and the fourth layer
114
d
are amorphous Si films with a thickness of &lgr;/4. The fifth layer
114
e
is an Al
2
O
3
film with a thickness of &lgr;/2. Thus, the protective film
114
attains a reflectance of approximately 85% or more.
Following description discusses a conventional manufacturing method of semiconductor laser devices.
First, in a semiconductor laser wafer
100
shown in
FIG. 13
, a cleavage line
117
is formed by scribe between an electrode
115
on a specified laser chip and an electrode
115
on a laser chip adjacent to the laser chip in direction orthogonal to a light emitting portion (channel)
118
. Then, the semiconductor laser wafer
100
is cleaved. This provides a laser bar (a bar of laser chips)
121
from the semiconductor laser wafer
100
as shown in FIG.
14
.
Next, the laser bars
121
are set into a laser bar locking apparatus
150
such that the electrode faces of the laser bars
121
are piled, as shown in FIG.
15
. The laser bars
121
are also set into the laser bar locking apparatus
150
such that the front-side emitting faces of all the laser bars
121
and the rear-side emitting faces thereof face in the same direction, respectively.
Next, a protective film having a specified reflectance is formed on the light emitting end surface of the laser bar
121
which is locked in the laser bar locking apparatus
150
. In this case, a vacuum depositor
170
is generally used as shown in FIG.
16
. The vacuum depositor
170
is equipped with a vapor source
172
, a rotating holder
173
for holding the above-described laser bar locking apparatus
150
, and a crystal oscillator
174
disposed in the vicinity of the rotating holder
173
for monitoring deposition thickness of film, all of which are housed in a chamber
171
.
Following description discusses a procedure of forming the protective film.
First, gas in the chamber
171
is exhausted through a duct
175
so as to put the chamber
171
in a vacuum. When a vacuum degree in the chamber
171
reaches a specified value, an deposition material
176
in the vapor source
172
is heated by an electron beam or the like for deposition. Thereby, the deposition material
176
is deposited on one light emitting end surface of the laser bar
121
to form a protective film.
After that, the rotating holder
173
is turned over by 180° rotation, and the deposition material
176
is again heated by an electron beam or the like for deposition. Thereby, the deposition material
176
is deposited on the other light emitting end surface of the laser bar
121
to form a protective film. A formation speed (deposition rate) of forming protective films on the both light emitting end surfaces of the laser bar
121
is so controlled as to be generally constant until completion of deposition. The deposition rate is controlled by a heating temperature, and therefore, the control in the electron beam deposition is performed by intensity of the electron beam. In the case of resistance heating, it is well known that control of the deposition rate is performed by controlling electric current applied to a resistive element. Specifically, when the deposition material is Al
2
O
3
, the deposition rate is generally set between several to 30 Å per sec. The deposition for the protective film is performed while film thickness of the protective film is monitored by the crystal oscillator
174
. The deposition is terminated when the film thickness of the protective film reaches a specified film thickness.
In the case where a protective film is formed on an end surface of a laser chip by deposition, a partial pressure of oxygen molecules rises immediately after start of deposition, the oxygen molecules being generated from oxide (Al
2
O
3
) as a material for the protective film. There is a high possibility that a damage is cause
Morrison & Foerster / LLP
Nelms David
Nguyen Thinh T
Sharp Kabushiki Kaisha
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