Laser diode and semiconductor light-emitting device...

Details Laser diode and semiconductor light-emitting device... Laser diode and semiconductor light-emitting device...

2000-08-04

2003-09-02

Ip, Paul (Department: 2828)

Coherent light generators

Particular active media

Semiconductor

C372S045013, C372S046012

Reexamination Certificate

active

06614821

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is based on Japanese priority applications No. 11-220649 filed on Aug. 4, 1999, No. 11-229794 filed on Aug. 16, 1999, No. 11-243745 filed on Aug. 30, 1999, No. 11-339267 filed on Nov. 30, 1999, No. 2000-057254 filed on Mar. 2, 2000, and No. 2000-144604 filed on May 12, 2000, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention generally relates to semiconductor devices and more particularly to semiconductor light-emitting devices and laser diodes.
Particularly, the present invention relates to a laser diode operable in a wavelength range of 630-680 nm. Further, the present invention relates to a laser diode for use in optical recording and optical reading of information or light-emitting display of information. Further, the present invention relates to a semiconductor light-emitting device based on a III-V compound semiconductor material.
Further, the present invention relates to a vertical-cavity laser diode suitable for an optical source of optical recording and reading of information or light-emitting display of information. The present invention further relates to an optical information recording apparatus such as a xerographic image recording system or an optical system and optical telecommunication system including an optical interconnection device that uses a vertical-cavity laser diode.
In these days, efforts are being made to develop a red-wavelength laser diode operable in the wavelength range of 630-680 nm as an optical source of optical disk recording apparatuses. Such an optical disk recording apparatus includes a DVD (Digital Video Disk or Digital Versatile Disk) player. The laser diode is used in such disk recording apparatuses as the optical source for reading and/or writing of information.
In order to increase the writing speed of information into the optical disk in such optical disk devices, it is necessary to increase the output power of the laser diode used therein.
Hereinafter, a brief review will be made on conventional red-wavelength laser diodes.
FIG. 1
shows the cross-sectional diagram of a conventional red-wavelength laser diode of an AlGaInP system disclosed in the Japanese Laid-Open Patent Publication 11-26880.
Referring to
FIG. 1
, a substrate
1
of n-type GaAs carries thereon a buffer layer
2
of n-type GaAs, a cladding layer
3
n-type AlGaInP, a quantum well active layer
4
including therein alternate and repetitive stacking of an AlGaInP layer and a GaInP layer, a cladding layer
5
of AlGaInP of low carrier concentration (2−6×10
17
cm
−3
), and an etching stopper layer
6
of p-type GaInP.
Further, there is provided a ridge structure
10
on a part of the etching stopper layer
6
wherein the ridge structure
10
includes a carrier-diffusion suppressing layer
7
of p-type AlGaInP, a cladding layer
8
of p-type AlGaInP, and a band-discontinuity relaxation layer
9
of p-type GaInP. Further, there are formed a pair of electric current blocking regions
11
of n-type GaAs on the surface part of the etching stopper layer
6
where the ridge structure
10
is not formed, and a contact layer
12
of p-type GaAs is formed continuously on the current blocking regions
11
and the band-discontinuity relaxation layer
9
therebetween. The contact layer
12
carries thereon a p-type electrode
13
, and an n-type electrode
14
is formed on the bottom surface of the substrate
1
.
In the laser diode of
FIG. 1
, there occurs a current confinement in the ridge structure
10
wherein the ridge structure
10
provides a current path between the current-blocking regions
11
, and the electric current is confined into the ridge structure
10
thus formed of p-type GaAs. Further, it should be noted that the current-blocking regions
11
absorb the optical radiation from the quantum well active layer
4
and there is induced a refractive-index difference between the ridge structure
10
and the region outside the ridge structure
10
as a result of such an optical absorption. Thereby, there occurs an optical confinement in the ridge structure
10
.
Such a ridge structure
10
, while being able to form so-called optical loss-guide structure in the laser diode, has a drawback in that it increases the threshold current of laser oscillation due to the optical absorption caused by the current-blocking regions
10
.
FIG. 2
shows the cross-sectional structure of a red-wavelength laser diode disclosed in the Japanese Laid-Open Patent Publication 9-172222.
Referring to
FIG. 2
, the laser diode is constructed on a substrate
15
of n-type GaAs and includes a buffer layer
16
of n-type GaAs, a cladding layer
17
of n-type AlGaInP, an active layer
18
of GaInP, a cladding layer
19
of p-type AlGaInP and an intermediate layer
20
of p-type GaInP, wherein the layers
16
-
20
are formed on the substrate
15
consecutively by an epitaxial process.
In the intermediate layer
20
, there are formed a pair of stripe grooves reaching the p-type cladding layer
19
, and the stripe grooves thus formed define a stripe ridge
21
therebetween. Further, current-blocking regions
22
are formed by filling the stripe grooves with a layer of n-type AlGaAs, and the entire structure is covered by a cap layer
23
of p-type GaAs formed by an epitaxial process.
In the case of the laser diode of
FIG. 2
, the current-blocking regions
22
are formed of AlGaAs having a bandgap larger than a bandgap of the active layer
18
. For example, the current-blocking regions
22
are formed to contain Al with a concentration of 39% in terms of atomic percent when the laser diode is designed to operate at the wavelength of 650 nm. In the case the laser diode is to be operated at the wavelength of 630 nm, the Al content in the current-blocking regions
22
should be 45% or more in terms of atomic percent. In such a case, the current-blocking regions
22
are transparent to the laser beam and the loss at the optical waveguide is minimized.
FIG. 3
shows the cross-sectional diagram of a red-wavelength laser diode disclosed in the Japanese Laid-Open Patent Publication 7-249838.
Referring to
FIG. 3
, the laser diode is constructed on a substrate
24
of GaAs and includes, on the substrate
24
, a cladding layer
25
of n-type AlGaInP having a composition (Al
0.6
Ga
0.4
)
0.5
In
0.5
P, an active layer
26
having a quantum well structure formed by an AlGaInP barrier layer and a GaInP quantum well layer, an inner cladding layer
27
of p-type AlGaInP having a composition of (Al
0.6
Ga
0.4
)
0.5
In
0.5
P, an etching stopper layer
28
of p-type GaInP having a composition of Ga
0.5
In
0.5
P, an outer cladding layer
29
of p type AlGaInP having a composition (Al
0.6
Ga
0.4
)
0.5
In
0.5
P, a buffer layer
30
of p-type GaInP having a composition of Ga
0.5
In
0.5
P, and a cap layer
31
of p-type GaAs.
The laser diode is formed with a mesa structure by a wet etching process, wherein the wet etching process is conducted while using an SiN mask formed on the cap layer
31
with a width of 6 &mgr;m, until the etching stopper layer
28
is exposed. After the mesa structure is thus formed, a pair of current-blocking regions
32
of n-type AlInP and a pair of cap regions
33
of n-type GaAs are formed on the mesa surface. Thereby, the current-blocking regions
32
are grown so as to have a composition of Al0.5In0.5P on the part making contact with the mesa surface. After removing the SiN mask, a contact layer
34
of p-type GaAs is formed so as to cover the cap regions
33
, the current-blocking regions
32
and the cap layer
31
on the mesa structure.
In the laser diode of
FIG. 3
, too, the problem of waveguide loss is avoided due to the large bandgap energy of AlInP used for the current-blocking regions
10
. Further, the use of the AlInP current-blocking regions
32
is advantageous in view of the fact that AlInP has a smaller refractive-index as compared with the inner and outer cladding layers of p-type AlGaInP. Thereby, it should be noted that there is f

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