Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-11-28
2004-07-27
Davie, James W. (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06768759
ABSTRACT:
RELATED APPLICATIONS
The present application claims benefit of priority under 35 U.S.C. §119 to the following Japanese patent Applications Nos. 2000-364387 (filed on Nov. 30, 2000) and 2001-360940 (filed on Nov. 27, 2001), each of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a semiconductor laser device and a method for fabricating the same, and more particularly to a so-called buried semiconductor laser device having a higher laser emission efficiency and a higher reproducibility of a current-optical output characteristic.
(b) Description of the Related Art
A semiconductor laser device having a lower threshold current density and a higher laser emission efficiency is desirable. A strained quantum well semiconductor laser device having a hetero-structure and a pair of current blocking layers is attracting public attention because of the excellent characteristics thereof. The semiconductor laser having a pair of current blocking layers in abutment to the semiconductor laser structure is generally called a buried semiconductor laser.
A conventional strained quantum well semiconductor laser device shown in JP-A-8(1996)-288589 will be described referring to FIG.
1
A.
As shown in idealized form in
FIG. 1A
, a conventional strained quantum-well semiconductor laser device
20
includes a layer structure having an n-type InGaP bottom cladding layer
2
, an active layer
3
, and a p-type InGaP top cladding layer
4
, sequentially and epitaxially grown on an n-type GaAs substrate
1
by using a metal organic chemical vapor deposition (MOCVD) method.
The active layer
3
is a five-layered structure including an InGaAsP layer
5
, a GaAs layer
6
, an InGaAs layer
7
, a GaAs layer
8
and an InGaAsP layer
9
.
The top cladding layer
4
, the active layer
3
and the top part of the bottom cladding layer
2
are configured to have a mesa structure
11
. Each of the side surfaces
12
of the mesa structure
11
and the adjacent surfaces of the bottom cladding layer
2
are covered with a p-type InGaP current blocking layer
14
and an n-type InGaP current blocking layer
15
, which are sequentially deposited.
A second p-type InGaP top cladding layer
16
and a p-type contact layer
17
are sequentially deposited on the n-type InGaP current blocking layer
15
, the p-type InGaP current blocking layer
14
and the top cladding layer
4
of the mesa structure
11
.
A p-side metal electrode layer
18
and an n-side metal electrode layer
19
are deposited on the top surface of the p-type contact layer
17
and the bottom surface of the substrate
1
, respectively.
The above publication points out a problem when the p-type current blocking layer
14
and the n-type current blocking layer
15
are grown by using an etching mask. Referring to
FIG. 1B
, structural defects such as hollows and grooves
40
are formed on the n-type current blocking layer
15
along the bottom surface of the etching mask due to the difference between the growth rates.
When the hollows
40
on the n-type current blocking layer
15
are large, crystal dislocations are liable to occur along the lines
41
shown in FIG.
1
B. The propagation of a crystal dislocation from a point within layer
15
to a point within the p-type contact layer
17
increases the threshold current of the fabricated laser device, which lowers the laser emission efficiency.
The above publication describes the growth conditions of the p-type and n-type current blocking layers
14
,
15
such that the substrate temperature is between 750° C., and 800° C. and a mixing ratio (concentration ratio) of a group V element gas with respect to a group III element gas is between 400:1 and 800:1 inclusive (V:III), thereby suppressing the occurrence of the structural defects (e.g., hollows) to decrease the probability and magnitude of the crystal dislocations. (As used later herein, we will abbreviate the conventional notation for the V:III chemical ratios from 400:1 to simply read as “400,” which means the molar amount of the group V element gas divided by the molar amount of group III element gas).
Since the disappearance of the structural defects thickens the n-type current blocking layer
15
in the vertical direction formed overlying the substrate
1
, the amount of leakage current flowing through the current blocking layers
14
,
15
is decreased, which in turn increases the laser emission efficiency when a voltage is applied between the electrodes
18
,
19
.
Further, Mitsubishi Denki Giho (Mitsubishi Electric Advance) Vol. 67, No. 8 (1993), p. 88 points out a decrease of the laser emission efficiency due to a leakage current which does not contribute to the laser emission and which flows along the interface between the mesa structure and the current blocking layer.
The buried semiconductor laser device with the reduced leakage current includes higher laser emission efficiency, good linearities of the higher output characteristic, and an excellent current-voltage characteristic. Accordingly, when the leakage current path width is reduced, the resistance of the current blocking layer increases to provide desirable laser characteristics.
Even when the current blocking layer is formed under the conditions described in the former publication such that the substrate temperature is between 750° C. and 800° C., and the mixing ratio between the group V element gas and the group III element gas is between 400 and 800, the leakage current path width is quite difficult to be formed in a narrower manner with the excellent reproducibility, and the values of the widths are difficult to be regulated and controlled.
Similarly, in the fabrication of the buried semiconductor laser device formed on the p-type substrate, an n-type InP contact layer is excessively grown to be in contact with an n-type InP contact layer, and a leakage current path width is increased.
As a result, the increased leakage current lowers the laser emission efficiency to worsen the output characteristic and the linearity of the current-voltage characteristic, and the buried semiconductor laser device with the higher output can be hardly fabricated with the excellent reproducibility.
SUMMARY OF THE INVENTION
The present invention encompasses buried semiconductor laser devices and methods of manufacturing the same. An exemplary general method according to the present invention comprising forming a mesa structure including a bottom cladding layer, an active layer and a top cladding layer overlying a semiconductor substrate. The mesa structure has at least one side surface extending from the top surface of the mesa toward the bottom cladding layer, with the active layer having an exposed side thereat. The mesa structure also has a skirt surface extending outward from each side surface to cover a portion of the substrate's surface. The exemplary general method further comprising growing a first current-confinement layer on the mesa's at least one side surface, with the first current-confinement layer comprising a semiconductor material and having a first conductivity type (e.g., p-type or n-type). A second current-confinement layer is then grown above at least a portion of the first current-confinement layer, the second current-confinement layer comprising a semiconductor material and having a second conductivity type which is opposite to the first conductivity type. The closest spacing distance between the second current-confinement layer and the active layer defines a “leakage current path width” (e.g., Tn or Tp). This spacing distance is normally shown in a cross-sectional plane which is perpendicular to the top surface of the substrate, and which is oriented to provide the smallest width of the mesa. The first confinement layer is grown at a temperature ranging from 610° C. to 700° C. using a raw material gas comprising a group V element gas and a group III element gas at a molar ratio of the group V element gas with respect to the group III element gas having a value between 50 and 500, inclusive,
Hattori Satoshi
Honkawa Yukio
Ono Takahiro
Sato Yoshihiro
Davie James W.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
LandOfFree
Semiconductor laser device and method for fabricating 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 laser device and method for fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser device and method for fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3232329