Semiconductor laser

A semiconductor laser including a first conductive type of lower clad layer, active layer, a second conductive type of upper first clad layer, the first conductive type of current blocking layer having a stripe shaped open portion, and the second conductive type of upper second clad layer laminated in order on the first conductive type of GaAs substrate, wherein each portion in contact with the lower clad layer, the active layer, the upper first and second clad layer and at least the upper second clad layer of the current blocking layer is composed of a compound semiconductor to be represented by a formula, in which (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P (x is 0<x.ltoreq.1 in the lower and upper first, second clad layers, 0.ltoreq.x<1 in the active layer, a given value y is approximately 0.5 for each layer) within of each range of 0<x.ltoreq.0.75 in the portion in contact with the upper second clad layer of the current blocking layer.

BACKGROUND OF THE INVENTION 
The present invention relates to a semiconductor laser. More particularly, 
the present invention relates to a visual light semiconductor laser using 
a compound semiconductor material of AlGaInP. 
The semiconductor laser using the compound semiconductor material, 
basically manufactured by laminated semiconductor layers having different 
compositions, requires steps of, except a step of semiconductor crystal 
layer growth, grasping etching or the like halfway although depending upon 
the shape thereof. Since the semiconductor wafer has to take out from a 
crystal growing furnace, the frequency of grasping the steps is better to 
be fewer in terms of productivity. Although it is general at present to 
take out the wafer twice halfway from the crystal growing furnace in the 
three continuous crystal growth steps, namely, before the uppermost 
semiconductor layer is completed in crystal growth, semiconductor lasers 
capable of being manufactured only with two steps of continuous crystal 
growing steps are disclosed in, for example, pages 1491 through 1496 
(hereinafter referred to as document) IEEE Journal of Quantum Electronics) 
Volume 27, No. 6, July 1991 or in Japanese Unexamined Patent Publication 
No. 218993/1992. One of the representative semiconductor lasers in the 
above description are shown in FIG. 3 and FIG. 4. 
FIG. 3 shows a semiconductor described in the document, where an n-type of 
AlGaInP clad layer 22, an n-type, a p-type or non-dope of GaInP active 
layer 23, a p-type of AlGaInP clad layer 24, and an n-type of GaAs current 
blocking layer 25 are laminated in order on an n-type of GaAs substrate 
21. 
Then, a stripe shaped groove reaching to the middle of the clad layer 24 
through the current blocking layer 25 is formed, etching these layers. 
Further, a p-type of AlGaInP light guide layer 26, a p-type of AlGaInP 
clad layer 27, a p-type of InGaP layer 28, a p-type GaAs contact layer 29, 
and an AuZn/Au electrode 30 are laminated in order in the layer. AuGe/Au 
electrode 31 is provided on the reverse face to constitute the 
semiconductor laser. 
Also, FIG. 4 shows another example of the conventional semiconductor laser 
described in the Japanese Unexamined Patent Publication No. 218993/1992. 
In the semiconductor laser described in FIG. 4, an n-type of AlGaInP clad 
layer 42, GaInP active layer 43, a p-type AlGaInP clad layer 44, a p-type 
of GaInP etching stop layer 45, a p-type of AlInP shutting in (or 
confining) layer 46, and an n-type GaAs current blocking layer 47 are 
laminated in order on an n-type GaAs substrate 41. Then, the current 
blocking layer 47 and the shutting in layer 46 are etched from the 
surface, forming a stripe shaped stripe groove reaching onto the surface 
of the etching stop layer 45. Further, a p-type of AlGaAs upper clad layer 
48, a p-type of GaAs cap layer 49, and a Cr/Au electrode 50 are laminated 
in order. An Au/Ge/Ni electrode 51 is provided on the reverse face. 
Such a conventional semiconductor laser has a problem in that the surface 
of the GaAs is deteriorated when the substrate temperature is raised under 
the atmosphere of PH.sub.3 gas at the next re-growing time in the use of 
GaAs or the like where an energy band gap is small having a light 
absorbing function as a current blocking layer so that the semiconductor 
crystal layer of the AlGaInP including P cannot be grown again in a good 
crystal condition. 
Also, a larger mixed crystal ratio of Al, for example, AlInP is desired to 
be used in the current blocking layer for provision of light shutting-in 
function without light absorption. There is another problem in that the 
degree of freedom in designing of the semiconductor laser is restricted, 
because better crystal of the AlGaInP to be re-grown cannot be obtained on 
it where the mixed crystal ratio of the Al is big as shown in Table 2 to 
be described later. 
SUMMARY OF THE INVENTION 
An object of the present invention is to settle such problems as described 
hereinabove and further, to provide a semiconductor laser superior in 
characteristics where better crystal is obtained in the case of re-growing 
a second clad layer composed of AlGaInP after the formation of the inner 
stripe type of current blocking layer even in use of any material for 
current blocking layer in accordance with the design object of the 
semiconductor laser. 
The semiconductor laser of the present invention has a first conductive 
type of lower clad layer, active layer, a second conductive type of upper 
first clad layer, the first conductive type of current blocking layer 
having a stripe shaped open portion, and the second conductive type of 
upper second clad layer laminated in order on the first conductive type of 
GaAs substrate. Each portion in contact with the lower clad layer, the 
active layer, the upper first and second clad layer and at least the upper 
second clad layer of the current blocking layer is composed of a compound 
semiconductor to be represented by a formula, in which (Al.sub.x 
Ga.sub.1-x).sub.y In.sub.1-y P (x is 0&lt;x.ltoreq.1 in the lower and upper 
first, second clad layers, 0.ltoreq.x&lt;1 in the active layer, a given value 
y is approximately 0.5 for each layer) within of each range of 
0&lt;x.ltoreq.0.75 in the portion in contact with the upper second clad layer 
of the current blocking layer. 
The first conductive type, and the second conductive type mean that the 
other of the p-type or the n-type is the second conductive type when one 
of the n-type or the p-type is the first conductive type. 
Also, in the current blocking layer, the larger value of x, namely, the 
larger composition of Al in the active layer, is preferable to have a 
function of light shut-in without absorption of the light. 
Also, for easier adjustment of the refractive index as the overall current 
blocking layer in the remaining portion, a portion to be represented by a 
composition formula of the current blocking layer: (Al.sub.x 
Ga.sub.1-x).sub.y In.sub.1-y P (0&lt;x.ltoreq.0.75, y is approximately 0.5) 
is preferable to be a semiconductor layer 300 .ANG. or lower. 
Further, it is preferable in terms of an object of having the light 
absorbing function that the current blocking layer contains the 
semiconductor layer composed of GaAs within the layer. 
According to the semiconductor laser of the present invention, a 
semiconductor laser superior in characteristics is obtained because of 
such construction as composed of semiconductor having Al composition of 
0&lt;x.ltoreq.0.75 in the composition formula: (Al.sub.x Ga.sub.1-x).sub.y 
In.sub.1-y P in at least the uppermost face of the current blocking layer, 
because crystal property of epitaxial layer to be re-grown on it after the 
etching of the current blocking layer or the Al composition in the 
re-growth semiconductor layer is selectable freely. 
Also, the uppermost layer is made 300 .ANG. or lower in thickness so that 
1/10 or lower of the overall current blocking layer in thickness. The 
degree of freedom in designing the semiconductor laser is expanded 
independently of influences upon the refractive index or the like as the 
current blocking layer.

DETAILED DESCRIPTION 
A semiconductor laser of the present invention will be described 
hereinafter according to one preferred embodiment of the present 
invention. FIG. 1(a), FIG. 1(b), FIG. 1(c) and FIG. 1(d) are sectional 
illustrating views of a first embodiment of the semiconductor laser of the 
present invention in accordance with the manufacturing steps. 
In the step of FIG. 1(a), each layer of an n-type of (Al.sub.s 
Ga.sub.1-s).sub.y In.sub.1-y (0.4.ltoreq.s.ltoreq.1.0, y is approximately 
0.5 which is a ratio where a lattice matching is obtained with respect to 
the GaAs substrate. Hereinafter, representation of y is omitted), a first 
conductive type of lower clad layer 2 (for example, s=0.5, approximately 
1.times.10.sup.18 /cm.sup.3 in carrier concentration, approximately 1.2 
.mu.m in thickness, Se dope), on the surface of, for example, an n-type of 
GaAs substrate 1, a non-dope or an n-type or a p-type of Al.sub.u 
Ga.sub.1-u InP (0.ltoreq.u.ltoreq.0.4, u&lt;s) active layer 3 (for example, 
u=0, approximately 0.07 .mu.m in thickness), a second conductive type of 
upper first clad layer 4 of, for example, a p-type of Al.sub.s Ga.sub.1-s 
InP (for example, s=0.5, approximately 1.times.10.sup.18 /cm.sup.3 in 
carrier concentration, approximately 0.2 .mu.m in thickness, Be dope), an 
n-type of AlInP first current blocking layer 5a (for example, 
2.times.10.sup.18 /cm.sup.3 in carrier concentration, approximately 0.3 
.mu.m in thickness, Se dope), and a second current blocking layer 5b of an 
n-type Al.sub.t Ga.sub.1-t InP (0&lt;t.ltoreq.0.75) (for example, t=0.5, 
approximately 2.times.10.sup.18 /cm.sup.3 in carrier concentration, 
approximately 0.03 .mu.m in thickness, Se dope) is lattice matched on the 
n-type GaAs substrate 1 and grown in crystal in order by a MOVPE (metal 
organic vapor phase epitaxy) method. 
The semiconductor laser of the present invention has the upper first clad 
layer 4, the first and second current blocking layers 5a, 5b formed of a 
material larger than the energy band gap in the active layer 3 in the 
energy band gap. Thus, the luminous efficiency can be raised, because the 
absorption of the light in the upper first clad layer 4 and the current 
blocking layer 5 can be prevented. An adjustment operation as a material 
large in the energy band gap can be effected, because the energy band gap 
becomes larger as the amount of Al (or X) is larger if the Al.sub.x 
Ga.sub.1-x InP is used as the semiconductor. When the Al.sub.u Ga.sub.1-u 
InP is used as the active layer, large mixed crystal ratio of Al such as 
AlInP or the like can be used. 
In the step of FIG. 1(b), the substrate is taken out from the growth 
chamber. In the photo resist step, a master pattern of, for example, 
approximately 3 .mu.m in width is formed. The substrate is etched from the 
surface in width, and a stripe shaped groove reaching to the upper first 
clad layer 4 is formed. As an etchant, for example, HCl:H.sub.2 O=1:2 
(25.degree. C.) is used to effect the etching operation for about 30 
seconds. The etchant may be a mixed liquid among HCl, HNO.sub.3 and 
H.sub.2 O. 
The selection etching of the current blocking layer is easier to operate as 
shown from data shown in Table 1, because the Al composition of the 
current blocking layer in the present invention is larger than the Al 
composition of the upper first clad layer. 
Namely, the current blocking layer 5 to be etched by the etchant can be 
effected easily with better reproducibility, because the selection ratio 
with respect to the upper first clad layer whose surface is exposed by the 
etching is near 10 as shown in Table 1. Therefore, the semiconductor laser 
which is better in reproducibility and is suitable for mass production is 
obtained. 
TABLE 1 
______________________________________ 
Etching velocity of (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P (T = 
25.degree. C.) 
HCl:H.sub.2 O 
x 1:1 1:2 1:4 
______________________________________ 
0 600.ANG./min 
0.ANG./min 0.ANG./min 
0.2 1600.ANG./min 
60.ANG./min 
0.ANG./min 
0.5 10800.ANG./min 
900.ANG./min 
150.ANG./min 
at least 
0.75 5 .mu.m/min 8300.ANG./min 
1500.ANG./min 
at least at least 
1.0 5 .mu.m/min 5 .mu.m/min 
12300.ANG./min 
______________________________________ 
Then, in the step of FIG. 1(c), the substrate is introduced again to the 
MOCVD apparatus through the removing, and washing of the resist film 10. 
The p-type Al.sub.s Ga.sub.1-s InP upper second clad layer 6 (for example, 
s=0.5, approximately 1.times.10.sup.18 /cm.sup.3 in carrier concentration, 
approximately 1.0 .mu.m in thickness, Be dope), and a p-type of GaAs cap 
layer 7 (for example, approximately 2.times.10.sup.19 /cm.sup.3 in carrier 
concentration, approximately 1.6 .mu.m in thickness) are grown in crystal 
on all the surface. 
There is found out upon eager consideration for improving the crystal 
property of the upper second clad layer 6 to be grown epitaxially on the 
current blocking layer 5 that (Al.sub.s Ga.sub.1-s)InP to be laminated on 
it is re-grown again in a good condition by the restriction of the Al 
composition of the current blocking layer to a certain ratio or lower. 
Namely, the result of the crystal property investigated through the change 
in the Al composition (t and s) is shown in Table 2, where the crystal 
property at the re-growth time of (Al.sub.s Ga.sub.1-s)InP on the 
(Al.sub.t Ga.sub.1-t)InP is usable if t.ltoreq.0.75 and more preferably 
t.ltoreq.0.5. 
TABLE 2 
______________________________________ 
Surface state of (Al.sub.s Ga.sub.1-s).sub.0.5 In.sub.0.5 P re-grown on 
(Al.sub.t Ga.sub.1-t).sub.0.5 In.sub.0.5 P 
re-grown 
t 0 0.2 0.5 0.75 1.0 
______________________________________ 
0 .smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
0.2 .smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
0.50 .smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.increment. 
0.75 .increment. 
.increment. 
.increment. 
.increment. 
x 
1.0 x x x x x 
______________________________________ 
.largecircle.: There are few defects, the half-value width of X-ray is 
narrow and crystal property is good. 
.DELTA.: There are some defects, but the half-value width of X-ray is 
narrow and crystal property is good. 
x: There are many defects, the half-value width is wide and crystal 
property is not good. 
Also, the carrier concentration is made higher so that the thickness of the 
current blocking layer 5 can be made as comparatively thin as 0.2 .mu.m 
through 0.4 .mu.m, and the stage difference may be made smaller, thus 
making it hard to have defects during the re-growth time. By the use as a 
p-type dopant of Be where change in adherence amount by the substrate 
temperature is comparatively smaller, elements of low operating voltage 
may be manufactured with better reproducibility. 
Further, since in the present invention, the semiconductor of AlGaInP all 
on the surface at the re-growth step time is not a semiconductor of GaAs 
after the etching step has been carried out halfway, the substrate 
temperature can be raised under phosphine (PH.sub.3) gas atmosphere. In 
this case, better re-grow can be carried out without deterioration of the 
surface. 
When bis(methylcyclopentadienyl)berylium (CH.sub.3 C.sub.5 H.sub.4).sub.2 
Be is used as metal organic metal for feeding Be of the p-type of dopant, 
the substrate temperature hardly changes even at 600.degree. through 
650.degree. C. in the epitaxy growth of, for example, GaS. When dimethyl 
zinc (DMZn) is used with Zn as a p-type of dopant as before, considerable 
improvement is provided as compared with one few-th in the carrier 
concentration in the temperature zone. 
Finally, in the step of FIG. 1(d), the n-type of GaAs substrate 1 is 
polished from the reserve face. In the steps up to FIG. 1(c), the overall 
thickness including the semiconductor layer laminated on the surface of 
the substrate 1 is made approximately 60 .mu.m. For example, Ti/Au is 
formed on the surface of the substrate 1, and for example, laminated ohmic 
electrodes 8, 9 are respectively formed on the reverse face to cleave for 
chipping. 
A second embodiment of the semiconductor laser of the present invention 
will be described hereinafter with the use of FIG. 2. The semiconductor 
laser in the second embodiment is same in sectional construction except 
for difference in the number of the semiconductor layers for constituting 
the current blocking layer although there is some difference with respect 
to the above described first embodiment in thickness of each layer and the 
composition. The like parts are designated by like reference numerals in 
FIG. 1 and FIG. 2. 
In the step of FIG. 2(a), each layer of an n-type (Al.sub.s 
Ga.sub.1-s).sub.y In.sub.1-y P(0.4.ltoreq.s.ltoreq.1.0, y is approximately 
0.5 which is a ratio where the grid matching is effected to GaAs 
substrate. Hereinafter, representation of y is omitted) first conductive 
lower clad layer 2, on the surface of, for example, an n-type GaAs 
substrate 1, a first conductive lower clad layer 2 (for example, s=0.5, 
approximately 1.times.10.sup.18 /cm.sup.3 in carrier concentration, 
approximately 1.2 .mu.m in thickness, Se dope), a non-dope or an n-type or 
a p-type of Al.sub.u Ga.sub.1-u InP (0.ltoreq.u.ltoreq.0.4, u&lt;s) active 
layer 3 (for example, u=0, approximately 0.07 .mu.m in thickness), a 
second conductive type of upper first clad layer 4 of, for example, a 
p-type of Als Ga1-s InP (for example, s=0.5, approximately 
1.times.10.sup.18 /cm.sup.3 in carrier concentration, approximately 0.2 
.mu.m in thickness, Be dope), an n-type Al.sub.p Ga.sub.1-p InP 
(0&lt;p.ltoreq.0.75) first current blocking layer 5a (for example, p=0.75, 
approximately 2.times.10.sup.18 /cm.sup.3 in carrier concentration, 
approximately 0.1 m in thickness, Se dope), an n-type GaAs second current 
blocking layer 5b (approximately 5.times.10.sup.18 /cm.sup.3 in carrier 
concentration, approximately 0.2 .mu.m in thickness, Se dope), and an 
n-type Al.sub.q Ga.sub.1-q InP (0&lt;q.ltoreq.0.75) third current blocking 
layer 5c (for example, q=0.5, 2.times.10.sup.18 /cm.sup.3 in carrier 
concentration, approximately 0.03 .mu.m in thickness, Se dope), are grid 
matched on the n-type GaAs substrate 1 and grown in crystal in order by a 
MOVPE (metal organic vapor phase epitaxy) method. 
Then, in the step of FIG. 2(b), the substrate is taken out from the growth 
chamber. In the photoresist step, a mask pattern of, for example, 
approximately 4 .mu.m is formed. For example, HCl:H.sub.2 O=1:2 
(25.degree. C.) is used as an etchant. The third current blocking layer 5c 
is removed by approximately 30 seconds' etching. Since the GaAs cannot be 
etched in the liquid, the H.sub.2 SO.sub.4 etchant is used. The 20 
second's etching is effected with the use of HCl:H.sub.2 O=1:2 (25.degree. 
C.) again so as to selectively remove the first current blocking layer 5a. 
In accordance with the steps (c), (d) of the contents the same as those of 
the first embodiment, the semiconductor laser can be obtained. Even in the 
second embodiment, the substrate temperature can be raised under the 
PH.sub.3 gas atmosphere so that the semiconductor layer surface is not 
deteriorated, because Al.sub.q Ga.sub.1-q InP covers without exposure of 
GaAs onto the surface when the upper second clad layer 6 is grown at the 
step of the (c). 
According to the present invention, even in the semiconductor laser for 
using as the current blocking layer a material higher in mixed crystal 
ratio of Al such as AlInP or the like where the light shutting-in function 
is provided in the current blocking layer and the characteristics of the 
low operating current is obtained, the AlGaInP series semiconductor 
crystal can be better in re-growth, thus improving the productivity. 
Since the AlGaInP material is laminated on the GaAs as the current blocking 
layer even in a waveguide type of low noise semiconductor laser of an 
anti-refractive index having a proper light absorption function, better 
crystal can be re-grown without roughing the substrate surface even in the 
rise in the temperature under the PH.sub.3 gas atmosphere without exposure 
of the GaAs onto the substrate surface in the re-growth time. As a result, 
a highly efficient semiconductor laser of an intermediate type between the 
refractive index guide wave and the gain guide wave by the covering of the 
above with Al.sub.q Ga.sub.1-q InP (0&lt;q.ltoreq.0.75) with the GaAs in the 
current blocking layer even in the semiconductor laser using the AlGaInP 
semiconductor in the luminous portion. 
Though several embodiments of the present invention are described above, it 
is to be understood that the present invention is not limited only to the 
above-mentioned and various changes and modifications may be made in the 
invention without departing from the spirit and scope thereof.