[0001] This invention relates to a novel semiconductor laser device. It provides a semiconductor
laser device in which longitudinal and transverse modes are stabilized.
[0002] Semiconductor laser devices have many merits such as small size, operation at high
efficiency, and capability of direct modulation by a drive current. There are therefore
hopeful as light sources for optical communication, optical information processing
etc.
[0003] Among various semiconductor lasers, the distributed-feedback semiconductor laser
has a corrugated surface therein. It achieves mode stabilization by exploiting a sharp
oscillation mode selectivity which is produced by the diffraction effect of light
based on the corrugated surface.
[0004] The distributed-feedback semiconductor laser devices have been reported in detail
in "Appl. Phys. Lett.," vol. 27, pages 403 to 405, October 1975, by M. Nakamura et
al., and in "IEEE J. Quantum Electron.," vol. QE-12, pages 597 to 603, October 1976,
by K. Aiki et al. A typical example of the distributed-feedback semiconductor laser
is disclosed in U.S. patent application Serial No. 512,969.
[0005] Figs. 1 and 2 of the accompanying drawings show an example of the distributed-feedback
semiconductor laser device. Fig. 1 is a sectional view taken orthogonally to the travelling
direction of light, while Fig. 2 is a sectional view taken along the travelling direction
of light. Here, numeral 1 designates an n-GaAs substrate, numeral 2 an n-Ga
1 -xAl
xAs layer (x ≃0.3), numeral 3 a GaAs active layer, numeral 4 a p-Ga
1-xAl
xAs layer, and numeral 5 periodic corrugations which are provided at the boandary between
the semiconductor layer 3 and the semiconductor layer 4. Numerals 6 and 7 indicate
ohmic electrodes. The layers 2, 3 and 4 constitute an optical waveguide. Light given
forth in active layer 3 is guided centering around the layer 3, and is subjected to
the Bragg reflection of 130° by the periodic corrugations 5 formed at the boundary
between the layers 3 and 4.
[0006] The distributed-feedback semiconductor laser device oscillates at a single longitudinal
mode and exhibits a spectral width of 0.5 Å or less, so that it is excellent in monochromaticity.
In addition, the temperature-dependency of the osicllation wavelength is low.
[0007] Even in the distributed-feedback semiconductor laser device controlled to the single
longitudinal mode, nowever, the generation of excess optical noise especially for
a modulated signal due to transverse mode instability is not avoided yet.
[0008] On the other hand, the buried heterostructure semiconductor laser device has been
proposed as a typical semiconductor laser device. In this case, there has also been
proposed a structure provided with an optical waveguide which produces the effect
of confining lateral carriers and light in the direction of the thickness of an active
layer. An example of the buried heterostructure semiconductor laser device of this
sort is described in U.S. patent application Serial No. 786,758.
[0009] Even in the buried heterostructure semiconductor laser devices oscillating at a single
transverse mode, however, the generation of the excess optical noise due to mode competition
is not avoided.
[0010] This invention has for its object to provide a novel semiconductor laser device in
which a longitudinal and transverse mode is stabilized singly and in which any excess
optical noise component for a modulated signal is not generated by mode competition.
[0011] In order to accomplish the object, a structure as stated below is employed. A first
semiconductor layer is disposed, and second and third semiconductor layers which are
greater in the band gap and lower in the index of refraction than the first semiconductor
layer are disposed in a manner to sandwich the first semiconductor layer therebetween,
whereby a double-heterostructure is constructed. With this structure, light is confined
in the vinicity of the active layer.
[0012] A substrate semiconductor on which the respective semiconductor layers are not carried
is naturally prepared. In some cases, a semiconductor layer or layers are further
stacked besides the semiconductor layers constituting the double-heterostructure.
Anyway, however, the basic optical confinement is effected by the structure as described
above. Subsequently, that region of at least one of the second and third semiconductor
layers which is remote from the first semiconductor layer is made a semiconductor
layer which corresponds substantially to a radiation region and which functions as
a light non-absorptive region in the shape of a stripe. Further, a semiconductor layer
is disposed which has portions lying on both sides of the semiconductor layer remote
from the first semiconductor layer and which makes a complex refractive index for
laser light discontinuous at both ends of the semiconductor layer remote from the
first semiconductor layer. Periodic corrugations which intersect orthogonally to the
lengthwise direction of the stripe-shaped light non-absorptive region are formed in
at least one interface among the aforesaid semiconductor layers.
[0013] Preferred embodiments of the invention will now be described with reference to the
drawings, in which:
Figs. 1 and 2, which have been referred to above, are sectional views of a distributed-feedback
semiconductor laser device of a prior art structure, which arc respectively taken
perpendicularly to, and along, the travelling direction of light;
Fig. 3 is a perspective view of a semiconductor laser device according to this invention;
Fig. 4 is a graph showing the relationship between the groove width and the distance
from an active layer to a light absorptive region;
Figs. 5 to 8 are diagrams showing the states of generation of excess optical noise
ascribable to mode competition in various semiconductor laser devices;
Figs. 9 and 10 are sectional views of a device of another embodiment of this invention,
which are respectively taken perpendicularly to, and along, the travelling direction
of light;
Fig. 11 is a graph showing the light output versus current characteristics of one
embodiment of the present invention;
Fig. 12 is a graph showing far-field intensity distributions in the junction plane;
Fig. 13 shows the lasing spectra of one embodiment of the present invention operating
under d.c. bias;
Fig. 14 shows the pialse response of one embodiment of the present invention at different
excitation levels; and
Figs. 15 and 16 are sectional views of devices of further embodiments of this invention
as taken perpendicularly to the travelling direction of light.
[0014] This invention will be described in detail with reference to a typical example. Fig.
3 is a perspective view of the typical example of this invention.
[0015] On an n-GaAs substrate 1 formed with a groove 9; an n-Ga
1-xAl
xAs (x = 0.3) layer 2, a GaAs active layer 3 and a p-Ga
1-yAl
yAs (y ≃ 0.3) layer 4 are successively formed by the well-known liquid-phase epitaxy.
The upper surface of the semiconductor layer 4 is formed with periodic corrugations
8. Numerals 6 and 7 designate ohmic electrodes.
[0016] In the present structure, light generated in the active layer 3 is confined in the
vertical direction around the active layer by the double-heterostructure Part of the
light evanesces to the GaAlAs layers 2 and 4 on both the sides. The light having evanesced
to the GaAlAs layer 2 reaches the GaAs substrate 1 in regions on both the sides of
the groove 9 because the n-Ga
1-xAl
xAs layer 2 in these regions is thin. In consequence, the complex refractive-index
for the light becomes different between the region corresponding to the groove 9 and
the regions corresponding to both the sides of the groove 9. For this reason, any
higher-order mode oscillation spreading to outside of the groove and the deviation
of the oscillation region are suppressed, and the effect that the light is stably
confined only to the region of the groove 9 in the lateral direction is produced.
[0017] On the other hand, the periodic corrugations 8 are provided at the interface between
the semiconductor layers 4 and 5. Therefore, the effective complex refractive-index
n for the light given forth in the active layer 3 varies periodically in the travelling
direction of the light. n
e can approximately be expressed as follows:
with i = 1, 2, 3,...
[0018] The travelling direction of the light is taken in the z-direction.
[0019] Therefore, the laser light is diffracted, and
where X: wavelength of the light, n : effective refractive index of waveguide, A:
period of the corrugations and a order of the diffraction. By fulfilling the condition,
the light is subjected to the Bragg reflection at 180°. Accordingly, the light is
confined in the waveguide, and the laser oscillation becomes possible.
[0020] In the above, the fundamental operation of the semiconductor laser of this invention
has been explained. In order to reallse the semiconductor laser intended by this invention
wherein a longitudinal and transverse mode is stabilized, especially any excess optical
noise com- ponenet for a modulated signal is not generated by mode competition, a
construction as described below is required.
[0021] The width of the stripe-shaped light non-absorptive region corresponding substantially
to the radiation region is made 2 um to 8 um. With widths below 2 um, especially the
threshold current density (the lowest current density necessary for attaining the
laser oscillation) increases rapidly. With widths above 8 µm, especially the instability
of the transverse mode increases.
[0022] As to the quantity of evanescence of the light to the regions which exist on both
sides of the light non-absorptive region and which make the complex refractive index
for the laser beam discontinuous, at least 3 x 10
-2% of the whole quantity of the light, preferably 5 x 10
-2% to 5 x 10 % of the same is appropriate. Thus, the absolute value of the index different
|An| in both the regions is preferably made 10
-3 to 10
-2. When the quantity of evanescence of the light is too small, especially the effect
of confinement in the lateral direction is unsatisfactory. On the other hand, when
the quantity of evanescence of the light is too large, the quantity of absorption
of the light increases, and the increase of the thrreshold current density is incurred.
Therefore, the thickness d of the active layer 3 and the thickness t of the semiconductor
layer 2 need to be selected. The thickness of the active layer is ordinarily set at
0.05 µm to 0.15 µm. When the thickness d of the active layer is 0.1 µm, it is favorable
to make the thickness t at most 0.5 µm; when the thickness d is 0.15 µm, it is favorable
to make the thickness t at most 0.2 µm; when the thickness d is 0.05 µm, it is favorable
to make the thickness t at most 0.7 µm. Regarding any intervening thickness of the
active layer, the thickness of the semiconductor layer 2 may be set by the interpolation
with the aforecited values.
[0023] On the other hand, the distance c between the active layer 3 and the periodic corrugations
8 which are provided at the interface between the semiconductor layers 4 and 5 is
made at most 1 µm, preferably at most 0.5 µm, and at least 0.03 µm. When the distance
c is below 0.03 µm, the carrier confinement effect owing to the semiconductor layer
4 becomes insufficient, and an increase of the threshold current density is incurred.
When the distance c is above 1 µm, the degree to which the radiation in the active
layer senses the periodic corrugations decreases abruptly, so that the laser oscillation
of the distributed feedback type does not take place.
[0024] The depth L of the corrugations is desirably selected in a range of 0.01 µm to 0.5
µm. When the depth L is less than 0.01 µm, the Bragg reflection of the light owing
to the periodic corrugation structure becomes insufficient, and the laser oscillation
of the distributed feedback type becomes difficult. Even when the depth L is selected
to be greater than 0.5 µm, the light is distributed in a limited range centering around
the active layer, so that the intensity of the Bragg reflection becomes substantially
constant and the effect based on the increase of the depth L diminishes.
[0025] In the above, the fundamental concept of this invention has been described in connection
with the typical example of this invention illustrated in Fig. 3.
[0026] Various modifications can be contrived as to how the light non-absorptive region
in the vicinity of the active layer and the retions situated on both the sides of
the non-absorptive region for making the complex refractive index for the laser beam
discontinuons are provided, at which interface among the stacked semiconductor layers
the periodic corrugation is provided at, etc. By way of example, the semiconductor
layer corresponding to the semiconductor substrate 1 in Fig. 3 may consist of a plurality
of layers. It is also allowed to form a separate semiconductor layer on the semiconductor
substrate and to provide a recess in tne semiconductor layer, the recess being used
as the groove 9 in Fig. 3. The purpose can be achieved even when a discontinuity in
only the refractive index (corresponding to the real part of the complex refractive
index) is produced. In any case, however, the technical items previously described
may be conformed with.
[0027] Although, in examples to be stated later, a GaAs-GaAlAs conductor will be referred
to as a semiconductive material, it is obvious that the present invention concerns
the property of a laser resonator including an optical waveguide and that it is independent
of materials. This invention is accordingly applicable, not only to semiconductor
lasers employing the above-mentioned semiconductor, but also to semiconductor lasers
employing e.g. a ternary system compound semiconductor such as GaInP, GaAsP and GaAlSb
and a quaternary system compound semiconductor such as GaInAsP and GaAlAsSb.
[0028] Hereunder, this invention will be described more in detail in connection with examples.
Example 1:
[0029] Description will be made with reference to Fig. 3. In an n-GaAs substrate 1 (Te-doped,
electron concentration n 1 x 10
18/cm
3) having the (100) face as its surface, a groove 9 having a depth of 1.5 µm and a
desired width in the range of 2 µm to 8 µm was formed in the (011) orientation. In
the formation, the conventional photolithography may be employed. As an etching mask,
photoresist was directly used. The chemical etching was conducted at 20°C for about
140 seconds with a mixed solution which contained phosphoric acid, hydrogen peroxide
solution and ethylene glycol at 1: 1 : 3.
[0030] On the resultant substrate 1, an n-Ga
1-xAl
xAs layer 2 (x = 0.3, electron concentration
n ≃ 5 x 1017 cm-3) being 0.3 µm thick, a GaAs layer 3 being 0.1 µm thick, and a p-Ga1-yAlyAs layer 4 (y = 0.3, hole concentration
p = 5 x 1017 cm-3) being 0.2 µm thick, were continuously grown by the conventional liquid-phase epitaxy
employing a slide boat.
[0031] As regards the GaAlAs system material, it is common to employ Ga
1-zAl
zAs (0 < z < 0.3) for the first semi- conductor layer, Ga
1-xAl
xAs (0.1 ≤ x ≤ 0.9) for the second semiconductor layer and Ga
1-Al As (0.1 < y ≦ 0.9) for the third semiconductor layer, where x, y, > z; r > z; and
y ≠ r.
[0032] Subsequently, corrugations 8 having a period of 3,700 Å and a depth of 1,500 Å were
formed in the surface of the semiconductor layer 4. In forming the corrugations, holographic
photolithography employing a laser beam and chemical etching were used. More specifically,
a film of the positive type photoresist as was 800 Å thick was formed on the surface
of the semiconductor layer 4. Subsequently, using an Ar laser at a wavelength of 4,579
Å] an interference fringe was formed on the photoresist. After completing exposure,
development was carried out for about 1 min with a mixed solution consisting of a
developer and water at 1 : 1. In this way, a diffraction grating made of the photoresist
was formed. The diffraction grating made of the photoresist was used as a mask, and
a mixed solution consisting of phosphoric acid, a solution of hydrogen peroxide and
ethylene glycol at 1 : 1 : 8 was used as an etchant. Periodic corrugations 8 having
a depth of 0.15 µm were formed by the etching at 20°C for 80 seconds. This method
is disclosed in Japanese Laid-Open Patent Application No. 111344/1976.
[0033] Subsequently, a p-Ga
1-Y Al
yAs layer
5 (γ = 0.1 and 17 in general, 0.05 < y ≤ 0.9; hole concentration p = 5 x 10
17 cm
-3) was formed to a thickness of 2.0 µm by employing the conventional liquid-phase epitaxial
growth again. Zn was diffused into a desired region of the p-side surface of the specimen
thus formed, whereupon Cr and Au were deposited by vacuum-evaporation so as to form
an electrode. The substrate side was lapped down to about 150 µm, whereupon Au-Ge-rJi
was brought into close contact to form an electrode. The laser length was made 300
µm.
[0034] As a result, when the groove width was 7 µm, the laser device oscillated at a threshold
value of 110 mA and a wavelength of 8,300 Å, and each of longitudinal and transverse
modes was single and stable. Any excess optical noise otherwise generated by mode
competition was not noted.
[0035] It is as previously stated that, in the present structure the width W of the groove
9, the thickness t of the semiconductor layer 2, the thickness d of the active layer
3, the distance C between the active layer and the periodic corrugations, the depth
L of the periodic corrugations, etc. have influence on the oscillation characteristics.
[0036] Fig. 4 shows the characteristics of semiconductor lasers employing various combinations
between the width W of the groove 9 and the thickness t of the semiconductor layer
2. While values of 0.05 µm to 0.15 µm are often employed as the thickness d of the
active layer 3, a value of 0.1 µm is given as a typical example. The depth L of the
periodic corrugations is 1,500 Å. Mark O indicates an example in which the laser device
oscillated in a single mode longitudinally and transversely without any optical noise,
mark A an example in which the laser device oscillated in a single longitudinal mode,
but excess optical noise was generated by mode competition, and mark X an example
in which the laser device did not reach the continuous oscillation on account of the
increase of the threshold current density.
[0037] From the results, it is understood that the width W of the groove 9 capable of achieving
the object is 2 µm to 8 µm. Regarding the thickness t of the semiconductor layer 2,
a value of 0.05 µm or less is the limit to which the layer can be stably fabricated
in the actual process, while a value of 0.45 µm or greater falls in a region in which
a desired light absorption was not attainable.
[0038] Figs. 5 to 8 illustrate the states of generation of excess optical noise attributed
to mode competition. A square wave signal current having a pulse width of 8 ns, a
pulse height of 160 mA (1.25 times a threshold value) and a recurrence frequency of
62.5 MHz was caused to flow through a semiconductor laser device having a threshold
current of 130 mA, and the optical output of the semiconductor laser was observed.
The optical output waveform is a result obtained by conversion into an electric signal
with a photodiode of which the wavelength band was the oscillation wavelength ±1 Å
and the frequency band was 1 MHz to 0.8 GHz. Fig. 5 shows an example of the optical
output waveform of the distributed-feedback semiconductor laser device exemplified
in Fig. 1, Fig. 6 shows an example of the optical output waveform of a prior art buried
heterostructure semiconductor laser device, Fig. 7 shows an example of the optical
output waveform of the semiconductor laser device of this invention, and Fig. 8 shows
an example of the optical output waveform of a semiconductor laser device which has
a structure similar to that of this invention but whose stripe-shaped non-absorptive
region is as broad as 12 pm. It is apprehended from the observation of the optical
output waveforms that the semiconductor laser device of this invention is excellent.
[0039] The semiconductor laser device of the structure of this example is advantageous in
that the deterioration is especially little and that the transverse mode is more easily
stabilized. This originates in that the periodic corrugations can be formed after
forming the active layer
Example 2:
[0040] Description will be made with reference to Figs. 9 and 10.
[0041] In the (011) orientation of an n-GaAs substrate 21 (Te-doped, electron concentration
n ≃ 1 x 10
18/cm
3) having the (100) face as its surface, a groove 29 having a depth of about 1.5 µm
and a desired width in a range of 2 µm to 8 µm was formed by the conventional photolithography
and chemical etching. Photoresist was used for an etching mask. The chemical etching
was conducted at 20°C for about 140 seconds with a mixed solution which consisted
of phosphoric acid, hydrogen peroxide silation and ethylene glycol at 1 : 1 : 3.
[0042] On the resultant substrate 21, an n-Ga
1-sAl
sAs layer 30 ( s = Q.07, and in general, 0.1 < s ≦ 0.9; Sn- doped; electron concentration
n = 5 x 10
17/cm
3) was grown to a thickness of 2.0 µm so as to fill up the groove flatly (to the extent
that the thickness was about 0.5 µm outside the groove) by the conventional liquid-phase
epitaxial growth employing a slide boat.
[0043] Subsequently, the surface of the grown layer was subjected to the chemical etching
until the substrate 21 was exposed on both sides of the groove. The chemical etching
was carried out at 20°C for about 70 seconds by the use of phosphoric acid, hydrogen
peroxide solution and ethylene glycol at 1 : 1 : 3.
[0044] Subsequently, corrugations 28 having a period of 3,750 Å were formed in the direction
orthogonal to the groove (in the (011) orientation) by the holographic photolithography
employing a laser beam and the chemical etching. As a mask at this time, photoresist
being about 800 Å thick was used. A mixed solution consisting of phosphoric acid,
a solution of hydrogen peroxide and ethylene glycol at 1 : 1 : 8 was employed as an
etchant, and the etching was conducted at 20°C for 80 seconds. As a result, the corrugations
28 being 0.15 µm deep were formed in the crystal surface.
[0045] Subsequently, an n-Ga Al
xAs layer 22 (x = 0.3; Sn- doped; electron concentration n ≃ 5 x 10
17 cm ) being 0.4 µm thick, an n-Ga
-zAl
zAs active layer 23 (z ≃ 0.05; undoped;
n = 1 x 10
16 cm
-3) being 0.1 µm, a p-G
1-xAl
xAs layer 24 ( x ≃ 0.3, Ge-doped; hole concentration p = 10
17 cm
-3) being 2 µm thick, and a p-GaAs layer 25 (Ge-doped; hole concentration p = 5 x 10
17 cm
-3) being 1 µm thick were successively grown by employing the conventional liquid-phase
epitaxial growth with the slide boat again.
[0046] Here, the Al contents of the respective layers must be so set that, with respect
to light produced in the active layer 23, the substrate 21 becomes an absorptive region,
while the stripe-shaped buried layer 30 becomes a non-absorptive region. The composition
ratio totwen the Ga
1-sAl
sAs layer 30 and the Ga
1-zAl
zAs layer 23 is made z < s, and it is desirable that (s - z) is approximately 0.01
or greater. On the other hand, the Al content s of the semiconductor layer 30 may,
in principle, be made 0.01 < s < 0.9. However, s < 0.1 must be held in order that
the crystal may be smoothly grown on this layer by the liquid-phase epitaxial growth
generally employed. When s > 0.1, the normal liquid-phase growth becomes difficult
in practice. As described above,(s - z) should desirably be approximately 0.01 or
greater. Therefore, even in case where the active layer 23 is made a GaAs (z = O in
Ga
1-zAl
zAs) layer it is necessary that s ≥ 0.01, and the lower limit value of s becomes 0.01.
[0047] Zn was diffused into the p-side surface of this specimen by approximately 0.1 µm,
whereupon Cr and Au were deposited by vacuum-evaporation so as to form an electrode
27. The substrate side was lapped down to approximately 150 µm, whereupon Au-Ge-Ni
was evaporated to form an ohmic electrode 26.
[0048] Fig. 11 is a graph showing the light output versus current characteristics of this
embodiment, while Fig. 12 is a graph showing the far-field intensity distributions
in the junction plane. The results were obtained in an example in which the semiconductor
laser device had a length of 300 µm and a groove width of 7 µm. The threshold current
value was 100 mA at room temperature, and the external differential quantum efficiency
was about 35%. Fig. 11 corresponds to the light output versus current characteristics
at this time. As apparent from the Figure, the laser oscillated in the fundamental
transverse mode, and the transverse mode was stable up to above double the threshold
value.
[0049] Fig. 13 shows the lasing spectra of the embodiment. The oscillation arose at a wavelength
of 8,360 Å, and even when the current value was increased double the threshold value,
no change was noted. Fig. 14 shows the pulse responses at the time when current pulses
having a width of 7 ns were impressed on the present laser device. Since the transverse
mode was stabilized, the relaxation oscillation to become an optical noise as observed
in the prior art distributed-feedback semiconductor laser was not noted.
Example 3:
[0050] Fig. 15 concerns another embodiment of this invention, and is a sectional view taken
perpendicularly to the travelling direction of light within a laser. In the present
element, corrugations 28 were formed on only the surface of a layer 30 grown in a
groove. The other features were the same as in the case of Fig. 9. In this example,
the feedback of light owing to the diffraction effect is selectively attained only
in the upper part of the groove, and the lasing occurs concentratedly in this part.
Therefore, the transverse mode is further stabilized. In case where the thickness
of the active layer 23 was 0.1 µm and where the thickness of the layer 22 was 0.3
µm, the laser oscillated in the fundamental transverse mode up to triple the threshold
value. Any excess optical noise for a modulated signal at the time of modulation as
otherwise generated by mode competition was not noted.
Example 4:
[0051] Fig. 16 is a sectional view showing another embodiment of this invention. In the
present laser device, an n-Ga
1-yAl
yAs layer 33 was grown on the whole surface of an n-GaAs substrate 21 in a manner to
fill up the groove of the substrate, and corrugations 34 were formed thereon. The
other features were the same as in Example 1. In this case, in order for light to
evanesce to the substrate on the lateral outer sides, the sum between the thickness
of the layer 33 and the layer 22 nedded to be made 0.6 µm or less when the thickness
of the active layer was 0.1 µm. By way of example, in case of a laser wherein the
thickness of the layer 33 outside the groove was 0.2 µm, the thickness of the layer
22 was 0.2 µm, the thickness of the active layer was 0.1 pm, the groove width was
7 µm and the length was 300 µm, the threshold current value of the oscillation was
100 mA and each of the longitudinal and transverse modes was single and stable up
to above double the threshold value.
[0052] As regards the arrangement of the periodic corrugations and the means for bestowing
a difference on the complex refractive index, only examples in which such means exists
on the substrate side have been explained above. This invention, however, is not restricted
to sach arrangement, but can adopt different constructions. For instance, a layer
overlying an active layer is formed with periodic corrugations, whereupon a layer
is formed which is provided with a protuberance corresponding sulhstantially to a
radiation portion. The protuberant layer is made a light noa-absorptive layer. On
this layer, a layer serving as a light absorptive layer is formed. With such a structure,
the same effects as in the foregoing can be achieved. Concrete methods of setting
the various constituents may conform with the methods stated in the general descrioption.
1. A semiconductor laser device, characterized by a first semiconductor layer (3;
23) and second and thif semiconductor layers (2, 4; 22, 24) which sandwich said first
semiconductor layer therebetween, which are greater in the band gap and lower in the
refractive index than said first semiconductor layer and which have conductivity types
opposite to each other; at least one of said second and third semiconductor layers
having a protuberant region or a fourth semiconductor layer (30; 33) which extends
in a travelling direction of the laser beam and in the shape of a stripe on its surface
side remote from said first semiconductor layer; a semiconductor layer (1; 21) having
portions on both sides of the protuberant region or fourth semiconductor layer and
rendering the effective complex refractive index for the laser beam discontinuous
in a direction perpendicular to said travelling direction of the laser beam; and periodic
corrugations (8; 28; 34) formed in at least one interface of the semiconductor layers
constituting said semiconductor laser device, in a manner to intersect orthogonally
to the lengthwise direction of the stripe of said protuberant region or fourth semiconductor
layer and to include at least a region corresponding to the stripe-shaped region of
said protuberant region or fourth semiconductor layer.
2. A semiconductor laser device according to claim 1, characterized in that the protuberant
region is provided by one (2) of said second and third semiconductor layers (2, 4),
that the other (4) of said second and this semiconductor layers is formed with said
periodic corrugations (8) at its surface remote from said first semiconductor layer
(1), and that a fifth semiconductor layer (5) is disposed on a surface of said periodic
corrugations. (Fig. 3)
3. A semiconductor laser according to claim 1, characterized in that said periodic
corrugations (28) are formed at an interface between at least one (22) of said second
and third semiconductor layers (22, 24) and said fourth semiconductor layer (30) as
well as said semiconductor layer (21) with its portions lying on both sides of said
fourth semiconductor layer, in a manner to include at least an interface region corresponding
to said fourth semiconductor layer.(Figs. 9, 10; 15)
4. A semiconductor laser according to claim 1, characterized in that said fourth semiconductor
layer (33) includes said protuberant reqion, and that said periodic corrugations (34)
are formed at an interface botween at least one (22) of said second and third semiconductor
layers (22, 24) and said fourth semiconductor layer. (Fig. 16)
5. A semiconductor laser device according to any of claims 1 to 4, characterized in
that the absolute value of the difference between the effective complex refractive
indices discontinuous for the laser beam is 10-3 to 10-2
6. A semiconductor laser device according to any of claims 1 to 5, characterized in
that the width of the stripe-shaped protuberant region or stripe-shaped fourth semiconductor
layer (30; 33) is made 2 µm to 8 µm, and the distance from said first semiconductor
layer (3; 23) to said periodic corrugations (8; 28; 34) is made 0.03 µm to 1 µm.
7. A semiconductor laser device according to any of claims 1 to 6, characterized in
that the thickness of said first semiconductor layer (3; 23) is 0.05 µm to 0.15 µm.
8. A semiconductor laser device according to any of claims 1 to 7, characterized in
that said semiconductor layer (1; 21) disposed with its portions lying on both the
sides of said protuberant region or stripe-shaped fourth semiconductor layer (30;
33) is made of a semiconductor substrate which has a groove (9; 29) extending in said
travelling direction of the laser beam and in the shape of said stripe.
9. A semiconductor laser'device according to claim 8 as depending on claim 2, characterized
in that said semiconductor substrate (1) is a GaAs substrate, said first semiconductor
layer (3) is made of Ga1-zAlzAs (O ≤ z ≤ 0.3), said second semiconductor layer (2) is made of Ga 1-xAlxAs (0.1 ≤ x ≤ 0.9), said third semiconductor layer (4) is made of Ga1-yAlyAs (0.1 ≤ y ≦ 0.9), and said fifth semiconductor layer (5) is made of Ga1-yAlyAs (0.05 ≤ Y ≤ 0.9) (where x, y > z; y > z; and y 4 y). (Fig. 3)
10. A semiconductor laser device according to claim 8 as depending on claim 3,characterized
in that said semiconductor substrate (21) is a GaAs substrate, said first semiconductor
layer (23) is made of Ga1-zAlzAs (O ≦ z ≦ 0.3), said second semiconductor layer (22) is made of Ga11-xAlxAs (0.1 ≦ x ≦ 0.9), said third semiconductor layer (24) is made of Ga1-yAlyAs (0.1 ≦ y ≦ 0.9), and said fourth semiconductor layer (30) is made of Ga1-sAlsAs (0.01 ≦ s ≦ 0.9) (where x,y > z; s > z; and x ≠ s). (Figs. 9, 10; 15)
11. A semiconductor laser device according to claim 8 as depending on claim 4, characterized
in that said semiconductor substrate (21) is a GaAs substrate, said first semiconductor
layer (23) is made of Ga1-zAlzAs (0 ≦ z ≦ 0.3), said second semiconductor layer (22) is made of Ga1-xAlxAs (0.1 ≦ x < 0.9), said third semiconductor layer (24) is made of Ga1-yAlyAs (0.1 ≦ y ≦ 0.9), and said fourth semiconductor layer (33) is made of Ga1-yAlyAs (0.1 ≦ γ ≦ 0.9) (where x, y > z; y > z; and x ≠ y). (Fig. 16)