[0001] The invention relates to a semiconductor device for generating or intensifying coherent
electromagnetic radiation, comprising a semiconductor body having an active semiconductor
layer which comprises a p-n junction and which is bounded on either side by first
and second passive semiconductor layers having a lower refractive index for the said
radiation than the active layer, one of the passive layers comprising a strip-shaped
electrode structure for supplying current to a strip-shaped region of the active layer
in a direction substantially perpendicular to the layer so as to produce or intensify
the said radiation therein, at least the first passive layer comprising a strip-shaped
zone which, in projection, extends fully within the said strip-shaped region and which
has a different structure from the parts of the said passive layer adjoining same,
said strip-shaped zone having a width which is at most equal to that of the said strip-shaped
region.
[0002] A semiconductor device as described above is disclosed in United States Patent Specification
No. 3,883,821.
[0003] It should be stressed that, where in this specification the expression "refractive
index" is used, this relates to the reel part of the (generally complex) refractive
index for the relevant radiation.
[0004] The said p-n junction may extend between two parts of the active layer parallel to
the interfaces of the layer with the adjoining passive layers. However, the p-n junction
may alternatively be formed between the active layer and one of the two passive layers
adjoining same.
[0005] It is furthermore to be noted that the said strip-shaped region of the active layer,
while neglecting possibly occurring lateral spreading of the current, it is to be
understood to mean herein that region of the active layer which in projection is bounded
by the outline of the strip-shaped electrode structure.
[0006] Semiconductor devices for generating coherent electromagnetic radiation (lasers)
or for the intensification (amplification) thereof (traveling wave intensifiers) are
known in many constructions. The intensification occurs in a thin layer, the active
layer, of which, at least in the case of lasers, a part is situated within a resonant
cavity which is formed either between two reflective surfaces extending perpendicular
to the direction of propagation of the radiation, or differently, for example in the
laser with reduced feedback coupling which is described in Applied Physics Letters,
Vol. 18, February 15, 1971, pp. 152-T54.
[0007] The requirements which are imposed in many cases upon a laser intensifier of the
said kind are:
a) Low threshold current (that is the minimum current strength at which stimulated
radiation emission and intensification, respectively, occur should be as low as possible);
b) A cross-section which is as small as possible of the emanating beam both in a direction
perpendicular to the active layer and in a direction parallel thereto;
c) Oscillation in only one mode, preferably the fundamental (lowest-order) transversal
mode.
In order to obtain a low threshold current and a small beam cross-section parallel
to the activelayer, the current, through a strip-shaped electrode structure, i4 limited
to a narrow region of the active layer. The beam cross-section in a vertical direction,
perpendicular to the active layer, is restricted by providing the active layer between
two passive layers of lower refractive index (larger band gap) than the active layer.
For this purpose, a passive semiconductor layer having a composition differing from
that of the active layer is usually provided on one or on both sides of the active
layer, said passive layer forming a so-called hetero junction with the active layer.
[0008] The number of transversal modes in which the emanating beam oscillates can be restricted
by making the strip-shaped electrode configuration very narrow. Herewith the number
of transversal modes can even be restricted to one. However, the use of very narrow
electrode structures has for its disadvantage that the current density can easily
become so high that damage to the laser structure occurs. In addition, several modes
of oscillation may nevertheless occur in the case of currents which are considerably
above the threshold current.
[0009] In the above device known from United States Patent Specification 3,883,821, the
radiation is restricted to one transversal mode by making the active layer in a double
hetero junction laser having a strip-shaped electrode not homogeneous in thickness
but providing therein below the strip-shaped electrode a strip-shaped zone having
a larger thickness than the remaining part of the active layer. By suitable choosing
the ratio between the height and the width of the said thickened part of the active
layer a radiation beam oscillating only in one transversal mode can be obtained.
[0010] However, a disadvantage of this known device is that technologically it is particularly
difficult to provide the required very small and very narrow thickening in the active
layer without thereby adversely influencing the operation of the laser/intensifier.
First of all, the required processes (etching and growing after the etching step)
are difficult to carry out in a reproducible manner while maintaining the required
crystal perfection. In addition, the thin active layer within which the intensification
mechanism of the device occurs, is the most vulnerable part of the device. Therefore,
after providing the active layer said layer should be subjected to the least possible
number of further treatments.
[0011] In addition to the said technological problems a few further disadvantages are associated
with the said known structure. For example, the thicker central region of the active
layer underlying the strip- shaped electrode will pass less current and will hence
become active less rapidly. This has a detrimental influence on the stability of operation
and on the intensification. As a result of this, the threshold current is reached
first in the thinner parts of the strip-shaped region of the active layer underlying
the electrode on either side of the thickening. As a result of this, in principle
first a higher mode and only then the fundamental mode can be impulsed upon switching
on the device. And finally transversal higher-order modes in a direction perpendicular
to the active layer can more easily occur in the thicker region of the active layer.
[0012] One of the objects of the invention is to provide a semiconductor device for generating
or intensifying coherent radiation with strip-shaped electrode geometry, in which
the emanating beam oscillates only in the fundamental transversal mode also at current
values above the threshold current, which device moreover can be manufactured with
a greater reproducibility than known devices.
[0013] For that purpose the invention is based inter alia on the recognition that wave guidance
below the strip-shaped electrode can be obtained when an active layer is used which
has substantially the same thickness and preferably the same doping everywhere, by
means of measures which relate only to the construction and composition of a passive
layer.
[0014] According to the invention, a semiconductor device of the kind described in the preamble
is characterized in that the active layer has substantially the same thickness everywhere,
that at least the first passive layer comprises a first portion having a refractive
index n
1 and a second portion having a refractive index n
2 different from n
1 for the said radiation, said second portion being of the same semiconductor material
and having the same conductivity type as the first portion, the active layer adjoining
said first portion at least within said strip-shaped zone, and that the condition
is satisfied

wherein d
1 is the thickness of the first portion from the active layer to the second portion
within the strip-shaped zone, and d
2 is the thickness of the first portion in the region of the first passive layer adjoining
the strip-shaped zone.
[0015] The condition (n
1 - n
2) (d
1 - d
2)) 0 indicates that either n
1 must be > n
2 and also d
1 must be
d
2 or n
1 must be > n
2 and also d
1 must be > d
2.
[0016] In the semiconductor device according to the invention, after the growth of the active
layer said layer is not further subjected to treatments which might detrimentally
influence the properties thereof, since the measures to obtain the desired wave guidance
are restricted to the passive semiconductor layer or layers.
[0017] By making the strip-shaped zone narrower than the strip-shaped electrode structure,
the operation of the laser (or intensifier) in the fundamental mode becomes more stable.
According to an important preferred embodiment, therefore, the strip-shaped zone has
a width less than said strip-shaped region of the active layer. Since the electrode
width need not be extremely small, a comparatively larger power can be generated without
degradation of the device. Furthermore, the emanating beam in this case has a satisfactorily
flat wave front so that the beam is little astigmatic, which makes the optical coupling
to, for example, a glass fibre simple.
[0018] Although higher transversal oscillation modes can be suppressed already to a considerable
extent when the strip-shaped zone of higher refractive index is provided so as to
be slightly asymmetrical with respect to the electrode structure, the occurrence of
more than one oscillation mode can be suppressed to a much more considerable extent
in the case of a symmetrical structure. Therefore, according to an important preferred
embodiment, the strip-shaped zone is provided so as to be symmetrical with respect
to the strip-shaped region.
[0019] The strip-shaped zone can be realised in a number of different manners in the structure
of the first passive semiconductor layer. According to an important preferred embodiment,
the first passive semiconductor layer in the regions adjoining the strip-shaped zone
consists entirely of the portion having the lower refractive index. In this case,
during the manufacture there may be started from a first passive semiconductor layer
having a homogeneous composition, after which the desired zone can be formed in a
comparatively simple manner technologically by doping a narrow strip-shaped part of
said layer. This may be done, for example, by diffusion or by ion implantation, in
which a passive layer which consists, for example, of a ternary semiconductor mixed
crystal, for example Ga i-x AlxAsp is locally given a slightly different composition
having a .higher refractive index by a suitable doping.
[0020] In this manner a strip-shaped zone of higher refractive index can simply be formed
which extends from the surface of the first passive semiconductor layer remote from
the active layer over a part of the thickness of the layer, in which latter case the
strip-shaped zone consists entirely of the portion having the higher refractive index.
When ion implantation is used, a "buried" strip-shaped zone of higher refractive index
can also be obtained in a simple manner in the first passive semiconductor layer which
is surrounded, within the passive semiconductor layer,entirely by the portion having
the lower refractive index.
[0021] All the above-mentioned preferred embodiments have the advantage of being realisable
technologically in a comparatively simple manner.
[0022] The active and passive layers need not be flat and in some cases it may be preferred,
also in connection with the manufacturing method to be followed, to provide one or
more layers so as to be not flat and one or both passive layers to have an inhomogeneous
thickness. A preferred embodiment in which the active layer in the strip-shaped zone
adjoins the material having the lower refractive index (so n
1 n
2 and d
1 d
2) is characterized in that the first passive layer is provided on a substrate which
locally has a strip-shaped raised portion, the first passive layer at the area of
said raised portion showing a smaller overall thickness than beside the raised portbn.
Conversely, a preferred embodiment in which the active layer in the strip-shaped zone
adjoins the material having the higher refractive index (so n
1 > n
2 and d
1 > d
2) is characterized in that the first passive layer is provided on a substrate which
locally has a strip-shaped depressed portion, the first passive layer at the area
of said depressed portion showing a larger overall thickness than beside the depressed
portion.
[0023] As regards the strip-shaped electrode structure, several known configurations may
be used which may be situated either on one side or on the other side of the active
layer, or theoretically on both sides, although this may provide cooling problems.
[0024] The invention will now be described in greater detail with reference to a few embodiments
and the drawing, in which
Fig. 1 is a partly perspectkre and partly diagrammatic cross-sectional view of a device
according to the invention;
Figs. 2 to 6 are diagrammatic cross-sectional views through the active parts of modified
embodiments of devices according to the invention;
Figs 7 to 11 are diagrammatic cross-sectional views of the device shown in Fig. 1
with different strip-shaped electrode structures;
Figs. 12 and 13 are diagrammatic cross-sectional views of the active parts of two
other modified embodiments of the device according to the invention, and
Fig. 14 is a diagrammatic cross-sectional view of a modified embodiment of the device
shown in Fig. 7.
[0025] The figures are diagrammatic and not drawn to scale for clarity. In the cross-sectional
views, regions of the same conductivity type are as a rule shaded in the same direction.
Corresponding parts are generally referred to by the same reference numerals.
[0026] Fig. 1 shows partly as a perspective view and partly as a cross-sectional view a
semiconductor device according to the invention for intensifying or generating coherent
electromagnetic radiation. The device comprises a semiconductor body 1 having an active
semiconductor layer 2 which comprises a p-n junction 3 and is bounded on either side
by first and second passive semiconductor layers (4, 11) and 5 both having a lower
refractive index for the radiation to be generated or intensified than the active
layer 2. One of the passive layers, the layer (4, 11) has a strip-shaped electrode
structure. In this example this is a strip-shaped metal layer 7 which is provided
on a semiconductor contact layer 7 having the same conductivity type as but a lower
resistivity than the passive layer (4, 11). Current can be supplied to a strip-shaped
region 8 (situated between the broken lines) of the active layer 2 by the electrode
6 in a direction perpendicular to the layer. The other electrode (9) is situated on
a readily conductive substrate 10, on which the passive layer 5 is present, and extends
on the whole surface thereof. By applying a suitable voltage between the electrodes
6 and 9 via a current source 20, shown diagrammatically in Fig. 1, current is supplied
to the region 8 in a direction substantially perpendicular to the layer 2,namely in
the forward direction of the p-n junction 3, which current serves in known manner
to generate in the active layer 2 coherent electromagnetic radiation according to
the laser principle (if the strip-shaped region 8 is provided in a resonant cavity)
or to intensify it (if this is not the case).
[0027] The first passive layer (4, 11) has a strip-shaped zone (4A, 11) extending in projection
entirely within the strip-shaped region 8 and having a different structure than the
adjoining parts (4) of the layer as will be described in detail hereinafter. Said
strip-shaped zone (4A, 11) has a width which is at most equal to, and in this example
is smaller than, that of the strip-shaped region 8.
[0028] According to the invention the active layer (2) everywhere has about the same thickness,
while at least the first passive layer comprises a first portion (4, 4A) having a
refractive index n
1, and a second portion 11 of the same semiconductor material and the same conductivity
type as the first portion and having a refractive index n 2for said radiation which
is different from n
1. The active layer 2, at least within the strip-shaped zone (4A, 11) (and in this
example also outside the strip-shaped zone) adjoins the first portion (4, 4A). In
this example n
2) n
1, while the thickness d
1 of the first portion 4A from the active layer 2 to the second portion 11 within the
strip-shaped zone (4A, 11) is less than the thickness d
2 of the first portion 4 in the region of the first passive layer which adjoins the
strip-shaped zone.
[0029] Since n
2> n
1 and d
2 > d
1, the condition is satisfied that

[0030] The dimensions and compositions of the various layers are as follows:
Substrate 10: n-type gallium arsenide (GaAs); thickness approximately 80 microns;
refractive index approximately 3.61;resistivity approximately 0.001 Ohm.cm.
Passive layer 5: n-type gallium aluminium arsenide (Ga0.7Al0.3As); thickness approximately 3 microns; refractive index approximately 3.40.
Active layer 2: p-type GaAs; thickness approximately 0.5 micron; refractive index
approximately 3.61.
Passive layer 4: Outside the zone 11: E-type Ga0.7Al0.3As; thickness approximately 1.5 microns; refractive index approximately 3.40.
Zone 11: zinc-doped or germanium-doped p-type Ga0.7Al0.3As, d1 (Fig. 1) = 0.1 micron; refractive index approximately 3.41.
Contact layer 7: p- type GaAs; thickness approximately 1.5 microns; refractive index
approximately 3.61; resistivity approximately 0.003 Ohm. cm.
Width b of electrode layer 6: approximately 9 microns. The device may operate as a
laser or as a traveling wave intensifier. When used as a laser, for example reflective
surfaces are provided in the usual manner perpendicular to the strip-shaped electrode
6; for this purpose may serve, for example, the end faces of the crystal which are.
then constructed as cleavage surfaces, or periodic structures as described in the
above-mentioned article in Applied Physics Letters. The generated laser radiation
in the device described then has a wavelength (in vacuum) of approximately 0.9 micron
and emanates in the direction of the arrow in Fig. 1.
[0031] When used as a traveling wave intensifier, no reflective surfaces are used; the emanating
radiation emanates in the direction of the arrow in Fig. 1, and the entering radiation
enters in the same direction through the oppositely located end face, the emanating
radiation of wavelength 0.9 micron being intensified with respect to the entering
radiation of the same wavelength.
[0032] In both applications, with the device described, for different widths a in microns
of the strip-shaped zone (see Fig. 1) the following results are calculated for d
1 = 0.1 micron:

[0033] The indicated values apply to a strip length L (see Fig. 1) of 300 microns with the
given current densities in kA/cm2.


in which the relative phase is, for example, chosen with respect to the phase in the-centre
of the strip-shaped region 8. Many modifications of the embodiment shown in Fig. 1
are possible;the principal modifications are shown in Figs. 2 to 6 as cross-sectional
views in so far as the layers 4, 2 and 5 are concerned. 11 is always the region having
the higher refractive index, while the remaining part of the layer 4 has a lower refractive
index. The strip-shaped zone in all these cases is provided symmetrically with respect
to the strip-shaped region 8. In the devices shown in Figs. 1, 2 and 3 the passive
layer 4 in the regions adjoining the strip-shaped zone consists entirely of the material
of lower refractive index, the strip-shaped zone of the layer 4 in Fig. 2 consisting
entirely of the material of the higher refractive index, in other words the zone 11
extends over the whole thickness of the layer 4. In Fig. 3 the portion 11 of higher
refractive index is surrounded entirely by the portion 4 of lower refractive index.
[0034] In Figs. 4 to 6 the region 11 also has a higher refractive index than the remainder
of the layer (4, 11). In the devices shown in Figs. 4 and 5 the region 11 adjoins
the active layer 2; so in these devices it holds that n
1 > n
2 and d
1 > d
2. In the device shown in Fig. 6 where the region of lower refractive index adjoins
the active layer 2, it holds on the contrary that n
1 < n
2 and d
1 <
d2.
[0035] For the devices shown in Figs. 2 to 6 the same results hold to an approximation as
indicated in Table 1 for the device shown in Fig. 1. For example, the results shown
in Table II are obtained for the device shown in Fig. 2.

in which the abbreviations have the same meaning as in Table I.
[0036] From the above it appears that the device according to the invention, both as regards
relative power intensification and as regards horizontal concentration and relative
astigmatism, shows a considerable improvement as compared with devices in which the
passive layer 4 is homogeneous in thickness and composition and in which thus the
region 11 is lacking, Also for the above-mentioned reasons, the device is technologically
better realisable than that described in United States Patent Specification 3,883,821,
since the active layer 2 has substantially the same thickness everywhere and mechanical
or physical-chemical treatments need not be carried out on or in said layer after
the growth thereof.
[0037] It should be stressed that both in Table I B. (for a

9µm) and in Table II A. (for a

6µm) and in Table II B. (for a ≈ 6
/um) there is an optimum value for R.I.; in Table I B. this is the case for H.C. as
well. In the calculatbn of these values losses at the edge of the strip-shaped active
laser region have not been taken into account. If these losses are taken into account
in a more complicated calculation, the resulting values are slightly different and
one finds that there is always an optimum value which occurs for values of a which
are in the order of the width b of the said strip-shaped region of the layer 2.
[0038] Figs. 7 to 11 show various embodiments for the strip-shaped electrode structure which
are all known per se.They may be used in the structure shown in Fig. 1, as shown in
the drawing, but also in any other device according to the invention. In Fig. 7, an
electrode layer is provided on the upper side of the device over the whole surface,
which layer, however, contacts the semiconductor surface only via a slot-shaped aperture
in the insulating layer 12 situated on the surface. In Fig. 8, a contact layer is
provided on the p- conductive passive layer 4 and consists of a strip-shaped part
13 of
E-type gallium arsenide and beside it n-type gallium arsenide regions 14, so that in
the forward direction current flows only through the p-n junction 3 via the region
13. In Fig. 9 a strip-shaped electrode 6 is provided directly on the passive layer
4.In Fig. 10 the strip-shaped electrode structure is provided in contact with the
passive layer 5 by restricting the current to a strip-shaped region by means of the
buried p-type GaAs regions 15 between the n-type GaAlAs layer 5 and the n-type GaAs
substrate 10. In Fig. 11 finally the current is restricted to a strip-shaped region
by providing insulating zones 16 (crosswise shading),for example, by a proton bombardment.
[0039] In the devices described so far, all the successive layers were bounded by substantially
flat surfaces. That this is not necessary is illustrated with reference to the examples
of Figs. 12 and 13. For clarity, these figures only show the small active part of
the device as diagrammatic cross-sectional view perpendicular to the strip-shaped
configuration.
[0040] In the device shown in Hg. 12 the first passive layer 4, that is, the passive layer
comprising the strip-shaped zone according to the invention, is provided on a substrate
10 which locally has a strip-shaped raised portion 10A, in which the first passive
layer 4 at the area of said raised portion shows a smaller overall thickness than
beside the raised portion. In the structure shown in Fig. 12 the electrode 6 again
has a width of approximately 9 microns, the raised portion 10A has a width of approximately
4 microns and a height of approximately 2 microns, and the lowermost portion of the
passive layer 4 consists of n-type Ga
1-xAl
xAs having such a composition that its refractive index n
2 is approximately 3.50, while the uppermost portion of the layer 4 adjoining the active
layer 2 consists of n-type Ga
1-yAl
yAs having such a composition that its refractive index n
1 is approximately 3.40. The passive layer 5 also has a refractive index 3.40. The
thickness d
1 is approximately 0.4 micron, the thickness d
2 at the indicated place is approximately 0.8 micron. The thickness of the active layer
2 (n-type GaAs, refractive index approximately 3.61)is approximately 0.2 micron everywhere,
that of the passive layer 5 (p-type Ga
1-xAl
yAs) is approximately 1.5 microns. An electrode layer 9 is provided on the substrate
10 consisting of n-type GaAs and having a low resistivity and refractive index 3.61.
[0041] Conversely, a laser or intensifier structure as shown in Fig. 13 may also be obtained.
In this figure the first passive layer 4 is provided on a substrate 10 which locally
shows a strip-shaped depressed portion 10B in which the layer 4 at the area of said
depressed portion shows a larger overall thickness than beside the depressed portion.
The depressed portion 10B has a width of approximately 4 microns and a height of approximately
3 microns. The layer 4 consists of a lowermost portion of n-type Ga
1-yAl
yAs having a refractive index n
2 = 3.40, and an uppermost portion of n-type Ga Al As having a refractive index n
1 = 3.50 and adjoining the active layer 2. The regions and layers 10, 2 and 5,for example,
have the same thickness and composition as in Fig. 12. The thickness d
1 is approximately 0.25 micron, the thickness d
2 is approximately 0.1 micron. As in the example of Fig. 12, it now also holds that

Both in the device shown in Fig. 12 and in that shown in Fig. 13 the active layer
2 has substantially the same thickness everywhere. The devices shown in Figs. 12 and
13 may be manufactured, for example, by using epitaxial growth methods as described
in Journal of Applied Physics, Volume 47, No. 10, October 1976, pp. 4578-4589. In
these methods use is made of the fact that upon depositing an epitaxial layer from
the liquid phase on a substrate having an unevenness, the layer grows thinner on a
raised portion and grows thicker in a depressed portion than beside it, in which thus
in both cases a certain "equalisation effect" occurs. According as the unevenness
on which the layer is grown is less pronounced, the grown layer.becomes more uniform
in thickness. In addition gallium arsenide proves to demonstrate the effect to a smaller
extent than does gallium arsenide.As a result of this,both in the structure of Fig.
12 and in that of Fig. 13 an active layer 2 of gallium arsenide of substantially uniform
thickness can be grown on the passive layer 4 of gallium aluminium arsenide.
[0042] In this manner, by starting from the substrates in question, the desired structure
is obtained both in Fie. 12 and in Fig. 13 by direct epitaxial growth of the successive
layers from the liquid phase without it being necessary to carry out further operations
after the growth of the layer 4 thereon so as to obtain the desired strip-shaped inhomogeneity.
[0043] The successive epitaxial growth of semiconductor layers of different compositions
is generally known in the technology of the hetero junction lasers and is described
in detail in the technical literature on various occasions. In this connection reference
may be had to the book by D. Elwell and J.J. Scheel, Crystal Growth from High Temperature
Solutions, Academic Press 1975, pp. 433-467, hereby incorporated by reference. So
the manufacture of the devices described need not be further entered into. The portions
of different refractive indices in the passive layer 4 (Figs. 1 to 11) can be obtained
by first growing a layer of homogeneous refractive index and then introducing into
a portion of said layer, while using a suitable masking, a material which increases
the refractive index (Figs. 1 to 3, 6 to 11) or a material which reduces the refractive
index (Fig. 4 and 5), for example, by diffusion or by ion implantation. As a result
of this the forbidden bandgap of the layer is locally reduced (so as to increase the
refractive index) or increased (so as to reduce the refractive index).For example,
the refractive index can be increased in p-type Ga Al As by the addition of an acceptor,
such as Zn or Ge. This could also be done by increasing the content of gallium. Conversely
the refractive index can be reduced by increasing the content of aluminium.
[0044] The invention is not restricted to the embodiments described. For example, suitable
semiconductor materials other than GaAs and Ga
1-xAl
xAs may alternatively be used. Furthermore, the conductivity type of the active layer
is not of essential importance; in the embodiments described the layer 3 may be both
n-conductive and p-conductive. Alternatively, a portion of the layer 2 may be n-conductive
and a portion may be p-conductive, said portions constituting a p-n junction parallel
to the faces of the layer 2.
[0045] It is furthermore of importance to note that a strip-shaped zone of different construction
which in the embodiments described occurs only in the first passive layer 4, may be
provided, if desired, both in the first passive layer 4 and in the second passive
layer 5. The structures of said two zones need not be the same; for example, a region
11 in the layer 4 of Fig. 2 may be combined with a region 11' according to one of
the structures of Figs. 3 to 6 in the layer 5. Fig. 4 serves as an illustration in
which an n-type region 11' of higher refractive index than the remainder of the layer
5 is provided in the n-type passive layer 4 and the reference numerals otherwise have
the same meaning as in Fig. 7. In this case the strip-shaped zones in the layers 4
and 5 have the same construction and it can be calculated that to an approximation
double the effect occurs with respect to the device shown in Fig. 7.
[0046] The strip-shaped electrode structure may be situated at the side of the layer 4,
but alternatively, instead thereof, at the side of the layer 5.
[0047] Finally it is to be noted that, although the invention has been described with reference
to embodiments relating to lasers or intensifiers having hetero junctions, the invention
may in principle also be applied to lasers or intensifiers which are constructed from
a semiconductor body which is built up entirely of the same semiconductor material
and the same semiconductor compound, respectively, without showing hetero junctions
between different semiconductor materials.
1. A semiconductor device for generating or intensifying coherent electromagnetic
radiation, comprising a semiconductor body having an active semiconductor layer which
comprises a p-n junction and which is bounded on either side by first and second passive
semiconductor layers having a lower refractive index for the said radiation than the
active layer, one of the passive layers comprising a strip-shaped electrode structure
for supplying current to a strip-shaped region of the active layer in a direction
substantially perpendicular to the layer so as to generate or intensify therein the
said radiation, at least the first passive layer comprising a strip-shaped zone which,
in projection, extends fully within the said strip-shaped region and which has a different
structure from the parts of the said passive layer adjoining same, said strip-shaped
zone having a width which is at most equal to that of the said active strip-shaped
region, characterized in that the active layer has substantially the same thickness
everywhere, that at least the first passive layer comprises a first portbn having
a refractive index n
1 and a second portion having a refractive index n
2 different from n
1 for the said radiation, said second portion being of the same semiconductor material
and having the same conductivity type as the first portion, the active layer adjoining
said first portion at least within said strip-shaped zone, and that the condition
is satisfied

wherein d
1 is the thickness of the first portion from the active layer to the second portion
within the strip-shaped zone, and d
2 is the thickness of the first portion in the region of the first passive layer adjoining
the strip-shaped zone.
2. A semiconductor device as claimed in Claim 1, characterized in that the strip-shaped
zone has a width less than said strip-shaped region of the active layer.
3. A semiconductor device as claimed in Claim 1 or 2, characterized in that the strip-shaped
zone is provided so as to be symmetrical with respect to the strip-shaped region.
4. A semiconductor device as claimed in anyone of the preceding Claims, characterized
in that the first passive semiconductor layer in the regions adjoining the strip-shaped
zone consists entirely of the portion having the lower refractive index.
5. A semiconductor device as claimed in anyone of the preceding Claims, characterized
in that the portion having the higher refractive index extends within the strip-shaped
zone from the surface of the first passive semiconductor layer remote from the active
layer over at least a part of the thickness of said layer.
6. A semiconductor device as claimed in Claims 4 and 5, characterized in that the
strip-shaped zone consists entirely of the material having the higher refractive index.
7. A semiconductor device as claimed in Claim 4, characterized in that the strip-shaped
zone comprises a region of the portion having the higher refractive index surrounded
entirely by the portion having the lower refractive index.
8. A semiconductor device as claimed in Claim 1 in which n1 < n2 and d1 < d2, characterized in that the first passive layer is provided on a substrate which locally
has a strip-shaped raised portion, the first passive layer at the area of said raised
portion showing a smaller overall thickness than beside the raised portion.
9. A semiconductor device as claimed in Claim 1 in which n1 > n2 and d1 > dz,characterized in that the first passive layer is provided on a substrate which locally
has a strip-shaped depressed portion, the first passive layer at the area of said
depressed portion having a larger overall thickness than beside the depressed portion.
10. A semiconductor device as claimed in anyone of the preceding claims, characterized
in that said second passive layer also comprises two portions having different refractive
indices, a said strip-shaped zone being equally provided in said second passive layer.