AlInGaN-BASED SUPERLUMINESCENT DIODE

Abstract

The invention relates to an AlInGaN alloy based superluminescent diode, comprising a gallium nitride bulk substrate, a lower cladding layer with n-type electrical conductivity. Further it includes a lower light-guiding layer with n-type electrical conductivity, a light emitting layer, an electron blocking layer with p-type electrical conductivity, an upper light-guiding layer, an upper cladding layer with p-type electrical conductivity, and a subcontact layer with p-type electrical conductivity. The gallium nitride bulk substrate has a spatially varying surface misorientation in the relation to the crystallographic plane M in range of 0 to 10.

Claims

1. AlInGaN alloy based superluminescent diode, comprising: a gallium nitride bulk substrate; a lower cladding layer with n-type electrical conductivity; a lower light-guiding layer with n-type electrical conductivity; a light emitting layer; an electron blocking layer with p-type electrical conductivity; an upper light-guiding layer; an upper cladding layer with p-type electrical conductivity; and a subcontact layer with p-type electrical conductivity; wherein the gallium nitride bulk substrate has a spatially varying surface misorientation in a direction perpendicular to a crystallographic plane M in range of 0 to 10.

2. The superluminescent diode according to claim 1, wherein the substrate misorientation is increasing from a back light guide window towards a front light guide window.

3. The superluminescent diode according to claim 2, wherein the increase of substrate misorientation in the direction of the front light guide window is continuous, linear, approximately linear, or non-linear in relation to a light guide axis.

4. The superluminescent diode according to claim 3, wherein the substrate misorientation, expressed by an angle in relation to a direction parallel to a crystallographic plane C and perpendicular to the crystallographic plane M, has an approximately linear character satisfying the relation: $=\mathrm{arc}.Math..Math.\mathrm{tg}\left(\frac{h}{\mathrm{wl}}.Math.y\right),$ wherein y is a coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, w is a parameter specifying a chip width of the manufactured superluminescent diode, l is a parameter specifying a chip length of the manufactured superluminescent diode, whereas h is a maximum depth at which the substrate is formed.

5. The superluminescent diode according to claim 3, wherein the substrate misorientation, expressed by an angle in relation to a direction parallel to a crystallographic plane C and perpendicular to the crystallographic plane M, has a non-linear character satisfying the relation: $=\frac{{}_{\min }-{}_{\max }}{\exp \left(\frac{y-l}{b}\right)+1}+{}_{\max },$ wherein y is a coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, .sub.max is a maximum misorientation angle in the direction perpendicular to the y direction, .sub.min is the minimum misorientation angle in the direction perpendicular to the y direction, b is a parameter affecting a profile shape, l is a parameter specifying a chip length of the manufactured superluminescent diode.

6. The superluminescent diode according to claim 3, wherein the substrate misorientation, expressed by an angle in relation to the direction parallel to a crystallographic plane C and perpendicular to the crystallographic plane M, has a non-linear character satisfying the relation: $=\left(\frac{a_1}{\exp \left(\frac{y-{\mathrm{ld}}_1}{b_1}\right)}+\frac{a_2}{\exp \left(\frac{y-{\mathrm{ld}}_2}{b_2}\right)}\right).Math.\left(\frac{{}_{\min }-{}_{\max }}{a_1+a_2}\right)+{}_{\max },$ wherein y is a coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, .sub.max is a maximum misorientation angle in the direction perpendicular to the y direction, .sub.min is a minimum misorientation angle in the direction perpendicular to the y direction, a.sub.1 and a.sub.2 are parameters affecting a relative heights of the first and second level, b.sub.1 and b.sub.2 are parameters affecting a profile shape of the first and second level, d.sub.1 and d.sub.2 are parameters affecting a location of a first and second level, l is a parameter specifying a chip length of the manufactured superluminescent diode.

7. The superluminescent diode according to claim 1, wherein a front light guide window is covered with a dielectric layer having a reflectivity coefficient lower than 5%.

8. The superluminescent diode according to claim 1, wherein a back light guide window is covered with a dielectric layer having a reflectivity coefficient higher than 80%.

9. The superluminescent diode according to claim 1, wherein the subcontact layer is doped with acceptors above a concentration of 10.sup.20 cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawings, wherein:

[0012] FIG. 1 shows a diagram of irradiation of the photoresist on semiconductor substrate according to the first embodiment of the invention;

[0013] FIG. 2 is a plot presenting the thickness distribution of substrate of FIG. 1;

[0014] FIG. 3 shows the profile of misorientation variation along the superluminescent diode light guide for the shape of the substrate presented in FIG. 2;

[0015] FIG. 4 is a cross section of one embodiment of the superluminescent diode of the present invention;

[0016] FIGS. 5A and 5B show exemplary shapes of the light guides applied in superluminescent diodes in a top view, pursuant to one embodiment of the invention;

[0017] FIGS. 6A-E shows the subsequent technological steps of manufacturing the mesa of the superluminescent diode of one embodiment of the present invention;

[0018] FIG. 7A shows the emission spectrum of the superluminescent diode according to the first embodiment of the present invention;

[0019] FIG. 7B shows the emission spectrum of a reference device;

[0020] FIG. 8 is a plot presenting the thickness distribution of substrate according to the second embodiment of the present invention;

[0021] FIG. 9 shows the profile of misorientation variation in the y direction of the superluminescent diode for the shape of the substrate presented in FIG. 8;

[0022] FIG. 10 shows the emission spectrum of the superluminescent diode according to the second embodiment of the invention;

[0023] FIG. 11 is a plot presenting the thickness distribution of substrate according to the third embodiment of the present invention;

[0024] FIG. 12 shows the profile of misorientation variation in the y direction of the superluminescent diode for the shape of the substrate presented in FIG. 11; and

[0025] FIG. 13 shows the emission spectrum of the superluminescent diode according to the third embodiment of the invention.

DETAILED DESCRIPTION

[0026] The technical problem faced by the present invention is to propose such a AlInGaN based superluminescent diode structure that would be characterised by improved optical parameters, in particular a wider emission spectrum and reduced modulation depth in the spectrum. Simultaneously, there is a desire for a problem solution that would not involve any significant change in the present manufacturing process, thereby not causing a significant increase of the cost of a single device. Moreover, an ability to modify the shape of the emission spectrum of such a superluminescent diode is desired. Unexpectedly, the technical problems mentioned above have been solved by the present invention.

[0027] The present invention relates to AlInGaN alloy based superluminescent diode, comprising a gallium nitride bulk substrate, a lower cladding layer with n-type electrical conductivity, a lower light-guiding layer with n-type electrical conductivity, a light emitting layer, an electron blocking layer with p-type electrical conductivity, an upper light-guiding layer, an upper cladding layer with p-type electrical conductivity, and a sub-contact layer with p-type electrical conductivity, characterised in that the gallium nitride bulk substrate has a spatially varying surface misorientation in the direction perpendicular to the crystallographic plane M in range of 0 to 10. In a preferred embodiment of the invention the substrate misorientation is increasing from the back light guide window towards the front light guide window. In another preferred embodiment of the invention the increase of the substrate misorientation in the direction of the front light guide window is continuous, linear, approximately linear or non-linear in relation to the light guide axis. In another preferred embodiment of the invention the substrate misorientation, expressed in terms of the angle in relation to the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, has an approximately linear character satisfying the relation:

[00001]$\begin{array}{cc}=\mathrm{arc}.Math..Math.\mathrm{tg}\left(\frac{h}{\mathrm{wl}}.Math.y\right),& \left(\mathrm{W3}\right)\end{array}$

where y is the coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, w is a parameter specifying the chip width of the manufactured superluminescent diode, l is a parameter specifying the chip length of the manufactured superluminescent diode, whereas h is the maximum depth at which the substrate is formed. Equally preferably, the substrate misorientation, expressed in terms of the angle in relation to the direction parallel do the crystallographic plane C and perpendicular to the crystallographic plane M, has a non-linear character satisfying the relation:

[00002]$\begin{array}{cc}=\frac{{}_{\min }-{}_{\max }}{\exp \left(\frac{y-l}{b}\right)+1}+{}_{\max },& \left(\mathrm{W4}\right)\end{array}$

where y is the coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, .sub.max is the maximum misorientation angle in the direction perpendicular to the y direction equal to arctg(h/w), .sub.min is the minimum misorientation angle in the direction perpendicular to the y direction, b is a parameter affecting the profile shape, l is a parameter specifying the chip length of the manufactured superluminescent diode. More preferably, the substrate misorientation, expressed in terms of the angle in relation to the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, has a non-linear character satisfying the relation:

[00003]$\begin{array}{cc}=\left(\frac{a_1}{\exp \left(\frac{y-{\mathrm{ld}}_1}{b_1}\right)}+\frac{a_2}{\exp \left(\frac{y-{\mathrm{ld}}_2}{b_2}\right)}\right).Math.\left(\frac{{}_{\min }-{}_{\max }}{a_1+a_2}\right)+{}_{\max },& \left(\mathrm{W6}\right)\end{array}$

where y is the coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, .sub.max is the maximum misorientation angle in the direction perpendicular to the y direction equal to arctg(h/w), .sub.min is the minimum misorientation angle in the direction perpendicular to the y direction, a.sub.1 and a.sub.2 are parameters affecting the relative heights of the first and second level, b.sub.1 and b.sub.2 are parameters affecting the profile shape of the first and second level, d.sub.1 and d.sub.2 are parameters affecting the location of the first and second level, l is a parameter specifying the chip length of the manufactured superluminescent diode. In a preferred embodiment of the invention the front light guide window is covered with a dielectric layer with the reflection coefficient lower than 5%. In another preferred embodiment of the invention the back light guide window is covered with a dielectric layer with the reflection coefficient higher than 80%. In another preferred embodiment of the invention the subcontact layer is doped with acceptors in concentration higher than 10.sup.20 cm.sup.3.

[0028] The goal of substrate forming is obtaining an increase of substrate misorientation along the superluminescent diode light guide, from the back to the front light guide window. The direction of the misorientation vector can be perpendicular, as well as parallel, to the light guide axis. It is also possible to perform the substrate forming such that the misorientation direction is arbitrary in relation to the waveguide axis and varying in different regions along the waveguide.

[0029] The invention enables an improvement of the optical properties of the superluminescent diode by widening the emission spectrum and reducing modulation in the spectrum. The regions with different substrate misorientation result in different indium content in the light generating active layer, and therefore a different central light emission wavelength. As a result, the light leaving the front light guide window has an emission spectrum that is a sum of the emission spectra of individual light guide fragments reduced by the waveguide optical losses. Applying an increase of substrate misorientation along the light guide in the direction of the exit window entails a decrease of indium content, and therefore an increase of the active region band gap width. Such order allows reducing the reabsorption of light in the system.

[0030] The invention also enables a detailed modification of the shape of the superluminescent diode emission spectrum by applying a smooth, non-linear variation of the misorientation value along the diode light guide. Increasing the part of a particular misorientation in the total shape of the substrate allows increasing the part of the emission spectrum associated with the corresponding indium content in the active region. By means of a proper design of the misorientation profile along the light guide it is possible to, among others, increase the part of the highest and lowest wavelengths in the final emission spectrum, which leads to a significant widening of the spectrum. It is also possible to obtain a shape of the emission spectrum that is approximately rectangular. The invention also allows creating a light guide with reduced losses relative to the light guide formed on a substrate with a step change of misorientation (flat regions with uniform misorientation), due to the lack of losses on interfaces between the regions with different misorientation, which are folds of the light guide. The invention can also be applied as a light source of a tunable external cavity laser. In such case, the invention will enable a significant widening of the laser tuning wavelength range, due to a wide emission spectrum. An advantage of the invention is also its compatibility with the conventional process of device manufacturing and assembly. The only thing required is a proper preparation of the gallium nitride bulk substrate. The further technological steps do not require changes, thus the change of the manufacturing cost is negligible and the invention does not require a separate production line.

[0031] Exemplary embodiments of the invention have been presented in the drawings, wherein FIG. 1 shows a diagram of irradiation of the photoresist on semiconductor substrate according to the first embodiment of the invention, FIG. 2 is a plot presenting the thickness distribution of substrate of FIG. 1, FIG. 3 shows the profile of misorientation variation along the superluminescent diode light guide for the shape of the substrate presented in FIG. 2, FIG. 4 is a cross section of the superluminescent diode of the present invention, FIGS. 5a and 5b show exemplary shapes of the light guides applied in superluminescent diodes in a top view, FIG. 6 shows the subsequent technological steps of manufacturing the mesa of the superluminescent diode of the present invention, FIG. 7 shows the emission spectrum of the superluminescent diode (a) according to the first embodiment of the present invention, and (b) the reference device, FIG. 8 is a plot presenting the thickness distribution of substrate according to the second embodiment of the present invention, FIG. 9 shows the profile of misorientation variation in the y direction of the superluminescent diode for the shape of the substrate presented in FIG. 8, FIG. 10 shows the emission spectrum of the superluminescent diode according to the second embodiment of the invention, FIG. 11 is a plot presenting the thickness distribution of substrate according to the third embodiment of the present invention, FIG. 12 shows the profile of misorientation variation in the y direction of the superluminescent diode for the shape of the substrate presented in FIG. 11, FIG. 13 shows the emission spectrum of the superluminescent diode according to the third embodiment of the invention.

Example 1

[0032] The first embodiment of the present invention is a superluminescent diode with a widened emission spectrum and a linear variation of the misorientation angle in the y direction, created on a uniform GaO.sub.xN.sub.1-x substrate obtained in high-pressure growth. In the first step of manufacturing of such a superluminescent diode a GaO.sub.0.0005N.sub.0.9995 substrate was created by means of growing from a gallium solution of nitrogen under the pressure of 1000 MPa and at temperature of 1500 C. The obtained crystal was cut and polished so as to obtain a parallel-flat plate with typical thickness of 200 m. After appropriate mechano-chemical polishing, the crystal surface with gallium polarity had an atomic smoothness, demonstrated by the atomic steps in an Atomic Force Microscope image. The crystal surface was disoriented by 0.1 in relation to the direction of the crystallographic axis c of the GaN hexagonal (wurtzite) structure.

[0033] Next, a 2 m thick positive photoresist 1 layer was deposited on the substrate. The layer was irradiated by means of a laser writer apparatus with a 405 nm wavelength emission laser as the light source. The irradiation was performed by scanning the photoresist 1 surface by a light beam, wherein the light intensity was changing according to the design of the substrate 4 forming. This example uses the irradiation pattern shown in FIG. 1, enabling to create on the substrate 4, in the region of one superluminescent diode, a shape with the surface described by the equation W1,

[00004]$\begin{array}{cc}z=\frac{h}{\mathrm{wl}}.Math.x.Math.y,& \left(\mathrm{W1}\right)\end{array}$

where x is a coordinate in the direction parallel to the crystallographic plane C of the crystal and simultaneously parallel to the crystallographic plane M, y is a coordinate in the direction parallel to the crystallographic plane C and perpendicular to the crystallographic plane M, z is a coordinate in the direction perpendicular to the crystallographic plane C and parallel to the crystallographic plane M, w is a parameter specifying the chip width of the manufactured superluminescent diode, l is a parameter specifying the chip length of the manufactured superluminescent diode, whereas h is the maximum depth at which the substrate is formed. An example of such surface is presented in FIG. 1. In this embodiment the substrate surface profile in the x direction is linear and described by the equation:

[00005]$\begin{array}{cc}z=\frac{h.Math.y_a}{\mathrm{wl}}.Math.x,& \left(\mathrm{W2}\right)\end{array}$

where y.sub.a is a parameter specifying the value of y coordinate for which the profile was made. In such case the dependence of the misorientation angle on the y coordinate is an approximately linear described by the equation:

[00006]$\begin{array}{cc}=\mathrm{arc}.Math..Math.\mathrm{tg}\left(\frac{h}{\mathrm{wl}}.Math.y\right).& \left(\mathrm{W3}\right)\end{array}$

[0034] In the present embodiment, the following parameters were applied: h=2 m, w=100 m, and l=700 m. The brightness change in FIG. 1 corresponded to the change of laser light intensity, and thus the change of the photoresist 1 layer thickness after developing. The dotted line 2 specifies the future placement of the superluminescent diode light guide. Substrate 4 with formed photoresist 1 was subjected to the reactive ions dry etching method using argon-chlorine plasma. The etching time was 17.5 minutes. The process allowed the photoresist 1 structure to be transferred to the gallium nitride bulk substrate 4. The obtained plane is shown in FIG. 2, having a varying misorientation angle in the y direction, shown in FIG. 3.

[0035] The formed substrate is indicated by number 4 on the diagram of FIG. 4. Next, the substrate 4 was placed in a MOVPE reactor, where 800 nm thick Ga.sub.0.92Al.sub.0.08N layer 5, doped with silicon to the 510.sup.18 cm.sup.3 level, was created, at the temperature of about 1050 C. Then, at the same temperature, a 100 nm thick layer of undoped GaN was created, acting as the lower waveguide 6. After lowering the temperature to 820 C. a light emitting region 7 was created, as an In.sub.0.1Ga.sub.0.9N/In.sub.0.02Ga.sub.0.98N multiple quantum well, where the number of quantum wells was three. Then, after increasing the reactor temperature to 1050 C., a Al.sub.0.2Ga.sub.0.98N:Mg layer 8 was created, for blocking the escape of the electrons. Afterwards, an undoped GaN layer was created, acting as the upper light guide 9. The next layer was the 430 nm thick Al.sub.0.05Ga.sub.0.95N upper cladding layer 10. The structure's growth was finished by a thin GaN:Mg subcontact layer 11 with magnesium concentration higher than 10.sup.20 cm.sup.3. After completion of the structure growth the reactor was cooled in nitrogen atmosphere.

[0036] Next, photolithography defining the mesa shape as a curved strip was performed (FIG. 5b). The ending curvature of the light guide 14 in relation to the crystal cleavage planes (the future exit windows of the light guide 15) was 6.

[0037] FIG. 6 schematically illustrates the process of creating the mesa and the upper contact. The first technological step was depositing a 2 m thick photoresist layer 12a on the area of the designed light guide. Afterwards, a reactive ions dry etching of the crystal to the depth of 500 nm was performed. In this way, a mesa in the cladding layer 10 and the subcontact layer 11 was created, which is shown in the diagram of FIG. 6b. Next, a 200 nm thick layer of isolating material SiO.sub.2 12 was deposited on the whole crystal, shown in FIG. 6c. Due to the high thickness of the photoresist, its side edges are not fully covered by the isolator 12. Performing the wet etching enables uncovering the mesa's ridge (FIG. 6d), whilst leaving the isolator 12 on the sides of the mesa and in the area around the mesa. The next technological step was depositing the upper 13 and lower contacts (on the substrate 4) made of a nickel-gold alloy with thickness of 100 nm.

[0038] Then, the crystal was divided along the crystal cleavage planes forming strips containing many devices, wherein the division took place along the designed locations of the light guide windows, i.e. the front window 15 and back window 16 of individual device. The first step enabling the division was scratching the crystal along the intended division lines. Next, due to the mechanical stresses, the crystal was broken along the cleavage planes.

[0039] The next step was dividing the strips on the individual devices performed in an analogical way to the division on the strips, except not along the cleavage planes, but perpendicularly to them.

[0040] The last step was the assembly of the devices in a standard TO-56 housing. A thin layer of SnPb solder was placed on the housing socket. The device was placed on said layer with the substrate 4 side towards the solder. The device was connected with the support by the annealing process at temperature of 200 C. Afterwards, an electrical contact with the upper contact 13 material was made, using the ball-bonding technique. Then, the housing of the diode was hermetically closed, using protective atmosphere preventing water condensation inside the housing. By applying the formed substrate the emission spectrum was widened and the modulation depth in the superluminescent diode emission spectrum was reduced (FIG. 7a) relative to the reference device with the same geometry, created in the same process, except on a substrate fragment with constant misorientation (FIG. 7b).

Example 2

[0041] The second embodiment of the present invention is a superluminescent diode with a widened emission spectrum and a linear variation of the misorientation angle in the y direction, described by the equation W4, created on a uniform GaO.sub.xN.sub.1-x substrate obtained in high-pressure growth. In the first step a GaO.sub.0.0005N.sub.0.9995 substrate was created by means of growing from a gallium solution of nitrogen under the pressure of 1000 MPa and at temperature of 1500 C. The obtained crystal was cut and polished so as to obtain a parallel-flat plate with typical thickness of 250 m. After appropriate mechano-chemical polishing, the crystal surface with gallium polarity had an atomic smoothness, demonstrated by the atomic steps in an Atomic Force Microscope image. The crystal surface was disoriented by 0.1 in relation to the direction of the crystallographic axis c of the GaN hexagonal (wurtzite) structure. Next, a 3 m thick positive photoresist 1 layer was deposited on the substrate. The layer was irradiated by means of a laser writer apparatus with a 405 nm wavelength emission laser as the light source. The irradiation was performed by scanning the photoresist 1 surface by a light beam, wherein the light intensity was changing according to the design of the substrate 4 forming. This example uses the irradiation pattern enabling to create on the substrate 4, in the region of one superluminescent diode, a misorientation angle in the y direction described by the equation W4:

[00007]$\begin{array}{cc}=\frac{{}_{\min }-{}_{\max }}{\exp \left(\frac{y-l}{b}\right)+1}+{}_{\max },& \left(\mathrm{W4}\right)\end{array}$

where .sub.max is the maximum misorientation angle in the direction perpendicular to the y direction equal to arctg(h/w), .sub.min is the minimum misorientation angle in the direction perpendicular to the y direction, b is a parameter affecting the profile shape. In this embodiment, the shape of the substrate surface can be described by the equation:

[00008]$\begin{array}{cc}z=\mathrm{xtg}\left(\frac{{}_{\min }-{}_{\max }}{\exp \left(\frac{y-l}{b}\right)+1}+{}_{\max }\right)& \left(\mathrm{W5}\right)\end{array}$

[0042] In the presented embodiment, the following parameters were applied: h=2.5 m, w=150 m, l=900 m, b=30, .sub.max=0.95, and .sub.min=0.1.

[0043] Substrate 4 with formed photoresist 1 was subjected to the reactive ions dry etching method using argon-chlorine plasma. The etching time was 17.5 minutes. The process allowed the photoresist 1 structure to be transferred to the gallium nitride bulk substrate 4. The obtained plane, in a form of wide, approximately flat areas, is shown in FIG. 8, having a varying misorientation angle in the y direction, shown in FIG. 9.

[0044] Next, the substrate 4 was placed in a MOVPE reactor, where 800 nm thick Ga.sub.0.92Al.sub.0.08N layer 5, doped with silicon to the 510.sup.18 cm.sup.3 level, was created, at the temperature of about 1050 C. Then, at the same temperature, a 100 nm thick layer of undoped GaN was created, acting as the lower waveguide 6. After lowering the temperature to 820 C. a light emitting region 7 was created, as an In.sub.0.1Ga.sub.0.9N/In.sub.0.02Ga.sub.0.98N multiple quantum well, where the number of quantum wells was three. Then, after increasing the reactor temperature to 1050 C. a Al.sub.0.2Ga.sub.0.98N:Mg layer 8 was created, for blocking the escape of the electrons. Afterwards, an undoped GaN layer was created, acting as the upper light guide 9. The next layer was the 430 nm thick Al.sub.0.05Ga.sub.0.95N upper cladding layer 10. The structure's growth was finished by a thin GaN:Mg subcontact layer 11 with magnesium concentration higher than 10.sup.20 cm.sup.3. After completion of the structure growth the reactor was cooled in nitrogen atmosphere.

[0045] Next, photolithography defining the mesa shape as a curved strip was performed (FIG. 5b). The ending curvature of the light guide 14 in relation to the crystal cleavage planes (the future exit windows of the light guide 15) was 6.

[0046] The process of creating the mesa and the upper contact, as well as division of the crystal on strips was carried in a way analogical to that described in the example 1. Then, a dielectric SiO.sub.2 layer was deposited on the edge of the chip strip, on the side of the front light guide window 15, the layer having a thickness such that its reflectivity coefficient was equal to 0.001. The layer allowed the additional reducing of the reflectivity coefficient of the front light guide widow 15. In the next step the division of the strip on chips was performed, as well as their assembly in a manner analogical to that described in the example 1.

[0047] Due to applying the substrate with a surface described by equation W5, the shape of the superluminescent diode emission spectrum was changed to a two-peak form, whilst making it wider at the same time. The example shows that the invention allows a significant influence on the shape of superluminescent diode emission spectrum. FIG. 10 presents the shape of superluminescent diode emission spectrum obtained according to the second embodiment of the present invention. Applying a substrate with wide, approximately flat areas allowed obtaining an increased intensity of light generation for chosen wavelengths, which allowed widening of the superluminescent diode emission spectrum.

Example 3

[0048] The third embodiment of the present invention is a superluminescent diode with a widened emission spectrum and a linear variation of the misorientation angle in the y direction, described by the equation W6, created on a uniform GaO.sub.xN.sub.1-x substrate obtained in high-pressure growth. In the first step a GaO.sub.0.0005N.sub.0.9995 substrate was created by means of growing from a gallium solution of nitrogen under the pressure of 1000 MPa and at temperature of 1500 C. The obtained crystal was cut and polished so as to obtain a parallel-flat plate with typical thickness of 250 m. After appropriate mechano-chemical polishing, the crystal surface with gallium polarity had an atomic smoothness, demonstrated by the atomic steps in an Atomic Force Microscope image. The crystal surface was disoriented by 0.2 in relation to the direction of the crystallographic axis c of the GaN hexagonal (wurtzite) structure.

[0049] Next, a 3 m thick positive photoresist 1 layer was deposited on the substrate 4. The layer was irradiated by means of a laser writer apparatus with a 405 nm wavelength emission laser as the light source. The irradiation was performed by scanning the photoresist 1 surface by a light beam, wherein the light intensity was changing according to the design of the substrate 4 forming. This example uses the irradiation pattern enabling to create on the substrate 4, in the region of one superluminescent diode, a misorientation angle in the y direction described by the equation W6:

[00009]$\begin{array}{cc}=\left(\frac{a_1}{\exp \left(\frac{y-{\mathrm{ld}}_1}{b_1}\right)}+\frac{a_2}{\exp \left(\frac{y-{\mathrm{ld}}_2}{b_2}\right)}\right).Math.\left(\frac{{}_{\min }-{}_{\max }}{a_1+a_2}\right)+{}_{\max },& \left(\mathrm{W6}\right)\end{array}$

where .sub.max is the maximum misorientation angle in the direction perpendicular to the y direction equal to arctg(h/w), .sub.min is the minimum misorientation angle in the direction perpendicular to the y direction, a.sub.1 and a.sub.2 are parameters affecting the relative heights of the first and second level, b.sub.1 and b.sub.2 are parameters affecting the profile shape of the first and second level, d.sub.1 and d.sub.2 are parameters affecting the location of the first and second level in the y direction. In this embodiment, the shape of the substrate surface can be described by the equation:

[00010]$\begin{array}{cc}z=\mathrm{xtg}\left(\left(\frac{a_1}{\exp \left(\frac{y-{\mathrm{ld}}_1}{b_1}\right)}+\frac{a_2}{\exp \left(\frac{y-{\mathrm{ld}}_2}{b_2}\right)}\right).Math.\left(\frac{{}_{\min }-{}_{\max }}{a_1+a_2}\right)+{}_{\max }\right)& \left(\mathrm{W7}\right)\end{array}$

In the presented embodiment, the following parameters were applied: h=3.6 m; w=150 m; l=1300 m; .sub.max=1.4; .sub.min=0.2; a.sub.1=1; a.sub.2=1.5; b.sub.1=0.3; b.sub.2=0.35; d.sub.1=0.36; and d.sub.2=0.58.

[0050] Substrate 4 with formed photoresist 1 was subjected to the reactive ions dry etching method using argon-chlorine plasma. The etching time was 17.5 minutes. The process allowed the photoresist 1 structure to be transferred to the gallium nitride bulk substrate 4. The obtained plane, with two smoothed levels, is shown in FIG. 11, having a varying misorientation angle in the y direction, shown in FIG. 12. Next, the substrate 4 was placed in a MOVPE reactor, where 800 nm thick Ga.sub.0.92Al.sub.0.08N layer 5, doped with silicon to the 510.sup.18 cm.sup.3 level, was created, at the temperature of about 1050 C. Then, at the same temperature, a 100 nm thick layer of undoped GaN was created, acting as the lower waveguide 6. After lowering the temperature to 820 C. a light emitting region 7 was created, as an In.sub.0.1Ga.sub.0.9N/In.sub.0.02Ga.sub.0.98N multiple quantum well, where the number of quantum wells was three. Then, after increasing the reactor temperature to 1050 C. a Al.sub.0.2Ga.sub.0.98N:Mg layer 8 was created, for blocking the escape of the electrons. Afterwards, an undoped GaN layer was created, acting as the upper light guide 9. The next layer was the 430 nm thick Al.sub.0.05Ga.sub.0.95N upper cladding layer 10. The structure's growth was finished by a thin GaN:Mg subcontact layer 11 with magnesium concentration higher than 10.sup.20 cm.sup.3. After completion of the structure growth the reactor was cooled in nitrogen atmosphere.

[0051] Next, photolithography defining the mesa shape as a curved strip was performed (FIG. 5b). The ending curvature of the light guide 14 in relation to the crystal cleavage planes (the future exit windows of the light guide 15) was 6.

[0052] The process of creating the mesa and the upper contact, as well as division of the crystal on strips and the assembly of the chips, was carried in a way analogical to that described in the example 1.

[0053] Due to applying the substrate described by equation W7, the shape of the superluminescent diode emission spectrum was changed to an approximately rectangular form. In this embodiment, the misorientation profile in y direction had a shape of two smoothed levels, wherein their heights can be different. The wide, approximately flat areas cause an increased light generation for the chosen wavelengths. As a result, in this embodiment, the superluminescent diode emission spectrum exhibits an approximately rectangular shape and is significantly wider in relation to the classical devices, which is shown in FIG. 13. The example shows, that the invention allows a substantial influence on the shape of the superluminescent diode emission spectrum.

[0054] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms including and in which are used as the plain-English equivalents of the terms comprising and wherein. Moreover, in the following claims, the terms first, second, and third, are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. 112, sixth paragraph, unless and until such claim limitations expressly use the phrase means for followed by a statement of function void of further structure.