KR101778016B1 - Distributed feedback laser diode diode and manufacturing method thereof - Google Patents

Abstract

A distributed feedback laser diode according to an embodiment of the present invention includes an InP substrate; a diffraction grating layer, a lower separate confinement heterostructure (SCH) layer, an active layer, an upper SCH layer, a p-InP layer, and a p-InGaAs layer which are sequentially grown and crystallized from the upper part of the InP substrate; an injection current blocking layer buried around the side surface of a mesa formed to have a predetermined width from the p-InP layer to a lower direction; an n-electrode and a p-electrode respectively formed on the lower part of the InP substrate and the upper part of the p-InGaAs layer; and an anti-reflection film and a high reflection film respectively formed on the front output face of one side and the rear output face of the other side. The diffraction grating layer includes a plurality of diffraction gratings along a longitudinal direction defined in a direction from the front output face to the rear output face. The cross-sectional area of the diffraction grating and a distance between the diffraction grating and the active layer are varied by a selective region nodule growth method. It is possible to provide a new DFB laser structure that reduces the generation of spatial hole burning.

Description

TECHNICAL FIELD [0001] The present invention relates to a distributed feedback laser diode and a method of manufacturing the same. [0002] DISTRIBUTED FEEDBACK LASER DIODE DIODE AND MANUFACTURING METHOD THEREOF [

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a single-wavelength semiconductor laser diode used as a high-speed modulation light source for optical communication, and more particularly, to a distributed feedback (DFB) laser diode capable of mitigating spatial hole burning phenomenon.

In the conventional case, a DFB laser oscillating at a designated single wavelength in the wavelength band of 1260 nm to 1630 nm has been used as a direct modulation light source for optical communication. Especially, as the transmission capacity of the optical communication system is increasing, the modulation speed of the direct modulation DFB laser is required to be increased from the existing 1.25 Gbps or 2.5 Gbps to 10 Gbps or 25 Gbps.

On the other hand, in the case of DFB laser, spatial hole burning phenomenon may be a problem. In the spatial hole burning phenomenon, the photon density in the longitudinal direction of the laser resonator is not uniform, This is caused by insufficient charge replenishment from the region, which means that the hole has a small excess or a small degree of mobility.

Especially, the increase of the modulation speed of the direct modulation DFB laser deepens the spatial hole burning phenomenon and maximizes the effect caused thereby. For example, in a DFB laser having a uniform grating (diffraction grating), k * L (where k is the optical feedback coefficient of the diffraction grating and L is the length of the resonator) is 1.5 or less and reflectance 1 The photon density inside the resonator becomes minimum at the rear output surface and becomes maximum between the center of the resonator and the front output surface, and consequently, the photon density inside the resonator becomes maximum The maximum / minimum ratio of " 2 "

That is, the photon density curve induces a hole density curve of a reversed phase (a vertical inversion), and a region that is significantly lower than the average of the charge density curves is a spatial hole burning region, and the spatial hole burning region described above occurs in the longitudinal direction of the resonator The direct modulation speed decreases, the modulation line chirping increases, distortion of the modulated waveform becomes large, and single wavelength stability becomes low.

In order to mitigate such spatial hole burning phenomenon, a 90-degree phase shift region is inserted in a DFB laser diode to change the duty of the diffraction grating continuously (U.S. Patent No. 6,577,660 B1) and the diffraction grating period Patent US 2014/0211823 A1) has been studied, but it is difficult to apply to the uniform diffraction grating type DFB laser of the present invention, and further, there is a disadvantage that expensive exclusive e-beam lithography equipment must be used to realize this.

US Patent No. 6,577,660 B1 United States Patent Application Publication 2004/0211823 A1

Disclosed is a distributed feedback laser diode and a method of manufacturing the same according to an embodiment of the present invention to solve the above-mentioned problems.

It is an object of the present invention to provide a novel DFB laser structure that mitigates the occurrence of spatial hole burning by moderately changing the photon density distribution inside the laser resonator and moderately changing the distribution of the charge density corresponding thereto.

The solution to the problem of the present invention is not limited to those mentioned above, and other solutions not mentioned can be clearly understood by those skilled in the art from the following description.

A distributed feedback laser diode according to an embodiment of the present invention includes an InP substrate; A diffraction grating layer, a bottom SCH, an active layer, an upper SCH layer, a p-InP layer, and a p-InGaAs layer, which are sequentially grown from the top of the InP substrate; An injection current blocking layer buried around the side surface of the mesa formed so as to have a predetermined width in the downward direction from the p-InP layer; An n-electrode and a p-electrode respectively formed on the lower portion of the InP substrate and the upper portion of the p-InGaAs layer; And an anti-reflection film and a high reflection film respectively formed on a front output face of one side and a rear output face of the other side, wherein the diffraction grating layer is formed along a longitudinal direction defined by a direction from the front output face to the rear output face Wherein a cross-sectional area of the diffraction grating and a distance between the diffraction grating and the active layer are varied by a selective region nodule growth method.

Wherein the distance between the rear output surface and the front output surface is defined as L, the optical feedback coefficient by the diffraction grating is maximized near the rear output surface, and the distance from the rear output surface to the front output surface is from 0.5L to 0.6 It is preferable that it is the minimum in any one of the portions.

Preferably, the active layer is a multiple quantum well structure including a barrier layer of InGaAsP or InGaAlAs composition and a quantum well layer of InGaAsP or InGaAlAs composition, wherein the barrier layer and the quantum well layer are repeatedly deposited five to ten times.

The diffraction grating is not formed in the region adjacent to the rear output surface, and the n-InP layer is filled.

The injection current blocking layer may include a p-InP layer and an n-InP layer.

It is preferable that the injection current blocking layer is an InP layer having semi-insulating properties by doping Fe or Ru.

The band gap energy of the diffraction grating layer is preferably adjusted to be 0.1 eV or more higher than the band gap energy of the active layer.

The band cap energy of the diffraction grating layer is preferably adjusted to be smaller than or equal to 0.1 eV or less than the band gap energy of the active layer.

It is preferable that the diffraction grating layer is formed in a bulk type or a multiple quantum well type.

In addition, a distributed feedback laser diode according to an embodiment of the present invention includes a diffraction grating layer, a lower SCH layer, an active layer, an upper SCH layer, a p-InP layer, and a p-InGaAs layer on the n- InP doped p-InP layer and n-InP layer are formed on the p-InP layer and the p-InP layer, respectively. and a p-InGaAs layer. In the DFB laser, the active layer is a multi-quantum well structure in which a barrier layer and a quantum well layer of InGaAsP or InGaAlAs composition are repeatedly laminated five to ten times. The optical gain wavelength is about 1310 nm The diffraction grating layer of the InGaAsP composition has a band gap energy of about 1.08 eV and a band gap energy of 0.1 eV or more higher than that of the active layer. The DFB laser diode has an anti-reflection film having a reflectance of 5% And a p-electrode is provided above the n-InP substrate and the p-InGaAs layer, respectively. The DFB laser diode has a resonator length L of about 300 [mu] m, The cross sectional area of the diffraction grating having a period of about 1900 nm in the length direction of the resonator from the output face to the front output face is varied by the selective area crystal growth (SAG) method and the optical feedback coefficient by the diffraction grating is changed to the rear output The maximum is 100 / cm in the vicinity of the surface, 25 / cm in the middle (0.5L) or 0.6L of the resonator, and continuously changes to 50 / cm in the vicinity of the front output surface.

The n-InP layer can be filled without forming a diffraction grating in the 20 to 30 um region adjacent to the rear output surface.

The oscillation wavelength can be adjusted between 1260 and 1630 nm by adjusting the band gap energy of the active layer and the diffraction grating layer and adjusting the period of the diffraction grating.

The resonator length can be adjusted between 200 and 300 μm.

Instead of the p-InP layer for injecting current blocking and the n-InP layer, Fe or Ru may be doped to replace the InP layer having semi-insulating properties.

The bandgap energy of the diffraction grating layer may be adjusted to be less than or equal to 0.1 eV below the band gap energy of the active layer to exhibit complex coupled grating characteristics.

The diffraction grating layer can be fabricated in a bulk or multiple quantum well structure.

In the cross-sectional structure of the PBH, the remaining region can be etched and removed from the p-electrode to a portion of the upper portion of the n-InP substrate while leaving only a width of less than 10 .mu.m left and right around the resonator.

A method of manufacturing a distributed feedback laser diode according to an embodiment of the present invention comprises the steps of: (a) forming two thin film masks formed of SiO ₂ or Si ₃ N ₄ dielectric on an InP substrate so as to have a variable width, G; (b) crystal growth of an InGaAsP layer, an n-InP layer and an InGaAsP layer based on a width of the thin film mask using a selective area growth (SAG) method; (c) partially etching the InGaAsP layer using an optical hologram method to form a plurality of diffraction gratings having different thicknesses; (d) filling the diffraction grating with an n-InP layer to planarize the diffraction grating; And (e) sequentially forming a lower SCH (Separate Confinement Heterostructure) layer, an active layer, an upper SCH layer, and a part of the p-InP layer on the n-InP layer.

(F) forming a mesa having a predetermined width in a downward direction from the p-InP layer by etching; And (g) planarizing the p-InP layer and the p-InGaAs layer by crystallizing the p-InP layer and the p-InGaAs layer on the upper side after filling the periphery of the mesa with the injection current blocking layer.

In step (g), (h) an n-electrode and a p-electrode are formed on the lower portion of the InP substrate and the p-InGaAs layer, respectively, and a reflectance of 5% or less And a high reflective film having a reflectance of 90% or more.

The distributed feedback laser diode and the method for fabricating the same according to an embodiment of the present invention are advantageous for high-speed modulation because the photon density distribution and the charge density distribution in the length direction of the resonator are maximally planarized, It is advantageous for long-distance transmission because the modulation line width is narrow and the distortion of the modulation waveform is small, and the single wavelength oscillation stability is also high.

In addition, uniform grating with constant grating period without 90 ° phase shifting region can be manufactured by optical hologram method, so it is simple to manufacture and it is economically advantageous for mass production of DFB laser diode.

The effects of the present invention are not limited to those mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the following description.

1 is a vertical structure view of a distributed feedback laser diode of a general uniform diffraction grating.
2 is a cross-sectional view of a general PBH (Planar Buried Heterostructure) type distributed feedback laser diode.
3 (a) is a graph showing the optical feedback coefficient k in accordance with the longitudinal direction of the resonator of a general distributed feedback type laser diode. FIG. 3 (b) is a graph showing the photon density and the charge density along the length direction of the resonator to be.
4 is a vertical structure view of an embodiment of a distributed feedback laser diode according to an embodiment of the present invention.
5 (a) is a graph showing the optical feedback coefficient k along the longitudinal direction of the resonator of the distributed feedback laser diode according to the embodiment of the present invention, and Fig. 5 (b) And charge density.
6 is a diagram illustrating a vertical structure fabrication method of an embodiment of a distributed feedback laser diode according to an embodiment of the present invention.
7 is a vertical structure view of another embodiment of a distributed feedback laser diode according to an embodiment of the present invention.
8 is a view illustrating a vertical structure manufacturing method of another embodiment of the distributed feedback laser diode according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

Hereinafter, a distributed feedback laser diode and a distributed feedback laser diode manufacturing method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The oscillation wavelength of the distributed feedback laser is determined by the period of the diffraction grating. In the present invention, the description is made on the basis of 1310 nm, and the technique of the present invention can be similarly applied to fabrication of DFB lasers of different wavelengths.

1 shows a vertical structure of a distributed feedback laser having a general uniform diffraction grating in the longitudinal direction of a resonator. The diffraction grating layer, the lower SCH (separate confinement heterostructure) layer 14, The active layer 17, the upper SCH layer 18, the p-InP layer 19, and the p-InGaAs layer 20 are shown.

The active layer 17 serving as an optical gain medium with respect to the 1310 nm wavelength is formed of an InGaAsP or InGaAlAs barrier layer 15 having a thickness of 10 nm or less and an InGaAsP or InGaAlAs quantum well layer 16 having a thickness of 5 nm or less The optical waveguide core of the resonator is constituted together with the lower SCH layer 14 (18) of InGaAsP or InGaAlAs having n-type, p-type and 50-100 nm thick layers each having a multiple quantum well structure repeated five to ten times do.

In the diffraction grating layer, an n-InP layer 12 and an InGaAsP layer 13 having a band gap energy of about 1.08 eV are grown on the n-InP substrate 11, and then an optical hologram system is used to set the period to about 190 nm The InGaAsP layer 13 is partly etched and covered with the n-InP layer 12 again.

A plurality of diffraction gratings are formed in the diffraction grating layer. The thickness of the diffraction grating 13 is generally 20 to 50 nm, and the thickness of the n-InP layer 12 on the diffraction grating is 100 to 200 nm. Particularly, the diffraction grating 13 is manufactured using an optical hologram method. In this case, it is possible to fabricate a diffraction grating with simple equipment, which is superior in terms of mass production. However, the insertion of the phase shift region or the variation of the intensity of the diffraction grating It is impossible.

After the formation of the n-electrode 21 and the p-electrode 22, the distributed feedback laser diode having the vertical structure growth has a reflectance of 90% at the front output face and an anti-reflection film 23 having a reflectance of 5% The high reflection film 24 is vapor deposited so that the optical output of the DFB laser is mostly output through the front output surface.

2 is a cross-sectional view of a general planar buried heterostructure (PBH) type distributed feedback laser diode, in which only the active layer 17 with a narrow width W injected through the n-electrode 21 and the p- InP layer 31 and n-InP layer 32 are buried so as to be injected. For reference, a vertical structure of a distributed feedback laser diode having a general uniform diffraction grating shown in FIG. 1 in the longitudinal direction of the resonator corresponds to the plane A-A 'in FIG.

A general PBH type distributed feedback laser diode is fabricated by forming a diffraction grating 13 by primary crystal growth and fabricating up to a portion of the p-InP layer 19 by secondary crystal growth, The mesa is formed by etching. The mesa is buried with the p-InP layer 31 and the n-InP layer 32 by the third crystal growth, and then the p-InP layer 19 and the p-InGaAs layer 20 are planarized planar). Herein, the p-InP layer 31 and the n-InP layer 32 for injecting charge blocking can be replaced with semi-insulating InP layers.

The structure of the above-described PBH type distributed feedback type laser diode has good current injection efficiency for the active layer 17 and high stability of the single transverse mode operation of the laser. In addition to the fabrication of the diffraction grating by the optical hologram method, Is widely used in the fabrication of laser diodes and adopts the same structure and method in the present invention.

FIG. 3 shows a distribution curve of the optical feedback coefficient (k), photon density and charge density of a diffraction grating along the longitudinal direction of the resonator in a distributed feedback laser diode having a general uniform diffraction grating.

When the distance between the high reflection film 24 and the anti-reflection film 23 is defined as L, this is the length of the laser resonator. The reflectance of the high reflection film 24 = 90%, the reflectivity of the reflection-free film 23 = 1%, k * L (the optical feedback coefficient k of the diffraction grating) (L)) = ~ 1.5, the optical feedback coefficient k of the diffraction grating has a constant value of 50 / cm over the length L of the resonator.

The photon density distribution inside the resonator becomes maximum at around 0.6 L due to the high reflection film 24 and the anti-reflection film 23, becomes minimum at L = 0 with the high reflection film 24, and the maximum / minimum ratio exceeds 2. The charge density inside the resonator means the residual amount after the injected charge is consumed by the induced discharge, and since the induced emission is proportional to the photon density, it always has the distribution curve of the reverse phase (upside down) of the photonic density distribution curve.

Therefore, the maximum photon density distribution near 0.6L induces a small amount of charge in this region, but the charge replenishment from the adjacent resonator region is not smooth, especially the filling of the hole with a low mobility is delayed, and the spatial hole burning (SHB) region.

4 is a vertical structural view of an embodiment of a distributed feedback laser diode according to an embodiment of the present invention and shows an example of adjusting the intensity of the diffraction grating so that the optical feedback coefficient of the diffraction grating 43 varies in the longitudinal direction of the resonator . That is, by making the optical feedback coefficient curve of the reverse phase based on the photon density distribution curve generated in the distributed feedback laser diode having the conventional uniform diffraction grating, the photon density distribution and the charge density distribution are flattened, .

Here, the intensity of the diffraction grating for determining the optical feedback coefficient of the diffraction grating can be varied by adjusting the effective refractive index variation of the diffraction grating and the interval between the diffraction grating and the active layer. The effective refractive index variation of the diffraction grating is proportional to the cross sectional area of the InGaAsP layer 43 having a high refractive index in the form of a diffraction grating buried in the n-InP layer 42 having a low refractive index, so that the sectional area is increased or the diffraction grating 43 and the active layer 17 The intensity of the diffraction grating can be increased and the optical feedback coefficient can also be increased. Conversely, in a section where the cross-sectional area of the diffraction grating 43 is reduced or the interval between the diffraction grating 43 and the active layer 17 is widened, the optical feedback coefficient becomes small.

 FIG. 5 is a graph showing the optical feedback coefficient k, the photon density, and the distribution of charge density according to the longitudinal direction of the resonator of the distributed feedback laser diode according to an embodiment of the present invention. In FIG. 5, a distributed feedback laser diode And has an optical feedback coefficient curve of a reverse phase with respect to a photon density distribution curve generated in the optical fiber. Specifically, k = 25 / cm at the maximum photon density of 0.6L and k = 50 / cm at the lowest photon density, k = 100 / Value is maintained at about 50 / cm as in the conventional case.

As described above, the photon density distribution curve in the resonator due to the variable optical feedback coefficient has a spatial hole burning (SHB) in the charge density curve as the ratio between the maximum and minimum is 1.4 times or less as shown in FIG. 5 (b) Area generation is suppressed or spatial hole burning is greatly mitigated.

6 illustrates a method of fabricating a distributed feedback laser diode according to an embodiment of the present invention. The method includes forming a diffraction grating 43 having a variable optical feedback coefficient using a selective area growth (SAG) The implementation is characterized.

6A is a horizontal view of a mask shape for the SAG. _Two SiO ₂ or Si ₃ N ₄ dielectric thin film masks 100 having a thickness of 100 to 300 nm formed on the InP substrate 11 are spaced apart at intervals of 10 to 20 μm (G ), And the mask width V is symmetrically variable. The SAG utilizes the principle that the growth rate in the opening G between the masks 51 increases in proportion to the mask width V when the crystal growth is performed using the metal organic chemical vapor deposition (MOCVD) apparatus (a) Mask induces the growth of the InGaAsP layer 41, the n-InP layer 42 and the InGaAsP layer 43 of variable thickness as in (b).

When the minimum value of the mask width (V) is set to about 20um and the maximum value is set to about 80um and placed at positions 0.6L and L = 0 (rear output face), the layer thickness at the position L = 0 (rear output face) 0.6 times larger than the layer thickness at 0.6 L, and when the maximum value of the mask width (V) is increased to 120 μm, the thickness ratio is ~ 2 times. The dotted line between the openings G in (a) represents a resonator region having a width of 1 to 2 um and a length L of 300 um and the band gap energy of the InGaAsP layer 43 on which the diffraction grating is to be formed is 1.08 eV It is near.

6C shows a diffraction grating formed by partially etching the InGaAsP layer 43 so that the period becomes about 190 nm by using an optical hologram method. The diffraction grating is formed by thinning the InGaAsP layer 43 to a thickness of about 20 to 50 nm The cross section of the diffraction grating increases.

6D shows a state in which the diffraction grating 43 is buried and planarized by the n-InP layer 42 by the secondary crystal growth and the lower SCH layer 14, the active layer 17, the upper SCH layer 18 ) And p-InP (19). In this case, since the thickness of the n-InP layer 42 for embedding the diffraction grating 43 and planarizing the surface is 100 to 200 nm, it has a variable thickness to strengthen the intensity of the diffraction grating at the position of L = 0 (rear output surface) The InGaAsP layer 41 having a high refractive index is added to increase the transverse mode size of the laser light.

After the secondary crystal growth shown in (d) of FIG. 6, mesa formation, third-order crystal growth of the current blocking layer, and planar fourth-order crystal growth are performed. The same as the production of the distributed feedback laser diode, so that a detailed description thereof will be omitted.

7 is a vertical structural view of another embodiment of a distributed feedback laser diode according to an embodiment of the present invention. Specifically, a diffraction grating is not formed in a region adjacent to the rear output surface on which the high reflective film 24 is formed .

Generally, in the case of a distributed feedback laser diode with an uniform diffraction grating, the oscillation wavelength (DFB mode) is determined by the combination of the phases of the diffraction gratings on the front and rear output planes, It is mainly dependent on the phase of the grating, which can produce two distributed feedback laser diodes, two DFB mode oscillations, a first order DFB mode oscillation, a first order DFB mode oscillation, a first order DFB mode oscillation, A gap mode oscillation or the like.

Therefore, the diffraction grating is not formed in the region (20 to 30 μm) of the length (N) adjacent to the rear output surface, that is, the rear output surface, thereby stabilizing the laser oscillation mode by blocking the influence of the phase value of the diffraction grating on the rear output surface .

Here, the length N of the portion where the diffraction grating is not formed is 20 to 30 um, which is 10% or less of the entire length of the resonator, so that the optical feedback coefficient k, photon density and charge density distribution curve characteristics shown in FIG. The SHB relaxation effect can be ensured and the stabilization effect of the laser oscillation mode can be obtained.

8 shows a vertical structure fabrication method of another embodiment of a distributed feedback laser diode according to an embodiment of the present invention. The vertical structure of a diffraction grating vertical structure (41, 42, 43) And the crystal growth is blocked in the region of 20 to 30 um in length (N) adjacent to the rear output surface during crystal growth.

8A is a mask shape for the SAG, and has a variable width equal to the mask shown in FIG. 6A and has a length (N) of 20 to 30 μm adjacent to the rear output surface connected to each other (b) As shown in FIG.

The manufacturing process and principle of FIGS. 8B, 8C, and 8D are the same as those of FIGS. 6B and 6B except that a diffraction grating is not formed in a region of a length (N) (c) and (d).

Although the distributed feedback type laser diode of the present invention in which the spatial hole burning (SHB) is relaxed according to the present invention and the method of manufacturing the same are described with the assumption that the resonator length is 300 μm, The same applies to 250um and 200um which are widely used.

In addition, the bandgap energy of the diffraction gaps layer 43 is set to be around 1.08 eV and the refractive index of the pure refractive index combination type index coupled) uniform diffraction grating distributed feedback type laser diode. However, when the band gap energy of the diffraction gap layer is set to 1.0 eV or less, it is necessary to consider that the diffraction grating absorbs light at an oscillation wavelength of 1310 nm The principle of SHB relaxation of the present invention can be applied as it is to a refractive index + complex coupled uniform diffraction grating type distributed feedback laser diode.

Here, the diffraction gap layer may be a bulk or multi-quantum well type crystal growth layer having a specific band gap energy.

The embodiments and the accompanying drawings described in the present specification are merely illustrative of some of the technical ideas included in the present invention. Therefore, it is to be understood that the embodiments disclosed herein are not intended to limit the scope of the present invention but to limit the scope of the present invention. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. It should be interpreted.

11: n-InP substrate 14: lower SCH layer
15: barrier layer 16: quantum well layer
17: multiple quantum well active layer 18: upper SCH layer
21: n- electrode 22: p-electrode
23: antireflection film 24: highly reflective film
41: InGaAsP layer 42: n-InP layer
43: InGaAsP diffraction grating 51, 52: SAG mask

Claims (9)

InP substrate;
A diffraction grating layer, a bottom SCH, an active layer, an upper SCH layer, a p-InP layer, and a p-InGaAs layer, which are sequentially grown from the top of the InP substrate;
An injection current blocking layer buried around the side surface of the mesa formed so as to have a predetermined width in the downward direction from the p-InP layer;
An n-electrode and a p-electrode respectively formed on the lower portion of the InP substrate and the upper portion of the p-InGaAs layer; And
An antireflection film and a high reflection film respectively formed on a front output face of one side and a rear output face of the other side;
/ RTI >
Wherein the diffraction grating layer includes a plurality of diffraction gratings along a longitudinal direction defined in a direction from the front output face to the rear output face, the cross-sectional area of the diffraction grating and the distance from the active layer to the rear output face, Lt; / RTI >
The distance between the rear output surface and the front output surface is defined as L,
the thickness of the InGaAsP layer formed between the n-InP substrate and the diffraction grating layer and the optical feedback coefficient due to the diffraction grating are maximized near the rear output surface, and the distance from the rear output surface to the front output surface And a minimum value in any one of 0.5L to 0.6L.
delete The method according to claim 1,
And an n-InP layer is filled in the region adjacent to the rear output surface without forming a diffraction grating.
The method according to claim 1,
Wherein the injected current blocking layer is formed of an InP layer having semi-insulating properties by doping Fe or Ru without using p-InP / n-InP.
The method according to claim 1,
Wherein the band cap energy of the diffraction grating layer is adjusted to be smaller than or equal to 0.1 eV than the band gap energy of the active layer to increase the optical coupling efficiency of the diffraction grating.
The method according to claim 1,
Wherein the diffraction grating layer is formed in a bulk or multiple quantum well structure.
(a) disposing two thin film masks formed of SiO ₂ or Si ₃ N ₄ dielectric on the InP substrate so as to be variable in width and spaced apart from each other by a predetermined gap G;
(b) crystal growth of an InGaAsP layer, an n-InP layer and an InGaAsP layer based on a width of the thin film mask using a selective area growth (SAG) method;
(c) partially etching the InGaAsP layer using an optical hologram method to form a plurality of diffraction gratings having different thicknesses;
(d) filling the diffraction grating with an n-InP layer and planarizing the diffraction grating to form a diffraction grating layer; And
(e) sequentially forming a lower SCH (Separate Confinement Heterostructure) layer, an active layer, an upper SCH layer, and a part of a p-InP layer on the n-InP layer;
Lt; / RTI >
Wherein the diffraction grating layer includes a plurality of the diffraction gratings along a longitudinal direction defined by a direction from a front output surface to a rear output surface, wherein a cross-sectional area of the diffraction grating and a distance between the diffraction grating and the active layer Lt; / RTI >
The distance between the rear output surface and the front output surface is defined as L,
the thickness of the InGaAsP layer formed between the n-InP substrate and the diffraction grating layer and the optical feedback coefficient due to the diffraction grating are maximized near the rear output surface, and the distance from the rear output surface to the front output surface Wherein the minimum value is at least one of 0.5L to 0.6L.
8. The method of claim 7, wherein after step (e)
(f) forming a mesa having a predetermined width in a downward direction from the p-InP layer by etching; And
(g) filling the periphery of the mesa with an injection current blocking layer, and planarizing a p-InP layer and a p-InGaAs layer by crystal growth on the upper side;
Further comprising the steps of: forming a laser diode on the substrate;
The method of claim 8, wherein after step (g)
(h) forming an n-electrode and a p-electrode on the lower part of the InP substrate and the upper part of the p-InGaAs layer, respectively, and forming an antireflection film having a reflectance of 5% Depositing a high reflective film;
Further comprising the steps of: forming a laser diode on the substrate;

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