KR100691623B1 - Semiconductor laser diode and manufacturing method thereof - Google Patents

Abstract

A semiconductor laser diode having a low internal loss and a method of manufacturing the same are provided. A semiconductor laser diode according to the present invention includes a first cladding layer formed on a substrate; A lower light guide layer formed on the first cladding layer; An active layer formed on the lower light guide layer; An upper light guide layer formed on the active layer; It includes a second clad layer formed on the upper light guide layer. The first clad layer includes an n-type doped layer formed on the substrate; And a first undoped layer formed on the n-type doped layer and adjacent to the lower light guide layer. The second cladding layer may further include: a second undoped layer formed on the upper light guide layer adjacent to the upper light guide layer; And a p-type doped layer formed on the second undoped layer.

Description

Semiconductor laser diode and its manufacturing method {SEMICONDUCTOR LASER DIODE AND METHOD FOR MANUFACTURING THE SAME}

1 is a view schematically showing an energy band structure of a semiconductor laser diode according to a conventional example.

2 is a view schematically showing an energy band structure of a semiconductor laser diode according to another conventional example.

3 is a schematic side cross-sectional view of a semiconductor laser diode according to an embodiment of the present invention.

4 is a diagram schematically illustrating an energy band structure of the semiconductor laser diode of FIG. 3.

FIG. 5 is a graph showing input current vs. light output of semiconductor laser diodes according to an embodiment of the present invention and a comparative example. FIG.

6 to 8 are cross-sectional views illustrating a method of manufacturing a semiconductor laser diode according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

101: substrate 102a: n-type doping layer

102b: first undoped layer 102: first cladding layer

103a: lower light guide layer 103b: upper light guide layer

104: active layer 105: second clad layer

105a: p-type doped layer 105b: second undoped layer

106: contact layer

The present invention relates to a semiconductor laser diode, and more particularly, to a high power semiconductor laser diode having a low internal loss and a method of manufacturing the same.

Currently, semiconductor laser diodes are widely used as optical devices and optical communication devices for recording or reading data in CD-ROMs, DVDs, HD-DVDs, and Blu-Ray players. In recent years, the application range has been extended to display devices using lasers.

In order to fabricate a high power semiconductor laser element used for a dual laser display device or the like, the resonator length or the ridge width must be increased. However, when the resonator length is increased, the mirror loss (output coming out of the laser diode) becomes small, thereby reducing slope efficiency (slope efficiency (inclination of the input current vs. light output graph)). The following equation shows the relationship between internal losses and slope efficiency.

In Equation 1, 'L' represents the resonator length, 'R' represents reflectance of the semiconductor laser diode cross section, and 'α _i ' represents internal loss. When the resonator length is increased for high power, the slope efficiency as a whole decreases as shown in Equation 1 above. Therefore, in order to maintain the slope efficiency while increasing the resonator length, a structure for reducing internal losses is required.

Most of the internal losses of the semiconductor laser diode are proportional to the proportion of the overlapped portion between the doped region and the optical mode. Among the n-type and p-type doped regions, in particular, the ratio of overlapping with the p-type doped region has a greater influence on the internal loss. Using this property, a method of using an asymmetric waveguide structure to reduce internal loss or forming a thick optical guide layer such that the total thickness of the undoped optical guide layer is generally 500 nm or more has been proposed.

1 is a view schematically showing an energy band structure of a semiconductor laser diode according to a conventional example. In FIG. 1, 'Ec' represents the edge of the conduction band. Referring to FIG. 1, the semiconductor laser diode 10 includes an n-type cladding layer and a p-type cladding layer, and two light guide layers and an active layer interposed therebetween. In Fig. 1, the hatched portions represent the doped regions and the hatched portions represent the artificially doped (undoped) regions. By interposing the light guide layers sandwiching the active layer between the n-type and p-type cladding layers, the semiconductor laser diode 10 has a SCH (Separate Confinement Heterostructure) structure.

As shown in FIG. 1, the refractive indices of the cladding layer and the light guide layer (n-type cladding layer and the light guide layer adjacent thereto) of the n-side are represented by Layer) is larger than the refractive index. This can be seen from the fact that the energy bandgap of the cladding layer and the light guide layer on the n side is smaller than the energy bandgap of the cladding layer and the light guide layer on the p side, respectively. Gap becomes smaller). As a method of increasing the refractive index of the n-side region, a layer having a large refractive index may be periodically inserted into the n-side region.

Thus, by making the refractive index of the cladding layer and the light guide layer on the n side larger than that of the cladding layer and the light guide layer on the p side, an asymmetric waveguide structure as a whole can be obtained. According to this asymmetric waveguide structure, the optical mode is biased to the n-type cladding layer, thereby reducing the ratio of overlapping portions between the p-type doped region (p-type clad layer) and the optical mode, thereby causing internal loss of the laser diode 10. Will be reduced.

However, in order to form an asymmetric waveguide structure as shown in FIG. 1, more compound semiconductor materials having different properties or compositions are required, which complicates the manufacturing process. In addition, the optical confinement factor (OCF) between the active layer and the light mode, which emits light, is reduced, thereby increasing the possibility of increasing the threshold current.

2 is a view schematically showing an energy band structure of a semiconductor laser diode 20 according to another conventional example. Referring to FIG. 2, by increasing the total thickness of the undoped light guide layer to about 500 nm or more, the ratio of the optical modes overlapping with both the highly doped clad layers is minimized, thereby reducing the internal loss. However, according to the present method, it is difficult to reduce the overall beam size, so that the shape of the far field may be slightly increased, and there is a problem that there is a high possibility that there are multiple optical modes in the vertical direction.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a high quality semiconductor laser diode in which internal losses are reduced, threshold currents are suppressed, and multiple optical modes in the vertical direction are prevented.

It is another object of the present invention to provide a method for manufacturing a semiconductor laser diode which can reduce internal losses, suppress an increase in munturn current, and prevent generation of multiple optical modes in the vertical direction.

In order to achieve the above technical problem, a semiconductor laser diode according to the present invention, the first cladding layer formed on a substrate; A lower light guide layer formed on the first cladding layer; An active layer formed on the lower light guide layer; An upper light guide layer formed on the active layer; It includes a second clad layer formed on the upper light guide layer. The first clad layer includes an n-type doped layer formed on the substrate; And a first undoped layer formed on the n-type doped layer and adjacent to the lower light guide layer. The second cladding layer may further include: a second undoped layer formed on the upper light guide layer adjacent to the upper light guide layer; And a p-type doped layer formed on the second undoped layer.

Preferably, the total thickness of the lower light guide layer and the upper light guide layer is 0.05 to 0.5 ㎛, the thickness of the first undoped layer and the second undoped layer are each 0.3 ㎛ or less. In addition, preferably the thickness of the active layer is 1 to 15nm.

The lower light guide layer and the upper light guide layer may be formed of a material having an Al _x Ga _{1 - x} As composition formula, where 0.2 ≦ _x ≦ 0.4, and the first clad layer and the second clad layer may be Al _y Ga _{1 - y} As can be made of a material having a composition formula (where 0.40≤y≤1), the active layer is a material having a GaAs _{1 - z} P _z composition formula (here, 0≤z≤0.1) Can be done. The upper and lower light guide layers and the active layer are formed of an undoped layer without artificial doping. In addition, the upper and lower light guide layers have a larger refractive index (smaller energy band gap) than the first and second clad layers to form an SCH structure.

According to the semiconductor laser diode, the first and second clad layers and the lower and upper light guide layers may have a symmetrical structure up and down about the active layer. In addition, the semiconductor laser diode may further include a contact layer formed on the second clad layer.

In order to achieve the other technical problem of the present invention, the method of manufacturing a semiconductor laser diode according to the present invention comprises the steps of forming a first clad layer by sequentially growing an n-type doping layer and a first undoped layer on a substrate; ; Forming a lower light guide layer adjacent to the first undoped layer on the first undoped layer; Forming an active layer on the lower light guide layer; Forming an upper light guide layer on the active layer; Forming a second clad layer by sequentially growing a second undoped layer and a p-type doped layer adjacent to the upper light guide layer on the upper light guide layer.

Preferably, the lower light guide layer and the upper light guide layer is formed to have a total thickness of 0.05 to 0.5㎛, so that the first undoped layer and the second undoped layer each have a thickness of 0.3㎛ or less It is formed, the active layer is formed to have a thickness of 1 to 15nm.

The lower light guide layer and the upper light guide layer may be formed to have an Al _x Ga _1-x As composition formula (where 0.2 ≦ _x ≦ 0.4), and the first clad layer and the second clad layer may be formed of Al. It may be formed to have a _y Ga _1-y As composition formula (where 0.40 ≦ _y ≦ ₁ ), the active layer may be formed to have a GaAs _1-z P _z composition formula (where 0 ≦ _z ≦ 0.1). . The upper and lower light guide layers and the active layer may be formed as an undoped layer without artificial doping.

The manufacturing method may further include forming a contact layer on the second clad layer.

The present invention provides a method of reducing the internal losses of the semiconductor laser diode to reduce the threshold current and to improve the slope efficiency. To this end, the present invention places the first and second undoped layers in the clad layer portions adjacent to the lower light guide layer and the upper light guide layer. By having such an undoped layer, not only the internal loss is reduced, but also the possibility of multiple optical modes being present is suppressed and far field performance is maintained.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity, and the elements denoted by the same reference numerals in the drawings are the same elements.

3 is a sectional view of a semiconductor laser diode according to an embodiment of the present invention. Referring to FIG. 3, the semiconductor laser diode 100 includes a first cladding layer 102, a lower light guide layer 103a, an active layer 104, and an upper light guide layer sequentially stacked on a GaAs substrate 101. 103b, the second cladding layer 105, and the contact layer 106 form a SCH structure as a whole. The first cladding layer 102 includes an n-type doped layer 102a and a first undoped layer 102b. In addition, the second cladding layer 105 includes a p-type doped layer 105a and a second undoped layer 105b. The upper and lower light guide layers 103a and 103b and the active layer 104 are included in the undoped region without artificial doping.

As shown in FIG. 3, the first undoped layer 102b and the second undoped layer 105b belong to the clad layers 102 and 105 and have a lower light guide layer 103a and an upper light guide layer 103b. Adjacent to). In other words, a portion of the clad layer adjacent to the light guide layers 103a and 103b in both cladding layers 102 and 105 is an undoped layer in which doping is removed. By arranging the first and second undoped layers 102b and 105b in the clad layer portion adjacent to the light guide layer in this manner, the ratio of overlapping portions between the doped region and the optical mode is reduced. As a result, the internal loss of the semiconductor laser diode 100 is reduced.

In the conventional semiconductor laser diode structure (see FIGS. 1 and 2), the light guide layer is undoped but the entire clad layer is doped. In addition, the optical mode of the semiconductor laser diode is present over the light guide layer and part of both clad layers. However, in the present invention, the doping is removed from a part of the clad layer adjacent to the light guide layer, thereby reducing the overlapping ratio between the light mode and the doped region. This reduction in overlap rate results in a reduction in internal losses.

According to the semiconductor laser diode 100, the internal loss can be reduced without using a thick light guide layer of 500nm or more as shown in FIG. Thus, the overall beam size can be reduced, the possibility of multiple optical modes being present is suppressed, and performance degradation is prevented even in the shape of a far field. In addition, since there is no need to use an asymmetric structure as shown in FIG. 1, the number of types of compound semiconductor materials required for the construction of the semiconductor laser diode 100 is not increased, and the increase in the moon turn voltage is suppressed.

Preferably, the total thickness of the lower light guide layer 103a and the upper light guide layer 103b is 0.05 to 0.5 μm. If the total thickness of the light guide layer is too large, multiple light modes in the vertical direction may occur. In addition, the thickness of the first undoped layer 102b and the second undoped layer 105b is preferably 0.3 μm or less, respectively. It is preferable that the thickness of the active layer 104 is 1-15 nm. Preferably, the first and second cladding layers 102 and 105 and the lower and upper light guide layers 103a and 103b have a vertically symmetrical structure around the active layer 104.

The lower light guide layer 103a and the upper light guide layer 103b may be made of a material having an Al _x Ga _1-x As composition formula, where 0.2 ≦ _x ≦ 0.4, and the first cladding layer 102 The second clad layer 105 may be formed of a material having an Al _y Ga _1-y As composition formula, where 0.40 ≦ _y ≦ ₁ . The active layer 104 may be made of a material having a GaAs _1-z P _z composition formula, where 0 ≦ _z ≦ 0.1. The contact layer 106 may be made of GaAs (P ⁺ -GaAs) doped with a p-type dopant.

4 is a diagram schematically illustrating an energy band structure of the semiconductor laser diode 100 of FIG. 3. In FIG. 4, the hatched portion corresponds to the doped region and the hatched portion corresponds to the undoped region. Referring to FIG. 4, light guide layers 103a and 103b sandwiching the active layer are interposed between the two clad layers 102 and 105. The light guide layers 103a and 103b serve to limit the injected carrier to the active layer 104. In addition, the light guide layers 103a and 103b have a smaller energy bandgap (and therefore a larger refractive index) than the cladding layers 102 and 105, thereby collecting light generated in the active layer in the waveguide region.

The energy bands of the lower light guide layer 103a and the upper light guide layer 103b form a symmetrical structure with respect to the active layer 104. In addition, the energy bands of the first cladding layer 102 and the second cladding layer 105 also form a symmetrical structure with respect to the active layer 104. Due to this symmetrical structure, the degree of coupling (OCF) between the active layer 104 and the light mode, which emits light, is increased and the threshold current is reduced.

In addition, a portion of the first cladding layer 102 adjacent to the lower light guide layer 103a is formed of the undoped first undoped layer 102b, and the upper light guide layer 103b of the second cladding layer 105 is formed. Some regions adjacent to) are made of the undoped second undoped layer 105b. Therefore, there is no need to increase the thickness of the light guide layer (see FIG. 2) in order to reduce the internal loss of the semiconductor laser diode. This reduces the overall beam size, prevents the far field shape from growing and reduces the possibility of multiple optical modes.

5 is a graph showing simulation (simulation) results of the light output of the semiconductor laser diode. In particular, FIG. 5 shows the input current vs. light output of the laser diodes according to the Examples and Comparative Examples. In the embodiment, a portion of the clad layer adjacent to the light guide layer is not doped as shown in FIGS. In the comparative example, the entire cladding layer was evenly doped, except that the laser diode of the comparative example was the same as the laser diode of the example.

Referring to FIG. 5, it can be seen that the Moonturn current decreases and the slope efficiency increases in the embodiment compared to the comparative example. That is, by placing the undoped layer in the region adjacent to the light guide layer in the cladding layer as in the present invention, the minimum current (threshold current) for generating substantial light output is reduced, and the slope of the input current vs. light output curve (slope) Efficiency) is increased.

Next, with reference to FIGS. 6-8, the manufacturing method of the semiconductor laser diode which concerns on one Embodiment of this invention is demonstrated.

First, referring to FIG. 6, the n-type doped layer 102a and the first undoped layer 102b are sequentially grown on the GaAs substrate 101. Accordingly, the first cladding layer 102 for electron injection is formed on the substrate 101. The first clad layer 102 may be formed of a material having an Al _y Ga _1-y As composition formula, where 0.40 ≦ _y ≦ ₁ . It is preferable that the thickness of the 1st undoped layer 102b is 0.3 micrometer or less.

Next, as shown in FIG. 7, the lower light guide layer 103a, the active layer 104, and the upper light guide layer 103b are sequentially formed on the first undoped layer 102b. The lower light guide layer 103a is formed to be adjacent to the first undoped layer 102b. Each of the lower light guide layer 103a and the upper light guide layer 103b may be formed of a material having an Al _x Ga _1-x As composition formula, where 0.2 ≦ _x ≦ 0.4. The light guide layers 103a and 103b are preferably formed to have a total thickness of 0.05 to 0.5 μm. The active layer 104 may be formed of a material having a GaAs _1-z P _z composition formula, where 0 ≦ _z ≦ 0.1. The active layer 104 is preferably formed to have a thickness of 1 to 15nm.

Next, as shown in FIG. 8, the second undoped layer 105b and the p-type doped layer 105a are sequentially grown on the upper light guide layer 103b. Accordingly, the second cladding layer 105 for hole injection is formed on the upper light guide layer 103b. The second undoped layer 105b is formed to be adjacent to the upper light guide layer 103b. Like the first cladding layer 102, the second cladding layer 105 may be formed of a material having an Al _y Ga _1-y As composition formula, where 0.40 ≦ _y ≦ ₁ . It is preferable that the thickness of the 2nd undoped layer 105b is 0.3 micrometer or less similarly to the 1st undoped layer 102b. Thereafter, a contact layer 106 for contact with the p-side electrode (not shown) is formed on the second clad layer 105. This contact layer 106 may be formed of, for example, a p-type doped GaAs semiconductor.

According to the semiconductor laser diode manufacturing method described above, both cladding layers 102 and 105 have undoped layers 102b and 105b at portions adjacent to the light guide layers 103a and 103b. Accordingly, it is evident in view of the foregoing that the internal loss of the semiconductor laser diode and the munturn current can be reduced and the occurrence of multiple optical modes can be suppressed.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. In addition, it will be apparent to those skilled in the art that the present invention may be substituted, modified, and changed in various forms without departing from the technical spirit of the present invention described in the claims.

As described above, according to the present invention, the internal loss is reduced by disposing the first undoped layer and the second undoped layer on a part of both clad layers adjacent to the light guide layer. In addition, since there is no need to use an asymmetrical structure or a thick light guide layer, an increase in the threshold current can be suppressed and generation of multiple optical modes can be prevented. In addition, in the existing material growth conditions, the doping process is manufactured by simply adjusting the doping process, and the design of the optical waveguide is much freer.

Claims (17)

A first clad layer formed on the substrate; A lower light guide layer formed on the first clad layer; An active layer formed on the lower light guide layer; An upper light guide layer formed on the active layer; And A second cladding layer formed on the upper light guide layer, The first clad layer includes an n-type doped layer formed on the substrate; A first undoped layer formed on the n-type doped layer and adjacent to the lower light guide layer, The second clad layer includes: a second undoped layer formed on the upper light guide layer adjacent to the upper light guide layer; And a p-type doped layer formed on the second undoped layer. The method of claim 1, The total thickness of the lower and upper light guide layer is a semiconductor laser diode, characterized in that 0.05 to 0.5㎛. The method of claim 1, And the thickness of the first undoped layer and the second undoped layer is 0.3 탆 or less, respectively. The method of claim 1, The thickness of the active layer is a semiconductor laser diode, characterized in that 1 to 15nm. The method of claim 1, And the lower light guide layer and the upper light guide layer are made of a material having an Al _x Ga _{1 - x} As composition formula, where 0.2 ≦ _x ≦ 0.4. The method of claim 1, The first cladding layer and the second cladding layer is a semiconductor laser diode, characterized in that made of a material having an Al _y Ga _{1 - y} As composition formula, wherein 0.40≤y≤1. The method of claim 1, The active layer is a semiconductor laser diode, characterized in that made of a material having a GaAs _{1 - z} P _z composition formula, wherein 0≤z≤0.1. The method of claim 1, And the upper and lower light guide layers and the active layer are undoped. The method of claim 1, And the first and second clad layers and the lower and upper light guide layers have a symmetrical structure up and down about the active layer. The method of claim 1, And a contact layer formed on the second clad layer. The method of claim 1, And the lower and upper light guide layers have larger refractive indices than the first and second clad layers, respectively. Forming a first clad layer by sequentially growing an n-type doped layer and a first undoped layer on the substrate; Forming a lower light guide layer adjacent to the first undoped layer on the first undoped layer; Forming an active layer on the lower light guide layer; Forming an upper light guide layer on the active layer; And And forming a second clad layer by sequentially growing a second undoped layer and a p-type doped layer adjacent to the upper light guide layer on the upper light guide layer. Way. The method of claim 12, The lower light guide layer and the upper light guide layer is a manufacturing method of a semiconductor laser diode, characterized in that formed to have a total thickness of 0.05 to 0.5㎛. The method of claim 12, And the first undoped layer and the second undoped layer are each formed to have a thickness of 0.3 μm or less. The method of claim 12, The active layer is a method of manufacturing a semiconductor laser diode, characterized in that formed to have a thickness of 1 to 15nm. The method of claim 12, And forming a contact layer on the second clad layer. The method of claim 12, And the lower and upper light guide layers are formed to have larger refractive indices than the first and second clad layers, respectively.

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