KR102301306B1 - Semiconductor laser diode device and manufacturing method - Google Patents

Abstract

An object of the present invention is to increase the doping concentration of the high-power laser diode device as a whole compared to the conventional method, but as it is closer to the region of the lower clad layer 2 where light is distributed, the doping concentration is lowered in three steps and then the region where the light is intensively distributed. In this study, the doping concentration is gradually lowered in 4 steps to realize the production of high-power laser diodes of several hundred mW or more that minimizes optical loss due to free carrier absorption. will be.
According to the present invention, the internal resistance is decreased while increasing the overall doping concentration of the high-power laser diode, and the doping of the lower cladding layer 2 is lowered to three stages and gradually lowered in the last four stages, free carriers in the region with high optical density. Light loss due to free carrier absorption is minimized, improving the performance of high-power laser diodes.

Description

Semiconductor laser diode device and its manufacturing method TECHNICAL FIELD

The present invention relates to a semiconductor laser diode device used in optical devices such as an optical recording medium, a laser printer, a distance measuring sensor, a factory automation sensor, and a motion recognition sensor, and a method for manufacturing the same.

Recently, laser diodes have been widely used as lighting sources for augmented and virtual reality and 3D depth sensors, and are being applied to various industries such as mobile phones, security, and games. In particular, as facial recognition sensors for mobile phones and security fields used outdoors as well as indoors become popular, laser diodes require high power.

One of the factors limiting the high output of laser diodes is the internal resistance and losses that occur when the output increases or the temperature rises. If the carrier concentration is too low, the current flow is not smooth and the resistance increases. On the other hand, if the carrier concentration is too high, free carrier absorption occurs in the light distribution region close to the active layer, thereby increasing the internal loss. This result reduces the efficiency by increasing the heat generation of the laser diode, and lowers the high temperature reliability and Catastrophic Optical Damage (COD) level. In the conventional GaAs/AlGaAs structure, the doping concentration of the high-power laser diode is about 1E+18cm ^-3 for the P region and 5E+17cm ^{-3 for the} N region, respectively, and there is a limit in achieving high power.

In addition, as a related art, Japanese Patent No. 04833671 proposes to arrange an intermediate layer (GaAs) between QW/barrier (QW/GaAs/barrier) while proposing an Al-free active layer to solve the COD problem, but complicating the layered structure It cannot be seen as more effective in problem-solving than doing it.

The present invention intends to optimize the doping concentration as follows in order to solve this problem.

That is, it is an object of the present invention to increase the doping concentration as a whole compared to the conventional method for a high-power laser diode of several hundred mW or more. In the intensively distributed region, the doping concentration is gradually and continuously lowered in four steps to realize high-power laser diode fabrication that minimizes optical loss due to free carrier absorption.

The semiconductor laser diode device according to the present invention has a ridge-type upper second clad on a lower clad layer 2, an active layer 3, an upper first clad layer 4 and an etch stop layer 5 on a semiconductor substrate 1 A current blocking layer (9) is provided on the side of the layer (6) and the upper second cladding layer (6). “The doping concentration of the lower cladding layer is divided into steps 1 to 4, and the method of gradually lowering the doping concentration in the last 4 steps” is characterized.

In accordance with the above object, the present invention uses Carbon (carbon), Mg (magnesium), Be (beryllium) or Zinc (zinc) to adjust the doping concentrations of the upper cladding layers (4) and (6) of the high-power laser diode to 1E+ Doping 18cm ^-3 or more.

In addition, the doping concentration of the lower cladding layer 2 of the high-power laser diode is doped in four steps using Silicon (silicon), Te (tellurium), or Se (selene).

That is, the doping concentration and doping depth of the lower clad layer 2 of the present invention may be made as follows.

The first-stage doping region is doped with a ^{concentration of 8.0E+17cm -3} or higher on the substrate by 1.5-2.5um, and the second-stage doping region is doped with 0.2-0.6um over the first-stage region with a concentration ^{of 7.0E+17cm-3 or higher.} In addition, the third-stage doping region is doped by 0.2-0.6 μm ^{over the second-stage doping region at a concentration of 6.0E+17cm -3} or higher, and the fourth-stage doping region is ^{from a concentration of 6.0E+17cm -3} or higher to 1.0E+17cm ^-3 or lower. Doping to a depth of 1.0~1.4um while gradually lowering it. The doping concentration and the depth error may be within ±10%.

As described above, the overall doping concentration is increased, but the doping concentration of the lower cladding layer 2 is stepwise lowered from the first to the third steps, and the last four steps are parabolic or linear, and a doping method is provided.

In addition, in the semiconductor laser diode device of the present invention, between the active layer 3 and the upper first cladding layer 4, the Alx composition gradually increases from the active layer 3 to the first cladding layer 4 toward the GRIN-SCH. (Graded Index Separate Confinement Hetero Structures).

In addition, optical damage (COD) is avoided by including an asymmetric structure in which the lower clad layer 2 and the upper first clad layer 4 have different Alx compositions to diffuse light into the lower clad layer 2 region. do.

In addition, the semiconductor laser diode device is a single mode high-power semiconductor laser diode device, and includes a selective buried ridge type structure.

Also, between the lower clad layer 2 and the active layer 3, a GRIN-SCH (Graded Index Separate Confinement Hetero Structures) structure in which the Alx composition is gradually lowered from the lower clad layer 2 toward the active layer 3 is included.

In addition, the active layer 3 includes InGaAs SQW (Single Quantum Well) and is undoped.

In addition, the doping concentration of the doping region of the lower clad layer 2 is stepwise lowered from the first-stage doping region to the third-stage doping region, and the doping concentration change in the last four-stage doping region is gradually lowered in a parabolic or linear manner. provides

In addition, the etch stop layer 5 includes p-type AlxGaAs (Alx composition is 0.6 or more).

According to the present invention, the internal resistance is decreased while the overall doping concentration of the high-power laser diode is increased, and the doping of the lower cladding layer 2 is lowered to 3 steps and gradually decreased in the last 4 steps to absorb free carriers in the high optical density region ( Optical loss due to free carrier absorption is minimized.

When the device evaluation conditions were operated at room temperature, light output 300mW, and CW (continuous wave) input current, the effects due to this were as follows.

Resistance (Rd) decreased by about 15%, voltage (Vop) decreased by about 10%, slope (Slop Efficiency) increased by about 10%, and optical damage level (COD level) increased by about 20% did.

In addition, when the device evaluation conditions were driven under high temperature 60℃, light output 300mW, and automatic power control APC (Auto Power Control) mode, the effects due to this were as follows.

In terms of high-temperature reliability, the high-temperature current is reduced by about 5% and the high-temperature current change rate is also reduced by about 5%.

Overall, the present invention greatly improves the efficiency of a high-power laser diode of several hundred mW by minimizing the internal resistance and internal loss of the high-power laser diode through the optimization of the doping concentration.

1 is a schematic diagram of a selective buried ridge type single mode high power semiconductor laser diode.
2 is a schematic diagram of doping concentrations of an upper clad layer and a lower clad layer according to the present invention.
3 is a flow chart of a fabrication process for manufacturing a single mode high-power laser diode according to the present invention.
4 and 5 are graphs showing the effect of room temperature and high temperature device characteristics according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view showing the structure of a selective buried ridge type semiconductor laser according to an embodiment of the present invention. On the compound semiconductor substrate 1, the lower clad layer 2, the active layer 3, the upper first clad layer 4, and the etch stop layer 5 are placed on the ridge-type upper second clad layer 6 and the upper third in order. 2 A current blocking layer 9 is formed on the side of the cladding layer 6 .

When the material of the primary growth of the high-power laser diode and the growth sequence are described in detail, the substrate 1 is composed of an n-type GaAs compound semiconductor. In this case, the lower clad layer 2 is composed of n-type AlxGaAs (Alx composition is 0.3 to 0.4), and the doping of the lower clad layer 2 is doped at a predetermined thickness by varying the concentration in 4 steps. The layered structure for each thickness according to the doping concentration is shown as a graph in FIG. 2 . Silicon (silicon) is used as the dopant of the lower cladding layer 2 . In addition, Te (tellurium) and Se (selene) dopants may be used.

The first-stage doping region is doped with a ^{concentration of 8.0E+17cm -3} or higher on the substrate by 1.5-2.5um, and the second-stage doping region is doped with 0.2-0.6um over the first-stage region with a concentration ^{of 7.0E+17cm-3 or higher.} In addition, the third-stage doping region is doped by 0.2-0.6 μm ^{over the second-stage doping region at a concentration of 6.0E+17cm -3} or higher, and the fourth-stage doping region is ^{from a concentration of 6.0E+17cm -3} or higher to 1.0E+17cm ^-3 or lower. Doping to a depth of 1.0~1.4um while gradually lowering it.

That is, in the embodiment of the present invention, the doping concentration and doping depth of the lower clad layer 2 were made as follows.

Step 1: 8.0E+17cm ^-3 or more, 2.0um above the substrate,

2nd stage: 7.0E+17cm ^-3 or more, 0.4um above 1st stage,

3rd stage: 6.0E+17cm ^-3 or more, 2nd stage up 0.4um,

Step 4: Lowered from 6.0E+17cm ^-3 or higher to 1.0E+17cm ^-3 or lower, and 1.2um doped above the third step. The doping concentration and the depth error may be within ±10%.

The doping concentration and doping depth for each doping region are graphically shown in FIG. 2 . While the doping concentration change of the first to third-stage doping regions changes step by step, the doping concentration change of the fourth-stage doping region is gradual and continuous, and forms a parabolic or linear profile. In addition, the upper clad layer has a higher doping concentration than the lower clad layer, so that light is diffused into the lower clad layer, thereby avoiding the risk of optical damage (COD).

The active layer 3 is made of InGaAs SQW (Single Quantum Well) and is undoped. And, in order to increase the carrier confinement effect, the Alx composition between the lower cladding layer 2 and the active layer 3 is gradually lowered, and the Alx composition is gradually lowered between the active layer 3 and the upper first clad layer 4 . It consists of a GRIN-SCH (Graded Index Separate Confinement Hetero Structures) structure. The upper first cladding layer 4 is composed of p-type AlxGaAs (Alx composition is 0.35 to 0.45), and the doping is 1E+18cm ^-3 or more. Carbon (carbon) or Zinc (zinc), Mg (magnesium), and Be (beryllium) may be used as dopants of the upper cladding layers (4) and (6). ^{The doping concentration of the upper cladding layers (4) and (6) is 1E+18cm -3} or higher using Carbon (carbon), Mg (magnesium), Be (beryllium) or Zinc (zinc).

The reason why the Alx composition of the lower clad layer 2 and the upper first clad layer 4 is different is that it forms an asymmetric structure that spreads light to the lower clad layer 2 region, resulting in high temperature reliability and optical damage (COD: This is to improve Catastrophic Optical Damage) avoidance.

The etch stop layer 5 is composed of p-type AlxGaAs (Alx composition is 0.6 or more).

The upper second cladding layer 6 is composed of p-type AlxGaAs (Alx composition is 0.35 to 0.45), and the doping is 1E+18cm ^-3 or more. The p-contact layer 7 is doped with p-type GaAs with a doping of 1E+19cm ^-3 or more. Primary growth is completed in this order.

The following is the fabrication of a single mode high-power laser diode (Fabricati process sequence (see Fig. 3)).

A ridge mask is made on the wafer where the primary growth is completed, and the ridge is formed by etching up to the etch stop layer through wet etching or dry etching. The current blocking layer 9 is composed of n-type AlxGaAs (Alx composition is 0.45 to 0.55) using MOCVD (Metal Organic Chemical Vapor Deposition). The ridge mask is removed and the p-type GaAs cap layer 10 is formed.

Through the EPI structure and FAB process technology as described above, there is an advantage in that the internal resistance and loss of the single-mode high-power laser diode can be minimized to improve the laser performance.

The high-power laser diode device manufactured according to the embodiment of the present invention was operated at a room temperature of 23° C., an output of 300 mW, and a CW driving condition to obtain a result as shown in FIG. 4 .

Resistance (Rd) decreased by about 15%, voltage (Vop) decreased by about 10%, slope (Slop Efficiency) increased by about 10%, and optical damage level (COD level) increased by about 20% It was confirmed that

That is, it can be seen that the resistance at the driving voltage of the laser diode device of the present invention is much lower than that of the prior art (Fig. 4(a)), which shows that a higher output and a higher threshold current can be reached soon. (Fig. 4(b)).

In addition, excellent reliability was demonstrated by continuously operating normally for 1000 hours under high temperature 60° C., output 300 mW, and APC driving conditions (FIG. 5).

That is, in terms of high-temperature reliability, the high-temperature current decreased by about 5% and the high-temperature current change rate also decreased by about 5%.

The right of the present invention is not limited to the AlGaAs system described above, but is also applicable to the InGaAlP system. That is, in the dopant concentration control for controlling the carrier concentration of the lower clad layer of the InGaAlP-based laser diode device, the dopant concentration is changed step by step and the dopant concentration of the upper clad layer is high, as described above, and the Al composition is changed between the upper clad layer and the lower part. Asymmetry in the cladding layer lowers the resistance during operation, increases the output, and solves the COD problem.

In addition, it is not limited to the embodiments described above, but it is defined by what is described in the claims, and it is obvious that a person of ordinary skill in the art can make various modifications and adaptations within the scope of the claims. .

1: substrate layer
2: lower cladding layer
3: active layer
4: upper first cladding layer
5: etch stop layer
6: upper second cladding layer
7: contact layer
8 : Ridge
9: current blocking layer
10: cap layer

Claims (1)

A method for manufacturing a semiconductor laser diode device, comprising:
preparing a semiconductor substrate 1;
forming a lower clad layer (2) on the semiconductor substrate (1);
forming an active layer (3) on the lower clad layer (2);
forming an upper first clad layer (4) on the active layer (3);
forming an etch stop layer (5) on the upper first clad layer (4);
forming a ridge-shaped upper second clad layer (6) on the etch stop layer (5);
Forming a current blocking layer (9) on the side of the upper second cladding layer (6);
The lower clad layer is doped with a dopant for controlling the carrier concentration, the concentration of the dopant is divided into 1 to 4 steps, and the first doping region in the direction from the substrate toward the active layer, the second doping region on the first doping region, 2 A method for manufacturing a semiconductor laser diode device, characterized in that a three-step doping region is placed on the step-doped region and a four-step doped region is placed on the third-step doped region, and the dopant concentration is doped gradually from the first-step doping region to the fourth-step doping region.

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