JP2007149939A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser of which the manufacturing process has simplicity, a superior laser characteristic and high reliability. <P>SOLUTION: Al ions are implanted into an area 10 aside a mesa stripe 6 in a ridged laser wherein a GaInNAs quantum well layer 4 is an active layer. Since Al and N are strongly joined with each other after annealing, electric conductivity is lowered, and a band gap is increased because of the crystal mixing effect of guide layers 3 and 5 and the quantum well layer 4 so as to form a current block layer. Thus, a semiconductor laser of which the structure has a small threshold current and high reliability can be formed by nearly the same manufacturing step as that of the ridged laser. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a technique effective when applied to a transmission light source for optical fiber communication.

Semiconductor lasers widely used in various industries such as optical communication and optical recording are required to be low in cost and high in performance. GaInNAs quantum well lasers that can grow crystals on GaAs substrates and oscillate in the 1.3 μm band suitable for optical fiber communications are ideal bands compared to lasers using InGaAsP already formed on InP substrates. Since it has a structure, it is expected that laser characteristics at high temperatures are improved (see Non-Patent Document 1).
Furthermore, since a high-speed operation can be realized reflecting that a GaInAs quantum well laser that does not contain N has a high relaxation oscillation frequency, GaInNAs in which only a few percent of N is introduced can be expected to operate at high speed.
However, a laser on a GaAs substrate such as GaInNAs generally uses a ridge type that narrows the current by forming a part of the upper p-type cladding layer in a stripe shape without cutting the active layer.

FIG. 3 shows a GaInNAs quantum well laser according to the prior art. This figure shows a GaInNAs long-wavelength laser crystal grown on a GaAs substrate 1 by the MBE method, an n-type GaInP cladding layer 2 having a thickness of 1.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ and a carrier having a thickness of 120 nm. N-type GaAs guide layer 3 with a concentration of 1 × 10 ¹⁸ cm ⁻³ , GaInNAs-3 quantum well active layer 4, a p-type GaAs guide layer 5 with a thickness of 120 nm and a carrier concentration of 7 × 10 ¹⁷ cm ⁻³ , a thickness of 1.5 A p-type GaInP cladding layer 6 having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ at μm and a p-type GaAs contact layer 7 having a thickness of 200 nm and a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ are sequentially stacked.

  The width of the GaInNAs quantum well layer of the GaInNAs quantum well active layer is 5 nm, the width of the GaAs of the barrier layer is 30 nm, and the quantum well layers and the barrier layers are alternately stacked. In this example, the GaAs substrate is n-type conductivity, the n-type electrode 9 is ohmically connected to the substrate, and the p-type electrode 8 is ohmically connected to the GaAs contact layer 7. The p-type GaInP cladding layer is etched on the inverted mesa trapezoid with a hydrochloric acid-based etching solution to form stripes. This etching solution etches only GaInP, and the GaAs guide layer 5 is not etched.

  In FIG. 1, the width called the mesa width, that is, in contact with the GaAs guide layer 6, the length of the lower side of the trapezoid on the reverse mesa is 2 μm. The region of the GaInNAs quantum well active layer 4 below the mesa width becomes an effective active layer region. However, the ridge type laser has a drawback that the threshold current is larger than that of the buried type laser.

Koji Nakahara et al., “Characteristics of MBE-grown GaInNAs / GaAs laser with suppressed impurities”, IEICE Technical Report Vol.104, ED2004-142, P.41-44, October 2004

  As described above, a laser on a GaAs substrate such as GaInNAs generally uses a ridge type in which a part of the upper p-type cladding layer is striped to narrow the current without cutting the active layer. . In such a ridge type laser, the current injected from the upper electrode 8 shown in FIG. 3 spreads to the active layer 4 other than the current injection region immediately below the ridge structure. There was a drawback that the threshold current increased.

  An object of the present invention is to provide a semiconductor laser capable of reducing a threshold current in a GaInNAs quantum well laser. Furthermore, it is providing the semiconductor laser which can reduce manufacturing cost.

  According to the present invention, at least two sets of reflecting mirrors or distributed feedback type resonator structures are provided, and at least a first cladding layer, a first guide layer, an active layer, a first layer on a semiconductor substrate or an insulator substrate. In the semiconductor laser in which the two guide layers and the second cladding layer are sequentially stacked, the active layer is formed of a GaInNAs quantum well layer, and the upper second cladding layer is formed in a stripe shape. And at least a part of a multilayer film including the active layer, the first guide layer, the first cladding layer, the second guide layer, and the second cladding layer other than the current injection region immediately below the ridge structure. This is achieved by a semiconductor laser device having a structure in which Al is introduced in this region.

  By introducing Al into the GaInNAs quantum well layer by such ion implantation, the photoluminescence intensity is reduced and the electrical conductivity is reduced. Further, the GaInNAs quantum well layer and the barrier layer are mixed by Al ion implantation, and the band gap of the well layer is increased. Due to the above effects, it becomes difficult for current to flow in the ion-implanted region 10, and the current can be narrowed only under the mesa stripe where ions are not implanted (see Non-Patent Document 1).

  According to the present invention, it is possible to provide a semiconductor laser capable of reducing the threshold current in a GaInNAs quantum well laser and reducing the manufacturing cost.

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

FIG. 1 shows a cross-sectional structure of an embodiment in which the present invention is applied to a 1.3 μm band semiconductor laser used as a transmission light source for optical communication. The figure shows a 1.3 μm-band GaInNAs long-wavelength laser crystal grown on the GaAs substrate 1 by the MBE method. The n-type GaInP cladding layer 2 has a thickness of 1.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ^−3. N-type GaAs guide layer 3 with 120 nm thickness and carrier concentration 1 × 10 ¹⁸ cm ⁻³ , GaInNAs-3 quantum well active layer 4, p-type GaAs guide layer 5 with 120 nm thickness and carrier concentration 7 × 10 ¹⁷ cm ⁻³ A p-type GaInP cladding layer 6 having a thickness of 1.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ is laminated. On the GaInP cladding layer 6, a thickness of 200 nm and a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ is formed. A p-type GaAs contact layer 7 is laminated.

The width of the GaInNAs quantum well layer of the GaInNAs quantum well active layer is 5 nm, the width of the GaAs of the barrier layer is 30 nm, and the quantum well layers and the barrier layers are alternately stacked. The p-type GaInP cladding layer 6 is etched on a reverse mesa trapezoid with a hydrochloric acid-based etching solution to form a mesa stripe structure having a mesa width of 2 μm. In addition, Al ion-implanted regions 10 exist in the GaAs guide layers 3 and 5 and the GaInNAs quantum well active layer 4 beside the mesa. As shown in FIG. 2, Al ions are implanted parallel to the slope of the mesa stripe ((111) A plane). It is necessary to inject twice on the left and right.
Here, the implantation angle for ion implantation of Al may be an arbitrary angle from an angle parallel to the A plane in FIG. 2 to an angle perpendicular to the substrate to be implanted.
Also, the amount of Al implanted is a concentration on the order of 10 ¹⁶ cm ⁻² , which is such an amount that a high resistance layer is formed in the GaInNAs quantum well active layer 4.

  Here, effects produced by injecting Al into the GaInNAs quantum well active layer 4 will be described. It has been disclosed by T. Takeuchi et al. On pages 35 to 36 of IEEE LEOS 2003, MD1 that GaInNAs degrades the photoluminescence intensity when Al is present in the atmosphere during growth. This is presumably because Al and N are easy to bond. The same applies to the case where Al is introduced into the GaInNAs quantum well layer by ion implantation, in which the photoluminescence intensity decreases and the electrical conductivity decreases. Further, the GaInNAs quantum well layer and the barrier layer are mixed by Al ion implantation, and the band gap of the well layer is increased. Due to the above effects, it is difficult for current to flow in the ion-implanted region 10, and the current can be narrowed only under the mesa stripe where ions are not implanted.

  After ion implantation, annealing is performed at 400 ° C. for 30 minutes. There is also a technique of increasing the resistance by injecting protons, ie, H, into the active layer. However, in this case, the characteristics of the semiconductor laser deteriorate rapidly, which is not suitable for practical use. Al ion implantation has long-term reliability because the bond between Al and N is strongly stabilized after annealing.

  The GaInNAs semiconductor laser fabricated in this example is a FP laser with a resonator length of 200μm and a front mirror of 70% and a rear mirror of 90%, and has a low threshold current equivalent to a 1.8mA buried laser at 25 ° C. I was able to get it. In addition, it was a low threshold current of 3.9 mA even at a high temperature of 85 ° C. The slope efficiencies were 0.23 W / A and 0.19 W / A at 25 ℃ and 85 ℃, respectively. A reliability test was performed at 85 ° C and a constant light output of 10 mW, and the operating current degradation rate after 180 hours was 0.2% or less.

  In this embodiment, the active layer is a GaInNAs quantum well layer, but it goes without saying that the same effect can be obtained even if Sb is introduced into GaInNAs.

FIG. 4 shows a sectional structure of an embodiment in which the present invention is applied to a 1.3 μm band semiconductor laser used as a transmission light source for optical communication. The multilayer structure of the semiconductor is the same as that of the first embodiment. In forming the mesa stripe, the p-type GaInP cladding layer 6 was formed by dry etching using chlorine gas (Cl ₂ ), and the remaining thickness of the p-type GaInP cladding layer 6 was set to 100 nm. The mesa width is 1.8 μm. In the GaAs guide layers 3 and 5 and the GaInNAs quantum well active layer 4 beside the mesa, there are regions 10 in which Al ions are implanted. In this embodiment, since the side walls of the mesa stripe are perpendicular to the substrate, one ion implantation is sufficient. As in Example 1, after ion implantation, annealing is performed at 400 ° C. for 30 minutes.

  The GaInNAs semiconductor laser fabricated according to this example is a FP laser with a resonator length of 300μm and a front mirror of 50% and a rear mirror of 90%, and has a low threshold current equivalent to a 2.5mA buried laser at 25 ° C. I was able to get it. In addition, it was a low threshold current of 5.3 mA even at a high temperature of 85 ° C. The slope efficiencies were 0.42 W / A and 0.33 W / A at 25 ℃ and 85 ℃, respectively. A reliability test was performed at 85 ° C and a constant light output of 10 mW, and the degradation rate of the operating current at 360 hours was 0.15% or less.

It is a structural diagram showing the Example of this invention. It is explanatory drawing of the one part process of the Example of this invention. It is a structural diagram which shows a prior art example. 1 is a structural diagram showing an embodiment of the present invention.

Explanation of symbols

1 ... GaAs substrate,
2 ... n-type GaInP cladding layer,
3 ... n-type GaAs guide layer,
4 ... GaInNAs 3 quantum well active layer,
5 ... p-type GaAs guide layer,
6 ... p-type GaInP cladding layer,
7 ... p-type GaAs contact layer,
8… Upper electrode,
9 ... bottom electrode,
10… Al ion implantation area.

Claims (9)

At least two sets of reflectors or distributed feedback resonator structures;
A multilayer film in which at least a first cladding layer, a first guide layer, an active layer, a second guide layer, and a second cladding layer are stacked in this order on a semiconductor substrate or an insulator substrate;
The active layer is composed of a GaInNAs quantum well layer,
Forming a ridge structure in which the second cladding layer is formed in a stripe shape;
A semiconductor laser device having a structure in which Al is introduced into a region including at least the active layer and further to a region other than a current injection region through which a current injected into the active layer passes.   2. The semiconductor laser device according to claim 1, wherein Sb is introduced into the GaInNAs quantum well layer of the active layer.   2. The semiconductor laser device according to claim 1, wherein the first and second cladding layers are made of GaInP.   3. The semiconductor laser device according to claim 2, wherein the first and second cladding layers are made of AlGaAs.   2. The semiconductor laser device according to claim 1, wherein the first and second guide layers are made of GaAs.   3. The semiconductor laser device according to claim 2, wherein the first and second guide layers are made of GaAs.   4. The semiconductor laser device according to claim 3, wherein the stripe shape is constituted by an inverted mesa structure.   4. The semiconductor laser device according to claim 3, wherein the stripe shape is a vertical mesa structure. 5. The semiconductor laser device according to claim 4, wherein the stripe shape is constituted by a vertical mesa structure.

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