JPH07106694A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a structure of ridge stripe type semiconductor laser having high electrical and thermal reliability and generating a fundamental transverse- mode oscillation. CONSTITUTION:A ridge stripe is provided with a plurality of wide parts W1, W3 and the resonator plane is designed to have a wide part. The wide parts ensure reliability in contact and the optical density is lowered by increasing the area of resonator resulting in the enhancement of thermal reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a semiconductor laser which can be used as a light source for optical communication.

[0002]

2. Description of the Related Art A semiconductor laser used as a light source for optical communication has a low threshold current and low operating current.
Since it is necessary to suppress the coupling loss with the optical fiber, it is necessary to oscillate in the fundamental transverse mode. Various semiconductor lasers such as a buried type and an internal stripe type have been proposed as structures that satisfy such requirements. However, the ridge waveguide type semiconductor laser can achieve a low threshold value, a low operating current, and crystal growth. However, there is an advantage that a process that is difficult to control such as diffusion of impurities is unnecessary. This ridge waveguide type semiconductor laser has a structure in which current is confined by embedding both sides of the ridge portion with an insulator, and it is necessary to make the width of the ridge portion as narrow as possible in order to reduce the threshold current. Furthermore, since the oscillation mode of the ridge waveguide type semiconductor laser is affected by the ridge width and the effective refractive index of the active layer immediately below the ridge portion, the ridge width is considerably narrowed in order to make the oscillation mode the basic transverse mode. For example, when the effective refractive index of the active layer directly under the ridge is 0.5% higher than that of the peripheral portion, the ridge width needs to be 2.5 μm or less.

However, when the ridge width is narrowed in this way, the area of the ridge head becomes small, so that the contact resistance with the electrode increases and the area of the resonator surface inevitably becomes small. As the optical density increases, the temperature of the cavity surface rises, and COD (Catastrophic O
There is a problem that the life of the device is shortened due to the occurrence of optical damage.

Further, a semiconductor laser used as a pumping light source for an EDFA (erbium-doped fiber amplifier) requires precise wavelength control because the pumping wavelength range of the EDFA is narrow. Has a large wavelength shift due to injection current and temperature changes
There is a problem that the excitation efficiency of A is lowered.

[0005]

SUMMARY OF THE INVENTION The present invention has a structure capable of causing a laser beam to oscillate in a fundamental transverse mode, and reduces the contact resistance at the ridge head and heat generation at the resonator surface. It is an object of the present invention to provide a structure of a semiconductor laser capable of achieving the above. Also,
Another object of the present invention is also to increase the wavelength selectivity of the emitted beam.

[0006]

The present invention has been made in view of the above problems, and has a ridge portion provided by etching the semiconductor layers on both sides to directly above the active layer. In a ridge waveguide type semiconductor laser in which both sides of a ridge portion are filled with a material having a large refractive index difference with a semiconductor layer, a plurality of wide portions and narrow portions are provided in the ridge portion along the cavity direction. At the same time, the semiconductor laser device is characterized in that the resonator surface is provided in the wide portion of the ridge portion, and further, the wide portion and the narrow portion are λ / 2 or an integral multiple of λ / 2 ( (λ is the oscillation wavelength)
The semiconductor laser device is characterized in that the semiconductor laser device is repeatedly formed in a cycle.

[0007]

EXAMPLES The contents of the present invention will be described below based on examples. FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention, and FIG. 2 is a plan view showing the shape of a ridge portion in the embodiment.

In FIG. 1, 1 is an n-type GaAs substrate, and 2 is
Is an n-type InGaP cladding layer with a thickness of 1.5 μm, 3 is an InGaAs well layer with a thickness of 9 nm, and GaA with a thickness of 30 nm.
s barrier layer is a quantum well active layer, and 4 is a film thickness 2 μ
m is a p-type InGaP clad layer, 5 is a high carrier concentration p-type GaAs contact layer having a film thickness of 0.8 μm, and 6 is SiN.
x film (x is a natural number), 7 is a p-side electrode, 8 is an n-side electrode, and 9 is formed by etching the p-type InGaP cladding layer 4 to a distance of 0.5 μm directly above the active layer. It is a ridge.

Here, the shape of the ridge portion 9 is, as shown in FIG. 2, formed by etching using a lithography technique.
A plurality of wide portions having a width w1 and a plurality of narrow portions having a width w2 are formed along the cavity direction, and correspondingly, a wide portion having a width w3 and a narrow portion having a width w4 are formed in the SiNx film 6. The resonator surface is provided in the wide portion of the ridge portion 9.

With such a structure, the ohmic contact width of the ridge head portion is widened by w3-w4, so that the contact resistance of this portion can be reduced, and the area of the resonator surface is also reduced. Similarly, since the width is increased by w1-w2, the light density on the resonator surface is reduced, and the temperature rise on the resonator surface can be suppressed.

In this case, current is injected into the entire lower portion of the ridge of the active layer 3 to emit light, but light is propagated only in the w2 portion, and in the w1-w2 portion. Since light and gain coexist in the light propagation direction, light propagation hardly occurs. Therefore, if w2 is set to a sufficiently small value, fundamental transverse mode oscillation can be obtained even if w1 is set to a considerably large value. For example, in this embodiment, when w2 is 2.5 μm, w1
, A fundamental transverse mode oscillation can be obtained even if the width is increased to 10 μm.

The shape of the ridge portion does not necessarily have to be a phrase shape as shown in FIG. 2, and any shape such as a corrugated shape or a sawtooth shape may be used as long as it has a plurality of wide portions and narrow portions. The effect can be obtained, and the wide portions and the narrow portions do not necessarily have to have a periodic shape. Further, the present invention can be applied to any ridge waveguide type semiconductor laser, and is not limited to the materials used in the description of the present embodiment, and the active layer is formed of a bulk semiconductor. In that case, the same effect can be obtained when another dielectric or polyimide is used for current narrowing.

Next, in addition to the above configuration, the shape of each wide portion and the shape of each narrow portion are unified, and the repetition period T of the wide portion and the narrow portion is λ / 2 or λ / 2. It is possible to enhance the wavelength selectivity of the emitted beam by forming a periodic shape in which the wide portion and the narrow portion having the same shape are repeated at an integer multiple of the period. That is, by changing the shape of the ridge portion 9 to λ / 2 or a repeating shape with a cycle of an integral multiple of λ / 2, the shape of the ridge portion 9 changes with respect to the light leaked into the cladding layer from the light propagation path. It is possible to feel a periodical effective refractive index change corresponding to the above, and the periodic shape of the ridge portion 9 functions similarly to the grating in the distributed feedback laser, and thereby the emitted beam has wavelength selectivity. Is something that can be done.

[0014]

As is apparent from the above description, the ridge waveguide type semiconductor laser adopting the structure of the present invention reduces the contact resistance of the ridge head and maintains the resonator while maintaining the fundamental transverse mode oscillation. There is an advantage that it is possible to prevent the reliability of the element from being lowered due to the temperature rise of the surface, and the basic length of the outgoing beam is changed by changing the shape of the ridge portion 9 to λ / 2 or a periodic shape of an integral multiple of λ / 2. The advantage is that the modes can be controlled.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a semiconductor laser manufactured in an example of the present invention.

FIG. 2 is a plan view showing the shape of a ridge portion according to the embodiment of the present invention.

[Explanation of symbols]

 1 is an n-type GaAs substrate 2 is an n-type InGaP clad layer 3 is a quantum well active layer 4 is a p-type InGaP clad layer 5 is a p-type GaAs contact layer 6 is a SiNx film 7 is a p-side electrode 8 is an n-side electrode 9 is a ridge Department

Claims (2)

[Claims] 1. A ridge portion having a convex shape is provided by etching the semiconductor layers on both sides to just above the active layer, and both sides of the ridge portion are filled with a material having a large difference in refractive index from the semiconductor layer. In the ridge waveguide type semiconductor laser described above, the ridge portion is provided with a plurality of wide portions and narrow portions along the cavity direction, and the resonator surface is provided in the wide portion of the ridge portion. Characteristic semiconductor laser. 2. The wide portion and the narrow portion of the ridge portion are repeatedly provided at λ / 2 or an integral multiple period of λ / 2 (λ is an oscillation wavelength). Semiconductor laser.