JPS6367348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device capable of stabilizing oscillation mode and extending operating life.

What is most important in semiconductor laser devices is unifying the oscillation transverse mode and extending the operating life. In general, the double heterojunction structure used in semiconductor laser devices has the effect of confining light in the vertical direction, but not in the horizontal direction, and if left as is, high-order transverse modes will occur during oscillation. An abnormal characteristic curve may easily occur in the current vs. light output characteristic. Furthermore, in most of the conventional semiconductor laser devices, the active layer, which is the light emitting region by current injection, is the main light guide layer, and the maximum light intensity point of the edge emission near-field image is in the active layer region. When light is guided by an active layer, light having a wavelength matching the bandgap of the active layer causes destruction of the active layer due to light absorption, shortens the operating life of the device, and becomes an important problem especially during laser oscillation.

FIG. 1 is a schematic cross-sectional view showing a conventional insulating film stripe type double heterojunction semiconductor laser device. n- on the GaAs substrate 1
A GaAlAs layer (first cladding layer) 2, a GaAs layer (active layer) 3, and a p-GaAlAs layer (second cladding layer) 4 are successively crystal-grown to form a heterojunction structure. A SiO ₂ film 5 is selectively attached on the second cladding layer 4 to form stripes for current confinement. Note that 6 and 7 in the figure indicate electrodes, respectively. With such a structure, light is confined in the active layer 3 in the vertical direction due to the difference in refractive index between the active layer 3 and the cladding layers 2 and 4. However, since there is no light confinement effect in the horizontal direction, there are problems such as high-order transverse modes are likely to occur as described above. Furthermore, since the maximum light intensity point is located in the active layer 3 region, there are problems such as shortened operating life as described above.

Therefore, the present inventors developed a semiconductor laser device as shown in FIG. 2 as a solution to the above problem. This device performs mesa etching on the first cladding layer 2 to form a mesa stripe portion 8, and then etches the cladding layer 2 on which the mesa stripe portion 8 is formed.
Each of the layers 3 and 4 is crystal-grown on top of the active layer 3, and the active layer 3 is bent to cause laser oscillation in an intermediate region thereof. This is because, in the refractive index distribution in the horizontal direction (dotted chain line A in Fig. 2) shown in Fig. 3a, two active layers with high refractive index induce mutually dependent mode guidance, as shown in Fig. 3b. By creating a mode. By adjusting the width of the region sandwiched by the active layer 3, the oscillation mode thus created can suppress higher-order modes and oscillate only in the fundamental transverse mode.
Furthermore, the maximum point of emission intensity in this case is the active layer 3
Since the active layer is located outside of the active layer, destruction of the active layer due to light absorption can be suppressed as much as possible.

However, in this type of device, a layer with a low refractive index (first cladding layer 2) exists at the position where the emission intensity is maximum as shown in FIGS. There was a problem in that the oscillation mode fluctuated in the direction of the substrate.

The present invention has been made in consideration of the above circumstances.
The purpose is to provide a semiconductor laser device that can stabilize the oscillation mode and extend its operating life, as well as reliably prevent fluctuations in the oscillation mode.

That is, the present invention forms a waveguide layer with a relatively high refractive index in the region sandwiched by the active layer,
The aim was to achieve the above objective.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 4 is a schematic cross-sectional view showing a schematic structure of an embodiment of the present invention. Note that the same parts as in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted. The difference between this embodiment and the one shown in FIG. 2 is that the upper part of the mesa stripe section 8 is formed of a GaAlAs layer (waveguide layer) 9 having a higher refractive index than the cladding layers 2 and 4. be. This structure is obtained by sequentially growing crystals of the first cladding layer 2 and the waveguide layer 9 on the substrate 1, and then performing mesa etching to a depth up to the cladding layer 2.

With such a configuration, let the refractive index of the first cladding layer 2, waveguide layer 9, active layer 3, and second cladding layer 4 be n ₁ , n ₂ , n ₃ , and n _{4 ,} respectively. , the relationship between these refractive indices is n ₃ > n ₂ > n ₄ = n ₁ . Therefore, the refractive index distributions in the vertical direction (dotted chain line B in the figure) and the horizontal direction (dotted chain line C in the figure) are as shown in FIGS. 5a and 5b, respectively. That is, since the layer with a relatively high refractive index (waveguide layer 9) is located at the position where the light intensity of laser oscillation is maximum, the fluctuation of the oscillation mode at the high injection level described above is eliminated. Also, as is clear from the horizontal refractive index distribution shown in Figure 5b, the layer with a high refractive index gives priority to the fundamental mode over the higher-order modes, so the fundamental mode becomes more can be stabilized. Therefore, the device not only achieves the effects shown in FIG. 2, that is, stabilizes the oscillation mode and extends the operating life, but also reliably prevents fluctuations in the oscillation mode. It has the effect that it can.

FIG. 6 is a schematic cross-sectional view showing the schematic structure of another embodiment. Note that the same parts as in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted. This embodiment differs from the previously described embodiment in that the first
A refractive index n ₅ (n ₅
= n ₁ = n ₄ ).

With such a configuration, the refractive index distribution in the vertical direction (dotted chain line D in the figure) and horizontal direction (dotted chain line E in the figure) becomes as shown in FIGS. It has a similar effect. Further, there is an advantage that carrier leakage from the active layer 3 to the waveguide layer 9 can be prevented.

Note that the present invention is not limited to the embodiments described above. For example, the refractive indices n ₁ , n ₄ , n ₅ of the first to third cladding layers do not necessarily have to be equal, as long as they satisfy the relationship n ₅ ≧n ₄ ≧n ₁ . good. Further, the thickness of each layer, the shape of the mesa stripe portion, etc. may be determined as appropriate according to specifications. Furthermore, in addition to GaAs-GaAl, the semiconductor composition forming the substrate and each layer is InP-
Of course, it can also be applied to InGaAsP.
In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view showing the general configuration of a conventional device, and Figure 2 is a GaAs-- which is the basis of the present invention.
A schematic cross-sectional view showing the general structure of a GaAlAs laser device, FIGS. 3a and 3b are schematic views for explaining the operation of the laser device, and FIG. 4 is a schematic cross-sectional view showing the schematic structure of an embodiment of the present invention. , FIGS. 5a and 5b are schematic diagrams for explaining the operation of the above embodiment, FIG. 6 is a cross-sectional schematic diagram showing the schematic configuration of another embodiment, and FIGS. 7a and 7b are schematic diagrams for explaining the operation of the above embodiment. It is a schematic diagram for explaining the utilization of. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... First cladding layer, 3...
Active layer, 4... Second cladding layer, 8... Mesa stripe portion, 9... Waveguide layer, 10... Third cladding layer.

Claims (1)

[Claims] 1. A semiconductor substrate, and a first semiconductor substrate having a refractive index n ₁ on this substrate.
A cladding layer and a waveguide layer having a refractive index of n ₂ are sequentially crystal-grown, and these are mesa-etched to a depth that reaches the substrate or the first cladding layer to form an edge-shaped mesa stripe portion, and a mesa stripe portion is grown on the mesa stripe portion. an active layer with a refractive index of n ₃ and a second cladding layer with a refractive index of n ₄ grown on the active layer, each refractive index being such that n ₃ > n ₂ > n ₄ ≧n A semiconductor laser device characterized by having a relationship of ₁ . 2. The active layer is grown on the mesa stripe portion through a third cladding layer having a refractive index n ₅ that is thinner than the height of the mesa stripe portion, and has a refractive index n _3. The semiconductor laser device according to claim 1, wherein the relationship is 3 > n ₂ > n ₅ ≧n ₄ ≧n ₁ .