JPH02254782A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To make a semiconductor laser device of this design stable in wavelength up to a high output power by a method wherein the reflectivity of one of the end faces of a resonator is made lower than that of the other. CONSTITUTION:A protrudent part 2 is provided to a P-GaAs substrate 1 except the vicinity of a low reflective end face, an N-GaAs current blocking layer provided with groove 4 which reaches to the protrudent part 2 is formed on the protrudent part 2, and a non-current injection region is provided to the other end face. Laser oscillation takes place in an active layer 7 above the groove 4, and light is taken out from the end face as being guided through an optical guide layer 6 under the active layer 7. At this time, the active layer 7 has been removed from the low reflective end face, light is reflected by the part where the active layer has been removed, and a large compound resonance effect is realized. Moreover, the active layer 7 is not exposed at a low reflectivity end face where light is large in density, a current is not injected into the part where the active layer is exposed, so that a high output power can be obtained. By this setup, a semiconductor laser stable in wavelength and high in output power can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser device used in optical information processing equipment, two-optical communication, and the like.

BACKGROUND OF THE INVENTION In recent years, there has been a demand for semiconductor lasers with high output and stable longitudinal modes in the fields of recording/erasable optical disk memories and optical communication in space. Particularly in the field of optical disk memory, a shift in the oscillation wavelength appears as a shift in focus on the disk, so the resonant wavelength of the semiconductor laser that serves as the light source varies with respect to both temperature and optical output. It is desirable to be as stable as possible. For this reason, various efforts have been made to stabilize the wavelength of semiconductor lasers. Examples include an external composite resonator laser in which a mirror is attached to the outside of a semiconductor laser, and a DFB laser in which a grating is formed in a waveguide, but these are not yet sufficient for practical use.

Problems to be Solved by the Invention As mentioned above, stabilizing the oscillation wavelength of a semiconductor laser is very important. However, the oscillation wavelength of a semiconductor laser essentially tends to become longer as the temperature is higher and the optical output is higher, and a phenomenon called mode hop is observed in normal Fabry-Perot lasers.

For this reason, attempts have been made to suppress mode hops by attaching an external mirror to a semiconductor laser to form a composite resonator. However, in this case,
It was necessary to attach an external mirror to the high reflection end on the opposite side of the light emission side of the semiconductor laser. For this reason, it was not possible to obtain light feedback that would give a sufficient composite resonator effect to the semiconductor laser, and it was not possible to stabilize the wavelength up to high output.

In view of the above-mentioned drawbacks, the present invention aims to provide a semiconductor laser device that solves these problems.

Means for Solving the Problems The semiconductor laser device of the present invention has a semiconductor substrate of one conductivity type having a small number of striped protrusions that do not reach one of the resonator end faces (both have a semiconductor substrate of one conductivity type on one main surface, and a semiconductor laser device of this semiconductor substrate). A first semiconductor layer of a conductivity type opposite to one conductivity type formed on one main surface, and a protrusion formed on this first semiconductor layer reaching this protrusion, A striped groove with a depth that does not reach the substrate in the part where it does not exist,
A second semiconductor layer of one conductivity type is formed on the first semiconductor layer to a thickness that fills the groove, and a second semiconductor layer is formed on the second semiconductor layer and has a higher energy a third semiconductor layer of one conductivity type with a small gap; a fourth semiconductor layer formed on the third semiconductor layer except for a portion near the one resonator end face and having a smaller energy gap; A fifth semiconductor layer of an opposite conductivity type, which is formed on a portion of the third semiconductor layer where the fourth semiconductor layer does not exist and on the fourth semiconductor layer, and has a larger energy gap than the third semiconductor layer. The reflectance of the one resonator end face is lower than the reflectance of the other resonator end face.

Effect: With this configuration, reflection of light occurs inside the semiconductor laser at the portion where the fourth semiconductor layer is interrupted.
Furthermore, since the reflection occurs only on the end face, which has a low reflectance, a large composite resonator effect can be obtained. Furthermore, the fourth semiconductor layer as an active layer has a high optical density (i.e., is not exposed to the end face with lower reflectance, and no current is injected in this part, so high output can be obtained). , a semiconductor laser device with high output and wavelength stability can be obtained.

Embodiment FIG. 1(a) is a perspective view showing a central portion of a resonator in a semiconductor laser device according to an embodiment of the present invention, cut in a direction perpendicular to the end face. The resonator end face is coated asymmetrically, and Figure 1(b) shows the low reflection end face, and Figure 1(C) shows the low reflection end face.
) is a diagram showing a high reflection end face.

A p-GaAs substrate 1 has protrusions 2 except near the low-reflection end face, and a groove 4 reaching the protrusions 2 thereon.
- There is a current blocking layer 3 made of GaAs, which forms a current non-injection region at one end face. Laser oscillation occurs in the active layer 7 above the groove 4, but light is guided to the light guide layer 6 below the groove 7 and extracted to the end face. At this time, the active layer 7 is removed at the low-reflection end face portion, and the structure is such that light is reflected at this portion. Above the active layer 7 is a layer 8 for confining carriers and light in the active layer, and above that is a layer 9 in which the mixed crystal ratio of AL' is lowered for embedding by MOCVD. 10.1
1 is n-GaA grown by MOCVD method.
A cladding layer made of eAs and a contact layer made of n-GaAs.

The manufacturing process will be explained below with reference to FIG.

Projections 2 are formed on a P-type GaAs substrate 1 by etching except for the vicinity of one end face. Figure 2 (a)) On top of that, n
- A current blocking layer 3 made of GaAs is grown, and a groove 4 is formed by etching so as to reach the protrusion 2. (Figure 2 (b)) Figure 2 (C) is Figure 2 (b)
It is a sectional view along xx' in . Then L again
By PE method, p-G ao, 5sAe O, 41A
Cladding layer 5 consisting of S, I) Gao, 5sAe
Light guide layer 6 made of 0.31AS, Gao, 5xA
Active layer 7 consisting of i' g, oeA s, n - Ga
layer 8 consisting of oI, sAe O,4+A s, n-G
A layer 9 consisting of aO, (16A!! 0.20A S) is grown. 9 is a layer with a low mixed crystal ratio of Ae (second layer) in order to facilitate buried growth by MOCVD method later.
Figure (d)). Next, the end face portion without the projection 2 is etched to the active layer 7 (Fig. 2(e)
). ) Then, using the MOCVD method, n Gaq,
Cladding layer 10 consisting of 5sAeO, HAs, n-G
A contact layer 11 made of aAs is grown (see FIG. 2 (
r)〉. Figure 2 (g) is Y-Y' in Figure 2).
FIG. Finally, coating is performed so that the cross-sectional side where the active layer is etched is the low reflectance side. In this example, in order to obtain high output, the low reflection end face reflectance was set to 4% and the high reflection end face reflectance was set to 96%.

FIG. 3 shows the current-light output characteristics.

At room temperature and in CW operation, an optical output of 150 mW or more has been obtained. This is considered to be due to the fact that the active layer was removed to obtain a composite resonator on the low reflectance side, which is the light emission side, resulting in a window structure. In fact, the maximum light output is determined by thermal saturation,
No end face failure occurred.

FIG. 4 shows experimental results when the length of the portion from which the active layer was removed was varied. Temperature range ΔT where the oscillation wavelength is stable
It can be seen that the maximum value is reached when L=25 μm.

Here, the resonant wavelength of the entire laser is 230 μm. This can be explained as follows. In Figure 5(a),
The temperature dependence of the oscillation wavelength when L=10 am and L=95 μm is shown in FIG. 5(b). When L=10 μm, irregular small mode hops appear between the large mode hops exhibited by the complex resonator effect. this is,
This shows that L is too small, and the wavelength selectivity to limit the number of longitudinal modes to only one is insufficient. Next, when L=45 μm, mode hops occur only at wavelength intervals of approximately 2 nm, which is indicated by the composite resonator effect. However, if L is too large, a mode hop will occur with a small wavelength interval (small ΔT).A similar phenomenon has also been observed in a composite resonator laser having an external mirror.

Finally, the characteristics when L=25 μm, where ΔT was the largest, are shown.

Figure 6 shows the temperature dependence of the oscillation wavelength at 50 mW output, and Figure 7
The figure shows the dependence of the oscillation wavelength on the optical output. Even with respect to temperature,
It can be seen that the oscillation wavelength is sufficiently stable with respect to the optical output.

Effects of the Invention According to the present invention 1, the semiconductor laser 1 can stabilize the longitudinal mode even during high-output operation, and has great effects as a light source for recordable/erasable optical discs and the like.

[Brief explanation of drawings]

Figure 1 is a structural diagram of the semiconductor laser of the present invention, Figure 2 is a diagram showing the manufacturing process, Figure 3 is a diagram of current-light output characteristics, and Figure 4 is a diagram of the temperature range ΔT in which the oscillation wavelength is stable. FIGS. 5 and 6 are diagrams showing the temperature dependence of the oscillation wavelength, and FIG. 7 is a diagram showing the optical output dependence of the oscillation wavelength. 1...Substrate, 2...Protrusion, 3...
...Current blocking layer, 4...Groove portion, 5.
..... Cladding layer, 6 ..... Light guide layer, 7
...Active layer, 8...Layer for confining light in the active layer 7, 9...Layer, 10...
- Cladding layer, 11...Contact layer. Name of agent: Patent attorney Shigetaka Awano and one other person Figure (b) 2. Sui zu Jia zu V 4θθ UR (Sail A) Fig. 1/ 礪 fig υ ((L) (b) dρ 〼, crush (°C) Ball: II C'c,)

Claims (1)

[Claims] a semiconductor substrate of one conductivity type having a striped protrusion on at least one main surface that does not reach one resonator end surface;
a first semiconductor layer of a conductivity type opposite to the one conductivity type formed on one main surface of the semiconductor substrate;
A striped groove portion formed on the first semiconductor layer has a depth that reaches the protrusion portion directly above the protrusion portion and does not reach the substrate in a portion where the protrusion portion does not exist; the second semiconductor layer of one conductivity type, which is formed to a thickness that fills at least the groove;
the third semiconductor layer of one conductivity type, which is formed on the semiconductor layer and has a smaller energy gap than the second semiconductor layer; and the third semiconductor excluding a portion near the one resonator end face. a fourth semiconductor layer formed on the third semiconductor layer and having a smaller energy gap than the third semiconductor layer; and a portion of the third semiconductor layer where the fourth semiconductor layer does not exist and the fourth semiconductor layer. a fifth semiconductor layer of the opposite conductivity type, which is formed on the layer and has a larger energy gap than the third semiconductor layer;
A semiconductor laser device, wherein a reflectance of the one resonator end face is lower than a reflectance of the other resonator end face.