JPS61137387A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To suppress burying light loss by sequentially forming 3 semiconductor growing layers having different band gaps on a semiconductor substrate, and burying a ring waveguide in which two semiconductor thin films are alternately grown with different band gaps. CONSTITUTION:An N type Al0.3Ga0.7As layer (band gap Eg1)2, an N type GaAs active layer (Eg2)3, a P type Al0.3Ga0.7As layer (Eg3)4, and a P type GaAs layer 5 are sequentially grown on an (100) N type GaAs substrate by a liquid phase growing method. In this case, the relationship of Eg1approx.=Eg2 is satisfied. A mesa etching at least deeper than the layer 3 is formed at a wafer, and a bar-like light producing waveguide 7 is also formed. SiO2 films 8, 9 are formed on a circular ring 6 and the waveguide 7, an N type Al0.7Ga0.3As and an N type GaAs are alternately grown until the layer 3 is buried by an MO-CVD method. AlGaAs and GaAs are removed by a fluoric acid on the films 8, 9, and ohmic electrodes 10, 11 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser that does not use cleavage, and is used in fields such as communications and measurement.

2. Description of the Related Art In general, Fabry-Perot resonators formed by cleavage are widely used as resonators for semiconductor lasers. Lasers with this structure are now widely used as single lasers for audio, video discs, and the like. However, the above-mentioned cleavage process still has drawbacks in that it is difficult to automate and it is difficult to shorten the resonator length. Structures that can escape from such a cleavage process Physics Vol. 16, Wash. 8.1977))
According to this ring laser, a laser oscillator can be fabricated anywhere in a semiconductor substrate by a crystal growth process and a photoetching process without a cleavage process, so it is an extremely convenient laser for optical integrated circuits.

A conventional configuration of a ring laser is shown in FIG.

A double hetero p-n junction 12 is formed in an annular mesa shape on a semiconductor substrate. The relationship between the refractive index tl-n2 of the active layer and the refractive index n1 of the material in which it is embedded is n,! >> n 1 ・・・・・・・・・
・・・・・・・・・(1) is desirable. That is, since the ring laser has a curved waveguide, the loss of light is extremely large.

In order to reduce the loss, the ring diameter can be increased, but this is not a practical value. One possible method for satisfying the relationship expressed by equation (1) is to form an air layer without filling it with a semiconductor material. However, if the refractive index difference becomes too large, the coupling efficiency with the light extraction optical waveguide 13 will deteriorate.Problems to be Solved by the Invention In conventional ring lasers, it is difficult to embed the ring laser with an optimal refractive index. For example, in a laser made of AlGaAs/GaAs, the composition with the lowest refractive index as an embedding material is AIAs, but AlAs is an unstable material, and in practice, the refractive index is about Ae0.7Ga0.3A8. This is the upper limit, and with this material, the loss is large and a semiconductor ring laser with a sufficiently low threshold cannot be obtained.

Means for Solving the Problems The present invention uses AlGaAs and GaAs in a stable composition range.
This method effectively embeds A7Ag by growing thin films alternately and embedding a ring waveguide.

By embedding a working ring waveguide, it is more effective to
s to suppress embedded optical loss.

Example [Example 1] An example will be described according to the drawings. As shown in FIG. 1, an n
-A10.3Ga□,yAs(3IIm)2. n-Ga
As active layer (0,2-)3. p-Ado, 3Ga0.7
As(2-)4°p-GaAs(211rn)5 is grown sequentially.

Such a grown wafer is grown in an annular manner at least n-G.
aA s Etching is performed by means of photonography so as to reach deeper than the active layer 3.

Figure 2 shows a perspective view. In the figure, the diameter of the outer ring of the ring 6 is 1oOIXn. Further, the width l is 1ourrL. Incidentally, a positive bar-shaped light extraction waveguide 7 is also formed. The width of the waveguide 7 was also 10 μm. Further, S102 films 8 and 9 are formed on the ring and the waveguide 7. Such processed wafers are then subjected to nAl□,7Gao,gkm by the No-CVD method.

Grow n-G a A a alternately. Each layer is approximately 60 nm thick and grows until at least the n-GaAs active layer is embedded. FIG. 3 shows a cross section of the wafer after embedding, which is cleaved from the annular portion.

S1028, and 9f'Ic grown polycrystalline AlGaAs.

G a As is removed by removing S i O2 with hydrofluoric acid. Next, an ohmic electrode 10 and a substrate-side ohmic electrode 11 are attached only to the annular portion of this wafer.

FIG. 4 is a comparison of the current-light output characteristics of the laser of the present invention and the laser before embedding as shown in FIG. 2, that is, the conventional laser. In each case, the optical output was obtained from the optical waveguide for light extraction. As can be seen from the figure, when there is no buried layer, that is, when the refractive index difference is large, the threshold current is as large as about 200 mA. On the other hand, the one in which the multilayer embedding of the present invention was performed showed a threshold current of 100 mA, about half that.

Also, although not shown in the figure, only AlAs single layer and A
None of the samples embedded with a single layer of 10.7Ga0.3Ag led to laser oscillation.

[Example 2] n-Alo, 7Gao, aAs made by MO-CVD method in the same structure as described in Example 1.

The thickness of the n-G a AB growth layer was varied from 10 to 300 to examine changes in the firing threshold current. The results are shown in Figure 5. In FIG. 5, the horizontal axis represents n-AlGaAs.

The thickness of each n-GaAs film and the vertical axis are the oscillation threshold currents. As can be seen from the figure, when the film thickness is between 10A and 12OA, the oscillation threshold current is 100mA or less. From a practical point of view, the upper limit current value for continuous oscillation at room temperature is considered to be about 100 mA, so the optimal film thickness is in the range of 10 to 120 people.

[Example 3] In a similar experiment described in Example 2, n-AlGaAs
were set to four types of thickness: 10, 20, 50, and 120A, and similarly, the thickness of n-GaAs was changed to 10, 20, 50, and 120 for each n-AdGaAs thickness line.As a result, Example 2 Similarly, the thickness of each is 1
Within the range of 0 to 120 people, the oscillation threshold current was 100 mA or less even with different film thicknesses. Therefore n-
GaAt5. The n-AdQaAs film thicknesses do not have to be the same, but each thickness must be in the range of 10-120.

In the examples, AlGaAa and GaAs semiconductors were described, but similar results were obtained for semiconductor lasers made of InGaAsP and InP.

Effects of the Invention The present invention makes it possible to provide a semiconductor laser that improves the large optical loss, which is a disadvantage of ring lasers, without using a cleavage process by selecting the energy gaps of the constituent layers in a specific relationship.

[Brief explanation of drawings]

1 and 2 are a side view and a perspective view of a semiconductor laser according to an embodiment of the present invention, FIG. 3 is a sectional view of the same semiconductor laser, and FIG. 4 is a characteristic of the same semiconductor laser and a conventional semiconductor laser. Figure 6 is a diagram showing the relationship between film thickness and threshold current 61
η Shin f first cow hat + 44 rays + 5 J length 1). 1, 3--kawa・n-GaAs, 2----・-n-
A7GaAs, 4-------p-AIGaAa,
5------- p-GaAs, 8. 9------・-
3102, 10, 11... Ohmic electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 3 Figure 4

Claims (2)

[Claims] (1) On the semiconductor substrate, band gaps Eg_1, Eg
Semiconductor growth layers of _2 and Eg_3 (Eg_1≒Eg_3>Eg_2) are formed in sequence, mesa-etched in an annular shape until reaching the semiconductor layer having a band gap of at least Eg_3, and the mesa-etched portions are formed into Eg_5 and Eg_3.
A semiconductor laser has a structure in which multiple layers of semiconductor thin films having a band gap of 4 (Eg_5>Eg_4≧Eg_3) are grown alternately and an active layer is embedded. (2) The semiconductor laser according to claim 1, wherein the thickness of the semiconductor thin film of band gaps Eg_5 and Eg_4 is 10 to 120 Å.