JPS63305582A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a single longitudinal mode laser easily, by etching/removing an active layer on a position where an internal reflection surface is located and next by burying a clad layer again. CONSTITUTION:After a clad layer 6, an active layer 7, a first clad layer 8, and a mask layer 14 are formed on a substrate 1, a striped opening is formed from a resist in the mask layer 14 perpendicularly to the active layer 7 by photolithography. The resist is used as a mask to etch the layer 14 and to form an opening. Next, after the resist is removed, the layer 14 is used as a mask to form an opening 13 in the first clad layer 8 so as to attain to the active layer 7. The etching is performed more to form an internal reflection surface 14 on the active layer 7 and next a second clad layer 9 is made to grow. Hence, a single longitudinal mode laser with a low threshold current can be obtained easily.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to light sources for optical communication, particularly to improvements in longitudinal mode controlled semiconductor lasers for broadband transmission and internal reflection interference longitudinal mode controlled semiconductor lasers.

BACKGROUND OF THE INVENTION In recent years, improvements in optical communication technology have led to wider transmissions and longer distances. However, conventional semiconductor lasers do not necessarily have a single longitudinal mode and cannot be said to have sufficient performance for this purpose. For this reason, various I'A structures such as distributed feedback type (DFB) and distributed Bragg reflection type (DBR) have been studied. It has been demonstrated that semiconductor lasers using these structures have extremely good characteristics in the laboratory stage. However, these lasers require the creation of a diffraction grating adjacent to the active layer, and an index-guided structure is essential, so the yield, especially the characteristic stability within the wafer plane, is extremely low. There's a big problem. For this reason, there are other simple
Various attempts have been made to obtain longitudinal mode oscillation. Internal reflection interference (IRI) lasers represent an example of one of these that is easier to fabricate, and the principle thereof will therefore be explained. ';A3 Figure a shows the end face of an IRI laser, which is no different from a conventional semiconductor laser.

20 is a substrate, 21 is a buffer layer, 22 is a 'DC blocking layer, 23 is an n-type cladding layer, 24 is an active layer, 25 is a p-type cladding layer, 26 is a cap layer, 27 is a p-type', an E pole,
28 is an n-type 'llf pole. The features of the IRIV-Z are illustrated in FIG. 3, which is a lateral cross-sectional view including the active region. 29 is a dividing portion that divides the active region 21 into two. The section is made of a material whose refractive index is slightly different from that of the active region, and the internal reflection surface 29 is made of a material having a slightly different refractive index from the active region 2.
Granted to 1.

By energizing the electrodes 26 and 27, an oscillation mode with a larger wavelength period is superimposed on the normal oscillation mode due to end face reflection as a result of internal reflection interference caused by the reflective surface 30. Therefore, the effective end face reflectance is modulated, in other words, sharp selectivity is imparted to the overall laser gain, resulting in single-longitudinal mode oscillation.

Problems to be Solved by the Invention However, in the conventional IRI laser, the formation of the segmented areas is done by chemical etching, so although the formation is said to be relatively easy, it is not necessarily completely easy. I could not say it. Furthermore, in order to utilize the crystal orientation selectivity of etching, it is difficult to make the angle of the internal reflection surface 30 completely perpendicular to the active region. The active region is curved at this point, which is a factor that increases the threshold.

It is an object of the present invention to solve the above-mentioned problems of the conventional techniques i and Iff, and to provide an IRI laser having a structure that is even easier to manufacture.

Means to solve problems The present invention provides at least a first cladding layer on a substrate.

After sequentially laminating the active layer and the second cladding layer, forming a groove from which the second cladding layer and the active layer are removed at a position where the internal reflection surface is to be formed, and filling the groove with the second cladding layer again. It is characterized by

According to the above structure, the active layer is etched away at the position where the internal reflective surface is to be installed after the active layer is formed, so that chemical etching is facilitated, and the active layer is curved at the internal reflective surface. Therefore, it is possible to easily provide a single-longitudinal mode laser having a negative threshold current as low as that of a normal semiconductor laser.

Embodiment 1 FIG. 1 is a diagram illustrating a cavity end face of a longitudinal mode control laser in an embodiment of the present invention, and a cross-sectional view including an active layer viewed from the lateral direction. FIG. 2 is a cross-sectional view including the active layer during the second post-growth etching process.

In Figure 1 B, n-InP by the first +ix a
A substrate 1 is provided with an n-InP buffer layer 2. P-InP3 and n-4nP4 are grown as current blocking layers, and n-InGaAsP layer 6 is grown as an etching mask layer.

Next, on the etching mask layer 5, about 1 layer of resist is formed.
．． A striped opening with a width of 57 zm was formed by photolithography, and n2So was formed using the above resist as a mask.
The n-In (lraAsP layer s
After etching and then removing the resist, n-
Using the InGaAsP layer 6 as a mask, etching is performed using HCl as an etchant to form striped grooves having a cross-section with a zigzag shape. Subsequently, a second growth is performed to form an n-InPn-type cladding layer en-
An InGaASP active layer 7, a p-InP i1 cladding layer 8 and a p-InGaAsP mask layer 14 are grown.

A cross-sectional view including the active layer after the second formation is shown in FIG. 2a.

This will be explained below using FIG. 2. After the second performance, p-I
A stripe-shaped opening is formed from a resist on the nGaAsP layer 14 in a direction perpendicular to the active layer 7 by photolithography. Using the resist as a mask, an H2SO4 thread etchant is used to etch the p-InGaAsP layer 14 to form the opening. After forming and then removing the resist, p-In
Using the GaAsP layer 14 as a mass layer 4, an opening 13 reaching the active layer 7 is formed in the p-InP first cladding layer 8 using an HCl etchant (FIG. 2b). Furthermore H2S
Etching is performed using an O4 etchant to form an internal reflective surface 14 in the active layer 7 (FIG. 2C).

By the third growth, the p-InP second cladding layer 9°p-
The InGaAsP gear knob layer 10 is lengthened by one length.

The gap between the p-InP cladding layer and the n-1nP cladding layer is 1.3 csev, and the refractive index is 3.4.
0, the bandgap of the active layer was 0.95ev, and the refractive index was 3.51. The width of the active layer is approximately 2.2 μm, and the thickness near the center is approximately 0.15/1 m. Ohmic electrodes 10 and 11 were attached to such a wafer.

FIG. 1 is a sectional view after electrode formation. The distance between the end facet formed by cleavage and B, that is, the resonator length (L=
L, +L, , ) is approximately 200 μm T.

Also, it is designed so that the internal reflection surface 14 is located at a position where -L2=70 μm.

Ohmic' of a laser with such a structure, F pole 11°1
When electricity is applied between 2, the oscillation wavelength is 1.371 m and the oscillation threshold value Ith = 30~aom, which is due to the internal reflection surface 14.
This is almost the same as not providing . Moreover, most of the elements exhibited single-longitudinal mode operation at about 1.2 times Ith, and extremely stable single-longitudinal mode oscillation without mode hopping up to about 4 times rth.

In addition, in the above embodiment, I n? /InGaA
Although we have described a short-wavelength laser using sP,
It goes without saying that a similar effect can be obtained with a laser using the material /GaA(7As, f8).

Effects of the Invention As described above, according to the present invention, the active layer at the position where the internal reflection surface of the IRI laser is to be provided can be etched away and refilled with a cladding layer.
Once you get a longitudinal mode laser, you can do it.

[Brief explanation of drawings]

Figures 1a and 1b are an end lI'Ii diagram of a resonator of a longitudinal mode controlled semiconductor laser according to an actual example of the present invention, and a cross-sectional view including the active region viewed from the lateral direction, and Figures 2i and 2a are ~C
3 is a partial process diagram of a semiconductor laser according to an embodiment of the present invention, and FIGS. 3i and 3b are sectional views of a conventional semiconductor laser. 1...n-xnpu board, e=----n-xn
p cladding layer, 7--n-InCyaAsP active layer,
B.-p-4nP first cladding layer, 9...p-
InP second cladding layer, 14... Internal reflection surface, 1
5. i6°゛“°Name of agent Patent attorney Toshio Nakao and 1 other person゛l'4 Naikanten Cafe

Claims (1)

[Claims] At least a first cladding layer, an active layer, and a second cladding layer sequentially laminated on a substrate, and a groove formed by removing the second cladding layer and the active layer at a position where an internal reflective surface of the laminated portion is to be installed. . A semiconductor laser comprising a layer of the same quality as the second cladding layer embedded in the groove.