KR20010011142A - Gain coupled single mode semiconductor laser and method for fabricating the same - Google Patents

Abstract

PURPOSE: A gain-coupled type of single mode semiconductor laser is provided to minimize an optic loss and simplify the manufacturing process. CONSTITUTION: In a method of making a semiconductor laser having a diffracting grating, a silicon nitride film or a silicon oxide film is formed as the diffracting grating on the first epitaxial layer. The second epitaxial layer is developed on the whole surface on which the silicon nitride film or the silicon oxide film was formed. In a gain-coupled type of single mode semiconductor laser, an active layer(22) and the first clad layer(23) are applied sequently on the substrate(21). a diffracting grating (24) of a silicon nitride or a silicon oxide is formed on the first clad layer. The second clad layer(25) and a resistive electrode contact layer(26) are applied sequently over the diffracting grating layer.

Description

Gain coupled single mode semiconductor laser and method for fabricating the same {Gain coupled single mode semiconductor laser and method for fabricating the same}

The present invention relates to a structure of a gain-coupled single mode semiconductor laser with minimized light loss and a method of manufacturing the same.

Conventional single mode light sources utilize a principle that allows a diffraction grating layer whose refractive index changes at regular intervals to adjoin the active layer and cause an optical mode corresponding to the period of the diffraction grating to oscillate while light travels between both mirror surfaces of the laser. Although the light source is manufactured, the single mode yield is less than 30% due to the occurrence of phase difference due to the mirror position and reflection. As a countermeasure, a new single-mode semiconductor laser mainly focusing on the function of gain coupling has been proposed, but a separate process must be performed to invert the diffraction grating or conduction form to generate a separate gain change periodically. Particularly, the buried laser structure is preferred as a method for obtaining stable light waves. In this case, at least one or two regrowth processes should be added.

Figure 1 shows a cross-sectional structure of a typical conventional light absorption type gain coupled single mode semiconductor laser. In Fig. 1, reference numeral 1 denotes a resistive p-electrode contact layer such as, for example, p ⁺ -InGaAs, 2 denotes a p-type cladding layer such as, for example, p-InP layer, and 3 denotes, for example, InGaAs (P) / InGaAsP multiquantum well. In the active layer, 4 represents a light absorption diffraction grating of (In) GaAs material, and 5 represents a substrate of n ⁺ -InP.

Referring to FIG. 1, in order to form the light absorption type diffraction grating 4, before forming the active layer 3, the light absorbing diffraction grating 4 must be removed from the crystal growth apparatus and subjected to various processes such as dielectric deposition, holography, dry etching, and wet etching. And again, the necessary epilayers must be recrystallized on it. The complexity of the process in such a single mode semiconductor laser is an obstacle to commercialization not only in terms of technology but also in economics. In addition, when using the light absorption type diffraction grating there is a disadvantage that includes the basic performance weakness of the light loss.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above, and an object thereof is to provide a gain-coupled single mode semiconductor laser in which light loss is minimized.

It is another object of the present invention to provide a gain coupled single mode semiconductor laser for simplifying the manufacturing process to improve commerciality.

1 is a cross-sectional view showing the structure of a conventional light absorption type gain coupling single mode semiconductor laser.

2A and 2B are cross-sectional views showing a characteristic technical configuration of the present invention;

3 is a perspective view showing a schematic structure of a gain coupled single mode semiconductor laser according to the present invention;

4 is a cross-sectional view showing an application example of a gain-coupled single mode semiconductor laser having a buried structure using a silicon nitride diffraction grating.

* Explanation of symbols for main parts of the drawings

21: n ⁺ -InP substrate

22: InGaAs (P) / InGaAsP multi-quantum well active layer

23: p-InP cladding layer

24: silicon nitride diffraction grating

25: p ⁺ -InP cladding layer

26: p ⁺ -InGaAs resistive p-electrode contact layer

27: electrode stripe

40: InP current blocking layer

The semiconductor laser manufacturing method of the present invention for achieving the above object comprises a first step of forming a silicon nitride film or a silicon oxide film as the diffraction grating on a first epitaxial layer; And a second step of growing a second epitaxial layer on the entire surface of the finished product of the first step, wherein the duty of the diffraction grating is about 50% or less.

According to the present invention, first, by using the silicon nitride or silicon oxide as an insulator as a diffraction grating, it is possible to give a large change in the intensity of the carrier periodically injected, thereby forming a gain change in the active layer without light loss. Second, a good quality p-type clad layer can be formed without lattice defects by designing the duty of the diffraction grating on the silicon nitride or silicon oxide, which is usually used as a mask for selective crystal growth, in consideration of the diffusion distance during colon growth.

In addition, in the gain-coupled single mode semiconductor laser of the present invention, an active layer and a first cladding layer are stacked on a substrate, and a diffraction grating of silicon nitride or silicon oxide is formed on the first cladding layer. The second cladding layer and the resistive electrode contact layer are sequentially stacked.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do.

2A to 2B are cross-sectional views showing a characteristic technical configuration of the present invention, in which an InGaAs (P) / InGaAsP multi-quantum well active layer 22 and a p-InP clad layer 23 are formed on an n ⁺ -InP substrate 21. Next, the silicon nitride diffraction grating 24 is formed by using a holography method, and a p ⁺ -InP clad layer 25 is formed thereon.

In general, the growth of compound semiconductor crystals is impossible on silicon nitride, and crystal growth is selectively performed at sites other than those masked with silicon nitride. However, if the width of the nitride mask is reduced to 1000 nm or less, since the diffusion distance of atoms in the crystal growth reaches thousands of nm depending on the process conditions, the grain growth of the crystal growth naturally stays on the nitride, and thus the selectivity drops sharply. Therefore, the first period of the diffraction grating corresponding to the 1.55μm center wavelength is about 235 nm, and if the duty value is formed to 50% or less, crystal growth naturally occurs on the open semiconductor crystal surface, and the side effects such as diffusion on the silicon nitride Growth is possible and good quality semiconductor crystals are formed without defects. Here, the duty value is a ratio occupied by the diffraction grating during the period, which means L / Λ in FIG. 2A.

3 is a perspective view showing a schematic structure of a gain coupled single mode semiconductor laser according to the present invention. Referring to FIG. 3, a gain-coupled single mode semiconductor laser according to the present invention, an InGaAs (P) / InGaAsP multi-quantum well active layer 22 and a p-InP clad layer 23 on an n ⁺ -InP substrate 21. ) Is sequentially grown, and a silicon nitride diffraction grating 24 is formed on the p-InP cladding layer 23, on top of which the p ⁺ -InP cladding layer 25 and the p ⁺ -InGaAs resistive p-electrode contact layer. (26) is formed. The electrode stripe 27 is formed on the resistive p-electrode contact layer 26 so that the laser resonator is formed in a direction perpendicular to the diffraction grating 24.

FIG. 4 shows an application example of a gain-coupled single mode semiconductor laser having a buried structure using a silicon nitride diffraction grating. The semiconductor laser having the structure as shown in FIG. 3 is applied to the current blocking layer 40 by Fe-doped semi-insulating InP. By embedding, high quality recrystallization at the interface and flattening of the upper surface can be achieved, and it can be utilized as a laser for high speed modulation due to the advantage of low capacitance.

In this embodiment, the InP-based semiconductor laser is described as an embodiment, but the present invention may be applied to all structures using compound semiconductors other than InP.

As such, although the technical idea of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

According to the present invention, since the insulating nitride is used as the diffraction grating without undergoing a separate epi layer forming process for the diffraction grating, it is possible to periodically change the gain of the active layer without light loss. In addition, the silicon nitride used in the general process can be used as it is, thereby reducing the process step, thereby improving the economical efficiency by reducing the manufacturing cost, and forming a diffraction grating without etching or growing the epi layer, thereby controlling and reproducing the duty. It is advantageous to secure a single mode semiconductor laser which is technically reliable.

Claims (5)

In the semiconductor laser manufacturing method having a diffraction grating, Forming a silicon nitride film or a silicon oxide film on the first epitaxial layer as the diffraction grating; And And a second step of growing a second epitaxial layer on the entire surface of the resultant of the first step. The method of claim 1, And forming a duty of the diffraction grating below about 50%. In a gain-coupled single mode semiconductor laser, An active layer and a first cladding layer are stacked on a substrate, and a diffraction grating of silicon nitride or silicon oxide is formed on the first cladding layer, and a second cladding layer and a resistive electrode contact layer are sequentially stacked thereon. Gain-coupled single mode semiconductor laser, characterized in that the. The method of claim 3, And a stripe electrode formed on the resistive electrode contact layer so that a laser resonator is formed in a direction perpendicular to the diffraction grating. The method of claim 3, A gain-coupled single mode semiconductor laser in which each layer stacked on the substrate is embedded in a semi-insulating current blocking layer.