CN100468090C - Fabrication method of absorbing gain-coupled distributed feedback laser - Google Patents

Abstract

A method for manufacturing an absorption-type gain-coupling distributed feedback laser, comprising the steps of: depositing a silicon dioxide film on a gallium arsenide or indium phosphide substrate in a large area; coating a layer of photoresist on the silicon dioxide film ; The photoresist is exposed and developed to obtain a photoresist Bragg grating mask; the photoresist Bragg grating mask is used as a mask, and the silicon dioxide film is etched to obtain a silicon dioxide Bragg grating mask; The mask and the silicon dioxide Bragg grating mask together act as a mask, etch the gallium arsenide or indium phosphide substrate, and obtain the Bragg grating on the gallium arsenide or indium phosphide substrate; remove the photoresist Bragg grating mask mode, keep the silica Bragg grating mask; epitaxially grow the absorbing layer, fill the concave part of the Bragg grating to form the absorption type gain coupling distributed feedback Bragg grating; remove the silica Bragg grating mask; in the absorption type gain coupling On the distributed feedback Bragg grating, the secondary epitaxy grows the lower confinement layer, the active region, the upper confinement layer, the cover layer and the contact layer in sequence.

Description

Fabrication method of absorbing gain-coupled distributed feedback laser

technical field

The invention belongs to the technical field of optoelectronics and relates to a novel manufacturing method of an absorption-type gain-coupling distributed feedback Bragg grating. One of the key points is to introduce the oxide dielectric film as a mask for fabricating Bragg gratings on the surface of the semiconductor epitaxial wafer. Compared with the photoresist, the oxide dielectric film is more stable in the process of making the grating, so it is beneficial to flexibly control the shape and depth of the grating to be carved. Another key point is that after the grating on the surface of the epitaxial wafer is completed, under the condition of keeping the mask of the oxide dielectric Bragg grating, epitaxial growth is used to fabricate the absorbing layer of the absorbing gain-coupling distribution feedback Bragg grating. The advantage of this is that it fundamentally solves the problem that the shape of the grating is flattened and the shape of the grating is difficult to maintain due to the volatilization and migration of the semiconductor material during the epitaxial growth of the semiconductor surface after the grating is engraved. The invention is mainly used for making absorption type gain coupling distributed feedback laser.

Background technique

Distributed feedback lasers are the main light sources in high-capacity long-distance optical fiber communication systems. Distributed Feedback The feedback required for laser lasing is not provided by the concentrated reflection of the end face of the laser, but by the built-in Bragg grating distributed feedback. This feedback effect couples forward-propagating and backward-propagating light waves in the active layer. Between two beams of light propagating in opposite directions, coherent coupling occurs only at wavelengths that satisfy the Bragg condition, which makes distributed feedback lasers have good monochromaticity and stability. Distributed feedback Bragg gratings mainly have two feedback methods, that is, the refractive index periodically changes the refractive index coupling distribution feedback Bragg grating and the gain coupling distribution feedback Bragg grating whose gain changes periodically. The refractive index distribution feedback grating is formed by engraving a Bragg grating on the transparent separate confinement layer, and then burying the filling layer. The refractive index coupled distributed feedback laser has two modes with the same loss and the lowest at the place symmetrical about the Bragg wavelength. , so in principle this type of laser is dual longitudinal mode lasing. Usually, the gain-coupling distributed feedback grating is formed by directly carving a Bragg grating in the active area, and then burying the filling layer, which can realize single-mode lasing. But this type of gain-coupled distributed feedback grating is easy to bring defects to the active region, which reduces the luminous efficiency. If the traditional transparent grating fabricated on the respective confinement layers is changed into an absorbing grating with absorption, an absorbing gain-coupling distributed feedback Bragg grating can be obtained.

There are two key steps in the fabrication of absorbing gain-coupled distributed feedback gratings. One is to engrave the required Bragg grating on the semiconductor epitaxial wafer, which requires precise control of the period, depth and shape of the Bragg grating. Generally, the Bragg grating pattern is obtained by exposing and developing the photoresist coated on the surface of the epitaxial wafer, and then uses the Bragg grating pattern of the photoresist as a mask to form a periodic Bragg grating on the semiconductor epitaxial wafer by using a wet and dry etching process. Since the general photoresist's resistance to dry and wet etching is not very good, when etching a semiconductor epitaxial wafer, the depth and uniformity of the engraved Bragg grating are limited, which is not conducive to improving the distributed feedback. Laser performance. The second key step is to epitaxially grow a buried filling layer on the surface of the epitaxial wafer on which the Bragg gratings are engraved. Due to the volatilization and migration of the semiconductor compound on the surface of the grating during the heating process, the depth of the Bragg grating becomes shallower and the shape changes. This problem will seriously affect the feedback performance of the grating, and even make the grating lose its feedback function. At present, the volatilization of semiconductor compounds on the grating surface is mainly suppressed by changing the epitaxial growth conditions on the grating surface (reference: ①J.Crystal Growth, 1998, Vol.195, P.503-509 and ②J.Crystal Growth, 2003, Vol. 248, P. 384-389). Generally, this approach can only slow down the volatilization of the semiconductor compound on the surface of the grating, and needs to be improved if this problem is to be completely solved. The main purpose of the present invention is to solve the problems existing in the above two key steps in the process of manufacturing the distributed feedback laser Bragg grating.

Contents of the invention

The object of the present invention is to provide a manufacturing method of an absorption-type gain-coupling distributed feedback laser. The oxide dielectric is introduced to act as a mask for engraving a grating on the surface of the semiconductor epitaxial wafer. Since the oxide dielectric mask is more stable in the process of engraving the grating compared with the photoresist, the shape and depth of the engraved grating can be better controlled. In addition, after the grating on the surface of the epitaxial wafer is completed, the oxide dielectric mask used for the Bragg grating is retained, and the epitaxial growth absorption type gain coupling distribution is fed back to the absorbing layer of the Bragg grating. Therefore, it fundamentally solves the problem that the grating becomes shallower and the shape of the grating is difficult to maintain due to the volatilization and migration effects of the semiconductor compound material when the absorbing layer is epitaxially grown on the semiconductor surface of the grating.

The specific steps of the manufacturing method of this absorbing gain-coupled distributed feedback laser are described as follows:

A kind of manufacturing method of absorption type gain coupling distributed feedback laser of the present invention is characterized in that, comprises the following steps:

(1) Large-area deposition of a silicon dioxide film on a gallium arsenide or indium phosphide substrate;

(2) coating a layer of photoresist on the silicon dioxide film;

(3) exposing and developing the photoresist to obtain a photoresist Bragg grating mask;

(4) using a photoresist Bragg grating mask as a mask to etch a silicon dioxide film to obtain a silicon dioxide Bragg grating mask;

(5) Use the photoresist Bragg grating mask and the silicon dioxide Bragg grating mask together as a mask to etch the gallium arsenide or indium phosphide substrate, and obtain the Bragg on the gallium arsenide or indium phosphide substrate Grating;

(6) Remove the photoresist Bragg grating mask and keep the silicon dioxide Bragg grating mask;

(7) epitaxially growing the absorbing layer to fill the concave part of the Bragg grating to form an absorbing gain-coupling distributed feedback Bragg grating;

(8) remove the silicon dioxide Bragg grating mask;

(9) Secondary epitaxial growth of the lower confinement layer, the active region, the upper confinement layer, the cap layer and the contact layer in sequence on the absorbing gain-coupling distributed feedback Bragg grating.

Wherein the thickness of the silicon dioxide film is less than 100 nanometers.

The exposure in step (3) adopts holographic exposure technology or electron beam exposure technology.

The etching in step (5) adopts a combination of wet etching and dry etching, and the dry etching adopts electron cyclotron resonance plasma etching technology, reactive ion etching technology or inductively coupled plasma etching technology.

The period of the Bragg grating mask of the photoresist corresponds to the required laser wavelength.

When the absorbing layer is epitaxially grown, it is required to control the growth time so that the absorbing layer just fills up the concave part of the Bragg grating.

The energy bandgap of the absorbing layer material is required to be smaller than the energy bandgap corresponding to the lasing wavelength of the designed active region.

Description of drawings

In order to further illustrate content of the present invention, below in conjunction with accompanying drawing and example the present invention is described in detail, wherein:

Fig. 1 is a schematic diagram after depositing an oxide dielectric thin film on an epitaxial wafer;

Fig. 2 is the schematic diagram after being coated with photoresist on epitaxial wafer;

Fig. 3 is a schematic diagram after engraving a photoresist Bragg grating mask;

Fig. 4 is a schematic diagram after engraving an oxide dielectric Bragg grating mask;

Fig. 5 is a schematic diagram after engraving a Bragg grating on the epitaxial wafer surface;

Fig. 6 is a schematic diagram after removing the photoresist Bragg grating mask;

Fig. 7 is a schematic diagram after growing an absorbing layer of an absorbing gain-coupling distributed feedback Bragg grating;

Fig. 8 is a schematic diagram after removing the oxide dielectric Bragg grating mask;

FIG. 9 is a schematic structural view of an epitaxial wafer after secondary epitaxy.

Detailed ways

Please refer to Fig. 1 to Fig. 9, a kind of manufacturing method of absorbing gain coupling distributed feedback laser of the present invention, comprises the following steps:

(1) On the epitaxial substrate 1, deposit a layer of oxide dielectric thin film 2 (see Figure 1); the epitaxial substrate 1 adopts gallium arsenide or indium phosphide compound semiconductor material; the thickness of the oxide dielectric thin film 2 less than 100 nanometers, the oxide dielectric film 2 is made of silicon dioxide or silicon nitride;

(2) Coating a layer of photoresist 3 on the epitaxial wafer deposited with the oxide dielectric film 2 (see FIG. 2);

(3) The photoresist is exposed and developed to obtain the Bragg grating mask 4 (see Figure 3) of the photoresist; the photoresist is exposed and developed to obtain the Bragg grating mask 4 of the photoresist, and the exposure adopts holographic exposure technology or electron beam exposure technology; wherein the period of the Bragg grating mask 4 of the photoresist corresponds to the required laser wavelength;

(4) Use the photoresist Bragg grating mask 4 as a mask to etch the oxide dielectric film 2 to obtain a Bragg grating mask 5 (see FIG. 4 ) of the oxide dielectric;

(5) With the photoresist Bragg grating mask 4 and the oxide dielectric Bragg grating mask 5 serving as a mask together, the semiconductor compound is etched to obtain a Bragg grating 6 (see FIG. 5 ) on the epitaxial wafer; wherein the etching is Combining wet and dry methods to etch epitaxial wafers, dry etching uses electron cyclotron resonance plasma etching, reactive ion etching or inductively coupled plasma etching technology;

(6) Remove the photoresist Bragg grating mask 4 (see Figure 6) on the epitaxial wafer, and keep the oxide dielectric Bragg grating mask 5;

(7) On the epitaxial wafer that retains the oxide dielectric Bragg grating mask 5, the epitaxial growth absorption type gain coupling distribution feeds back the absorbing layer 7 of the Bragg grating (see FIG. 7), filling the concave part of the grating;

(8) remove the oxide dielectric Bragg grating mask 5 (see Figure 8) on the epitaxial wafer;

(9) The lower confinement layer 8, the active region 9, the upper confinement layer 10, the capping layer 11 and the contact layer 12 are respectively grown by secondary epitaxy on the epitaxial wafer grown with the absorber layer 7 (see FIG. 9 ).

When growing the absorbing layer 7, it is required to control the growth time so that the absorbing layer 7 just fills up the concave part of the previously engraved Bragg grating; the energy band gap of the material of the absorbing layer 7 is required to be smaller than the designed lasing wavelength of the active region The corresponding energy band gap.

Example

Please refer to Figure 1 to Figure 9 again:

(1) As shown in FIG. 1 , a silicon dioxide oxide dielectric thin film 2 is deposited on an epitaxial substrate 1 in a large area. The epitaxial substrate 1 may be gallium arsenide or indium phosphide material, and indium phosphide material is selected in the embodiment. The oxide dielectric film 2 can be made of silicon dioxide or silicon nitride, and silicon dioxide is used in the embodiment. This layer of silicon dioxide oxide dielectric film 2 will be used to make a Bragg grating mask. Compared with the traditional photoresist 3, the silicon dioxide oxide dielectric film 2 is more stable in the grating carving process and has a better masking effect, so that a Bragg grating with a suitable shape can be carved. In addition, since the compound semiconductor is difficult to grow on the silicon dioxide medium, the Bragg grating mask 5 of the silicon dioxide medium can also be used as a mask for growing the compound semiconductor. The thickness of the silicon dioxide oxide dielectric film 2 directly affects the production effect of the Bragg grating, which is generally less than 100 nanometers, and is 20 nanometers in the embodiment;

(2) As shown in FIG. 2 , spray glue on the epitaxial wafer on which the silicon dioxide dielectric film 2 has been deposited, and coat a layer of photoresist 3 . This layer of photoresist 3 will be used later to make a Bragg grating mask 4;

(3) As shown in FIG. 3 , the photoresist 3 on the epitaxial wafer is exposed and developed to obtain the required photoresist Bragg grating mask 4 . The exposure method can adopt holographic exposure or electron beam exposure technology. Holographic exposure technology can only form a periodic grating pattern in one exposure, and the equipment is relatively cheap. Electron beam exposure technology can form grating patterns with different periods at one time, but the equipment is relatively expensive. Holographic exposure technology is used here. The grating period corresponds to the desired lasing wavelength. The quality of the Bragg grating mask 4 of the photoresist here is crucial, and will be used as a mask for engraving the grating on the oxide dielectric film 2;

(4) As shown in FIG. 4 , using the photoresist Bragg grating mask 4 as a mask, the silicon dioxide oxide dielectric thin film 2 is wet etched to obtain a silicon dioxide oxide dielectric Bragg grating mask 5 . Because the thickness of the silicon dioxide oxide dielectric film 2 is very small, several experiments are required to determine the optimum etching conditions during the wet etching process, so as to obtain a suitable silicon dioxide oxide dielectric Bragg grating mask. Compared with the photoresist Bragg grating mask 4, the oxide dielectric Bragg grating mask 5 is more stable in the process of engraving the grating, so the shape and depth of the engraved grating can be better controlled;

(5) As shown in FIG. 5 , the photoresist Bragg grating mask 4 and the oxide dielectric Bragg grating mask 5 are used as a mask to etch the semiconductor compound, and the Bragg grating 6 is fabricated in the epitaxial wafer. The combination of dry etching process and wet etching process is beneficial to engraving high-quality Bragg gratings on semiconductor epitaxial wafers. For the dry etching process, many methods such as reactive ion etching process or electron cyclotron resonance plasma etching process can be selected, and electron cyclotron resonance plasma etching process is selected here. After dry etching to obtain the basic morphology of the Bragg grating, the epitaxial wafer is soaked in a wet etching solution for a certain period of time in order to smooth the surface of the Bragg grating. Due to the use of a silicon dioxide Bragg grating mask, the engraving depth of the grating here can be larger, and a good grating shape can be maintained;

(6) As shown in FIG. 6 , remove the photoresist Bragg grating mask 4 on the epitaxial wafer, and keep the silicon dioxide oxide dielectric Bragg grating mask 5 . The remaining silicon dioxide oxide dielectric Bragg grating mask will act as a mask when epitaxially growing the absorber layer;

(7) As shown in FIG. 7 , on the epitaxial wafer with the oxide dielectric Bragg grating mask 5 remaining, the absorbing layer 7 of the absorbing gain-coupling grating is epitaxially grown to fill the concave portion of the Bragg grating 6 . Here, the absorption layer 7 is grown by a metal organic chemical vapor deposition method. The growth time is controlled so that the absorbing layer 7 just fills up the concave portion of the previously carved Bragg grating 6 . The energy bandgap of the absorbing layer 7 is smaller than the energy bandgap corresponding to the designed lasing wavelength of the active region, and has a certain absorption effect. In the example, the absorption layer 7 is an InGaAsP material with an energy bandgap wavelength of 1.32 microns matched to the substrate, which is used to make an absorption-type gain-coupling distributed feedback laser epitaxial wafer with a lasing wavelength of 1.3 microns. During the heating process, due to the protective effect of the silicon dioxide Bragg grating dielectric mask 5, the volatilization and migration of the semiconductor compound can be suppressed, so that the grating maintains its original shape. At the same time, since the compound semiconductor is difficult to grow on the surface of the oxide dielectric Bragg grating 5, but easy to grow on the surface of the compound semiconductor, the absorption layer 7 is just grown on the concave part of the Bragg grating 6, and an ideal absorption-type gain-coupling distribution feedback grating is obtained. structure;

(8) As shown in FIG. 8 , remove the oxide dielectric Bragg grating mask 5 on the epitaxial wafer, and prepare to carry out secondary epitaxial growth absorption type gain-coupling distribution feedback active region and other parts of the laser;

(9) As shown in FIG. 9 , the lower confinement layer 8 , the active region 9 , the upper confinement layer 10 , the capping layer 11 and the contact layer 12 are grown in sequence by secondary epitaxy on the epitaxial wafer grown with the absorber layer 7 . In the example, the lower confinement layer 8 is made of aluminum indium arsenic material matching the indium phosphide substrate, the active region 9 is an indium gallium aluminum arsenic multiple quantum well structure with a lasing wavelength of 1.31 microns, and the upper confinement layer 10 is made of phosphorus The aluminum indium arsenic material matching the indium phosphide substrate, the cover layer 11 is a p-type indium phosphide material, and the contact layer 12 is a p-type heavily doped indium gallium arsenic material matching the indium phosphide substrate. So far, the distributed feedback laser epitaxial wafer containing the absorbing gain-coupling grating is completed.

The characteristics of this kind of distributed feedback laser with absorption-type gain-coupling grating are: the manufacturing process is simple, no anti-reflection film on the end face is required; the single-mode selectivity is not affected by the reflectivity of the end face, so the yield of single-mode is improved; The frequency broadening is very small; it has the ability to generate single-mode ultrashort optical pulses.

The present invention relates to the manufacturing method of absorbing gain-coupling distributed feedback laser, and its most important feature and significance have two points: one is to introduce the oxide dielectric thin film to act as the mask of engraving the grating on the surface of the semiconductor epitaxial wafer, because the oxide Compared with the photoresist mask, the dielectric mask is more stable in the process of engraving the grating, so the shape and depth of the engraved grating can be better controlled. Another point is that after the grating on the surface of the epitaxial wafer is completed, under the condition of retaining the oxide dielectric mask when the Bragg grating was carved, the epitaxial growth absorption type gain coupling distribution is fed back to the absorbing layer of the Bragg grating, thus fundamentally solving the problem of the Bragg grating. When epitaxially growing the absorbing layer on the semiconductor surface of the grating, the volatilization and migration effects of the semiconductor compound material make the grating shallow and the grating shape is difficult to maintain.

Claims (7)

1, a kind of manufacture method of absorption type gain coupling distributed feedback laser, is characterized in that, comprises the steps: (1) Large-area deposition of a silicon dioxide film on a gallium arsenide or indium phosphide substrate; (2) coating a layer of photoresist on the silicon dioxide film; (3) exposing and developing the photoresist to obtain a photoresist Bragg grating mask; (4) using a photoresist Bragg grating mask as a mask to etch a silicon dioxide film to obtain a silicon dioxide Bragg grating mask; (5) Use the photoresist Bragg grating mask and the silicon dioxide Bragg grating mask together as a mask to etch the gallium arsenide or indium phosphide substrate, and obtain the Bragg on the gallium arsenide or indium phosphide substrate Grating; (6) Remove the photoresist Bragg grating mask and keep the silicon dioxide Bragg grating mask; (7) epitaxially growing the absorbing layer to fill the concave part of the Bragg grating to form an absorbing gain-coupling distributed feedback Bragg grating; (8) remove the silicon dioxide Bragg grating mask; (9) Secondary epitaxial growth of the lower confinement layer, the active region, the upper confinement layer, the cap layer and the contact layer in sequence on the absorbing gain-coupling distributed feedback Bragg grating. 2. The method for manufacturing an absorption-type gain-coupled distributed feedback laser according to claim 1, wherein the thickness of the silicon dioxide film is less than 100 nanometers. 3. The manufacturing method of an absorption-type gain-coupled distributed feedback laser according to claim 1, wherein the exposure in step (3) adopts holographic exposure technology or electron beam exposure technology. 4. The manufacturing method of an absorption-type gain-coupled distributed feedback laser according to claim 1, wherein the etching in step (5) adopts a combination of wet etching and dry etching, and dry etching Electron cyclotron resonance plasma etching technology, reactive ion etching technology or inductively coupled plasma etching technology is used. 5. The method for manufacturing an absorption-type gain-coupled distributed feedback laser according to claim 1, wherein the period of the photoresist Bragg grating mask corresponds to the required lasing wavelength. 6. The manufacturing method of an absorbing gain-coupled distributed feedback laser according to claim 1, wherein when the absorbing layer is epitaxially grown, it is required to control the growth time so that the absorbing layer just fills up the concave part of the Bragg grating . 7. The method for manufacturing an absorption-type gain-coupled distributed feedback laser according to claim 1 or 6, wherein the energy bandgap of the absorbing layer material is required to be smaller than the energy bandgap corresponding to the designed lasing wavelength in the active region .

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