A large-depth-of-field, narrow-interval double-beam base transverse mode semiconductor laser for laser printers and a preparation method thereof

Abstract

The application relates to a large-landscape-depth and narrow-interval double-beam base transverse mode semiconductor laser for a laser printer and a preparation method thereof. The method realizes complete electrical isolation and optical isolation between light emitting points of two ridge type strips by preparing a deep groove structure penetrating through an epitaxial layer between the two ridge type strips, the interval of the two ridge type strips can be very small, only 10-15 mu m, through the electrical isolation and optical isolation of the deep groove structure; meanwhile, a plurality of air column structures are prepared on two sides of the ridge type strip, the diffraction effect in the slow axis direction of the device is increased, the slow axis divergence angle of the device is effectively increased, the difference between the fast axis divergence angle and the slow axis divergence angle is reduced, and the problem that the landscape depth is small due to the large difference between the fast axis divergence angle and the slow axis divergence angle after the device passes through an optical shaping element is effectively improved. Meanwhile, electrodes are arranged on the two ridge type strips, independent regulation and control of light emission of the two ridge type strips are realized.

Description

Technical Field

[0001] This invention relates to a semiconductor laser light-emitting chip, specifically to a large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers and its fabrication method, belonging to the field of semiconductor laser technology. Background Technology

[0002] Laser printers typically use transverse-mode semiconductor lasers as their light source. Laser irradiation removes unwanted charges from the surface of the charged toner cartridge, creating a charged latent image on the cartridge surface. Due to the operating environment and assembly precision requirements, semiconductor lasers generally need a large depth of field. For semiconductor lasers, a large depth of field means a smaller difference in the divergence angles between the fast and slow axes, and that the beam waist positions of the fast and slow axes are consistent. However, due to the inherent structural limitations of semiconductor lasers, especially transverse-mode semiconductor lasers, the difference in divergence angles between the fast and slow axes is relatively large (typically 30° for the fast axis and 10° for the slow axis), and the beam waist positions also vary somewhat.

[0003] Meanwhile, the printing speed of a laser printer mainly depends on the scanning speed of its laser scanning unit. Most printers on the market currently use a single-beam laser scanning unit, which mainly consists of a semiconductor laser source emitting a single beam, a DOE diffraction collimation and shaping system, a high-speed motor system with multi-faceted mirrors, and a flat-field focusing lens. Currently, methods to improve the scanning speed of laser scanning printers generally involve increasing the rotation speed of the multi-faceted mirrors, increasing the number of reflective surfaces of the multi-faceted mirrors, and improving the response speed of the semiconductor laser. However, when the rotation speed of the mirrors reaches a certain point, the stability of the motor will fluctuate, and increasing the number of facets of the multi-faceted mirrors places significant demands on cost and processing precision. Furthermore, the response speed of the semiconductor laser cannot be continuously increased.

[0004] Currently, dual-beam scanning systems are generally used to improve the scanning speed of laser printers. The laser source emits two laser beams simultaneously, and the two laser beams scan at the same time to achieve the purpose of increasing the printing speed of the laser printer. Compared with single-beam scanning technology, dual-beam scanning technology can increase the scanning speed by two times. However, the requirements for printer resolution are getting higher and higher, so the spacing between the two beams should be as small as possible. The spacing between the two beams has become the main problem limiting the resolution of printers.

[0005] This invention addresses the problems of slow scanning speed, low resolution, large differences in divergence angles between the fast and slow axes, and certain differences in the beam waist position of laser printers. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers and its fabrication method. The method primarily involves fabricating an ultra-narrow trench structure between two ridge-type emission points. This trench structure completely penetrates the epitaxial layer, and an insulating film is deposited on the trench surface to achieve electrical isolation between the two ultra-narrow-pitch ridge-type emission points. To achieve a large depth-of-field mode, columnar pinhole structures are fabricated on both sides of the ridges, and an insulating film is rapidly deposited using PECVD to create an air column structure. Ultimately, this increases the slow-axis divergence angle, thereby increasing the device's depth of field.

[0007] The technical solution of the present invention is as follows:

[0008] A large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers comprises, from bottom to top: an N-face electrode, a substrate layer, an N-type confinement layer, an N-type waveguide layer, a light-emitting active layer, a P-type waveguide layer, and a P-type confinement layer; the P-type confinement layer includes a body layer and double ridges, the ridges being disposed on the upper surface of the body layer, and an ohmic contact layer being disposed on the upper surface of the ridges; a deep trench structure is disposed between the two ridges, the bottom surface of the trench being recessed into the substrate layer, and an insulating layer being disposed on the inner surface of the deep trench structure; columnar hole structures are disposed on both sides of each ridge, the bottom surface of the columnar hole structures being recessed into the P-type waveguide layer; an insulating layer and a P-face electrode are disposed sequentially from bottom to top on the upper surface of the P-type confinement layer body layer and on the columnar hole structures, and P-face electrodes are disposed on the side surfaces of the ridges and on the ohmic contact layer.

[0009] According to a preferred embodiment of the present invention, the spacing between the two ridge strips is 10–15 μm.

[0010] According to a preferred embodiment of the present invention, the ridge strips are arranged along the length or width direction of the P-type confinement layer body layer, and the two ridge strips are arranged symmetrically about the center line of the upper surface of the P-type confinement layer body layer along the length or width direction. When the ridge strips are arranged along the length direction of the P-type confinement layer body layer, the two ridge strips are arranged symmetrically about the center line of the upper surface of the P-type confinement layer body layer along the length direction; when the ridge strips are arranged along the width direction of the P-type confinement layer body layer, the two ridge strips are arranged symmetrically about the center line of the upper surface of the P-type confinement layer body layer along the width direction.

[0011] According to a preferred embodiment of the present invention, the ridge strip has a cuboid structure, with a length equal to or equal to the length or width of the P-type confinement layer body layer, a width of 3–4 μm, and a height of 500–600 nm. The height of the ridge strip does not exceed the thickness of the P-type confinement layer body layer. When the ridge strip is arranged along the length direction of the P-type confinement layer body layer, the length of the ridge strip is the same as the length of the P-type confinement layer body layer; when the ridge strip is arranged along the width direction of the P-type confinement layer body layer, the length of the ridge strip is the same as the width of the P-type confinement layer body layer.

[0012] According to the present invention, the material of the ridge strip is the same as that of the P-type confinement layer body layer.

[0013] According to a preferred embodiment of the present invention, a deep groove structure is provided at the middle position of the two ridge strips. The length of the deep groove structure is the same as the length of the ridge strip, the maximum width of the deep groove structure is 2 to 4 μm, and the depth of the deep groove structure is 3 to 4 μm.

[0014] According to the present invention, the type and thickness of the insulating layer provided on the inner surface of the deep trench structure are the same as those of the insulating layer provided on the upper surface of the body layer and the upper surface of the columnar hole structure.

[0015] According to a preferred embodiment of the present invention, the etching process for the deep trench structure and the columnar hole structure adopts the ICP dry etching process.

[0016] According to the present invention, the trench structure separates the P-surface electrode into two electrodes, thereby enabling separate control of the current injection of the two ridge-shaped light-emitting points.

[0017] According to a preferred embodiment of the present invention, the columnar aperture structure is vertically arranged with a circular surface as its base; the diameter of the columnar aperture structure is 1–1.5 μm, the height of the columnar aperture structure is 1000–1500 nm, and the depth of the columnar aperture structure in the P-type waveguide layer is 100–300 nm. The columnar aperture structure passes through the P-type confinement layer and reaches the P-type waveguide layer but does not penetrate the P-type waveguide layer.

[0018] According to a preferred embodiment of the present invention, the columnar hole structure is arranged in 2-4 rows on both sides of the ridge strip along the length direction of the ridge strip, and the shortest distance between the centers of two adjacent columnar hole structures is 1-4 μm.

[0019] According to the present invention, an insulating layer is covered on the columnar hole structure to form an air column structure.

[0020] According to the present invention, the material types and thicknesses of the N-side electrode, substrate layer, N-type confinement layer, N-type waveguide layer, light-emitting active layer, P-type waveguide layer, P-type confinement layer, ohmic contact layer, insulating layer, and P-side electrode can be based on existing technologies, and the present invention does not limit them.

[0021] The above-mentioned method for fabricating a large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers includes the following steps:

[0022] (1) An N-type confinement layer, an N-type waveguide layer, a light-emitting active layer, a P-type waveguide layer, a P-type confinement layer, and an ohmic contact layer are sequentially grown on the substrate.

[0023] (2) A layer of photoresist is uniformly covered on the ohmic contact layer, and a photoresist strip with the same width and length as the ridge strip is left on the upper surface of the ohmic contact layer and at the ridge strip position by photolithography.

[0024] (3) Use wet etching or dry etching process to etch away the area on the ohmic contact layer except for the photoresist strip, and etch to the upper surface of the P-type confinement layer body layer.

[0025] (4) After removing the photoresist, re-coat a layer of photoresist on the upper surface of the P-type confinement layer body layer and the ridge strip surface, and use photolithography to remove the photoresist in the trench area;

[0026] (5) A deep trench structure is fabricated in the trench area using a dry etching process;

[0027] (6) After removing the photoresist, a new layer of photoresist is applied to the upper surface of the P-type confinement layer body layer, the surface of the ridge strip, and the inner surface of the trench structure. The photoresist in the columnar hole structure area is removed by photolithography.

[0028] (7) The columnar hole structure was prepared by using a dry etching process;

[0029] (8) After removing the photoresist, an insulating layer is rapidly deposited by PECVD on the upper surface of the P-type confinement layer body layer, the inner surface of the deep trench structure, and the columnar hole structure, so that the insulating layer covers the columnar hole structure to form an air column structure.

[0030] (9) P-side electrodes are deposited on the insulating layer on the P-type confinement layer body layer, the insulating layer on the columnar hole structure and the outer surface of the ridge strip, and N-side electrodes are deposited on the lower surface of the substrate.

[0031] The technical features and beneficial effects of this invention are as follows:

[0032] 1. This invention achieves electrical isolation between the two ridge-shaped light-emitting points through an ultra-narrow trench structure, completely eliminating current crosstalk caused by current spread effect and achieving 100% electrical and optical isolation between the two ridges. Through the electrical and optical isolation of the deep trench structure, the spacing between the two ridges can be made very small, only 10-15 μm. Simultaneously, electrodes are placed on each of the two ridges, enabling independent modulation of the light emission from each ridge. Therefore, the semiconductor laser of this invention, when applied to laser printing, not only has a faster scanning rate but also effectively improves the printer's resolution.

[0033] 2. This invention prepares multiple rows of air column structures on both sides of the ridge strip. The air column structures pass through the P-type confinement layer and reach the P-type waveguide layer. Through the air column structures, the diffraction effect in the slow axis direction is effectively enhanced, thereby effectively increasing the slow axis divergence angle and improving the depth of field of the device, which is beneficial for its application in laser printers. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the structure of the large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers of the present invention;

[0035] Figure 2 This is a top view of the structure of the large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers of the present invention.

[0036] Among them, 1. Ridge strip; 2. P-side electrode; 3. P-type confinement layer; 4. P-type waveguide layer; 5. Light-emitting active layer; 6. N-type waveguide layer; 7. N-type confinement layer; 8. Substrate layer; 9. N-side electrode; 10. Deep trench structure; 11. Air column structure; 12. Insulating layer.

[0037] Figure 3 This is a light emission diagram of the semiconductor laser structure in Example 1. Detailed Implementation

[0038] The technical solution, implementation process, and principle of this invention will be further explained below with reference to the accompanying drawings, but are not limited thereto. Unless otherwise specified, the methods described are conventional methods; the reagents or materials described are commercially available unless otherwise specified.

[0039] Example 1

[0040] A large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser for laser printers, the structural schematic diagram of which is shown below. Figure 1 , 2 As shown, from bottom to top, it includes: N-face electrode 9, substrate layer 8, N-type confinement layer 7, N-type waveguide layer 6, light-emitting active layer 5, P-type waveguide layer 4, and P-type confinement layer 3;

[0041] The P-type confinement layer 3 includes a body layer and two ridges 1. The two ridges 1 are disposed on the upper surface of the body layer, and an ohmic contact layer is disposed on the upper surface of each ridge 1. The ridges 1 are arranged along the length of the body layer of the P-type confinement layer 3, and the two ridges are symmetrically arranged about the centerline of the upper surface of the body layer of the P-type confinement layer 3 along the length direction. Each ridge 1 is a cuboid, with the same length as the body layer of the P-type confinement layer 3, a width of 3 μm, and a height of 600 nm. The height of each ridge 1 does not exceed the thickness of the body layer of the P-type confinement layer 3. The distance between the two ridges 1 is 13.72 μm. The material of the ridges 1 is the same as that of the body layer of the P-type confinement layer 3.

[0042] A deep trench structure 10 is disposed in the middle between the two ridge strips 1. The deep trench structure 10 is a cuboid trench with the same length as the ridge strip 1, a width of 3 μm, and a depth of 4 μm. The bottom surface of the trench is recessed into the substrate layer 8 (to a depth of 0.1 μm in the substrate layer 8), and an insulating layer is disposed on the inner surface of the deep trench structure 10.

[0043] Columnar aperture structures are formed on the P-type confinement layer 3 on both sides of each ridge strip 1, with the bottom surface of the columnar aperture structure recessed into the P-type waveguide layer 4. The columnar aperture structure is vertically arranged with its circular bottom surface as the base; the diameter of the columnar aperture structure is 1.5 μm, the height of the columnar aperture structure is 1200 nm, and the depth of the columnar aperture structure in the P-type waveguide layer is 200 nm. The columnar aperture structure passes through the P-type confinement layer 3 and reaches the P-type waveguide layer 4 but does not pass through the P-type waveguide layer 4. Three rows of columnar aperture structures are arranged on each side of the ridge strip 1 along its length, with the shortest distance between the centers of two adjacent columnar aperture structures being 1 μm.

[0044] An insulating layer of the same thickness and type is provided on the upper surface of the P-type confinement layer 3 and on the columnar hole structure; the columnar hole structure is covered with an insulating layer to form an air column structure 11. P-surface electrodes 2 of the same thickness and type are provided on the insulating layer on the upper surface of the P-type confinement layer 3 and on the columnar hole structure, on the side surface of the ridge strip 1, and on the ohmic contact layer. The trench structure 10 separates the P-surface electrodes 2 into two electrodes, enabling separate control of the current injection at the two ridge strip light-emitting points.

[0045] The type and thickness of the insulating layer on the inner surface of the trench structure 10 are the same as those on the upper surface of the body layer and the upper surface of the columnar hole structure.

[0046] Example 2

[0047] A method for fabricating a large depth-of-field, narrow-pitch dual-beam transverse-mode semiconductor laser (the laser in Example 1) for a laser printer includes the following steps:

[0048] (1) An N-type confinement layer, an N-type waveguide layer, a light-emitting active layer, a P-type waveguide layer, a P-type confinement layer, and an ohmic contact layer are sequentially grown on the substrate.

[0049] (2) A layer of photoresist is uniformly covered on the ohmic contact layer, and a photoresist strip with the same width and length as the ridge strip is left on the upper surface of the ohmic contact layer and at the ridge strip position by photolithography.

[0050] (3) Using a dry etching process, the area on the ohmic contact layer except for the photoresist strip is etched away, and the etching depth is up to the upper surface of the P-type confinement layer body layer.

[0051] (4) After removing the photoresist, re-coat a layer of photoresist on the upper surface of the P-type confinement layer body layer and the ridge strip surface, and use photolithography to remove the photoresist in the trench area;

[0052] (5) A deep trench structure is fabricated in the trench area using a dry etching process;

[0053] (6) After removing the photoresist, a new layer of photoresist is applied to the upper surface of the P-type confinement layer body layer, the surface of the ridge strip, and the inner surface of the deep trench structure. The photoresist in the columnar hole structure area is removed by photolithography.

[0054] (7) The columnar hole structure was prepared by using a dry etching process;

[0055] (8) After removing the photoresist, an insulating layer is rapidly deposited by PECVD on the upper surface of the P-type confinement layer body layer, the inner surface of the deep trench structure, and the columnar hole structure, so that the insulating layer covers the columnar hole structure to form an air column structure.

[0056] (9) P-side electrodes are deposited on the insulating layer on the P-type confinement layer body layer, the insulating layer on the columnar hole structure and the outer surface of the ridge strip, and N-side electrodes are deposited on the lower surface of the substrate.

[0057] The semiconductor laser with the structure of Example 1 was fabricated, and then the P-side electrodes and N-side electrodes on both sides of the deep trench structure were connected by metal wires, respectively. The emission pattern is shown in the figure. Figure 3 As shown, independent modulation of the light emission from the two ridge strips was achieved.

Claims

1. A large depth of focus, narrow pitch double-beam base transverse mode semiconductor laser for laser printers, characterized by that, From bottom to top, it includes N-face electrode, substrate layer, N-type confinement layer, N-type waveguide layer, light-emitting active layer, P-type waveguide layer, P-type confinement layer; the P-type confinement layer includes body layer and double-ridge type strip, the ridge type strip is arranged on the upper surface of the body layer, and the upper surface of the ridge type strip is provided with an ohmic contact layer; a deep groove structure is arranged between the two ridge type strips, the bottom surface of the groove sinks to the substrate layer, and the inner surface of the deep groove structure is provided with an insulating layer; a columnar hole structure is arranged on both sides of each ridge type strip, and the bottom surface of the columnar hole structure sinks to the P-type waveguide layer; the upper surface of the body layer of the P-type confinement layer and the upper surface of the columnar hole structure are sequentially provided with an insulating layer and a P-face electrode from bottom to top, and the side surface of the ridge type strip and the upper surface of the ohmic contact layer are provided with a P-face electrode; The distance between the two ridge type strips is 10-15 μm; a deep groove structure is arranged at the middle position of the two ridge type strips, the length of the deep groove structure is the same as the length of the ridge type strip, and the maximum width of the deep groove structure is 2-4 μm; the depth of the deep groove structure is 3-4 μm; the columnar hole structure is vertically arranged with a circular surface as the bottom surface; the diameter of the columnar hole structure is 1-1.5 μm, the height of the columnar hole structure is 1000-1500 nm, the depth of the columnar hole structure in the P-type waveguide layer is 100-300 nm; the columnar hole structure is arranged in 2-4 rows on both sides of the ridge type strip along the length direction of the ridge type strip, and the shortest distance between the centers of two adjacent columnar hole structures is 1-4 μm.

2. The large-NA, narrow-pitch dual-beam base transverse mode semiconductor laser for a laser printer according to claim 1, wherein The ridge type strip is arranged along the length or width direction of the body layer of the P-type confinement layer, and the two ridge type strips are symmetrically arranged with the center line of the upper surface of the body layer of the P-type confinement layer as the center along the length or width direction.

3. The large-NA, narrow-pitch dual-beam base transverse mode semiconductor laser for laser printers according to claim 1, wherein The ridge type strip is a cuboid structure, the length of the ridge type strip is the same as the length or width of the body layer of the P-type confinement layer, the width of the ridge type strip is 3-4 μm, and the height of the ridge type strip is 500-600 nm, and the height of the ridge type strip does not exceed the thickness of the body layer of the P-type confinement layer.

4. The large-NA, narrow-pitch dual-beam base transverse mode semiconductor laser for laser printers according to claim 1, wherein The etching process of the deep groove structure and the columnar hole structure adopts ICP dry etching process.

5. The preparation method of the large-depth-of-field and narrow-distance double-beam base transverse mode semiconductor laser for the laser printer according to any one of claims 1-4, comprising the steps of: (1) sequentially growing an N-type confinement layer, an N-type waveguide layer, a light-emitting active layer, a P-type waveguide layer, a P-type confinement layer and an ohmic contact layer on a substrate layer; (2) uniformly coating a layer of photoresist on the ohmic contact layer, and leaving a photoresist strip with the same width and length as the ridge type strip on the upper surface of the ohmic contact layer and the position of the ridge type strip through a photoetching process; (3) using wet etching or dry etching process to remove the area of the ohmic contact layer except the photoresist strip, and the etching depth reaches the upper surface of the body layer of the P-type confinement layer; (4) after removing the photoresist, re-coating a layer of photoresist on the upper surface of the body layer of the P-type confinement layer and the surface of the ridge type strip, and removing the photoresist in the groove area through a photoetching process; (5) using dry etching process to prepare a deep groove structure in the groove area; (6) after removing the photoresist, re-coating a layer of photoresist on the upper surface of the body layer of the P-type confinement layer, the surface of the ridge type strip and the inner surface of the groove structure, and removing the photoresist in the columnar hole structure area through a photoetching process; (7) using dry etching process to complete the preparation of the columnar hole structure. (8) After the photoresist is removed, a layer of insulating layer is rapidly evaporated on the surface of the P-type confinement layer body layer, the inner surface of the deep trench structure and the surface of the columnar hole structure by PECVD, so that the insulating layer covers the columnar hole structure to form an air column structure; (9) P-face electrodes are evaporated on the insulating layer on the P-type confinement layer body layer, the insulating layer on the columnar hole structure and the outer surface of the ridge-shaped strip, and N-face electrodes are evaporated on the lower surface of the substrate.

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