Laser diode with ridge waveguide

Abstract

The present invention discloses a laser diode with a ridge waveguide, comprising a base substrate, a ridge waveguide layer arranged above the base substrate, and a metal conductive layer arranged above the ridge waveguide, wherein an anti-conductivity layer is arranged between the ridge waveguide layer and the base substrate, and an anti-conductivity layer is introduced at the bottom of the ridge waveguide layer, the refractive index of which is similar to that of a quantum well region, thereby further constraining an optical mode, increasing the effective refractive index of the optical mode, and extending the minimum size of the bottom of the ridge waveguide structure, thereby preventing the basic optical mode from losing its constraints in this region, thereby making the optical mode smaller in volume, which is conducive to further improving the performance of the device.

Description

Technical Field

[0001] The invention relates to the field of laser diodes, in particular to a laser diode with a ridge waveguide. Background Art

[0002] Traditional vertical ridge waveguide laser diodes are limited in their maximum practical bandwidth. One of the main limiting factors is the lateral diffusion and propagation of current in the vicinity of the ridge waveguide. Due to the structural characteristics of the buried heterojunction (BH) laser, its active region is surrounded by non-conductive materials that are secondarily epitaxially grown after physical etching, so that the current is confined to a multi-quantum well layer in a very narrow range (about 2 microns), so it is not subject to this limitation. However, the problem with buried heterojunction lasers is that their process is complex and the cost is high. As the requirements for laser modulation bandwidth continue to increase, the ridge width of the ridge waveguide is required to be narrower. However, a too narrow ridge waveguide will dramatically increase the difficulty of subsequent processes and the device yield. For this reason, the industry sometimes uses a dove-tail ridge waveguide structure for high-speed devices, but this structure still has certain problems, its optical mode has not been optimized, and there is still room for improvement in device performance. Summary of the invention

[0003] In view of the above problems, the present invention provides a ridge waveguide laser diode, which can further increase the modulation frequency of the laser and improve the relative intensity noise of the device.

[0004] The technical solution of the present invention is:

[0005] A laser diode with a ridge waveguide, comprising a base substrate, a ridge waveguide layer arranged above the base substrate, and a metal conductive layer arranged above the ridge waveguide layer, wherein an anti-conducting layer is arranged between the ridge waveguide layer and the base substrate, the thickness of the anti-conducting layer is 90-110 nm, and the material of the anti-conducting layer is AlInGaAs material, InAlAsP material, or quinary system material;

[0006] The ridge waveguide layer includes a lower cladding layer, an anti-conducting layer, a quantum well layer, a semiconductor isolation layer, a grating layer, a semiconductor upper cladding layer and a semiconductor covering layer stacked in sequence from bottom to top. The doping type of the semiconductor upper cladding layer is opposite to that of the lower cladding layer, and the doping type of the semiconductor covering layer is the same as that of the semiconductor upper cladding layer.

[0007] The ridge waveguide layer is a dove-tail ridge waveguide, the base substrate is an n-type or p-type doped semiconductor base layer, and the base substrate doping type is the same as the lower cladding layer of the ridge waveguide layer.

[0008] The method for preparing the conductive layer is as follows:

[0009] S1. During the wafer growth stage of the laser diode, an anti-conducting layer is generated under the waveguide layer;

[0010] S2, preparing dove-tail ridge waveguide;

[0011] S3, cleaning the laser diode wafer with the dove-tail ridge waveguide, and preparing a mixed etching solution of hydrochloric acid and phosphoric acid;

[0012] S4, placing the cleaned laser diode wafer into the mixed etching solution for wet etching;

[0013] S5. After wet etching, rinse and dry the laser diode wafer.

[0014] In step S3, the wafer is cleaned using a plasma surface cleaning device with an oxygen flow rate of 100 sccm, a chamber pressure of 200 mTorr, a power of 100 W, and a cleaning time of 1 min.

[0015] In step S3, the mass ratio of hydrochloric acid to phosphoric acid is 1:6, and the mixture needs to be left to stand for 15 minutes.

[0016] In step S4, the etching time is 90 seconds.

[0017] The beneficial effects of the present invention are:

[0018] An anti-conducting layer is introduced at the bottom of the ridge waveguide layer, and the refractive index of this layer is similar to that of the quantum well region (high refractive index material), so as to achieve more ideal lateral and longitudinal constraints on the optical mode. The compression of the optical mode volume can effectively improve the bandwidth characteristics of the laser, thereby reducing the relative intensity noise of the device. At the same time, this technology expands the minimum size of the bottom of the ridge waveguide structure, preventing the basic optical mode from losing its constraints in this area, making the optical mode volume smaller, which is conducive to further improving the performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the overall structure of a laser diode with a ridge waveguide according to an embodiment of the present invention;

[0020] Figure 2 is a schematic structural diagram of an existing vertical ridge waveguide according to an embodiment of the present invention;

[0021] Figure 3 is a schematic structural diagram of an existing dove-tail ridge waveguide according to an embodiment of the present invention;

[0022] Figure 4 is a schematic structural diagram of a ridge waveguide with an anti-conducting layer according to an embodiment of the present invention;

[0023] Figure 5 is the optical basic optical mode profile of the conventional vertical ridge waveguide described in the embodiment of the present invention;

[0024] Figure 6 is the optical basic optical mode profile of the existing dove-tail ridge waveguide described in the embodiment of the present invention;

[0025] Figure 7 is the optical basic optical mode profile of the dove-tail ridge waveguide with an anti-guiding layer according to an embodiment of the present invention;

[0026] Figure 8 is a distortion comparison of different ridge waveguides according to the embodiments of the present invention;

[0027] Fig. 9 1 is a comparison of bandwidths of different ridge waveguides according to the embodiments of the present invention.

[0028] Description of reference numerals:

[0029] 1 is a base substrate, 2 is a ridge waveguide layer, 3 is a metal conductive layer, 4 is an anti-conductive layer, 5 is a lower cladding layer, 21 is a quantum well layer, 22 is a semiconductor isolation layer, 23 is a grating layer, 24 is a semiconductor upper cladding layer, and 25 is a semiconductor covering layer. DETAILED DESCRIPTION

[0030] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0031] Example:

[0032] like Figure 1 As shown, a laser diode with a ridge waveguide includes a base substrate 1, a ridge waveguide layer 2 arranged above the base substrate 1, and a metal conductive layer 3 arranged above the ridge waveguide layer 2. An anti-conducting layer 4 is arranged between the ridge waveguide layer 2 and the base substrate 1. The thickness of the anti-conducting layer 4 is 100nm, and the thickness of the anti-conducting layer 4 is 90-110nm. The material of the anti-conducting layer 4 is AlInGaAs material or InAlAsP material or quinary system material. This embodiment uses InGaAsP material.

[0033] The ridge waveguide layer 2 is a dove-tail ridge waveguide, the base substrate 1 is an n-type or p-type doped semiconductor base layer, and a lower cladding layer 5 of the same doping type as that deposited in the semiconductor base layer is arranged above the base substrate 1. The ridge waveguide layer 2 includes a quantum well layer 21, a semiconductor isolation layer 22, a grating layer 23, a semiconductor upper cladding layer 24 and a semiconductor cover layer 25 stacked in sequence from bottom to top, the doping type of the semiconductor upper cladding layer 24 is opposite to that of the lower cladding layer 5, and the doping type of the semiconductor cover layer 25 is the same as that of the semiconductor upper cladding layer 24.

[0034] The method for preparing the exemplary conductive layer is as follows:

[0035] S1. During the wafer growth stage of the laser diode, an InGaAsP anti-conducting layer is generated under the waveguide layer;

[0036] S2, preparing dove-tail ridge waveguide;

[0037] S3, cleaning the laser diode wafer with the dove-tail ridge waveguide, and preparing a mixed etching solution of hydrochloric acid and phosphoric acid;

[0038] S4, placing the cleaned laser diode wafer into the mixed etching solution for wet etching;

[0039] S5. After wet etching, rinse and dry the laser diode wafer.

[0040] Step S3, the wafer is cleaned using a plasma surface cleaning device with an oxygen flow rate of 100 sccm, a chamber pressure of 200 mTorr, a power of 100 W, and a cleaning time of 1 min.

[0041] In step S3, the mass ratio of hydrochloric acid to phosphoric acid is 1:6, and the mixture needs to be left to stand for 15 minutes after mixing.

[0042] Step S4, etching time is 90s.

[0043] Compared with the existing dove-tail ridge waveguide solution, this method introduces a 100nm thick InGaAsP anti-conducting layer underneath it, which is perfectly compatible with the existing ridge waveguide semiconductor process and effectively realizes the control of the light field mode. The current dove-tail ridge waveguide formation process is wet etching, which mainly forms the structure through an etching solution containing HBr. This method adds a 100nm InGaAsP anti-conducting layer under the ridge waveguide during the wafer growth stage. After the dove-tail ridge waveguide is formed through the existing process, only one wet etching step is required to remove the excess anti-conducting layer material, and the wet etching is selective etching, which will not change the already formed dove-tail ridge waveguide structure.

[0044] like Figure 2 - Fig. 9As shown in the figure, the basic optical mode profile is obtained by using Rsoft software, where the solid line is the vertical ridge waveguide and the dotted line is the dove-tail ridge waveguide with an anti-conducting layer. HD2, HD3 and IMD3 are different distortion indicators, a indicates the vertical ridge waveguide with a reference 12G 3dB bandwidth, b indicates the vertical ridge waveguide with a narrower 17G 3dB bandwidth, c indicates that the dove-tail ridge waveguide can reach 22G 3dB bandwidth, and d indicates that the dove-tail ridge waveguide with an anti-conducting layer reaches 27G 3dB bandwidth. It can be proved that the peak intensity of the vertical ridge wave is located in the multi-quantum well layer, and the peak intensity of the dove-tail ridge waveguide without an anti-conducting layer is located in the multi-quantum well layer, and its optical field mode is narrower than that of the vertical ridge waveguide. After adding a 100nm InGaAsP anti-conducting layer at the bottom of the dove-tail ridge waveguide, further constraints can be formed on the optical mode, making the optical mode smaller, and expanding the minimum size of the bottom of the ridge waveguide structure to prevent the basic optical mode from losing its constraints in this area, thereby increasing the 3dB bandwidth by about 10 GHz. Compared with the vertical ridge waveguide, the dove-tail ridge waveguide with an anti-conducting layer can increase the distortion parameter by about 5 dB. If there is no anti-conducting layer, the base size becomes smaller, the basic optical mode will leak and ultimately fail to obtain effective light field constraints, resulting in excessive laser loss and affecting the device's luminous efficiency and light field mode stability. The introduction of the anti-conducting layer enhances the ability of the dove-tail ridge waveguide to compress the optical mode. Among them, Figure 6 and Figure 7 They are comparisons of the light field distribution of the dove-tail ridge waveguide structure with and without an anti-conducting layer. It can be seen from the light field intensity distribution diagram that, with the same ridge waveguide size, the lateral distribution of the light field with the anti-conducting layer is significantly more concentrated in the ridge waveguide area.

[0045] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A laser diode having a ridge waveguide, characterized in that It includes a base substrate, a ridge waveguide layer arranged on the base substrate, and a metal conductive layer arranged on the ridge waveguide layer, wherein an anti-conductive layer is arranged between the ridge waveguide layer and the base substrate, the thickness of the anti-conductive layer is 90-110nm, and the material of the anti-conductive layer is AlInGaAs material or InAlAsP material or quinary system material; The ridge waveguide layer includes a lower cladding layer, an anti-conducting layer, a quantum well layer, a semiconductor isolation layer, a grating layer, a semiconductor upper cladding layer and a semiconductor cover layer stacked in sequence from bottom to top, wherein the doping type of the semiconductor upper cladding layer is opposite to that of the lower cladding layer, and the doping type of the semiconductor cover layer is the same as that of the semiconductor upper cladding layer; The ridge waveguide layer is a dove-tail ridge waveguide, the base substrate is an n-type or p-type doped semiconductor base layer, and the base substrate doping type is the same as the lower cladding layer of the ridge waveguide layer.

2. The laser diode with a ridge waveguide according to claim 1, characterized in that: The method for preparing the conductive layer is as follows: S1. During the wafer growth stage of the laser diode, an anti-conducting layer is generated under the waveguide layer; S2, preparing dove-tail ridge waveguide; S3, cleaning the laser diode wafer with the dove-tail ridge waveguide, and preparing a mixed etching solution of hydrochloric acid and phosphoric acid; S4, placing the cleaned laser diode wafer into a mixed etching solution for wet selective etching; S5. After wet etching, rinse and dry the laser diode wafer.

3. The laser diode with a ridge waveguide according to claim 2, characterized in that: In step S3, the wafer is cleaned using a plasma surface cleaning device with an oxygen flow rate of 100 sccm, a chamber pressure of 200 mTorr, a power of 100 W, and a cleaning time of 1 min.

4. The laser diode with a ridge waveguide according to claim 2, characterized in that: In step S3, the mass ratio of hydrochloric acid to phosphoric acid is 1:6, and the mixture needs to be left to stand for 15 minutes.

5. The laser diode with a ridge waveguide according to claim 2, characterized in that: In step S4, the etching time is 90 seconds.

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