阅读说明：本技术 使用相同材料形成的激光面和钝化装置的移位预处理 (Shift pretreatment of laser facets and passivation devices formed using the same material ) 是由 亚伯兰雅库维奇 马丁苏埃斯 于 2019-06-04 设计创作，主要内容包括：具有镜面的边缘发射激光二极管,其包括钝化涂层,所述钝化涂层使用移位工艺处理,以处理用于形成钝化层的绝缘材料。利用外部能量源(激光、闪光灯、电子束)以给定的剂量和足够的时间照射材料,以处理钝化层的整个厚度。这种移位激光处理被应用于覆盖激光二极管的两个端面的层(可能包括钝化层和涂层),以稳定整个端面涂层。重要的是,当装置仍处于条形状态时,可以执行该移位工艺。(An edge-emitting laser diode with a mirror includes a passivation coating processed using a shift process to process an insulating material used to form the passivation layer. The material is irradiated with an external energy source (laser, flash lamp, electron beam) at a given dose and for a sufficient time to treat the entire thickness of the passivation layer. This shifted laser treatment is applied to the layers (possibly including passivation layers and coatings) covering both facets of the laser diode to stabilize the entire facet coating. Importantly, this shift process can be performed while the device is still in the stripe state.)

1. A method of passivating an facet of an edge-emitting laser diode, comprising:

a) depositing one or more passivation layers on the surface of the exposed surface of the edge-emitting laser diode in a reaction chamber to form an end-face coating of a predetermined thickness;

b) removing the edge-emitting laser diode from the reaction chamber; and

c) irradiating the end coating with an energy source sufficient to treat the end coating through the predetermined thickness.

2. The method of claim 1, wherein in performing step c), the end coating is irradiated using a laser source.

3. The method of claim 1 wherein in performing step c) the end coating is irradiated with a flash lamp.

4. The method as recited in claim 1, wherein in performing step c), the end coating is irradiated with an electron beam.

5. The method of claim 1, wherein the method is applied before the laser diode is diced into individual devices.

6. The method of claim 1, wherein the one or more passivation layers are comprised of a material selected from the group consisting of silicon, germanium, antimony, and oxides, nitrides, or combinations thereof of silicon, germanium, antimony.

7. The method of claim 1, wherein pulses are used as the energy source.

8. The method of claim 1, wherein continuous waves are used as the energy source.

9. The method of claim 1, wherein a coating is deposited on each of the passivation layers while performing step a) and before performing the irradiating of step c).

10. The method of claim 9, wherein the coating comprises a material selected from the group consisting of silicon, germanium, gallium arsenide, silicon oxide, silicon nitride, aluminum oxide, titanium oxide, aluminum nitride, tantalum oxide, or combinations thereof.

11. An edge-emitting laser diode comprising

A semiconductor substrate having a waveguide structure formed thereon for generating light at an operating wavelength;

a pair of cut surfaces formed on opposite sides of the waveguide structure;

a passivation layer of a predetermined thickness formed to cover the pair of cutting surfaces, wherein the passivation layer penetrating the predetermined thickness is sufficiently processed; and

a reflective coating formed directly on at least one of the passivation layers.

12. The edge-emitting laser diode of claim 11, wherein the application of the reflective coating is substantially treated in conjunction with the passivation layer.

13. The edge-emitting laser diode of claim 11, wherein the passivation layer comprises a laser-irradiated material selected from the group consisting of silicon, germanium, antimony, and oxides, nitrides, or combinations thereof.

14. The edge-emitting laser diode of claim 11, wherein the reflective coating is formed of a material of silicon, germanium, gallium arsenide, silicon oxide, silicon nitride, aluminum oxide, titanium oxide, aluminum nitride, tantalum oxide, or combinations thereof.

Technical Field

The present invention relates to a laser device, and more particularly, to an edge-emitting laser diode having a mirror surface processed by a shift process.

Background

High power semiconductor laser diodes have become an important component of optical communication technology, particularly because such laser diodes can be used for fiber pumping (amplification of optical signals) and other high power applications. In most cases, the laser diode is usually required to have the characteristics of long service life, reliable and stable output, large output power, high photoelectric efficiency, good beam quality and the like. One key to the long term reliability of modern high power laser diodes is the stability of the laser facets, which form the two opposing mirrors of the laser cavity.

Physical degradation of the laser facet is a complex reaction that can be driven by light, current, and heat, resulting in power degradation and, in severe cases, Catastrophic Optical Damage (COD) to the mirror itself. A process developed by IBM and referred to as "E2 passivation" has been used to solve these problems and minimize the potential for COD. As described in IBM's U.S. patent 5,063,173 entitled "method of mirror passivation for semiconductor laser diodes," issued to m.gasser et al, the E2 process involves depositing a layer of silicon (or possibly germanium or antimony) as a coating on the surface of the bare facet (mirror). The presence of the coating acts as a passivation layer that prevents diffusion of impurities that can react with the mirror interface.

The operating power of today's laser diodes is relatively high and these prior art passivation layers, which are formed by deposition, have been found to decompose, possibly leading to mirror damage. Therefore, it has become standard practice to "treat" the passivation layer in order to obtain a stable mirror for an infrared high power laser diode. In operation today, the process is a very time consuming process requiring the laser diode to be operated at reduced current levels for extended periods of time (e.g., tens to hundreds of hours) to form crystalline structures within the deposited amorphous passivation layer to form a stable interface between the passivation layer and the mirror. In addition to the time required for this processing, it must be performed on a device-by-device basis, further extending the time and expense of the manufacturing process.

Disclosure of Invention

The present invention addresses the need to reduce the time required for laser facet processing, and relates to laser devices, and more particularly to edge emitting laser diodes having a mirror passivation coating that is processed using a "shift" irradiation process instead of the traditional reduced current operation method.

In accordance with the teachings and principles of the present invention, a material used as an end passivation layer is irradiated with an external energy source. Preferably, the passivation layer is insulating (or low conductive). In particular, it may be formed using a material such as silicon, germanium, or antimony. The irradiation process itself takes only a few seconds or minutes, as compared to the extended time required for the "aging" process of the prior art.

The external energy source may include a laser, a flash lamp, an electron beam, or other suitable radiation source. The energy source may be operated in a Continuous Wave (CW) or pulsed mode, wherein the passivation layer is irradiated with an irradiation dose sufficient to treat the entire thickness of the passivation material layer. This displacement processing method is suitable for the end face of the laser diode, and is preferably performed when the device is in a stripe shape (i.e., before dicing). However, it should be understood that the displacement process of the present invention may also be applied to singulated devices, with the displacement process being performed on a single unmounted die or a mounted die (e.g., a device mounted on a card, carrier, or submount).

An exemplary shifting method of passivating an facet of an edge-emitting laser diode according to one or more embodiments of the present invention comprises the steps of: a) depositing one or more layers of passivation material on the surface of the exposed face of the edge-emitting laser diode in the reaction chamber to form an end-face coating of a predetermined thickness; b) removing the laser diode from the reaction chamber; and c) irradiating the end coating with a beam of light from an energy source for a time sufficient for the beam of light to penetrate the predetermined thickness to treat the end coating. In an alternative method, an outer coating may be deposited on the passivation layer (to adequately handle and provide stability of the passivation layer and coating combination) prior to performing the irradiation step.

Another embodiment of the invention takes the form of an edge-emitting laser diode that includes a semiconductor substrate having formed thereon a waveguide structure for generating light at an operating wavelength; a pair of cut surfaces formed on opposite sides of the waveguide structure; a passivation layer of a predetermined thickness is formed to cover the pair of cut surfaces, wherein the passivation layer penetrating the predetermined thickness is sufficiently processed, and a reflective coating is directly formed on at least one passivation layer.

Other and further embodiments and aspects of the invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.

Drawings

Fig. 1 is a schematic plan view of an edge-emitting semiconductor laser diode;

FIG. 2 shows an exemplary arrangement for performing a shift process of a laser diode passivation layer in accordance with one or more embodiments of the invention;

fig. 3 shows an alternative arrangement for performing the shift process, in this case providing sufficient processing or stabilization of the passivation layer and the cover coat; and

fig. 4 contains a set of graphs showing the improvement of COD by using the shift treatment according to the present invention.

Detailed Description

As will be described in detail below, it is an object of the present invention to fully treat the passivation layer used as a coating on the exposed face of the laser diode with a displacement process. The "shifting" as used herein is intended to emphasize the difference between a process formed in accordance with the principles of the present invention (i.e., a process provided using an external energy source) and a prior art "in-situ" process that is achieved by operating the laser diode device itself (typically at reduced current levels over a long period of time). Extended time). For the purposes of the present invention, the phrase "substantially treating" refers primarily to treating a material comprising a passivation layer (e.g., silicon, germanium, antimony) throughout the entire thickness of the layer. For the purposes of the present invention, "complete condition" may also be described as providing displacement stabilization of the entire face overlay layer, including the passivation layer and the standard coating overlying the passivation layer (and all interfaces between them, e.g., the passivation film-chip interface).

As will be discussed below, the shifting method of the present invention allows for execution on a strip of laser diodes (prior to dicing into individual devices), and thus the efficiency of the process is significantly improved over prior art product-by-product processes. In addition, depending on the size/area to be treated, the displacement process of the present invention only needs to be performed in a few seconds or minutes, rather than the time required by conventional equipment-operated treatment methods.

Turning now to the figures, an exemplary laser diode is schematically illustrated in plan view in fig. 1. The laser is formed in a semiconductor optoelectronic chip (or "bar") 10 having a front facet 12 and an opposing back facet 14. The strip 10 comprises a vertical structure (not shown in detail) typically consisting of layers of AlGaAs, GaAs and related III-V semiconductor materials epitaxially deposited on a GaAs substrate. However, it should be understood that other combinations of materials may be present within the scope of the present invention.

In the commercial production of these devices, a large number of such strips are formed simultaneously on a single gallium arsenide wafer (GaAs wafer), and the wafer is subsequently diced along the natural cleavage plane to form a large number of individual strips 10 having a front face 12, a back face 14, and vertically aligned side faces 16, 18, as shown in fig. 1. The semiconductor processing performed on the wafer also forms a waveguide structure 20 extending between the front and back end faces 12, 14 and perpendicular to the front and back end faces 12, 14. Although in most cases the waveguide structure 20 is a ridge waveguide, other configurations are possible (e.g., a buried heterostructure waveguide, which is preferred in high power applications). In many high power applications, the waveguide structure 20 has a width substantially greater than the lasing wavelength to form a wide-area laser.

As part of the manufacturing process, the cut surfaces 12, 14 are passivated using a conventional E2 passivation process. That is, the strip 10 is loaded into a reaction chamber and a passivation material is deposited to a predetermined thickness to provide a coating on the mirrored surface of the faces 12 and 14. The passivation material needs to be insulating (or of low conductivity), preferably comprising silicon, germanium or antimony, and may also comprise any oxide or nitride of these materials. In fig. 1, the deposited material is shown as passivation layers 22, 24. At this time, the shift processing method of the present invention can be used.

According to one or more embodiments of the invention, the processing of the passivation layers 22, 24 is provided by an external system 30, as shown in fig. 2. The external system 30 includes an energy source 32 for generating a beam 34 of light, the beam 34 typically being in the visible range (e.g., 532 nm), but may also include a UV or IR beam. The energy source 32 may be transmitted in a Continuous Wave (CW) or pulsed mode. In the particular embodiment shown in fig. 2, the beam 34 from the energy source 32 then passes through a focusing lens 36 and scans along a portion 38 of the passivation layer 22 overlying the active area of the laser diode bar 10. The laser diode bar 10 may be mounted on a conventional submount holder 40 and moved relative to the radiation from the energy source 32 so that the focused beam is scanned over the lateral extent of the passivation layer 22. The energy source 32 may include any source capable of radiating energy sufficient to uniformly treat the passivation material as desired. Specifically, the energy source 32 may include a laser source, a flash lamp, an electron beam source, or any other system that generates sufficient energy to process a beam of light through the entire thickness of the passivation layer 22.

A spectrometer 42, as shown in fig. 2, may be used to monitor the process. For example, the scattered/redirected radiation of the passivation layer 22 may be analyzed within the spectrometer 42 using conventional methods to determine the point in time when full processing is reached. Once the monitoring signal is stable, the external energy system may be deactivated.

It will be appreciated that the same displacement irradiation process may be used to fully treat the passivation layer 24 along the opposite end faces of the laser diode. In practice, a system can be configured to process both end faces simultaneously. It has been found that this shift irradiation process provides a treatment that achieves uniform treatment of the passivation material throughout the thickness of the passivation layer. This is a significant advantage over prior art methods of activating devices and processing at reduced power levels, which sometimes result in partially non-uniform states of passivation material.

As described above, the treatment process of the present invention can also be performed after both the passivation layer and the reflective coating are coated on the laser facet. Fig. 3 shows an exemplary laser diode having a structure similar to the configuration shown in fig. 1. In this case, further processing is performed to deposit a first coating 26 on the passivation layer 22 and a second coating 28 on the passivation layer 24. In most cases, silicon nitride is used for the coatings 26, 28. Other suitable coating materials include, but are not limited to, silicon, germanium, gallium arsenide, silicon oxide, aluminum oxide, titanium oxide, aluminum nitride, and tantalum oxide.

Similar to the embodiment of fig. 1, the coating 26 and the underlying passivation layer 22 are irradiated using an energy source 30 to sufficiently process and stabilize the laser diode structure. Under irradiation, the structure of both the coating and passivation layers will change in a manner that stabilizes the device and causes the desired high COD level to be produced. For example, when silicon nitride is used as the coating material, the silicon nitride remains amorphous (as opposed to crystalline) during irradiation, but the atomic configuration in the nitride material does change. At the same time, the irradiation crystallizes the passivation layer and forms an interface between the passivation layer and the chip.

Thus, according to the fig. 3 embodiment of the present invention, the phrase "substantially treating" refers to structurally modifying the coating, crystallizing the passivation layer, and forming an interface between the laser chip and the passivation layer. Thus, the shift process of the present invention can be thought of as "stabilizing" the laser diode itself by making changes to these layers.

The COD current of the device formed according to the present invention was compared to a device using a conventional aging process. It should be noted that "COD current" refers to the current at which the laser plane suffers from Catastrophic Optical Damage (COD). The results of this comparison are shown in fig. 4. In particular, fig. 4 contains a set of graphs I showing COD power as a function of current for devices subjected only to the conventional E2 process (without any post-treatment). Fig. II is associated with a device created using the same prior art E2 process, followed by a conventional "in-situ" treatment process that operates the device at a low current/power level. Clearly, the performance of these treated devices exceeded those of the first group, which had higher COD levels. Figure III relates to a device formed according to the present invention; that is, a shift process is used to provide complete processing of the passivation layer. In particular, the result shown in fig. 4 results from the device formed in conjunction with fig. 3 according to the above-described embodiment, wherein a displacement treatment process is formed to stabilize the coating and passivation layers.

It can be seen that the COD level of the apparatus formed according to the invention is slightly higher than that of the prior art apparatus. While this is clearly an object of the present invention, the fact that full processing can be performed on the entire laser bar (rather than at the individual device level) is also important and a significant improvement over the prior art. Furthermore, the inventive shift process is several orders of magnitude more efficient than the standard aging process, relative to tens to hundreds of hours required for low current level aging, which can adequately process/stabilize the structure in seconds or minutes.

In view of the foregoing, it has been found that the method of the present invention can uniformly and adequately treat standard E2 passivation layers (and overcoat layers, when present), eliminating the vertical and lateral processing non-uniformities found in the prior art. The method of the present invention was confirmed to maximize the current level (i.e., COD current/optical power) at which mirror damage occurs without burning. This eliminates the need for chip training through chip manipulation in the prior art. The distribution of COD current within the production batch was also reduced.

Further, as described above, the laser facet can be subjected to the shift completion process at the bar level (i.e., before chip separation). This allows sufficient handling of a large number of strips in a short time, which is preferable for mass production situations. In fact, the method of the present invention also eliminates the need for the customer to perform any processing steps on the device, as was the case in some past scenarios.

It will be understood that the principles of the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.