The invention relates generally to semiconductor laser devices and, more particularly, to a semiconductor laser device in which an edge-emitting laser and a reflector are integrated together on the same chip to form a surface-emitting semiconductor laser device.
Semiconductor lasers are commonly used in optical transceivers for telecommunications and data communication networks. The lasers used in such optical transceivers are commonly of the edge-emitting type. Edge-emitting lasers for optical transceivers are fabricated on semiconductor wafers using standard photolithographic and epitaxial methods, diced into chips, and portions of each chip coated with reflective and anti-reflective coatings. The finished chips can then be tested. It would be desirable to minimize the number of manufacturing steps as well as to enhance testability.
Vertical Cavity Surface Emitting Lasers (VCSELs) are often preferred by end-users because of their high coupling efficiency with optical fibers without the need to provide beam shape correction, thus reducing test/packaging costs. Currently, however, some VCSELs have problems with regard to single-mode yield control when manufactured for very high speed operation.
Efforts have also been made in the industry to convert an edge-emitting device into a vertical-emitting device. For example, U.S. Pat. No. 7,245,645 B2 discloses one or both of the laser facets etched at 45° angles to form a 45° minor that reflects the laser beam vertically. In this solution, however, the 45° minor is within the laser cavity. The inclusion of an etched mirror inside of the laser cavity requires performing a high quality facet etching process during fabrication. Any facet damage that occurs during the facet etching process can result in reliability issues, especially when operating under high power.
U.S. Pat. No. 5,671,243 discloses using conventional 90° laser facets that are outside of the lasing cavity, but in the same chip there is a reflection minor that turns the beam towards in the direction of the surface. Because the minor is formed in the active layers, the mirror height and position cannot be adjusted. For this reason, it is difficult or impossible to optimize the structure.
U.S. Pat. No. 7,450,621 to the assignee of the present application discloses a solution that overcomes many of the aforementioned difficulties. This patent discloses a semiconductor device in which a diffractive lens is integrated with an edge-emitting laser on the same chip. The diffractive lens is monolithically integrated with the edge-emitting laser on an indium phosphide (InP) substrate material. The monolithic integration of a diffractive lens on the same chip in which the edge-emitting laser is integrated requires the performance of multiple Electron Beam Lithography (EBL) exposure and dry etching processes, which increases device fabrication costs.
It would be desirable to provide a surface-emitting semiconductor device that implements an edge-emitting laser to obtain the benefits associated therewith and that is economical to manufacture and test.
The invention is directed to a surface-emitting semiconductor laser device and a method for fabricating the device. The device comprises a substrate having an upper surface and a lower surface, a plurality of semiconductor layers disposed on the substrate, an edge-emitting laser formed in the semiconductor layers for producing laser light of a lasing wavelength, a channel formed in the semiconductor layers, a polymer material disposed in the channel, and a reflector located on the angled side facet of the polymer material generally facing the second end facet of the laser. During operations of the laser, at least a portion of the laser light that passes out of the second end facet is reflected by the reflector in a direction generally normal to the upper surface of the substrate.
The fabrication method comprises depositing or growing a plurality of semiconductor layers on a substrate, forming an edge-emitting laser in one or more of the semiconductor layers for producing laser light of a lasing wavelength, forming a channel in the semiconductor layers, and disposing a polymer material in the channel, forming a reflector on the angled side facet of the polymer material generally facing the second end facet of the laser.
These and other features and advantages of the invention will become apparent from the following description, drawings and claims.
The invention is directed to a surface-emitting semiconductor laser device in which an edge-emitting laser formed in a semiconductor material and a reflector formed in a polymer material are integrated together in the surface-emitting semiconductor laser device. The device includes an edge-emitting laser formed in various layers of semiconductor material disposed on a semiconductor substrate, a polymer material disposed on the substrate laterally adjacent the layers in which the edge-emitting laser is formed, and a reflector formed in or on an angled surface of the polymer material facing the laser channel of the edge-emitting laser. Laser light propagating out of the laser channel of the edge-emitting laser is reflected by the reflector at an angle that is generally orthogonal to the angle of incidence of the laser light on the reflector to cause the light to be directed out of the surface-emitting semiconductor laser device in a direction generally normal to its surface.
Forming the reflector in the polymer material rather than monolithically in a semiconductor material provides advantages with respect to choosing the height and position of the reflector for optimization. Another advantage is that the angled surface of the polymer material is formed by an etching process that is separate from the etching process that is used to etch the semiconductor materials and that uses a different gas system than that which is used to etch the semiconductor materials. This feature provides an additional degree of freedom in designing the reflector. In addition, because the reflector can be formed in the polymer material through a coating process that is performed at the wafer level, all of the surface-emitting semiconductor laser devices can be tested while on the wafer, i.e., before singulation is performed. This latter feature also reduces manufacturing costs.
A p-metal contact 13 (shown in
The material of which the substrate 2 is made may be, for example, doped indium phosphide (InP) or gallium arsenide (GaAs). For exemplary purposes, it will be assumed that the semiconductor substrate 2 is made of InP. It will also be assumed that the buffer layer 3 is made of n-type InP. The layers 5 include an MQW active region, one or more p-type InP spacer layers, infill layers, and cladding and contact layers, which are typically grown using a known MOCVD technique. Persons skilled in the art will understand the manner in which such additional layers may be included in the device 1.
The edge-emitting laser 4 is typically a ridge structure, such as a reverse-mesa ridge structure, as is known in the art. Methods that may be used to form such a ridge structure are discussed in detail in U.S. Pat. No. 7,539,228, which is assigned to the assignee of the present application and which is incorporated by reference herein in its entirety. As disclosed in this patent, the ridge structure may be etched using convention techniques described in the background of the patent, or grown using techniques described in the detailed description the patent.
During operations, the edge-emitting laser 4 emits a light beam generally along an axis that is parallel to the plane of the substrate 2. The laser beam passes out of the exit facet of the laser 4 and is incident on the reflector 20 (or on the HR coating 15 if the reflector 20 is not needed) an angle of typically about 45° relative to the angled surface 10a of the polymer material 10. The laser beam is then reflected by the reflector 20 (or by the HR coating 15) in a direction generally toward an upper surface 10b of the polymer material 10, which is generally normal to the upper surface 2a of the substrate 2. Accordingly, a beam emerges from the device 1 oriented along an axis that is substantially perpendicular to the upper surface 2a of the substrate 2, i.e., substantially perpendicular to the upper surfaces of the device 1. For this reason, the device 1 is referred to herein as a “surface-emitting” device.
The device 30 includes a semiconductor substrate 2, a buffer layer 3 disposed on the upper surface of the substrate 2, an edge-emitting laser 4 formed in one or more layers 5 that are disposed on top of the buffer layer 3, a polymer material 10 disposed on the upper surface of the substrate 2 laterally adjacent the edge-emitting laser 4, and a reflector 20 disposed on an angled side facet 10a of the polymer material 10. In accordance with the illustrative embodiment of
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The invention has been described with reference to a few illustrative or exemplary embodiments for the purposes of describing the principles and concepts of the invention. The invention, however, is not limited to these embodiments, as will be understood by persons skilled in the art in view of the description provided herein. For example, while the substrate 2 and other layers of the devices 1 and 30 have been described as using InP, the substrate 2 and the other layers may comprise any suitable material, such as a GaAs substrate, aluminum gallium (AlGa), aluminum gallium indium arsenide (AlGaInAs), etc. In addition, various other metal configurations may be used for the p-metal and n-metal contacts. The surface-emitting semiconductor laser devices 1 and 30 may operate as single transverse mode or multimode lasers, or as a longitudinally single mode laser. Those skilled in the art will understand that various modifications may be made to the embodiments described herein and that it is intended that the present invention cover all such modifications and variations.