Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-09-19
2004-09-07
Pert, Evan (Department: 2829)
Coherent light generators
Particular active media
Semiconductor
C438S046000
Reexamination Certificate
active
06788720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical components. To be more precise, it relates to a semiconductor optical component and a method of fabricating it.
2. Description of the Prior Art
A laser type semiconductor optical component based on gallium arsenide is often used to pump solid lasers or optical amplifiers employing fibers doped with rare earths. This is known in the art. The operation of the above kind of component is based on the use of an active layer which, once supplied with current, emits radiation that can be amplified and can correspond to laser radiation, at wavelengths generally within a band around 808 nm, 920 nm, 940 nm, and in particular 980 nm, this latter wavelength being used for pumping monomode fiber amplifiers employed in optical telecommunication applications. Moreover, the above optical component, which is often of the parallelepiped-shaped type, can have cleaved front and rear lateral faces to form faceted mirrors so that Fabry-Pérot longitudinal propagation modes are established in the component.
Throughout the following description, the term “layer” designates either a single layer or a stack of layers fulfilling the same function.
On top of the active layer, the semiconductor optical component generally comprises two electrically isolated regions which are called plateaux because of their shape, these plateaux being situated on respective opposite sides of a current injection region in which current penetrates to the interior of the component.
The plateaux and the current injection region each contain a contact layer for making ohmic contact in the current injection region, i.e. to achieve a good flow of current toward the active layer. The contact layer, which is generally made from an alloy based on gallium arsenide (GaAs), is deposited onto a upper confinement layer, which is made from a semiconductor material and contributes to guiding radiation emitted by the active layer.
The monocrystalline semiconductor material active layer, upper confinement layer and contact layer are generally deposited by metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).
The plateaux comprise an isolation layer made from a dielectric material such as a metal oxide (alumina, titanium oxide, etc.), a polyimide, and usually a silicon nitride, which is chosen for its excellent dielectric properties.
Because of the presence of the isolation layer, the height of the plateaux is significantly greater than the height of the current injection region. In this configuration, the plateaux therefore protect the current injection region from mechanical damage (knocks, scratches, etc.) occurring during fabrication and/or use of the component. This type of configuration is favored over projecting configurations, i.e. configurations with no plateau type electrically isolated region.
Moreover, there are also components with a current injection region disposed between two electrically isolated regions in the form of channels, situated on respective opposite sides of the current injection region. These channels are themselves disposed between two plateaux protecting the current injection region. The expression “double channel component” is then used.
The adhesion to the GaAs of the dielectric materials previously cited constituting the isolation layer is critical. Adhesion problems arise during the step of depositing the layer and/or after deposition, during subsequent component fabrication steps. This lack of adhesion frequently leads to unsticking of the isolation layer on the plateaux. This unsticking can in particular occur during heat treatment at high temperatures and/or during cleaving of the component. For example, during cleaving, the mechanical energy delivered to break the crystal becomes greater than the cohesion force between the isolation layer and the contact layer in the vicinity of the faceted mirrors. A larger or smaller gap is formed between the isolation layer and the contact layer in this case.
Adhesion defects and unsticking are liable to propagate as far as the edges of the current injection region. This introduces spreading of the current lines, surface current leaks widening the current injection region at the level of the active layer, which degrades the electro-optical properties of the component. Moreover, the possibility of unsticking reduces the reliability and the service life of the component.
A first object of the present invention is to develop a semiconductor optical component that offers reliability and good performance and overcomes the problems of adhesion and of unsticking of the isolation layer on the contact layer.
SUMMARY OF THE INVENTION
To this end the invention proposes a semiconductor optical component comprising a current injection region and at least one electrically isolated region referred to as a first plateau, each region containing a contact layer of an alloy based on gallium arsenide, GaAs, deposited on a semiconductor material upper confinement layer, the component further comprising in the first plateau a dielectric material isolation layer on top of the contact layer, and in which component an attachment layer is disposed between the contact layer and the isolation layer to increase the adhesion of the isolation layer to the contact layer.
An appropriate material is chosen for the attachment layer in order to favor adhesion of the isolation layer not only during deposition but also during subsequent component fabrication steps (heat treatment, cleaving, etc.).
Furthermore, preparation of the surface of the attachment layer before deposition can be envisaged, for example using a wet method employing a deoxidizing agent and/or a dry method that effects brief oxide removal. Similarly, the choice may be made to optimize the deposition conditions, for example by using the plasma enhanced chemical vapor deposition (PECVD) process employing a plasma containing high-energy ions. This kind of oxide removal and high-energy deposition of the isolation layer cannot be envisaged in the case of a prior art component. In effect, energetic ions bombarding the contact layer damage its surface.
The attachment layer according to the invention can advantageously be made from an alloy based on phosphorus and preferably from an alloy based on phosphorus, gallium and indium, such as InGaP
2
.
In this way, the attachment layer can be deposited epitaxially at a high temperature and immediately after the contact layer, in the same epitaxial sequence and without returning the component to the open air. This does not necessitate any particular surface preparation of the contact layer as these layers have matching lattice parameters. Moreover, epitaxial deposition is carried out under conditions such that the surface of the contact layer is damaged during nucleation of the attachment layer.
Furthermore, unlike prior art methods, a deoxidizing agent such as a sulfuric acid can be used to prepare for deposition of the isolation layer without degrading the underlying contact layer.
The attachment layer according to the invention can advantageously have a thickness from 20 nm to 5000 nm and preferably of the order of 1000 nm.
A thickness of the order of 20 nm to 30 nm is sufficient to solve the adhesion problem. Nevertheless, the deposition of a thicker layer has another advantage. In effect, because the current injection region comprises no attachment layer, the thicker that layer the greater the height difference between the plateau or plateaux and the current injection region. Thus, with a deposit thickness of the order of 1000 nm, the current injection region is better protected from mechanical damage.
According to the invention, the isolation layer can be made from a dielectric material chosen from polyimides, metal oxides, silica, nitrides, and preferably from silicon nitrides.
Metal oxides such as alumina can be used. Silicon nitrides are materials based on nitrogen and silicon and can also contain a smaller quantity of oxygen and/or hydrogen. These nitrides are particularly rec
Brot Christian
Garabedian Patrick
Avanex Corporation
Moser, Patterson & Sheridan L.L.P.
Pert Evan
LandOfFree
Semiconductor optical component and a method of fabricating it does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor optical component and a method of fabricating it, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor optical component and a method of fabricating it will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3209227