Patent Description:
Strain compensation layers are known in the art. However, strain compensation layers, such as dielectric strain compensation layers, can be cumbersome to implement in some instances. Thus, alternative solutions are needed.

An example of a semiconductor device is disclosed in <CIT>. The device comprises a substrate and an epitaxial layer deposited on a top surface of the substrate. An epitaxial contact together with a contact extension are deposited on top of the epitaxial layer. A substrate contact is deposited on on a bottom surface of the substrate, A electrically conductive material covers the substrate contact and a submount is provided on the electrically conductive material.

This disclosure describes semiconductor devices, such as discrete semiconductor devices or arrays of semiconductor devices, exhibiting little to no distortion, and methods for producing the same. In one aspect, a semiconductor device is disclosed in claim <NUM>.

In some implementations, the semiconductor device includes a structured extension abutting the submount contact.

In some implementations, the contact extension is composed of the same material as the obverse submount contact, and the contact extension characterized by a substantially similar microstructure as the obverse submount contact.

In some implementations, the contact extension is composed of the same material as the submount contact, and the contact extension is characterized by a substantially dissimilar microstructure as the obverse submount contact.

In another implementation, the first side of the substrate and the first side of the epitaxial layer are characterized by intrinsic stresses within the vicinity of the first side of the substrate and the first side of the epitaxial layer.

In some implementations, the contact extension is operable to counteract the intrinsic stresses within the vicinity of the first side of the substrate and the first side of the epitaxial layer such that the array of semiconductor devices adopts a form that is substantially planar above the melting temperature of the electrically conductive adhesive material.

In some implementations, the electrically conductive adhesive material is operable to fix the array of semiconductor devices into the form that is substantially planar below the melting temperature of the electrically conductive adhesive material.

In some implementations, the array of semiconductor device further includes a structured extension abutting the submount contact.

In another aspect, the disclosure describes a method for manufacturing semiconductor devices according to claim <NUM>. The method includes the following:.

In some implementations, the method for manufacturing semiconductor devices further includes depositing a structured extension onto the submount contact.

In some implementations, mounting the assembly, the epitaxial contact, and contact extension onto a chuck includes depositing an organic compound between the chuck and the epitaxial layer, epitaxial contact, and contact extension.

In some implementations, depositing the contact extension includes depositing the contact extension by electrodeposition, physical vapor deposition or chemical vapor deposition.

In some implementations, depositing the structured extension includes depositing the structured extension by electrodeposition, physical vapor deposition or chemical vapor deposition.

In some implementations, depositing the epitaxial contact and/or the substrate contact includes depositing the contacts by electrodeposition, physical vapor deposition or chemical vapor deposition.

In another aspect, a method for manufacturing semiconductor devices according to claim <NUM>. The method includes the following:.

In some implementations, the method includes depositing a structured extension, which abuts the submount contact.

In some implementations, mounting the assembly, the substrate contact, and contact extension onto a chuck includes depositing an organic compound between the chuck and the substrate, substrate contact, and contact extension.

Other aspects, features and advantages will be apparent from the following detailed description, the accompanying drawings and the claims.

<FIG> depict example arrays of semiconductor device 100A, 100B, respectively. The array of semiconductor devices 100A is a top-emitting vertical-cavity surface-emitting laser, and the array of semiconductor device 100B is a bottom-emitting vertical-cavity surface-emitting laser. The following components disclosed herein are applicable to both types of vertical-cavity surface-emitting laser, as well as other semiconductor devices or arrays of semiconductor devices.

The following description refers to arrays of semiconductor devices, such as wafers of semiconductor devices or a smaller plurality of semiconductor devices designed to operate as a single device or module, the description is applicable to individual or discrete semiconductor devices separated (e.g., diced) from the arrays of semiconductor devices.

<FIG> include equivalent components and are referred to simultaneously in the following description. Some components, though positioned differently with respect to other components, are described using a common component name. Their common component name indicates their position with respect to a common component, the position of which is invariant in both arrays of semiconductor devices 100A, 100B. For example, a submount contact is a substrate contact in the embodiment depicted in <FIG>, and an epitaxial contact in the embodiment depicted in <FIG>. The common component name, submount contact in this example, is used in both embodiments to refer to the position of the substrate contact; that is, adjacent to the submount in the first embodiment, and not adjacent to the submount in the second embodiment; hence, the submount contact position is adjacent to the submount in any embodiment.

The arrays of semiconductor devices 100A and 100B each include a substrate <NUM> having first <NUM> and second <NUM> opposing sides, and an epitaxial layer <NUM> having first <NUM> and second <NUM> opposing sides. The substrate <NUM> and the epitaxial layer <NUM> can each be composed, for eaxmple, of crystalline, polycrystalline, or amorphous semiconducting or insulating material, such as gallium arsenide, aluminum gallium arsenide, indium antimonide, or silicon.

The compositions and thicknesses of the substrate <NUM> and the epitaxial layer <NUM> depend on the intended application of the semiconductor device and thus can vary in different implementations. For example, the substrate <NUM> can be composed of gallium arsenide that is <NUM> - <NUM> microns thick, and the epitaxial layer <NUM> can be composed of aluminum gallium arsenide that is <NUM> - <NUM> microns thick.

Typically, the epitaxial layer <NUM> is epitaxially grown as a crystalline layer on the first side <NUM> of the substrate <NUM> to a thickness substantially less than the substrate <NUM>. In such instances, the substrate <NUM> is also crystalline and is composed of a material having a similar, though not identical, lattice parameter as the epitaxial layer <NUM>. As the lattice parameters are not identical, stresses can occur within the vicinity of the first side <NUM> of the substrate <NUM> and the first side <NUM> of the epitaxial layer <NUM> causing both the substrate <NUM> and the epitaxial layer <NUM> to deviate from planarity (e.g., a bowing distortion).

Each of the arrays of semiconductor devices 100A, 100B further includes a substrate contact <NUM> abutting the second side <NUM> of the substrate <NUM>, an epitaxial contact <NUM> abutting the second side <NUM> of the epitaxial layer <NUM>, and a submount <NUM>. Typically, the substrate contact <NUM> and epitaxial contact <NUM> are operable to direct current to components within the semiconductor device, such as active regions configured to generate light <NUM> (e.g., including quantum wells) within the epitaxial layer <NUM>. The submount can be a printed circuit board, a lead frame, or a metallic layer intended for further processing, for example.

The submount <NUM> is mounted to a submount contact with an electrically conductive material <NUM>, such as a fusible metal alloy (e.g., indium-tin solder) or an electrically conductive composite (e.g., silver epoxy). The submount contact is adjacent to the submount <NUM> and can be either the substrate contact <NUM> or the epitaxial contact <NUM> depending on the embodiment. For example, the submount contact is the substrate contact <NUM> as depicted in <FIG> for top-emitting vertical-cavity surface-emitting lasers. In another example, the submount contact is the epitaxial contact <NUM> as depicted in <FIG> for bottom-emitting vertical-cavity surface-emitting lasers.

Each of the arrays of semiconductor devices 100A, 100B further includes an obverse submount contact. The obverse submount contact is the epitaxial contact <NUM> when the epitaxial contact <NUM> is not associated with the submount contact as depicted in <FIG>. The obverse submount contact is the substrate contact <NUM> when the substrate contact <NUM> is not associated with the submount contact as depicted in <FIG>.

Both the submount contact and the obverse submount contact (and therefore the substrate contact <NUM> and the epitaxial contact <NUM>) can be composed of electrically conducting metal. The electrically conducting metal can include an element selected from the group consisting of gold, copper, silver, aluminum, platinum, palladium, rhodium, indium, iridium, gallium, bismuth, antimony, and tin. Both the submount contact and the obverse submount contact can be deposited by chemical vapor deposition (e.g., metalorganic vapor deposition), physical vapor deposition (e.g., electron-beam physical vapor deposition), and/or electrodeposition (e.g., electron Damascene plating). In some instances, the obverse submount contact and/or the submount contact can include metallic barrier films (e.g., tantalum, tantalum nitride) and/or dielectric barriers (silicon nitride).

Each of the arrays of semiconductor devices 100A, 100B further includes a contact extension <NUM> abutting the obverse submount contact. <FIG> depicts the contact extension <NUM> abutting the epitaxial contact <NUM> as in this, and similar, implementations the epitaxial contact <NUM> is the obverses submount contact. <FIG> depicts the contact extension <NUM> abutting the substrate contact <NUM> as in this, and similar, implementations, the substrate contact <NUM> is the obverse submount contact.

In some instances, the contact extension <NUM> is composed of an electrically conducting metal. The electrically conducting metal can include an element selected from the group consisting of gold, copper, silver, aluminum, platinum, palladium, rhodium, indium, iridium, gallium, bismuth, antimony, and tin. Consequently, the contact extension <NUM> can be operable to direct current, via an electrical connection <NUM>, to components within the arrays of semiconductor devices 100A, 100B, such as active regions configured to generate light <NUM> (e.g., including quantum wells) within the epitaxial layer <NUM> as depicted in <FIG>. The contact extension <NUM> need not be operable to direct current to components, however. For example, the substrate contact <NUM> may include a pad <NUM> for the electrical connection <NUM> as depicted in <FIG>. Accordingly, the contact extension <NUM> may be electrically isolated from the substrate contact <NUM> or even insulating in some implementations.

In some implementations, the contact extension <NUM> can be composed of the same material as the obverse submount contact and can be deposited by chemical vapor deposition, physical vapor deposition, and/or electrodeposition onto the obverse submount contact. Consequently, the contact extension <NUM> can be composed of the same material as the obverse submount contact, and can be characterized by a substantially similar microstructure as the obverse submount contact.

However, in some implementations, the contact extension <NUM> is composed of the same material as the obverse submount contact and can be deposited by different means as the obverse submount contact. For example, in some instances, the obverse submount contact is composed of gold deposited by physical vapor deposition (e.g., electron-beam physical vapor deposition), and the contact extension is composed of gold deposited by electrodeposition. Consequently, the contact extension <NUM> can be characterized by a substantially dissimilar microstructure as the obverse submount contact. For example, the contact extension <NUM> may adopt a substantially crystalline or polycrystalline microstructure, and the obverse submount contact may adopt a substantially amorphous microstructure.

Further, in some implementations, the contact extension <NUM> is composed of a material different from the obverse submount contact and can be deposited by means different from the obverse submount contact. For example, in some instances the obverse submount contact is composed of gold deposited by physical vapor deposition (e.g., electron-beam physical vapor deposition), and the contact extension is composed of copper deposited by electrodeposition. Consequently, the contact extension <NUM> can be characterized by a substantially dissimilar composition and microstructure as the obverse submount contact.

The contact extension <NUM> is operable to counteract the intrinsic stresses within the vicinity of the first side <NUM> of the substrate <NUM> and the first side <NUM> of the epitaxial layer <NUM> such that the array of semiconductor devices 100A, 100B adopts a form that is substantially planar above the melting temperature of the electrically conductive adhesive material <NUM>. The contact extension can be composed of gold from <NUM> to <NUM> microns thick in some implementations. However, the operability of the contact extension <NUM> depends on a number of factors, such as its composition, area, thickness, coefficient of thermal expansion, and the stresses within the vicinity the substrate <NUM> and epitaxial layer <NUM> as described above. Further, intrinsic stresses within the contact extension <NUM> induced by various processing parameters can be tailored to counteract the intrinsic stresses described above. For example, stresses within the microstructure of the contact extension <NUM> can be introduced by adjusting processing parameters during electrodeposition (e.g., solution pH, impurities, grain size).

Although the contact extension <NUM> is operable to counteract the intrinsic stresses at elevated temperatures (i.e., at or above the melting temperature of the electrically conductive adhesive <NUM>), the effect must be locked-in place at cooler temperatures. Consequently, the electrically conductive adhesive material <NUM> is operable to fix the array of semiconductor devices 100A, 100B into a substantially planar form below its melting temperature.

In some implementations, such as the implementations depicted in <FIG>, each of the arrays of semiconductor devices 100A, 100B further includes a structured extension <NUM> abutting the submount contact. The structured extension <NUM> is configured to improve adhesion of the electrically conductive adhesive material <NUM> and the submount contact. In some instances, the structured extension <NUM> can also be configured to counteract the intrinsic stresses described above via the same approaches as the contact extension <NUM>.

Both the contact extension <NUM> and the structured extension <NUM> along with the electrically conductive adhesive material <NUM> are configured such that the arrays of semiconductor devices 100A, 100B adopt a form that is substantially planar above the melting temperature of the electrically conductive adhesive material <NUM>. Then the electrically conductive adhesive material <NUM> and the structured extension <NUM> are operable to fix the array of semiconductor devices 100A, 100B into the form that is substantially planar below the melting temperature of the electrically conductive adhesive material <NUM>. In some instances, the structured extension <NUM> can include crenelated extensions <NUM> configured to increase the contact area between the structured extension <NUM> and the electrically conductive adhesive material <NUM> as depicted in <FIG>.

The arrays of semiconductor devices 100A, 100B further include a plurality of isolating components (not depicted) within the epitaxial layer <NUM>. The plurality of isolating components delineates each semiconductor device within the array of semiconductor devices 100A, 100B. For example, the isolating components within the epitaxial layer <NUM> can include a dielectric material, such as aluminum oxide. In some instances, the isolating components can include portions of the epitaxial layer characterized by damage caused by ion bombardment. In some instances, the isolating components within the epitaxial layer include removed portions of the epitaxial layer. The removed portions defining mesa structures, wherein each mesa structure delineates one of the semiconductor devices within the array of semiconductor devices.

An example method <NUM> for manufacturing the array of semiconductor devices depicted in <FIG> is illustrated in <FIG>. At <NUM>, an assembly is mounted onto an assembly holder, such as a vacuum chuck. The assembly includes the substrate <NUM> with first <NUM> and second <NUM> opposing sides, and the epitaxial layer <NUM> with the first <NUM> and second <NUM> opposing sides. The first side <NUM> of the epitaxial layer <NUM> abuts the first side <NUM> of the substrate <NUM>, and the second side <NUM> of the substrate <NUM> abuts the assembly holder. As described above, the epitaxial layer <NUM> can be epitaxially grown on the substrate <NUM> according to methods apparent to a person of ordinary skill in the art.

At <NUM>, the epitaxial contact <NUM> is deposited onto the second side <NUM> of the epitaxial layer <NUM>. As described above, the epitaxial contact <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the epitaxial contact <NUM> can be <NUM> - <NUM> angstroms, while in other instances, the epitaxial contact <NUM> can be <NUM> microns thick or more.

At <NUM>, the contact extension <NUM> is deposited onto the epitaxial contact <NUM>. As described above, the contact extension <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the contact extension <NUM> can be <NUM> micron or up to <NUM> microns, or even 3o microns, thick. In some instances, the epitaxial contact <NUM> acts a seed layer for the contact extension <NUM>.

At <NUM>, the assembly, the epitaxial contact <NUM>, and the contact extension <NUM> are mounted onto a chuck (e.g., a vacuum chuck) such that the epitaxial layer <NUM>, epitaxial contact <NUM>, and the contact extension <NUM> are adjacent to the chuck. In some instances, the assembly, the epitaxial contact <NUM>, and contact extension <NUM> are mounted onto the chuck with an organic compound positioned between the chuck and the epitaxial layer <NUM>, epitaxial contact <NUM>, and contact extension <NUM>. The organic compound can be a wax, resin, or other formable material designed to minimize damage to the aforementioned components.

At <NUM>, the assembly, epitaxial contact <NUM>, contact extension <NUM>, and chuck are dismounted from the assembly holder.

At <NUM>, portions of the substrate <NUM> are removed from the second side <NUM> of the substrate <NUM>. Portions of the substrate <NUM> can be removed by standard means, such as grinding, lapping, or polishing. For example, the substrate <NUM> may be <NUM> microns thick and may subject to grinding, lapping, or polishing until it is <NUM> to <NUM> microns thick, for example.

At <NUM>, the substrate contact <NUM> is deposited onto the second side <NUM> of the substrate <NUM>. As described above, the substrate contact <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the substrate contact <NUM> is <NUM> - <NUM> angstroms, while in other instances, the substrate contact <NUM> is <NUM> microns or more. In some instances, a structured extension <NUM> is deposited onto the substrate contact. The structured extension <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the structured extension <NUM> is <NUM> micron or up to <NUM> microns, or even <NUM> microns, thick. In some instances, the substrate contact <NUM> acts a seed layer for the structured extension <NUM>. In some instances, the structured extension <NUM> can be crenelated or structured in other ways to increase the structured extension surface area.

At <NUM>, the substrate contact <NUM>, the assembly, the epitaxial contact <NUM>, the contact extension <NUM>, and the chuck are positioned onto the submount <NUM> such that the submount <NUM> is adjacent to the second side <NUM> of the substrate <NUM> and the substrate contact <NUM>. The submount <NUM> is positioned with the electrically conductive material <NUM> between portions of the substrate contact <NUM> and the submount <NUM>.

At <NUM>, the submount <NUM>, the substrate contact <NUM>, the assembly, the epitaxial contact <NUM>, the contact extension <NUM>, the chuck, and the electrically conductive material <NUM> are heated to an elevated temperature at or above the melting temperature of the electrically conductive material <NUM> for a duration depending on the electrically conductive adhesive material <NUM>. For example, the aforementioned components may be heated to <NUM>, <NUM>, or even <NUM> for <NUM> minutes, one hour, or even several hours. In some instances, the aforementioned components may be heated in an inert (e.g., N<NUM>, Ar) or reducing atmosphere (e.g., <NUM>:<NUM> N<NUM>:H).

At <NUM>, the submount <NUM>, the substrate contact <NUM>, the assembly, the epitaxial contact <NUM>, the contact extension <NUM>, the chuck, and the electrically conductive material <NUM> are cooled to a temperature below the elevated temperature.

At <NUM>, the submount <NUM>, the substrate contact <NUM>, the assembly, the epitaxial contact <NUM>, the contact extension <NUM>, and the electrically conductive material <NUM> are dismounted from the chuck.

At <NUM>, the submount <NUM>, the substrate contact <NUM>, the assembly, the epitaxial contact <NUM>, the contact extension <NUM>, and the electrically conductive material <NUM> are separated (e.g., diced) into a plurality of discrete semiconductor devices, an array of semiconductor devices, or a plurality of arrays of semiconductor devices.

An example method <NUM> for manufacturing the array of semiconductor devices depicted in <FIG> is illustrated in <FIG>. At <NUM>, an assembly is mounted onto an assembly holder. The assembly includes the substrate <NUM> with the first <NUM> and the second <NUM> opposing sides, and the epitaxial layer <NUM> with the first <NUM> and the second <NUM> opposing sides. The first side <NUM> of the epitaxial layer <NUM> abuts the first side <NUM> of the substrate <NUM>, and the second side <NUM> of the epitaxial layer <NUM> abuts the assembly holder. As described above, the epitaxial layer <NUM> can be grown epitaxially on the substrate <NUM>.

At <NUM>, the substrate contact <NUM> is deposited onto the second side <NUM> of the substrate (<NUM>). As described above, the substrate contact <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the substrate contact <NUM> is <NUM> - <NUM> angstroms, while in other instances, the substrate contact <NUM> is <NUM> microns thick or more.

At <NUM>, the contact extension <NUM> is deposited onto the substrate contact <NUM>. As described above, the contact extension <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the contact extension <NUM> is <NUM> microns or up to <NUM> microns, or even <NUM> microns, thick. In some instances, the substrate contact <NUM> acts a seed layer for the contact extension <NUM>.

At <NUM>, the assembly, the substrate contact <NUM>, and contact extension <NUM> are mounted onto a chuck (e.g., vacuum chuck) such that the substrate <NUM>, substrate contact <NUM>, and contact extension <NUM> are adjacent to the chuck. In some instances, the assembly, the substrate contact <NUM>, and contact extension <NUM> are mounted onto the chuck with an organic compound positioned between the chuck and the substrate <NUM>, substrate contact <NUM>, and contact extension <NUM>. The organic compound can be a wax, resin, or other formable material designed to minimize damage to the aforementioned components.

At <NUM>, the assembly, substrate contact <NUM>, contact extension <NUM>, and chuck is dismounted from the assembly holder.

At <NUM>, the epitaxial contact <NUM> is deposited onto the second side <NUM> of the epitaxial layer <NUM>. As described above, the epitaxial contact <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the epitaxial contact <NUM> is <NUM> - <NUM> angstroms, while in other instances, the epitaxial contact <NUM> is <NUM> microns or more. In some instances, a structured extension <NUM> is deposited onto the epitaxial contact <NUM>. The structured extension <NUM> can be deposited via chemical vapor deposition, physical vapor deposition, and/or electrodeposition. In some instances, the structured extension <NUM> is <NUM> microns or up to <NUM> microns, or even <NUM> microns, thick. In some instances, the epitaxial contact <NUM> acts a seed layer for the structured extension <NUM>. In some instances, the structured extension <NUM> can be crenelated or structured in other ways to increase the structured extension surface area.

At <NUM>, the epitaxial contact <NUM>, the assembly, the substrate contact <NUM>, contact extension <NUM>, and chuck are positioned onto the submount <NUM> such that the submount <NUM> is adjacent to the second side <NUM> of the epitaxial layer <NUM> and the epitaxial contact <NUM>. The submount <NUM> is positioned with the electrically conductive material <NUM> between portions of the epitaxial contact <NUM> and the submount <NUM>.

At <NUM>, the submount <NUM>, the epitaxial contact <NUM>, the assembly, the substrate contact <NUM>, the contact extension <NUM>, the chuck, and the electrically conductive material <NUM> are heated to an elevated temperature at or above the melting temperature of the electrically conductive material <NUM> for a duration depending on the electrically conductive adhesive material <NUM>. For example, the aforementioned components may be heated to <NUM>, <NUM>, or even <NUM> for <NUM> minutes, one hour, or even several hours. In some instances, the aforementioned components may be heated in an inert (e.g., N<NUM>, Ar) or reducing atmosphere (e.g., <NUM>:<NUM> N<NUM>:H).

At <NUM>, the submount, the epitaxial contact <NUM>, the assembly, the substrate contact <NUM>, the contact extension <NUM>, the chuck, and the electrically conductive material <NUM> are cooled to a temperature below the elevated temperature.

At <NUM>, the submount <NUM>, the epitaxial contact <NUM>, the assembly, the substrate contact <NUM>, the contact extension <NUM>, and the electrically conductive material <NUM> are dismounted from the chuck.

At <NUM>, the submount <NUM>, the epitaxial contact <NUM>, the assembly, the substrate contact <NUM>, the contact extension <NUM>, and the electrically conductive material <NUM> are separated (e.g., diced) into a plurality of discrete semiconductor devices, an array of semiconductor devices, or a plurality of arrays of semiconductor devices.

Claim 1:
A semiconductor device (100A, 100B) comprising:
a substrate (<NUM>) having first (<NUM>) and second (<NUM>) opposing sides;
an epitaxial layer (<NUM>) having first (<NUM>) and second (<NUM>) opposing sides, the first
side (<NUM>) of the epitaxial layer abutting the first side (<NUM>) of the substrate;
wherein either
an epitaxial contact (<NUM>), configured for electrical connection, is deposited onto and abuts the second side (<NUM>) of the epitaxial layer,
a contact extension (<NUM>) is deposited onto the epitaxial contact (<NUM>);
a submount contact, which is a substrate contact (<NUM>) is deposited onto the second side (<NUM>) of the substrate (<NUM>),
a submount (<NUM>) is positioned adjacent to the second side (<NUM>) of the substrate, the submount is positioned onto the substrate contact (<NUM>) with an electrically conductive material (<NUM>) between portions of the substrate contact and the submount; or
an substrate contact (<NUM>), configured for electrical connection, is deposited onto and abuts the second side (<NUM>) of the substrate,
a contact extension (<NUM>) is deposited onto the substrate contact (<NUM>),
a submount contact, which is an epitaxial contact (<NUM>) deposited onto the second side (<NUM>) of the epitaxial layer (<NUM>),
a submount (<NUM>) positioned adjacent to the second side (<NUM>) of the epitaxial layer (<NUM>), the submount being positioned onto the epitaxial contact (<NUM>) with an electrically conductive material (<NUM>) between portions of the epitaxial contact and the submount.