Patent Description:
A vertical-emitting device, such as a vertical-cavity surface-emitting laser, VCSEL, is a laser in which a laser beam is emitted in a direction perpendicular to a surface of a substrate (e.g., vertically from a surface of a semiconductor wafer). Contrary to edge-emitting devices, vertical-emitting devices may allow for testing to occur at intermediate steps of wafer.

An example of a VCSEL is disclosed in <CIT>. The disclosed VCSEL comprises a substrate layer and epitaxial layers on the substrate layer. The epitaxial layers include an active layer, a first mirror, a second mirror, and oxidation regions. The oxidation regions are configured to control beam divergence of a laser beam emitted by the VCSEL. The oxidation regions have a tapered shape for controlling the beam divergence.

According to some possible implementations, a VCSEL may include a substrate layer and epitaxial layers on the substrate layer. The epitaxial layers may include an active layer, a first mirror, a second mirror, and multiple oxidation layers. The active layer may be between the first mirror and the second mirror, and the one or more oxidation layers may be proximate to the active layer. The multiple oxidation layers may have different proximities to the active layer. An oxidation layer closest to the active layer is not tapered, and another oxidation layer includes a tapered end that is tapered from a farthest side from the active layer to a closest side to the active layer. The other oxidation layer has a first aperture size at the farthest side from the active layer and a second aperture size at the closest side to the active layer, the first aperture size being less than the second aperture size. The multiple oxidation layers may be configured to control beam divergence of a laser beam emitted by the VCSEL based on: a proximity of the multiple oxidation layers to the active layer.

The other oxidation layer may be configured to create an effective refractive index step, between an active region of the active layer and an oxidation area associated with the other oxidation layer, to form a wide beam divergence of the laser beam when compared to a beam divergence created by a differently configured oxidation layer.

The multiple oxidation layers may include a third oxidation layer to control the beam divergence.

The shape of the multiple oxidation layers may be configured to control the beam divergence.

The thickness of the multiple oxidation layers may be configured to control the beam divergence.

The proximity of the multiple oxidation layers to the active layer may be configured to control the beam divergence.

According to some possible implementations, a method of controlling beam divergence in a VCSEL may include forming, on a substrate layer of the VCSEL, an active layer, a first mirror, and a second mirror. The active layer may be formed between the first mirror and the second mirror. The method may include forming multiple oxidation layers that have different proximities to the active layer. An oxidation layer closest to the active layer is not tapered, and another oxidation layer includes a tapered end that is tapered from a farthest side from the active layer to a closest side to the active layer. The other oxidation layer has a first aperture size at the farthest side from the active layer and a second aperture size at the closest side to the active layer, the first aperture size being less than the second aperture size. The multiple oxidation layers may be configured to control beam divergence of a laser beam emitted by the VCSEL based on: a proximity of the multiple oxidation layers to the active layer.

The other oxidation layer may be configured to create a relatively large effective refractive index step, proximate to an active region of the active layer, to form a relatively wide beam divergence of the laser beam.

The other oxidation layer may be configured to create a relatively small effective refractive index step, proximate to an active region of the active layer, to form a relatively narrow beam divergence of the laser beam.

According to some possible implementations, a VCSEL wafer may include a substrate layer and epitaxial layers on the substrate layer. The epitaxial layers may include an active layer between a first mirror and a second mirror, and multiple oxidation layers, configured to control beam divergence of an emitted laser beam by controlling an effective refractive index step proximate to an active region of the active layer based on: a proximity of the multiple oxidation layers, to the active region of the active layer. The multiple oxidation layers have different proximities to the active layer. An oxidation layer closest to the active layer is not tapered, and another oxidation layer includes a first tapered end that is tapered from a farthest side from the active layer to a closest side to the active layer. The other oxidation layer has a first aperture size at the farthest side from the active layer and a second aperture size at the closest side to the active layer, the first aperture size being less than the second aperture size.

A relatively large effective refractive index step may cause a relatively wide beam divergence of the emitted laser beam, and wherein a relatively small effective refractive index step may cause a relatively narrow beam divergence of the emitted laser beam.

The beam divergence may be controlled based on the quantity of oxidation layers included in the multiple oxidation layers.

The beam divergence may be controlled based on the shape of at least one oxidation layer of the multiple oxidation layers.

The beam divergence is controlled based on the thickness of at least one oxidation layer of the multiple oxidation layers.

The beam divergence may be controlled based on the proximity of at least one oxidation layer, of the multiple oxidation layers, to the active region of the active layer.

The implementations described below are merely examples and are not intended to limit the implementations to the precise forms disclosed. Instead, the implementations were selected for description to enable one of ordinary skill in the art to practice the implementations.

<FIG> are diagrams of different emitters (e.g., VCSELs) <NUM>, <NUM> with different beam divergences. A first emitter <NUM> may emit a laser beam <NUM> with a wider beam divergence, a higher numerical aperture, and a wider spectral width. A second emitter <NUM> may emit a laser beam <NUM> with a narrower beam divergence, a lower numerical aperture, and a narrower spectral width.

Emitters, such as VCSELs, may be used for a variety of applications requiring different optical mode characteristics, such as beam divergence, numerical aperture, and/or spectral width. For example, in consumer applications, such as three-dimensional sensing, an emitter with a higher numerical aperture, wider beam divergence, and wider spectral width (e.g., emitter <NUM>) may be desirable to improve safety by reducing the amount of light that may enter the human eye. As another example, in data communications, an emitter with a lower numerical aperture, narrower beam divergence, and narrower spectral width (e.g., emitter <NUM>) may be desirable to increase fiber coupling efficiency and/or increase the transmission distance. Some techniques described herein permit the flexible design of emitters <NUM>, <NUM> for a variety of applications that require different beam divergences, numerical apertures, and/or spectral widths.

As shown in <FIG>, emitters <NUM>, <NUM> may include a substrate layer <NUM> and epitaxial layers formed on the substrate layer <NUM>. The epitaxial layers may include an active layer <NUM>, a first mirror <NUM>, a second mirror <NUM>, and one or more oxidation layers <NUM>. The active layer <NUM> may be between the first mirror <NUM> (e.g., a top mirror) and the second mirror <NUM> (e.g., a bottom mirror). Additional details regarding example emitters <NUM>, <NUM> are described elsewhere herein.

The beam divergence, numerical aperture, and spectral width of a laser beam emitted by an emitter <NUM>, <NUM> are controlled by the optical mode of light emitted by the emitter <NUM>, <NUM>. The optical mode is controlled by an effective refractive index step between an active region <NUM>, of the active layer <NUM>, and an oxidation area <NUM> associated with the one or more oxidation layers <NUM>. The effective refractive index step may represent a relative difference between an effective refractive index of the oxidation area <NUM> relative to an effective refractive index of the active region <NUM>. Some techniques described herein modify an effective refractive index of the oxidation area <NUM>, which modifies an optical mode of the emitter <NUM>, <NUM>, which modifies the beam divergence, numerical aperture, and spectral width of a laser beam emitted by the emitter <NUM>, <NUM>. For example, increasing the effective refractive index of the oxidation area <NUM> results in a larger effective refractive index step proximate to the active region <NUM>, which increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by emitter <NUM> and laser beam <NUM>. Conversely, decreasing the effective refractive index of the oxidation area <NUM> results in a smaller effective refractive index step proximate to the active region <NUM>, which reduces optical confinement and produces a laser beam with a narrower divergence, a lower numerical aperture, and a narrower spectral width, as shown by emitter <NUM> and laser beam <NUM>.

Techniques described herein relate to modifying characteristics of oxidation layer(s) <NUM> to modify an effective refractive index of the oxidation area <NUM> and control optical mode characteristics of an emitter, such as a VCSEL. For example, emitter <NUM> includes a greater number of oxidation layers <NUM> (e.g., two oxidation layers <NUM>), which increases the effective refractive index of the oxidation area <NUM>, resulting in a wider beam divergence of laser beam <NUM>. As another example, emitter <NUM> includes a lesser number of oxidation layers <NUM> (e.g., one oxidation layer <NUM>), which decreases the effective refractive index of the oxidation area <NUM>, resulting in a narrower beam divergence of laser beam <NUM>. The quantity of oxidation layers <NUM> is one example of an oxidation layer characteristic that can be modified to modify the effective refractive index of the oxidation area <NUM>. Other characteristics include the shape, thickness, and/or proximity of the oxidation layer(s) <NUM> to the active layer <NUM>, and will be described in more detail elsewhere herein. By modifying characteristics of oxidation layer(s) <NUM>, emitters can be designed for a variety of applications with varying requirements.

In some implementations, the design of oxide layers <NUM> and resulting oxide apertures account for an overall lateral index profile created by thermal lensing associated with an oxide aperture, particularly when an effective refractive index step is small. For example, the VCSEL may be hotter closer to the center of the oxide aperture, and the temperature drop toward the edge of the oxide aperture creates a corresponding drop in the semiconductor refractive index from the center of the oxide aperture to the edge of the oxide aperture. Techniques described herein that modify the effective refractive index step do not affect this thermal lensing effect in the first order.

In some cases, multiple oxide layers <NUM> have been used to reduce parasitic capacitances that limit high-speed modulation (e.g., <NUM> and/or the like) of VCSELs in data communication applications. Some techniques described herein apply to high optical power VCSELs with limited modulation (e.g., <NUM> and/or the like), where multiple oxide layers <NUM> have not been used to reduce parasitic capacitances.

Furthermore, the design of a VCSEL requires not just control of the divergence of the laser beam, but also the uniformity of the angular distribution of light intensity (e.g., the far-field), particularly for the case of satisfying laser safety standards. In these standards, output power delivered through an aperture (e.g., of typically <NUM> diameter) placed typically <NUM> away from the source must be below a particular value depending upon wavelength and pulsing conditions. Furthermore, all the possible angular placements of the aperture relative to the source must be considered. Thus, for applications in which the far-field of the VCSEL or VCSEL array can be viewed by the human eye (e.g., either directly or through lenses), the far-field must not only have a minimum divergence, but also cannot have spikes or angular cones in which the light intensity is concentrated.

The divergence of individual lasing modes increases for smaller aperture sizes. However, high divergence cannot simply be achieved by making a smaller aperture diameter (e.g. < <NUM>) due to the inability to control the aperture size (or equivalently the oxidation length or depth) in manufacturing, as well as other engineering constraints such as the number of emitters in an array. Therefore, high divergence needs to be achieved with a larger individual VCSEL diameter (e.g., with a <NUM> to approximately <NUM> diameter aperture). To achieve this requires the laser to lase partially in higher order modes that have higher divergence, and that have multiple lobes in the far-field. To avoid concentrations of light near particular angles requires a mixture of both higher order and lower order modes to lase simultaneously. Multi-mode VCSELs used for data communication lase in a mixture of higher and lower order modes, but typically do not have wide enough divergence to meet requirements for free-space sensing applications because these VCSELs are typically engineered to have fewer modes to achieve a narrower spectral width as required by typical multi-mode fiber data communication standards.

To enable increased lasing of higher order modes, as compared to VCSELs used for data communication, requires a larger lateral effective index step, which may be achieved with multiple oxide apertures, a thicker oxide aperture, and/or other techniques described herein. The effective index is defined by the integral (along the vertical axis) of the refractive index weighted by the electrical field intensity. The effective index step may be calculated by the difference between the effective index along the vertical axis in the center of the device (without oxide) less the effective index along the vertical axis through the thickest portion of the oxide layers (near the edge of the device). Additionally, or alternatively, the effective index step may be calculated by comparing the resonant wavelength for plane waves travelling along the vertical axis in the center of the device to the plane waves traveling along the vertical axis at the edge of the device and encountering the thickest portion of the oxide layers.

One way to produce a large change in the effective index step is with an abrupt jump or step. However, a large abrupt step in lateral effective index has two problems. First, it requires blunt oxidation fronts, which are prone to increase the mechanical stress in the device. Second, it requires an abrupt step in effective refractive index, which increases scattering loss for the higher order modes, thereby inhibiting lasing in those modes. Therefore, the larger later index step must be achieved with some tapering of the lateral index profile.

Too long a taper or equivalently too low a lateral index gradient, however, can lead to two problems. In the extreme case, too long a taper will effectively appear like a small index step near the active region, and the higher order modes will be too wide spatially to overlap with the active region of the device (where the current flows into the quantum wells) and will not lase or will lase very little. But in the intermediate case, too long a taper (or equivalently too low a lateral index gradient), can reduce the scattering loss too much for the higher order modes such that they have almost the same loss as the lowest order modes. Such low loss can be a problem at low temperatures (e.g., -40C to 5C). Typically, in VCSELs operating at a low temperature, the peak of the gain spectrum of the active region will be shorter in wavelength than the lasing modes. At higher temperatures, both the peak of the gain spectrum and the lasing mode shift to longer wavelengths, but the peak of the gain spectrum shifts faster and better aligns with all the lasing modes. The higher order modes, however, lase at shorter wavelength than the lower order or the lowest order (e.g., fundamental) mode. Therefore, the threshold carrier density (and hence threshold current) will be lower for the higher order modes at low temperature when the scattering loss is low. Potentially, this difference can lead to lasing primarily on a single or a few higher order modes and lead to concentration of light in a particular angular cones, which is undesirable when trying to achieve a more uniform angular distribution of light intensity as is commonly required for sensing applications.

Consequently, for a given size and wavelength of VCSEL, there is both an upper and lower bound to the lateral index gradient and effective refractive index step in order to achieve sufficient divergence and a sufficiently uniform far-field profile. Although it is possible to determine the shape of the lateral modes of a waveguide with various finite element software, it is difficult to predict the relative optical power of the lasing modes in a VCSEL because the resulting combination of modes will depend upon the current injection profile, the temperature profile, the optical gain versus carrier density and carrier diffusion. In some cases, the aperture can be designed as follows: For lasers in the <NUM> to <NUM> wavelength range with an effective aperture diameter between <NUM> and <NUM> micrometer, the effective refractive index step required is at least <NUM> with an average effective index gradient between <NUM>-<NUM> and <NUM>-<NUM>, or equivalently a taper length between <NUM> and <NUM> micrometers to achieve a divergence of at least <NUM> NA at injection current density of 7kA/cm<NUM>, where NA is the numerical aperture defined as the sine of the half-angle of a cone that encircles <NUM>% of the optical power and such that the far-field is sufficiently uniform when the VCSEL is driven under continuous wave (CW) or quasi-CW conditions. To be sufficiently uniform requires that the optical power passing through a cone light with a half angle of <NUM> degrees (for any orientation with respect to the primary direction of the laser beam) is no more than <NUM>% a fraction of the total optical output power. The oxide aperture need not be exactly circular, so effective aperture diameter mentioned above is the diameter of a circle of equivalent area.

In the case of narrow divergence, for lasers in the <NUM> to <NUM> wavelength range with an effective aperture diameter between <NUM> and <NUM> micrometers, the effective refractive index step (in absence of thermal gradients) required is at most <NUM> to achieve a divergence of at most <NUM> NA at injection current density of at least approximately <NUM> kA/cm^<NUM>. Additionally, the aperture must be placed at most approximately <NUM> micrometers vertically from the active region in order ensure optical gain primarily excites the lowest order modes. Techniques described herein are capable of meeting the requirements described above.

Other examples are possible and may differ from what was described in connection with <FIG>.

<FIG> are diagrams depicting a top-view of an emitter <NUM> and an example cross-sectional view <NUM> of emitter <NUM>, respectively. As shown in <FIG>, emitter <NUM> may include a set of emitter layers constructed in an emitter architecture. For purposes of clarity, not all emitter layers of emitter <NUM> are shown in <FIG>. In some implementations, emitter <NUM> may correspond to emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, emitter <NUM> of <FIG>, and/or the like.

As shown in <FIG>, emitter <NUM> includes an implant protection layer <NUM> that is circular in shape in this example. In some implementations, implant protection layer <NUM> may have another shape, such as an elliptical shape, a polygonal shape, or the like. Implant protection layer <NUM> is defined based on a space between sections of implant material included in emitter <NUM> (not shown). As further shown in <FIG>, emitter <NUM> includes a P-Ohmic metal layer <NUM> that is constructed in a partial ring-shape (e.g., with an inner radius and an outer radius). As shown, P-Ohmic metal layer <NUM> is positioned concentrically over implant protection layer <NUM> (i.e., the outer radius of P-Ohmic metal layer <NUM> is less than or equal to the radius of implant protection layer <NUM>). Such configuration may be used, for example, in the case of a P-up/top-emitting emitter <NUM>. In the case of a bottom-emitting emitter <NUM>, the configuration may be adjusted as needed.

As further shown in <FIG>, emitter <NUM> includes a dielectric via opening <NUM> that is formed (e.g., etched) on a dielectric passivation/mirror layer that covers P-Ohmic metal layer <NUM> (not shown). As shown, dielectric via opening <NUM> is formed in a partial ring-shape (e.g., similar to P-Ohmic metal layer <NUM>) and is formed concentrically over P-Ohmic metal layer <NUM> such that metallization of the dielectric passivation/mirror layer contacts P-Ohmic metal layer <NUM>. In some implementations, dielectric opening <NUM> and/or P-Ohmic metal layer <NUM> may be formed in another shape, such as a full ring-shape or a split ring-shape.

As further shown, emitter <NUM> includes an optical aperture <NUM> in a portion of the emitter within the inner radius of the partial ring-shape of P-Ohmic metal layer <NUM>. Emitter <NUM> emits a laser beam via optical aperture <NUM>. As further shown, emitter <NUM> also includes a current confinement aperture <NUM> (e.g., an oxide aperture formed by an oxidation layer <NUM> of emitter <NUM>). Current confinement aperture <NUM> is formed below optical aperture <NUM>.

As further shown in <FIG>, emitter <NUM> includes a set of oxidation trenches <NUM> that are spaced (e.g., equally, unequally) around a circumference of implant protection layer <NUM>. How close oxidation trenches <NUM> can be positioned relative to the optical aperture <NUM> is dependent on the application, and is typically limited by implant protection layer <NUM>, P-Ohmic metal layer <NUM>, dielectric via opening <NUM>, and manufacturing tolerances.

The number and arrangement of layers shown in <FIG> are provided as an example. In practice, emitter <NUM> may include additional layers, fewer layers, different layers, or differently arranged layers than those shown in <FIG>. For example, while emitter <NUM> includes a set of six oxidation trenches <NUM>, in practice, other designs are possible, such as a compact emitter that includes five oxidation trenches <NUM>, seven oxidation trenches <NUM>, and/or the like. As another example, while emitter <NUM> is a circular emitter design, in practice, other designs are possible, such as a rectangular emitter, a hexagonal emitter, an elliptical emitter, or the like. Additionally, or alternatively, a set of layers (e.g., one or more layers) of emitter <NUM> may perform one or more functions described as being performed by another set of layers of emitter <NUM>, respectively.

Notably, the design of emitter <NUM> is described as including a VCSEL. Additionally, the design of emitter <NUM> may apply to emitters of any wavelength, power level, emission profile, or the like. In other words, emitter <NUM> is not particular to an emitter with a given performance characteristic.

As shown in <FIG>, the example cross-sectional view may represent a cross-section of emitter <NUM> that passes through a pair of oxidation trenches <NUM> (e.g., as shown by the line labeled "X-X" in <FIG>). As shown, emitter <NUM> may include a backside cathode layer <NUM>, a substrate layer <NUM>, a bottom mirror <NUM>, an active layer <NUM>, an oxidation layer <NUM>, a top mirror <NUM>, an implant isolation material <NUM>, a dielectric passivation/mirror layer <NUM>, and a P-Ohmic metal layer <NUM>. As shown, emitter <NUM> may have a total height that is approximately <NUM>.

Backside cathode layer <NUM> may include a layer that makes electrical contact with substrate layer <NUM>. For example, backside cathode layer <NUM> may include an annealed metallization layer, such as an AuGeNi layer, a PdGeAu layer, or the like.

Substrate layer <NUM> may include a base substrate layer upon which epitaxial layers are grown. For example, substrate layer <NUM> may include a semiconductor layer, such as a GaAs layer, an InP layer, and/or the like. In some implementations, substrate layer <NUM> may be a surface of a semiconductor wafer, and emitter <NUM> may be formed on the semiconductor wafer (e.g., to form an emitter wafer). In some implementations, substrate layer <NUM> may correspond to substrate layer <NUM>, described above in connection with <FIG>.

Bottom mirror <NUM> may include a bottom reflector layer of emitter <NUM>. For example, bottom mirror <NUM> may include a distributed Bragg reflector (DBR). In some implementations, bottom mirror <NUM> may correspond to second mirror <NUM>, described above in connection with <FIG>.

Active layer <NUM> may include a layer that confines electrons and defines an emission wavelength of emitter <NUM>. For example, active layer <NUM> may be a quantum well. In some implementations, active layer <NUM> may correspond to active layer <NUM>, described above in connection with <FIG>.

Oxidation layer <NUM> may include an oxide layer that provides optical and electrical confinement of emitter <NUM>. In some implementations, oxidation layer <NUM> may be formed as a result of wet oxidation of an epitaxial layer. For example, oxidation layer <NUM> may be an Al<NUM>O<NUM> layer formed as a result of oxidation of an AlAs or AlGaAs layer. Oxidation trenches <NUM> may include openings that allow oxygen (e.g., dry oxygen, wet oxygen) to access the epitaxial layer from which oxidation layer <NUM> is formed. Oxidation layer(s) <NUM> may be proximate to active layer <NUM>. In some implementations, oxidation layer <NUM> may correspond to oxidation layer <NUM>, described above in connection with <FIG>. As shown, oxidation layer <NUM> is farther from substrate layer <NUM> as compared to active layer <NUM> (e.g., substrate layer <NUM> is located on one side of active layer <NUM>, and oxidation layer <NUM> is located on the opposite side of active layer <NUM>).

As shown in <FIG>, when emitter <NUM> is a top-emitting laser, oxidation layer <NUM> is positioned between active layer <NUM> and optical aperture <NUM> from which emitter <NUM> emits a laser beam. In some implementations, when emitter <NUM> is a bottom-emitting laser, active layer <NUM> is positioned between oxidation layer <NUM> and optical aperture <NUM> from which emitter <NUM> emits a laser beam.

Current confinement aperture <NUM> may include an optically active aperture defined by oxidation layer <NUM>. A size of current confinement aperture <NUM> may range, for example, from approximately <NUM> to approximately <NUM>. In some implementations, a size of current confinement aperture <NUM> may depend on a distance between oxidation trenches <NUM> that surround emitter <NUM>. For example, oxidation trenches <NUM> may be etched to expose the epitaxial layer from which oxidation layer <NUM> is formed. Here, before dielectric passivation/mirror layer <NUM> is deposited, oxidation of the epitaxial layer may occur for a particular distance (e.g., identified as do in <FIG>) toward a center of emitter <NUM>, thereby forming oxidation layer <NUM> and current confinement aperture <NUM>. In some implementations, current confinement aperture <NUM> may include an oxide aperture. Additionally, or alternatively, current confinement aperture <NUM> may include an aperture associated with another type of current confinement technique, such as an etched mesa, a region without ion implantation, lithographically defined intra-cavity mesa and regrowth, or the like.

Top mirror <NUM> may include a top reflector layer of emitter <NUM>. For example, top mirror <NUM> may include a DBR. In some implementations, top mirror <NUM> may correspond to first mirror <NUM>, described above in connection with <FIG>.

Implant isolation material <NUM> may include a material that provides electrical isolation. For example, implant isolation material <NUM> may include an ion implanted material, such as an H implanted material or a Hydrogen/Proton implanted material. In some implementations, implant isolation material <NUM> may define implant protection layer <NUM>.

Dielectric passivation/mirror layer <NUM> may include a layer that acts as a protective passivation layer and that acts as an additional DBR. For example, dielectric passivation/mirror layer <NUM> may include one or more sub-layers (e.g., a SiO<NUM> layer, a Si<NUM>N<NUM> layer) deposited (e.g., via chemical vapor deposition) on one or more other layers of emitter <NUM>.

As shown, dielectric passivation/mirror layer <NUM> may include one or more dielectric via openings <NUM> that provide electrical access to P-Ohmic metal layer <NUM>. Optical aperture <NUM> may include a portion of dielectric passivation/mirror layer <NUM> over current confinement aperture <NUM> via which light may be emitted.

P-Ohmic metal layer <NUM> may include a layer that makes electrical contact via which electrical current may flow. For example, P-Ohmic metal layer <NUM> may include a TiAu layer, a TiPtAu layer, or the like, via which electrical current may flow (e.g., via a bondpad (not shown) that contacts P-Ohmic metal layer <NUM> through dielectric via openings <NUM>).

In some implementations, emitter <NUM> may be manufactured using a series of steps. For example, bottom mirror <NUM>, active layer <NUM>, oxidation layer <NUM>, and top mirror <NUM> may be epitaxially grown on substrate layer <NUM>, after which P-Ohmic metal layer <NUM> may be deposited on top mirror <NUM>. Next, oxidation trenches <NUM> may be etched to expose oxidation layer <NUM> for oxidation. Implant isolation material <NUM> may be created via ion implantation, after which dielectric passivation/mirror layer <NUM> may be deposited. Dielectric via openings <NUM> may be etched in dielectric passivation/mirror layer <NUM> (e.g., to expose P-Ohmic metal layer for contact). Plating, seeding, and etching may be performed, after which substrate layer <NUM> may be thinned and/or lapped to a target thickness. Finally, backside cathode layer <NUM> may be deposited on a bottom side of substrate layer <NUM>.

The number, arrangement, thicknesses, order, symmetry, or the like, of layers shown in <FIG> is provided as an example. In practice, emitter <NUM> may include additional layers, fewer layers, different layers, differently constructed layers, or differently arranged layers than those shown in <FIG>. Additionally, or alternatively, a set layers (e.g., one or more layers) of emitter <NUM> may perform one or more functions described as being performed by another set of layers of emitter <NUM>.

<FIG> are diagrams of example cross-sectional views of example emitters configured to control beam divergence and/or other optical mode characteristics. The emitters shown in <FIG> may include one or more elements described above in connection with <FIG>, <FIG>, and/or 2B. The emitters shown in <FIG> include substrate layer <NUM>, active layer <NUM>, top mirror <NUM>, bottom mirror <NUM>, oxidation layer(s) <NUM>, active region <NUM>, oxidation area <NUM>, and/or the like. Furthermore, while a single emitter is shown in each of <FIG>, techniques described herein may apply to an array of emitters. More particularly, techniques described herein may apply to an array of emitters that have both a common anode and a common cathode.

<FIG> are diagrams of different emitters (e.g., VCSELs) <NUM>, <NUM> with different beam divergences due to different quantities of oxidation layers <NUM>. Emitter <NUM> may emit a laser beam <NUM> with a wider beam divergence, a higher numerical aperture, and a wider spectral width, while emitter <NUM> may emit a laser beam <NUM> with a narrower beam divergence, lower numerical aperture, and a narrower spectral width. As shown in <FIG>, emitters <NUM>, <NUM> may produce laser beams <NUM>, <NUM> (respectively) with optical mode characteristics controlled by a quantity of oxidation layers <NUM> included in emitter <NUM>, <NUM>.

For example, emitter <NUM> includes a greater number of oxidation layers <NUM> (e.g., three oxidation layers <NUM>), which increases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layers <NUM>. Increasing the effective refractive index step proximate to active region <NUM> increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by laser beam <NUM>.

Conversely, emitter <NUM> includes a smaller number of oxidation layers <NUM> (e.g., one oxidation layer <NUM>), which decreases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layers <NUM>. Decreasing the effective refractive index step proximate to active region <NUM> decreases optical confinement and produces a laser beam with a narrower divergence, a lower numerical aperture, and a narrower spectral width, as shown by laser beam <NUM>. The oxidation layer <NUM> closest to the active layer active region <NUM> may have the greatest impact on the effective refractive index step, and oxidation layers <NUM> may have a lesser impact on the effective refractive index step.

The quantity of oxidation layers <NUM> shown in <FIG> are provided as examples, and different quantities of oxidation layers <NUM> may be included in an emitter (e.g., two oxidation layers <NUM>, four oxidation layers <NUM>, five oxidation layers <NUM>, and/or the like). By modifying a quantity of oxidation layers <NUM> included in an emitter and/or by modifying one or more other oxidation layer characteristics (e.g., described elsewhere herein), emitters may be flexibly designed for a variety of applications that require different beam divergences, numerical apertures, and/or spectral widths.

<FIG> are diagrams of different emitters (e.g., VCSELs) <NUM>, <NUM> with different beam divergences due to different thicknesses of one or more oxidation layers <NUM>. Emitter <NUM> may emit a laser beam <NUM> with a wider beam divergence, a higher numerical aperture, and a wider spectral width, while emitter <NUM> may emit a laser beam <NUM> with a narrower beam divergence, lower numerical aperture, and a narrower spectral width. As shown in <FIG>, emitters <NUM>, <NUM> may produce laser beams <NUM>, <NUM> (respectively) with optical mode characteristics controlled by a thickness of oxidation layer(s) <NUM> included in emitter <NUM>, <NUM>.

For example, emitter <NUM> includes a thicker oxidation layer <NUM> (e.g., <NUM>-<NUM> nanometers), which increases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Increasing the effective refractive index step proximate to active region <NUM> increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by laser beam <NUM>.

Conversely, emitter <NUM> includes a thinner oxidation layer <NUM> (e.g., <NUM>-<NUM> nanometers), which decreases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Decreasing the effective refractive index step proximate to active region <NUM> decreases optical confinement and produces a laser beam with a narrower divergence, a lower numerical aperture, and a narrower spectral width, as shown by laser beam <NUM>.

The thicknesses of oxidation layers <NUM> shown in <FIG> are provided as examples, and different thicknesses of oxidation layers <NUM> may be configured. Additionally, or alternatively, multiple oxidation layer characteristics may be configured to control optical mode characteristics (e.g., beam divergence, numerical aperture, spectral width, and/or the like). For example, different emitters may include different quantities of oxidation layers <NUM> and different thicknesses of one or more of the oxidation layers <NUM> to achieve a desired optical mode characteristic.

In some implementations, an emitter may include multiple oxidation layers <NUM> with different thicknesses (e.g., a thicker oxidation layer <NUM> closer to active layer <NUM> and a thinner oxidation layer <NUM> farther from active layer <NUM>, or a thinner oxidation layer <NUM> closer to active layer <NUM> and a thicker oxidation layer <NUM> farther from active layer <NUM>). By modifying a thickness of oxidation layer(s) <NUM> included in an emitter and/or by modifying one or more other oxidation layer characteristics (e.g., described elsewhere herein), emitters may be flexibly designed for a variety of applications that require different beam divergences, numerical apertures, and/or spectral widths.

<FIG> are diagrams of different emitters (e.g., VCSELs) <NUM>, <NUM> with different beam divergences due to different proximities of one or more oxidation layers <NUM> to active layer <NUM>. Emitter <NUM> may emit a laser beam <NUM> with a wider beam divergence, a higher numerical aperture, and a wider spectral width, while emitter <NUM> may emit a laser beam <NUM> with a narrower beam divergence, a lower numerical aperture, and a narrower spectral width. As shown in <FIG>, emitters <NUM>, <NUM> may produce laser beams <NUM>, <NUM> (respectively) with optical mode characteristics controlled by a proximity of one or more oxidation layers <NUM>, included in emitter <NUM>, <NUM>, to an active layer <NUM> included in emitter <NUM>, <NUM>.

For example, emitter <NUM> includes an oxidation layer <NUM> positioned closer to active layer <NUM>, which increases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Increasing the effective refractive index step proximate to active region <NUM> increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by laser beam <NUM>.

Conversely, emitter <NUM> includes an oxidation layer <NUM> positioned farther from active layer <NUM>, which decreases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Decreasing the effective refractive index step proximate to active region <NUM> decreases optical confinement and produces a laser beam with a narrower divergence, a lower numerical aperture, and a narrower spectral width, as shown by laser beam <NUM>.

The proximities of oxidation layers <NUM> to active layers <NUM> shown in <FIG> are provided as examples, and different proximities may be configured. Additionally, or alternatively, multiple oxidation layer characteristics may be configured to control optical mode characteristics (e.g., beam divergence, numerical aperture, spectral width, and/or the like). For example, different emitters may include different quantities of oxidation layers <NUM>, different thicknesses of one or more of the oxidation layers <NUM>, and/or different proximities of one or more oxidation layers <NUM> to active layer <NUM> to achieve a desired optical mode characteristic.

The emitter includes multiple oxidation layers <NUM> with different proximities to active layer <NUM>. In this case, a proximity of a single oxidation layer <NUM> to the active layer <NUM> (e.g., an oxidation layer <NUM> closest to the active layer <NUM>) may be configured to modify optical mode characteristics. Additionally, or alternatively, proximities of multiple oxidation layers <NUM> to the active layer <NUM> may be configured to modify optical mode characteristics. By modifying corresponding proximities of oxidation layer(s) <NUM> included in an emitter and/or by modifying one or more other oxidation layer characteristics (e.g., described elsewhere herein), emitters may be flexibly designed for a variety of applications that require different beam divergences, numerical apertures, and/or spectral widths.

<FIG> are diagrams of different emitters (e.g., VCSELs) <NUM>, <NUM> with different shapes of one or more oxidation layers <NUM>. Emitters <NUM>, <NUM> may emit laser beams <NUM>, <NUM> (respectively) with a wider beam divergence, a higher numerical aperture, and a wider spectral width. As shown in <FIG>, emitters <NUM>, <NUM> may produce laser beams <NUM>, <NUM> (respectively) with optical mode characteristics controlled by a shape of one or more oxidation layers <NUM> included in emitter <NUM>, <NUM>.

For example, emitter <NUM> includes an oxidation layer <NUM> with a tapered end (e.g., a tapered central end located closer to the center of mirror <NUM>). Tapering an end of oxidation layer <NUM> decreases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM> (e.g., as compared to an end that is not tapered). However, such tapering may increase mechanical reliability of emitter <NUM> to offset a decrease in mechanical reliability due to a configuration of another optical mode characteristic (e.g., a thicker oxidation layer <NUM>, an increased number of oxidation layers <NUM>, an oxidation layer <NUM> positioned closer to active layer <NUM>, and/or the like).

For example, as shown in <FIG>, emitter <NUM> includes a thick oxidation layer <NUM>, which increases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Increasing the effective refractive index step proximate to active region <NUM> increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by laser beam <NUM>. Furthermore, because oxidation layer <NUM> includes tapered ends, emitter <NUM> may exhibit improved mechanical stability and reliability as compared to a similar emitter with a similar thickness of an oxidation layer <NUM> that is not tapered (e.g., such as emitter <NUM> of <FIG>).

Similarly, as shown in <FIG>, emitter <NUM> includes an oxidation layer <NUM> positioned closer to active layer <NUM>, which increases an effective refractive index step between active region <NUM>, of the active layer <NUM>, and oxidation area <NUM> associated with the oxidation layer <NUM>. Increasing the effective refractive index step proximate to active region <NUM> increases optical confinement and produces a laser beam with a wider divergence, a higher numerical aperture, and a wider spectral width, as shown by laser beam <NUM>. Furthermore, because oxidation layer <NUM> includes tapered ends, emitter <NUM> may exhibit improved mechanical stability and reliability as compared to a similar emitter with a similar proximity between active layer <NUM> and an oxidation layer <NUM> that is not tapered (e.g., such as emitter <NUM> of <FIG>). However, in some implementations, one or more oxidation layers <NUM> may not be tapered (or may have less than a threshold degree of tapering) to improve ease of design of the VCSEL. In accordance with the present invention, an oxidation layer <NUM>, closest to the active layer <NUM>, is not tapered.

As shown in <FIG>, the oxidation layer <NUM> of emitter <NUM> is shown with a deeper depth of oxidation on a first portion of oxidation layer <NUM> positioned closer to active layer <NUM>, and a shallower depth of oxidation on a second portion of oxidation layer <NUM> positioned farther from active layer <NUM>. As shown in <FIG>, the oxidation layer <NUM> of emitter <NUM> is shown with a shallower depth of oxidation on a first portion of oxidation layer <NUM> positioned closer to active layer <NUM>, and a deeper depth of oxidation on a second portion of oxidation layer <NUM> positioned farther from active layer <NUM>. These shapes of oxidation layers are provided as examples, and other examples are possible. For example, a first portion of oxidation layer <NUM> positioned closer to active layer <NUM> may have a relatively shallow depth of oxidation, a second portion of oxidation layer <NUM> positioned farther from active layer <NUM> may have a relatively shallow depth of oxidation, and a third portion of oxidation layer <NUM> positioned between the first portion and the second portion may have a relatively deep depth of oxidation.

Additionally, or alternatively, multiple oxidation layer characteristics may be configured to control optical mode characteristics (e.g., beam divergence, numerical aperture, spectral width, and/or the like). For example, different emitters may include different quantities of oxidation layers <NUM>, different thicknesses of one or more of the oxidation layers <NUM>, different proximities of one or more oxidation layers <NUM> to active layer <NUM>, and/or different shapes of oxidation layers <NUM> to achieve a desired optical mode characteristic.

In some implementations, an emitter may include multiple oxidation layers <NUM> with different shapes. In this case, a shape of a single oxidation layer <NUM> (e.g., an oxidation layer <NUM> closest to the active layer <NUM>) may be configured to modify optical mode characteristics. Additionally, or alternatively, shapes of multiple oxidation layers <NUM> to the active layer <NUM> may be configured to modify optical mode characteristics. By modifying corresponding shapes of oxidation layer(s) <NUM> included in an emitter and/or by modifying one or more other oxidation layer characteristics (e.g., described elsewhere herein), emitters may be flexibly designed for a variety of applications that require different beam divergences, numerical apertures, and/or spectral widths.

<FIG> is a flow chart of an example process <NUM> for controlling beam divergence in a VCSEL.

As shown in <FIG>, process <NUM> may include forming, on a substrate layer of a VCSEL, an active layer, a first mirror, and a second mirror, wherein the active layer is formed between the first mirror and the second mirror (block <NUM>). In some implementations, the VCSEL is a top emitting VCSEL. In some implementations, the VCSEL is a bottom emitting VCSEL.

As further shown in <FIG>, process <NUM> includes oxidation layers proximate to the active layer, wherein one or more oxidation layers are configured to control beam divergence of a laser beam emitted by the VCSEL based on one or more oxidation layer characteristics (block <NUM>). In some implementations, the one or more oxidation layers are configured to create a relatively large effective refractive index step, proximate to an active region of the active layer, to form a relatively wide beam divergence of the laser beam. In some implementations, the one or more oxidation layers are configured to create a relatively small effective refractive index step, proximate to an active region of the active layer, to control beam divergence of the laser beam.

In some implementations, the beam divergence is controlled based on at least one of: a quantity of the one or more oxidation layers, one or more shapes of the one or more oxidation layers, one or more thicknesses of the one or more oxidation layers, or one or more proximities of the one or more oxidation layers to the active layer. For example, the one or more oxidation layers may include multiple oxidation layers to control the beam divergence. Additionally, or alternatively, a shape of the one or more oxidation layers may be configured to control the beam divergence. Additionally, or alternatively, a thickness of the one or more oxidation layers may be configured to control the beam divergence. Additionally, or alternatively, a proximity of the one or more oxidation layers to the active layer may be configured to control the beam divergence.

An oxidation layer, of the one or more oxidation layers, closest to the active layer is not tapered.

Some techniques described herein permit the flexible design of emitters (e.g., VCSELs) for a variety of applications that require different optical mode characteristics, such as beam divergences, numerical apertures, and/or spectral widths.

Claim 1:
A vertical cavity surface emitting laser (VCSEL), comprising:
a substrate layer; and
epitaxial layers on the substrate layer,
the epitaxial layers including an active layer, a first mirror, a second mirror,
and multiple oxidation layers located between the first mirror and the second mirror,
wherein the active layer is between the first mirror and the second mirror,
wherein the multiple oxidation layers have different proximities to the active layer,
wherein an oxidation layer closest to the active layer is not tapered, and
wherein another oxidation layer includes a tapered end that is tapered from a farthest side from the active layer to a closest side to the active layer,
wherein the other oxidation layer has a first aperture size at the farthest side from the active layer and a second aperture size at the closest side to the active layer,
the first aperture size being less than the second aperture size, and wherein the multiple oxidation layers are configured to control beam divergence of a laser beam emitted by the VCSEL based on:
a proximity of the multiple oxidation layers to the active layer.