KR102739381B1 - Single Mode Vertical Cavity Surface Emitting Laser - Google Patents

Abstract

Disclosure of a single mode vertical cavity surface emitting laser (VCSEL), the present embodiment forms a phase control layer on a second reflector layer, and forms a phase compensation layer in an aperture on the phase control layer, thereby forming a first region below the aperture and a second region around the aperture. By utilizing the difference in effective refractive index between the first region and the second region based on the difference in oscillation threshold gain between the first region and the second region, higher-order modes are suppressed, thereby providing a single mode vertical cavity surface emitting laser having an index-guiding structure with a refractive index difference.

Description

Single Mode Vertical Cavity Surface Emitting Laser

An embodiment of the present invention relates to a single mode vertical cavity surface emitting laser (VCSEL).

The content described below merely provides background information related to the present invention and does not constitute prior art.

Vertical cavity surface emitting lasers (VCSELs) have the advantages of excellent luminescence characteristics, the possibility of two-dimensional array production, and small size production. VCSELs are widely used in various fields such as light sources for high-speed short-distance optical communications in high-performance computers or data centers, laser printers, scanners, industrial high-power lasers, various sensors for smartphones such as proximity sensors or user face recognition, industrial sensors such as optical mice or gas sensors, and sensors for autonomous vehicles such as eye tracking systems or LiDAR (Light Detection and Ranging). However, stable mode characteristics and high output are required for these applications.

Figure 1 is a vertical cross-sectional view of a conventional vertical cavity surface-emitting laser.

As illustrated in FIG. 1, in a conventional VCSEL (see Patent Document 1), a first reflector layer (108), an active layer (118), and a second reflector layer (126) are formed on a semiconductor substrate (100), and carriers pass through the first reflector layer (108) and the second reflector layer (126) between the upper electrode (140) and the lower electrode (142) and are injected into the active layer (118).

Here, GaAs, GaP, InP, sapphire, GaN, etc. are used as materials for the semiconductor substrate (100).

The first reflector layer (108) and the second reflector layer (126) are formed of Al _x Ga _(1-x) As, and are formed by doping n-type or p-type dopants. Silicon (Si) is used as the n-type dopant, and carbon (C), zinc (Zn), etc. are used as the p-type dopant.

Each reflector layer (108, 126) includes a structure in which layers with high refractive index and layers with low refractive index are alternately laminated. When the layers with high refractive index (102, 120) and the layers with low refractive index (104, 122) are combined to form a pair (106, 124), each reflector layer is formed by laminating these pairs approximately 20 to 40 times.

When the substrate is GaAs, the difference in refractive index of each layer constituting the first reflector layer (108) and the second reflector layer (126) can be obtained by varying the composition of aluminum (Al).

The optical thickness including the high refractive index layer (102) and the low refractive index layer (104) for the first reflector layer (108) is formed to be λ/2 for the wavelength λ of light at which the VCSEL is designed to operate. In addition, one pair (124) of the second reflector layer (126) is also formed to have the same optical thickness.

The active layer (118) is a portion where electrons and holes recombine at the p-n junction to generate light, and has a basic structure of an n-type carrier confinement layer (110), a quantum well layer (112), and a p-type carrier confinement layer (116). The quantum well layer (112) may include multiple layers, and a barrier layer (114) may be formed between each layer.

The phase compensation layer (130) has a structure in which Al _x Ga _(1-x) As layers and GaAs layers are sequentially stacked.

The phase compensation layer (130) is doped with the same impurities as the second reflector layer (126), and the doping concentration of the impurities is set to 1×10 ¹⁹ /cm ³ or less. Preferably, it is doped to about 1 to 5×10 ¹⁸ /cm ³ .

The thickness of the phase compensation layer (130) is formed so that the optical thickness, including the thickness of the second reflector layer (126), becomes an integer multiple of λ/2, so that the threshold gain is minimized.

The phase compensation layer (130) has an optical thickness to compensate for phase interference caused by light reflection from the upper electrode (140), and is doped at a low concentration to minimize light loss at the aperture. In addition, the phase compensation layer (130) serves to prevent an oxide film from forming on the second reflector layer (126) when in contact with air.

The phase mismatching layer (132) is a structure in which Al _x Ga _(1-x) As layers and GaAs layers are sequentially stacked.

The Al _x Ga _(1-x) As layer in the phase mismatch layer (132) has x > 0.15 and is doped with the same impurity as the phase compensation layer (130) at the same concentration. In addition, the GaAs layer in the phase mismatch layer (132) prevents the formation of an oxide film in the opening and has the same structure as the second reflector layer (126) to reduce the electrode contact resistance and increase the current injection efficiency. It is doped with impurities in amounts of 1×10 ¹⁹ /cm ³ or more.

The phase mismatch layer (132) is formed to have an optical thickness of (2N-1)λ/4 (N is a natural number) times that causes destructive interference in the phase of light reflected from the first reflector layer (108) and the second reflector layer (126). Therefore, the threshold gain is maximized.

The VCSEL includes a current blocking layer (144) formed by injecting ions into a certain depth on both sides of the second reflector layer (126) or by oxidizing an oxidizable layer. The current blocking layer (144) restricts the path of carriers to the central portion, thereby limiting the current injected into the active layer (118) to a certain area.

An upper electrode (140) is formed by evaporating Au, Zn, Cr, etc. on a phase mismatch layer (132), and a lower electrode (142) is formed by evaporating a metal such as Ni, AuGe, Au, etc. on the lower surface of a semiconductor substrate (100).

In the conventional VCSEL as described above, when current is injected through two electrodes (140, 142), electrons and holes that have passed through the first reflector layer (108) and the second reflector layer (126) combine in the active layer (118), thereby generating light. The generated light initially diverges into all solid angles, but only light that satisfies the Bragg wavelength of each reflector layer (108, 126) remains after constructive interference. When this light creates stimulated emitting light according to carrier concentration inversion in the active layer (118), laser light is emitted to the outside through a surface aperture in the vertical direction from the semiconductor substrate.

By performing phase compensation only on the aperture and making the surrounding area phase-mismatched, the conventional VCSEL maximizes the optical loss around the aperture and suppresses the transverse mode of the laser light. In addition, the conventional VCSEL uses a structure that increases only the doping concentration of the phase-mismatched layer (132), which is the part where the metal electrode comes into contact, excluding the aperture, to reduce the contact resistance while minimizing the optical absorption in the aperture. Therefore, the conventional VCSEL has the advantages of excellent optical output and reduced threshold current. However, the conventional VCSEL shows the possibility of implementing a single mode by suppressing the transverse mode of the laser light, but has the problem of not clearly presenting the conditions for implementing a single mode.

As shown in Fig. 1, the biggest problem of the existing single-mode VCSEL, in which the radius of the upper electrode aperture is smaller than the radius of the current blocking region aperture, is that it is a gain-guiding structure that utilizes the difference in threshold gain. In general, the gain-guiding structure shows significantly lower mode stability than the index-guiding structure.

Therefore, a single-mode VCSEL with an index-guiding structure is urgently required to efficiently suppress multi-mode by operating in a single mode by controlling the refractive index difference or the radius of the aperture.

Patent Document 1: Korean Patent No. KR 10-0475846 (Vertical Cavity Surface-Emitting Laser, Registered on 2005.03.02)

The present disclosure forms a phase control layer on a second reflector layer, and forms a phase compensation layer in an aperture on the phase control layer, thereby forming a first region below the aperture and a second region around the aperture. The main purpose of the present disclosure is to provide a single-mode vertical cavity surface emitting laser (VCSEL) having an index-guiding structure by suppressing higher-order modes by utilizing the difference in effective refractive index between the first region and the second region based on the difference in oscillation threshold gain between the first region and the second region.

According to an embodiment of the present invention, there is provided a semiconductor substrate formed of a semiconductor material; a first reflector layer formed on the semiconductor substrate and doped with a first conductive impurity; an active layer formed on the first reflector layer and generating light; a second reflector layer formed on the active layer and doped with a second conductive impurity; a phase control layer formed on the second reflector layer and controlling a phase of light reflected by the second reflector layer to control an optical gain and an effective refractive index of a transverse mode of the light; The present invention provides a vertical cavity surface emitting laser, characterized by including: a phase compensation layer formed at the center of the phase control layer to form an aperture and to control the phase of light reflected from the phase control layer to control the optical gain and effective refractive index of the transverse mode; a current blocking layer formed on the outer side inside the second reflector layer; an upper electrode formed on the phase control layer and positioned around the aperture; and a lower electrode formed on a lower surface of the semiconductor substrate.

As described above, according to the present embodiment, a vertical cavity surface-emitting laser is provided that suppresses higher-order modes by utilizing the effective refractive index difference between the first region and the second region based on the difference in oscillation threshold gain between the first region under the phase compensation layer and the second region around it, thereby enabling the production of a single-mode laser having a refractive index difference waveguide structure with excellent mode stability.

In addition, according to the present embodiment, a vertical cavity surface-emitting laser having a reduced serial resistance of the laser is provided because the aperture radius of the upper electrode is smaller than the radius of the current blocking region aperture, thereby reducing heat generation and increasing the maximum optical output.

Figure 1 is a vertical cross-sectional view of a conventional vertical cavity surface-emitting laser.
FIG. 2 is a vertical cross-sectional view of a vertical cavity surface-emitting laser according to one embodiment of the present invention.
FIG. 3 is a vertical cross-sectional view of a vertical cavity surface-emitting laser according to another embodiment of the present invention.
Figure 4 is a structural diagram of a cylindrical optical waveguide.
Figure 5 is a conceptual diagram of the threshold gain in a laser having an optical gain layer between two reflectors.
Figure 6 shows the maximum size of the opening according to the thickness of the phase control layer and the phase compensation layer according to one embodiment of the present invention. This is an example showing.

Hereinafter, embodiments of the present invention will be described in detail with reference to exemplary drawings. When adding reference numerals to components in each drawing, it should be noted that identical components are given the same numerals as much as possible even if they are shown in different drawings. In addition, when describing the present embodiments, if it is determined that a specific description of a related known configuration or function may obscure the gist of the present embodiments, the detailed description thereof will be omitted.

In addition, when describing components of the present embodiments, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only intended to distinguish the components from other components, and the nature, order, or sequence of the components are not limited by the terms. Throughout the specification, when a part is said to "include" or "have" a component, this does not mean that other components are excluded, unless otherwise specifically stated, but rather that other components may be further included. In addition, terms such as "part," "module," etc. described in the specification mean a unit that processes at least one function or operation, and this may be implemented by hardware, software, or a combination of hardware and software.

The detailed description set forth below, together with the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced.

The present invention discloses a single mode vertical cavity surface emitting laser (VCSEL). More specifically, a single mode vertical cavity surface emitting laser (VCSEL) having an index-guiding structure that suppresses higher-order modes by utilizing the difference in effective refractive index between a first region under a phase compensation layer and a second region under an outer portion of a phase control layer is provided.

Single-mode laser light refers to laser light having a single frequency and a single field distribution. Here, the single frequency is determined from the longitudinal mode of the light, and the single field distribution is determined from the transverse mode of the light. Since the distance between the two reflector layers is short, on the order of several ㎛, the free spectral range is wide, so generating a single frequency according to the longitudinal mode of the VCSEL is not a big problem. Therefore, the single-mode implementation of the VCSEL mainly depends on the control of the transverse mode.

FIG. 2 is a vertical cross-sectional view of a vertical-cavity surface-emitting laser according to an embodiment of the present invention. In the embodiment of the present invention, a vertical-cavity surface-emitting laser (VCSEL) generates single-mode laser light. As illustrated in FIG. 2, the VCSEL is formed on a semiconductor substrate (substrate) 100, and includes all or part of a first reflector layer 108, an active layer 118, and a second reflector layer 126 related to light generation, a phase compensation layer 200 and a phase control layer 202 for controlling a phase of light, a current blocking layer 144 related to the flow of current, a lower electrode 142, and an upper electrode 140.

The first reflector layer (108) is a distributed Bragg reflector (DBR) and reflects the laser light toward the active layer (118). The first reflector layer (108) is formed by alternately stacking two Al _x Ga _{(1-x) As layers doped with a first conductive impurity and having different refractive indices. For example, an n-type impurity such as Si is used as the first conductive impurity. Additionally, as a material of the first reflector layer (108)} , if the laser wavelength is in the ultraviolet to infrared range, an AlGaInN or AlGaAsP semiconductor is used, if the laser wavelength is in the red to near-infrared range, an AlGaAsP semiconductor is used, and if the wavelength is in the 1 to 2 ㎛ range for optical communication, an InGaAsP semiconductor can be used.

When a layer (102) with a high refractive index and a layer (104) with a low refractive index are sequentially laminated by an epitaxy method, and this is called a pair (106), the first reflector layer (108) is formed by laminating such pairs (106) 20 to 40 times. The optical thickness of each of the layer (102) with a high refractive index and the layer (104) with a low refractive index of the first reflector layer (108) is formed to be λ/4, and therefore the optical thickness of the layer (106) is formed to be λ/2.

Here, λ represents the wavelength at which the VCSEL is designed to operate. And, the optical thickness is the product of the physical thickness of the optical element and the refractive index.

The difference in refractive index between the high refractive index layer (102) and the low refractive index layer (104) is formed by changing the composition of aluminum (Al) of Al _x Ga _(1-x) As. The reflectance of the reflector layer (108) formed in this way can be 99% or more. The difference in refractive index can also be controlled by changing the material composition for semiconductors of the AlGaInN, AlGaAsP, or InGaAsP series.

The active layer (118, or resonator) is a layer where light is generated, and is formed by sequentially stacking an n-type carrier confinement layer (110), an In _x Ga _(1-x) As quantum well layer (112), an Al _x Ga _(1-x) As or GaAs _x P _(1-x) barrier layer (114), and a p-type carrier confinement layer (116) using an epitaxy method. Here, the n-type or p-type carrier confinement layer is formed using an AlGaAs series material. In addition, each of the layers (110, 112, 114, 116) constituting the active layer (118) may be composed of a single layer or multiple layers of a heterostructure (not shown). The wavelength of the laser light can also be controlled by changing the material composition for semiconductors of the AlGaInN, AlGaAsP, or InGaAsP series.

The second reflector layer (126) is also a DBR and reflects the laser light toward the active layer (118). The second reflector layer (126) is formed by alternately stacking two Al _x Ga _(1-x) As layers with different refractive indices doped with second conductive impurities. For example, the second conductive impurities include Carbon (C), zinc (Zn), magnesium (Mg), etc., which are p-type impurities, can be used. Additionally, semiconductors of the AlGaInN, AlGaAsP, or InGaAsP series are used as the material of the second reflector layer (126), and the difference in refractive index can be controlled by changing the material composition thereof.

When a layer (120) with a high refractive index and a layer (122) with a low refractive index are sequentially laminated by an epitaxy method and are referred to as a pair (124), such pairs (124) are laminated 10 to 40 times to form a second reflector layer (126). The optical thickness of each of the layer (120) with a high refractive index and the layer (122) with a low refractive index of the second reflector layer (126) is formed to be λ/4, and therefore the optical thickness of the layer (124) is formed to be λ/2. The reflectivity of the reflector layer (126) formed in this way can be 95% or more.

The phase control layer (202) adjusts the light phase reflected from the second reflector layer (126) so that a specific optical characteristic in the second region becomes an optimal value. corresponding The optical gain and effective refractive index of the transverse mode are controlled. Here, the optical characteristics represent the characteristics of the laser and include optical output, optical efficiency, threshold current, etc. The phase control layer (202) is formed by sequentially stacking Al _x Ga _(1-x) As layers and GaAs layers grown by an epitaxy method. In addition, a semiconductor of the AlGaInN, AlGaAsP, or InGaAsP series can also be formed as the phase control layer (202) by controlling the material composition.

The Al _x Ga _(1-x) As layer in the phase control layer (202) is made of aluminum that implements an energy gap ( Eg) that is optically transparent to the wavelength of light emitted. The phase control layer (202) has a composition ratio (x). The upper surface of the phase control layer (202) should have a high doping concentration and an energy gap as small as possible to reduce the ohmic contact resistance between the upper electrode (140) and the phase control layer (202). To this end, the second conductive impurity is doped at 1×10 ¹⁹ /cm ³ or more. Accordingly, the phase control layer (202) may be formed of multiple layers.

In addition, in another embodiment of the present invention, the aperture under the phase compensation layer (200) and the phase control layer (202) under the upper electrode (140) may have different thicknesses.

The optical thickness of the phase control layer (202) is adjusted so that the optical gain and effective refractive index of the corresponding transverse mode are adjusted according to the adjustment of the light phase reflected from the second reflector layer (126). At this time, the optical thickness of the phase compensation layer (200) may be a preset value. In the second region, the threshold gain for oscillation becomes large, so that oscillation does not occur. Accordingly, carrier recombination also occurs weakly, so that the laser efficiency or maximum output of the first region is not lowered.

The phase compensation layer (200) adjusts the reflected light phase together with the phase control layer (202) so that a specific optical characteristic in the first region becomes an optimal value. Controls the optical gain and effective refractive index of the corresponding transverse mode. Here, the optical characteristics include optical output, optical efficiency, threshold current, etc.

The phase compensation layer (200) is formed on the phase control layer (202) and forms an opening through which laser light is emitted. As illustrated in FIG. 2, the lower portion of the opening forms a first region. The phase compensation layer (200) is formed of a dielectric material such as SiN _x or SiO ₂ and is formed such that the opening and a portion of the upper electrode (140) are connected to each other. The optical thickness of the phase compensation layer (200) is controlled so that the optical gain and effective refractive index of the corresponding transverse mode in the second region are controlled according to the control of the optical phase by combining the phase compensation layer (200) and the phase control layer (202). In addition, the optical thickness of the phase compensation layer (200) may be intentionally controlled to a value greater than the minimum value so as to satisfy a single-mode operation condition and increase the optical output.

In another embodiment of the present invention, the phase compensation layer (200) may be formed of a semiconductor such as AlGaAs, and the opening and the upper electrode (140) may be formed to be separated from each other.

The semiconductor substrate (100) is a semiconductor material layer doped with a first conductive type impurity. For example, it may be a semiconductor material layer selected from among GaAs, GaP, AlGaAs, GaN, InP, Sapphire, and GaN doped with an n-type impurity.

The lower electrode (142) is formed on the lower surface of the semiconductor substrate (100) and is formed by depositing one or more metals selected from Ni, AuGe, and Au.

The upper electrode (140) is positioned on the upper side of the phase control layer (202) and formed around the opening, and is formed by laminating one or more metal layers selected from AuZn, Au, AuBe, Cr, Ti, and Pt.

The current blocking region (144) is formed by injecting ions into a certain depth on both sides of the second reflector layer (126) as in the example of Fig. 2, or by oxidizing the oxidizable layer as in the example of Fig. 3. The current blocking region (144) restricts the path of carriers to the central portion, thereby restricting the current injected into the active layer (118) to the first region and the second region and preventing it from flowing to the third region.

The opening formed by the phase compensation layer (200) (a portion looking down on the first region from above) may have a shape such as a circle, a diamond, a polygon, etc., and this shape is determined when forming the upper electrode (140), and the diameter of the opening (or the length of the diagonal, A in the example of FIG. 2) may be determined according to the single mode implementation described later.

As described above, according to the present embodiment, a vertical resonance surface-emitting laser having a reduced series resistance of the laser is provided because the radius of the opening of the upper electrode is smaller than the radius of the opening of the current blocking region, thereby reducing heat generation and increasing the maximum optical output.

In the VCSEL according to the present embodiment, when current is injected through two electrodes (140, 142), electrons and holes that have passed through the first reflector layer (108) and the second reflector layer (126) recombine in the active layer (118), thereby generating light. The generated light initially diverges into all solid angles, but only light that satisfies the Bragg wavelength of each reflector layer (108, 126) remains after undergoing constructive interference. In addition, by making only the aperture corresponding to the first region phase-compensated and the peripheral region corresponding to the second region phase-mismatched, the threshold gain of the second region increases and the effective refractive index decreases. Therefore, the VCSEL according to the present embodiment operates in a single mode because the high-order mode oscillation is suppressed due to the suppression of the occurrence of laser oscillation in the second region.

In addition, by increasing the effective refractive index of the first region and decreasing the effective refractive index of the second region to create an effective refractive index difference, the VCSEL according to the present embodiment can operate in a single mode by controlling the effective refractive index difference and the thickness of the first region. The VCSEL of the index-guiding structure has excellent mode stability compared to the gain-guiding structure.

Suppressing the transverse mode of laser light utilizes the principle of a cylindrical light waveguide as illustrated in FIG. 4. In the diagram of FIG. 4, a is the radius of the core, and n ₁ and n ₂ are refractive indices or effective refractive indices of the core and cladding layers, respectively. As described above, by controlling the optical thickness of the phase control layer (202) and the phase compensation layer (200), the oscillation threshold gain of the first region is reduced and the effective refractive index is increased. By controlling the optical thickness of the phase control layer (202), the oscillation threshold gain of the second region is increased and the effective refractive index is reduced. The first region, where oscillation becomes easy due to the reduced oscillation threshold gain and the effective refractive index increases, becomes the core of the light waveguide. The second region, where oscillation becomes difficult and the effective refractive index decreases, becomes the clad layer of the light waveguide.

It is known that the condition for an optical waveguide to suppress the transverse mode and operate in a single mode is that the V-number must satisfy mathematical expression 1.

To reduce the V-number of laser light with wavelength λ, the radius a of the core is reduced as shown in mathematical expression 1, or The numerical aperture (NA) expressed as a must be reduced. Instead of the method of reducing a, which faces a physical limit, the present embodiment implements a single-mode VCSEL by reducing the numerical aperture. However, if the numerical aperture is reduced excessively, the operation of the optical waveguide may be weakened from the perspective of the laser light, making it difficult to maintain the mode stability of the laser device. Therefore, according to mathematical expression 1, the core radius and the numerical aperture can be appropriately compromised.

In this embodiment, the refractive indices of each layer constituting the first region and the second region are values that change depending on the position in the vertical direction. However, in the lasing mode that emits light, each has a single effective refractive index n _eff,1 and n _eff,2 , and the condition for implementing a single mode can be expressed as in mathematical expression 2.

When the refractive indices according to the vertical direction of the first and second regions are n ₁ (z) and n ₂ (z), they depend on the material composition of each layer constituting the vertical direction. Therefore, the effective refractive indices n _eff,1 and n _eff,2 can be expressed by mathematical expression 3.

Here, φ ₁ (z) and φ ₂ (z) are the electric field profiles of the vertical lasing modes in the first and second regions, respectively.

The electric field profiles φ ₁ (z) and φ ₂ (z) can be controlled by the refractive indices and optical thicknesses of the phase control layer (202) and the phase compensation layer (200). In addition, the resonator characteristics including the threshold gain are determined according to the electric field profiles φ ₁ (z) and φ ₂ (z). Therefore, by controlling the combination of the optical thickness and refractive indices of the phase control layer (202) and the phase compensation layer (200), not only the effective refractive indices of the first region and the second region but also the characteristics of the resonator, i.e., the characteristics of the laser, can be controlled.

When the distance between two reflector mirrors having reflectances R ₁ and R ₂ as shown in Fig. 5, i.e. the resonator length, is L, the oscillation threshold gain is expressed by mathematical expression 4.

As the number of DBR pairs increases and the refractive index difference increases and constructive interference occurs in the phase control layer (202) and the phase compensation layer (200), the reflectivity of the DBR increases. Therefore, the reflectivity can be controlled. When the reflectivity increases and the oscillation threshold gain decreases, light is concentrated in the active layer (118) with the highest refractive index and optical gain, i.e., the resonant cavity. Accordingly, when the electric field profile increases in the active layer (118) with the high refractive index, the effective refractive index also increases according to Equation 3. That is, the effective refractive index can be controlled by controlling the oscillation threshold gain for each region. Therefore, as shown in Equation 2, it becomes possible to satisfy the condition of the V-number for implementing a single mode by controlling the effective refractive indices of the first region and the second region. In addition, since n _eff,1 must be greater than n _eff,2 in order for the numerical aperture to be positive, the lasing threshold gain g _th,1 of the first region is adjusted to be smaller than the lasing threshold gain g _th,2 of the second region. Accordingly, laser lasing occurs only in the first region, and the effective refractive index of the first region becomes higher than that of the second region, thereby creating an optical waveguide structure.

Referring to the example of Fig. 2, the refractive indices n ₁ (z) and n ₂ (z) in the vertical direction are the same except for the phase control layer (202) and the phase compensation layer (200). Therefore, g _th,1 and φ ₁ (z) can be changed by changing the optical thickness of the two layers of the phase control layer (202) and the phase compensation layer (200). In addition, g _th,2 can be changed by changing the optical thickness of the phase control layer (202). and φ ₂ (z) can be changed. Consequently, by changing the optical thicknesses of the two layers, i.e., the phase control layer (202) and the phase compensation layer (200), the effective refractive indices n _eff,1 and n _eff,2 can be changed.

Meanwhile, the description of the derivation process of mathematical expressions 1 and 4 is beyond the scope of the present disclosure, so further detailed description is omitted.

Below, an example of the influence according to the optical thickness of two layers, the phase control layer (202) and the phase compensation layer (200), is described.

Figure 6 shows the maximum size of the opening according to the thickness of the phase control layer and the phase compensation layer according to one embodiment of the present invention. This is an example showing.

The diagram of FIG. 6 shows the change in the maximum size (A _max ) of the aperture (A) according to the optical thickness of the phase control layer (202) and the phase compensation layer (200) for laser light having a wavelength λ of 850 nm. Here, AlGaAs can be used as the phase control layer (202), and SiN _x can be used as the phase compensation layer (200). The aperture (A) is formed in a circular shape, and its maximum size is a value satisfying mathematical expression 2. As the thickness of the phase control layer (202) increases, the maximum size (A _max ) of the aperture (A) increases, and the difference in oscillation threshold gain between the second region and the first region (Δg _{th =} g _{th,2 -} g _th,1 ) decreases. This trend is repeated periodically based on the thickness of the phase control layer (202) of a constant size.

As shown in mathematical expression 2, the A _max value is related to the difference between effective refractive indices, and the difference in effective refractive indices can be easily controlled by the thickness of the phase control layer (202), and the difference in the oscillation threshold gain can also be easily controlled by the thickness of the phase control layer (202). The thickness of the phase control layer (202) is very useful as a variable that determines the condition of a single mode, and the same applies to the phase compensation layer (200). Therefore, in determining the condition of a single mode, adjusting the effective refractive indices and the oscillation threshold gain of the first and second regions by utilizing the change in these two layers can be a simple yet powerful tool.

The phase control layer (202) is composed of a single layer or multiple layers, but can usually be composed of a single layer. The phase of the laser light formed in the resonator can be changed depending on the size of the optical thickness (physical thickness × material refractive index) of the phase control layer (202). For example, in a waveguide composed of a GaAs/AlGaAs epilayer, an AlGaAs layer or a GaAs layer can be used as the phase control layer (202) depending on the oscillation wavelength.

When the size of the aperture (A) is implemented as 4 to 15 ㎛, the upper and lower limits of the aperture diameter (A _max ) can be set based on the following grounds. The lower limit of the diameter depends on the minimum size of the VCSEL that ensures reliability under commercial operating conditions. Meanwhile, the upper limit of the diameter is set in consideration of maintaining the VCSEL characteristics of the index-guiding structure. That is, when the size of the aperture becomes excessively large, the difference between the effective refractive index n _eff,1 of the aperture (A) and the effective refractive index n _eff,2 of the second region decreases, so that the operation of the index-guiding structure is weakened from the perspective of laser light. As described above, such a laser device may have difficulty in maintaining mode stability.

When the radius of the first region is secured to the maximum size, the VCSEL has the advantage of lowering the junction temperature due to the decrease in series resistance and increasing the light output. In addition, since the reliability and process margin are increased, it has the effect of increasing the productivity of the product.

Meanwhile, with respect to the maximum radius of the first region capable of single-mode operation according to mathematical expression 1, the radius of the first region may be set to be larger than the maximum radius by a predetermined ratio. Even if the radius of the first region is slightly larger than the maximum radius, the VCSEL according to the present embodiment can increase luminous efficiency by minimizing the ratio of laser light that is blocked by the upper electrode (140) and cannot be emitted while operating in a single mode. Since a number of variables must be comprehensively considered, it may be simpler and more accurate to determine the predetermined ratio using experiments.

The above description is merely an illustrative description of the technical idea of the present embodiment, and those with ordinary skill in the art to which the present embodiment belongs may make various modifications and variations without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of the present embodiment, but to explain it, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The protection scope of the present embodiment should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present embodiment.

100: Semiconductor substrate
108: 1st reflector layer
118: Active layer (or resonator)
126: Second reflector layer
140: Upper electrode
142: Lower electrode
144: Current blocking area
200: Phase compensation layer
202: Phase control layer

Claims (14)

A semiconductor substrate formed of a semiconductor material;
A first reflector layer formed on the semiconductor substrate and doped with a first conductive impurity;
An active layer formed on the first reflector layer and generating light;
A second reflector layer formed on the above active layer and doped with a second conductive impurity;
A phase control layer formed on the second reflector layer to control the phase of light reflected from the second reflector layer, thereby controlling the optical gain and effective refractive index of the transverse mode of the light;
A phase compensation layer formed at the center of the phase control layer to form an aperture and adjust the phase of light reflected from the phase control layer to adjust the optical gain and effective refractive index of the transverse mode;
A current blocking layer formed on the outer side of the inside of the second reflector layer;
An upper electrode positioned around the opening and formed on the phase control layer; and
A lower electrode formed on the lower surface of the semiconductor substrate
Including,
For the common region including the first reflector layer, the active layer, the second reflector layer and the phase control layer,
A first region including the above phase compensation layer and a common region below the above phase compensation layer;
A third region in which the current-blocking region is a common region that blocks current; and
A second area, which is a common area located between the first area and the third area
A vertical cavity surface emitting laser, characterized by including a. delete In the first paragraph,
A vertical cavity surface-emitting laser characterized in that a single mode is implemented by utilizing the difference between the effective refractive index of the first region and the effective refractive index of the second region. In the third paragraph,
A vertical-cavity surface-emitting laser characterized in that the single mode is implemented by making the effective refractive index of the first region greater than the effective refractive index of the second region, and making the difference between the effective refractive index of the first region and the effective refractive index of the second region close. In the first paragraph,
A vertical-cavity surface-emitting laser characterized in that the threshold gain of the first region is determined by controlling the optical thickness of the phase control layer and the phase compensation layer, and the effective refractive index of the first region is determined using the threshold gain. In the first paragraph,
A vertical cavity surface-emitting laser characterized in that the oscillation threshold gain of the second region is determined by controlling the optical thickness of the phase control layer, and the effective refractive index of the second region is determined using the oscillation threshold gain. In the first paragraph,
A vertical cavity surface-emitting laser, characterized in that the phase control layer is configured by sequentially stacking an Al _x Ga _{(1-x) As layer formed by growing Al x Ga (1-x) As by} an epitaxy method, and a GaAs layer formed by growing GaAs. In Article 7,
The Al _x Ga _(1-x) As layer in the above phase control layer is made of aluminum that implements an energy gap greater than or equal to the optically transparent energy gap for the light emission wavelength. A vertical cavity surface-emitting laser characterized by having a composition ratio (x). In the first paragraph,
A vertical cavity surface-emitting laser, characterized in that the upper surface of the phase control layer in contact with the upper electrode is doped with 1×10 ¹⁹ /cm ³ or more of the second conductive type impurities. In the first paragraph,
A vertical-cavity surface-emitting laser, characterized in that the phase control layer is formed with an optical thickness such that the optical gain and effective refractive index of the transverse mode in the second region are controlled by controlling the phase of light reflected from the phase control layer in a situation where the optical thickness of the phase compensation layer is preset. In the first paragraph,
A vertical cavity surface-emitting laser, characterized in that the thickness and composition of the phase control layer under the opening and the phase control layer under the upper electrode are respectively set. In the first paragraph,
A vertical cavity surface-emitting laser, characterized in that the phase compensation layer is formed of a dielectric material or a semiconductor material. In the first paragraph,
The sum of the above phase compensation layer and the above phase control layer is A vertical cavity surface-emitting laser characterized in that the optical thickness is formed such that the optical gain and effective refractive index of the transverse mode in the first region are controlled according to the control of the phase of the light. In the third paragraph,
A vertical cavity surface-emitting laser, characterized in that the maximum radius is calculated to satisfy a single mode condition set using the wavelength of the light, the effective refractive index of the first region, and the effective refractive index of the second region, and the radius of the first region is set to be larger than the maximum radius by a preset ratio.

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