Vertical cavity surface emitting laser and method of forming the same

Abstract

The application provides a vertical cavity surface emitting laser and a forming method thereof. The vertical cavity surface emitting laser comprises a substrate, a first mirror, an active layer, an oxidation layer, an aperture, a second mirror, a high-contrast grating and a passivation layer. The first mirror is located on the substrate. The active layer is located on the first mirror. The oxidation layer is located on the active layer. The aperture is located on the active layer and surrounded by the oxidation layer. The second mirror is located on the aperture and the oxidation layer. The high-contrast grating is located on the second mirror and comprises a first grating part and a second grating part, and the first grating part and the second grating part are separated from each other by an air gap. The passivation layer is located on the high-contrast grating. The first thickness of the passivation layer on the top surface of the first grating part is greater than the second thickness of the passivation layer on the first sidewall of the first grating part.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a vertical-cavity surface-emitting laser (VCSEL), and particularly to a high-contrast grating vertical-cavity surface-emitting laser (HCG VCSEL) and a method of forming the same. BACKGROUND

[0002] A vertical-cavity surface-emitting laser is a semiconductor laser diode that emits a laser beam in a direction perpendicular to its surface. The vertical-cavity surface-emitting laser can be tested during the production process. The vertical-cavity surface-emitting laser is widely used in various fields, such as fiber-optic communication and biometric identification.

[0003] A high-contrast grating can be used to partially or completely replace a distributed Bragg reflector (DBR) in a vertical-cavity surface-emitting laser. The high-contrast grating vertical-cavity surface-emitting laser can be thinner, lighter, and can reduce manufacturing costs. A passivation layer on the high-contrast grating in the high-contrast grating vertical-cavity surface-emitting laser device is necessary to protect the underlying structure and is crucial to the performance of the high-contrast grating vertical-cavity surface-emitting laser.

[0004] Although the existing vertical-cavity surface-emitting laser is sufficient for the original purpose, it is not satisfactory in all aspects and needs to be improved. SUMMARY

[0005] Embodiments of the present application provide a vertical-cavity surface-emitting laser, comprising: a substrate, a first mirror, an active layer, an oxidation layer, an aperture, a second mirror, a high-contrast grating, and a passivation layer. The first mirror is located on the substrate. The active layer is located on the first mirror. The oxidation layer is located on the active layer. The aperture is located on the active layer, and the aperture is surrounded by the oxidation layer. The second mirror is located on the aperture and the oxidation layer. The high-contrast grating is located on the second mirror, and the high-contrast grating comprises a first grating part and a second grating part, and the first grating part and the second grating part are separated from each other by an air gap. The passivation layer is located on the high-contrast grating, and a first thickness of the passivation layer on a top surface of the first grating part is greater than a second thickness of the passivation layer on a first sidewall of the first grating part.

[0006] Embodiments of the present disclosure also provide a vertical cavity surface emitting laser, comprising: a substrate. A first distributed Bragg reflector is on the substrate. A first active layer is on the first distributed Bragg reflector. A first oxide layer is on the active layer. An aperture is on the active layer, the aperture being surrounded by the first oxide layer. A second distributed Bragg reflector is on the aperture and the first oxide layer. A high-contrast grating is on the second distributed Bragg reflector, the high-contrast grating comprising grating elements that protrude

[0007] a second oxide layer on the second distributed Bragg reflector; and a passivation layer on the grating elements and the second oxide layer, the passivation layer having a first thickness on top surfaces of the grating elements that is greater than a second thickness of the passivation layer on the second oxide layer between two adjacent grating elements.

[0008] Embodiments of the present disclosure also provide a method of forming a vertical cavity surface emitting laser, comprising: providing a semiconductor structure, the semiconductor structure comprising a substrate, a first mirror on the substrate, an active layer on the first mirror, a first oxide layer on the active layer, an aperture on the active layer, the aperture being surrounded by the first oxide layer, and a second mirror on the aperture and the first oxide layer. The method also comprises forming a high-contrast grating on the second mirror of the semiconductor structure, the high-contrast grating comprising grating elements that are spaced apart from each other. The method also comprises forming a passivation layer on the grating elements, the passivation layer having a first thickness on top surfaces of the grating elements that is greater than a second thickness of the passivation layer on sidewalls of the grating elements. BRIEF DESCRIPTION OF DRAWINGS

[0009] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. It should be noted that various features are not drawn to scale and are only intended to illustrate examples. In fact, the dimensions of the devices can be enlarged or reduced to clearly show the technical features of the embodiments of the present disclosure.

[0010] Figures 1A-1H 、 Figures 1I-1 、 Figures 1J are cross-sectional views of stages of forming a vertical cavity surface emitting laser according to some embodiments.

[0011] Figures 1I-2 and Figures 1I-3 are enlarged cross-sectional views of a vertical cavity surface emitting laser according to some embodiments.

[0012] Figure 2 is an enlarged cross-sectional view of a modified vertical cavity surface emitting laser according to some embodiments.

[0013] Figure 3A and Figure 3B-1 are cross-sectional views of alternative vertical cavity surface emitting lasers according to some embodiments.

[0014] Figure 3B-2 is an enlarged cross-sectional view of an optional vertical cavity surface emitting laser according to some embodiments.

[0015] Figure 4 is a cross-sectional view of an optional vertical cavity surface emitting laser according to some embodiments.

[0016] Description of reference numerals:

[0017] 10a, 10b, 10c, 10d: Vertical Cavity Surface Emitting Lasers

[0018] 100:Substrate

[0019] 102: First Mirror

[0020] 104: Active layer

[0021] 106: Oxide layer

[0022] 108: Pores

[0023] 109: Second Mirror

[0024] 110: semiconductor layer

[0025] 112: semiconductor layer

[0026] 114: Oxide layer

[0027] 115: film layer

[0028] 116: film layer

[0029] 118: Contact metal

[0030] 120: High contrast grating

[0031] 120a: Grating parts

[0032] 120a': lower part

[0033] 120a”: upper part

[0034] 122: passivation layer

[0035] 122a: First sublayer

[0036] 122b: Second sublayer

[0037] 122P: protruding part

[0038] 124:Metal layer

[0039] 126: Opening

[0040] 128: Opening

[0041] 400: semiconductor layer

[0042] 402: first insulating layer

[0043] 404: Groove

[0044] 406: second insulating layer

[0045] 407:Isolated Area

[0046] 408: third insulating layer

[0047] 410: fourth insulating layer

[0048] 412: fifth insulating layer

[0049] G1: Air gap

[0050] T1, T2, T3: thickness

[0051] S1: Spacing

[0052] H1,H2:Height DETAILED DESCRIPTION

[0053] The following disclosure provides many different embodiments or examples for implementing the different features of the present invention. The following disclosure describes specific examples of various components and their arrangements to simplify the description. Of course, these specific examples are not intended to be limiting. For example, if an embodiment of the present invention describes a first characteristic component formed on or above a second characteristic component, it means that it may include an embodiment in which the first characteristic component and the second characteristic component are in direct contact, and may also include an embodiment in which an additional characteristic component is formed between the first characteristic component and the second characteristic component, so that the first characteristic component and the second characteristic component may not be in direct contact. In addition, repeated numbers or marks may be used in different embodiments. These repetitions are only for the purpose of simply and clearly describing the embodiments of the present invention and do not represent a specific relationship between the different embodiments and / or structures discussed.

[0054] In addition, spatially relative terms may be used, such as "below," "beneath," "lower," "above," "upper," and similar terms. These spatially relative terms are intended to facilitate describing the relationship between one device or feature and another device or feature in the drawings. These spatially relative terms include different orientations of the device in use or operation, as well as the orientations depicted in the drawings. When the device is rotated 90 degrees or in other orientations, the spatially relative adjectives used therein will also be interpreted based on the rotated orientation.

[0055] Herein, the terms "about," "approximately," and "substantially" generally mean within 20%, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5% of a given value or range. It should be noted that the quantities provided in the specification are approximate quantities, that is, even if "about," "approximately," or "substantially" is not specifically stated, the meaning of "about," "approximately," or "substantially" may still be implied.

[0056] Although the steps in some embodiments are described as being performed in a specific order, these steps may be performed in any other logical order. In different embodiments, some of the steps described may be replaced or omitted, and other operations may be performed before, during, and / or after the steps described in the embodiments of the present invention. The semiconductor structures of the embodiments of the present invention may include additional features. In different embodiments, some features may be replaced or omitted.

[0057] Embodiments of the present invention provide a high-contrast grating vertical-cavity surface-emitting laser (VCSEL). A thicker passivation layer is formed on the top surface of the grating components, rather than on the sidewalls and between the grating components. This balances the performance and reliability of the high-contrast grating VCSEL. Furthermore, an air gap is formed between the passivation layers on the sidewalls of adjacent grating components.

[0058] According to some embodiments, Figures 1A-1H 、 Figures 1I-1 and Figures 1J Cross-sectional views are shown at various stages of forming a vertical cavity surface emitting laser 10a.

[0059] According to some embodiments, Figure 1A As shown, a substrate 100 is provided. The substrate 100 may be a semiconductor substrate. For example, the substrate 100 may include a III-V semiconductor, such as GaAs, GaN, AlGaN, AlN, AlGaAs, InP, InAlAs, InGaAs, or combinations thereof. In some embodiments, the substrate 100 includes GaAs.

[0060] According to some embodiments, Figure 1AAs shown, a first mirror 102 is formed on a substrate 100. In some embodiments, the first mirror 102 includes a first semiconductor layer and a second semiconductor layer. The first mirror 102 includes alternating stacks of first and second semiconductor layers on the substrate 100. The first and second semiconductor layers are used in pairs. The first and second semiconductor layers may include III-V semiconductors, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or combinations thereof. The first and second semiconductor layers may be made of different materials with different refractive indices. The first and second semiconductor layers may have a first conductivity type. In some embodiments, the first conductivity type is N-type. The first mirror 104a may be referred to as a first conductivity type distributed Bragg reflector. The thickness of each of the first and second semiconductor layers depends on the central wavelength of the laser light generated in the vertical cavity surface emitting laser 10a. The first and second semiconductor layers may be formed using a low pressure chemical vapor deposition (LPCVD) process, an epitaxial growth process, other suitable processes, or a combination thereof. The epitaxial growth process may include molecular-beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), or vapor phase epitaxy (VPE). The total number of pairs of the first semiconductor layer and the second semiconductor layer is not limited thereto and depends on design requirements.

[0061] Then, according to some embodiments, as Figure 1A As shown in FIG, an active layer 104 is formed above the first mirror 102. The active layer 104 may include a plurality of quantum wells and quantum well barriers. The quantum wells and quantum well barriers may include III-V semiconductors, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or combinations thereof. The quantum wells and quantum well barriers may be made of different materials, and the quantum well barriers may have a larger band gap than the quantum wells. The active layer 104 can generate the optical power of the vertical cavity surface emitting laser 10a. The active layer 104, including the quantum wells and quantum well barriers, may be formed using a low-pressure chemical vapor deposition process, an epitaxial growth process, other suitable processes, or a combination thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy. The active layer 104 can separate the underlying first mirror 102 from the subsequently formed second mirror.

[0062] Then, according to some embodiments, as Figure 1AAs shown in FIG, a semiconductor layer 400 is formed on the active layer 104. The semiconductor layer 400 may include a Group III-V semiconductor, such as GaAs, AlGaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or a combination thereof. In some embodiments, the semiconductor layer 400 includes AlGaAs. The semiconductor layer 400 may include a Group III-V semiconductor having a gradient refractive index. The semiconductor layer 400 may be formed using a low-pressure chemical vapor deposition process, an epitaxial growth process, other suitable processes, or a combination thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy.

[0063] Then, according to some embodiments, as Figure 1A As shown in FIG, a second mirror 109 is formed on the active layer 104. The second mirror 109 may include a third semiconductor layer and a fourth semiconductor layer, alternately stacked on the active layer 104. The third and fourth semiconductor layers may include Group III-V semiconductors, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or combinations thereof. The third and fourth semiconductor layers may be made of different materials with different refractive indices. In some embodiments, the third and fourth semiconductor layers have the second conductivity type. In some embodiments, the second conductivity type is P-type. The second mirror 109 may be referred to as a second conductivity type distributed Bragg reflector. Light generated by the active layer 104 may be reflected by the first mirror 102 and the second mirror 109. Light may resonate between the first mirror 102 and the second mirror 109. The process used to form the second mirror 109 may be similar or identical to the process used to form the first mirror 102 described above and will not be repeated here for the sake of brevity. The number of third and fourth semiconductor layers is not limited and depends on design requirements. The second mirror 109 may be thinner than the first mirror 102 .

[0064] Then, according to some embodiments, as Figure 1A As shown in FIG, a semiconductor layer 110 is formed on the second mirror 109. The semiconductor layer 110 may include a Group III-V semiconductor, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or a combination thereof. The semiconductor layer 110 may be formed using a low-pressure chemical vapor deposition process, an epitaxial growth process, other suitable processes, or a combination thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy.

[0065] Then, according to some embodiments, as Figure 1AAs shown in FIG, semiconductor layer 112 is formed on semiconductor layer 110. Semiconductor layer 112 may include a Group III-V semiconductor, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or combinations thereof. In some embodiments, semiconductor layer 112 is made of AlGaAs with a gradient Al composition. Semiconductor layer 112 may be formed using a low-pressure chemical vapor deposition process, an epitaxial growth process, other suitable processes, or combinations thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy.

[0066] Then, according to some embodiments, as Figure 1A As shown in FIG, a film layer 115 is formed on semiconductor layer 112. Film layer 115 may include a Group III-V semiconductor, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, a low-refractive-index metal oxide such as ITO, a dielectric film such as SiO2, SiON, SiN, a polymer material, or a combination thereof. Film layer 115 may be formed using a low-pressure chemical vapor deposition process, an epitaxial growth process, other suitable processes, or a combination thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy.

[0067] Then, according to some embodiments, as Figure 1A As shown in FIG, a film layer 116 is formed on film layer 115. Film layer 116 may include a III-V semiconductor or metal, such as GaAs, AlGaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, Al, or a combination thereof. Film layer 116 may be formed by a low-pressure chemical vapor deposition process, an epitaxial growth process, electron beam evaporation, resistance heating evaporation, electroplating, sputtering, physical vapor deposition (PVD), atomic layer deposition (ALD), other available processes, or a combination thereof. The epitaxial growth process may include molecular beam epitaxy, metal organic chemical vapor deposition, or vapor phase epitaxy. In some embodiments, the refractive index of the material of film layer 116 is greater than the refractive index of the material of film layer 115.

[0068] Then, according to some embodiments, as Figure 1AAs shown in FIG, contact metal 118 is formed on film layer 116. In some embodiments, an ohmic contact is formed between contact metal 118 and film layer 116. Contact metal 118 may include Pt, Ti, Au, Al, Pd, Cu, W, other suitable metals, alloys thereof, or combinations thereof. Contact metal 118 may be formed on film layer 116 by electron beam evaporation, resistance heating evaporation, electroplating, sputtering, physical vapor deposition, chemical vapor deposition, atomic layer deposition, other suitable methods, or combinations thereof. In some embodiments, the contact metal material is formed by electron beam evaporation. Subsequently, the electrode material is patterned by photolithography and etching processes to form contact metal 118.

[0069] Then, according to some embodiments, as Figure 1B As shown in FIG, a first insulating layer 402 is conformally formed on the contact metal 118 and the film layer 116. Figure 1B As shown in FIG. 4 , the first insulating layer 402 is located above the second mirror 109. The first insulating layer 402 can be made of silicon nitride, aluminum oxide, other suitable insulating materials, or a combination thereof. In some embodiments, the first insulating layer 402 includes silicon nitride. The first insulating layer 402 can be formed by a deposition process. The deposition process can include a chemical vapor deposition process (e.g., low pressure chemical vapor deposition, plasma assisted chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, or flowable chemical vapor deposition), an atomic layer deposition process, other available methods, or a combination thereof. In some embodiments, the thickness of the first insulating layer 402 is about to about within the range.

[0070] Then, according to some embodiments, as Figure 1CAs shown in FIG, a trench 404 is formed through the first insulating layer 402, the film layer 116, the film layer 115, the semiconductor layer 112, the semiconductor layer 110, the second mirror 109, the semiconductor layer 400, the active layer 104, and stops at the first mirror 102. A patterning process can be performed to form the trench 404. The patterning process can include a photolithography process and an etching process. Examples of photolithography processes include photoresist coating, soft baking, mask alignment, exposure, post-exposure baking, photoresist development, cleaning, and drying. The etching process can be a dry etching process or a wet etching process. In some embodiments, the etching process is reactive ion etching (RIE) using inductively coupled plasma (ICP) as an etchant. In some embodiments, the trench 404 passes through the first insulating layer 402 and reaches the top of the first mirror 102. In some embodiments, the trench 404 exposes the sidewalls of the first insulating layer 402, the film layer 116, the film layer 115, the semiconductor layer 112, the semiconductor layer 110, the second mirror 109, the semiconductor layer 400, the active layer 104, and the first mirror 102. In some embodiments, the first mirror 102 is exposed from the trench 404. In some embodiments, the bottom surface of the trench 404 is below the bottom surface of the active layer 104. In some embodiments, the bottom surface of the trench 404 is within the first mirror 102.

[0071] Then, if Figure 1D As shown in FIG. 1 , a portion of the oxidized semiconductor layer 400 is used to form an oxide layer 106 on the active layer 104. The semiconductor layer 400 may be an Al-doped layer with a high Al content. The Al content can affect the oxidation rate. Maintaining a stable oxidation rate is preferred. In some embodiments, the active layer 104 comprises AlGaAs. The oxide layer 106 may comprise Al2O3. In some embodiments, the oxide layer 106 is formed using a furnace oxidation process.

[0072] like Figure 1D As shown, only a portion of the semiconductor layer 400 is oxidized. In some embodiments, the unoxidized portion of the semiconductor layer 400 can serve as the pore 108. The pore can comprise a III-V semiconductor, such as AlGaAs, GaAs, AlAs, GaN, AlGaN, AlN, InP, InAlAs, InGaAs, or a combination thereof. In some embodiments, the pore 108 is surrounded by the oxide layer 106. In some embodiments, the second mirror 109 is above the pore 108 and the oxide layer 106. The pore 108 can limit current flow from the contact metal 118 through the underlying active layer 104 and the first mirror 102.

[0073] Then, according to some embodiments, as Figure 1EAs shown in FIG, a second insulating layer 406 is conformally formed on the first insulating layer 402 and on the sidewalls and bottom surface of the trench 404. The second insulating layer 406 can be formed on the first insulating layer 402 and extend into the trench 404. The second insulating layer 406 can be made of silicon nitride, aluminum oxide, other suitable insulating materials, or a combination thereof. The second insulating layer 406 can be formed by a chemical vapor deposition process (such as low pressure chemical vapor deposition, plasma assisted chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, or flowable chemical vapor deposition), an atomic layer deposition process, other available methods, or a combination thereof. In some embodiments, the second insulating layer 406 and the first insulating layer 402 are made of the same material. Therefore, there may be no obvious interface between the second insulating layer 406 and the first insulating layer 402, and the boundary is drawn as a dotted line. In some embodiments, the thickness of the second insulating layer 406 is about to about within the range.

[0074] Then, according to some embodiments, as Figure 1F As shown in FIG, an isolation region 407 is formed using an implantation process. The isolation region 407 may penetrate the active layer 104 for wafer isolation. In some embodiments, the bottom surface of the isolation region 407 is lower than the bottom surface of the active layer 104. The isolation region 407 may surround the active region of the vertical cavity surface emitting laser 10a. In some embodiments, the isolation region 407 is doped with helium or boron.

[0075] Then, according to some embodiments, as Figure 1G As shown in FIG, a third insulating layer 408 is conformally formed on the second insulating layer 406 and on the sidewalls and bottom surface of the trench 404. The third insulating layer 408 can be formed on the second insulating layer 406 and extend into the trench 404. The third insulating layer 408 can be made of silicon nitride, aluminum oxide, other suitable insulating materials, or a combination thereof. The third insulating layer 408 can be formed by a chemical vapor deposition process (such as low pressure chemical vapor deposition, plasma assisted chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, or flowable chemical vapor deposition), an atomic layer deposition process, other available methods, or a combination thereof. In some embodiments, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402 are made of the same material. Therefore, there may be no obvious interface between them, and the boundary is drawn as a dotted line. In some embodiments, the thickness of the third insulating layer 408 is about to about within the range.

[0076] Next, the third insulating layer 408, the second insulating layer 406, the first insulating layer 402, the film layer 116, and the film layer 115 are patterned to form a high contrast grating 120 on the semiconductor layer 112 above the aperture 108. According to some embodiments, as Figure 1H As shown in FIG, a high contrast grating 120 may be formed in an active region surrounded by an isolation region 407. The high contrast grating 120 may include a plurality of grating elements 120a.

[0077] After patterning film layer 116 and film layer 115, film layer 115 may be exposed. Next, an oxidation process is performed to oxidize a portion of film layer 115 and form oxide layer 114 in the active region. Oxide layer 114 may be made of an insulator such as silicon oxide or aluminum oxide. In some embodiments, oxide layer 114 is located above semiconductor layer 112. In some embodiments, film layer 115 is located above semiconductor layer 112 and surrounds oxide layer 114.

[0078] In some embodiments, the oxide layer 114 is also patterned and forms the lower portion 120a' of the grating element 120a in the high-contrast grating 120. In some embodiments, the lower portion 120a' of the grating element 120a and the oxide layer 114 are integrally formed. The patterned film layer 116 can form the upper portion 120" of the grating element 120a in the high-contrast grating 120. In some embodiments, the refractive index of the material of the film layer 116 is greater than the refractive index of the material of the oxide layer 114.

[0079] Then, according to some embodiments, as Figures 1I-1 As shown in FIG, a fourth insulating layer 410 is conformally formed on the third insulating layer 408, on the sidewalls and bottom surface of the trench 404, and on the sidewalls and bottom surface of the air gap G1 between the grating parts 120a of the high contrast grating 120. The fourth insulating layer 410 can be formed on the third insulating layer 408 and extend into the trench 404 and the air gap G1. The fourth insulating layer 410 can be made of silicon nitride, aluminum oxide, other suitable insulating materials, or a combination thereof. The fourth insulating layer 410 can be formed by a chemical vapor deposition process (such as low pressure chemical vapor deposition, plasma assisted chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, or flowable chemical vapor deposition), an atomic layer deposition process, other available methods, or a combination thereof. In some embodiments, the fourth insulating layer 410, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402 are made of the same material. Therefore, there may be no obvious interface between them, and the boundary is drawn as a dotted line. In some embodiments, the thickness of the fourth insulating layer 410 is about to about The fourth insulating layer 410, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402, alone or in combination, may serve as the passivation layer 122. In some embodiments, the passivation layer 122 includes an insulating layer (e.g., silicon nitride, aluminum oxide, other suitable insulators, or combinations thereof).

[0080] Figures 1I-2 is an enlarged cross-sectional view of a vertical cavity surface emitting laser 10a according to some embodiments. Figures 1I-2 As shown, the high contrast grating 120 includes a plurality of grating elements 120a spaced apart from each other. In some embodiments, the passivation layer 122 on the sidewalls of adjacent grating elements 120a is spaced apart from each other. Figures 1I-2 As shown in FIG, the air gap G1 and the spacing S1 between adjacent grating elements 120a may be defined by the sidewalls of the adjacent grating elements 120a.

[0081] In some embodiments, as Figures 1I-2 As shown, a passivation layer 122 is formed on the high contrast grating 120. The passivation layer 122 may partially fill the air gap G1. In some embodiments, as shown in FIG. Figures 1I-2 As shown, the thickness T1 of the passivation layer 122 on the top surface of the grating feature 120 a is greater than the thickness T2 of the passivation layer 122 on the sidewalls of the grating feature 120 a .

[0082] In some embodiments, the ratio of thickness T1 to thickness T2 may be in the range of about 3 to about 100. In some embodiments, the ratio of thickness T1 to thickness T2 may be greater than 1 and less than or equal to 3 (1 <T1 / T2≤3)。在一些实施例中,厚度T1与厚度T2的比例可在约3至约5的范围内。如果厚度T1与厚度T2的比例太大,垂直腔面发射激光器10的功率可能衰减。如果厚度T1与厚度T2的比例太小,钝化可能不足,且可靠度可能变差。在一些实施例中,厚度T2与间距S1的比例可在约0.05至约0.5的范围内。如果厚度T2与间距S1的比例太大,邻近光栅零件120a的侧壁上的钝化层122可能合并。如果厚度T2与间距S1的比例太小,钝化可能不足,且可靠度可能变差。

[0083] In some embodiments, as Figures 1I-2As shown in FIG, the thickness T1 of the passivation layer 122 on the top surface of the grating element 120a is greater than the thickness T3 of the passivation layer 122 on the second mirror 109 between adjacent grating elements 120a. The ratio of the thickness T1 to the thickness T3 may be in the range of about 3 to about 100. In some embodiments, the ratio of the thickness T1 to the thickness T3 may be greater than 1 and less than or equal to 3 (1 <T1 / T2≤3)。在一些实施例中,厚度T1与厚度T3的比例可在约3至约5的范围内。在一些实施例中,厚度T2与厚度T3大致相等。

[0084] like Figures 1I-2 As shown in FIG. 1 , the grating component 120a may include a lower portion 120a′ and an upper portion 120″. The lower portion 120a′ and the upper portion 120″ may be formed of different materials. In some embodiments, the refractive index of the upper portion 120″ is greater than the refractive index of the lower portion 120a′. In some embodiments, the refractive index of the upper portion 120″ is greater than the refractive index of the passivation layer 122. In some embodiments, the upper portion 120″ includes a metal, a semiconductor (e.g., a III-V semiconductor), or a combination thereof. In some embodiments, the lower portion 120a′ includes an insulator (e.g., an oxide). In some embodiments, the lower portion 120a′ is formed by patterning the oxide layer 114. In some embodiments, as Figures 1I-3 As shown in FIG, the lower portion 120a' is formed by patterning the upper portion of the oxide layer 114, and thus the lower portion 120a' of the grating feature 120a protrudes from the lower portion of the oxide layer 114. In some embodiments, the bottom surface of the passivation layer 122 is lower than the interface between the lower portion 120a' and the upper portion 120".

[0085] Figures 1I-3 is an enlarged cross-sectional view of a vertical cavity surface emitting laser 10a according to some embodiments. Figures 1J As shown, the passivation layer 122 includes a first sublayer 122a and a second sublayer 122b on the first sublayer 122a. In some embodiments, the first sublayer 122a and the second sublayer 122b are made of different materials. The first sublayer 122a can be made of silicon nitride, and the second sublayer 122b can be made of aluminum oxide. The first sublayer 122a can be formed on the top surface of the grating component 120a, and the first sublayer 122a may not be formed on the sidewalls of the grating component 120a. The second sublayer 122b can be lined with the sidewalls of the grating component 120a, the sidewalls of the first sublayer 122a, and the top surface of the first sublayer 122a. The fourth insulating layer 410 can be made of aluminum oxide and can be referred to as the second sublayer 122b of the passivation layer 122. The third insulating layer 408 , the second insulating layer 406 , and the first insulating layer 402 are made of silicon nitride and may be referred to as the first sub-layer 122 a of the passivation layer 122 .

[0086] Next, an opening is formed through the passivation layer 122 on the contact metal 118. The contact metal 118 may be exposed through the opening. The opening may be formed in the passivation layer 122 by a photolithography process, an etching process (e.g., a wet etching process, a dry etching process, other suitable processes, or a combination thereof), other suitable processes, or a combination thereof.

[0087] Then, if Figure 2 As shown in FIG, a metal layer 124 is formed over the passivation layer 122, the high-contrast grating 120, and within the trench 404. In some embodiments, the metal layer 124 is in direct contact with the contact metal 118. The trench 404 may be filled with the metal layer 124. The metal layer 124 may include a conductive material such as Au, Ti, Al, Pd, Pt, Cu, W, other suitable metals, alloys thereof, or combinations thereof. The metal layer material may be formed by electroplating, electron beam evaporation, resistance heating evaporation, sputtering, physical vapor deposition, chemical vapor deposition, atomic layer deposition, other suitable methods, or combinations thereof. In some embodiments, the metal layer 124 is formed by electroplating. The metal layer material is then patterned using photolithography and etching processes to form an opening 126 in the grating component 120a. The opening 126 in the metal layer 124 may be directly above the aperture 108.

[0088] The thicker passivation layer 122 on the top surface of the grating element 120 a relative to the sidewalls of the grating element 120 a and between the grating elements 120 a can improve reliability and maintain performance.

[0089] Many variations and / or modifications may be made to the embodiments of the present invention. Figure 2 is an enlarged cross-sectional view of a vertical cavity surface emitting laser 10b according to some embodiments. Some processes or devices are the same or similar to those in the above embodiments, so these processes and devices are not repeated here. Different from the above embodiments, according to some other embodiments, such as Figure 2 As shown, a fifth insulating layer 412 is further formed on the fourth insulating layer 410 .

[0090] According to some embodiments, Figure 3AAs shown in FIG, a fifth insulating layer 412 is conformally formed on the fourth insulating layer 410. The fifth insulating layer 412 may also be formed on the sidewalls and bottom surface of the trench 404, as well as on the sidewalls and bottom surface of the air gap G1 between the grating elements 120a of the high-contrast grating 120. The fifth insulating layer 412 may be formed on the fourth insulating layer 410 and extend into the trench 404 and the air gap G1. The fifth insulating layer 412 may be made of silicon nitride, aluminum oxide, other suitable insulating materials, or combinations thereof. The fifth insulating layer 412 may be formed using a chemical vapor deposition process (e.g., low-pressure chemical vapor deposition, plasma-assisted chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, or flowable chemical vapor deposition), an atomic layer deposition process, other suitable methods, or combinations thereof.

[0091] In some embodiments, the fifth insulating layer 412 is made of a different material than the fourth insulating layer 410, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402. In some embodiments, the fifth insulating layer 412 is made of aluminum oxide, and the fourth insulating layer 410, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402 are made of silicon nitride. The fifth insulating layer 412 can be referred to as the second sub-layer 122b of the passivation layer 122. The fourth insulating layer 410, the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402 can be referred to as the first sub-layer 122a of the passivation layer 122. In some embodiments, the first sub-layer 122a is formed on the sidewalls and top surface of the grating component 120a. In some embodiments, the first sub-layer 122a lines the top surface and sidewalls of the grating component 120a.

[0092] A thicker passivation layer 122 is formed on the top surface of the grating element 120a relative to the sidewalls and between the grating elements 120a to improve reliability and maintain performance. A second sublayer 122b of the passivation layer 122 may also be formed on the top surface and sidewalls of the grating element 120a. The first sublayer 122a and the second sublayer 122b may be formed of different materials.

[0093] Many variations and / or modifications may be made to the embodiments of the present invention. Figure 3B-1 and Figure 3A is a cross-sectional view of a vertical cavity surface emitting laser 10c according to some embodiments. Some processes or devices are the same or similar to those in the above embodiments, so these processes and devices are not repeated here. Different from the above embodiments, according to some other embodiments, such as Figure 3A As shown in FIG. 4 , the third insulating layer 408 , the second insulating layer 406 and the first insulating layer 402 are removed before forming the high-contrast grating 120 .

[0094] According to some embodiments, Figure 3B-1As shown in FIG, an opening 128 is formed through the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402. The film layer 116 can be exposed through the opening 128. The opening 128 can be formed in the third insulating layer 408, the second insulating layer 406, and the first insulating layer 402 by a photolithography process, an etching process, other suitable processes, or a combination thereof.

[0095] Then, according to some embodiments, as Figure 3B-1 As shown in FIG, a high-contrast grating 120 is formed in the film layer 116 through the opening 128. Subsequently, an oxide layer 114 is formed in the film layer 115 below the high-contrast grating 120. The process for forming the high-contrast grating 120 and the oxide layer 114 may be similar to or the same as the process for forming the high-contrast grating 120 and the oxide layer 114 in the previous embodiment, and for the sake of brevity, it will not be repeated here.

[0096] Then, according to some embodiments, as Figure 3B-1 As shown in FIG. 1 , the fourth insulating layer 410 is formed on the sidewalls and bottom surface of the air gap G1 between the grating elements 120a of the high contrast grating 120. In some embodiments, the fourth insulating layer 410 directly contacts the top surface of the film layer 116 and the sidewalls of the grating elements 120a. In some embodiments, the fourth insulating layer 410 is formed by atomic layer deposition, and thus the fourth insulating layer 410 can be uniformly deposited on the small pitch S1 of the grating elements 120a (e.g., about 1 / 4 of the gap S1). to about , thereby improving the reliability of the vertical cavity surface emitting laser 10c.

[0097] In some embodiments, as Figure 3B-2 As shown in FIG, the passivation layer 122 formed on the grating element 120a is thinner than the passivation layer 122 in the previous embodiment. Therefore, the power of the vertical cavity surface emitting laser 10c can be enhanced and the performance can be improved.

[0098] According to some embodiments, Figure 3B-2 An enlarged cross-sectional view of a vertical cavity surface emitting laser 10c is shown. Figures 1I-2 As shown in FIG. 4 , the passivation layer 122 on the high contrast grating 120 only includes the fourth insulating layer 410. Therefore, the thickness of the passivation layer 122 on the top of the grating part 120a is greater than that of the fourth insulating layer 410. Figure 3B-2 In the embodiment shown in FIG. 1 , the passivation layer 122 is thin.

[0099] In some embodiments, as Figure 3B-2As shown in FIG, by adjusting the parameters of the deposition process (e.g., atomic layer deposition) for forming the fourth insulating layer 410, the thickness T1 of the passivation layer 122 on the upper surface of the grating component 120a is greater than the thickness T2 of the passivation layer 122 on the sidewall of the grating component 120a. In some embodiments, the ratio of the thickness T1 to the thickness T2 may be in the range of about 3 to about 100. In some embodiments, the ratio of the thickness T1 to the thickness T2 may be greater than 1 and less than or equal to 3 (1 <T1 / T2≤3)。在一些实施例中,厚度T2与间距S1的比例可在约0.05至约0.5的范围内。

[0100] In some embodiments, as Figure 3B-2 As shown in FIG, the thickness T1 of the passivation layer 122 on the top surface of the grating element 120a is greater than the thickness T3 of the passivation layer 122 on the second mirror 109 between adjacent grating elements 120a. The thickness T3 may also be the thickness of the passivation layer 122 on the oxide layer 114 between adjacent grating elements 120a. In some embodiments, the ratio of the thickness T1 to the thickness T3 may be greater than 1 and less than or equal to 3 (1 <T1 / T2≤3)。在一些实施例中,厚度T2与厚度T3大致相等。

[0101] In addition, if Figure 3B-2 As shown in FIG, due to the formation of the opening 128, a protruding portion 122P of the passivation layer 122 is formed. In some embodiments, the top surface of the protruding portion 122P is lower than the top surface of the passivation layer 122 directly above the contact metal 118. In some embodiments, the sidewalls of the protruding portion 122P are offset from the sidewalls of the high-contrast grating 120. Figure 4 As shown in FIG, the top surface of the protruding portion 122P is higher than the top surface of the passivation layer 122 on the high-contrast grating 120 by a height H1, and the top surface of the protruding portion 122P is lower than the top surface of the passivation layer 122 directly above the contact metal 118 by a height H2.

[0102] A thicker passivation layer 122 is provided on the top surface of the grating elements 120a relative to the sidewalls and spaces between the grating elements 120a, thereby improving reliability and maintaining performance. Etching back the passivation layer 122 on the grating elements 120a can enhance the power of the VCSEL 10c and improve performance.

[0103] Many variations and / or modifications may be made to the embodiments of the present invention. Figure 4 is a cross-sectional view of a vertical cavity surface emitting laser 10d according to some embodiments. Some processes or devices are the same or similar to those in the above embodiments, so these processes and devices are not repeated here. Different from the above embodiments, according to some other embodiments, such as ​As shown in FIG. 1 , the oxide layer 114 is not patterned, and the grating feature 120 a only includes the membrane layer 116 .

[0104] In some embodiments, the top surface of the oxide layer 114 is flush with the bottom surface of the grating component 120a. In some embodiments, the top surface of the oxide layer 114 is flush with the bottom surface of the passivation layer 122 formed in the air gap G1. In some embodiments, the oxide layer 114 has a substantially flat upper surface.

[0105] The grating elements 120a may comprise a single portion of the film layer 116. ...

[0106] As described above, embodiments of the present invention provide a vertical cavity surface emitting laser (VCSEL) and a method for forming the VCSEL. The passivation layer on the top surface of the grating component is thicker than the passivation layer on the sidewalls of the grating component and between the grating components, thereby improving reliability and maintaining performance.

[0107] It should be noted that although some benefits and effects are described in the above embodiments, not all embodiments need to achieve all benefits and effects.

[0108] The above text summarizes the characteristic components of many embodiments so that those skilled in the art can better understand the embodiments of the present invention from various aspects. Those skilled in the art should understand and can easily design or modify other processes and structures based on the embodiments of the present invention, and thereby achieve the same purpose and / or achieve the same advantages as the embodiments introduced herein. Those skilled in the art should also understand that these equivalent structures do not deviate from the spirit and scope of the invention of the embodiments of the present invention. Various changes, replacements or modifications can be made to the embodiments of the present invention without departing from the spirit and scope of the invention of the embodiments of the present invention, so the scope of protection of the present invention should be based on the scope of protection described in the claims. In addition, although the present invention has been disclosed as above with a plurality of preferred embodiments, it is not intended to limit the present invention, and not all advantages have been described in detail herein.

Claims

1. A vertical cavity surface emitting laser, characterized in that: include: a substrate; a first mirror, located on the substrate; an active layer located on the first mirror; an oxide layer located on the active layer; a pore located above the active layer, wherein the pore is surrounded by the oxide layer; a second mirror located above the aperture and the oxide layer; a high-contrast grating located on the second mirror, wherein the high-contrast grating comprises a first grating component and a second grating component, and an air gap is separated between the first grating component and the second grating component; and a passivation layer located on the high-contrast grating, wherein a first thickness of the passivation layer located on a top surface of the first grating component is greater than a second thickness of the passivation layer on a first sidewall of the first grating component, and a third thickness of the passivation layer on the second mirror between the first grating component and the second grating component is less than the first thickness.

2. The vertical cavity surface emitting laser according to claim 1, wherein: The air gap is partially filled with the passivation layer.

3. The vertical cavity surface emitting laser according to claim 1, wherein: An upper portion of the high-contrast grating includes a first material, and a lower portion of the high-contrast grating includes a second material different from the first material.

4. The vertical cavity surface emitting laser according to claim 3, characterized in that The first material includes a III-V compound semiconductor or a metal, and the second material includes an insulator.

5. The vertical cavity surface emitting laser according to claim 3, wherein: A first refractive index of the first material is greater than a second refractive index of the second material.

6. The vertical cavity surface emitting laser according to claim 3, wherein: A bottom surface of the passivation layer is lower than an interface between the first material and the second material.

7. The vertical cavity surface emitting laser according to claim 1, wherein: The passivation layer includes silicon nitride, aluminum oxide, or a combination thereof.

8. The vertical cavity surface emitting laser according to claim 1, wherein: The passivation layer includes a first sublayer on the high-contrast grating and a second sublayer on the first sublayer.

9. The vertical cavity surface emitting laser according to claim 8, characterized in that: The first sub-layer lines the top surface of the first grating component and the first sidewalls of the first grating component.

10. The vertical cavity surface emitting laser according to claim 8, characterized in that: The second sub-layer is lined with the first sidewall of the first grating component, a sidewall of the first sub-layer, and a top surface of the first sub-layer.

11. The vertical cavity surface emitting laser according to claim 8, characterized in that: The first sub-layer or the second sub-layer includes silicon nitride, and the other of the first sub-layer or the second sub-layer includes aluminum oxide.

12. A vertical cavity surface emitting laser, characterized in that: include: a substrate; a first distributed Bragg reflector, located on the substrate; an active layer located on the first distributed Bragg reflector; a first oxide layer located on the active layer; a pore located above the active layer, wherein the pore is surrounded by the first oxide layer; a second distributed Bragg reflector located above the aperture and the first oxide layer; a high-contrast grating located on the second distributed Bragg reflector, wherein the high-contrast grating comprises a plurality of grating features protruding from a second oxide layer located on the second distributed Bragg reflector; and a passivation layer located above the grating components and the second oxide layer, wherein a first thickness of the passivation layer on the top surface of the plurality of grating components is greater than a third thickness of the passivation layer on the second oxide layer between two adjacent grating components, and a second thickness of the passivation layer on the sidewalls of the plurality of grating components is less than the first thickness.

13. The vertical cavity surface emitting laser according to claim 12, wherein: The passivation layers on sidewalls of adjacent grating features are separated from each other.

14. The vertical cavity surface emitting laser according to claim 12, wherein: A lower portion of the plurality of grating components and the second oxide layer are formed integrally.

15. The vertical cavity surface emitting laser according to claim 12, wherein: An upper portion of the plurality of grating components includes a first material having a first refractive index, and the passivation layer includes a second material having a second refractive index lower than the first refractive index.

16. The vertical cavity surface emitting laser according to claim 15, characterized in that A bottom surface of the passivation layer is flush with a top surface of the second oxide layer.

17. A method for forming a vertical cavity surface emitting laser, characterized in that: include: A semiconductor structure is provided, wherein the semiconductor structure includes a substrate, a first mirror on the substrate, an active layer on the first mirror, a first oxide layer on the active layer, a hole on the active layer and surrounded by the first oxide layer, and a second mirror on the hole and the first oxide layer; forming a high-contrast grating on the second mirror of the semiconductor structure, wherein the high-contrast grating comprises a plurality of grating elements spaced apart from each other; and forming a passivation layer on the plurality of grating components, wherein a first thickness of the passivation layer on the top surfaces of the plurality of grating components is greater than a second thickness of the passivation layer on the sidewalls of the plurality of grating components, and the first thickness of the passivation layer on the top surfaces of the plurality of grating components is greater than a third thickness of the passivation layer on the second mirror between two adjacent grating components.

18. The method for forming a vertical cavity surface emitting laser according to claim 17, wherein: Also includes: forming an insulating layer on the pores; The insulating layer on the pores is removed before forming the passivation layer.

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