CN114336282B - GaN-based vertical cavity surface emitting laser with conductive DBR structure and manufacturing method thereof - Google Patents

Abstract

The application discloses a GaN-based Vertical Cavity Surface Emitting Laser (VCSEL) with a conductive DBR structure and a preparation method thereof. The VCSEL comprises a first semiconductor layer, a second semiconductor layer and an active layer arranged between the first semiconductor layer and the second semiconductor layer, wherein the first semiconductor layer and the second semiconductor layer are respectively connected with a first DBR structure and a second DBR structure, the second DBR structure is a conductive DBR structure, and the conductive DBR structure is formed by processing a dielectric DBR structure by adopting an electrical breakdown process; either one of the first and second semiconductor layers is an n-type semiconductor layer, and the other is a p-type semiconductor layer. The VCSEL adopts the conductive medium DBR structure, so the electrode injection efficiency is high, the stable operation can be realized under a larger current, the service life is long, the manufacturing process is simple, the controllability is good, the cost is low, and the product yield is high.

Description

GaN-based vertical cavity surface emitting laser with conductive DBR structure and manufacturing method thereof

Technical Field

The present application relates to a GaN-based vertical-cavity surface-emitting laser (VCSEL), and in particular to a GaN-based vertical-cavity surface-emitting laser with a conductive DBR structure and a manufacturing method thereof.

Background technique

Semiconductor lasers based on group III nitride materials have attracted widespread attention due to their high efficiency, low loss, small size, long life, and light weight. Traditional edge-emitting lasers generate optical gain based on a resonant cavity perpendicular to the film surface and are the mainstream structure of lasers. Compared with edge-emitting lasers, GaN-based vertical-cavity surface-emitting lasers (VCSELs) have the advantages of small active area, easy single longitudinal mode luminescence, low lasing threshold, small divergence angle, and high coupling efficiency with optical fibers and other optical components; in addition, VCSEL lasers can achieve high-speed modulation and can be used in long-distance, high-speed fiber-optic communication systems. Based on these characteristics, VCSEL devices have great application prospects in the fields of displays, biosensors, optical communications, etc.

Since Redwing et al. successfully prepared the optically pumped GaN-based VCSEL for the first time in 1996, VCSELs emitting in the visible band have entered people's field of vision. Some researchers have successfully prepared a continuous wavelength electrically injected GaN-based dual dielectric Bragg reflector (DBR) VCSEL at room temperature for the first time using bonding and substrate laser lift-off technology, with a threshold current of 7mA and a light emission wavelength of about 414nm. Some researchers have developed an electrically injected GaN-based VCSEL by optimizing the laser lift-off process of the sapphire substrate, optimizing the gain zone design and the manufacturing process of the high-reflectivity dielectric DBR, and achieved lasing under room temperature optical pumping conditions, with a light emission wavelength of 449.5nm and a threshold of 6.5mJ/ ^cm2 . For the reported GaN VCSELs, the technical difficulty is to obtain a high-reflectivity reflector. The upper reflector generally uses a relatively mature dielectric DBR, such as _SiO2 / _HfO2 , which is grown periodically and alternately with materials with a large refractive index difference, while the material of the lower reflector can be both dielectric DBR and nitride DBR. For example, using AlN/GaN epitaxial film as the lower DBR can avoid the yield and cost issues caused by the chip flip-chip process. However, due to the serious lattice mismatch and thermal mismatch between the AlN/GaN interface, the crystal quality of the nitride DBR is not high, and the difference in the refractive index of AlN/GaN is small. In order to achieve a higher reflectivity, a DBR with a large number of growth cycles must be grown, which further increases the difficulty of epitaxy and the risk of film cracking. If a dielectric DBR is used as the lower DBR, since the nitride active layer cannot be directly epitaxially grown on the dielectric material, bonding and epitaxial layer laser lift-off technology must be used to prepare a flip chip, thereby preparing a dual-dielectric GaN VCSEL.

Whether using nitride DBR or dielectric DBR, its conductivity is poor, so it is impossible to directly transmit and expand current through DBR. It can only form a step structure on the side through the etching process and deposit an ohmic contact electrode. This often brings multiple problems, such as: easy to appear current congestion effect, low device stability, easy aging, complex preparation process, high cost, low yield, etc.

In order to alleviate such problems, one solution is to develop a DBR with high conductivity to prepare vertical structure VCSEL devices, improve current congestion effects, increase current density, and reduce the lasing threshold. Some researchers have proposed using transparent conductive materials ITO or TiN to provide reflections, and to prepare through holes in the DBR based on etching technology. In addition to using transparent conductive layers as conductive DBR materials, some researchers have also used porous conductive GaN DBRs, in which the DBRs are electrochemically etched to form a multi-period DBR structure in which porous GaN with high porosity and porous GaN with low porosity are alternately stacked, and a GaN-based VCSEL with a porous GaN conductive DBR structure is prepared.

The key to obtain high-power, low-threshold, and high-current-injection GaN-based VCSEL devices is to prepare conductive DBRs with high refractive index difference and high crystal quality. Although the process of preparing conductive DBRs with transparent conductive films (such as ITO) is simple and feasible, it is difficult to achieve a large refractive index difference in actual operation. If you want to obtain a DBR with a higher reflectivity, you need to grow a considerable number of transparent conductive layers, which is economically and time-consuming. The use of porous GaN to prepare conductive DBR structures also requires the growth of more layers to obtain a higher reflectivity. In addition, the electrochemical corrosion used in porous GaN makes it difficult to accurately control the refractive index of each layer of GaN, resulting in a decrease in the overall reflectivity of the device. The process stability needs to be improved, which affects the luminous efficiency of the device.

Summary of the invention

The purpose of the present application is to provide a GaN-based vertical cavity surface emitting laser with a conductive DBR structure and a manufacturing method thereof, so as to overcome the deficiencies in the prior art.

To achieve the above objectives, this application provides the following technical solutions:

An embodiment of the present application provides a GaN-based vertical cavity surface emitting laser with a conductive DBR structure, which includes a first semiconductor layer, a second semiconductor layer and an active layer arranged between the first semiconductor layer and the second semiconductor layer, the first semiconductor layer and the second semiconductor layer are respectively connected to the first DBR structure and the second DBR structure, the second DBR structure is a conductive DBR structure, the conductive DBR structure is formed by processing a dielectric DBR structure using an electrical breakdown process, and the first semiconductor layer is also electrically connected to a first electrode; either the first semiconductor layer or the second semiconductor layer is an n-type semiconductor layer, and the other is a p-type semiconductor layer.

In some embodiments, the second DBR structure is bonded to a conductive substrate, which serves as at least a second electrode.

In some embodiments, the GaN-based vertical cavity surface emitting laser includes a substrate, a first DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer and a second DBR structure arranged in sequence along a specified direction, and the first semiconductor layer and the second DBR structure are electrically combined with a first electrode and a second electrode, respectively.

The embodiment of the present application also provides a method for manufacturing a GaN-based vertical cavity surface emitting laser having a conductive DBR structure, which comprises:

sequentially growing and forming a first semiconductor layer, an active layer, and a second semiconductor layer;

Growing a dielectric DBR structure on the second semiconductor layer, and forming a conductive channel in the dielectric DBR structure by an electrical breakdown process to obtain a conductive second DBR structure, and bonding the second DBR structure to a conductive substrate, wherein the conductive substrate is at least used as a second electrode;

A first DBR structure is grown on a first semiconductor layer, and a first electrode is disposed on the first semiconductor layer.

The embodiment of the present application also provides a method for manufacturing a GaN-based vertical cavity surface emitting laser having a conductive DBR structure, which comprises:

Growing a nitride DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer and a dielectric DBR structure in sequence, wherein the nitride DBR structure is used as a first DBR structure;

A conductive channel is formed in the dielectric DBR structure through an electrical breakdown process to obtain a conductive second DBR structure; a first electrode and a second electrode are respectively arranged on the first semiconductor layer and the second DBR structure.

In some embodiments, the electrical breakdown process includes: depositing one or more metal dots on the dielectric DBR structure, and then applying a breakdown voltage between the one or more metal dots and the second semiconductor layer to form a conductive channel in the dielectric DBR structure, thereby obtaining a conductive DBR structure.

Compared with the prior art, the technical solution proposed in the embodiment of the present application has at least the following beneficial effects:

(1) The conductive DBR is obtained by the electrical breakdown process. The electrode and the conductive DBR are in direct contact. The vertical circuit structure formed avoids the current congestion effect between p-GaN and the electrode, improves the electrode injection efficiency, alleviates the local Joule overheating of p-GaN, and prolongs the device life;

(2) The injection area of the p-type metal contact electrode is the entire area of the conductive DBR. The increase in the injection area is beneficial for the device to operate at a larger current.

(3) When a flip-chip structure is used, the heat generated during the operation of the device can be dissipated through the conductive substrate, and the heat dissipation capacity is significantly enhanced.

(4) When the flip-chip structure is adopted, the upper and lower Bragg reflectors in the device are both made of oxide DBR, and the refractive index difference between the dielectric films is large, which can achieve a higher reflectivity;

(5) The device manufacturing process is simple, controllable, low cost and high product yield.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the structure of an existing GaN-based VCSEL;

FIG2 is a schematic structural diagram of a GaN-based VCSEL in one embodiment of the present application;

FIG3 is a schematic diagram of a manufacturing process of a GaN-based VCSEL in an embodiment of the present application;

FIG4 is a schematic structural diagram of a GaN-based VCSEL in another embodiment of the present application;

FIG5 is a schematic diagram of a manufacturing process of a GaN-based VCSEL in another embodiment of the present application;

FIG6 is an I-V curve diagram of a conductive medium DRB before and after being electrically broken down in Example 1 of the present application.

Specific implementation plan

In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of this application after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

As mentioned above, the various existing solutions for preparing vertical structure VCSEL devices using DBRs with high conductivity all have some defects to a greater or lesser extent. In view of this, the inventors of this case have conducted a lot of research and found in the process that directly preparing a conductive medium by electrical breakdown can theoretically realize a conductive DBR structure, thereby hopefully realizing a vertical structure VCSEL device and overcoming the defects in the prior art. However, no relevant reports have been found in the field so far.

Although some researchers have used electrical breakdown to obtain conductive structures and applied them to LEDs. For example, some researchers deposited a thinner (8nm) AlN on the top of the LED p-AlGaN, and combined it with a transparent conductive film ITO for electrical breakdown, thereby obtaining a new type of AlN/ITO transparent conductive layer, which is conducive to extracting the generated photons from the top and improving the photon extraction efficiency of the LED. For another example, some researchers deposited Ni metal on the surface of 40nm AlN, prepared a conductive Ni/AlN omnidirectional reflector structure (ODR) by electrical breakdown, and further deposited metal aluminum with high ultraviolet reflectivity to reflect the photons generated by the LED and extract them from the substrate. However, the fundamental starting point of these works is to improve the photon extraction efficiency of the LED, that is, by forming a balance between contact resistance and photon reflectivity (or transmittance), comprehensively improving the luminous power of the LED device, which does not help to solve the technical problems existing in existing VCSEL devices.

Moreover, considering the significant differences between LED and VCSEL in structure and working principle, the aforementioned scheme applicable to LED cannot be directly applied in the preparation process of GaN-based VCSEL devices. For example, for LED, most of the layers that need to be electrically broken down are single-layer or thin AlN or oxide films, and it is not necessary to apply a very high voltage. However, the thickness of the DBR in VCSEL is usually large, and the traditional method cannot achieve electrical breakdown. For another example, the chip area of LED is large, while the gain area of VCSEL is small (about 10 microns). When preparing the conductive DBR for VCSEL devices, the uniformity of the conductive channel must be ensured, so the speed and frequency of the electric field application need to be adjusted (for example, the electric field adopts a positive and negative alternating electric field, the amplitude gradually increases from 5V to 50V, the frequency of the positive and negative voltage application is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s). In addition, compared with LED, VCSEL requires a larger working current density (kA/cm2 level), so it is more sensitive to the current congestion effect.

Based on the above findings, the inventor of this case, through further research and extensive practice, was able to propose the technical solution of this application, which will be explained in more detail below.

One aspect of an embodiment of the present application provides a GaN-based vertical cavity surface emitting laser with a conductive DBR structure, including a first semiconductor layer, a second semiconductor layer and an active layer arranged between the first semiconductor layer and the second semiconductor layer, the first semiconductor layer and the second semiconductor layer are respectively connected to the first DBR structure and the second DBR structure, the second DBR structure is a conductive DBR structure, and the first semiconductor layer is also electrically connected to the first electrode; either the first semiconductor layer or the second semiconductor layer is an n-type semiconductor layer, and the other is a p-type semiconductor layer.

Furthermore, the conductive DBR structure is formed by processing the dielectric DBR structure using an electrical breakdown process, and thus can be defined as a conductive dielectric DBR structure.

In some embodiments, the second DBR structure is bonded to a conductive substrate, which serves as at least a second electrode.

Furthermore, the conductive substrate includes a metal sheet with a mirror-polished surface (such as Cu, Al, Ag sheet, etc.), a transparent conductive film (such as ITO, etc.), or a high-doping concentration Si sheet with an ohmic electrode deposited on the bottom, etc., but is not limited thereto.

Furthermore, the conductive substrate used as the p-type contact electrode includes, but is not limited to, materials with good conductive properties such as diamond, graphite, Si, and SiC.

In some embodiments, the GaN-based vertical cavity surface emitting laser includes a conductive substrate, a second DBR structure, a second semiconductor layer, an active layer, a first semiconductor layer and a first DBR structure arranged in sequence along a specified direction, and the first semiconductor layer is electrically combined with a first electrode. In these embodiments, the GaN-based vertical cavity surface emitting laser can be considered as a flip-chip structure.

Furthermore, the first semiconductor layer forms an ohmic contact with the first electrode.

Furthermore, the entire surface of one end surface of the second DBR structure away from the second semiconductor layer is bonded to the conductive substrate.

In the aforementioned embodiment, the first DBR structure may adopt various types of DBRs known in the art, such as nitride DBR, oxide DBR, etc.

Furthermore, the material of the nitride DBR includes any one or more combinations of AlN, GaN, InGaN, and AlGaN, but is not limited thereto.

Furthermore, the material of the oxide DBR includes any one or more combinations of SiO ₂ , HfO ₂ , TiO ₂ , and ZnO, but is not limited thereto.

In some embodiments, the GaN-based vertical cavity surface emitting laser includes a substrate, a first DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer, and a second DBR structure arranged in sequence along a specified direction, and the first semiconductor layer and the second DBR structure are electrically combined with a first electrode and a second electrode, respectively. In these embodiments, the GaN-based vertical cavity surface emitting laser can be considered to be a front-mounted structure.

Furthermore, the first semiconductor layer forms an ohmic contact with the first electrode.

Furthermore, the substrate may be a sapphire substrate, a Si substrate, a SiC substrate, a GaN substrate, etc., but is not limited thereto.

Furthermore, the injection area of the second electrode is the entire area of an end surface of the second DBR structure away from the second semiconductor layer.

Furthermore, the second electrode directly injects current into the optical confinement hole.

In these embodiments, the first DBR structure adopts a nitride DBR, and its material includes but is not limited to any one or more combinations of nitrides such as AlN, GaN, InGaN, and AlGaN.

In this specification, the aforementioned designated direction may be from top to bottom, from bottom to top, from left to right, from right to left, from front to back or from back to front, and so on.

In some embodiments, the active layer is a quantum well active region, and its material can be a type known in the art, such as InGaN/GaN multiple quantum wells, etc., but is not limited thereto.

In some embodiments, the dielectric DBR structure used to form the second DBR structure includes an oxide DBR, and its material includes but is not limited to any one or more combinations of oxides such as SiO ₂ , HfO ₂ , TiO ₂ , and ZnO.

In some embodiments, the first semiconductor layer is an n-type semiconductor layer, and the second semiconductor layer is a p-type semiconductor layer.

In some embodiments, the first electrode may be defined as an n-type contact electrode or an n-type metal contact electrode, and the second electrode may be defined as a p-type contact electrode or a p-type metal contact electrode.

In addition, according to the needs of actual applications, the GaN-based vertical cavity surface emitting laser provided in the above embodiments of the present application may also include other structural layers commonly used in the art, such as an electron blocking layer, a current limiting layer, a current spreading layer, etc.

For GaN-based VCSEL devices, compared with other VCSEL devices, the operating current density is higher, and the current congestion effect has a greater impact on its performance. Some of the above embodiments of the present application directly prepare the conductive DBR structure on the conductive substrate, which can avoid the plasma table etching step of the lateral structure and save the preparation process of the bottom electrode. While ensuring the high reflectivity of the dielectric DBR, the process steps of the device are greatly simplified. In addition, the current injection area is greatly increased, the current congestion effect caused by the ring electrode is effectively alleviated, and the current injection efficiency is improved.

Another aspect of an embodiment of the present application provides a method for manufacturing the GaN-based vertical cavity surface emitting laser, comprising:

sequentially growing and forming a first semiconductor layer, an active layer, and a second semiconductor layer;

Growing a dielectric DBR structure on the second semiconductor layer, and forming a conductive channel in the dielectric DBR structure by an electrical breakdown process to obtain a conductive second DBR structure, and bonding the second DBR structure to a conductive substrate, wherein the conductive substrate is at least used as a second electrode;

A first DBR structure is grown on a first semiconductor layer, and a first electrode is disposed on the first semiconductor layer.

Furthermore, the first DBR structure may adopt various types of DBRs known in the art, such as nitride DBR, oxide DBR, etc. Typical nitride DBR materials include but are not limited to any one or more combinations of AlN, GaN, InGaN, AlGaN. Typical oxide DBR materials include but are not limited to any one or more combinations of SiO ₂ , HfO ₂ , TiO ₂ , ZnO.

Furthermore, the dielectric DBR structure used to form the second DBR structure includes an oxide DBR, and its material includes but is not limited to any one or more combinations of oxides such as SiO ₂ , HfO ₂ , TiO ₂ , and ZnO.

Another aspect of an embodiment of the present application provides a method for manufacturing the GaN-based vertical cavity surface emitting laser, comprising:

Growing a nitride DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer and a dielectric DBR structure in sequence, wherein the nitride DBR structure is used as a first DBR structure;

A conductive channel is formed in the dielectric DBR structure through an electrical breakdown process to obtain a conductive second DBR structure; a first electrode and a second electrode are respectively arranged on the first semiconductor layer and the second DBR structure.

Furthermore, the material of the nitride DBR structure includes but is not limited to any one or more combinations of AlN, GaN, InGaN, and AlGaN.

Furthermore, the material of the dielectric DBR structure includes but is not limited to any one or more combinations of oxides such as SiO ₂ , HfO ₂ , TiO ₂ , and ZnO.

In some embodiments, the electrical breakdown process includes: depositing one or more metal dots on the dielectric DBR structure, and then applying a breakdown voltage between the one or more metal dots and the second semiconductor layer to form a conductive channel in the dielectric DBR structure, thereby obtaining a conductive second DBR structure.

Furthermore, the conditions of the electrical breakdown process include: the electric field adopts a positive and negative alternating electric field, the amplitude gradually increases from 5V to 50V, the frequency of applying positive and negative voltages is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s.

In some embodiments, the material of the metal dots includes but is not limited to metal systems such as Cr/Al, Cr/Ni, Al, Ni, Ag, Ti/Al/Ni/Au, etc.

In some embodiments, the metal dots are in plurality and are arranged in order on the dielectric DBR structure.

In the above embodiments of the present application, the conductive property of the dielectric DBR, especially the oxide DBR, is achieved by preparing orderly arranged metal dots on the dielectric DBR, applying a certain voltage to achieve electrical breakdown of the dielectric layer, and in the local breakdown process, the metal ions near the negative electrode are reduced to metal conductive filaments, and/or the anions in the oxide near the positive electrode are oxidized to leave anion vacancies, forming a conductive channel running through the dielectric DBR, thereby converting the dielectric DBR into a conductive DBR.

By adopting the above-mentioned scheme provided in the embodiment of the present application, not only the photon extraction efficiency of the GaN-based VCSEL device can be improved, but more importantly, by forming a vertical structure VCSEL through a conductive DBR, the current congestion effect can be well eliminated, and the current collapse at the contact between the second DBR structure and the electrode can be avoided. In addition, the injection area of the second electrode can be the entire area of the end surface of the second DBR structure away from the second semiconductor layer. Therefore, the electrode area is much larger than the corresponding electrode in the existing VCSEL device, and it is easier to reach the stimulated emission threshold of the VCSEL device.

The following will describe in detail the technical solutions in several embodiments of the present application in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

Referring to FIG. 1 , an existing GaN-based VCSEL device includes a substrate 1, a lower DBR structure 2, an n-doped-GaN layer 3 (n-GaN layer), a quantum well active region 4, a p-doped-GaN layer 5 (p-GaN layer), a SiO ₂ current limiting layer 6, an ITO current spreading layer 7, an upper DBR structure 8, an n-type contact electrode 9, a p-type contact electrode 10, etc. Among them, the lower DBR structure 2 is a nitride DBR formed by epitaxial growth, and the upper DBR structure 8 is a dielectric DBR. The defects of the GaN-based VCSEL device include:

(1) The device has a planar structure, which is prone to current congestion and uneven current input;

(2) The electrode injection area is limited, and excessive Joule heat is generated locally in the device, which cannot effectively dissipate heat, causing the junction temperature of the device to increase and the stability to decrease;

(3) The preparation process is complicated and requires the deposition of _SiO2 current limiting layer, ITO current expansion layer, etc., which reduces the yield and increases the preparation cost;

(4) The local current density is large, and the electromigration of metal is more serious at the edge of the mesa, which accelerates device degradation.

In view of the problem that in existing GaN VCSEL devices, due to the insulating characteristics of the dielectric DBR, the metal electrode must be deposited outside the resonant cavity, resulting in current congestion and other problems, the embodiments of the present application provide a type of VCSEL device with a conductive dielectric DBR.

Please refer to Figure 2. A GaN-based vertical cavity surface emitting laser with a conductive DBR structure provided in one embodiment of the present application is a flip-chip structure, which includes a conductive substrate 108, a second DBR structure 105 (conductive DBR), a second semiconductor layer 104, an active layer (quantum well active region 103), a first semiconductor layer 102 and a first DBR structure 101 (dielectric DBR) arranged in sequence from bottom to top.

The first semiconductor layer 102 and the second semiconductor layer 104 may be an n-doped GaN layer and a p-doped GaN layer, respectively.

The entire surface of one end face of the second DBR structure 105 away from the second semiconductor layer 104 is bonded to a conductive substrate 108 via a bonding metal 107 , and the conductive substrate 108 can be regarded as a p-type contact electrode.

An n-type contact electrode 109 is disposed on the first semiconductor layer 102 , and forms an ohmic contact with the first semiconductor layer 102 .

In the flip-chip structure VCSEL device provided in this embodiment, the flip-chip structure epitaxial layer and the conductive DBR are bonded to the conductive substrate through a metal bonding process, and the conductive substrate includes a Cu, Al, Ag sheet with a mirror-polished surface or a high-doping concentration Si sheet with an ohmic electrode deposited on the bottom. Due to the use of a vertical chip structure, not only can the current injection area be increased, current injection under large currents can be achieved, and the device lasing threshold can be reduced, but also the current congestion effect caused by the electrode being located outside the resonant cavity in the traditional process can be alleviated, local Joule overheating can be reduced, and the device life can be extended.

Referring to FIG. 3 , a method for preparing the flip-chip structure VCSEL device includes the following steps:

(a) First, an n-GaN layer 102, an active layer 103 and a p-GaN layer 104 are epitaxially grown on a substrate 100 (such as a sapphire, Si, or SiC substrate), and a dielectric DBR structure 105' (oxide DBRs such as _SiO2 , _HfO2 , _TiO2 , or ZnO may be used but are not limited thereto) is grown on the p-GaN layer 104;

(b) depositing metal dots 106 on the dielectric DBR structure 105';

(c) applying voltage between the p-GaN layer 104 and the metal dot 106 through an electrical breakdown process, so that a conductive channel is formed inside the dielectric DBR structure 105' to form a conductive DBR (which can be considered as a p-DBR, that is, the aforementioned second DBR structure). In the electrical breakdown process, the electric field adopts a positive and negative alternating electric field, and the amplitude gradually increases from 5V to 50V. The frequency of applying positive and negative voltages is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s;

(d) removing the metal point 106;

(e) using a metal bonding process, after depositing a bonding metal 107 on the surface of the p-DBR, the epitaxial layer is bonded to a conductive substrate 8 such as a Cu, Al or Ag sheet or a highly doped Si substrate. The conductive substrate 8 serves as a p-type metal contact electrode (i.e., the aforementioned p-type contact electrode) and also as a supporting substrate for the epitaxial layer. The substrate 100 is then removed by a substrate laser lift-off process, or by a grinding, polishing or wet etching process;

(f) A dielectric DBR structure 101 (i.e., the aforementioned first DBR structure, which may be, but not limited to, oxide DBRs such as _SiO2 , _HfO2 , _TiO2 , and ZnO) is grown on the surface of the epitaxial layer after stripping, i.e., the surface of the n-GaN layer 102, and an n-type metal contact electrode 109 (i.e., the aforementioned n-type contact electrode) is prepared.

Please refer to Figure 4. A GaN-based vertical cavity surface emitting laser with a conductive DBR structure provided in another embodiment of the present application is a face-up structure, which includes a substrate 201, a first DBR structure 202 (epitaxial nitride DBR), a first semiconductor layer 203, an active layer 204 (quantum well active region), a second semiconductor layer 205 and a second DBR structure 206 (conductive DBR) arranged in sequence from bottom to top.

The first semiconductor layer 203 and the second semiconductor layer 205 may be an n-doped GaN layer (n-GaN layer) and a p-doped GaN layer (p-GaN layer), respectively.

The entire surface of one end of the second DBR structure 206 away from the second semiconductor layer 205 is combined with a p-type metal contact electrode 209 (p-type contact electrode, also defined as a second electrode).

An n-type metal contact electrode 208 (n-type contact electrode, also defined as a first electrode) is disposed on the first semiconductor layer 203 , and the two form an ohmic contact.

In the upright structure VCSEL device provided in this embodiment, the epitaxial nitride DBR structure (i.e., the aforementioned first DBR structure) can adopt an AlN/GaN DBR epitaxially grown by the MOCVD method, while the conductive DBR structure (i.e., the aforementioned second DBR structure) is prepared by an electrical breakdown process, and the p-type contact electrode can be directly added on the conductive DBR structure, and large-area current injection can also be achieved, thereby solving the current congestion problem of the ring electrode and p-GaN, and the current is directly injected into the limiting hole, thereby improving the current injection efficiency.

Referring to FIG. 5 , a method for preparing the upright structure VCSEL device includes the following steps:

(a) First, a nitride DBR structure 202 (i.e., the aforementioned first DBR structure, such as a group III nitride DBR structure), an n-GaN layer 203, a quantum well 204, and a p-GaN layer 205 are epitaxially grown on a substrate 201 (such as a sapphire, Si, or SiC substrate), and a dielectric DBR structure 206′ is grown on the p-GaN layer 205;

(b) depositing metal dots 207 on the dielectric DBR structure 206';

(c) applying voltage between the p-GaN layer 205 and the metal dot 207 through an electrical breakdown process, so that a conductive channel is formed inside the dielectric DBR structure 206' to form a conductive DBR structure 206 (i.e., the aforementioned second DBR structure). In the electrical breakdown process, the electric field adopts a positive and negative alternating electric field, and the amplitude gradually increases from 5V to 50V. The frequency of applying positive and negative voltages is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s.

(d) removing the metal dots and etching to form an n-type contact electrode mesa;

(e) Depositing an n-type contact electrode 208 and a p-type contact electrode 209 on the n-type contact electrode terrace and the conductive DBR structure 206 respectively.

More specifically, a method for manufacturing a GaN-based vertical cavity surface emitting laser provided in Example 1 of the present application includes:

a. Based on metal organic chemical vapor deposition (MOCVD), a blue laser epitaxial film is grown on a sapphire substrate, including n-GaN with a thickness of about 531nm (doping concentration 5×10 ¹⁸ cm ^-3 ), 5 pairs of quantum well active regions (In _0.21 Ga _0.79 N 3nm/GaN 4nm), a p-type Al _0.18 Ga _0.82 N electron blocking layer with a thickness of about 20nm, and p-GaN with a thickness of about 180nm (doping concentration 8×10 ¹⁷ cm ^-3 ).

b. SiO ₂ /HfO ₂ (76nm/53nm) p-oxide DBRs are alternately grown using an electron beam deposition device (e-beam), and the required optical confinement hole size is etched based on a photolithography process. At the same time, steps are formed on the surface of the p-oxide DBR and p-type GaN to facilitate electrical breakdown.

c. Based on the photolithography process, using photoresist as a mask, using e-beam to deposit several metal dots Cr/Al on the p-oxide, with a diameter of about 10μm, and using an electrochemical workstation to apply voltage between the metal dots and the p-type GaN until the p-oxide DBR is broken down (the electric field uses a positive and negative alternating electric field, the amplitude gradually increases from 5V to 50V, the frequency of positive and negative voltage application is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s), and then HCl solution is used to remove the metal dots above the p-oxide DBR. The voltage-current curve of the p-oxide DBR before and after breakdown is shown in Figure 6.

d. Deposit metal (Cr/Ni/Au) on the p-oxide DBR and the substrate, and bond the p-oxide DBR to the metal based on a bonding process, and then use laser lift-off technology to lift off the sapphire substrate.

e. Use electron beam evaporation to grow oxide DBR (SiO ₂ /HfO ₂ , 76nm/53nm), use photolithography and dry etching to etch through the SiO ₂ /HfO ₂ DBR to form a step structure between the DBR and n-GaN. Use electron beam evaporation equipment to grow n-type metal contact electrodes Ni/Au with a thickness of 20nm/100nm.

More specifically, a method for manufacturing a GaN-based vertical cavity surface emitting laser provided in Example 2 of the present application includes:

a. Blue laser epitaxial thin films were grown epitaxially on sapphire substrates by metal organic chemical vapor deposition (MOCVD), including 25 pairs of AlN/GaN (52nm/46nm) epitaxial DBRs, n-GaN with a thickness of about 890nm (doping concentration 5×10 ¹⁸ cm ^-3 ), 5 pairs of quantum well active regions (In _0.21 Ga _0.79 N 3nm/GaN 4nm), a p-type Al _0.18 Ga _0.82 N electron blocking layer with a thickness of about 20nm, and p-GaN with a thickness of about 250nm (doping concentration 8×10 ¹⁷ cm ^-3 ).

b. TiO ₂ /ZnO (76nm/53nm) p-oxide DBRs are alternately grown using an electron beam deposition device (e-beam). Based on the photolithography process, the required optical confinement hole size is etched out, and steps are formed on the surface of the p-oxide DBR and p-type GaN to facilitate electrical breakdown.

c. Based on the photolithography process, using photoresist as a mask, use e-beam to deposit several metal dots Ag on the p-oxide with a diameter of 10μm. Use a DC power supply to apply voltage between the metal dots and the p-type GaN until the oxide is broken down (the electric field uses a positive and negative alternating electric field, the amplitude gradually increases from 5V to 50V, the frequency of positive and negative voltage application is 1Hz-100Hz, and the rate of increase of the voltage amplitude is between 0.1V/s-10V/s, which eventually causes a sudden increase in current), and then use HCl solution to remove the metal dots above the p-oxide DBR.

d. Etching the mesa to the n-type GaN region based on photolithography and dry etching processes facilitates the preparation of n-type metal contact electrodes.

e. Use e-beam equipment to grow n-type metal contact electrodes Ni/Au with a thickness of 20nm/100nm, and then use e-beam equipment to grow p-type metal contact electrodes Ti/Al/Ni/Au with a thickness of 10nm/100nm/20nm/50nm.

The GaN-based vertical cavity surface emitting laser provided in the above embodiments of the present application has at least the following advantages due to the inclusion of the aforementioned conductive DBR structure:

(1) It can alleviate the current congestion effect caused by the distribution of electrodes of GaN-based VCSEL devices outside the resonant cavity and the limited contact area between the p-type GaN layer and the p-type contact electrode due to the non-conductivity of the dielectric DBR. Specifically, the above embodiments of the present application use an electrical breakdown process to obtain a conductive DBR. The electrode and the conductive DBR are in direct contact. The vertical circuit structure formed avoids the current congestion effect between p-GaN and the electrode, improves the electrode injection efficiency, alleviates the local Joule overheating of p-GaN, and prolongs the device life.

(2) The current injection area can be significantly increased. In the above embodiments of the present application, the injection area of the p-type metal contact electrode is the entire area of the conductive DBR. The increase in the injection area is conducive to the device operating at a larger current.

(3) It is beneficial to the heat dissipation of the device. In the above embodiments of the present application, the heat generated by the flip-chip device during operation can be dissipated from the conductive substrate, which greatly enhances the heat dissipation capacity compared with sapphire substrates.

(4) Dual-medium Bragg reflectors have a high reflectivity. In the above embodiments of the present application, both the upper and lower Bragg reflectors in the flip-chip device use oxide DBRs, and the refractive index difference between the dielectric films is large, which can achieve a high reflectivity.

It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

The above is only a specific implementation scheme of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims (19)

1. The GaN-based vertical cavity surface emitting laser with the conductive DBR structure is characterized by comprising a first semiconductor layer, a second semiconductor layer and an active layer arranged between the first semiconductor layer and the second semiconductor layer, wherein the first semiconductor layer and the second semiconductor layer are respectively connected with the first DBR structure and the second DBR structure, the first DBR structure is a dielectric DBR, the second DBR structure is a conductive DBR structure, the conductive DBR structure is formed by processing the dielectric DBR structure by adopting an electrical breakdown process, and the first semiconductor layer is further electrically connected with a first electrode; either one of the first semiconductor layer and the second semiconductor layer is an n-type semiconductor layer, and the other one is a p-type semiconductor layer;

wherein the conditions of the electrical breakdown process include: the electric field adopts positive and negative alternating electric fields, the amplitude is gradually increased from 5V to 50V, the increasing rate of the voltage amplitude is between 0.1V/s and 10V/s, and the frequency of positive and negative voltage application is between 1Hz and 100Hz.

2. The GaN-based vertical cavity surface emitting laser according to claim 1, wherein: the second DBR structure is bonded to a conductive substrate that serves as at least a second electrode.

3. The GaN-based vertical cavity surface emitting laser according to claim 2, wherein: the conductive substrate includes a metal sheet with mirror-polished surface, a transparent conductive film, or a high doping concentration Si sheet with an ohmic electrode deposited on the bottom, and the metal sheet includes a Cu sheet, an Al sheet, or an Ag sheet.

4. The GaN-based vertical cavity surface emitting laser of claim 2, comprising a conductive substrate, a second DBR structure, a second semiconductor layer, an active layer, a first semiconductor layer, and a first DBR structure disposed in that order along a prescribed direction, the first semiconductor layer being electrically coupled to the first electrode.

5. The GaN-based vertical cavity surface emitting laser according to claim 1, comprising a substrate, a first DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer, and a second DBR structure disposed in that order along a prescribed direction, the first semiconductor layer, the second DBR structure being electrically coupled to a first electrode, a second electrode, respectively.

6. The GaN-based vertical cavity surface emitting laser according to claim 4 or 5, wherein: the first semiconductor layer forms an ohmic contact with the first electrode.

7. The GaN-based vertical cavity surface emitting laser according to claim 5, wherein: the implantation area of the second electrode is the whole area of an end face of the second DBR structure away from the second semiconductor layer.

8. The GaN-based vertical cavity surface emitting laser according to claim 1, wherein: the dielectric DBR comprises an oxide DBR or a nitride DBR, the material of the oxide DBR comprises any one or a combination of a plurality of SiO ₂、HfO₂、TiO₂ and ZnO, and the material of the nitride DBR comprises any one or a combination of a plurality of AlN, gaN, inGaN, alGaN.

9. The GaN-based vertical cavity surface emitting laser according to claim 1, wherein: the dielectric DBR structure used for forming the conductive DBR structure is selected from oxide DBR, and the material of the oxide DBR comprises any one or a combination of a plurality of SiO2, hfO2, tiO2 and ZnO.

10. The GaN-based vertical cavity surface emitting laser according to any one of claims 1 to 5, wherein: the first semiconductor layer is an n-type semiconductor layer, and the second semiconductor layer is a p-type semiconductor layer.

11. A method of fabricating a GaN-based vertical cavity surface emitting laser having a conductive DBR structure, comprising:

sequentially growing a first semiconductor layer, an active layer and a second semiconductor layer;

Growing a dielectric DBR structure on the second semiconductor layer, forming a conductive channel in the dielectric DBR structure through an electrical breakdown process to obtain a conductive second DBR structure, and bonding the second DBR structure with a conductive substrate, wherein the conductive substrate is at least used as a second electrode;

growing a first DBR structure on the first semiconductor layer, and disposing a first electrode on the first semiconductor layer;

wherein the first DBR structure and the dielectric DBR structure used for forming the second DBR structure are oxide DBR;

the conditions of the electrical breakdown process include: the electric field adopts positive and negative alternating electric fields, the amplitude is gradually increased from 5V to 50V, the increasing rate of the voltage amplitude is between 0.1V/s and 10V/s, and the frequency of positive and negative voltage application is between 1Hz and 100Hz.

12. The manufacturing method according to claim 11, characterized in that it comprises: and then applying breakdown voltage between more than one metal point and the second semiconductor layer to form a conductive channel in the dielectric DBR structure, thereby obtaining the second DBR structure.

13. The method of manufacturing according to claim 11 or 12, wherein: the oxide DBR material comprises any one or a combination of a plurality of SiO ₂、HfO₂、TiO_2、 ZnO.

14. The method of manufacturing according to claim 12, wherein: the metal points are a plurality of and are orderly arranged on the dielectric DBR structure.

15. A method of fabricating a GaN-based vertical cavity surface emitting laser having a conductive DBR structure, comprising:

sequentially growing a nitride DBR structure serving as a first DBR structure, a first semiconductor layer, an active layer, a second semiconductor layer and a dielectric DBR structure for forming a second DBR structure;

forming a conductive channel in the dielectric DBR structure through an electrical breakdown process to obtain a conductive second DBR structure; a first electrode and a second electrode are respectively arranged on the first semiconductor layer and the second DBR structure;

wherein the conditions of the electrical breakdown process include: the electric field adopts positive and negative alternating electric fields, the amplitude is gradually increased from 5V to 50V, the increasing rate of the voltage amplitude is between 0.1V/s and 10V/s, and the frequency of positive and negative voltage application is between 1Hz and 100Hz.

16. The method of claim 15, wherein the electrical breakdown process comprises: and depositing more than one metal point on the dielectric DBR structure, and then applying breakdown voltage between the more than one metal point and the second semiconductor layer to form a conductive channel in the dielectric DBR structure, thereby obtaining the conductive DBR structure used as the second DBR structure.

17. The method of manufacturing according to claim 16, wherein: the metal dots are a plurality of and are orderly arranged on the second DBR structure.

18. The method of manufacturing according to claim 15 or 16, wherein: the dielectric DBR structure comprises an oxide DBR, and the material of the oxide DBR comprises any one or a combination of a plurality of SiO ₂、HfO₂、TiO_2、 ZnO.

19. The method of manufacturing according to claim 15, wherein: the nitride DBR material may comprise any one or a combination of a plurality of AlN, gaN, inGaN, alGaN.