Semiconductor light-emitting element with plasmon coupling layer

Abstract

The invention discloses a semiconductor light-emitting element provided with a plasmon coupling layer. The semiconductor light-emitting element comprises a first conductive type semiconductor layer, an active layer comprising at least one quantum well layer, a second conductive type semiconductor layer and a surface plasmon excitation layer, the core is that the second conductive type semiconductor layer is used as a functional spacing layer, the thickness of the second conductive type semiconductor layer is accurately set to be a preset coupling distance, and the second conductive type semiconductor layer is used for separating the quantum well layer from the surface plasmon excitation layer. And the predetermined coupling distance is optimized, so that the surface plasmon and carriers in the quantum well are subjected to optimal resonance coupling, thereby maximizing the Pelsel effect to enhance the spontaneous radiation recombination rate, and effectively inhibiting the non-radiation quenching effect of the metal layer at the same time. The invention has the beneficial effects that the internal quantum efficiency of the device can be obviously improved, the efficiency reduction under high current is inhibited, the modulation bandwidth is improved, and the structure has strong compatibility with the existing semiconductor process.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronics technology, and in particular to a semiconductor light-emitting element and its manufacturing method that improves internal quantum efficiency and light-emitting performance through surface plasmon coupling effect. Background Technology

[0002] Semiconductor light-emitting elements, such as light-emitting diodes (LEDs) and laser diodes (LDs), are central to modern lighting, display, and optical communication technologies. One of the key bottlenecks in their luminous efficiency lies in the limitation of internal quantum efficiency (IQE). IQE depends on the competition between radiative and non-radiative recombination processes within the active region. Especially under the high current densities required for high-power applications, non-radiative recombination (such as Auger recombination) intensifies, leading to an "efficiency doop" phenomenon that severely restricts the improvement of device performance.

[0003] To overcome this limitation, coupling surface plasmons (SPs) generated by metal nanostructures with the active region of a semiconductor to accelerate radiative recombination via the Purcell effect is considered a promising technological approach. However, the practical application of this technology faces a sharp contradiction: on the one hand, to achieve strong coupling enhancement, the metal layer needs to be sufficiently close to the active region (quantum well); on the other hand, the ohmic loss characteristics of metals mean that excessively close distances will lead to a large amount of non-radiative "quenching" of the quantum well's energy, thus reducing efficiency. Therefore, achieving the optimal balance between enhancement and quenching, and precisely controlling the coupling strength, is a key technical challenge that urgently needs to be solved in this field. Existing technological solutions often fail to provide a structurally clear and controllable, and process-stable solution to effectively resolve this contradiction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects in the prior art where the surface plasmon enhancement effect is not ideal or is canceled out by the quenching effect due to the inability to precisely control the coupling distance. The present invention provides a technical solution that can actively and precisely control the interaction strength between the quantum well and the surface plasmon excitation source, thereby maximizing radiation enhancement while suppressing non-radiative loss, and ultimately significantly improving the quantum efficiency and overall performance of the semiconductor light-emitting element.

[0005] To address the aforementioned technical problems, this invention provides a semiconductor light-emitting element. The basic structure of this element includes a first conductivity type semiconductor layer (e.g., an N-type layer), an active layer disposed thereon, and a second conductivity type semiconductor layer (e.g., a P-type layer) disposed on the active layer. The active layer is the core light-emitting region of the device, and it contains at least one quantum well layer, in which injected charge carriers (electrons and holes) recombine to generate photons.

[0006] The core innovation of this invention lies in the introduction of a surface plasmon excitation layer on the above-mentioned basic structure, and the creative design of the function and structural parameters of the second conductivity type semiconductor layer.

[0007] Specifically, the surface plasmon excitation layer is disposed above the second conductivity type semiconductor layer, i.e., on the side away from the active layer. More importantly, the second conductivity type semiconductor layer itself is given a completely new functional role: it is no longer just a conventional carrier injection layer, but is precisely designed as a functional spacer layer.

[0008] The core function of this spacer layer is to physically and precisely define and control the spatial separation distance between the quantum well layer in the active layer and the surface plasmon excitation layer above it, through its own thickness. This invention defines this precisely controlled distance as the predetermined coupling distance.

[0009] The concept of this invention is not simply to introduce an interval, but to optimize the value of the predetermined coupling distance with a clear physical purpose. The goal of this configuration is to enable the system to enter an optimal physical operating state: when photons generated in the quantum well layer arrive at the surface plasmon excitation layer in the form of near-field evanescent waves, they can efficiently excite the surface plasmons therein (e.g., collective oscillations of free electrons in a metal); at the same time, the strong localized electromagnetic fields generated by these excited surface plasmons can, in turn, undergo strong resonant coupling with the charge carriers (or the excitons they form) in the quantum well layer.

[0010] The physical essence of this resonant coupling is to provide excitons in the quantum well with an additional, extremely fast energy relaxation channel. Compared to the slow spontaneous emission in conventional free space, excitons can now preferentially release energy through a "shortcut" (exciton energy → surface plasmon energy → emitted photons). According to Fermi's golden rule, the introduction of this new channel greatly increases the photon density of states of the system, thereby significantly enhancing the spontaneous recombination rate in the quantum well layer, which is known as the Purcell effect.

[0011] By setting the thickness of the second conductivity type semiconductor layer to this "predetermined coupling distance", the present invention successfully resolves the contradiction between "enhancement" and "quenching" mentioned in the background art.

[0012] If the distance is too close (less than the predetermined range), the near-field interaction will be too strong, and the energy will be mainly absorbed and lost by the metal layer through non-radiative pathways (quenching effect dominates).

[0013] If the distance is too far (greater than the predetermined range), the near-field evanescent wave will attenuate almost completely, the coupling effect will be weak, and no effective enhancement can be obtained.

[0014] The "predetermined coupling distance" defined in this invention is precisely this optimal balance point or balance range. At this distance, the enhancement effect of the Purcell effect on the radiative rate far outweighs the negative impact of metal loss, thereby achieving a net gain in luminous efficiency.

[0015] In a preferred embodiment, the predetermined coupling distance is limited to a range of 5 nanometers to 100 nanometers. This range is an effective operating interval derived through theoretical calculations and experimental verification based on the physical properties of common semiconductor materials (such as GaN) and plasmonic materials (such as Ag and Au). To obtain better performance, this distance can be further optimized to a range of 10 nanometers to 50 nanometers.

[0016] The surface plasmon excitation layer can be composed of various materials and morphologies. In one embodiment, it is a metal layer. Considering the plasmon characteristics in the visible and near-ultraviolet light bands, the metal layer is preferably selected from the group consisting of silver (Ag), gold (Au), aluminum (Al), copper (Cu), platinum (Pt), or alloys thereof. Among them, silver (Ag) has the lowest loss in the blue-green light band and is a particularly ideal choice.

[0017] The morphology of this excitation layer can also be selected in various ways to support different types of surface plasmon resonance modes. For example, it can be a continuous metal thin film to support propagating surface plasmon polaritons (SPPs); or it can be an array of nanoparticles (e.g., nanoislands formed by annealing self-assembly) to support localized surface plasmon resonances (LSPRs) with extremely strong local field enhancement effects; in addition, it can also be a nanowire lattice or a nanostructure with a predetermined pattern fabricated by techniques such as electron beam lithography to achieve precise control over the resonance wavelength, polarization, and other characteristics.

[0018] In a typical application scenario of this invention, the first conductivity type semiconductor layer is an N-type semiconductor layer, and the second conductivity type semiconductor layer is a P-type semiconductor layer. This configuration corresponds to the most common NP-junction light-emitting device. To further optimize device performance, an additional electron blocking layer (EBL) can be provided between the active layer and the P-type semiconductor layer to prevent electron leakage and improve the recombination efficiency of charge carriers in the active region.

[0019] The technical concept of this invention has broad applicability and can be applied to various semiconductor material systems, such as the currently mainstream III-V group nitride semiconductor material systems (e.g., GaN, InGaN, AlGaN) or phosphide semiconductor material systems (e.g., AlGaInP, InGaAsP). Furthermore, the devices of this invention can be various semiconductor light-emitting elements such as light-emitting diodes (LEDs), laser diodes (LDs), or superluminescent diodes (SLDs).

[0020] Compared to existing technologies, this invention creatively designs the second conductivity type semiconductor layer as a functional spacer layer. Its thickness precisely defines and optimizes the coupling distance between the quantum well and the surface plasmon excitation layer, thereby maximizing the Purcell enhancement effect while effectively suppressing non-radiative quenching. This design brings a series of significant benefits: it fundamentally accelerates the spontaneous radiative recombination process of the device, directly leading to a substantial increase in internal quantum efficiency (IQE); by accelerating carrier consumption, it effectively alleviates carrier accumulation in the active region, thus significantly suppressing efficiency degradation under high injection current, enabling the device to maintain high-efficiency output during high-power operation; simultaneously, the increased radiation rate is equivalent to a shortened carrier lifetime, which directly translates into a significant increase in the device's modulation bandwidth, paving the way for applications such as high-speed optical communication. Crucially, the technical solution of this invention has a clear structure, and its core distance control can be precisely achieved through standard semiconductor epitaxial growth processes (such as MOCVD) without the need for complex post-processing steps, thus possessing strong process compatibility and commercial potential. Attached Figure Description

[0021] none. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Example 1 This embodiment discloses a high-efficiency blue light-emitting diode (LED) based on a GaN material system. The vertical structure of this LED, in order of growth from substrate to top, comprises the following layers: First, there is the substrate, which can be, for example, sapphire, silicon carbide, or silicon. A low-temperature GaN buffer layer is epitaxially grown on it to improve the crystal quality of subsequent materials.

[0024] Above the buffer layer is a first conductivity type semiconductor layer, which in this embodiment is an N-type semiconductor layer. Specifically, it is a silicon (Si) doped N-type GaN layer (n-GaN) with a thickness of approximately 2-4 micrometers. This layer serves as an electron injection layer.

[0025] Above the N-type GaN layer lies the core light-emitting region of the device—the active layer. This active layer employs a multiple quantum well (MQW) structure, consisting of, for example, five cycles of In0.2Ga0.8N / GaN quantum well pairs. Each cycle comprises an In0.2Ga0.8N quantum well layer approximately 2.5 nanometers thick and a GaN barrier layer approximately 10 nanometers thick. Electrons and holes recombine within this quantum well layer, generating blue photons with a wavelength of approximately 450 nanometers.

[0026] An electron blocking layer (EBL) can be deposited above the active layer, such as a P-type doped AlO layer with a thickness of about 20 nanometers. 15 Ga0. 85 The N layer is used to prevent electrons from leaking into the P region.

[0027] Above the electron blocking layer is one of the key layers of this invention. The second conductivity type semiconductor layer, in this embodiment, is a P-type semiconductor layer. Specifically, it is a magnesium (Mg)-doped P-type GaN layer (p-GaN). According to the core idea of ​​this invention, the thickness of this P-type GaN layer is precisely controlled, allowing it to act as a "spacer layer." This thickness is the "predetermined coupling distance" between the quantum well layer (especially the quantum well closest to the P-type layer) and the subsequent surface plasmon excitation layer. In this embodiment, by precisely controlling the MOCVD growth time and rate, the thickness d of the P-type GaN layer is set to 20 nanometers.

[0028] A surface plasmon excitation layer is formed on top of a p-type GaN spacer layer. In this embodiment, this layer is formed by electron beam evaporation of a silver (Ag) film several nanometers thick, followed by rapid thermal annealing (RTA) to allow the Ag film to spontaneously aggregate into an array of silver nanoparticles.

[0029] A transparent conductive layer, such as an indium tin oxide (ITO) film, is deposited on top of the P-type GaN layer and the silver nanoparticle array to facilitate uniform spread of the P-region current.

[0030] Finally, P electrodes are fabricated on the transparent conductive layer and N electrodes are fabricated on the N-type GaN layer exposed by etching using standard photolithography, etching, and metal evaporation processes, thereby completing the fabrication of the device.

[0031] In this embodiment, a predetermined coupling distance of 20 nm is optimal. If this distance is too small (e.g., less than 5 nm), the quantum well's energy will be largely quenched nonradiatively due to its proximity to the metallic silver, resulting in reduced luminous efficiency. Conversely, if this distance is too large (e.g., greater than 100 nm), the near-field coupling effect becomes weak, and Purcell enhancement is not significant. By precisely controlling the distance at 20 nm, the system achieves optimal net gain, significantly improving optical output power at the same injection current compared to a reference device without silver nanoparticles, and effectively suppressing efficiency degradation at high currents.

[0032] Example 2 This embodiment is a variation of Embodiment 1, and its structure and materials are mostly the same as those of Embodiment 1. The main difference lies in the morphology of the surface plasmon excitation layer.

[0033] In this embodiment, a continuous gold (Au) thin film with a thickness of approximately 15 nanometers is directly deposited on a P-type GaN spacer layer with a thickness precisely controlled to 25 nanometers, serving as a surface plasmon excitation layer. The continuous metal thin film primarily excites and supports propagating surface plasmon polaritons (SPPs), rather than localized surface plasmon resonances (LSPRs) as in Embodiment 1.

[0034] Although the excited plasmon modes differ, their physical enhancement mechanisms are similar. Similarly, precisely controlling the coupling distance through the p-type GaN spacer layer is key to achieving net gain. Due to the different material properties of gold and the field distribution of SPPs compared to the LSPRs of silver nanoparticles, the optimal coupling distance is adjusted to 25 nanometers. This embodiment demonstrates that the core concept of this invention can be flexibly applied to surface plasmon excitation layers of different materials and morphologies.

[0035] Example 3 This embodiment discloses a semiconductor laser diode (LD) applying the ideas of this invention. Unlike LEDs, LDs require an optical resonant cavity to achieve stimulated emission.

[0036] The vertical structure of the LD, from the N-type substrate upwards, may sequentially include: an N-type lower waveguide / confining layer (e.g., N-type AlGaN), an active layer (e.g., InGaN / GaN multiple quantum wells), a P-type electron blocking layer, and a P-type upper waveguide / confining layer (e.g., P-type AlGaN).

[0037] The core structure of this invention is integrated into the LD. Specifically, a P-type GaN layer with precisely controlled thickness is epitaxially grown on top of the P-type waveguide / confining layer as a functional spacer layer. A surface plasmon excitation layer (e.g., the structure in Embodiment 1 or 2) is then formed on top of this spacer layer. Above that is a heavily doped P-type contact layer and a P-electrode. Parallel reflective cavity surfaces are formed at both ends of the device through a cleaving process, constituting a Fabry-Perot resonator.

[0038] In this embodiment, the surface plasmon coupling effect enhances the spontaneous emission rate, which brings multiple benefits to laser oscillation. The enhanced spontaneous emission is more efficiently "injected" into the laser mode, while the faster carrier recombination rate reduces the carrier concentration required to reach the lasing threshold. This results in a lower threshold current, higher differential gain, and better high-temperature operating characteristics compared to conventional LDs. This embodiment demonstrates that the technical concept of the present invention is not only applicable to incoherent light sources but can also significantly optimize the performance of coherent light sources.

Claims

1. A semiconductor light-emitting element, characterized in that, include: First conductivity type semiconductor layer; An active layer is disposed on the first conductivity type semiconductor layer, the active layer including at least one quantum well layer, the quantum well layer being used to generate photons upon recombination of injected carriers; A second conductivity type semiconductor layer is disposed on the active layer; as well as A surface plasmon excitation layer is disposed above the second conductivity type semiconductor layer; Wherein, the second type of conductive semiconductor layer serves as a spacer layer, separating the quantum well layer from the surface plasmon excitation layer by a predetermined coupling distance; Furthermore, the predetermined coupling distance is configured such that the surface plasmons excited by the photons in the surface plasmon excitation layer resonantly couple with the charge carriers in the quantum well layer, thereby enhancing the spontaneous recombination rate in the quantum well layer.

2. The semiconductor light-emitting element according to claim 1, characterized in that, The predetermined coupling distance ranges from 5 nanometers to 100 nanometers.

3. The semiconductor light-emitting element according to claim 2, characterized in that, The preferred value range for the predetermined coupling distance is 10 nanometers to 50 nanometers.

4. The semiconductor light-emitting element according to claim 1, characterized in that, The surface plasmon excitation layer is a metal layer.

5. The semiconductor light-emitting element according to claim 4, characterized in that, The metal layer is selected from the group consisting of silver (Ag), gold (Au), aluminum (Al), copper (Cu), platinum (Pt), or alloys thereof.

6. The semiconductor light-emitting element according to claim 4, characterized in that, The surface plasmon excitation layer can be a continuous thin film, a nanoparticle array, a nanowire lattice, or a nanostructure with a predetermined pattern.

7. The semiconductor light-emitting element according to claim 1, characterized in that, The first conductivity type semiconductor layer is an N-type semiconductor layer, and the second conductivity type semiconductor layer is a P-type semiconductor layer.

8. The semiconductor light-emitting element according to claim 7, characterized in that, The semiconductor light-emitting element is based on a III-V group nitride semiconductor material system or a phosphide semiconductor material system.

9. The semiconductor light-emitting element according to claim 7, characterized in that, It also includes an electron blocking layer (EBL) disposed between the active layer and the P-type semiconductor layer.

10. The semiconductor light-emitting element according to claim 1, characterized in that, The semiconductor light-emitting element is a light-emitting diode (LED), a laser diode (LD), or a superluminescent diode (SLD).