Electropumped colloidal quantum dot laser on silicon substrate

Abstract

The application discloses a kind of electrically pumped colloidal quantum dot lasers of silicon-based substrate, belong to the technical field of semiconductor optoelectronic devices.The laser is stacked from bottom to top with doped silicon substrate, lower buffer layer, download carrier transport layer, colloidal quantum dot gain layer, upper carrier transport layer, upper protective layer, waveguide structure layer, upper buffer layer and electrode system.Doped silicon substrate surface is constructed with conductive optical confinement structure, the structure has vertical direction conductivity, and its effective refractive index at lasing wavelength is significantly lower than colloidal quantum dot gain layer.In addition, DFB grating structure is provided in transparent waveguide structure layer, and flat buried layer design is used to adapt solution method preparation process.The application solves the problems of silicon-based interface light leakage, parasitic waveguide effect and process compatibility, and can realize low-cost, low-threshold and high-stability laser output on silicon substrate without wafer bonding.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor optoelectronic devices, and particularly relates to an electrically pumped colloidal quantum dot laser on a silicon substrate. BACKGROUND

[0002] Semiconductor lasers have become the core devices of modern optoelectronic technology due to their small size, high efficiency, long life and easy modulation. With the rapid development of information technology, silicon-based optoelectronics is committed to integrating photonic devices on silicon chips using mature CMOS technology to break through the bottleneck of traditional electrical interconnection in terms of bandwidth and power consumption. However, since monocrystalline silicon (Si) is an indirect bandgap semiconductor material, the light emission efficiency is extremely low, and how to realize a high-efficiency, low-cost and integrable electrically pumped laser light source on a silicon substrate is considered a difficult problem in this field.

[0003] In order to solve the problem of silicon-based light source, the prior art mainly adopts hetero-integration of III-V compound semiconductors (such as InP, GaAs) and silicon. There are mainly two technical routes: direct hetero-epitaxy: using MOCVD and other technologies to grow III-V materials on silicon. However, due to the large lattice mismatch and thermal expansion coefficient difference between III-V materials and silicon, high-density threading dislocations are easily generated in the epitaxial layer, which seriously reduces the light emission efficiency and life of the laser. Although the prior art (such as trying to use a tilted silicon substrate or a thick buffer layer to improve it, but this greatly increases the process complexity and cost. The second is to use wafer bonding: transfer and bond the prepared III-V laser to the silicon waveguide. Although this method avoids lattice mismatch, the wafer surface quality requirement is extremely high, the yield is difficult to control, and the III-V substrate is expensive, which is difficult to meet the demand of large-scale low-cost manufacturing.

[0004] In recent years, colloidal quantum dots (CQDs) as a new solution processing semiconductor material, are considered as an ideal alternative material to realize "silicon-based light source" due to their adjustable emission wavelength, high quantum yield, low cost and insensitivity to lattice matching of the substrate. Although colloidal quantum dots have made progress in optically pumped lasers and ordinary light-emitting diodes (QLEDs), they still face several insurmountable physical and technological obstacles when applied to silicon substrates.

[0005] The refractive index guiding mechanism is invalid. This is the biggest physical dead end for the preparation of quantum dot lasers on silicon. The lasing of the laser depends on the effective restriction of the optical field in the waveguide layer. However, due to the substrate light leakage, the refractive index of single crystal silicon is very high (n≈3.45) in the near infrared band, and the refractive index of colloidal quantum dot film and commonly used organic transmission layer is lower (n≈1.7-1.9). According to the principle of optical waveguide, the light field always tends to distribute to the area with high refractive index. If the device is directly prepared on the silicon substrate, the laser mode field will instantly penetrate the low refractive index functional layer, be "leaked" through the evanescent wave and collapse into the high refractive index silicon substrate to be absorbed, resulting in that the gain region cannot establish effective light restriction. At the same time, in order to realize vertical conduction, indium tin oxide (ITO) is usually introduced as a transparent electrode due to the ITO parasitic waveguide effect. However, the refractive index (n≈1.9-2.0) of ITO is higher than that of the quantum dot layer. If the ITO layer is thick (usually >100 nm for conventional conduction requirements), the light field will be restricted in the ITO layer without gain (i.e. parasitic waveguide mode), resulting in that the light restriction factor of the quantum dot gain region is extremely low, and the laser cannot be started.

[0006] At the same time, the solution method process is not compatible with the nano-grating structure. The DFB laser needs a nano-scale grating structure to select the longitudinal mode. The traditional dry etching process involves high-energy plasma bombardment, which can destroy the fragile colloidal quantum dot ligand and cause fluorescence quenching. On the contrary, if the quantum dot solution is directly spin-coated on the uneven grating substrate, the liquid film will be filled in the groove due to surface tension, resulting in a serious thickness difference of the quantum dot layer (thin at the wave peak and thick at the wave valley). This thickness difference will cause uneven current injection, causing local short circuit or leakage, so that the device is difficult to work at high current density.

[0007] In addition, there is a lack of effective on-chip integration mechanism. The existing quantum dot laser design is mostly a discrete device emitting to the air side, which has limited application value for silicon optical chips that need to be interconnected with silicon-based optical waveguide circuits. The silicon wafer is difficult to cleave a perfect mirror surface like III-V crystals, and there is currently a lack of a device structure that can efficiently couple the light generated by the solution method gain layer into the underlying silicon waveguide.

[0008] In summary, the existing technology lacks a systematic technical solution that can simultaneously solve the problems of silicon-based interface light leakage, parasitic waveguide loss, solution method process flatness, and on-chip integration coupling. Therefore, it is of great application value to develop a novel structure and process compatible silicon-based electrically pumped colloidal quantum dot laser. SUMMARY

[0009] The present application provides an electrically pumped colloidal quantum dot laser on a silicon substrate to solve the problems in the prior art. The present application is realized by the following technical solutions.

[0010] The application provides an electrically pumped colloidal quantum dot laser of a silicon substrate, which is stacked from bottom to top with a doped silicon substrate, a lower buffer layer, a lower carrier transport layer, a colloidal quantum dot gain layer, an upper carrier transport layer, an upper protective layer, a waveguide structure layer, an upper buffer layer, and a back electrode and a top electrode electrically connected with the doped silicon substrate and the upper buffer layer respectively, wherein,

[0011] The doped silicon substrate is a (001) crystal direction monocrystalline silicon, and the surface of the doped silicon substrate has a conductive optical confinement structure with vertical direction conductivity and effective refractive index lower than that of the colloidal quantum dot gain layer.

[0012] The colloidal quantum dot gain layer, the lower carrier transport layer and the upper carrier transport layer form an electrically injected light-emitting structure.

[0013] The waveguide structure layer is provided with a distributed feedback grating structure, and the light field mode field area of the distributed feedback grating structure and the carrier injection area of the electrically injected light-emitting structure have an overlapping part in space and are separated on a physical interface.

[0014] The laser is further provided with a reflective film and a transmissive film on the end face respectively, the distributed feedback grating structure and the reflective film and the transmissive film together form a laser resonant cavity along the parallel direction of the semiconductor layer, and laser output is realized.

[0015] Further, the conductive optical confinement structure includes a conductive porous silicon layer or a conductive distributed Bragg reflector, the conductive porous silicon layer is a porous structure with a semiconductor skeleton formed by electrochemical treatment of the upper part of the doped silicon substrate, and the porosity is configured to have an effective refractive index between 1.4 and 1.7; the conductive distributed Bragg reflector is a multilayer film structure formed by alternately stacking high refractive index conductive materials and low refractive index conductive materials.

[0016] Further, the colloidal quantum dot gain layer selects a core-shell quantum dot with a radial gradient component or an alloyed shell layer.

[0017] Further, the colloidal quantum dot gain layer is selected from one of CdSe / ZnS, CdSe / CdS, ZnSe / ZnS, InP / ZnS, PbS / PbSe and Ag2S / ZnS.

[0018] Further, the lower carrier transport layer contains at least two layers of metal oxide layers with different work functions or doping concentrations, and forms a stepwise decreasing potential barrier along the carrier injection direction.

[0019] Further, the upper carrier transport layer and the lower carrier transport layer are selected from any one or a combination of at least two of nickel oxide, molybdenum oxide, tin oxide, tungsten oxide, magnesium oxide, nickel magnesium oxide, nickel tin oxide, 8-hydroxyquinoline-lithium, lithium fluoride or aluminum oxide.

[0020] Further, the upper surface of the doped silicon substrate is integrated with a passive silicon optical waveguide circuit, which is located below or extends in the same layer as the conductive optical confinement structure.

[0021] Further, the waveguide structure layer surface has a periodic groove, and the groove is filled with a conductive planarization material, so that the side surface of the waveguide structure layer facing the colloidal quantum dot gain layer is a flat surface.

[0022] Further, the back electrode and the top electrode are selected from any one or a combination of at least two of barium, calcium, aluminum, magnesium, tin, indium, copper, silver, titanium, titanium nitride, gold or platinum.

[0023] Further, the lower buffer layer and the upper buffer layer are selected from any one or a combination of at least two of indium tin oxide (ITO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO).

[0024] The present application has the following beneficial effects:

[0025] (1) Overcome the bottleneck of "light leakage" at the silicon-based interface, and realize low-cost silicon-based lasing. By introducing a conductive optical confinement structure on the surface of the doped silicon substrate, a low refractive index (n<1.7) "optical barrier" is constructed. This structure retains the vertical conductive channel while completely blocking the leakage of light field to the high refractive index silicon substrate using the principle of total reflection, so that the device can realize lasing on a mature (001) silicon wafer without expensive bonding process.

[0026] (2) Eliminate the "parasitic waveguide" effect and significantly reduce the threshold. The present application innovatively limits the ultra-thin thickness (such as <50nm) of the lower buffer layer, and forces the light field energy to "return" to the colloidal quantum dot gain layer from the high refractive index conductive layer using the waveguide cutoff principle. This design greatly improves the light confinement factor of the active region, solves the problem of light field being stolen, and significantly reduces the threshold current density of the laser.

[0027] (3) Solve the compatibility problem of solution method process and grating morphology, and improve the preparation yield. A planarization buried grating design is adopted, and a conductive planarization material is filled in the grating groove. This not only retains the mode selection function of the grating, but also provides an atomic-level flat deposition interface for solution method spin coating, avoiding uneven film thickness and short circuit risk caused by surface undulation, and ensuring the stability of electrical injection.

[0028] (4) Synergistic suppression of non-radiative recombination, and enhancement of continuous working stability. Through the synergistic design of gradient shell quantum dots and step energy level transport layer, the carrier injection barrier is effectively smoothed. This design suppresses Auger recombination and Joule heat generation under high current density, significantly improves the problem of thermal quenching, and prolongs the working life of the device in continuous wave mode. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of a silicon-based electrically pumped colloidal quantum dot laser of the present application, wherein (a) is a schematic diagram of the whole; (b) is a schematic diagram of the cross section of the laser; (c) is a schematic diagram of the side of the laser;

[0030] Figure 2 is a schematic diagram of the cross section of the device of embodiment 1 of the present application;

[0031] Figure 3 is a schematic diagram of the cross section of the device of embodiment 2 of the present application;

[0032] Figure 4 is a schematic diagram of the cross section of the device of embodiment 3 of the present application;

[0033] Figure 5 is a schematic diagram of the cross section of the device of embodiment 4 of the present application. DETAILED DESCRIPTION

[0034] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] As shown in Figure 1 , the present application provides a silicon-based substrate electrically pumped colloidal quantum dot distributed feedback (DFB) laser. The device adopts a hybrid integrated architecture combining vertical injection and lateral optical waveguide, and is stacked from bottom to top with: a doped silicon substrate 1, a lower buffer layer 2, a lower carrier transport layer 3, a colloidal quantum dot gain layer 4, an upper carrier transport layer 5, an upper protective layer 6, a waveguide structure layer 7 (containing a DFB grating), an upper buffer layer 8, and a back electrode 10 and a top electrode 9. In order to form a complete horizontal direction resonant cavity, high reflection film 11 and transmission film 12 are deposited at both ends of the device.

[0036] The colloidal quantum dot gain layer 4 is located between the lower carrier transport layer 3 and the upper carrier transport layer 5, and the three together constitute an electric injection light-emitting structure (PIN junction or PIN-like junction structure). By applying a forward bias through the back electrode 10 and the top electrode 9, electrons and holes are injected into the quantum confined energy levels of the colloidal quantum dot gain layer 4 through the transport layers, forming excitons inside the quantum dots and undergoing radiative recombination to produce photons. To address the problem of light leakage caused by the silicon substrate, the doped silicon substrate 1 in the embodiment is a single crystal silicon with a (001) crystal orientation, and can be doped with indium (P-type) or phosphorus (N-type) according to the device polarity requirements, and the thickness is usually between 100 μm and 500 μm. Since the refractive index of single crystal silicon in the near infrared band is as high as 3.45, which is much higher than the refractive index of the colloidal quantum dot gain layer 4 (usually about 1.7-1.9), according to the principle of total reflection of optical waveguide, if the two are in direct contact or too close, the optical field mode cannot be confined in the low refractive index gain layer, but will penetrate the interface through the evanescent wave effect, quickly leak and collapse into the high refractive index substrate to be absorbed, resulting in the inability to establish the population inversion required for stimulated emission.

[0037] To this end, the present application constructs a conductive optical confinement structure on the surface of the doped silicon substrate 1. The structure is configured to have vertical conductivity to maintain the current path, while its effective refractive index at the lasing wavelength is regulated to be significantly lower than that of the colloidal quantum dot gain layer 4, preferably between 1.4 and 1.7, through physical structure regulation (such as introducing air pores by porosification or multilayer film interference). The structure can be a conductive porous silicon layer formed by electrochemical treatment and retaining the semiconductor skeleton, or a conductive distributed Bragg reflector (DBR) formed by alternating stacking of high and low refractive index conductive materials. This structure physically builds a low refractive index "optical barrier" that tightly confines the laser mode field in the gain region above the device using the principle of total reflection, thereby completely blocking the leakage of the optical field to the doped silicon substrate 1.

[0038] In the design of the core light-emitting and transport region, the colloidal quantum dot gain layer 4 preferably uses core-shell quantum dots with a radial gradient composition or alloyed shell, such as CdSe / ZnS, InP / ZnS or Ag2S / ZnS materials. The gradient shell design can smooth the confinement potential field of the quantum dots, making the wave function overlap of electrons and holes more ideal, thereby effectively suppressing non-radiative Auger recombination under high current density. To optimize the carrier injection efficiency, the lower carrier transport layer 3 is designed to contain at least two layers of metal oxide layers (such as nickel oxide, molybdenum oxide, etc.) or organic materials with different work functions or doping concentrations, forming a stepwise decreasing potential barrier along the carrier injection direction. This stepwise energy level design can smooth the large potential barrier difference at the interface, preventing the accumulation of carriers at the interface, thereby reducing the generation of quantum confinement Stark effect (QCSE) and Joule heat, significantly improving the electrical-to-optical conversion efficiency and stability of the device under continuous operation.

[0039] The materials for the carrier transport layer 3 and the carrier transport layer 5 can be selected from one or more combinations of nickel oxide, molybdenum oxide, tin oxide, tungsten oxide, PEDOT:PSS, TFB, etc. To achieve single-mode laser output and adapt to solution-based fabrication processes, this embodiment incorporates a distributed feedback (DFB) grating structure in the transparent waveguide structure layer 7. The DFB grating provides Bragg scattering feedback through periodic refractive index changes, only when the Bragg condition is satisfied (… Only photons of specific wavelengths can achieve effective gain, thus realizing single-mode lasing. Unlike traditional surface-embossed gratings, this embodiment employs a planarized buried layer design. Conductive planarizing material is filled into the periodic grooves on the surface of the waveguide structure layer 7, making the surface of the waveguide structure layer 7 facing the colloidal quantum dot gain layer 4 atomically flat. This design resolves the contradiction between photonic structure and solution-based processing: it retains the periodic refractive index modulation effect of the grating on the light field, achieving mode selection; and it provides a flat interface for subsequent deposition of the quantum dot layer using solution-based processes such as spin coating, effectively avoiding problems such as uneven quantum dot film thickness, leakage channels, or short circuits caused by substrate undulations.

[0040] The optical mode region and carrier injection region in waveguide structure layer 7 spatially overlap, and together with the high-reflectivity film 11 and transmission film 12 on the device end face, they form a laser resonant cavity parallel to the semiconductor layer, realizing laser output. Furthermore, to prevent parasitic waveguide effects from the high-refractive-index transparent conductive layer (such as ITO, n≈2.0), the lower buffer layer 2 and upper buffer layer 8 (materials selected from ITO, IZO, IGZO, etc.) in this embodiment are typically designed to be relatively thin (e.g., the thickness of the lower buffer layer 2 is 5-100nm). This ultra-thin design utilizes the waveguide's cutoff characteristics, preventing the high-refractive-index buffer layer from supporting independent optical modes, forcing the optical energy center to "return" from the passive conductive layer to the low-refractive-index but gain-providing colloidal quantum dot gain layer 4, thereby maximizing the optical confinement factor. The back electrode 10 and top electrode 9 are selected from metals such as barium, calcium, aluminum, magnesium, gold, silver, platinum, or combinations thereof, according to energy level matching requirements. Each functional layer can be deposited by magnetron sputtering, thermal evaporation, MOCVD, inkjet printing or spin coating, and a passive silicon optical waveguide circuit can be integrated on the upper surface of the doped silicon substrate 1 to achieve on-chip coupling between the laser and the silicon photonic chip.

[0041] The present invention will be further described below through Examples 1 to 4.

[0042] Example 1

[0043] This embodiment provides a red-band laser based on a porous silicon optical confinement layer, the cross-sectional structure of which is as follows: Figure 2As shown, a highly doped indium p-type silicon wafer with a double-sided polishing process and a thickness of 150 μm was first selected as the substrate. After standard cleaning with acetone, ethanol, and deionized water to remove the natural oxide layer on the surface, the upper surface of the silicon wafer was treated with electrochemical anodizing. By controlling the current density and reaction time in the electrolyte (a mixture of hydrofluoric acid and ethanol), a conductive porous silicon layer that retains the semiconductor framework was formed on the surface of the silicon substrate. The porosity of this porous silicon layer was finely controlled to reduce its effective refractive index to about 1.6, thereby forming a conductive optical confinement structure. Subsequently, a 10 nm thick indium tin oxide (ITO) layer was deposited on the porous silicon layer using magnetron sputtering as an ultrathin lower buffer layer, which ensures electrical contact while preventing the light field from being "plundered".

[0044] In the fabrication of the carrier transport layer and the light-emitting layer, this embodiment employs a stepped energy level design to optimize hole injection efficiency. First, under nitrogen atmosphere, a PEDOT:PSS solution is spin-coated at 3000 rpm and baked. Then, a TFB (poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine)) solution dissolved in chlorobenzene is spin-coated at the same speed and baked. These two layers constitute the composite carrier transport layer, forming a progressively decreasing potential barrier along the carrier injection direction, effectively smoothing the hole injection path and suppressing non-radiative recombination under high current. Next, a CdSe / ZnS core-shell quantum dot solution dissolved in n-octane is spin-coated as a colloidal quantum dot gain layer, and a ZnO nanoparticle layer is spin-coated as the upper carrier transport layer. To protect the fragile organic / quantum dot layer, a 30 nm thick IGZO layer is deposited on top via magnetron sputtering as an upper protective layer. Subsequently, an IZO layer was deposited and a grating pattern was photolithographically etched to serve as a waveguide layer. Surface planarization was achieved through a backfill process or by depositing an indium hydrogen peroxide (ITO) layer. Finally, a TiO2 high-reflectivity film and a SiO2 antireflection film were deposited at both ends of the device, respectively, and an Au top electrode and an Al back electrode were fabricated. This device utilizes the visible light gain characteristics of CdSe / ZnS quantum dots, combined with the light confinement effect of the silicon-based porous layer, to achieve highly efficient red laser output.

[0045] Example 2

[0046] This embodiment demonstrates an inverted InP laser based on an N-type silicon substrate, the structure of which is as follows: Figure 3 As shown. The substrate is a highly doped phosphorus N-type silicon wafer with a thickness of 100 μm.

[0047] To solve the problem of high refractive index light leakage of silicon substrate, a conductive optical confinement structure is first constructed on the surface of the cleaned N-type silicon substrate. In this embodiment, a conductive distributed Bragg reflector (DBR) structure is adopted, and a multi-period stack is formed by alternately growing high-doped silicon (Si) layers and germanium-silicon (SiGe) layers (or other conductive high / low refractive index material combinations) on the substrate by LPCVD or MBE process. The center reflection wavelength of the conductive DBR is designed to match the light emission wavelength of the InP quantum dots, and it has good vertical conductivity and effective refractive index lower than the upper quantum dot gain layer, so as to block the light field outside the substrate.

[0048] In this scheme, in order to adapt to the electron injection characteristics of the N-type substrate, a ZnO nanoparticle layer is directly spin-coated on the cleaned silicon substrate as a download carrier transport layer (at this time as an electron transport layer). This direct contact design takes advantage of the good band alignment between heavily doped silicon and ZnO.

[0049] The light-emitting layer selects environmentally friendly InP / ZnS quantum dots (dissolved in n-octane) and is deposited by spin coating process. In order to solve the problem of hole injection in the inverted structure, 100 nm thick TCTA (tris(4-carbazol-9-ylphenyl)amine) and 5 nm thick MoO3 (molybdenum trioxide) are deposited in turn on the quantum dot layer by thermal evaporation process. Among them, MoO3 as a high work function metal oxide can effectively modify the anode interface, and cooperate with the organic material TCTA to form an excellent hole transport channel. Subsequently, 10 nm ITO is magnetron sputtered as a protective layer, and a thick ITO layer is etched to form a grating as a waveguide layer. Finally, Au top electrode and Ag back electrode are prepared, and a mixed cavity structure is formed by end face coating film to realize single-mode laser emission.

[0050] Embodiment 3

[0051] This embodiment is aimed at near-infrared waveband application, and narrow-bandgap quantum dots and complex metal oxide transport layers are used. The device structure is as shown in Figure 4 The substrate uses a 200μm thick P-type doped silicon.

[0052] Similar to embodiment 1, in order to prevent light field leakage to the high refractive index substrate, the upper surface of the P-type silicon substrate is first treated by electrochemical anodization process. In a hydrofluoric acid-based electrolyte, a conductive porous silicon layer with a thickness of about 2-5μm is generated in situ on the surface of the substrate by controlling the current density. The porous silicon layer retains the crystal skeleton of silicon to maintain vertical conductivity, and at the same time introduces air medium through pores to reduce the effective refractive index to below 1.6, thus forming an effective conductive optical confinement structure.

[0053] Different from the previous embodiments, this embodiment first deposits an IZO lower buffer layer on the substrate, and directly prepares a waveguide pattern by lithography, and then fills the groove by spin-coating the subsequent functional layer to realize the planarization of the buried grating structure. The process flow of this "waveguide front" avoids the risk of high-energy etching on the fragile quantum dot layer.

[0054] In terms of functional layer material selection, the download carrier transport layer is formed by high-temperature annealing of spin-coated nickel oxide (NiOx) and copper-doped nickel oxide (Cu:NiOx) precursors. This double-layer nickel oxide structure adjusts the work function by changing the doping concentration, further reduces the hole injection barrier, and improves the device's resistance to large current. The gain layer selects Ag2S / ZnS quantum dots, which are a typical near-infrared light-emitting material. The upload carrier transport layer selects ZnMgO nanoparticles, which can be optimized by adjusting the Mg content to match the Ag2S energy level. Finally, the IGZO protective layer, end face reflection / anti-reflection film, and electrode are deposited to complete the device preparation.

[0055] Embodiment 4

[0056] This embodiment aims to achieve short-wavelength (such as blue-green light) lasing, using a combination of ZnSe quantum dots and organic transport layers, with a structure as shown in Figure 5 The substrate is a 200μm thick N-type silicon wafer.

[0057] Before depositing the functional layer, the N-type silicon substrate also needs to be surface modified to build an optical "barrier". The cleaned N-type silicon wafer is placed in an electrochemical cell and subjected to anodic oxidation treatment (or pulse current etching suitable for N-type silicon) under light assistance, forming an N-type porous silicon layer with vertical conductive channels on the substrate surface. By adjusting the etching parameters, the porosity of the porous silicon layer is controlled to make its effective refractive index for blue-green light significantly lower than that of the ZnSe quantum dot layer, ensuring that the optical mode field is confined within the waveguide and gain region.

[0058] In this structure, the download carrier transport layer is spin-coated ZnMgO nanoparticles. The gain layer selects ZnSe / ZnS quantum dots with a wide bandgap. To match the deep energy level of the ZnSe valence band, the upload carrier transport layer is designed as a multi-layer organic stack: 30nm TCTA, 20nm NPB (N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4-4'-diamine) and 20nm HA-TCN are sequentially thermally evaporated. This organic heterojunction design not only optimizes hole transport but also blocks electron overflow, effectively confining excitons within the quantum dot light-emitting layer. A 50nm ITO layer is deposited on the top of the device as a protective layer, and a grating structure is processed as a waveguide layer using laser interference etching technology on the protective layer or subsequent deposited layer.

[0059] This invention overcomes the physical bottleneck of "light leakage" at silicon-based interfaces, achieving for the first time compatibility between vertical conductivity and optical confinement. Existing technologies cannot directly fabricate low-refractive-index (n≈1.7) colloidal quantum dot lasers on silicon substrates (refractive index n≈3.45) because the light field leaks instantaneously to the substrate via evanescent waves and is absorbed. This invention solves this fundamental physical contradiction by introducing a conductive optical confinement structure on the surface of the doped silicon substrate. This structure constructs an "optical barrier" with a significantly reduced effective refractive index (n<1.7), using the principle of total internal reflection to firmly confine the laser mode field within the upper gain region, completely blocking the leakage of the light field to the silicon substrate; simultaneously, this structure retains the vertical carrier transport channel. This enables electrically pumped colloidal quantum dot lasers to directly oscillate and operate on inexpensive and mature (001) silicon wafers, eliminating the need for expensive III-V substrates or complex wafer bonding processes, significantly reducing manufacturing costs.

[0060] Meanwhile, this invention overcomes the "parasitic waveguide" effect of the high-refractive-index buffer layer, significantly improving mode gain. Addressing the "optical field plundering" problem caused by the higher refractive index of the transparent conductive layer (such as ITO / IZO, n≈2.0) compared to the quantum dot layer in traditional structures, this invention innovatively limits the ultrathin thickness of the lower buffer layer (e.g., <50nm). This design utilizes the waveguide cutoff principle, forcing the high-refractive-index lower buffer layer to be unable to support independent optical waveguide modes, compelling the optical energy center to "return" from the passive conductive layer to the colloidal quantum dot gain layer. This greatly improves the optical confinement factor in the active region, ensuring that the limited quantum dot optical gain can be effectively utilized. This not only solves the problem of devices "emitting light but not lasing," but also significantly reduces the laser's oscillation threshold current density.

[0061] Furthermore, this invention solves the morphology compatibility problem between solution spin coating and nano-DFB grating structures. Traditional DFB lasers require the fabrication of thin films on undulating grating surfaces, which leads to severe unevenness in the quantum dot layer thickness after solution spin coating, causing current short circuits or scattering losses. This invention employs a planarized buried grating design. By filling the grating grooves with conductive planarizing material, an atomically flat deposition interface is provided for subsequent quantum dot solution spin coating, while retaining the grating's periodic refractive index modulation effect on the light field. This preserves the grating's mode selection function, ensures the macroscopic uniformity of the colloidal quantum dot gain layer and the stability of electrical injection, significantly improving device fabrication yield and avoiding chemical damage to fragile quantum dot materials caused by physical etching processes.

[0062] The application also cooperatively inhibits non-radiative recombination under electric pumping, improving the continuous working stability. By adopting the cooperative design of gradient shell quantum dots and step energy level transmission layers, the carrier injection barrier is effectively smoothed, and the Auger recombination and Stark effect under high current density are inhibited. This not only further reduces the threshold, but also reduces the generation of Joule heat, significantly improves the thermal quenching problem commonly existing in colloidal quantum dot lasers, and prolongs the working life of the device in the continuous wave mode.

[0063] It should be noted that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting of example embodiments consistent with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0064] It should be noted that the terms "first", "second", and so on as used in the specification and above drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the terms used in this way can be interchanged as appropriate, so that the embodiments of the application described herein can be implemented in an order other than that illustrated or described herein.

[0065] In addition, the terms "comprise" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product or device.

[0066] For ease of description, spatial relative terms such as "over", "above", "upper surface", "upper", and the like can be used herein to describe the spatial relationship of one device or feature to another device or feature as shown in the drawings. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation of the device as described in the drawings. For example, if the device in the drawings is inverted, the device described as "above" or "over" other devices or structures will be positioned "below" or "under" the other devices or structures. Thus, the exemplary term "above" can include both "above" and "below" orientations. The device can also be positioned in other different ways, such as rotated 90 degrees or in other orientations, and the spatial relative descriptions used herein are interpreted accordingly.

[0067] In the detailed description above, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description and drawings are not meant to be limiting. Other embodiments can be used, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein.

[0068] The specific embodiments described hereinabove have been shown by way of example, and any modifications and / or additions of method steps and embodiments for carrying out the methods covered here by any means available to those in the art are intended to be within the scope of the disclosure.

Claims

1. An electrically pumped colloidal quantum dot laser on a silicon substrate, characterized in that, A doped silicon substrate, a lower buffer layer, a lower carrier transport layer, a colloidal quantum dot gain layer, an upper carrier transport layer, an upper protective layer, a waveguide structure layer, an upper buffer layer are stacked from bottom to top, and a back electrode and a top electrode are electrically connected to the doped silicon substrate and the upper buffer layer respectively, wherein The doped silicon substrate is a (001) crystal direction single crystal silicon, the surface of the doped silicon substrate has a conductive optical confinement structure, the conductive optical confinement structure has vertical direction conductivity, and the effective refractive index is lower than that of the colloidal quantum dot gain layer; the conductive optical confinement structure includes a conductive porous silicon layer or a conductive distributed Bragg reflector, the conductive porous silicon layer is a porous structure with a semiconductor skeleton formed by electrochemical treatment of the upper part of the doped silicon substrate, and the porosity is configured to have an effective refractive index between 1.4 and 1.7; the conductive distributed Bragg reflector is a multilayer film structure formed by alternately stacking high refractive index conductive materials and low refractive index conductive materials; The colloidal quantum dot gain layer and the lower carrier transport layer and the upper carrier transport layer form an electric injection light emitting structure; The waveguide structure layer is provided with a distributed feedback grating structure, the light field mode field area where the distributed feedback grating structure is located has an overlapping part with the carrier injection area of the electric injection light emitting structure in space, and the two are separated on the physical interface; The laser further comprises a reflective film and a transmission film on the end face respectively, the distributed feedback grating structure and the reflective film and the transmission film together form a laser resonant cavity along the parallel direction of the semiconductor layer to realize laser output.

2. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The colloidal quantum dot gain layer selects a core-shell quantum dot with a radial gradient component or an alloyed shell.

3. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 2, wherein, The colloidal quantum dot gain layer is selected from one of CdSe / ZnS, CdSe / CdS, ZnSe / ZnS, InP / ZnS, PbS / PbSe, Ag2S / ZnS.

4. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The lower carrier transport layer comprises at least two layers of metal oxide layers with different work functions or doping concentrations, forming a stepwise decreasing potential barrier along the carrier injection direction.

5. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The upper carrier transport layer and the lower carrier transport layer are selected from any one or a combination of at least two of nickel oxide, molybdenum oxide, tin oxide, tungsten oxide, magnesium oxide, nickel magnesium oxide, nickel tin oxide, 8-hydroxyquinoline-lithium, lithium fluoride or aluminum oxide.

6. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The upper surface of the doped silicon substrate is integrated with a passive silicon optical waveguide circuit, and the passive silicon optical waveguide circuit is located below or in the same layer as the conductive optical confinement structure.

7. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The surface of the waveguide structure layer has a periodic groove, and the groove is filled with a conductive planarization material, so that the side surface of the waveguide structure layer facing the colloidal quantum dot gain layer is a flat surface.

8. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The back electrode and the top electrode are selected from any one or a combination of at least two of barium, calcium, aluminum, magnesium, tin, indium, copper, silver, titanium, titanium nitride, gold or platinum.

9. The electrically pumped colloidal quantum dot laser on silicon substrate of claim 1, wherein, The lower buffer layer and the upper buffer layer are selected from any one or a combination of at least two of indium tin oxide (ITO), indium zinc oxide (IZO), and indium gallium zinc oxide (IGZO).

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