Low-threshold quantum dot laser and preparation method thereof

Abstract

The invention discloses a low-threshold quantum dot laser and a preparation method thereof. The low-threshold quantum dot laser comprises a quartz substrate, a silicon dioxide periodic grating, a quantum dot layer and a silicon dioxide protective layer which are sequentially stacked. The quantum dot layer is composed of densely stacked mercury selenide quantum dots with the diameter of 4.8 nm to 6.6 nm, mercury sulfide quantum dots with the diameter of 4 nm to 5.2 nm, and mercury selenide / mercury cadmium selenide / cadmium selenide core / alloy / shell structure quantum dots with the effective exciton diameter of 4.8 nm to 6.4 nm or mercury sulfide / mercury cadmium sulfide / cadmium sulfide core / alloy / shell structure quantum dots with the effective exciton diameter of 4 nm to 5 nm. According to the invention, environment-stable electron doping in the quantum dots is realized by controlling the size of the quantum dots, and the doped quantum dots are used as a gain medium of the laser, so that low gain threshold, low laser threshold, sustainable continuous laser output and designable output wavelength are realized.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronic devices, and in particular to a low-threshold quantum dot laser and a preparation method thereof. Background Art

[0002] Thanks to the quantum confinement effect, semiconductor quantum dots have shown many advantages as optical gain materials, such as gain wavelength that can be adjusted with size, potential low gain threshold, and temperature-insensitive optical gain threshold. However, the band edge states of quantum dots have at least two-fold degeneracy, and at least a portion of the quantum dots in the population must contain two or more excitons to achieve optical gain. In addition, the multi-excitons that induce optical gain in colloidal quantum dots will be rapidly consumed by Auger recombination, thereby limiting the optical gain lifetime. For lasers under continuous optical pumping, the pump rate must be greater than the rate of gain decay to maintain the optical gain state. The pump power that meets this requirement is close to or even exceeds the thermal limit that general quantum dots can withstand. Except for a few types of colloidal quantum dots that have achieved continuous laser output with a duration of sub-hours, most of the reported lasers rely on ultrafast pulse pumping.

[0003] In order to lower the gain threshold and achieve low-threshold quantum dot laser emission, the conduction band of the quantum dot can be pre-doped with electrons to "bleach" the ground state absorption, thereby lowering the gain threshold to below the basic single exciton limit, or even achieving zero-threshold optical gain. However, the electron doping methods currently used in quantum dot lasers to lower the gain threshold are not environmentally stable, and exposure of doped quantum dots to oxygen or water will lead to their dedoping. Summary of the invention

[0004] The present invention aims to solve the technical problems existing in the related art at least to a certain extent.

[0005] The purpose of the present invention is to provide a low-threshold quantum dot laser and a preparation method thereof, so as to obtain a laser transmitter with low gain threshold, low laser threshold, sustainable continuous laser output, designable emission wavelength and stable environment.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a low-threshold quantum dot laser on one hand, comprising a quartz substrate, a silicon dioxide periodic grating layer, a quantum dot layer and a silicon dioxide protective layer stacked in sequence, wherein the quantum dot layer is composed of densely stacked quantum dots.

[0007] Preferably, the quantum dots are mercury selenide quantum dots, mercury sulfide quantum dots, quantum dots with a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, or quantum dots with a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide.

[0008] Preferably, the quantum dots are mercury selenide quantum dots, which are in a zinc blende phase and have a diameter of 4.8 nm to 6.6 nm.

[0009] Preferably, the quantum dots are mercury sulfide quantum dots, which are in a sphalerite phase and have a diameter of 4 nm to 5.2 nm.

[0010] Preferably, the quantum dots are quantum dots of a core / alloy / shell structure of mercury selenide / cadmium selenide mercury / cadmium selenide, and the quantum dots of the core / alloy / shell structure of mercury selenide / cadmium selenide mercury / cadmium selenide are composed of a mercury selenide core in a sphalerite phase, a cadmium selenide amalgam layer coated on the surface of the mercury selenide core, and a cadmium selenide shell coated on the surface of the cadmium selenide amalgam layer, the cadmium element of the cadmium selenide amalgam layer gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dots of the core / alloy / shell structure of mercury selenide / cadmium selenide mercury / cadmium selenide is 4.8nm~6.4nm.

[0011] Preferably, the quantum dots are quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide, and the quantum dots of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide are composed of a mercury sulfide core in a sphalerite phase, a cadmium sulfide amalgam layer coated on the surface of the mercury sulfide core, and a cadmium sulfide shell coated on the surface of the cadmium sulfide amalgam layer, the cadmium element of the cadmium sulfide amalgam layer gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dots of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide is 4nm~5nm.

[0012] Preferably, the product of the grating period and the effective refractive index of the silicon dioxide periodic grating is equal to the band edge emission peak wavelength of the quantum dots in the quantum dot layer.

[0013] Preferably, the low-threshold quantum dot laser further comprises a pump source for exciting the quantum dot layer.

[0014] According to another aspect of the present invention, a method for preparing a low-threshold quantum dot laser is provided, comprising the following steps: S1. Preparation of quantum dots; S2, based on the quartz substrate, forming a silicon dioxide periodic grating layer on the quartz substrate by using a reactive ion etching method; S3, dispersing the quantum dots obtained in step S1 in a toluene solution to obtain a toluene dispersion of quantum dots, and then spin-coating the toluene dispersion of quantum dots on the silicon dioxide periodic grating layer obtained in step S2 to obtain a quantum dot layer; S4. On the quantum dot layer obtained in step S3, a silicon dioxide protective layer is obtained by spin coating spin-on glass.

[0015] Preferably, the quantum dots in step S1 are mercury selenide quantum dots, mercury sulfide quantum dots, quantum dots of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, or quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide. When the quantum dots are mercury selenide quantum dots, they are prepared by hot injection, and the diameter of the quantum dots is controlled by controlling the reaction temperature and the growth time. When the quantum dots are mercury sulfide quantum dots, they are prepared by hot injection method, and the diameter of the quantum dots is controlled by controlling the reaction temperature and growth time; When the quantum dot is a quantum dot of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, it is composed of a mercury selenide core, a cadmium selenide amalgam layer and a cadmium selenide shell, the mercury selenide core is prepared by a hot injection method, and the diameter of the mercury selenide core is controlled by controlling the reaction temperature and the growth time; the cadmium selenide amalgam layer and the cadmium selenide shell are prepared by a continuous ion layer adsorption reaction method, and the element proportion and thickness of the cadmium selenide amalgam layer are controlled by controlling the injection rate and injection amount of mercury ions, cadmium ions and selenium ions; the diameter of the effective exciton is controlled by controlling the diameter of the mercury selenide core and the thickness of the cadmium selenide amalgam layer; When the quantum dots are quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide, they are composed of a mercury sulfide core, a cadmium sulfide amalgam layer and a cadmium sulfide shell. The mercury sulfide core is prepared by a hot injection method, and the diameter of the mercury sulfide core is controlled by controlling the reaction temperature and the growth time; the cadmium sulfide amalgam layer and the cadmium sulfide shell are prepared by a continuous ion layer adsorption reaction method, and the element proportion and thickness of the cadmium sulfide amalgam layer are changed by controlling the injection rate and injection amount of mercury ions, cadmium ions and sulfur ions; the diameter of the effective exciton is controlled by controlling the diameter of the mercury sulfide core and the thickness of the cadmium sulfide amalgam layer.

[0016] Beneficial effects: 1. The present invention utilizes a size-controlled method to perform electron doping on the conduction band energy level. The electron doping in the quantum dots obtained by this method is stable in the atmospheric environment. The obtained quantum dot laser has the characteristics of low gain threshold, low laser threshold, programmable emission wavelength, and environmental stability.

[0017] 2. The present invention adopts a core / alloy / shell structure to construct a gentle interface barrier and passivate the surface of the quantum dots to suppress Auger recombination. The larger volume also helps the quantum dots to absorb pump photons more fully, which can further reduce the laser threshold to obtain sustainable continuous laser emission.

[0018] 3. The present invention uses densely packed quantum dots to form a quantum dot layer, thereby increasing the net mode gain of the quantum dot layer, which is beneficial to increasing the laser emission intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of a low-threshold quantum dot laser according to an embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the quantum dot structure of the present invention; Figure 2 (a) is a schematic diagram of the structure of mercury selenide quantum dots in Example 1 of the present invention; Figure 2 (b) is a schematic diagram of the structure of mercury sulfide quantum dots in Example 2 of the present invention; Figure 2 (c) is a schematic diagram of the quantum dot structure of the core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide in Example 3 of the present invention; Figure 2 (d) is a schematic diagram of the quantum dot structure of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide in Example 4 of the present invention.

[0021] Figure 3 Schematic diagram of the electron doping mechanism based on quantum dot size control of the present invention.

[0022] Figure 4 A schematic diagram of the gain threshold reduction mechanism of the doped quantum dots of the present invention; Figure 4 (a) is a schematic diagram of the gain threshold of quantum dots when all quantum dots in the quantum dot layer of the present invention are not doped with quantum dots; Figure 4 (b) is the 1S of all quantum dots in the quantum dot layer of the present invention. e Schematic diagram of the gain threshold of doped quantum dots when all energy levels are occupied by one doped electron; Figure 4 (c) is the 1S of all quantum dots in the quantum dot layer of the present invention. e Schematic diagram of the gain threshold of doped quantum dots when both energy levels are occupied by two doped electrons.

[0023] Figure 5 is an energy level position diagram of the quantum dots of the present invention; Figure 5 (a) is an energy level position diagram of the mercury selenide quantum dots in Example 1 of the present invention; Figure 5 (b) is an energy level position diagram of mercury sulfide quantum dots in Example 2 of the present invention.

[0024] Figure 6 It is the energy level doping probability diagram of the quantum dots of the present invention; Figure 6 (a) is an energy level doping probability diagram of the mercury selenide quantum dots in Example 1 of the present invention; Figure 6 (b) is an energy level doping probability diagram of mercury sulfide quantum dots in Example 2 of the present invention.

[0025] Figure 7 is a gain threshold diagram of the quantum dot of the present invention; Figure 7 (a) is a gain threshold diagram of the mercury selenide quantum dots in Example 1 of the present invention; Figure 7(b) is a gain threshold diagram of the mercury sulfide quantum dots in Example 2 of the present invention.

[0026] Figure 8 It is a pulse laser threshold diagram of the quantum dot of the present invention; Figure 8 (a) is a pulse laser threshold diagram of the mercury selenide quantum dots in Example 1 of the present invention; Figure 8 (b) is a pulse laser threshold diagram of mercury sulfide quantum dots in Example 2 of the present invention.

[0027] Fig. 9 is a continuous laser threshold diagram of the quantum dots of the present invention; Fig. 9 (a) is a continuous laser threshold diagram of the mercury selenide quantum dots in Example 1 of the present invention; Fig. 9 (b) is a continuous laser threshold diagram of the mercury sulfide quantum dots in Example 2 of the present invention.

[0028] Fig.10 It is the quantum dot pulse laser threshold diagram of the present invention; Fig.10 (a) is a quantum dot pulse laser threshold diagram of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide in Example 3 of the present invention; Fig.10 (b) is a quantum dot pulse laser threshold diagram of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide in Example 4 of the present invention.

[0029] Fig.11 It is the quantum dot continuous laser threshold diagram of the present invention; Fig.11 (a) is a continuous laser threshold diagram of quantum dots of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide in Example 3 of the present invention; Fig.11 (b) is a graph of the continuous laser threshold of quantum dots of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide in Example 4 of the present invention.

[0030] Fig.12 This is a diagram showing the saturation absorption coefficient values ​​of quantum dots with different diameters during the theoretical calculation process of the present invention.

[0031] Fig.13 is a graph showing the values ​​of the exciton lifetime of the bare core quantum dots of the present invention; Fig.13 (a) is a graph showing the values ​​of single exciton lifetimes of bare core quantum dots with different diameters and doping levels in the theoretical calculation process of the present invention; Fig.13 (b) is a graph showing the biexciton lifetime values ​​of bare core quantum dots of different diameters and doping levels in the theoretical calculation process of the present invention.

[0032] Fig.14 is the initial average number of excitons per quantum dot of the mercury selenide quantum dot with a diameter of 5.8 nm in Example 1 of the present invention. This is a graph of the photon number density in the cavity changing with time, calculated under the condition of 0.39.

[0033] Fig.15 This is a graph showing the absorption cross-sectional area values ​​of quantum dots with a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide and a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide at an excitation wavelength of 400 nm with different effective exciton diameters in the theoretical calculation process of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments, and they should not be understood as limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the description of the present invention, it should be understood that the terms used are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] Combine the following Figure 1-Figure 15 The invention describes a low-threshold quantum dot laser and a preparation method thereof.

[0036] Example 1: Figure 1 As shown, the present invention provides a low-threshold quantum dot laser, comprising a quartz substrate 1, a silicon dioxide periodic grating 2, a quantum dot layer 3 and a silicon dioxide protective layer 4 which are sequentially arranged upward.

[0037] Its working principle is: the low threshold quantum dot laser is subjected to an energy greater than or equal to the second hole energy level 1P of the quantum dot in the quantum dot layer 3. h and the second electron energy level 1P e The energy gap between the photons excites the quantum dots in the quantum dot layer 3. e Energy Levels and 1P e The energy level is doped with different numbers of electrons in an unexcited state, and the laser emission of the low-threshold quantum dot laser can be output from the upper surface of the silicon dioxide protective layer 4 or the lower surface of the quartz substrate 1 .

[0038] Furthermore, the product of the grating period and the effective refractive index of the silicon dioxide periodic grating 2 is equal to the band edge emission peak wavelength of the quantum dots in the quantum dot layer 3 .

[0039] Such a configuration can provide optical feedback for the gain medium of the laser, namely the quantum dot layer 3, thereby obtaining laser emission.

[0040] Furthermore, the low-threshold quantum dot laser also includes a pump source for exciting the quantum dot layer 3 .

[0041] The pump source can emit pulsed light or continuous light, and the wavelength of the emitted light is 400nm. e may be occupied by two doping electrons, resulting in a change from the first hole level 1S h To the first electron energy level 1S e The exciton transition of the energy level is completely blocked, therefore, the emission photon energy of the pump source should be greater than or equal to the second hole energy level 1P of the quantum dot in the quantum dot layer 3. h and the second electron energy level 1P e Pump photons are injected from the upper surface of the silicon dioxide protective layer 4 or the lower surface of the quartz substrate 1 to excite the low-threshold quantum dot laser, so that the laser emission of the laser is output from the upper surface of the silicon dioxide protective layer 4 or the lower surface of the quartz substrate 1.

[0042] Furthermore, the quantum dot layer 3 is composed of densely stacked quantum dots. Densely stacking the quantum dots can increase the net mode gain of the quantum dot layer, which is beneficial to improving the laser emission intensity.

[0043] Furthermore, the quantum dots are mercury selenide quantum dots 5, and their specific structure is as follows Figure 2 As shown in (a), the mercury selenide quantum dots 5 are in the sphalerite phase, with a diameter of 4.8 nm to 6.6 nm.

[0044] The present invention obtains electron-doped quantum dots based on a size-controlled method, and utilizes the electron-doped quantum dots to reduce the gain threshold of the quantum dot population, such as Figure 3 As shown, for small-sized quantum dots 16, strong quantum confinement effects give them a large band gap, with a double degenerate lowest electronic energy level 1S e Far above the ambient Fermi level of 15, 1S e There will be no electron doping at the energy level; the quantum confinement effect in medium-sized quantum dots 17 is weaker than that in small-sized quantum dots 16, and the band gap of the quantum dots becomes narrower, 1S e The energy level moves down to the ambient Fermi level 15, 1S e The energy level is occupied by electrons for about 50%. e There is an impurity electron on the energy level, so from 1S h Energy level to 1S e The ground state absorption of the energy level is partially blocked; the quantum confinement effect in large-sized quantum dots 18 is the weakest, and its band gap is the narrowest, 1S e The energy level is below the ambient Fermi level 15, which will lead to 1S eThe probability that the energy level is occupied by electrons is much greater than 50%. e If there are two doped electrons on the energy level, the ground state absorption is completely bleached. Figure 4 As shown in (a), assuming that the quantum dots in the quantum dot layer are uniformly doped and excited, when all the quantum dots in the quantum dot layer are not doped with quantum dots, the gain threshold is 1S of all the quantum dots in the quantum dot layer. e There is an excited electron at the energy level, that is, the gain threshold expressed by the average exciton per quantum dot is At this time, under the action of external photons 19, the probability of stimulated emission and stimulated absorption is equal, and the number of emitted photons 20 is the same as that of external photons 19; Figure 4 As shown in (b), when the 1S of all quantum dots in the quantum dot layer e If all energy levels are occupied by a doped electron, the gain threshold is 1S when half of the quantum dots in the quantum dot layer are occupied. e There is an excited electron on the energy level, that is, the gain threshold is ;like Figure 4 As shown in (c), when the 1S of all quantum dots in the quantum dot layer e The energy levels are occupied by two doped electrons, then the gain threshold is that there are no excited electrons in all quantum dots in the quantum dot layer, that is, the gain threshold is .

[0045] The calculation model based on which the diameter range of the mercury selenide quantum dots 5 is selected is as follows: Step 1: Determine the positions of various energy levels of mercury selenide quantum dots 5 with different diameters.

[0046] In order to determine the electron doping status of HgSe quantum dots 5 in the sphalerite phase with different diameters, it is necessary to calculate the energy level position of the quantum dots as the diameter changes, as well as the relative position of each energy level to the ambient Fermi level. First, the 1S e Energy level, 1P e Energy levels and 1D e Energy level relative to 1S h Energy difference of energy levels: (1) In the formula, is the band gap of the semiconductor material, is the Kane coefficient, is the mass of the free electron, for 1S e Energy level, 1P e Energy levels and 1D e The energy levels are: , and ,in is the radius of the quantum dot. For HgSe quantum dot 5, , The relative positions of the energy levels of HgSe quantum dots 5 with different diameters to the ambient Fermi level were determined based on the energy difference of 0.8 eV between the valence band top of HgSe material and the ambient Fermi level. and hole effective mass The ratio takes into account 1S h The energy level shifts slightly with the diameter of the quantum dot. For HgSe quantum dots 5, , Take 0.05 m 0, 0.67 m 0. The position of the ambient Fermi level relative to the vacuum level (0 eV) is taken as -4.3 eV, and the changes with the quantum dot material and size can be ignored, so as to obtain the position of each energy level relative to the vacuum level of the mercury selenide quantum dot 5 with the change of diameter, as shown in Figure 5 As shown in (a).

[0047] Step 2: Calculate the electron doping conditions in the mercury selenide quantum dots 5 with different diameters.

[0048] Based on the Fermi-Dirac statistical rate distribution of electrons in each energy level of the quantum dot under thermal equilibrium, the 1S e Energy level, 1P e Energy levels and 1D e The probability that an energy level is occupied by an electron: (2) In the formula, Represents quantum energy level The energy level is 1S e Energy level, 1P e Energy level or 1D e Energy level energy, For quantum energy level The probability of being occupied by an electron, is the Fermi energy, is the Boltzmann constant, is the thermodynamic temperature. e Energy level, 1P e Energy level, 1D e The curve of the electron occupancy rate at the energy level changing with the diameter of the quantum dot is as follows Figure 6 As shown in (a). Due to this distribution law, there is 1S in the quantum dot group. e The quantum dot branches with electron doping numbers of 0, 1 and 2 at the energy level (2-fold degeneracy) can be expressed by the following formula: (3) In the formula, Indicates 1S e Doped at energy level n The proportion of quantum dots with 1P electrons in the group. In addition, there are 1P e Quantum dot branches with electron doping numbers of 0 to 6 on energy levels (6-fold degeneracy): (4) In the formula, Indicates 1P e The proportion of quantum dots doped with m electrons at the energy level in the population.

[0049] Step 3: Calculate the gain threshold of HgSe quantum dots 5 with different diameters.

[0050] After completing the analysis of the electron doping in the quantum dots, we can further calculate the gain threshold of HgSe quantum dots 5 with different diameters. Total stimulated emission rate When they are equal, the corresponding average number of excitons per quantum dot is the optical gain threshold of the band edge energy level. , and Given by: (5) (6) In the formula, is the transition probability of a photon in a single spin-allowed transition, , and They are Doped at energy level When there are 2 electrons, the proportion of quantum dots containing 0, 1, and ≥2 excitons in the population. , and Collectively known as 1S e The number of electrons doped at the energy level is n If high-energy pulse light excitation is used, the proportion of quantum dots containing N excitons in the population can be expressed by the Poisson statistic: (7) In the formula, The average number of excitons per quantum dot is The percentage of quantum dots containing N excitons in a quantum dot population. Consider 1S e The proportion of three branches with 0, 1 and 2 electrons doped at the energy level in the quantum dot population, and the distribution of excitons in the corresponding branches , and It can be expressed as follows: (8) (9) (10) In addition, all quantum dots in the quantum dot group are 1S e Under the condition of double electron doping at the energy level, there is also 1P e There are seven branches with 0 to 6 electrons doped at the energy level. The exciton distribution in the corresponding branches can be expressed as follows: (11) (12) (13) In the formula, , and 1S respectively e The energy level is doped with 2 electrons, 1P e Doped at energy level When there are 2 electrons, the proportion of quantum dots containing 0, 1, and ≥2 excitons in the population. , and Collectively known as 1S e The number of electrons doped at the energy level is 2, and 1P e The number of electrons doped at the energy level is m The curve of the gain threshold of HgSe quantum dot 5 as a function of quantum dot diameter is shown in Figure 7 As shown in (a).

[0051] Step 4: Calculate the pulse laser threshold of mercury selenide quantum dots 5 with different diameters.

[0052] The calculation of quantum dot pulse laser threshold is more complicated than gain threshold. It is necessary to establish the overall dynamic equation describing the quantum dot-light field coupling system, and then calculate the average number of excitons per quantum dot at different initial values. Under the condition of , the overall dynamic equation is solved to obtain the function of the number of photons in the cavity changing with time , and then through analysis Get the pulse laser threshold We first established the kinetic equation describing the evolution of the exciton number in the undoped quantum dot branch during the lasing process: (14) (15) (16) In this equation, is the photon density in the cavity, and are the single exciton and biexciton lifetimes of undoped quantum dots, respectively. We also established e The dynamic equation of the exciton number evolution in the laser process of the branch of energy level single electron doping: (17) (18) (19) in, and 1S respectively e The single exciton and biexciton lifetimes of single electron-doped quantum dots at the energy level are also established to describe the 1S e Double electron doping and 1P e Doped at energy level indivual The dynamic equation of the evolution of the exciton number in the laser process is: (20) (twenty one) (twenty two) in, and 1S respectively e Double electron doping and 1P e Doped at energy level Single-exciton and biexciton lifetimes in quantum dots with 1 electron.

[0053] like Figure 6 As shown in (a), for HgSe quantum dots 5 with a diameter less than or equal to 5.8 nm, due to 1P e The probability of an energy level being occupied by electrons is extremely small, and it can be considered that there are only undoped, 1S e Energy level single electron doping, 1S e Energy level double electron doping and 1P e Considering the influence of the laser behavior in these three branches on the number of cavity photons, the following dynamic equation describing the evolution of the number of photons in the cavity can be established: (twenty three) In the formula, is the quantum dot density in the gain medium, is the photon lifetime in the cavity. For HgSe quantum dots 5 with a diameter less than or equal to 5.8 nm, the combination of equations (23) and (14) to (22) constitutes a set of total dynamic equations describing the quantum dot-light field coupling system. Figure 6 As shown in (a), for HgSe quantum dots 5 with a diameter greater than 5.8 nm, due to 1S e The probability that the energy level is occupied by electrons is close to 100%, and 1P e The electron occupancy rate on the energy level begins to increase gradually, and it can be considered that there is only 1S in the group. e Double electron doping and 1P e Seven branches with 0 to 6 electrons are doped at the energy level, and the following dynamic equation is used to describe the evolution of the number of photons in the cavity: (twenty four) For this equation, there exists as well as For HgSe quantum dots 5 with a diameter greater than 5.8 nm, the combination of equations (24) and (20) to (22) constitutes another set of overall dynamic equations describing the quantum dot-light field coupling system.

[0054] In order to start cavity photon accumulation, it is necessary to set the initial value of the total kinetic equation. At the initial moment, the exciton distribution of each doping degree quantum dot branch is determined by the initial average number of excitons per quantum dot. Combining equations (7) to (13), we can calculate that the photon number density at the initial moment is set to 1 photon per cubic centimeter, that is, In addition, the photon lifetime in the cavity is set to 10 ps, ​​the transition probability of a single spin-allowed photon in the transition The quantum dot saturation gain coefficient Determine that there is the following relationship: (25) Where, the refractive index of the gain medium is Assuming it is 1.5, is the speed of light in a vacuum, and the density of quantum dots in the gain medium The volume of quantum dots and quantum dot packing density related to, exist For the quantum dot layer 3, is 0.4 and does not change with the change of the volume of quantum dots in the quantum dot layer 3. Saturation gain coefficient and The reciprocal of is approximately linear. We assume that the diameter of the quantum dots is 3nm and 12nm respectively. 500cm -1 and 100cm-1 , other diameter quantum dots G 0 With these two values ​​as reference, the inverse of the relative quantum dot volume presents a linear distribution. The values ​​of the saturation absorption coefficient of quantum dots with different diameters are as follows Fig.12 The single exciton Auger lifetime and biexciton Auger lifetime of quantum dots with different diameters and doping conditions are calculated based on the volume scale of quantum dots and the statistical scale of the number of carriers. The following is a volume scale model used to calculate the biexciton Auger lifetime of undoped quantum dots. : (26) In the formula, is a proportionality factor, taken as 1ps / nm 3 According to the statistical model of the carrier population, the number of Auger recombination paths is proportional to the product of the number of all possible interband transitions and the number of carriers that can receive the energy released by a given interband transition. Therefore, for a Electronics and The exciton state of a hole, the Auger lifetime It can be expressed as: (27) In the formula, is a constant, which represents the recombination time of a single Auger recombination path. By using equation (27), we can determine the single exciton Auger lifetime, biexciton Auger lifetime and The ratio of is calculated based on formula (26) , combined with the above proportional relationship, the single exciton Auger lifetime and biexciton Auger lifetime of quantum dots with different doping levels can be determined. For the single exciton radiation lifetime and biexciton radiation lifetime of quantum dots with different doping levels, first assume that the single exciton radiation lifetime of undoped quantum dots is is 50ns and does not change with the diameter of the quantum dot. It is believed that the single exciton of the undoped quantum dot is purely radiative, that is, Single exciton lifetime compared to undoped quantum dots There exists Based on the relationship between the radiation lifetime and the number of carriers at the 1S energy level, the single exciton radiation lifetime of the doped quantum dot is determined to be In addition, regardless of whether the quantum dots are doped or not, their biexciton radiation lifetime is The single exciton, biexciton Auger and radiation lifetimes of quantum dots with different diameters and doping levels have been obtained. According to the following relationship, the single exciton and biexciton lifetimes of quantum dots with different diameters and doping levels can be calculated: (28) In the formula is the exciton lifetime, Represents the radiation lifetime. The single exciton lifetime values ​​of quantum dots with different diameters and doping levels are as follows: Fig.13 As shown in (a), the biexciton lifetimes of quantum dots with different diameters and doping levels are as follows: Fig.13 As shown in (b).

[0055] After determining all the initial values ​​and values ​​in the total kinetic equation, we can solve it and obtain the different initial average number of excitons per quantum dot. The function of the number of photons in the cavity changing with time under the condition Taking the mercury selenide quantum dot 5 with a diameter of 5.8nm as an example, Calculated under the conditions like Fig.14 In order to calculate the pulse laser threshold , need to Analyze and define The delay between the peak time and the initial time is ,along with The increase of The law of change is that it increases first, If a certain critical value is reached decreases rapidly, and this critical value is the laser threshold The curve of the pulse laser threshold of mercury selenide quantum dot 5 changing with the quantum dot diameter is shown in Figure 8 As shown in (a).

[0056] Step 5: Calculate the continuous laser threshold of mercury selenide quantum dots 5 with different diameters.

[0057] For the calculation of the continuous laser threshold of quantum dots, it is necessary to establish the exciton distribution equation of each doping degree quantum dot branch under continuous light pumping before the laser is established in a steady state, with 1S e Examples of single-level doping branches: (29) (30) (31) In the equation, the 0 on the far right of the equation indicates a steady state. is the continuous optical pump intensity expressed as photon flux density, is the absorption cross-section of the quantum dot at the excitation wavelength. and the intrinsic absorption coefficient The following relationship exists: (32) For HgSe quantum dots 5, at an excitation wavelength of 400 nm, Take 4.63×105cm-1. Since the proportion of this branch in the quantum dot population is , so there is Solving equations (29) to (31), we can obtain the steady-state , and relatively Function: (33) (34) (35) After obtaining the exciton distribution of quantum dot branches at different doping levels in steady state, the gain coefficient of the quantum dot group in steady state can be calculated according to the following formula : (36) In the formula, is the refractive index of the gain medium. For this equation, we have as well as Substituting the exciton distribution of quantum dot branches at different doping levels in the steady state into equation (36), we can establish and The pulse laser threshold Substituting the corresponding initial exciton distribution into equation (36), the laser threshold gain coefficient can be calculated If the gain coefficient of the quantum dot population in the steady state of continuous optical pumping is Just equal to the gain coefficient corresponding to the pulse laser threshold , then the continuous light pump intensity that satisfies this condition is The continuous laser threshold The curve of the continuous laser threshold of mercury selenide quantum dot 5 changing with the quantum dot diameter is shown in Fig. 9 As shown in (a).

[0058] This embodiment uses zinc blende phase mercury selenide quantum dots 5 with a diameter of 4.8nm to 6.6nm as the gain medium. Figure 5 (a) and Figure 6 As shown in (a), due to the weakened quantum confinement effect, when the diameter of the HgSe quantum dot 5 is large enough, its first electronic energy level 1S e will shift to the vicinity of the ambient Fermi level, which will cause 1S e The energy level is occupied by doped electrons in the unexcited state, and as the diameter of the quantum dot increases further, the 1S e The energy level will further move down below the ambient Fermi level, which will lead to 1S e The probability of an energy level being occupied by doped electrons increases. Figure 6 (a) and Figure 7 As shown in (a), the diameter of the HgSe quantum dots 5 is selected to be larger than 4.8 nm, which can ensure 1S e The probability that the energy level is occupied by electrons is large enough, that is, greater than 0.78, so that the gain threshold of the mercury selenide quantum dot 5 is lower than , as the diameter of the quantum dot increases further, the gain threshold will continue to decrease. Figure 6 (a) and Figure 8 As shown in (a), if the diameter of the HgSe quantum dot 5 is greater than 6.6 nm, the second electron energy level 1P e The probability of the electron occupying the 1P e The doped electrons on the energy level do not help the bleaching of the ground state absorption, but provide an additional pathway for Auger recombination. Too fast an Auger recombination rate is not conducive to the establishment of lasers and will lead to an increase in the laser threshold. Figure 8 As shown in (a), using zinc blende phase mercury selenide quantum dots 5 with a diameter of 4.8nm to 6.6nm as the gain medium of the laser, the pulse laser threshold expressed as the average number of excitons per quantum dot can be achieved. The pulsed laser emission is less than 1, and the emission wavelength of the exciter covers the range of 1500nm~2100nm. Among them, using 5.8nm diameter mercury selenide quantum dots 5 as the gain medium, the laser has achieved Pulsed laser emission.

[0059] This embodiment also provides a method for preparing a low-threshold quantum dot laser, which is used to prepare the above-mentioned low-threshold quantum dot laser. The preparation method comprises: (1) Using the hot injection method, the zinc blende phase mercury selenide quantum dots 5 with a diameter range of 4.8nm~6.6nm were prepared by controlling the reaction temperature and growth time; (2) providing a quartz substrate 1, and forming a silicon dioxide periodic grating 2 on the quartz substrate 1 by using a reactive ion etching method; (3) dispersing the mercury selenide quantum dots 5 in a toluene solution with a concentration of 20 mg / ml to obtain a toluene dispersion of the zinc blende phase mercury selenide quantum dots 5, and then spin coating the toluene dispersion of the zinc blende phase mercury selenide quantum dots 5 on the silicon dioxide periodic grating 2 at a speed of 2500 rpm to form a quantum dot layer 3; (4) On the quantum dot layer 3 obtained in step (3), 500F spin-on glass produced by Filmtronics was spin-coated at a rotation speed of 3000 rpm to obtain a silicon dioxide protective layer 4.

[0060] Example 2: Based on Example 1, the quantum dots in this example are mercury sulfide quantum dots 6, and their specific structure is as follows Figure 2As shown in (b), the mercury sulfide quantum dots 6 are in the sphalerite phase, with a diameter of 4 nm to 5.2 nm.

[0061] The calculation model based on which the diameter range of the mercury sulfide quantum dots 6 is selected is as follows: Steps 1 to 3 are the same as in Example 1. Formulas (1) to (13) are used to obtain: Figure 5 The positions of the energy levels of the mercury sulfide quantum dot 6 shown in (b) relative to the vacuum energy level as the diameter changes, as shown in Figure 6 (b) shows the 1S of HgS quantum dot 6 e Energy level, 1P e Energy level, 1D e The curve of the electron occupancy rate at the energy level changing with the diameter of the quantum dot, such as Figure 7 (b) shows a curve of the gain threshold of the mercury sulfide quantum dot 6 as a function of the quantum dot diameter. It should also be noted that the mercury sulfide quantum dot 6 , The values ​​are 0.65eV and 9.00eV respectively; the energy difference between the valence band top of mercury sulfide material and the ambient Fermi level is 1.15eV; the , Take 0.036 respectively m 0, 0.31 m 0.

[0062] Step 4 is the same as Example 1, but the quantum dot diameters adapted by formulas (23) and (24) are different: for mercury sulfide quantum dots 6 with a diameter less than or equal to 4.6 nm, formula (23) and formula (14) to formula (22) are combined to form a set of total dynamic equations describing the quantum dot-light field coupling system; for mercury sulfide quantum dots 6 with a diameter greater than 4.6 nm, formula (24) and formula (20) to formula (22) are combined to form another set of total dynamic equations describing the quantum dot-light field coupling system.

[0063] Finally, according to the calculation results, Figure 8 (b) is a graph showing the pulse laser threshold of the mercury sulfide quantum dot 6 as a function of the quantum dot diameter.

[0064] Step 5 is the same as in Example 1, and finally the following is obtained: Fig. 9 (b) shows a curve of the continuous laser threshold of the mercury sulfide quantum dot 6 as a function of the quantum dot diameter. It should also be noted that the mercury sulfide quantum dot 6 at an excitation wavelength of 400 nm Take 2.70×10 5 cm -1 .

[0065] This embodiment uses zinc blende phase mercury sulfide quantum dots 6 with a diameter of 4nm to 5.2nm as the gain medium. Figure 5 (b) and Figure 6 As shown in (b), due to the weakened quantum confinement effect, when the diameter of the mercury sulfide quantum dot 6 is large enough, its first electronic energy level 1S e will shift to the vicinity of the ambient Fermi level, which will cause 1S e The energy level is occupied by doped electrons in the unexcited state, and as the diameter of the quantum dot increases further, the 1S e The energy level will further move down below the ambient Fermi level, which will lead to 1S e The probability of an energy level being occupied by doped electrons increases. Figure 6 (b) and Figure 7 As shown in (b), the diameter of the mercury sulfide quantum dots 6 is selected to be larger than 4nm, which can ensure 1S e The probability that the energy level is occupied by electrons is large enough, i.e., greater than 0.90, so that the gain threshold of mercury sulfide quantum dots 6 is lower than , as the diameter of the quantum dot increases further, the gain threshold will continue to decrease. Figure 6 (b) and Figure 8 As shown in (b), if the diameter of the mercury sulfide quantum dot 6 is greater than 5.2nm, the second electron energy level 1P e The probability of the electron occupying the 1P e The doped electrons on the energy level do not help the bleaching of the ground state absorption, but provide an additional pathway for Auger recombination. Too fast an Auger recombination rate is not conducive to the establishment of lasers and will lead to an increase in the laser threshold. Figure 8 As shown in (b), using zinc blende phase mercury sulfide quantum dots 6 with a diameter of 4nm~5.2nm as the gain medium of the laser, the pulse laser threshold expressed as the average number of excitons per quantum dot can be achieved. The laser emits a pulsed laser with a wavelength of less than 1, and the emission wavelength of the exciter covers the range of 1100nm~1250nm. Among them, the laser achieves Pulsed laser emission.

[0066] This embodiment also provides a method for preparing a low-threshold quantum dot laser, which is used to prepare the above-mentioned low-threshold quantum dot laser. The difference between the preparation method and the embodiment 1 is that different quantum dots are prepared in the first step: (1) Using the hot injection method, zinc blende phase mercury sulfide quantum dots 6 with a diameter range of 4nm~5.2nm were prepared by controlling the reaction temperature and growth time.

[0067] like Fig. 9 As shown in FIG. 1 , the continuous laser threshold expressed by the excitation light intensity in a laser using mercury selenide quantum dots 5 or mercury sulfide quantum dots 6 as a gain medium More than 30 KW cm -2 and 300 KW cm -2 , exceeding the thermal limit that general quantum dots can withstand, making it difficult to obtain sustainable continuous laser emission. This is mainly because the Auger recombination rate of bare core quantum dots is still too fast, so a core / alloy / shell structure is needed to construct a gentle interface barrier and passivate the surface of the quantum dots to suppress Auger recombination. A larger volume also helps the quantum dots absorb pump photons more fully.

[0068] Example 3: Based on Example 1, the quantum dots described in this example are quantum dots 7 of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, and the specific structure thereof is as follows: Figure 2 As shown in (c), the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide is composed of a mercury selenide core 8 in a sphalerite phase, a cadmium selenide amalgam layer 9 coated on the surface of the mercury selenide core 8, and a cadmium selenide shell 10 coated on the surface of the cadmium selenide amalgam layer 9; the cadmium element of the cadmium selenide amalgam layer 9 gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide is 4.8nm~6.4nm.

[0069] The calculation method based on which the effective exciton diameter range of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide is selected is as follows: The calculation of the laser threshold of quantum dots with core / alloy / shell structures still uses the same model as that of bare core quantum dots. It should be pointed out that the energy level position and doping degree of quantum dots with core / alloy / shell structures with a specific effective exciton diameter are consistent with those of the corresponding bare core quantum dots with the same diameter. The core / alloy / shell structure only affects the Auger lifetime and absorption cross-sectional area of ​​the quantum dots. For the calculation of the total absorption cross-sectional area of ​​quantum dots with core / alloy / shell structures, the volume of the core material is calculated using the effective exciton diameter, and the volume of the shell material is calculated using the difference between the total diameter of the quantum dots and the effective exciton diameter. Then, based on the intrinsic absorption coefficients of the core and shell materials, the volume of the core material is calculated. The total absorption cross-sectional area is calculated by combining formula (32). The intrinsic absorption coefficient of the cadmium selenide shell 10 at an excitation wavelength of 400 nm is 0.80×10 5 cm -1 The absorption cross-sectional area values ​​of the core / alloy / shell structured quantum dots 7 of HgSe / CdSe / CdSe with different effective exciton diameters at an excitation wavelength of 400 nm are as follows: Fig.15As shown. In addition, the suppression of Auger recombination by the core / alloy / shell structure mainly comes from the spatial separation of electron-hole pairs and the gentle confinement potential. The effective exciton diameter has little effect on the Auger lifetime. Therefore, assuming that the biexciton lifetime of a quantum dot with a core / alloy / shell structure of 12nm in total diameter is 1.5ns in the undoped state, and ignoring its change with the effective exciton diameter, the single exciton and biexciton lifetimes of quantum dots with different doping degrees of core / alloy / shell structures can be calculated based on the statistical scale of the number of carriers. The specific values ​​are shown in the table below: Table 1. Single exciton lifetimes of quantum dots with core / alloy / shell structures at different doping levels

[0070] The table shows the single exciton (X), 1S e Energy level of single exciton (X-) and 1S in single-doped quantum dots e Energy level double doping and 1P e The lifetime of a single exciton (X2-,0-~X2-,6-) of a quantum dot doped with 0-6 extra electrons at the energy level ( )、Radiation Lifetime( ) and the Auger lifetime ( ).

[0071] Table 2. Biexciton lifetimes of quantum dots with core / alloy / shell structures at different doping levels

[0072] The table shows the biexcitons (XX), 1S e Energy level of biexcitons (XX-) and 1S in single-doped quantum dots e Energy level double doping and 1P e The lifetime of biexcitons (XX2-,0-~XX2-,6-) of quantum dots doped with 0-6 extra electrons at the energy level ( )、Radiation Lifetime( ) and the Auger lifetime ( ).

[0073] Substituting the single exciton and biexciton lifetimes of the above-mentioned quantum dots with different doping levels of the core / alloy / shell structure, and the absorption cross-sectional areas of the quantum dots 7 with core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide with different effective exciton diameters into steps 4 to 5 of Example 1, a curve of the pulsed laser threshold of the quantum dots 7 with core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide as the effective exciton diameter of the quantum dots with the core / alloy / shell structure can be obtained, as shown in FIG. Fig.10As shown in (a). The curve of the continuous laser threshold of the quantum dot 7 with the core / alloy / shell structure of mercury selenide / cadmium selenide and the effective exciton diameter of the quantum dot with the core / alloy / shell structure is shown in Fig.11 As shown in (a).

[0074] The total diameter of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide in this example is 12nm. The effective exciton diameter of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide is equal to the diameter of the mercury selenide quantum dot 5 with the same band edge emission wavelength as the quantum dot of the core / alloy / shell structure. The cadmium element proportion of the cadmium selenide mercury alloy layer 9 gradually increases linearly from 0% to 100% from the inside to the outside, and correspondingly, the mercury element decreases linearly from 100% to 0%. In the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide, the band gap width of the cadmium selenide shell 10 is much larger than that of the mercury selenide core 8, so the effect of the shell of the quantum dot of the core / alloy / shell structure on the effective exciton diameter can be ignored, and the effective exciton diameter is jointly determined by the core diameter, the alloy layer composition and the thickness. The effective exciton diameter of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide is equal to the sum of the diameter of the mercury selenide core 8 and the thickness of the cadmium selenide mercury alloy layer 9, and the diameter of the mercury selenide core 8 cannot be less than 2nm to prevent excessive defect states, and the thickness of the cadmium selenide mercury alloy layer 9 cannot be less than 2nm to prevent the failure to form a smooth interface barrier.

[0075] In this example, a cadmium selenide mercury alloy layer 9 with a cadmium content gradually increasing from the inside to the outside is coated on the surface of the zinc blende phase mercury selenide core 8 to construct a gentle interface barrier and passivate the surface of the quantum dot, thereby suppressing Auger recombination and further reducing the laser threshold to obtain sustainable continuous laser emission. Using the quantum dot 7 with a core / alloy / shell structure of mercury selenide / cadmium selenide / mercury cadmium selenide / cadmium selenide with an effective exciton diameter of 4.8nm~6.4nm as the gain medium, the first electron energy level 1S e has a larger electron occupation probability, and the second electron energy level 1P e The probability of electron occupation on will not be too large. Fig.10 (a) shows the pulse laser threshold of the laser expressed as the average number of excitons per quantum dot. As low as 0.52 and below, using the quantum dots 7 of core / alloy / shell structure of HgSe / CdSe / CdSe with an effective exciton diameter of 5.8nm as the gain medium, the laser achieved Pulsed laser emission. Fig.11 As shown in (a), using the quantum dots 7 of HgSe / CdSe / CdSe core / alloy / shell structure with effective exciton diameter of 4.8nm~6.4nm as the gain medium, the laser also achieves a continuous laser threshold expressed in terms of the excitation light intensity. Less than 1 KW cm -2 The laser emission wavelength covers 1500nm~2000nm. The laser uses the quantum dots 7 of core / alloy / shell structure of mercury selenide / cadmium selenide with an effective exciton diameter of 5.8nm as the gain medium. Continuous laser emission.

[0076] This embodiment provides a method for preparing a low-threshold quantum dot laser, which is used to prepare the above-mentioned low-threshold quantum dot laser. The difference between the preparation method and embodiment 1 is only that different quantum dots are prepared in the first step: (1) The mercury selenide core 8 is prepared by a hot injection method, and the diameter of the mercury selenide core 8 is controlled by controlling the reaction temperature and the growth time. The cadmium selenide mercury alloy layer 9 is prepared by a continuous ion layer adsorption reaction method, and the element ratio and thickness of the cadmium selenide mercury alloy layer 9 are controlled by controlling the injection rate and injection amount of mercury ions, cadmium ions and selenium ions. The cadmium selenide shell 10 is prepared by a continuous ion layer adsorption reaction method. The effective exciton diameter of the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide is controlled by controlling the diameter of the mercury selenide core 8 and the thickness of the cadmium selenide mercury alloy layer 9, and finally the quantum dot 7 of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide with a total diameter of 12nm and an effective exciton diameter ranging from 4.8nm to 6.4nm is obtained.

[0077] Example 4: Based on Example 3, the quantum dots described in this example are quantum dots 11 with a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide, and the specific structure thereof is as follows: Figure 2 As shown in (d), the quantum dot 11 of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide is composed of a mercury sulfide core 12 in a sphalerite phase, a cadmium sulfide amalgam layer 13 coated on the surface of the mercury sulfide core 12, and a cadmium sulfide shell 14 coated on the surface of the cadmium sulfide amalgam layer 13; the cadmium element of the cadmium sulfide amalgam layer 13 gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dot 11 of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide is 4nm~5nm.

[0078] The calculation method for selecting the effective exciton diameter of the quantum dot 11 of the core / alloy / shell structure of mercury sulfide / cadmium sulfide is the same as that of Example 3. It should be noted that the intrinsic absorption coefficient of the cadmium sulfide shell 14 at an excitation wavelength of 400 nm is 0.68×10 5 cm -1 . It can be concluded that Fig.15 The absorption cross-sectional area value of the quantum dot 11 of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide at an excitation wavelength of 400nm is shown; Fig.10 The curve of the pulse laser threshold of the quantum dot 11 with a core / alloy / shell structure of mercury sulfide / cadmium sulfide / mercury cadmium sulfide / cadmium sulfide as a function of the effective exciton diameter of the quantum dot with the core / alloy / shell structure shown in (b); Fig.11 (b) is a graph showing the continuous laser threshold of the quantum dot 11 with a core / alloy / shell structure of mercury sulfide / cadmium sulfide as a function of the effective exciton diameter of the quantum dot with the core / alloy / shell structure.

[0079] In this example, a cadmium sulfide mercury amalgam layer 13 with a cadmium content gradually increasing from the inside to the outside is coated on the surface of the zinc blende phase mercury sulfide core 12 to construct a gentle interface barrier and passivate the surface of the quantum dot, thereby suppressing Auger recombination and further reducing the laser threshold to obtain sustainable continuous laser emission. Using the quantum dot 11 with a core / alloy / shell structure of mercury sulfide / cadmium sulfide / mercury cadmium sulfide with an effective exciton diameter of 4nm~5nm as the gain medium, the first electron energy level 1S e has a larger electron occupation probability, and the second electron energy level 1P e The probability of electron occupation on will not be too large. Fig.10 (b) shows the pulse laser threshold of the laser expressed as the average number of excitons per quantum dot. As low as 0.35 and below, using the quantum dots 11 of core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide with an effective exciton diameter of 4.6nm as the gain medium, the laser achieved Pulsed laser emission. Fig.11 As shown in (b), using the quantum dots 11 of core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide with an effective exciton diameter of 4nm~5nm as the gain medium, the laser also achieves a continuous laser threshold expressed in terms of the excitation light intensity. Less than 1 KW cm -2 The laser emission wavelength covers the range of 1100nm~1230nm. The laser uses the quantum dots 11 with core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide with an effective exciton diameter of 4.8nm as the gain medium. Continuous laser emission.

[0080] This embodiment provides a method for preparing a low-threshold quantum dot laser, which is used to prepare the above-mentioned low-threshold quantum dot laser. The difference between the preparation method and embodiment 3 is only that different quantum dots are prepared in the first step: (1) The mercury sulfide core 12 is prepared by a hot injection method, and the diameter of the mercury sulfide core 12 is controlled by controlling the reaction temperature and the growth time. The cadmium sulfide mercury alloy layer 13 is prepared by a continuous ion layer adsorption reaction method, and the element ratio and thickness of the cadmium sulfide mercury alloy layer 13 are controlled by controlling the injection rate and injection amount of mercury ions, cadmium ions and sulfur ions. The cadmium sulfide shell 14 is prepared by a continuous ion layer adsorption reaction method. The effective exciton diameter of the quantum dots 11 of the core / alloy / shell structure of mercury sulfide / cadmium sulfide / mercury cadmium sulfide / cadmium sulfide is controlled by controlling the diameter of the mercury sulfide core 12 and the thickness of the cadmium sulfide mercury sulfide mercury sulfide / cadmium sulfide mercury sulfide / cadmium sulfide, and finally the quantum dots 11 of the core / alloy / shell structure of mercury sulfide / cadmium sulfide / mercury cadmium sulfide with a total diameter of 12nm and an effective exciton diameter ranging from 4nm to 5nm are obtained.

[0081] The above embodiment is based on the quantum confinement effect, and controls the electron energy level 1S by adjusting the diameter of the quantum dot. e and 1P e The relative position to the ambient Fermi level controls the 1S e Energy Levels and 1P e The electron doping probability at the energy level, obtained by this method, is 1S e Energy Levels and 1P e The electron doping at the energy level is stable in the atmospheric environment, and the obtained quantum dot laser has the characteristics of low gain threshold, low laser threshold, sustainable continuous laser output, programmable emission wavelength and stable environment.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-threshold quantum dot laser, characterized in that: The invention comprises a quartz substrate, a silicon dioxide periodic grating layer, a quantum dot layer and a silicon dioxide protective layer which are stacked in sequence, wherein the quantum dot layer is composed of densely stacked quantum dots.

2. The low-threshold quantum dot laser according to claim 1, characterized in that: The quantum dots are mercury selenide quantum dots, mercury sulfide quantum dots, quantum dots with a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, or quantum dots with a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide.

3. The low-threshold quantum dot laser according to claim 2, characterized in that: The quantum dots are mercury selenide quantum dots, which are in a sphalerite phase and have a diameter of 4.8 nm to 6.6 nm.

4. The low-threshold quantum dot laser according to claim 2, characterized in that: The quantum dots are mercury sulfide quantum dots, which are in a sphalerite phase and have a diameter of 4nm to 5.2nm.

5. The low-threshold quantum dot laser according to claim 2, characterized in that: The quantum dots are quantum dots of a core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide, which are composed of a mercury selenide core in a sphalerite phase, a cadmium selenide amalgam layer coated on the surface of the mercury selenide core, and a cadmium selenide shell coated on the surface of the cadmium selenide amalgam layer, wherein the cadmium element of the cadmium selenide amalgam layer gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dots of the core / alloy / shell structure of mercury selenide / cadmium selenide / cadmium selenide is 4.8nm~6.4nm.

6. The low-threshold quantum dot laser according to claim 2, characterized in that: The quantum dots are quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide, and the quantum dots of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide are composed of a mercury sulfide core in a sphalerite phase, a cadmium sulfide amalgam layer coated on the surface of the mercury sulfide core, and a cadmium sulfide shell coated on the surface of the cadmium sulfide amalgam layer, the cadmium element of the cadmium sulfide amalgam layer gradually increases from the inside to the outside, and the effective exciton diameter of the quantum dots of the core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide is 4nm~5nm.

7. The low-threshold quantum dot laser according to claim 1, characterized in that: The product of the grating period of the silicon dioxide periodic grating and the effective refractive index is equal to the band edge emission peak wavelength of the quantum dots in the quantum dot layer.

8. The low-threshold quantum dot laser according to claim 1, characterized in that: The low-threshold quantum dot laser also includes a pump source for exciting the quantum dot layer.

9. A method for preparing a low-threshold quantum dot laser, for preparing the low-threshold quantum dot laser according to any one of claims 1 to 8, characterized in that: The following steps are included: S1. Preparation of quantum dots; S2, based on the quartz substrate, forming a silicon dioxide periodic grating layer on the quartz substrate by using a reactive ion etching method; S3, dispersing the quantum dots obtained in step S1 in a toluene solution to obtain a toluene dispersion of quantum dots, and then spin-coating the toluene dispersion of quantum dots on the silicon dioxide periodic grating layer obtained in step S2 to obtain a quantum dot layer; S4. On the quantum dot layer obtained in step S3, a silicon dioxide protective layer is obtained by spin coating spin-on glass.

10. The method for preparing a low-threshold quantum dot laser according to claim 9, characterized in that: The quantum dots in step S1 are mercury selenide quantum dots, mercury sulfide quantum dots, quantum dots of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, or quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide. When the quantum dots are mercury selenide quantum dots, they are prepared by a hot injection method, and the diameter of the quantum dots is controlled by controlling the reaction temperature and the growth time; When the quantum dots are mercury sulfide quantum dots, they are prepared by hot injection method, and the diameter of the quantum dots is controlled by controlling the reaction temperature and growth time; When the quantum dot is a quantum dot of a core / alloy / shell structure of mercury selenide / mercury cadmium selenide / cadmium selenide, it is composed of a mercury selenide core, a cadmium selenide amalgam layer and a cadmium selenide shell, the mercury selenide core is prepared by a hot injection method, and the diameter of the mercury selenide core is controlled by controlling the reaction temperature and the growth time; the cadmium selenide amalgam layer and the cadmium selenide shell are prepared by a continuous ion layer adsorption reaction method, and the element proportion and thickness of the cadmium selenide amalgam layer are controlled by controlling the injection rate and injection amount of mercury ions, cadmium ions and selenium ions; the diameter of the effective exciton is controlled by controlling the diameter of the mercury selenide core and the thickness of the cadmium selenide amalgam layer; When the quantum dots are quantum dots of a core / alloy / shell structure of mercury sulfide / mercury cadmium sulfide / cadmium sulfide, they are composed of a mercury sulfide core, a cadmium sulfide amalgam layer and a cadmium sulfide shell. The mercury sulfide core is prepared by a hot injection method, and the diameter of the mercury sulfide core is controlled by controlling the reaction temperature and the growth time; the cadmium sulfide amalgam layer and the cadmium sulfide shell are prepared by a continuous ion layer adsorption reaction method, and the element proportion and thickness of the cadmium sulfide amalgam layer are changed by controlling the injection rate and injection amount of mercury ions, cadmium ions and sulfur ions; the diameter of the effective exciton is controlled by controlling the diameter of the mercury sulfide core and the thickness of the cadmium sulfide amalgam layer.

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