CN114914333A - Method and system for increasing luminous efficiency by increasing injection recombination zone - Google Patents
Method and system for increasing luminous efficiency by increasing injection recombination zone Download PDFInfo
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Abstract
The invention belongs to the technical field of semiconductor light-emitting devices, and discloses a method and a system for increasing luminous efficiency by increasing an effective injection composite region, wherein the thickness of a quantum well is adjusted according to the distribution condition of an electric field, the electric field directions of the quantum well region and a barrier region are adjusted to be opposite, and the leakage of current carriers is reduced; and (3) increasing the effective recombination area: after the current carrier reaches a region through a tunneling effect, the barrier thickness of the region is increased, the current carrier is prevented from escaping to two ends, the purpose of effectively injecting a composite region is achieved, and the luminous efficiency is further increased. The method for increasing the luminous efficiency by increasing the effective injection composite region adjusts the thickness of the quantum well according to the distribution condition of the electric field, and adjusts the area of the injection region to the maximum: after a carrier reaches an area through a tunneling effect, the thickness of a quantum well in the area is increased to increase an injection recombination area, so that the luminous efficiency can be effectively increased, and the bottleneck problems of low efficiency, efficiency droop and the like of the conventional semiconductor device are solved.
Description
Technical Field
The invention belongs to the technical field of semiconductor light-emitting devices, and particularly relates to a method and a system for increasing luminous efficiency by increasing an injection recombination region.
Background
The white light LED based on the InGaN material is a mainstream product applied in the current illumination market, has the advantages of high efficiency, energy conservation, environmental protection, high reliability, small volume, no pollution and the like, is known as a fourth generation illumination light source, and has great market prospect to attract great attention of the industry and the academic world. At present, there are two schemes for obtaining white light by using InGaN material, one is to convert an InGaN blue light chip and YAG fluorescent powder into a white light LED, although the scheme has mature technology and high internal quantum efficiency, the luminous efficiency of the white light LED obtained by using the fluorescent powder conversion method is difficult to break through 2001m/W due to the non-radiative recombination characteristic of the fluorescent powder. Another very promising approach is to mix the RGB three primary colors to obtain white light, which enables the limit value of its luminous efficiency to exceed 2501m/w due to the absence of phosphor powder in the light emitting process, which is also the inevitable trend of the future white LED lighting development. InGaN materials are the most important choice, whether currently mainstream white light solutions or future LED solutions.
The semiconductor light emitting device has the characteristics of small volume, light weight, high reliability, long service life, low power consumption and the like, and is widely applied to military and civil fields such as illumination, display, laser communication, optical storage and the like. At present, high-quality semiconductor light-emitting chip materials are mostly prepared by Molecular Beam Epitaxy (MBE) and Metal Organic Chemical Vapor Deposition (MOCVD) methods in an epitaxial manner. Although the epitaxial technology of semiconductor light-emitting materials has been greatly developed, the semiconductor light-emitting device still has the bottleneck problems of low light-emitting efficiency, efficiency droop and the like, and the application of the semiconductor light-emitting device in the related field is limited.
While the true cause of the efficiency drop is not yet clear, auger recombination, electron leakage, and carrier delocalization are considered as the mechanism of the efficiency drop. In addition, the polarization-induced internal electric field in InGaN multiple quantum wells has a large impact on efficiency degradation. As the internal electric field strength increases, the leakage of electrons from the MQW to the p-GaN layer increases, and holes are injected into the MQW active region, which becomes increasingly inefficient, exacerbating the efficiency degradation problem. In addition, the internal electric field increases the auger recombination rate, which also results in a decrease in efficiency.
Through the above analysis, the problems and defects of the prior art are as follows:
(1) the existing semiconductor light-emitting device still has the problem of low luminous efficiency, the improvement of the performance of the existing semiconductor light-emitting device is seriously limited, and the application of the existing semiconductor light-emitting device in related fields is restricted.
(2) Defects In GaN-based materials are closely related to the In content, and the higher the In content, the higher the defect density. An effective method for reducing the In content is to lower the temperature, but lowering the temperature causes lattice defects, which have a serious influence on the luminous efficiency.
Due to the lack of suitable substrate materials, the growth process of InGaN/GaN materials mostly adopts heteroepitaxy, which causes a large amount of strain defects in the materials, and causes a strong piezoelectric field to be generated in the materials, thereby causing Quantum Confined Stark Effect (QCSE).
Due to the influence of interface state, impurity contamination or strain on the surface of the semiconductor material, non-radiative recombination occurs in electron-hole pairs generated by light absorption near the resonant cavity surface, which causes large energy loss, reduces the luminous efficiency of the device, and further influences the output performance of the device.
The difficulty in solving the above problems and defects is:
researchers research the influence of material defects on luminescence by photoluminescence spectra (PL) of materials, and find that obvious multimodal phenomenon, namely defect luminescence phenomenon exists in PL. However, the research method only remains in the relation between high energy peaks and interband recombination in multiple peaks, low energy peaks are derived from various defect states, and the more complex reasons behind the multiple peaks are not clear.
Indium incorporation is very sensitive to variations In growth temperature and Bedair et al have found In studies that the rate of In removal from the crystal lattice increases exponentially with temperature, so increasing the In composition In InGaN is most effectively achieved by lowering the growth temperature. However, lowering the growth temperature also introduces a large number of micro-domain defects into the material, such as threading dislocations, V defects, In aggregation, an increase In N vacancies, severe carbon contamination, and the like, which finally results In a decrease In lattice quality and a decrease In luminous efficiency.
The electric field caused by spontaneous polarization and piezoelectric polarization in InGaN/GaN Quantum Well (QW) can reach MV/cm order, and has important influence on the performance of material device. With the increase of In component, the Quantum Confined Stark Effect (QCSE) In the quantum well is more serious, and In order to overcome the influence of QCSE, researchers have adopted various methods, such as growth of non-polar/semi-polar quantum wells, quantum dot technology, and addition of a strained layer In the quantum well, which have certain problems.
The significance for solving the problems and the defects is as follows:
(1) although the nature of the "Efficiency drop" phenomenon is controversial, the more discussed mechanisms for generating the "Efficiency drop" effect are mainly: non-radiative recombination of defect states to carriers, polarization effects, carrier delocalization, electron leakage, and the like. However, the intrinsic connection between these complex electric field mechanisms and optical properties and the carrier leakage mechanism are still poorly understood. These have all inhibited further development of solid state lighting technology. Therefore, the application provides a method and a system for increasing the luminous efficiency by increasing the injection recombination region, and the purpose of increasing the effective injection recombination region is achieved by regulating and controlling the internal electric field of the material and effectively solving the problem of carrier leakage, so that the carrier recombination efficiency is improved, and the bottleneck problems of efficiency droop and the like are effectively reduced.
(2) In the aspect of realizing ultra-high energy efficiency solid state lighting, the InGaN material not only has a direct band gap, but also has a band gap range from 0.64 to 3.4eV which is continuously adjustable, so that high-efficiency light emission from near infrared to near ultraviolet can be realized theoretically, and the InGaN material is considered to be the most important material for preparing light-emitting devices and photovoltaic devices. Currently, the InGaN-based solid-state lighting technology has developed to suffer from several bottleneck problems, such as "Efficiency Droop", that is, the LED Efficiency is significantly reduced with the increase of the injection current, and this "Efficiency drop" phenomenon limits the use of the LED at high current density. In addition to efficiency issues, the high cost of efficient LED light sources has also prevented LEDs from entering the common light source market to some extent. Therefore, improving the luminous efficiency of the material and effectively reducing the efficiency drop have very important strategic significance to the development of the solid-state lighting technology.
Disclosure of Invention
In view of the problems of the prior art, the present invention provides a method and system for increasing the luminous efficiency by increasing the injection recombination zone.
The invention is realized in such a way that a method for increasing the luminous efficiency by increasing the injection recombination zone comprises the following steps: and adjusting the thickness of the quantum well according to the distribution of the electric field, and adjusting the area of the injection region to be maximum.
Further, the method for maximizing the area of the implantation region includes: after the carrier reaches an area through the tunneling effect, the thickness of the quantum well in the area is increased, and the injection recombination area is increased.
Further, the method for maximizing the area of the implantation region specifically includes:
step one, determining the direction of a piezoelectric field. In the case of the GaN/InxGa (1-x) N structure, the negative charge centers of N atoms move to the opposite C direction due to the compressive strain, which means that lattice mismatch and different thermal expansion coefficients of InxGa (1-x) N and GaN layers form an electric field in the C direction; further, in the InGaN/GaN quantum well structure, InGaN is generally subjected to compressive stress, and thus its piezoelectric field direction is along the [0001] direction (as shown in (b) of fig. 5).
And step two, calculating the magnitude of the piezoelectric field. The invention determines the relation between the stress and the electric field by the relation formula of In component and stress, thus accurately calculating the electric field size of the quantum well region.
Drawing a structure diagram of an energy band of p-i (MQW) -n, wherein the direction of a piezoelectric field points to the substrate due to the compressive strain in the quantum well region and is opposite to the built-in PN field;
adjusting the thickness of the quantum well according to the distribution condition of the electric field, adjusting the inclination angle of the triangular potential well of the quantum well region to the direction of limiting electrons, and reducing the overflow of carriers;
fifthly, after partial carriers reach a quantum well area through the tunneling effect, the thickness of the quantum well in the area is increased, and the effective injection composite area is increased;
and step six, adding an effective barrier layer in the last quantum well region to further reduce the overflow of current carriers, thereby achieving the purpose of increasing the luminous efficiency.
Furthermore, in the fourth step, the inclination angle of the triangular potential well of the quantum well region is adjusted to the direction of limiting electrons, the process of inhibiting the rapid carrier recombination is dominated by a built-in PN electric field, and the direction of the electric field in the well is the same as that of the electric field in the potential barrier region.
Another objective of the present invention is to provide a novel quantum structure for implementing the method for increasing the light emitting efficiency by excessively increasing the injection recombination region, wherein the novel quantum structure is an LED structure based on electric field regulation and tunneling, and the barrier thickness is sequentially reduced in the middle quantum well region to reduce the internal electric field, so as to enlarge the overlapping degree of the wave functions of electrons and holes; electrons tunnel in the middle quantum well regions, non-radiative recombination of the electrons is reduced, and the injection recombination region is increased, so that the electrons are limited at the bottom of the triangular potential well (as shown in (b) in fig. 5), carriers are difficult to escape from the potential well, and the recombination efficiency of the carriers is greatly improved.
Furthermore, when electrons tunnel to the last quantum well, an AlGaInN electron blocking layer is added to limit the escape of the electrons, and the thickness of the quantum well is increased to further increase the recombination area of injected electrons and holes.
Another object of the present invention is to provide a method for preparing a novel quantum structure, which comprises: and (3) growing the novel quantum structure on the c-plane sapphire substrate by adopting an MBE growth method.
Further, the preparation method of the novel quantum structure further comprises the following steps:
step 1, annealing the sapphire substrate for 5 minutes at 1400 ℃ in flowing air, and reducing the average roughness of the piezoelectric field direction surface from 0.8 to 0.3 nm;
step 2, growing a double buffer layer on the annealed (0001) surface sapphire, wherein the double buffer layer is composed of a medium-temperature GaN buffer layer grown at 690 ℃ and a traditional AlN buffer layer deposited at 740 ℃;
step 3, raising the growth temperature to 1050 ℃ to grow an undoped u-GaN epitaxial layer with the thickness of 1.5 microns and a silicon-doped n-GaN epitaxial layer with the thickness of 4 microns;
and 4, reducing the growth temperature to 760 ℃, and growing an InGaN/GaN active region.
Further, the step 4 of growing the InGaN/GaN active region includes:
(1) growing GaN: after cleaning the sapphire substrate at the high temperature of 1100 ℃, growing a GaN nucleation layer with the thickness of 30nm at the low temperature of 550 ℃;
(2) then the growth temperature was increased to 1050 ℃ to grow an undoped u-GaN epitaxial layer with a thickness of 1.5 μm and a silicon-doped n-GaN epitaxial layer with a thickness of 4 μm with an electron concentration of 8X 1018cm -3 ；
(3) Then, the growth temperature is reduced to 750-800 ℃ to grow 11 pairs of quantum well structures; InGaN3.0nGaN11.0nm multi-quantum well active layer and 21.0 nm-thick u-GaN LQB;
(4) then the growth temperature was increased to 950 ℃ to grow 8 p-Al0 doped with Mg; generating a field-modulated and tunneling-effect LED structure based on electricity; InGaN3.4nGaN11.0nEBL and a 150 nm-thick Mg-doped p-GaN layer, and the hole concentration is 2 multiplied by 1017cm -3 。
Another object of the present invention is to provide a semiconductor light emitting device implementing the method of increasing the recombination zone for implantation to increase the luminous efficiency.
By combining all the technical schemes, the invention has the advantages and positive effects that: the method for increasing the luminous efficiency by increasing the injection recombination region adjusts the thickness of the quantum well according to the distribution condition of the electric field, and adjusts the area of the injection region to the maximum: after a carrier reaches an area through a tunneling effect, the thickness of a quantum well in the area is increased to increase an injection recombination area, so that the luminous efficiency can be effectively increased, and the problem of low luminous efficiency of the conventional semiconductor laser device is solved.
In the GaN material lattice, there is spontaneous polarization in the material due to the lattice constant c/a ratio that slightly deviates from the ideal value of 1.633; in addition, when a thin single-crystal layer of InxGa (1-x) N is grown on a GaN substrate, the interface between GaN and the InxGa (1-x) N layer is strained due to lattice mismatch, and this strain causes generation of a piezoelectric field. These two factors cause a large amount of electric field in the GaN material system, thereby causing quantum stark effect (QCSE), which has a great influence on the material and device performance, such as red shift of emission spectrum, reduction of overlap of electron hole wave function, and reduction of luminous efficiency. Therefore, adjusting the electric field distribution and magnitude in GaN-based material systems is critical to increasing the size and efficiency of the implanted region.
In order to overcome the influence of QCSE, researchers have adopted various methods, such as growth of a nonpolar/semipolar quantum well, a quantum dot technology, and addition of a strain layer in the quantum well, however, most of the technologies have certain problems, such as an immature process, low stability, and the like.
According to the invention, on the basis of fully analyzing the influence of an electric field mechanism on the optical characteristics and carrier dynamics of the material, an electric field model is constructed, and then the electric field is regulated and controlled to reduce carrier leakage, so that the purposes of increasing a recombination region and increasing the luminous efficiency are achieved.
In order to achieve the above object, the present invention provides a system for adjusting the electric field direction to be favorable for collecting electrons by adjusting the electric field direction and size of the quantum well region and the barrier region, so as to reduce the overflow of electrons, increase the collection of carriers when the device works at a high current, reduce auger recombination and other non-radiative recombination, and effectively avoid the bottleneck problems of "efficiency droop" and the like faced by the semiconductor light emitting device at present by increasing the system for injecting the recombination region to increase the light emitting efficiency.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a method for increasing luminous efficiency by increasing an injection recombination region according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a method for increasing the luminous efficiency by increasing the injection recombination region according to an embodiment of the present invention.
Fig. 3 is a schematic structural diagram of InGaN p-i (mqw) -n provided in the embodiment of the present invention.
Fig. 4 is a schematic diagram of a PIN band structure provided by an embodiment of the present invention, in which electrons are confined in a triangular potential well and are difficult to escape.
Fig. 5 is a schematic diagram of an electric field regulation mechanism of the novel quantum structure provided by the embodiment of the invention.
Fig. 6 is a graph of calculated piezoelectric field along the 0001 direction in fig. 5 as a function of InN mole content in InGaN/GaN provided by an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In view of the problems of the prior art, the present invention provides a method and system for increasing the luminous efficiency by increasing the injection recombination region, and the present invention is described in detail below with reference to the accompanying drawings.
Example 1
As shown in fig. 1, the method for increasing the luminous efficiency by increasing the injection recombination region according to the embodiment of the present invention includes the following steps:
s101, determining the direction of the piezoelectric field. In the GaN/In x Ga (1-x) In the case of the N structure, the N atom is subjected to compressive strain to shift the center of the negative charge In the opposite C direction, which means that In x Ga (1-x) Lattice mismatch and differential heat of N and GaN layersThe expansion coefficient forms an electric field in the C direction; furthermore, in InGaN/GaN quantum well structures, InGaN is typically under compressive stress, so its piezoelectric field direction is along [0001]]Direction ((b) diagram in fig. 5)).
And S102, calculating the magnitude of the piezoelectric field. The invention determines the relation between the stress and the electric field by the relation formula of In component and stress, thus accurately calculating the electric field size of the quantum well region.
FIG. 6 shows the calculated piezoelectric field in InGaN/GaN as a function of InN molar content along the 0001 direction in FIG. 5, where
From this, Ebi can be calculated.
S103, drawing an energy band structure diagram of p-i (MQW) -n, wherein the direction of the piezoelectric field is directed to the substrate and is opposite to the built-in PN field due to the compressive strain in the quantum well region.
And S104, adjusting the thickness of the quantum well according to the distribution condition of the electric field, adjusting the inclination angle of the triangular potential well of the quantum well region to the direction of limiting electrons, and reducing the overflow of carriers.
And S105, after part of carriers reach a quantum well region through the tunneling effect, increasing the thickness of the quantum well in the region, and increasing the effective injection recombination region.
And S106, adding an effective barrier layer in the last quantum well region, and further reducing the overflow of carriers, thereby achieving the purpose of increasing the luminous efficiency.
In step S104, the inclination angle of the triangular potential well of the quantum well region is adjusted to the direction of limiting electrons, and the process of suppressing the rapid carrier recombination is dominated by the built-in PN electric field, and the electric field in the well is in the same direction as the electric field in the barrier region.
Example 2
Based on embodiment 1, as a preferred embodiment of the present invention, since the suppression of the fast carrier recombination process is dominated by the built-in PN electric field, the electric field in the well should be in the same direction as the electric field of the barrier region. As the field directions of the trap and the barrier region are the same, and the slope of the built-in PN field is larger, the fast initial decay process of the TRPL measured by TCPC proves that electrons and holes are easier to escape from QW in the tunneling process;
carriers escape from the quantum well within a few nanoseconds and drift to two ends of the material to shield a built-in PN field; due to the drift of carriers in the quantum well, the shielding in the well exists at the same time; due to the fact that the piezoelectric field is weak, the electric field directions of the materials in the quantum well region and the barrier region are the same.
The GaN-based solid-state light-emitting device has the advantage of large peak current, so that the efficiency of the GaN-based solid-state light-emitting device is improved, and the current overshoot effect in the traditional structure under the condition of large current is avoided.
Example 3
In order to achieve the purpose, the quantum well and the barrier thickness are optimized, and the quantum well structure is reasonably designed to be beneficial to electron collection. Generally, electrons in the quantum well cannot escape from the quantum well due to insufficient energy, and the electrons are bound in the quantum well. However, when the barrier is thin, the electron wavefunction in the quantum well has not yet decayed to 0, at which time electrons may cross the barrier, become free electrons or reach another quantum well. The invention adjusts the quantum well thickness according to the electric field distribution condition, and adjusts the area of the injection region to the maximum; after the carriers reach an area through the tunneling effect, the thickness of the quantum well in the area is increased, the injection recombination area is increased, and the light emitting efficiency is further increased.
Example 4
The embodiment of the invention also provides a novel quantum structure with the characteristic of high luminous efficiency, the novel quantum structure is an LED structure based on electric field regulation and tunnel effect, the thickness of a potential barrier is sequentially reduced in a middle quantum well region, an internal electric field is reduced, and the overlapping degree of wave functions of electrons and holes is enlarged; electrons tunnel in the middle quantum well regions, non-radiative recombination of the electrons is reduced, and the injection recombination region is increased, so that the electrons are limited at the bottom of the triangular potential well (as shown in a figure (b) in figure 5), carriers are difficult to escape from the potential well, and the recombination efficiency of the carriers is greatly improved.
When electrons tunnel to the last quantum well, an AlGaInN electron blocking layer is added to limit the escape of electrons, and the thickness of the quantum well is increased to further increase the recombination area of injected electrons and holes.
The structure has the characteristics of large effective recombination region and less electron escape, improves the radiation recombination efficiency of the GaN luminescent device, and solves the problems of serious electric field effect and low radiation recombination efficiency caused by more carrier escape of the traditional GaN luminescent device. The invention optimizes the thicknesses of the quantum wells and the potential barriers, and sequentially reduces the thicknesses of the potential barriers in the middle quantum well regions (from the second quantum well to the last quantum well), thereby not only reducing the internal electric field, enlarging the overlapping degree of wave functions of electrons and holes and increasing the radiation recombination efficiency, but also tunneling the electrons in the middle quantum well regions and reducing the non-radiation recombination of the electrons, thereby achieving the purpose of increasing the injection recombination region. In addition, when electrons tunnel to the last quantum well, an AlGaInN electron blocking layer is added to limit escape of the electrons, the thickness of the quantum well is increased, the recombination area of injected electrons and holes is further increased, and the light emitting efficiency of the device is improved.
According to the novel quantum structure provided by the embodiment of the invention, the barrier thickness is sequentially reduced in the middle quantum well region for the LED structure based on electric field regulation and tunnel effect, so that the internal electric field is reduced, the wave function overlapping degree of electrons and holes is enlarged, and the radiation recombination efficiency is increased; electrons tunnel in the middle quantum well regions, non-radiative recombination of the electrons is reduced, and the injection recombination region is increased.
When electrons tunnel to the last quantum well, an AlGaInN electron blocking layer is added to limit the escape of electrons, and the thickness of the quantum well is increased to further increase the recombination area of injected electrons and holes.
Example 5
The embodiment of the present invention provides a method for preparing a novel quantum structure, which includes: and (3) growing the novel quantum structure on the c-plane sapphire substrate by adopting an MBE growth method.
The method specifically comprises the following steps:
the effective composite area enlarging structure can be prepared by adopting a chemical vapor deposition method and a molecular beam epitaxy method, an MBE growth method is preferably selected in the invention, and the novel structure is grown on a c-plane sapphire substrate.
For sapphire substrates, annealing at 1400 ℃ for 5 minutes under flowing air can reduce the average roughness of the (0001) plane from 0.8 to 0.3 nm.
And (3) growing double buffer layers on the annealed (0001) plane sapphire, wherein the double buffer layers are respectively composed of an intermediate-temperature GaN buffer layer grown at 690 ℃ and a traditional AlN buffer layer deposited at 740 ℃, and the step can optimize the quality of the film.
The growth temperature was then increased to 1050 ℃ to grow 1.5 μm thick undoped u-GaN epitaxial layers and 4 μm thick silicon-doped n-GaN epitaxial layers.
Further, the growth temperature was lowered to 760 ℃, and InGaN/GaN active regions were grown, including: (1) growing GaN: and a reference LED A sample is grown on the sapphire substrate on the c surface by adopting a metal organic chemical vapor deposition method. After the sapphire substrate was cleaned at a high temperature of 1100 deg.c, a 30nm thick GaN nucleation layer was grown at a low temperature of 550 deg.c.
(2) Then the growth temperature was increased to 1050 ℃ to grow an undoped u-GaN epitaxial layer with a thickness of 1.5 μm and a silicon-doped n-GaN epitaxial layer with a thickness of 4 μm with an electron concentration of 8X 1018cm -3 。
(3) Then the growth temperature is reduced to 750-800 ℃ to grow 11 pairs of quantum well structures. InGaN 3.0nGaN 11.0nm multi-quantum well active layer and 21.0nm thick u-GaN LQB.
(4) The growth temperature was then increased to 950 ℃ to grow 8 p-Al0 doped with Mg. InGaN 3.4nGaN 11.0nEBL and a 150nm thick Mg-doped p-GaN layer with a hole concentration of 2X 1017cm-3 for the LED B sample, the structural parameters were the same as for the reference LED A sample, except that 8 pairs of p-AlGaN (3.5nm)/InGaN (2.5nm) SLs EBL were used instead of the original p-AlGaN/GaN SLs EBL structure.
To achieve the goal of strain compensating AlGaN/InGaN-SLs, the aluminum content in the AlGaN layer is 15%. The indium content in the InGaN layer was 3.1%. As a result, the GaN layer having compressive strain is strain-compensated by the tensile strained AlGaN.
In order to ensure the crystal quality of the EBL and the component absorption in the InGaN trap, a variable temperature growth method in a nitrogen atmosphere is adopted. The growth temperature of the InGaN well layer is 850 ℃, and the growth temperature of the AlGaN barrier layer is 950 ℃. After growth, a size of about 400X 400 μm can be prepared by a chip fabrication process 2 The LED chip of (1).
Example 6
The invention attempts to map the band structure of p-i (MQW) -n. Due to the compressive strain in the quantum well region, the direction of the piezoelectric field is directed towards the substrate, opposite to the built-in PN field. Note that it is possible for the well and barrier regions to see exactly the same or opposite electric fields, depending on the exact value of the piezoelectric field. For the samples of the present invention, the present invention can conclude that the electric field in the well should be in the same direction as the electric field in the barrier region, since the suppression of the fast carrier recombination process is dominated by the built-in PN electric field, not the piezoelectric field. The schematic diagram of the belt structure is shown in fig. 4. Because the field directions of the trap and the barrier region are the same, and the slope of the built-in PN field is larger, electrons and holes can more easily escape from QW in the tunneling process. This is demonstrated by the rapid initial decay process of TRPL measured with TCPC. Carriers escape from the quantum well within a few nanoseconds and drift across the material to shield the built-in PN field. Of course, the in-well shielding is also present due to the drift of the carriers in the quantum wells. The electric field direction of the sample in the well and the barrier region is the same, probably due to the weak piezoelectric field.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A method for increasing luminous efficiency by increasing injection recombination zone, comprising: and adjusting the thickness of the quantum well according to the distribution of the electric field, and adjusting the area of the injection region to be maximum.
2. The method of increasing the luminous efficiency by increasing the number of recombination implanted regions according to claim 1, wherein the step of maximizing the area of the implanted region comprises: after the carrier reaches an area through the tunneling effect, the thickness of the quantum well in the area is increased, and the injection recombination area is increased.
3. The method of claim 1, wherein the maximizing the area of the implanted region comprises:
determining the direction of a piezoelectric field, wherein the negative charge center of N atoms moves in the opposite direction due to the compressive strain of a GaN/InxGa (1-x) N structure, and the lattice mismatch and different thermal expansion coefficients of InxGa (1-x) N and a GaN layer form an electric field in the opposite direction of the negative charge center;
step two, calculating the magnitude of the piezoelectric field, determining the relation between the stress and the electric field through a relation formula of In components and the stress, and calculating the magnitude of the electric field of the quantum well region;
drawing a structure diagram of an energy band of p-i (MQW) -n, wherein the direction of a piezoelectric field points to the substrate due to the compressive strain in the quantum well region and is opposite to the built-in PN field;
adjusting the thickness of the quantum well according to the distribution condition of the electric field, adjusting the inclination angle of the triangular potential well of the quantum well region to the direction of limiting electrons, and reducing the overflow of carriers;
fifthly, after partial carriers reach a quantum well area through the tunneling effect, the thickness of the quantum well in the area is increased, and the effective injection composite area is increased;
and step six, adding an effective barrier layer in the last quantum well region to further reduce the overflow of carriers.
4. The method according to claim 3, wherein the tilt angle of the triangular potential well of the quantum well region is adjusted to the direction of confining electrons in step four, and the suppression of the fast carrier recombination process is dominated by the built-in PN electric field, and the electric field in the well is in the same direction as the electric field in the barrier region.
5. A novel quantum structure for implementing the method of increasing the light emitting efficiency by excessively increasing the injection recombination region according to any one of claims 1 to 4, wherein the novel quantum structure is an LED structure based on electric field regulation and tunneling, the barrier thickness is sequentially reduced in the middle quantum well region, the internal electric field is reduced, and the overlapping degree of the wave functions of electrons and holes is enlarged; electrons tunnel in the middle quantum well regions, non-radiative recombination of the electrons is reduced, and an injection recombination region is increased, so that the electrons are limited at the bottom of the triangular potential well, and carriers cannot escape from the potential well.
6. A novel quantum structure as claimed in claim 5 wherein, when electrons tunnel into the last quantum well, an AlGaInN electron blocking layer is added to limit the escape of electrons and increase the thickness of the quantum well to further increase the recombination zone of injected electrons and holes.
7. A preparation method of a novel quantum structure is characterized by comprising the following steps: and (3) growing the novel quantum structure on the c-plane sapphire substrate by adopting an MBE growth method.
8. The method of claim 7, wherein the method of preparing the novel quantum structure comprises:
step 1, annealing a sapphire substrate at 1400 ℃ in flowing air for 5 minutes, and reducing the average roughness of a piezoelectric field direction surface from 0.8 to 0.3 nm;
step 2, growing double buffer layers on the annealed sapphire on the surface of the piezoelectric field direction, wherein the double buffer layers are respectively composed of a medium-temperature GaN buffer layer grown at 690 ℃ and a traditional AlN buffer layer deposited at 740 ℃;
step 3, raising the growth temperature to 1050 ℃ to grow an undoped u-GaN epitaxial layer with the thickness of 1.5 mu m and a silicon-doped n-GaN epitaxial layer with the thickness of 4 mu m;
and 4, reducing the growth temperature to 760 ℃, and growing an InGaN/GaN active region.
9. The method for fabricating a novel quantum structure of claim 8 wherein the step 4 growing an InGaN/GaN active region comprises:
(1) growing GaN: after cleaning the sapphire substrate at the high temperature of 1100 ℃, growing a GaN nucleation layer with the thickness of 30nm at the low temperature of 550 ℃;
(2) then the growth temperature was increased to 1050 ℃ to grow an undoped u-GaN epitaxial layer with a thickness of 1.5 μm and a silicon-doped n-GaN epitaxial layer with a thickness of 4 μm with an electron concentration of 8X 1018cm -3 ；
(3) Then, the growth temperature is reduced to 750-800 ℃ to grow 11 pairs of quantum well structures; InGaN3.0nGaN11.0nm multi-quantum well active layer and 21.0 nm-thick u-GaN LQB;
(4) then the growth temperature was increased to 950 ℃ to grow 8 p-Al0 doped with Mg; finally generating a field-modulated and tunnel-effect LED structure based on electricity; InGaN3.4nGaN11.0nEBL and 150nm thick Mg-doped p-GaN layer with hole concentration of 2 x 1017cm -3 。
10. A semiconductor light emitting device, characterized in that the semiconductor light emitting device implements the method of increasing the light emitting efficiency by excessively increasing the injection recombination zone as set forth in any one of claims 1 to 4.
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