TW497276B - High efficiency light emitters with reduced polarization-induced charges - Google Patents

Abstract

Naturally occurring polarization-induced electric fields in a semiconductor light emitter with crystal layers grown along a polar direction are reduced, canceled or re-versed to improve the emitter's operating efficiency and carrier confinement. This is accomplished by reducing differences in the material compositions of adjacent crystal layers, grading one or more layers to generate space charges and quasi-fields that oppose polarization-induced charges, incorporating; various impurities into the semiconductor that ionize into a charge state opposite to the polarization induced charges, inverting the sequence of charged atomic layers, inverting the growth sequence of n- and p-type layers in the device, employing a multilayer emission system instead of a uniform active region and/or changing the in-plane lattice constant of the material.

Description

497276 A7 B7 V. Description of the invention (1) Related applications This application claims the benefit of provisional patent application number No. 60 / 168,495, with an application date of 12,2,1999. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a light-emitting hybrid semiconductor crystal grown on an electrode surface in more detail. It relates to reducing or eliminating polarization induced charges that naturally occur to improve emission performance. Description of related techniques Most semiconductor light emitters have a double heterostructure, that is, a light emitting layer that is effective or grows between two cladding layers. Each layer of the double heterostructure is made of more than one material. A cladding layer is n-type, meaning that it contains excessive electrons, and a cladding layer is P-type, meaning that it contains excessive pinholes. In short, the cladding layer has a larger band gap than the effective layer. This results in that the emitted electrons and pinholes are confined to the effective layer, and the free carrier is effectively localized and effectively recombined by the effective layer space to generate light. In addition, the laser dipole (LD) transmitter also has a separate light-limiting layer. The standard includes a material with a wider band gap that surrounds a double heterostructure. Double heterostructure semiconductor devices have been published in many publications, including "Introduction to Lasers and Their Applications" by O'Shea and colleagues11, Addison Wesley Publishing Company, December 1978, pages 166-167. In this structure, polarization Induced charge occurs when the polarization direction of the basic crystalline structure of the material composition changes. The definition of the polarization direction is any polarization vector that is not related to the crystal, P, positive cross-crystallization direction. This definition has natural directivity for crystalline bonds and Even the slightly ionized material is very real. Example -4- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm).

497276 A7 B7 5. Description of the invention (2) For example, III-V or II-VI semiconductors. In the case of crystalline lattice mismatched materials, this charging may be related to strain (piezoelectricity), due to the difference in ionic strength of the crystalline bonds of different materials, and to the composition (spontaneous), or a combination of the two. The induced electric field or potential gradient of the induced charge has the same effect on the free carrier and the external electric field. This phenomenon has been discussed in some journals, including Bernardini and colleagues, spontaneous polarization and piezoelectric constant of π III-V nitrides ", Journal of the American Physical Society, Physical Review B, Volume 56, No. 16, 1997, Page R10 024-027, and Takeuchi and colleagues, "Finite Quantum Stark Effect Due to the Piezoelectric Field of a Strained GalnN Quantum Well", Japanese Journal of Applied Physics, Vol. 36, Part 2, No. 4, 1997, Page L3 82 -L3 85. The electric field strength is estimated to be up to 2.5 X 106 V / cm, a double heterostructure of nitride grown on a crystalline polarized surface, Bykhovski and colleagues, π elastic strain retraction and GaN-AIN, Gan-AlGaN and GaN-InGaN supercrystals Grid's Piezoelectric Effect '', Japanese Journal of Applied Physics, Vol. 81, No. 9, 1997, pages 6332-6338 ° If you consider the electrical characteristics of heterostructures grown on crystalline polarized surfaces, you must consider polarization-induced charges. Wurtzite GaN crystals, with a crystalline layer growing along the 0001 orientation, or sphalerite GaAs crystals, growing along the 111 orientation. These are two examples of crystal-polarized surfaces. The Bravais lattice of the wurtzite structure is hexagonal, and the vertical hexagonal axis is usually marked as the C axis or 0001 orientation. The structure along this axis can be conceived as a series of atomic layers of the same element (for example, all gallium Ga or all nitrogen N) forming a regular hexagon. Because of this consistency, the layers (or surfaces) are polarized and have a positive or a negative charge, creating a bipolar layer that spans the atomic layer. The charge state of each layer depends on its constituent atoms. Various -5- This paper size applies Chinese National Standard (CNS) A4 specification (210 X 297 mm) 497276 A7 B7 V. Description of the invention (3) For other examples of crystalline planes in the growth direction, please refer to Streetman, "Solid State Electronic Devices, , Second Edition, Prentice-Hall, 1980, pages 1-24, and Shuji Nakamura and colleagues, `` Blue Laser Dipole, GaN-Based Light Emitter and Laser, Springer, 1997, page 21- 24. Until recently, the active and cladding-related internal polarization fields associated with light-emitting heterostructures were no longer raised as important issues. This is because more light-emitting dipoles (LEDs) are based on non-polarized crystalline surfaces. A growing Al-Ga-In-As-P material system was established (especially the 001 sphalerite surface). Recently, however, a considerable amount of light emitters have been based on the Al-Ga-In-N (nitride) material system Mostly, it grows along the 0001 direction of wurtzite crystal, which is a highly polarized surface. However, the nitride double heterostructure is based on the traditional non-polar design. Figure 1A is a schematic cross-sectional view showing a standard nitride Semiconductors with double heterostructures growing in the direction of polarization The base layer 1 may be any material suitable for nitride semiconductor growth, including spinel (MgAl204), sapphire (Al203), SiC (including 6H, 4H, and 3C), ZnS, ZnO, GaAs, A1N, and GaN. The thickness of the base layer is generally 100 micrometers to 1 mm. The buffer layer 2 on the base layer 1 can be made of AIN, GaN, AlGaN, InGaN or other. The buffer layer helps reduce the possibility However, if the lattice constant of the base layer 1 is approximately equal to the constant of the nitride semiconductor, the buffer layer 2 can be omitted. The buffer layer 2 can also be omitted using some nitride growth techniques. Depending on the material composition, the buffer layer The band gap of 2 ranges from 2.1 eV to 6.2 eV, and its thickness is about 0.5 micrometers to 1.0 micrometers. The η-type contact layer 3 is also generally made of a nitride semiconductor, preferably GaN or InGaN, with a thickness of 0.5 micrometers to 5.0 Micron, and band gap GaN is about 3.4 eV and -6-This paper size is applicable to China National Standard (CNS) A4 specification (210 X 297 mm)

Line 497276 A7 B7 V. Description of the invention (4)

InGaN is less (depending on the indium content). The lower η-type or non-doped coating layer 4 contains GaN or AlGaN on the conductive layer 3-the band gap of GaN is 3.4 eV and the AlGaN is larger (depending on the content). Its thickness can range from 1 nm to 100 nm. The nitride double heterostructure uses InGaN as the active region 5 above the low cladding layer and has a thickness of 1 nm to 100 nm. The band gap of this layer is generally 2.0 eV, but it varies depending on the indium content. A top p-type or non-doped layer 6 generally includes AlGaN or GaN above the active region, and its thickness and band gap energy are similar to those of the low n-type cladding layer 4. A p-type GaN conductive contact layer 7 has an energy band gap above the cladding layer 6 of about 3.4 eV and a thickness of 10 nm to 500 nm. In short, the structure grows in the direction of polarization, such as 0001. Due to different constituent substances, polarization-induced charge plates are generated between the interfaces of the layers. Of particular relevance to the operation of the light emitter is a polarization-induced charge plate close to the active region 5. As shown in FIG. 1A, the density of a negatively-polarized induced charge plate σ 1 is, for example, 1013 electrons / cm 2, and is generally generated at the interface between the active region 5 and the lower cladding region 4. A plate density σ 2 of a positively charged plate of the same strength is generated at the interface between the active region 5 and the upper cladding layer 6. The polarity of these charges depends on the adhesion of the crystalline layer, that is, directional and slightly ionized as described above. In summary, the density of a charge plate depends on the spontaneous factors caused by the difference in composition between the two layers and the piezoelectric strain caused by the lattice mismatch between the two layers. For example, σ1 is between an In0.2 Ga0. 8N active region 5 and an 8.3 x 1012 electrons / cm12 GaN cladding layer 4. This is because the indium content in the In0.2Ga.8N active region 5 (spontaneous polarization) is 20% and the strain (piezoelectric polarization) is induced due to the lattice mismatch with the underlying GaN layer. The interface charge plate creates a cross-region dipole along the opposite surface of the active region. This dipole is equivalent to an electric field whose strength is based on the strength of the plate charges σΐ and σ2, and the paper size applies the Chinese National Standard (CNS) A4 specification (210X 297 mm). 5. Description of the invention (5). In the above situation, -The board charges 83xl012cm.2 provides an electric field of 1.5x10 V / Cm. According to its original conditions, ', ^ m ±,. This electric field is regarded as the polarization induction factor = the generated electrostatic potential intensity drop is based on the dipole The thickness of the layer is determined. The thickness of the dipole layer refers to the physical length in the growth direction, that is, the distance between ... and .... This distance can be used to determine the decrease in the electrostatic potential. … The capacitance potential generated by the distance between Axu Valley and Axu Valley decreases. The distance between the above charge density σΐ and σ2 is 10 °, which will cause the polarization-induced potential of the active region to decrease by .5V. The net electric field across the active region It is also determined according to a political parameter, including the doping concentration around the cladding layer, the voltage across the p_n connection surface and the free carrier resistance, so it is generally not equal to the polarization induction field. However, due to its strength, the polarization induction field is still An important factor in determining the net electric field The growth of nitride emitters on the crystalline surface of 001 (pole) has a low emission efficiency of about 1% to 10%. This may be due to the existence of a significant polarization induction field in or near the active region, which causes the efficiency to be affected. Restrictions. Figure 1B shows the energy band equivalent to the device of Figure VIII. When the device is operating, the polarization electric field naturally generated by σ1 & σ2 will reduce the efficiency in a number of ways. First, the dipole causes the Separate 2 (moving in the opposite direction). As shown, the holes of the electron valence band ν are attracted to the negative charge plate σ i at the 5-end of the active region, while the electrons of the conductive band are attracted to the positive charge plate C72 at the other end. The separation space reduces the probability of recombination radiation and reduces the radiation efficiency. Second, the energy barrier of conductive and electron valence band quantum wells is reduced due to the quantization of the electric field. In this way, carriers below Εν and above Ec pass the path shown by the dotted line Escape from the well. Third, the presence of the polarization induced field also causes the carrier to overshoot, as shown by the carrier orbital B, from the higher potential Ec at the σ 1 end to the lower potential EC at the σ 2 end of the active region, and _________- 8 -This paper size applies the Chinese National Standard (CNS) A4 specification (210X 297 mm) 497276 A7 B7 V. Description of the invention (6) From the lower potential at the σ 2 end of the active area to the higher potential at the σ 1 end ν Application engineers are also concerned about the stability of the emission wavelength when the application deviation increases. If there is a strong polarization induction field, the emission wavelength will move blue with the increase in device offset. Because the device offset increases, the Many free-loading volumes are concentrated in the conductive and electron valence band wells. Because the free carriers are spatially separated, they will form a dipole opposite or contain a polarization induced field. Because the net electric field decreases, the quantified state of the quantum well changes, causing the emission wavelength Blue moving. Figure 1C shows the energy bands of the active layer 5 and the cladding layers 4 and 6 of a light emitter operating on a non-polarized surface with no polarized induced charge. The others are equal, and their radiation efficiency is higher, because the three effects discussed above either disappear or decrease significantly. Several methods have been used to increase the efficiency of GaN-based LEDs. U.S. patents 5,959,307 and 5,578,839, both Nakamura and colleagues, discussed the addition of aluminum to the coating layer to increase the barrier height of the active area to achieve more efficient restrictions on free carriers. However, this addition also changes the composition of the cladding material, from GaN to AlGaN, and its role is to increase the spontaneity and piezoelectric field. The AlmGao. ^ N cladding layer containing b% A1 will generate a double polarization field of 3x106 v / cm in the emitting layer. This kind of electric field will reduce the carrier limitation and increase the spatial separation due to the change of the energy band of the optical transmitter, thus reducing the emission rate. SUMMARY OF THE INVENTION The present invention seeks to improve the operating efficiency of a compound semiconductor LED including layers grown in the direction of polarization by reducing or eliminating the polarization induced charge naturally generated by the crystal to improve carrier limitation, reduce its spatial separation, and reduce

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Line V. Description of the invention (7) Less carrier overshoot. In a specific embodiment, this charging is reduced by reducing the difference in the material composition of the crystalline layer near the active region. The cladding layer can also be composed of different elements, and each element tends to eliminate the polarization effect of other elements. One or more components or dopants in the active layer can also be graded to generate space charges against polarization induced charges, and quasi electric fields against polarization induced electric fields generated by polarization induced charges. The rating can be continuous or discrete. The compound semiconductor crystal may also have a multi-layer emission system composed of cross-light emission and non-emission layers to reduce the average polarization electric field, which improves the emission efficiency. The average electric field of the layer emission system as a whole is reduced or eliminated compared with a single uniform active region of a specific thickness. Various impurities can be incorporated into the crystal, i.e., ionized into a charge state based on their energy potential to counter polarization induced charges to reduce or eliminate their effects. Impurities, ideally contain II, IV, or VI element groups. The sign of polarized induced charge can also be reversed to encourage, rather than resist, the carrier limiting efficiency. These charges are reversed as the atomic layer order of the crystalline layer is reversed. The direction of the carrier emission can also be reversed to reverse the growth order of the p & n-type layer to block polarization-induced charges. The lattice constant of the low buffer layer, contact layer, or cladding layer can also be changed by external growth techniques to achieve a lattice constant closer to the active region of the complex. This reduces the strain-induced piezoelectric effect in the active region and reduces the polarization-induced field to make light emission more efficient. Those skilled in the art will understand these and other features of the present invention from the following detailed description and the accompanying drawings, of which: Brief description of the formula 1 497276 A7 B7 5. Description of the invention (8) Figure 1A is a nitride light Sectional view of the known structure of the emitter; Figure 1B is the energy band of the device growing on the pole surface equivalent to that of Figure 1A; Figure 1C is the energy band of the known light emitter growing in the pole direction; Figure 2A Active area with various impurities and coating 2B is an impurity distribution curve; FIG. 3A is a cross-sectional view of a light emitter with an InGan coating according to the present invention; FIG. 3B is an energy band of the device of FIG. 3A; and FIGS. 4A and 4B are Energy bands of ternary A1 Gan and quaternary A1 InGan cladding nitride semiconductors; Figure 5 is a graph showing the relationship between the atomic concentration as a time culmination during cladding growth; Figure 6A is the energy band of a quasi-electric field active region Figures 6B and 6C are the energy bands of the continuously graded active area, respectively; Figure 7A is the energy band of the multilayer light emission system; Figure 7B is a dagger with a single active area equivalent to the width of the multilayer light emission system of Figure 7A π, FIG. 8A is an atomic layer corresponding to the single-layer structure shown in FIG. 1A Fig. 8B is a cross-sectional view of a reversed atomic layer structure of a single semiconductor layer; Fig. 8C is an energy band equivalent to the coating and emission layer of the device structure of Fig. 8B; A cross-sectional view of a nitride light emitter; Figure 9B is the energy band equivalent to the device of Figure 9A; Figure 10A is a nitride with a new buffer layer that matches the crystal lattice constant of the active area-11-This paper size applies Chinese national standards ( CNS) Α4 size (210X 297 mm)

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A cross-sectional view of an object light emitter; and FIG. 10B is an energy band equivalent to the device of FIG. 10A. The detailed description of the specific embodiments of the invention refers to a nitride emitter system having a double heterostructure layer and a crystal whose growth direction is perpendicular to the polar direction of the crystal. The nitride emitter has a wurtzite crystal structure "layer, Wherein the coating layer is-unless stated, the crystals are private: 10,000 digits have the polarity of the full-time table group 111. The nitrogen north X shown in Fig. 1A and the ⑯γ structure of Fig. 1B will be used as specific Reference to the examples. Selecting doping, this method can reduce or eliminate the polarity induction by incorporating various dopants into the semiconductor. Impurities of the dopant must be of a type that will not diffuse from a predetermined position. The ionization of the dopant becomes a positive or negative charge state according to its energy, which is opposite to the interface polarization induced charge state to reduce or eliminate its effect. The type of dopant used should indicate the interface polarization induced charge state. Positive charge The required dopant must be ionized to a negatively charged state, which in turn charges the negative interface. The band structure shown in Figure 2 ^ is a coating / active / coating layer incorporating about ιππ atoms / Cm3 as a positive charge source To reduce or eliminate negative The surface charge density cr 1. To reduce or eliminate the source of positive charge density "§ σ2, 1〇π electrons / cm3 can be used as the source of the negative charge. The concentration distribution of the dopant is based in part on the ionization energy of the dopant and the amount of donor / acceptor. For example, if using zinc (Zn) as a negative charge source to reduce the dopant to σ2, a higher dopant concentration is required. The impurity content of the dyeing agent _____- 12- This paper size is applicable to China National Standard (CNS) A4 specification (2l0x297 mm)

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497276 A7 B7 V. Description of the invention (10) It is impossible for the cloth to fully cooperate / eliminate the polarization induced charge to prove the effect. Other dopant impurities. Contains group II, IV, or VI elements. There are many ways to distribute (incorporate) qualitatively into semiconductors. For the rapidly changing material composition, in which the polarization is charged and is generated on a plane interface, it is more desirable that the qualitative distribution is T doped at or near the plane. The rapid change is one in which the molecular portion of a known component changes by more than 1% of a fully monolayer, a single crystal atomic layer. 7 Dyeing is intended to limit the dopant to a monoatomic layer, creating a dopant sheet rather than a dopant volume. For fractional composition changes, regardless of separation or continuous steps, the impurity distribution is also ideally classified. Fig. 2B shows that various types of impurity distribution include 7 61, separation step classification 62 and continuous classification 63. Medium composition blocking This specific embodiment refers to improving the emission efficiency of a light emitter with a GaN cladding layer. The material composition of the one or two cladding layers is made according to the material of the nearby layer, so as to reduce or eliminate the bimorph and spontaneous interface polarization induced charges. About 5% 锢 (In), for example, can be added to the GaN cladding layer of the nitriding system of FIG. 1A to change the composition cladding layer to In0.05Ga0.95N. As a result, the composition of the cladding layer is medium. In.20Ga.0.8N active region 5 contains 20% indium and GaN conductive layer 3 contains 0% rhenium. As shown in Figure 3A, indium reduces the difference in material composition between the two adjacent layers, achieving a 25% lower interface polarization induced charge plate density σ 1A between the active area and the cladding layer of 0.75 × 1013 electrons / cm2. σ 1B is about 0.25 × 1013 electrons / cm2. If there is a donor-type doping with σ 1A or σIB between one or two interfaces, some piezoelectric-induced charges will be screened out, as discussed above for selective doping. Because σ 1Α or σ 1B are both smaller than σ 1Α + σ 1B, which is a more traditional structure, this device structure loses the ability to select and filter out some polarization-induced charges, and the dimensions of this paper apply Chinese national standards (CNS ) Α4 size (210 X 297 mm) binding

497276 A7 B7 V. Description of the invention (11) Hold the dopant out of the active area. This is done by heavy-duty η-type doping with the σ 1B interface so that all such charges are effectively screened. In this way, the electric field in the active area is reduced by as much as 25% over the conventional structure, increasing the emission efficiency. Figure 3B shows the band diagram for this case. If the η-type doping extends to the σ 1A-containing interface, a further reduction is obtained. The cladding layer uses more rhenium, and the electric field in the active region is lower. However, with too much indium, the carrier restrictions can be discarded. The same technique can be applied to the upper cladding, except that charge screening must use P-type doping. By adding indium to one or two cladding layers, the polarization-induced electric field of the active area decreases under the operation of the device, resulting in an increase in emission efficiency, regardless of the lower barrier. Improved LED efficiency in the range of 450 nm to 470 nm confirms that the lower cladding layer 4 uses a low indium content of about 5% compared to an indium-free cladding layer. Quaternary blocking This specific embodiment refers to improving the emission efficiency of a light emitter with a ternary AlGaN cladding layer. The technique of adding aluminum nitride (A1N) to the native GaN cladding layer to produce a ternary AlGaN cladding layer is known. The band gap of the cladding layer caused by this addition is larger than the band gap of the adjacent and active regions so as to generate a higher energy barrier on the opposite side of the active region, thereby improving the carrier limitation. However, the addition of aluminum also increases the change in material composition and generates polarization-induced charges. In fact, the spontaneous and piezoelectric polarization-induced charges are determined by the change in the polarity of Ga to N bonding from one layer and the next layer, which actually increases in the active area / cladding interface. The increase in charge is due to the difference in piezoelectric strain and spontaneous polarization between the two materials. As a result, a south electric field exists in the active area of the device. A feature of the present invention is to reduce the difference between strain and polarization by making the material composition closer. Add indium nitride (InN) to one or two ternary AlGaN cladding layers to produce -14-This paper size applies Chinese National Standard (CNS) A4 specifications (210X 297 mm) 497276 A7 ______B7 V. Description of the invention (12) The formation of the quaternary AlInGaN cladding layer 'causes the average polarities of the adhesion between the two cladding layers and the active region to be similar. The inclusion of europium in the layer will have an adverse effect on the piezoelectric polarization induced charge of the interface generated by the aluminum at the cladding / active area interface. That is, compared with the ternary AlGaN cladding layer and the InGaN active region, there is a smaller charge plate between the quaternary AunGaN cladding layer and the InGaN active region. Most of the polarization-induced charges in the structure are limited by the heavily doped regions within the coating or contact layer, that is, they are removed from the active region and can be effectively screened. The amount of indium added to these layers is generally based on layer thickness, material composition, and growth restrictions ^ For example, an Al0.12In0.03Ga.85N cladding layer and then an In0055Ga 0.95N active layer reduce the interface pressure The electric charge density is about 30%, reaching 0.7 × 1013 electrons / cm2. Compared with the next same active layer Alo.uGao. ^ N, the electric field in the active region is reduced by about 30%. The quaternary cladding's indium and aluminum components result in elimination of the energy blocking effect of each other in the relevant active region. Although the addition of rhenium to the AlGaN cladding layer reduces the energy barrier of the active region, it actually limits the increase in efficiency because the polarization induced charge decreases. The cladding does not need the same composition to alter the efficiency of the emitter. For example, the LED efficiency is improved by about 25%, and the wavelength of 380 nm has been confirmed to use only one or four quaternary Al0.15In0.03Ga0.82N cladding layers that can block 0.26eV Ec and 0.08 eV Εν. The composition of the lower cladding layer was maintained at Al0.155Ga (). 85N. In a forward-biased condition approaching an LED turn on (eg, near the low emission limit), schematic diagrams of ternary AlGaN and quaternary AlInGaN cladding layers are shown in Figures 4A and 4B, respectively. The cladding layers 4 and 6 contain the same aluminum concentration in both configurations, but there is no indium in the binary structure. In both figures, the slope of the centerline 30 of the active region 5 represents the polarization-induced field. Its strength is based on the offset between the contact layers 3 and 7, the doping of the coating layers 4 and 6, and the density of the interface polarized charge plate. Two constructions

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Line ______- 15- This paper size applies Chinese National Standard (CNS) A4 specification (210X 297 public love) 497276 A7 B7 V. Description of the invention (13) Offset coating 4 used, about 2,6V, η- Type (Si) doping concentration is about lxl018 / cm3, and coating layer 6, about lxl019 / cm3, p type (Mg) doping concentration. The polarization-induced electric field generated by the ternary AlGaN cladding layer passing through the active region 5 is about 8.8 x 105 V / cm. As shown in Fig. 4A, this electric field causes the electrons and holes emitted from the Gan contact layers 3 and 7 to be spatially separated by restricting the carrier from approaching the interface 31 furthest from the emission contact layer. This phenomenon reduces the possibility of carrier recombination. The quaternary AlInGaN cladding layers 4 and 6 shown in FIG. 4B have a lower polarization induced electric field in the active region. The lower Al0.05In0.025Ga0.925N cladding layer 4 and the upper Al0.20In0.10Ga0.70N cladding layer 6 have an electric field of approximately 4 · 6 × 105 V / cm. The formation of these layers also has a lower polarization energy 31, reducing the spatial separation of free carriers to improve radioactive recombination. This is a compromise between reducing the polarization-induced charge and maintaining the maximum carrier-bound high-energy barrier, which can be determined experimentally. Coating layer with graded components In this specific embodiment, the components of one or two coating layers are graded to generate a space charge, that is, to produce an inverse interface polarizing effect with the interface between the coating layer and the active region. The grade changes the composition of the material in the pole direction to generate a piezoelectric charge. Grades can be continuous or discrete. The polarity of the distributed charge must be opposite to that of the target interface. The polarity is determined by the composition of the hierarchical layer and its two adjacent layers. For example, the low GaN contact layer 3 and the low AlGaN contact layer 4 of FIG. 1A produce a positive interface charge plate density. This charge can distribute the entire volume of the coating layer 4 by the gradual Al content of this layer. In more detail, the low cladding layer 4 can be classified from the GaN component containing 0% A1 close to the GaN conductive layer 3 to Alo.ioGao.9oN containing 10% A1 close to the InGaN active region 5. The positive space charge generated must be divided and measured 0 · 75χ1013 _-16- This paper size applies to the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 497276 A7 B7 V. Description of the invention (14) Electron / cm2 negative charge The density of the plate is 1 at the interface of Al0.10Ga0.9〇N / In0.05Ga0.95N. Negatively-charged plate. The density is the presence of the upper GaN contact layer 7 and the upper AlGaN cladding layer 6 and the entire volume of the cladding layer 6 can be distributed by the Al content. The resulting negative space charge must be split to measure the positive charge plate density2 to reduce or eliminate the effect on the active area. The magnitude of the space charge is based on the distance at which the classification takes place. Figure 5 shows that the AlGaN cladding layer is graded from the addition of A1 atoms per unit time (continuous 41 or separation step 42) to the surface of the crystal. The initial concentration of 0% A and the concentration of added gallium and nitrogen atoms 40 remain uniform throughout the growth period. When the proper coating thickness and classification are reached, the operation is stopped. The changing superlattice period of the two materials can also be used for composition classification. This is a compromise between better device performance due to the availability of free vectors near the active area and the counter-effects of dopant entry. The space charge generated by the graded coating allows the dopant impurities to be placed outside the graded layer (for example, only in the conductive layer), attracting its free carrier. The space charge of the graded components naturally attracts the free dopant carrier into the coating layer adjacent to the conductive layer. Therefore, the dopant impurities need not be close to the active area to create a free carrier to this area, and can be eliminated or reduced in the adjacent coating. Graded or mixed component active area The effect of a change in the composition of a semiconductor device on a free carrier may be similar to that of an electric field, and is treated as a quasi-electric field. See Herbert Kroemei *, π-Band Bias and Chemical Bonding: Heterostructure Applications ", Physica Scripta Journal, Volume T68, Pages 10-16, 1996. This embodiment of the present invention uses a quasi-electric field to measure the polarization-induced electric field of a free carrier It is possible to establish a quasi-electric field in the active area, and there is no need for any charging in the system. Figure 6A shows the quasi-electric field system -17- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm) 497276 A7 B7 V. Description of the invention (15) The rate of rise and fall of the energy band 51 is generated instead of the actual charging. The rate of rise and fall can be generated by the composition of the active area 5. In a quasi electric field, the electrons in the conductive band move to one. A low energy-oriented positive charge moves the pores in the atomic valence band to a high-energy negative charge. Note that the active zone in the electric field is non-parallel. Conversely, the energy bands in the electric field have a parallel relationship. As shown in Figure 1B. The active area can be graded by composition to produce an ideal rise and fall rate of the belt structure, and an ideal quasi-electric field effect. A quasi-electric field is generated, but should be related to the real electric field of at least one carrier It should be the opposite. The material composition of the active zone can be classified (continuous or discontinuous) by changing the indium composition. Depending on the width of the zone and the ideal radioactivity, it can be combined from a low to high or opposite indium composition into a graded composition. Important properties are generally Includes emission wavelength and operating current. Figures 6B and 6C show the net effect of the quasi-electric field on the energy band of active region 5. The active region in Figure 6B has a continuously graded indium concentration from low 5% to high 10%, with a rise and fall rate of approximately 1% / nm. The indium concentration at the interface between the cladding layer 4 and the active region 5 is the lowest, and increases to the highest concentration on the opposite side of the active region. In this case, the quasi electric field reduces the polarization induction of the atomic valence band. Electric field. The classification in the opposite direction will cause the electric field of the conductive band to shift. In FIG. 6C, the active region has a rise and fall rate and concentration of indium from 5% to 10% and an average rise and fall rate of 1% / nm, but in opposite directions. Because it is a kind of carrier, electrons or holes are diffusing outward, and there is better carrier space overlap, which increases the emission efficiency. Multi-Layer Emission with Electric Field Compensation Blocking Figure 7A shows a multi-layer with electric field compensation block 93 Launching system 90. In this embodiment, the launching system 90 is composed of alternating active regions 91 (such as light emission) and a cladding layer 92 (non-emission). Standards apply to Chinese National Standard (CNS) A4 specifications (210X297 mm) 497276 A7 ------------- B7 V. Description of the invention (16) Restrict active area emission carrier and resist its polarization induction The dual work of the electric field. The generated electric field and the total thickness of the multi-layer emission system 90 are generally based on the number 1 ′ and the composition of the active region 91 and the cladding layer 92. The multi-layer system 90 contains four InO.iGa〇. 9N, active region 91 each 2 nm thick and Ai005Ga95N and three cladding layers 92 each 5 nm thick. The total thickness of the multilayer system is 23 ηηη and the average average polarization induced electric field strength is 4.5x105 V / cm. The band structure with a specific volume of 100 in the single active region, as shown in FIG. 7B, may have a polarization electric field strength of 9 × j0 5 V / cm. The use of a multi-layer emission system will increase the total volume of the active area and ensure that the average electric field due to polarization-induced charges is reduced, comparing the specific volume of a single active area structure. Reverse Polarization In this embodiment, the polarization induced charge naturally generated by a compound semiconductor is reversed in order to improve carrier confinement. The internal atomic bonding in the anti-growth order of the atomic layer is naturally ionized because the gallium atom is slightly positive and the nitrogen atom is negative, creating a dipole through the bonding. Figure 8 shows the gallium and nitrogen atom layers grown along the polar direction of the crystal surface, respectively. In the order shown, the continuous atomic layers are alternated between Ga and N, with each layer containing only the bottom surface 70 of the Qa atomic layer and the top surface 71 of the single N atomic layer. Each dipole 72 is added through each GaN atom pair to generate an average polarization induced electric field 73 across the layer in the indicated direction. Its effect on the energy band of the active zone is as described in Fig. 1B above. This naturally occurring polarization induced electric field 73 can be inverted and reversed by the direction of each atomic dipole. That is, the growth order of Ga and N atomic layers is reversed. In FIG. 8B, the reverse growth order of the atomic layer starts from n, and then alternates with the N atomic layer until the top reaches the Ga layer 74. The growth order of the atomic layer can be -19- This paper size applies to China National Standard (CNS) A4 specification (210X 297 public love)

Binding

Line 497276 A7 B7 V. Description of Invention (17) It can be changed in various ways. First, if the N-terminated GaN or AlGaN base layer is initially used, it is not difficult to grow the N-plane polarity. However, most of the growth is done on sapphire or SiC and the growth is naturally the ideal Ga polarity. There are techniques to change the polarity. One technique uses MBE growth under high N content to change polarity. The second technique uses a single layer of manganese deposited on the surface, causing subsequent layers to be N-polar. The third method is to use an epitaxial layer epitaxially grown by MOCVD or MBE to try to force nucleation in the correct polarity. Each dipole 75 generates a polarization induced electric field 76 in a direction opposite to the electric field 73 of FIG. 8A. The effect of the band of the active region is shown in Figure 8C. Although this growth sequence is continuous to generate a polarization-induced electric field in the active region, the dipole system of the electric field is reversed. In this way, the launching carrier can be opened before the device is opened. ) Polarization-induced charge densities σ 1 and σ 2. Electrons emitted from the cladding layer 4 higher than Ec toward the active region accumulate close to σ2 on the cladding / active region interface. The accumulated charge of these free carriers neutralizes j2. Similarly, the neutralization j 1 of the emission hole 6 from the cladding layer 6 lower than Ev is close to the cladding / active area interface. This method "levels" the active zone energy band before the device is opened, similar to 7F in Figure 1C. As a result, the efficiency of the device is not reduced by the polarization induced charge. Another advantage of this device structure is that the carrier is overshooting, and the path A is greatly reduced, compared with the traditional structure. In addition, electron and hole carrier restrictions are increased. Inverted structure In a conventional LED, the n-type layer is grown before the p-type. This specific embodiment reverses this order of growth. FIG. 9A is a sectional view showing the new growth times of the LED

Pretend

497276 A7 B7 V. Description of the invention (18) In the order, the p-type contact layer and the cladding layers 83, 84 grow before the n-type cladding layer and the contact layers 86 and 87. The thickness and material composition of each layer in this embodiment are similar to the nitride emitter of FIG. 1A. Despite the inversion layer structure, the interface polarization-induced charge plate densities σΐ and σ2 are still moving forward due to changes in the material composition of each layer. The band effect in the active region is shown in Fig. 9B, which is similar to that in Fig. 1B. However, inversion of the growth order of the p-type and n-type layers will also change the direction in which the emitted electrons and holes enter the active region. In this method, electrons that must be emitted from the n-type contact layer are incident from the contact layer 87 higher than Ec into the active region 85 from the left. The hole is projected from the right by a p-type contact layer 83 which is lower than ν. This reversed layer order allows the carrier to be similar to the previous embodiment in that the charge density is screened before the device is opened, in which the direction of the electric field replaces the layer structure. This structure is also similar to the previous specific embodiment, reducing carrier overshoot and increasing carrier limitation. Changing the Lattice Constant Figures 10A and 10B show another method to improve the polarization induced electric field in the structure. By changing the lattice constant in the plane of the structure under the active region 113 so that the active layer is less strained or the direction of the strain is reversed, the piezoelectric polarization induced electric field can be reduced, eliminated or reversed in the active region as shown by the energy band curve in FIG. 10B Show. The lower lattice constant can be changed using a variety of methods. First, the buffer layer 110 can be grown with different material components, such as InAlGaN, so that the in-plane lattice constant of the buffer layer is close to the in-plane lattice constant of the InGaN active layer. The band gap of the InAlGaN buffer layer is also larger than that of the InGaN active layer, resulting in no light absorption. The second method for changing the lattice constant in the plane is to use a conventional buffer layer, but at least η contact layer 111 is grown using a different material composition, such as AlInGaN, resulting in an in-plane lattice constant of the buffer layer -21-This paper Standards apply to Chinese National Standard (CNS) A4 specifications (210 X 297 mm) 497276 A7 B7

5. Description of the invention (19) Change the lattice constant in the plane close to the active layer. In this way, the above advantages can be seen. The third method is the same as the n-contact layer described above: changing the lattice constant in the bottom cladding layer 112. In the fourth method, the growth thickness of the active region is sufficient to cause strain release, so that, in addition to the induced electric field in the active layer. The method selection is generally a method that provides a minimum amount of material dislocation packages to maintain the quality of the materials and provide the advantages of the device structure described above. There are many ways to further reduce or eliminate most of the residual polarization induced charges. The various specific embodiments described above can be mixed and matched and applied to any or all suitable layers, emissive or non-emissive. Any known application, particularly a specific embodiment or combination of specific embodiments, must be based on the nature of the application and can be determined experimentally. For example, one possibility is to merge the AlGaN cladding layer 92 & InGaN active region 91 contains the counter-effects of blocking the aluminum and indium four times. In addition, the aluminum component of the at least one cladding layer 92 is graded and / or impurities are added to ionize into a state of charge in which the interface polarization induced charges are opposite. Although many specific embodiments of the present invention have been shown and described, those skilled in the art will still have some changes and modifications of the specific embodiments. For example, although the description refers to a nitride emitter, any or all of the specific embodiments may be used to illustrate the problem of polarization induced charge of a light emitter containing other materials. Specific embodiments of those changes and modifications are contemplated and can be made without departing from the spirit of the invention as defined by the scope of the appended patents. _____- 22- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Pretend

Claims (1)

497276 A8 B8 C8 1 · An optical transmitter, which includes: j-South efficiency double heterostructure including type 11 and? -Type contact layer and cladding layer three | Meiji-type active light emitting region and growth along a crystalline pole, | The high-efficiency double heterostructure has a poor structure since a basic heterostructure contains i and f The dipoles pass through the active region to generate a polarization-induced electric field, and the binary or ternary cladding layer contains an n-type contact layer. The growth order is i before the p-type contact layer. Polarization of high-efficiency double-heterostructure active region Reduced efficiency of induced electric field effect. Compare the polarization of the basic heterostructure | Induced electric field. : 2 · If the light emitter of the first patent application scope, the active region contains | InGaN and the poor structure includes adding ιη to at least one of the cladding layers, so that at least one of the cladding layers contains AlxInyGabx -yN, where 0 € X $ 1: and OSyS 1. 1 ding 3 · The light emitter of item 1 in the patent application range, wherein the structural difference includes | a component elevation rate of at least one of the coating layers to counteract at least one of the coating layer i and the interface between the active regions Interface polarization effect. 4 · If the light emitter of the scope of the patent application, the structure difference includes :; at least the component rise and fall rate of the active area to counter the polarization induced electricity 丨. 5 · If the scope of the patent application of the light An emitter, wherein the poor structure includes adding a dye to at least one of the coating layers and reducing the polarization induced electric field. 6. The light emitter as described in the scope of the patent application, where the structural difference includes 1 -23- This paper size applies to China National Standard (CNS) A4 (210X297 mm) 497276 An opposite phase of the active area atomic dipole. 7. The light emitter of item 丨 in the scope of patent application, wherein the structural difference includes the P-type contact layer whose growth order precedes the n-type contact layer. 8 · The light emitter according to item 丨 of the patent application, wherein the structural difference includes alternating multiple active regions and cladding layers. 9 · The light emitter according to item 丨 of the patent application, wherein the structural difference includes at least a part of the lower cladding with a strain release, which has an in-plane lattice constant close to the in-plane lattice constant value of the strain-free active region material. . 10 · If the scope of patent application is the first! The item of the light emitter, wherein the n-type contact layer including the difference in soil release strain has an in-plane crystal lattice constant close to the in-plane lattice constant value of the strain-free active region material. U. For example, the light emitter of the scope of patent application, grows on a buffer layer, the structure difference includes that the buffer layer releases at least part of the strain and has a plane with a lattice constant close to the plane of the strain-free active region material. Internal lattice constant value. 12. A hybrid semiconductor device each grown along a vertical crystalline pole, comprising at least two crystalline layers whose material composition changes along the direction of the pole; at least one of the three layers has a material composition with a medium material composition. Compare two adjacent layers 13. For example, the device in the scope of patent application No. 12, wherein the at least-, AlxInyGa ^ x-yN cladding layer, which is called 14 · a hybrid semiconductor device that grows along each vertical crystal pole, 勹The material composition of the plurality of crystalline layers along the polar direction includes: 乂 produces ", a polarization induced charge is concentrated in at least one of the layers; soil ^ -24- k 497276 A8 B8 C8 D8 6. Scope of patent application At least one of the layers includes a coating layer whose composition is graded to produce a volume with a space charge exceeding the grade to resist the charge concentration. 15. For the device in the scope of application for patent item 14, the graded coating layer includes AlxInyGa ^ x-yN, of which 0 $ xS 1 and 0 $ 1. 16. —A hybrid semiconductor device that grows along a vertical crystalline pole, comprising: a plurality of crystalline layers whose material composition changes along the direction of the pole; at least one of the layers has a graded component that generates a space charge exceeding a volume of the grade to The dopant is allowed to precipitate from the adjacent layer exogenously. 17. As for the device under the scope of the patent application, the hierarchical layer includes AlxInyGar X · yN, where OSx ^ l and O ^ ySl. 18. —A hybrid semiconductor device growing along each vertical crystalline pole, comprising: a plurality of crystalline layers whose material composition changes along the direction of the pole to generate a polarization induced electric field in at least one of the layers; one of the layers The composition includes an active region that is graded to generate a quasi-electric field to resist the polarization-induced electric field. 19. The device according to item 18 of the scope of patent application, wherein the level generates a band elevation rate of the active region to generate the quasi electric field. 20. For the device in the scope of application for patent No. 18, the active area includes AUIiiyGamN, of which 0 $ xS 1 and OS yS 1. 21. A hybrid semiconductor device growing along each vertical crystalline pole, comprising: a plurality of crystalline layers whose material composition changes along the direction of the pole to generate a polarization-induced charge concentrated on at least one of the layers; at least the layers One of the combined dopant impurities is ionized to a state of charge that is at least opposite to one of the charge concentrations. -25- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm) 49497 (5 AB c D 6. Application scope 22. A hybrid semiconductor device that grows along the vertical crystal poles, including: a crystal with a pole direction; and a plurality of crystal layers whose material composition changes along the pole direction To generate a polarization induced electric field in at least one of the layers; at least one of the layers has an atomic order with alternating polarities, that is, the direction of the polarization induced electric field in at least one of the layers is reversed. -A hybrid semiconductor device that grows along each vertical crystalline pole, including: a crystal having a pole direction; and at least one of each of the p-type and n-type crystalline layers whose material composition changes along the pole direction to generate a polarization-induced charge Focus on at least one of the layers; the growth order of the p-type layer before the n-type layer resists the effect of the charge concentration on the performance of the device. 24.-a hybrid semiconductor device that grows along each of the vertical crystalline poles, Containing: a plurality of crystalline layers whose material composition changes along the polar direction to generate a polarization induced electric field in at least one of the layers; one of the layers includes alternating Emissive and non-emissive layers, using the non-emissive layer to limit the emission carrier within the emissive layer and resist the electric field. 25. For example, the device in the scope of patent application No. 24, wherein the material composition of at least one of the non-emissive layers is graded to generate a quasi-electric field Resist the electric field. 26. If the device of the scope of the patent application is applied for, the material composition of at least one of the emitting layers is graded to generate a quasi electric field to resist the electric field. The material composition of one of the non-emissive layers is graded to generate a quasi-electric field that resists the electric field. 28. For the device in the scope of application for patent No. 24, at least the non-emissive layer is -26- This paper size applies to China National Standard (CNS) A4 specifications (210X 297 mm) 497276 A8 B8 C8 D8 VI. One of the scope of patent application includes the transformation of dopant to provide space charge, which is to resist the electric field. 29. A hybrid semiconductor device comprising: a crystal having a pole direction, and a plurality of crystal layers whose material composition changes along the pole direction to generate a polarization induced electric field in at least one of the layers; at least one of the layers One is an active region; one of the layers is lower than the active region, and at least part of the strain is released causes the crystal lattice constant in the plane of the layer lower than the active region to approach the crystal lattice constant in the plane of the unstrained active region material, This reduces, eliminates or reverses the electric field in the active region. 30. A hybrid semiconductor device comprising: a crystal having a pole direction; and a plurality of crystal layers whose material composition changes along the pole direction to generate a polarization induced electric field in at least one of the layers; at least one of the layers One is an active region; the growth of the active region causes the material in the device to release strain at least partially, thereby reducing the electric field in at least the active region. -27- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)