Heterojunction bipolar transistor and electronic device

Abstract

The application provides a heterojunction bipolar transistor and an electronic device. The heterojunction bipolar transistor comprises a collector layer, a base layer and an emitter layer; the base layer comprises a first base layer, a second base layer and a third base layer; the first base layer is located between the second base layer and the collector layer; the third base layer is located between the second base layer and the emitter layer; the band gap of the second base layer is smaller than the band gap of the first base layer; the band gap of the second base layer is smaller than the band gap of the third base layer; and the absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is smaller than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer. The heterojunction bipolar transistor can reduce the turn-on voltage of the HBT, thereby reducing the overall power consumption of the HBT.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor, in particular to a heterojunction bipolar transistor and an electronic device. BACKGROUND

[0002] Heterojunction bipolar transistors (HBTs) utilize two or more different semiconductor materials to construct its emitter layer and base layer, forming so-called heterojunctions, to improve the injection efficiency of electrons, reduce the resistance and capacitance of the base layer, and thus increase the amplification factor and operating frequency of the HBT. The theoretical foundation of HBT was proposed by Herbert Kroemer in 1957, and he won the Nobel Prize in Physics in 2000 for his contributions in this field. However, the actual production of HBTs did not begin until 1977, mainly using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) techniques. Common materials for HBTs include gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium phosphide (InP), indium gallium arsenide (InGaAs), silicon (Si), and silicon-germanium alloy (SiGe), among others. Different material combinations can meet different performance requirements and application scenarios. For example, GaAs / AlGaAs HBTs are known for their high speed, low noise, high temperature stability, and lower power consumption, while Si / SiGe HBTs are favored for their low cost, high integration, high linearity, and compatibility with CMOS technology. HBTs have been widely used in the fields of microwave, millimeter wave, optoelectronics, and high-speed digital.

[0003] In the development process of HBTs, optimizing the overall power consumption of HBTs is a key consideration in the design and manufacturing process of the device. SUMMARY

[0004] The embodiments in the present specification provide a heterojunction bipolar transistor and an electronic device that can reduce overall power consumption.

[0005] The embodiments in the present specification provide a heterojunction bipolar transistor, which includes a collector layer, a base layer, and an emitter layer.

[0006] The base layer includes a first base layer, a second base layer and a third base layer; the first base layer is located between the second base layer and the collector layer; the third base layer is located between the second base layer and the emitter layer; the band gap of the second base layer is smaller than the band gap of the first base layer; the band gap of the second base layer is smaller than the band gap of the third base layer; the absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is smaller than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer.

[0007] Optionally, the collector layer is a GaAs layer; the first base layer is a GaAs layer, the second base layer is an InxGa1-xAsySb1-y layer, where 0 < x < 1, 0 < y < 1; the third base layer is a GaAs layer; and the emitter layer is an InGaP layer or an AlGaAs layer.

[0008] Optionally, 0 < x < 0.7, 0.35 < y < 1.

[0009] Optionally, when x is any fixed value in the range of 0 to 0.7,

[0010] Optionally, when y is any fixed value in the range of 0.35 to 1,

[0011] Optionally, the second base layer has a first surface facing the first base layer and a second surface facing the third base layer; x gradually increases from the first surface to the second surface.

[0012] Optionally, x linearly changes from 0 to 0.7 with the thickness from the first surface to the second surface.

[0013] Optionally, x gradually increases from 0 to 0.7 with the thickness from the first surface to the second surface, and the increasing amplitude gradually increases.

[0014] Optionally, the thickness of the base layer falls within the range of 10-60 nm; the thickness of the first base layer and the third base layer both falls within the range of 0-10 nm.

[0015] The electronic device provided by the embodiments of the present application includes the heterojunction bipolar transistor provided by the present application.

[0016] In some embodiments of the present disclosure, the second base layer has a smaller band gap, so that the band gap of the whole base layer is reduced. The absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is smaller than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer. Thus, even if the second base layer has a smaller band gap, the better conduction band continuity at the interface between the base layer and the emitter layer can be maintained. Therefore, the turn-on voltage of the HBT can be reduced, and the overall power consumption of the HBT can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A structure schematic diagram of a heterojunction bipolar transistor provided by an embodiment of the present disclosure.

[0018] Figure 2 A band diagram of a heterojunction bipolar transistor provided by another embodiment of the present disclosure.

[0019] Figure 3 Theoretical curves of the band gap and lattice constant of InxGa1-xAsySb1-y with respect to the composition.

[0020] Figure 4 A band diagram of a base layer of a heterojunction bipolar transistor provided by another embodiment of the present disclosure.

[0021] Figure 5 A band diagram of a base layer of a heterojunction bipolar transistor provided by another embodiment of the present disclosure.

[0022] 110, collector layer; 120, base layer; 121, first base layer; 122, second base layer; 1221, first surface; 1222, second surface; 123, third base layer; 130, emitter layer; 140, substrate; 150, sub-collector layer; 160, first emitter cap layer; 170, second emitter cap layer. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, but not all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present disclosure.

[0024] In the description of the embodiments of the present application, it should be understood that the terms "first", "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly and specifically limited.

[0025] In the related art, the turn-on voltage of the HBT refers to the forward bias voltage from the emitter layer to the base layer, which determines the electron injection efficiency from the emitter to the base. Generally, the turn-on voltage of the HBT is lower than that of the traditional homojunction bipolar transistor (BJT), because the HBT uses a material with a larger band gap in the emitter layer, and the emitter-base junction has a larger valence band offset, which enhances the built-in electric field between the emitter and the base. The turn-on voltage of the HBT is one of the key parameters affecting the performance and application of the HBT, including power dissipation, noise, linearity and frequency response. Optimizing and controlling the turn-on voltage of the HBT can achieve lower power consumption, lower noise, higher linearity and faster frequency response, and thus is a key consideration in the design and manufacturing process.

[0026] In the related art, the band gap refers to the energy difference between the conduction band and the valence band in a solid material. In a solid material, the energy of an electron is not arbitrary, but is distributed in a specific energy band. Specifically, in an atom, electrons move around the atomic nucleus, but they can only be on specific orbits, each of which corresponds to a certain energy value. The energy value of these orbits is the energy level of the electron. The energy band is formed by the overlap and extension of a large number of atomic energy levels. The valence band is the energy band of the highest energy level that can be occupied by valence electrons in a solid. At absolute zero, the valence band is usually filled with electrons. The conduction band is above the valence band and is the energy band to which electrons can jump to the next energy level. Under certain conditions, electrons in the valence band can obtain enough energy to jump to the conduction band and become free electrons to participate in conduction.

[0027] In the related art, in a semiconductor heterojunction structure, the conduction band continuity at the interface between the base layer and the emitter layer refers to whether the conduction band energy level is smoothly connected without obvious energy level steps at the interface of two different semiconductor materials. The conduction band continuity has an important influence on the transmission efficiency of electrons and the performance of the device, especially for high-performance semiconductor devices such as HBT.

[0028] The inventor has found that the turn-on voltage of the HBT is affected by the band gap of the material, the continuity of the conduction band at the interface between the base layer and the emitter layer, and the like. At present, InGaP and GaAs are commonly used semiconductor materials for making the emitter and the base, and these material combinations can provide high power output and high linearity. Specifically, if the band gap of the base layer is wider, the voltage required for the excited electron transition is higher, thereby resulting in an increase in the overall power consumption. If the band gap of the base layer is narrower, the continuity of the conduction band at the interface between the base layer and the emitter layer is poorer, which also results in an increase in the turn-on voltage of the HBT, and further results in an increase in the overall power consumption.

[0029] Based on this, the inventor proposes an HBT, in which the base layer is provided to include a first base layer, a second base layer, and a third base layer. The first base layer is located between the collector layer and the second base layer, and the third base layer is located between the second base layer and the emitter layer. The band gap of the second base layer is smaller than the band gap of the first base layer, and the band gap of the second base layer is smaller than the band gap of the third base layer. The band gap of the second base layer is smaller, thereby reducing the band gap of the entire base layer. The absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is smaller than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer. Thus, even if the band gap of the second base layer is smaller, the continuity of the conduction band at the interface between the base layer and the emitter layer can be maintained. Therefore, the turn-on voltage of the HBT can be reduced, and further the overall power consumption of the HBT can be reduced.

[0030] Referring to Figure 1 An embodiment of the present specification provides an HBT, which includes a collector layer 110, a base layer 120, and an emitter layer 130. The base layer 120 includes a first base layer 121, a second base layer 122, and a third base layer 123. The first base layer 121 is located between the second base layer 122 and the collector layer 110. The third base layer 123 is located between the second base layer 122 and the emitter layer 130. The band gap of the second base layer 122 is smaller than the band gap of the first base layer 121, and the band gap of the second base layer 122 is smaller than the band gap of the third base layer 123. The absolute value of the difference between the conduction band of the third base layer 123 and the conduction band of the emitter layer 130 is smaller than the absolute value of the difference between the conduction band of the second base layer 122 and the conduction band of the emitter layer 130.

[0031] The band gap of the second base layer 122 is small, thereby reducing the band gap of the whole base layer. The absolute value of the difference between the conduction band of the third base layer 123 and the conduction band of the emitter layer 130 is smaller than the absolute value of the difference between the conduction band of the second base layer 122 and the conduction band of the emitter layer 130. Thus, even if the band gap of the second base layer 122 is small, the good conduction band continuity at the interface between the base layer 120 and the emitter layer 130 can be maintained. Therefore, the turn-on voltage of the HBT can be reduced, and the overall power consumption of the HBT can be reduced.

[0032] In addition, the third base layer 123 arranged between the emitter layer 130 and the second base layer 122 can effectively reduce the current gain reduction caused by the conduction band discontinuity.

[0033] Furthermore, the structure of the base layer 120 provided by the embodiments of the present disclosure helps to form a stable double heterojunction structure, effectively controls the movement of charge carriers, and improves the current driving capability and frequency response of the HBT.

[0034] Optionally, the conduction band of the third base layer 123 is between the conduction band of the second base layer 122 and the conduction band of the emitter layer 130, and the conduction band of the second base layer 122 is lower than the conduction band of the emitter layer 130. Thus, the conduction band continuity at the interface between the second base layer 122 and the third base layer 123 is also good, and the band gap of the base layer 120 is narrow, thereby better reducing the turn-on voltage of the HBT.

[0035] Further optionally, the valence band of the second base layer 122 is higher than the valence band of the emitter layer 130, thereby better ensuring that the base layer 120 has a narrow band gap.

[0036] Optionally, the absolute value of the difference between the conduction band of the first base layer 121 and the conduction band of the collector layer 110 is smaller than the absolute value of the difference between the conduction band of the second base layer 122 and the conduction band of the collector layer 110. Thus, the good conduction band continuity at the interface between the base layer 120 and the collector layer 110 can be ensured, and the current blocking effect between the base layer 120 and the collector layer 110 can be effectively reduced, thereby reducing the probability that part of the electrons are blocked at the base-collector (B-C) heterojunction, reducing the collector current and the current gain reduction, and further reducing the knee effect.

[0037] Further optionally, the conduction band of the first base layer 121 is between the conduction band of the second base layer 122 and the conduction band of the collector layer 110, and the conduction band of the second base layer 122 is lower than the conduction band of the collector layer 110. Thus, the conduction band continuity at the interface between the second base layer 122 and the third base layer 123 is also good, and the band gap of the base layer 120 is narrow, thereby better reducing the turn-on voltage of the HBT.

[0038] Further, the valence band of the second base layer 122 is higher than that of the collector layer 110, so as to ensure that the base layer 120 has a narrower band gap.

[0039] In the embodiment, the collector layer 110 is a GaAs layer. The first base layer 121 is a GaAs layer, the second base layer 122 is an InxGa1-xAsySb1-y layer, where 0 < x < 1 and 0 < y < 1, and the third base layer 123 is a GaAs layer. The band gap of the second base layer 122 is smaller than that of the first base layer 121, and the band gap of the second base layer 122 is smaller than that of the third base layer 123. The emitter layer 130 is an InGaP layer or an AlGaAs layer. Therefore, the conduction band of the first base layer 121 is smaller than that of the collector layer 110, and the conduction band of the third base layer 123 is smaller than that of the emitter layer 130.

[0040] It can be understood that the collector layer 110 and the first base layer 121 are both GaAs layers, but have different structures. The collector layer 110 and the first base layer 121 form a PN junction, i.e. the surface of the base layer 120 in contact with the collector layer 110, so the collector layer 110 and the first base layer 121 have different types of doping. For example, the collector layer 110 has a light N-type doping, and the first base layer 121 has a heavy P-type doping.

[0041] In a conventional HBT, the base layer is GaAs, and GaAs and other wide band gap materials, such as InGaP or AlGaAs, form an I-type band arrangement. This arrangement limits its use in some applications, especially in situations where wide band gap materials are needed to increase the breakdown voltage of the collector layer, such as in applications requiring high voltage and high current processing capability, high power applications, and high speed hybrid mode circuits. Under this band arrangement, if a wide band gap material is used to increase the breakdown voltage of the collector layer, a collector current blocking effect may occur, which will seriously affect the performance of the device.

[0042] To overcome these problems, in conventional HBTs, a specific material layer, such as InGaP or InGaAsP, is inserted between the base layer and the collector layer to form a tunnel collector layer. The purpose of this is to increase the continuity of the conduction band at the interface between the base layer and the collector layer, thereby improving the performance of the device. In addition, in some HBTs, the bandgap of the base layer is adjusted by changing the material of the base layer to indium gallium arsenide nitride (InxGa1-xAsyN1-y), gallium arsenide antimony (GaAsxSb1-x) or indium gallium arsenide antimony (InxGa1-xAsySb1-y), thereby changing the turn-on voltage between the base layer and the emitter layer. This method can optimize the performance of the device, such as reducing the turn-on voltage and improving the electron mobility, by adjusting the content of In and N or Sb.

[0043] However, the introduction of N elements into the material forming the base layer can bring new problems, such as an increase in non-radiative recombination centers, which can reduce the quality of the material and have a negative impact on the performance of the device. In addition, the mobility of electrons can be improved by increasing the content of In in the base layer material. Because an increase in the content of In will result in a decrease in the energy gap of the material, thereby reducing the effective mass of the electrons. But this method requires precise control of the composition of In in the material, so that the height of the valence band of the InxGa1-xAsySb1-y material is not lower than the height of the valence band of the GaAs material, to balance the performance improvement of the HBT and the possible negative effects.

[0044] However, in the embodiments provided in the present specification, the second base layer 122 is an InxGa1-xAsySb1-y layer, although it also contains In and Sb, but due to the arrangement of the first base layer 121 and the third base layer 123, the requirement for the control accuracy of x is reduced, and the adjustable range of the bandgap of the base layer is larger.

[0045] Further, optionally, 0 < x < 0.7, 0.35 < y < 1. The values of x and y will also affect the lattice constant of the second base layer 122. The value range of x and y can make the lattice mismatch between the second base layer 122 and the first base layer 121 less than 5%, thereby avoiding the occurrence of lattice relaxation when the second base layer 122 is generated.

[0046] Referring to Figure 2, x and y are fixed values, wherein x and y are selected to satisfy the conditions of 0 < x < 0.7 and 0.35 < y < 1, the band diagram of the HBT. As can be seen from the figure, at this time, the band gap of the second base layer 122 is smaller than the band gap of the first base layer 121, and also smaller than the band gap of the third base layer 123, thereby reducing the overall band gap of the base layer 120. In addition, the conduction band of the third base layer 123 is located between the second base layer 122 and the emitter layer 130. The conduction band of the emitter layer 130 to the second surface 1222 is stepped, so that the conduction band peak height of the emitter-base junction is reduced, and the conduction band barrier that the electron needs to overcome each time is relatively small. Therefore, the conduction band continuity at the interface between the base layer 120 and the emitter layer 130 is better, so as to better reduce the opening voltage of the HBT.

[0047] Referring to Figure 3 , the theoretical curve of the band gap and the lattice constant of the InxGa1-xAsySb1-y quaternary alloy with the composition. Among them, the straight line is the equal lattice constant line of the second base layer 122 and the first base layer 121 with a lattice mismatch of 5%. The curve marked with numbers is the equal band gap line. As can be seen from the figure, when 0 < x < 0.7 and 0.35 < y < 1, the lattice mismatch of InxGa1-xAsySb1-y and GaAs is less than 5%. And, with the increase of x, or with the increase of y, the lattice constant of InxGa1-xAsySb1-y gradually increases and the band gap gradually decreases.

[0048] Optionally, when x is any fixed value in the range of 0 to 0.7, In this way, the base layer 120 can not only maintain a low band gap, but also avoid the phenomenon of lattice stress mismatch, thereby ensuring the stability and reliability of the heterojunction bipolar transistor.

[0049] Optionally, when y is any fixed value in the range of 0.35 to 1, In this way, the base layer 120 can not only maintain a low band gap, but also avoid the phenomenon of lattice stress mismatch, thereby ensuring the stability and reliability of the heterojunction bipolar transistor.

[0050] Optionally, the second base layer 122 has a first surface 1221 facing the first base layer 121, and a second surface 1222 facing the third base layer 123. From the first surface 1221 to the second surface 1222, x gradually increases. Therefore, from the first surface 1221 to the second surface 1222, the band gap of the second base layer 122 gradually decreases. In one aspect, the first surface 1221 of the second base layer 122 has a wider band gap, so that the second base layer 122 has better conduction band continuity at the interface with the first base layer 121; on the other hand, from the first surface 1221 to the second surface 1222, the band gap of the second base layer 122 gradually decreases, so that the overall band gap of the second base layer 122 is lower, and thus the band gap of the base layer 120 is lower, so as to reduce the on-voltage of the transistor and reduce power consumption. In addition, as x gradually increases, the In content gradually increases, the electron mobility increases, the resistance of the base layer 120 of the heterojunction bipolar transistor decreases, so that the heterojunction bipolar transistor has good frequency characteristics.

[0051] Optionally, from the first surface 1221 to the second surface 1222, x linearly changes with the thickness from 0 to 0.7, that is, linearly increases, and the corresponding band diagram is shown in FIG. 12B. Figure 4 As can be seen from FIG. 12B, the band gap of the second base layer 122 also linearly changes, and from the first surface 1221 to the second surface 1222, the band gap of the second base layer 122 gradually decreases. Figure 4 In the second base layer 122, x linearly increases, and the In content linearly increases, so as to induce the formation of built-in potential in the base layer 120, which helps to accelerate the transmission of carriers (usually electrons) in the base layer 120, thereby reducing the transit time of the carriers in the base layer 120, thereby improving the current gain. In addition, the reduction of the transit time can also make the response speed of the heterojunction bipolar transistor faster.

[0052] Optionally, from the first surface 1221 to the second surface 1222, x gradually increases with the thickness from 0 to 0.7, and the increasing amplitude gradually increases, and the corresponding band diagram is shown in FIG. 12C. Figure 5 As can be seen from FIG. 12C, from the second surface 1222 to the first surface 1221, the band gap of the second base layer 122 gradually increases, and the increasing amplitude gradually decreases, so as to effectively reduce the current blocking effect in the collector layer 110. Figure 5 In addition, since the conduction band is continuous between the gradually changing base layer 120 and the collector layer 110, that is, there is no conduction band discontinuity phenomenon, the current blocking effect of the collector layer 110 does not occur, thereby avoiding the problem that the current gain sharply decreases when the current density in the collector layer 110 is high.

[0053] Optionally, the thickness of the base layer 120 falls within the range of 10nm-60nm; wherein the thickness of the first base layer 121 and the third base layer 123 both fall within the range of 0-10nm. The third base layer 123 and the first base layer 121 are arranged to be thinner, so as to make the conduction band between the base layer 120 and the collector layer 110 and the base layer 120 and the emitter layer 130 can be smoothly connected, and also to reduce the time of carrier transmission in the base layer 120.

[0054] Referring to Figure 1 In the embodiment shown, the HBT further comprises a substrate 140, a sub-collector layer 150, a first emitter cap layer 160, and a second emitter cap layer 170. The substrate 140 is located on the side of the sub-collector layer 150 away from the collector layer 110; the sub-collector layer 150 is located on the side of the collector layer 110 away from the base layer 120; the first emitter cap layer 160 is located on the side of the emitter layer 130 away from the base layer 120; and the second emitter cap layer 170 is located on the side of the first emitter cap layer 160 away from the emitter layer 130. Optionally, the substrate 140 is a GaAs substrate; the sub-collector layer 150 is a GaAs layer; and the first emitter cap layer 160 is formed of GaAs and / or InGaAs.

[0055] One embodiment of the present specification provides an electronic device. The electronic device comprises the HBT provided by the embodiments of the present specification.

[0056] The electronic device described above, the band gap of the second base layer is smaller, thereby reducing the band gap of the whole base layer. The absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is smaller than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer. Therefore, even if the band gap of the second base layer is smaller, the better conduction band continuity at the interface between the base layer and the emitter layer can be maintained. Therefore, the turn-on voltage of the HBT can be reduced, thereby reducing the overall power consumption of the HBT, and further reducing the overall power consumption of the electronic device.

[0057] Optionally, the electronic device is a power converter. Specifically, the power converter can be an inverter or a rectifier, etc. Of course, the electronic device can also be an amplifier, a switching circuit, a wireless communication device, a radar device, a satellite communication device, an optical communication device, a frequency synthesizer, a micro-electro-mechanical system (MEMS), etc.

[0058] It can be understood that the specific examples herein are only to help those skilled in the art better understand the embodiments of the present specification, and not to limit the scope of the present application.

[0059] It can be understood that, in various embodiments in the specification, the magnitude of the serial number of each step does not mean the order of execution, the execution order of each step should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the specification.

[0060] It can be understood that the various embodiments described in the specification can be implemented alone or in combination, and the embodiments of the specification do not limit this.

[0061] Unless otherwise specified, all technical and scientific terms used in the embodiments of the specification are the same as those commonly understood by those skilled in the art of the technical field of the specification. The terms used in the specification are only for the purpose of describing the specific embodiments and are not intended to limit the scope of the specification. The term "and / or" used in the embodiments of the specification includes any and all combinations of one or more related listed items. The singular forms "a", "an" and "the" used in the embodiments of the specification and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. Further, the terms "up", "down", etc. used in the specification are only used to express the relative positional relationship between the features in conjunction with the drawings, and do not constitute a necessary limitation on the product form when located in the real world.

[0062] The above is only a specific embodiment of the specification, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the specification, which should be covered within the protection scope of the specification. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A heterojunction bipolar transistor, characterized in that, The heterojunction bipolar transistor includes a collector layer, a base layer, and an emitter layer; The base layer includes a first base layer, a second base layer, and a third base layer; the first base layer is located between the second base layer and the collector layer; the third base layer is located between the second base layer and the emitter layer; the bandgap of the second base layer is smaller than the bandgap of the first base layer; the bandgap of the second base layer is smaller than the bandgap of the third base layer; the absolute value of the difference between the conduction band of the third base layer and the conduction band of the emitter layer is less than the absolute value of the difference between the conduction band of the second base layer and the conduction band of the emitter layer; The conduction band of the second base layer is respectively smaller than the conduction bands of the first base layer and the third base layer, the conduction band of the first base layer is smaller than the conduction band of the collector layer, and the conduction band of the third base layer is smaller than the conduction band of the emitter layer; the valence band of the second base layer is respectively higher than the valence bands of the collector layer and the emitter layer.

2. The heterojunction bipolar transistor according to claim 1, characterized in that, The collector layer is a GaAs layer; the first base layer is a GaAs layer, the second base layer is an InxGa1-xAsySb1-y layer, where 0 < x < 1 and 0 < y < 1; the third base layer is a GaAs layer; the emitter layer is an InGaP layer or an AlGaAs layer.

3. The heterojunction bipolar transistor according to claim 2, characterized in that, 0 < x < 0.7, 0.35 < y < 1.

4. The heterojunction bipolar transistor according to claim 3, characterized in that, When x is any fixed value in the range of 0 to 0.7, .

5. The heterojunction bipolar transistor according to claim 3, characterized in that, When y is any fixed value in the range of 0.35 to 1, .

6. The heterojunction bipolar transistor according to claim 3, characterized in that, The second base layer has a first surface facing the first base layer and a second surface facing the third base layer; from the first surface to the second surface, x gradually increases.

7. The heterojunction bipolar transistor according to claim 6, characterized in that, From the first surface to the second surface, x linearly changes from 0 to 0.7 with thickness.

8. The heterojunction bipolar transistor according to claim 6, characterized in that, From the first surface to the second surface, x gradually increases from 0 to 0.7 with thickness, and the increasing amplitude gradually increases.

9. The heterojunction bipolar transistor according to any one of claims 3 to 8, characterized in that, The thickness of the base layer falls within the range of 10 nm to 60 nm; wherein, the thicknesses of the first base layer and the third base layer both fall within the range of 0 to 10 nm.

10. An electronic device, characterized in that, Comprising the heterojunction bipolar transistor according to any one of claims 1 to 9.

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