CN212676277U

CN212676277U - Novel AlGaN-based multi-channel field effect transistor

Info

Publication number: CN212676277U
Application number: CN202021936515.XU
Authority: CN
Inventors: 孙海定; 张昊宸; 宋康; 邢宠
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2021-03-09
Anticipated expiration: 2030-09-07

Abstract

The utility model provides a novel AlGaN base multichannel field effect transistor, the transistor includes: the multi-quantum well structure comprises a substrate, an AlN buffer layer, a back barrier layer, a multi-quantum well structure, a GaN cap layer, a source electrode, a drain electrode and a gate electrode, wherein the multi-quantum well structure comprises N layers of AlGaN channel layers with gradually changed aluminum components and AlN quantum barrier layers arranged between every two layers of AlGaN channel layers with gradually changed aluminum components, and N is more than or equal to 2. The utility model utilizes polarization induction doping, realizes the combination of high-density two-dimensional electron gas or two-dimensional hole gas at the heterojunction interface and three-dimensional electron gas or three-dimensional hole gas in the AlGaN channel layer with gradually changed aluminum components, and is beneficial to the application of high frequency and heavy current of devices; the back barrier is utilized to realize more effective carrier limiting effect, effectively reduce the electric leakage of the device and realize better off-state breakdown characteristic and current saturation of the device under large on-state bias voltage.

Description

Novel AlGaN-based multi-channel field effect transistor

Technical Field

The utility model relates to a semiconductor device technical field, concretely relates to novel AlGaN base multichannel field effect transistor.

Background

Field Effect Transistors (FETs) based on aluminum gallium nitrogen (AlGaN) alloys can typically be doped by two means, impurity doping and polarization-induced doping. Impurity doping of AlGaN materials generally employs a silicon (Si) element as a donor impurity, and generates electrons by ionization; polarization-induced doping is achieved by utilizing the unique polarization characteristics of group III nitrides, and utilizing electrons in the polarization charge inducer region to form a conductive channel.

The problems of the existing doping technology and device structure are as follows: 1. in an AlGaN material having a high aluminum content, impurity doping efficiency is significantly reduced, and carrier concentration is limited. The carrier can be scattered by larger impurities, and the mobility is obviously reduced; 2. under the conditions of high frequency and high voltage, the concentration of two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction interface is too high, and the problems of electron mobility and saturation rate inhibition, namely the carrier concentration and mobility, exist in compromise. The decrease of the electron mobility and the saturation rate can cause the great decrease of the transconductance of the transistor, and cause the problems of nonlinear transmission characteristics, signal distortion and the like; 3. For the problem in 2, one solution is to use an AlGaN channel layer with gradually changed components, and to improve the high-frequency linearity of the transistor by using a three-dimensional electron gas or a three-dimensional hole gas formed by polarization-induced doping. However, the surface density of three-dimensional electron gas or three-dimensional hole gas is low, the series resistance of a source and a drain path is high, alloy scattering in a channel is severe, the mobility of a current carrier is limited, and the current density of a device is limited; 4. Most of the existing commonly used HEMT devices are based on a metal polarity AlGaN/GaN heterojunction structure, and the devices have the problems of high surface Al component and long distance between a 2DEG conducting channel and the surface of the device, so that the contact resistance and the series resistance are large, and the current density and the power density of the device are inhibited; 5. generally, no special structural design is arranged below a conductive channel in the AlGaN-based field effect transistor, and the phenomena of poor current carrier limiting capability and large device electric leakage generally exist, so that the phenomena are not beneficial to the off-state breakdown characteristic of the device and the current saturation under large on-state bias voltage.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The above 5-point existing doping technology and device structure have problems.

(II) technical scheme

In order to solve the above problem, the utility model provides a novel AlGaN base multichannel field effect transistor, the transistor includes: a substrate 1; an AlN buffer layer 2 and a back barrier layer 3 sequentially provided on the substrate 1; the multiple quantum well structure 4 is arranged on the back barrier layer 3, the multiple quantum well structure 4 comprises N layers of AlGaN channel layers 401 with gradually changed aluminum components and AlN quantum barrier layers 402 arranged between every two layers of AlGaN channel layers 401 with gradually changed aluminum components, and N is more than or equal to 2; a GaN cap layer 5 arranged on the multiple quantum well structure; a source electrode 6 and a drain electrode 7 which respectively extend to the multiple quantum well structure 4 from two ends of the GaN cap layer 5 by a preset depth, and; and a gate electrode 8 disposed on the GaN cap layer 5 and between the source electrode 6 and the drain electrode 7.

Optionally, the aluminum composition in the AlGaN aluminum composition gradient doping layer 401 gradually changes from k1 to k2 along the growth direction of the AlGaN channel layer 401 with gradually changing aluminum composition, wherein k1 is greater than or equal to 0 and is less than 1, k2 is greater than or equal to 0 and is less than 1, and the relationship between k1 and k2 is not specifically required, that is, the aluminum composition may gradually change, or may gradually change.

Optionally, the starting values and the ending values of the gradual change of the aluminum composition in each layer of the AlGaN channel layer 401 with the gradual change of the aluminum composition are the same.

Optionally, the initial values and the end values of the gradual change of the aluminum composition in each layer of the AlGaN channel layer 401 with the gradual change of the aluminum composition are different.

Optionally, when N is greater than 3 in all the AlGaN channel layers 401 with gradually changing aluminum compositions, the initial values and the final values of the gradual changes of the aluminum compositions in at least two of the AlGaN channel layers 401 with gradually changing aluminum compositions are the same.

Optionally, the aluminum-graded AlGaN channel layer 401 in the multiple quantum well structure may also be B_xAl_yGa_1-x-yN-Al composition graded channel layer or In_zAl_fGa_1-z-fAnd an N-aluminum composition graded channel layer.

Optionally, B is_xAl_yGa_1-x-yGraded layer of N-Al composition or In_zAl_fGa_1-z-fThe aluminum component in the N aluminum component gradient layer is between k1 and k2 along the B_xAl_yGa_1-x-yGraded layer of N-Al composition or In_zAl_fGa_1-z-fThe growth direction of the N aluminum component gradient layer is gradually changed, wherein k1 is more than or equal to 0 and less than 1, k2 is more than or equal to 0 and less than 1, and the relation between k1 and k2 does not make specific requirements, namely, the aluminum component can be gradually changed in an increasing way or can be gradually changed in a decreasing way.

Optionally, the back barrier layer 3 is Al_mGa_1-mN、B_xAl_yGa_1-x-yN or In_zAl_fGa_1-z-fAnd N, the energy gap of the back barrier layer 3 is greater than the energy gap of the AlGaN alloy corresponding to the gradual change starting point of the AlGaN channel layer 401 with gradually changed aluminum composition in the first layer in the multiple quantum well structure 4. For example, the aluminum composition in the first layer (401) is gradually changed from 0.1 to 0.2, and the gradual change starting point is Al_0.1Ga_0.9N, the forbidden band width of the back barrier is larger than that of Al_0.1Ga_0.9And N corresponds to the forbidden bandwidth.

Optionally, the thickness of the substrate 1 is 0.1-10 μm; the thickness of the back barrier layer 3 is 0.1-5 μm, and the thickness of the GaN cap layer 5 is 1-5 nm; the AlGaN channel layer 401 with gradually changed aluminum components is 1-100 nm thick, and the AlN quantum barrier layer (402) is 1-10 nm thick.

Alternatively, the source electrode 6 and the drain electrode 7 adopt a Ti/Al/Ni/Au ohmic contact metal stack layer, and the grid electrode 8 adopts a Ni/Au metal stack layer.

(III) advantageous effects

The utility model discloses following beneficial effect has at least:

the embodiment of the utility model provides an utilize the polarization characteristic of III group nitride, through the gradual change gradient of aluminium composition in the AlGaN channel layer 401 of regulation and control aluminium composition gradual change, realized the three-dimensional electron gas or the three-dimensional hole gas conducting channel that need not impurity doping source. The linearity of the transistor under a high-frequency condition can be effectively regulated and controlled by regulating and controlling the doping curve of the three-dimensional carrier in the channel, and the signal distortion and gain attenuation in a high-frequency electronic circuit are favorably reduced; in addition, a heterojunction interface formed by the AlGaN channel layer with gradually changed aluminum components and the AlN quantum barrier simultaneously has high-area-density two-dimensional electron gas or two-dimensional hole gas formed by polarization-induced doping, and the output power density of the device is favorably improved. Meanwhile, by combining the special energy band structure of the AlGaN/AlN multi-quantum well, the more effective carrier limiting effect is realized, the electric leakage of the device is effectively reduced, and the better off-state breakdown characteristic and the current saturation under the large on-state bias voltage of the device can be realized. The AlN quantum barrier is used as an insertion layer, so that alloy scattering at a channel can be reduced, and the carrier mobility is further improved. Therefore, the transistor with the multi-quantum well structure simultaneously realizes three-dimensional electron/hole gas and two-dimensional electron/hole gas conduction channels by utilizing the polarization effect, and combines good output power density and good high-frequency linearity; the transistor can be based on metal polarity or nitrogen polarity's III family nitride, wherein, N type field effect transistor based on nitrogen polarity AlGaN material is favorable to forming low contact resistance's ohmic contact because device surface aluminium component content is lower, improves the current density of device.

Drawings

Fig. 1 is a schematic structural diagram of a novel AlGaN based multi-channel field effect transistor according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a multi-quantum well structure in a novel AlGaN based multi-channel fet according to an embodiment of the present invention;

fig. 3 is a schematic view of an AlGaN channel layer with a gradually changing aluminum composition in a metal polarity N-type field effect transistor according to an embodiment of the present invention; wherein, the aluminum component is gradually increased and gradually changed;

fig. 4 is a band diagram of the metal polar nfet of fig. 3 according to the present invention;

fig. 5 is a graph showing an electron concentration distribution of the mosfet of fig. 3 according to the present invention;

fig. 6 is a schematic view of an AlGaN channel layer with a gradually changing aluminum composition in a metal polarity pfet according to another embodiment of the present invention; wherein, the aluminum component is gradually decreased;

fig. 7 is a band diagram of the mosfet of fig. 6 according to the present invention;

fig. 8 is an electron concentration distribution diagram of the mosfet of fig. 6 according to the present invention;

fig. 9 is a schematic view of an AlGaN channel layer with a gradually changing aluminum composition in a metal polarity N-type field effect transistor according to another embodiment of the present invention; wherein, the aluminum component is gradually increased and gradually changed;

fig. 10 is a band diagram of the metal polar nfet of fig. 9 according to the present invention;

fig. 11 is a graph showing an electron concentration distribution of the mosfet of fig. 9 according to the present invention;

fig. 12 is a flowchart of a method for manufacturing a multiple quantum well structure according to an embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood that the description is intended to be illustrative only and is not intended to limit the scope of the present invention. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

The embodiment of the utility model provides a novel AlGaN base multichannel field effect transistor, see figure 1, the transistor includes: a substrate 1; an AlN buffer layer 2 and a back barrier layer 3 sequentially provided on the substrate 1; the multiple quantum well structure 4 is arranged on the back barrier layer 3, the multiple quantum well structure 4 comprises N layers of AlGaN channel layers 401 with gradually changed aluminum components and AlN quantum barrier layers 402 arranged between every two layers of AlGaN channel layers 401 with gradually changed aluminum components, and N is more than or equal to 2; a GaN cap layer 5 arranged on the multiple quantum well structure 4; a source electrode 6 and a drain electrode 7 which respectively extend to the multiple quantum well structure 4 from two ends of the GaN cap layer 5 by a preset depth, and; and a gate electrode 8 disposed on the GaN cap layer 5 and between the source electrode 6 and the drain electrode 7.

First, a group III nitride having a metal polarity and a nitrogen polarity: the group III nitride is composed of metal elements (Al, Ga, In) and nitrogen (N) elements, and stably exists In a wurtzite structure at room temperature. Taking GaN as an example, Ga atoms and N atoms are bonded in a tetrahedral form while forming Ga atomic layers and N atomic layers alternately arranged along the c-axis. The different arrangement of the Ga-N diatomic layers determines the different polarities of the GaN material: if the Ga (metal) atomic layer is on top, the material is Ga polar (metal polar); if the atomic layer of N (nitrogen) is on top, the material is N (nitrogen) polar. The utility model provides a novel AlGaN base many channel field effect transistor can be for the field effect transistor based on polarity of metal AlGaN material, also can be for the field effect transistor based on polarity of nitrogen AlGaN material. By adjusting the gradient of the aluminum component in the AlGaN channel layer with the gradually changed aluminum component, and by polarization-induced doping, a high-concentration three-dimensional electron gas or three-dimensional hole gas conducting channel can be formed without introducing doping impurities. The N-type field effect transistor based on the nitrogen polarity has lower aluminum components at the position of a device, so that the source-drain ohmic contact with low contact resistance is formed, and the current density and the power density of the device are improved.

Therefore, the AlN buffer layer 2 is extended on the substrate 1 in the embodiment of the invention, so that the crystal quality of subsequent extension can be ensured; an intrinsically doped back barrier layer is epitaxially grown on the AlN buffer layer 2, which can be used to suppress leakage caused by drift of electrons in the channel back barrier at high voltage. The AlGaN channel layer 401 with gradually changed aluminum components in the multi-quantum well structure 4 is used as a quantum well, and the AlN quantum barrier layer 402 is used as a quantum barrier, so that the device has a plurality of AlGaN/AlN heterojunction structures.Referring to FIG. 2, the III-nitride material has spontaneous polarization and piezoelectric polarization, and the lattice constants of AlN and GaN in the embodiment of the present invention are

And

calculating residual polarization charges at the interfaces of the heterojunctions, wherein (1) in a device based on the metal polarity AlGaN material, when an AlN quantum barrier is epitaxially grown on an AlGaN channel layer with gradually changed aluminum components, polarization positive charges exist at the interfaces of the AlGaN channel layer and the AlGaN quantum barrier; when the AlGaN channel layer with gradually changed aluminum composition is extended on the AlN quantum barrier, polarized negative charges are generated at the interface of the AlGaN channel layer and the AlN quantum barrier. (2) In a device based on a nitrogen polarity AlGaN material, when an AlN quantum barrier is epitaxially grown on an AlGaN channel layer with gradually changed aluminum components, polarization negative charges exist at an interface; when an AlGaN channel layer with a gradually changing aluminum composition is epitaxially grown on an AlN quantum barrier, a polarized positive charge is generated at the interface. Polarization charges generated at the heterojunction interface cause bending of energy bands and realize polarization-induced doping to form a conductive channel.

Meanwhile, the AlGaN channel layer with gradually changed aluminum components can be equivalent to a plurality of tiny abrupt heterojunctions, wherein each heterojunction has a polarization electric field. Referring to fig. 3, in the AlGaN channel with a metal polarity and a gradually changed aluminum composition, polarization charges are expanded in a three-dimensional direction, a high-concentration fixed polarization positive charge can be formed in the entire gradient layer, and finally, a three-dimensional electron gas is formed by using a polarization induction effect to conduct electricity. Similarly, four three-dimensional carrier doping can be realized by adjusting the polarity (metal polarity and nitrogen polarity) and the gradient (increasing and increasing): doping metal polar three-dimensional electron gas; doping metal polar three-dimensional hole gas; doping nitrogen polarity three-dimensional electron gas; and (3) doping nitrogen polar three-dimensional hole gas.

It can be seen that the embodiment of the present invention utilizes the polarization characteristic of group III nitride, and realizes the combination of two-dimensional electrons or hole gas at the heterojunction and three-dimensional electron gas or three-dimensional hole gas in the AlGaN channel with gradually changed aluminum composition. The concentration of the three-dimensional electron/hole gas is only determined by the gradient of the gradual change of the aluminum component, the doping curve is beneficial to realizing constant transconductance of the device, the linear transmission characteristic under high frequency is realized from the design angle of the device, and the gain attenuation and signal distortion in signal transmission are reduced; the two-dimensional electron/hole gas at the heterojunction interface has higher carrier density and mobility, and is beneficial to the output current and power density of the device; the AlN quantum barrier can effectively reduce alloy scattering, and the carrier mobility is improved; meanwhile, by combining the special energy band structure of the AlGaN/AlN multi-quantum well, the more effective carrier limiting effect is realized, the electric leakage of the device can be effectively reduced, and the better off-state breakdown characteristic and the current saturation under the large on-state bias voltage of the device can be realized.

Note, among others, the above-described polarization effect of the group III nitride (i.e., polarization characteristic of the group III nitride): the group III nitrides of wurtzite structure do not coincide with the center of positive negative charge in the c-axis direction to produce macroscopic polarization, called Spontaneous polarization (spinotaneous polarization); meanwhile, the pressure in the material can also cause the separation of positive and negative charge centers in the III-nitride material, and the effect is called Piezoelectric polarization (Piezoelectric polarization), and the polarization effect has important influence on the III-nitride material and the performance of the device.

In addition, the above-mentioned N layers of AlGaN channel layers 401 with gradually changed aluminum compositions and AlN quantum barrier layers 402 disposed between each two layers of AlGaN channel layers 401 with gradually changed aluminum compositions, N is greater than or equal to 2; the method comprises the following steps: the back barrier layer 3 is provided with a first AlGaN channel layer 401 with gradually-changed aluminum composition, a first AlN quantum barrier layer 402 is extended on the first AlGaN channel layer 401 with gradually-changed aluminum composition, a second AlGaN channel layer 401 with gradually-changed aluminum composition is extended on the first AlN quantum barrier layer 402, a second AlN quantum barrier layer 402 is extended on the second AlGaN channel layer 401 with gradually-changed aluminum composition, and by analogy, a third AlGaN channel layer 401 with gradually-changed aluminum composition, a third AlN quantum barrier layer 402, … … and an Nth channel layer AlGaN 401 with gradually-changed aluminum composition are extended on the second AlN quantum barrier layer 402 in sequence. Then, a GaN cap layer 5 can be disposed on the N-th AlGaN channel layer 401 with gradually changed aluminum composition.

In a feasible embodiment of the present invention, the aluminum composition in the AlGaN channel layer 401 with gradually changed aluminum composition is gradually changed between k1 and k2 along the growth direction of the AlGaN channel layer 401 with gradually changed aluminum composition, wherein k1 is greater than or equal to 0 and is less than 1, and k2 is greater than or equal to 0 and is less than 1. The gradual change specifically means: in the formula Al_xGa_1-xThe value of x in N may be gradually graded. For example, in the AlGaN thin film, the Al composition x increases linearly from k1 to k2, 0.3, and x decreases linearly from k1 to k2, 0.2, and the like. The value of x is any number from 0 to 1, for example, Al_0.001Ga_0.999Gradual change of N to Al_0.231Ga_0.769N, and so on. In general, the growth direction of the AlGaN conductive layer 401 having a graded aluminum composition is from the bottom to the top.

It should be noted that, for a field effect transistor based on metal polarity and nitrogen polarity AlGaN material, the AlGaN channel layer 401 with gradually changed aluminum composition may have the following growth and corresponding doping schemes, respectively:

(1) polarity of the metal:

the aluminum component in the AlGaN channel layer 401 with gradually changed aluminum component gradually increases along the growth direction of the AlGaN channel layer 401 with gradually changed aluminum component to form a three-dimensional electron gas channel, and the transistor is of an N type. For example: first, a graded layer 1 is epitaxially grown with Al component from a₁Fade to a₂I.e. Al_a1Ga_1-a1N-Al_a2Ga_1-a2N(a₁＜a₂< 1); extending a first AlN quantum barrier on the gradient layer 1; subsequent epitaxy of a graded layer 2, Al composition from b₁Fade to b₂I.e. Al_b1Ga_1-b1N-Al_b2Ga_1-b2N(b₁＜b₂< 1); extending a second AlN quantum barrier on the epitaxial layer; and so on until the last epitaxial graded layer n (n is more than or equal to 2), the Al component is formed by n₁Gradation to n₂I.e. Al_n1Ga_1-n1N-Al_n2Ga_1-n2N(n₁＜n₂< 1); and extending a GaN cap layer on the gradient layer n to improve the effective barrier height of the surface of the device.

AlGaN channel with gradually changed componentsThe aluminum composition in the layer 401 gradually decreases along the growth direction of the AlGaN channel layer 401 with gradually changed aluminum composition to form a three-dimensional hole air channel, and the transistor is of a P type. For example: first, a graded layer 1 is epitaxially grown with Al component from a₁Fade to a₂I.e. Al_a1Ga_1-a1N-Al_a2Ga_1-a2N (1＞a₁＞a₂) (ii) a Extending a first AlN quantum barrier on the gradient layer 1; subsequently epitaxially forming a graded layer 2 having an Al component of b₁Fade to b₂I.e. Al_b1Ga_1-b1N-Al_b2Ga_1-b2N(1＞b₁＞b₂) (ii) a Extending a second AlN quantum barrier on the epitaxial layer; and so on until the last epitaxial graded layer n (n is more than or equal to 2), the Al component is formed by n₁Gradation to n₂I.e. Al_n1Ga_1-n1N-Al_n2Ga_1-n2N(1＞n₁＞n₂) (ii) a And extending a GaN cap layer on the gradient layer n to improve the effective barrier height of the surface of the device.

(2) Nitrogen polarity: the aluminum component in the AlGaN aluminum component gradient doping layer 401 is gradually reduced along the growth direction of the AlGaN aluminum component gradient doping layer 401 to form a three-dimensional electron gas channel, and the transistor is of an N type. For example: first, a graded layer 1 is epitaxially grown with Al component from a₁Gradually and decreasingly gradual change to a₂I.e. Al_a1Ga_1-a1N-Al_a2Ga_1-a2N(a₁＞a₂> 1); extending a first AlN quantum barrier on the gradient layer 1; subsequently epitaxially a graded layer 2, the Al component being in the growth direction from b₁Gradually and decreasingly gradual change to b₂I.e. Al_b1Ga_1-b1N-Al_b2Ga_1-b2N(b₁＞b₂> 1); extending a second AlN quantum barrier on the epitaxial layer; and so on until the last epitaxial graded layer n (n is more than or equal to 2), the Al component grows from n along the growth direction₁Gradually decreasing to n₂I.e. Al_n1Ga_1- _n1N-Al_n2Ga_1-n2N(n₁＞n₂> 1); and extending a GaN cap layer on the gradient layer n to improve the effective barrier height of the surface of the device.

AlGaN channel with gradually changed aluminum componentThe aluminum composition in the channel layer 401 gradually increases along the growth direction of the AlGaN channel layer 401 with gradually changed aluminum composition to form a three-dimensional electron gas channel, and the transistor is of a P type. For example: first, a graded layer 1 is epitaxially grown with Al component from a₁Fade to a₂I.e. Al_a1Ga_1-a1N-Al_a2Ga_1-a2N(a₁＜a₂< 1); extending a first AlN quantum barrier on the gradient layer 1; subsequent epitaxy of a graded layer 2, Al composition from b₁Fade to b₂I.e. Al_b1Ga_1-b1N-Al_b2Ga_1-b2N(b₁＜b₂< 1); extending a second AlN quantum barrier on the epitaxial layer; and so on until the last epitaxial graded layer n (n is more than or equal to 2), the Al component is formed by n₁Gradation to n₂I.e. Al_n1Ga_1-n1N-Al_n2Ga_1-n2N(n₁＜n₂< 1); and extending a GaN cap layer on the gradient layer n to improve the effective barrier height of the surface of the device.

In a feasible manner of the embodiment of the present invention, each layer of the AlGaN gradient doping layer 401 has the same initial value and the same end value of the gradient of the aluminum component. For example, 3 layers of AlGaN aluminum component gradient doped layers are shared, and the first layer of AlGaN aluminum component gradient doped layer, the second layer of AlGaN aluminum component gradient doped layer and the third layer of AlGaN aluminum component gradient doped layer are all Al components r in the AlGaN film which are linearly increased from 0.1 to 0.3 or are linearly decreased from 0.6 to 0.2.

In a feasible manner, the initial values and the ending values of the gradual change of the aluminum component in the AlGaN channel layer 401 with the gradual change of the aluminum component are different. For example, 3 layers of AlGaN aluminum composition gradient doped layers are shared, and the Al composition in the first aluminum composition gradient AlGaN channel layer is changed from a₁Fade to a₂I.e. Al_a1Ga_1-a1Gradual change of N to Al_a2Ga_1-a2N(0≤a₁＜ a₂Less than 1) and the Al component in the AlGaN channel layer with gradually changed aluminum component of the second layer is changed from b₁Fade to b₂I.e. Al_b1Ga_1-b1Gradual change of N to Al_b2Ga_1-b2N(0≤b₁＜b₂< 1); andthe Al component in the AlGaN channel layer with the gradually changed aluminum component of the third layer is n₁Gradation to n₂I.e. Al_n1Ga_1-n1N-Al_n2Ga_1-n2N(0≤n₁＜n₂< 1). At this time, a₁、b₁And n₁Inequality a₂、b₂And n₂Not equal. Here, the Al composition is illustrated as linearly increasing, and those skilled in the art will understand that the Al composition may be decreased as well.

In another possible embodiment of the present invention, when N > 3, all of the AlGaN channel layer 401 having a gradually changing aluminum composition has at least two layers, the initial value and the final value of the gradually changing aluminum composition are the same in the AlGaN channel layer 401 having a gradually changing aluminum composition. That is, the starting value of the gradual change of some layers may be equal, the ending value may be equal, and the rest of the layers may be different.

In addition, the aluminum composition graded channel layer 401 in the multiple quantum well structure 4 may also be B_xAl_yGa_1-x-yN-Al composition graded channel layer or In_zAl_fGa_1-z-fAnd an N-aluminum composition graded channel layer. B is_xAl_yGa_1-x-yN-Al composition graded doping layer or In_zAl_fGa_1-z-fThe aluminum component in the N aluminum component gradient doped layer is between k1 and k2 along the B_xAl_yGa_1-x-yN-Al composition graded channel layer or In_zAl_fGa_1-z-fThe N aluminum component gradual change channel layer has gradual change in thickness, wherein k1 is more than or equal to 0 and less than 1, k2 is more than or equal to 0 and less than 1, and the relation between k1 and k2 does not make specific requirements, namely the aluminum component can be gradually changed in an increasing way or gradually changed in a decreasing way.

The back barrier layer 3 is Al_mGa_1-mN、B_xAl_yGa_1-x-yN or In_zAl_fGa_1-z-fAnd one of N, wherein m is more than or equal to 0 and less than 1, x is more than or equal to 0 and less than 1, y is more than or equal to 0 and less than 1, z is more than or equal to 0 and less than 1, and f is more than or equal to 0 and less than 1. Here, in order to realize sufficient carrier confinement effect and prevent leakage current increase and device breakdown under high voltage operating conditions, it is necessary to ensure that the forbidden bandwidth of the back barrier layer 3 is larger than that of the second quantum well structure 4The forbidden bandwidth of the alloy corresponding to the gradual change starting point of the aluminum composition gradual change channel layer 401. For example, the aluminum composition in the first layer (401) is gradually changed from 0.1 to 0.2, and the starting point of the gradual change is Al_0.1Ga_0.9N, the forbidden band width of the back barrier is larger than that of Al_0.1Ga_0.9And N corresponds to the forbidden bandwidth.

Referring to fig. 3-5, fig. 6-8, and fig. 9-11, band diagrams and carrier doping profiles of field effect transistors comprising multiple quantum well structures as described in the three patents are provided as typical examples, respectively.

Fig. 3 shows an N-type field effect transistor based on metal polarity AlGaN material, in which the composition of the AlGaN channel layer 401 with gradually changed composition increases linearly in the direction of growth, and the transistor includes three AlGaN channel layers 401 with gradually changed composition and two AlN quantum barriers 402. Referring to fig. 4, it can be seen that a very narrow conductive channel is formed in a heterojunction interface formed by two AlGaN channel layers 401 and AlN quantum barriers 402, whose aluminum compositions are gradually changed; meanwhile, a gentle conduction band lower than the fermi level is formed in the AlGaN channel layer 1 with gradually changed composition. The electron doping distribution of the transistor structure referring to fig. 5, electron concentrations of 2.9 × 10 are respectively present in heterojunction interfaces formed by two AlGaN channel layers 401 and AlN quantum barriers 402 whose aluminum compositions are gradually changed¹⁹cm^-3And 4.3X 10¹⁹cm^-3While forming the AlGaN channel layer 1 having a gradually changing composition at a density of about 1 x 10¹⁹cm^-3The three-dimensional electron gas conducting channel.

Fig. 6 shows a P-type field effect transistor based on metal polarity AlGaN material, in which the composition of the graded AlGaN channel layer 401 in the channel decreases linearly in the direction of growth, and the transistor includes three graded AlGaN channel layers 401 and two AlN quantum barriers 402. Referring to fig. 7, it can be seen that a very narrow conductive channel is formed in the heterojunction interface formed by two AlGaN channel layers 401 and AlN quantum barriers 402, whose aluminum compositions are gradually changed; meanwhile, a gentle valence band higher than the fermi level is formed in the AlGaN channel layer 1 with gradually changed composition. The electron doping profile of the transistor structure is shown in fig. 8, where two AlGaN channel layers 401 with gradually changed aluminum compositions and AlN quantumThe heterojunction interfaces formed by the barriers 402 have hole concentrations of 2.3 × 10¹⁹cm^-3And 5.6X 10¹⁹ cm^-3While forming the AlGaN channel layer 1 having a gradually changing composition at a density of about 1 x 10¹⁹cm^-3The three-dimensional hole gas conducting channel.

Fig. 9 shows an N-type field effect transistor based on a metal polarity AlGaN material, in which the composition of the graded AlGaN channel layer 401 in the channel decreases linearly in the direction of growth, and the transistor includes two graded AlGaN channel layers 401 and an AlN quantum barrier 402. Referring to fig. 10, it can be seen that a very narrow conductive channel is formed in a heterojunction interface formed by an AlGaN channel layer 401 and an AlN quantum barrier 402, whose aluminum composition is gradually changed; meanwhile, gentle conduction bands lower than the Fermi level are formed in the

AlGaN channel layers

1 and 2 with gradually changed compositions. The electron doping profile of the transistor structure referring to fig. 11, an electron concentration of 4 × 10 is present in the heterojunction interface formed by the AlGaN channel layer and the AlN quantum barrier 402 having a gradually-changed aluminum composition¹⁹cm^-3While forming the AlGaN channel layer 1 having a gradually changing composition at a density of about 1 x 10¹⁹cm^-3The three-dimensional hole gas conduction channel is formed on the AlGaN channel layer 2 with gradually changed composition, and the density is about 4 multiplied by 10¹⁹cm^-3Electron doping of (3). The electron doping shape formed by the AlGaN channel layer 2 with gradually changed components is similar to the delta doping technology in impurity doping, and is a feasible scheme for improving the high-frequency linearity of the transistor.

The substrate 1 is a sapphire substrate, and the thickness of the substrate 1 is 0.1-10 μm, preferably 2 μm; the back barrier layer 3 has a thickness of 0.1 to 5 μm, preferably 3 μm. The thickness of the GaN cap layer 5 is 1-5 nm; the thickness of the aluminum component gradual change channel layer 401 is 1-100 nm, and the thickness of the AlN quantum barrier layer 402 is 1-10 nm.

The source electrode 6 and the drain electrode 7 adopt Ti/Al/Ni/Au ohmic contact metal stacked layers, and the grid electrode 8 adopts a Ni/Au metal stacked layer. Wherein, before preparing source electrode and drain electrode, can carry out the sculpture to electrode pattern region, the sculpture degree of depth is specifically in the example of the utility model does not do not make specific restriction. The electrode length and the width dimension of grid, source electrode and drain electrode to and the distance between the three electrode are in the example of the utility model discloses all do not do specific restriction.

In addition, the source electrode 6 and the drain electrode 7 extending from both ends of the GaN cap layer 5 to the multiple quantum well structure 4 by a predetermined depth, respectively, are described above. Wherein the embodiment of the utility model provides a do not do specific restriction to this predetermined degree of depth, it can be for extending to partial multiple quantum well structure 4, for example extend to 2 nd layer aluminium composition gradual change channel layer 401, also can be for extending to whole multiple quantum well structure 4.

Referring to fig. 12, in an embodiment of the present invention, a method for manufacturing a field effect transistor may include: step S1, growing an AlN buffer layer on the sapphire substrate, step S2, epitaxially growing a back barrier layer on the AlN buffer layer, step S3, alternately growing an aluminum composition graded channel layer 401 and an AlN quantum barrier layer 402 on the back barrier layer N times to obtain a multiple quantum well structure, step S4, epitaxially growing a GaN cap layer on the multiple quantum well structure, step S5, and preparing a source electrode, a drain electrode, and a gate electrode 8 on the product obtained through steps S1 to S4.

The above-mentioned embodiments, further detailed description of the objects, technical solutions and advantages of the present invention, it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A novel AlGaN based multi-channel field effect transistor, said transistor comprising:

a substrate (1);

an AlN buffer layer (2) and a back barrier layer (3) which are sequentially arranged on the substrate (1);

the multiple quantum well structure (4) is arranged on the back barrier layer (3), the multiple quantum well structure (4) is an AlGaN channel layer (401) with gradually changed N layers of aluminum components and an AlN quantum barrier layer (402) arranged between every two AlGaN channel layers (401) with gradually changed aluminum components, and N is more than or equal to 2;

a GaN cap layer (5) arranged on the multiple quantum well structure (4);

a source electrode (6) and a drain electrode (7) which respectively extend to the multiple quantum well structure (4) from two ends of the GaN cap layer (5) by a preset depth, and;

and a gate electrode (8) disposed on the GaN cap layer (5) and between the source electrode (6) and the drain electrode (7).

2. The FET of claim 1, wherein the substrate (1) has a thickness of 0.1-10 μm; the thickness of the back barrier layer (3) is 0.1-5 mu m, and the thickness of the GaN cap layer (5) is 1-5 nm; the thickness of the AlGaN channel layer (401) with gradually changed aluminum components is 1-100 nm, and the thickness of the AlN quantum barrier layer (402) is 1-10 nm.