Pseudo-lattice-matched high-electron-mobility transistor, low-noise amplifier, and related apparatus

Abstract

This application provides a pseudomorphic high electron mobility transistor (PHEMT), a low noise amplifier, and related devices. The PHEMT includes a channel layer, a lower barrier layer and an upper barrier layer disposed on either side of the channel layer, the lower barrier layer being connected to the channel layer, and a first isolation layer and a first doped layer disposed between the channel layer and the upper barrier layer, the first isolation layer configured to isolate the first doped layer from the channel layer, and the first doped layer configured to provide a two-dimensional electron gas. When the output current of the PHEMT is less than a first threshold, the conduction band energy level of the channel layer is lower than the Fermi energy level. This improves the linearity of the PHEMT under small output currents and reduces intermodulation distortion caused by LNA nonlinearity.

Description

Technical Field

[0001] Pseudo child The application relates to the field of semiconductor device technology, and more particularly to pseudo lattice-matched high electron mobility transistors, low noise amplifiers, and related devices.

Background Art

[0002] As shown in FIG. 1, when a received signal passes through a low noise amplifier (LNA), an intermodulation signal is generated between the received signal on the receive link at the antenna end of a wireless communication product and the transmitted signal leaking into the receive link, resulting in intermodulation distortion (IMD). This is caused by the non-linear characteristics of the LNA. Since the frequency of the third-order intermodulation product is very close to the frequency of the received signal, the third-order intermodulation product cannot be suppressed by subsequent filters in the receive link, causing interference to the received signal on the link.

Summary of the Invention

[0003] Embodiments of this application provide a pseudo lattice-matched high electron mobility transistor (PHEMT), a low noise amplifier, and related devices. When the output current of the PHEMT is less than a first threshold value, the conduction band energy level of the channel layer is lower than the Fermi energy level. This improves the linearity of the PHEMT under a small output current and reduces the intermodulation distortion caused by LNA non-linearity.

[0004] According to a first aspect, an embodiment of this application provides a pseudo lattice-matched high electron mobility transistor (PHEMT), the PHEMT including: a channel layer; a lower barrier layer and an upper barrier layer disposed on both sides of the channel layer respectively, the lower barrier layer being connected to the channel layer, the lower barrier layer and the upper barrier layer; A first isolation layer and a first doped layer disposed between the channel layer and the upper barrier layer, the first isolation layer being configured to separate the first doped layer from the channel layer, and the first doped layer being configured to provide a two-dimensional electron gas, the first isolation layer and the first doped layer; including When the output current of the PHEMT is less than the first threshold, the conduction band energy level of the channel layer is lower than the Fermi energy level.

[0005] The energy level structure of the channel layer in the PHEMT is adjusted so that when the output current of the PHEMT is less than the first threshold, the conduction band energy level of the channel layer is lower than the Fermi energy level. This improves the linearity of the PHEMT at low output currents and reduces the intermodulation distortion caused by the LNA non-linearity.

[0006] In one possible implementation, the lower barrier layer is directly connected to the channel layer.

[0007] By removing the lower doped layer in the PHEMT, the gradient of the energy level of the channel layer in the thickness direction becomes smaller, and the conduction band energy level of the channel layer becomes lower than the Fermi energy level during operation at low currents.

[0008] In one possible implementation, the first doped layer is silicon-doped, and the doping concentration is from 3e12 cm -2 to 5e12 cm -2 is.

[0009] In one possible implementation, the doping concentration of the first doped layer is instead , 5e12 cm -2 to 6e12 cm -2 is You can .

[0010] By increasing the concentration of the first doped layer in the PHEMT, the gain of the PHEMT is increased.

[0011] In one possible implementation, the lower barrier layer is connected to the channel layer via a second separation layer and a second doped layer, the second separation layer is configured to separate the channel layer from the second doped layer, and the second doped layer is configured to provide a two-dimensional electron gas.

[0012] The PHEMT is a double-doped PHEMT, for example, a double δ-doped PHEMT.

[0013] In one possible implementation, the doping concentration of the first doped layer is from 3.5e12 cm -2 to 4.5e12 cm -2 and the doping concentration of the second doped layer is from 3e11 cm -2 to 5e11 cm -2

[0014] In one possible implementation, the doping concentration of the first doped layer is from 4e12 cm -2 to 6e12 cm -2 and the doping concentration of the second doped layer is from 2e8 cm -2 to 3e11 cm -2

[0015] In one possible implementation, the ratio of the doping concentration of the first doped layer to the doping concentration of the second doped layer is greater than a preset value.

[0016] Optionally, the preset value is a positive number greater than 6, for example, 9, 10, 15, 30, 70, 100, or 150.

[0017] ​​If the total doping concentration of the PHEMT remains unchanged or does not decrease, the doping concentration of the lower doped layer (second doped layer) is reduced, or the ratio of the doping concentration of the upper doped layer (first doped layer) to the doping concentration of the lower doped layer (second doped layer) is increased, thereby reducing the energy level gradient of the channel layer in the thickness direction, and causing the conduction band energy level of the channel layer to fall below the Fermi energy level during operation under low current.

[0018] In one possible implementation, the channel layer thickness is 15-20nm, 18-20nm, or 20-25nm, for example, 18nm.

[0019] In one possible implementation, when the output current of the PHEMT is less than a second threshold, the conduction band energy level of the channel layer decreases substantially in the thickness direction.

[0020] The thickness of the channel layer of the PHEMT is increased. Re, When the device is operating to Below the channel layer electrons that accumulate This was avoided. By doing so, electrons More uniform It is distributed. This improves the linearity of the PHEMT in question.

[0021] In one possible implementation, the PHEMT further includes a cap layer, a source, a drain, and a gate, wherein the cap layer is located on the side of the upper barrier layer furthest from the channel layer and has a through-hole for providing ohmic contact, the gate is located within the through-hole, and the source and drain are both located on the side of the cap layer furthest from the upper barrier layer and on either side of the through-hole, respectively.

[0022] In one possible implementation, the channel layer is made of indium gallium arsenide, and the upper barrier layer, lower barrier layer, or separation layer is made of aluminum gallium arsenide.

[0023] According to a second aspect, one embodiment of the present application further provides a low-noise amplifier including a PHEMT according to the first aspect or any one of the possible implementations of the first aspect.

[0024] According to a third aspect, one embodiment of this application further provides a radio frequency circuit including a low-noise amplifier according to a second aspect.

[0025] According to a fourth aspect, one embodiment of the present application further provides a radio frequency chip comprising at least one of a PHEMT according to the first aspect or any one of the possible implementations of the first aspect, a low-noise amplifier according to the second aspect, and a radio frequency circuit according to the third aspect.

[0026] According to a fifth aspect, one embodiment of the present application further provides an electronic device comprising at least one of the following: a PHEMT according to the first aspect or any one of the possible implementations of the first aspect; a low-noise amplifier according to the second aspect; a radio frequency circuit according to the third aspect; and a radio frequency chip according to the fourth aspect. [Brief explanation of the drawing]

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings illustrating the embodiments are briefly described below. [Figure 1] This is a schematic diagram illustrating an intermodulation signal generated on an antenna terminal receiving link according to one embodiment of this application. [Figure 2A] This is a schematic diagram of the structure of a double-delta-doped PHEMT according to conventional technology. [Figure 2B] Figure 2A is an example of a DC output characteristic curve for a PHEMT. [Figure 2C] Figure 2A is a schematic diagram of the energy band structure of PHEMT. [Figure 2D] Figure 2A shows an example of a curve illustrating the OIP3 value of the PHEMT under different output currents. [Figure 3]This is a schematic diagram defining the OIP3 value in conventional technology. [Figure 4] This is a schematic diagram of the cross-sectional structure of a single δ-doped PHEMT according to one embodiment of this application. [Figure 5] This is a schematic diagram of the cross-sectional structure of a double δ-doped PHEMT according to one embodiment of this application. [Figure 6A] Figures 6A and 6B show examples of OIP3 value curves for a conventional double-δ-doped PHEMT and a single-δ-doped PHEMT according to one embodiment of this application, under different output currents. [Figure 6B] Figures 6A and 6B show examples of OIP3 value curves for a conventional double-δ-doped PHEMT and a single-δ-doped PHEMT according to one embodiment of this application, under different output currents. [Figure 7A] This is an example of an energy band diagram for a double-delta doped PHEMT according to conventional technology. [Figure 7B] This is an example of a diagram of the energy bands of a single δ-doped PHEMT according to one embodiment of this application. [Figure 7C] This is an example of a diagram showing the conduction band structure of single-δ-doped PHEMT and double-δ-doped PHEMT in the channel layer according to one embodiment of this application. [Figure 8] This diagram shows the electron concentration distribution of a double delta-doped PHEMT with channel layers of 12 nm and 18 nm thickness, respectively, under an output current of 60 mA / mm. [Figure 9] This is a schematic diagram of the circuit structure of an LNA according to one embodiment of this application. [Figure 10] This is a schematic diagram of a radio frequency system according to one embodiment of this application. [Modes for carrying out the invention]

[0028] Generally, there are two methods to reduce interference caused to the received signal by intermodulation signals.

[0029] One approach is to increase the isolation of the duplexer to suppress the leakage of the transmitted signal to the receive link. A duplexer, also known as a diplexer, functions to isolate the transmitted signal sent by a shared antenna from the received signal received by the same antenna, ensuring that both the transmit and receive links can operate simultaneously. When increasing the duplexer's isolation to suppress interference caused by intermodulation signals to the received signal, the duplexer's cavity needs to be larger. This increases the size of the duplexer and significantly increases its cost.

[0030] Another approach involves improving the linearity of the low-noise amplifier (LNA) to reduce intermodulation signals generated by the leakage signal and the received signal that cannot be completely suppressed by the filter. The linearity of the LNA is determined by the transistor core. The transistor may be a pseudo-lattice-matched high-electron mobility transistor (PHEMT).

[0031] Figure 2A shows a typical structure of a gallium arsenide (GaAs)-based PHEMT. The epitaxial layer of the PHEMT core is a buffer layer from top to bottom. layer, Lower barrier layer, lower δ-doped layer, lower separation layer, channel layer,The components are an upper isolation layer, an upper delta-doped layer, an upper barrier layer, and a cap layer. In the case of a gallium arsenide (GaAs)-based PHEMT, the buffer layer on the substrate can be made of gallium arsenide or aluminum gallium arsenide and is configured to prevent defects in the substrate from entering other layers of the PHEMT. The lower barrier layer and upper barrier layer can be made of aluminum gallium arsenide (AlGaAs) and are configured to prevent the two-dimensional electron gas from entering the buffer layer. Both the lower delta-doped layer and the upper delta-doped layer can be silicon (Si) doped and are configured to provide the two-dimensional electron gas. The upper isolation layer and lower isolation layer can be made of aluminum gallium arsenide (AlGaAs) and are configured to separate the doped layer from the channel layer. The channel layer can be made of indium gallium arsenide (InGaAs). The cap layer can be made of highly doped gallium arsenide and connects the source and drain. The electron concentration in the channel layer is controlled by using a gate voltage, allowing control of the output current between the source and drain. This enables signal amplification. Figure 2B shows the DC output characteristic curve of the PHEMT shown in Figure 2A. For example, Figure 2B shows five different gate voltages to distinguish the five operating states of the PHEMT: off (1), partially on (2), on (3), fully on (4), and linear operating (5).

[0032] Figure 2C is a schematic diagram of the energy band structure of the PHEMT shown in Figure 2A under five different operating states. It should be understood that each energy band structure diagram in Figure 2C simply shows the conduction band structure of all layers, and from left to right, i.e., in the thickness direction, it includes the conduction bands of the cap layer, upper barrier layer, upper δ-doped layer, upper isolation layer, channel layer, lower isolation layer, lower δ-doped layer, and lower barrier layer in that order. Only the locations of the upper δ-doped layer, lower δ-doped layer, and channel layer are indicated in the diagram.

[0033] As shown in Figure 2C, when PHEMT is in the off state (1), the conduction band energy level of the channel layer is equal to the Fermi energy level. E F It is much higher than that. As the gate voltage increases, when the PHEMT is in the process of turning on (2), the conduction band energy level of the channel layer is at the Fermi energy level. E F It approaches the Fermi energy level. As the gate voltage increases further, the conduction band energy level of the channel layer partially approaches the Fermi energy level. E F When the voltage drops below a certain level, a specific amount of free electrons appear in the channel layer. In this case, the PHEMT is in the ON state (3). As the gate voltage increases further, the conduction band structure of the channel layer changes sequentially from the left-upward, right-downward configuration in the ON state (3) to the configuration in the fully ON state (4), and then to the configuration in the linear operating state (5). That is, carriers tend to be located on the upper side of the channel layer (i.e., the left side in Figure 2D, i.e., the side adjacent to the upper isolation layer).

[0034] However, to meet the low power consumption and low noise requirements in the receiving link of a radio frequency system, the LNA operates with its output current density effectively limited to 60-100 mA / mm, i.e., in the ON state of the PHEMT in Figure 2C (3).

[0035] To meet the requirements of low power consumption and low noise coefficient for LNAs in radio frequency circuits, the operating point output current is practically limited to 60-100 mA / mm. Due to its high electron mobility characteristics, the PHEMT can reach the operating state current with only a low concentration of two-dimensional electron gas. As a result, most operating points are near the PHEMT's turn-on voltage. However, the linearity of the PHEMT in this range is small and cannot meet the requirements of the application. The linearity of the PHEMT is represented by the output third-order intercept point (OIP3). A higher OIP3 indicates higher linearity. As shown in Figure 2D, the curves of the PHEMT's OIP3 values ​​shown in Figure 2A under different output currents can be obtained by calculation based on the DC output characteristic curve shown in Figure 2B. As can be seen from Figure 2D, when the output current is 60 mA, the OIP3 value of the PHEMT is approximately 36 dBm, which cannot meet the requirement of 41 dBm or higher. Therefore, the most pressing technical issue that needs to be addressed now is how to improve the linearity of the device when the output current is small, that is, when the PHEMT is just turned on.

[0036] The following is a description of the technical terms used in the embodiments of this application.

[0037] (1) LNA

[0038] The LNA (Longband Amplifier) ​​is a crucial circuit in wireless communication systems. It is an amplifier with a very low noise coefficient, and its function is to amplify the signal received by the antenna. The signal received from the antenna is weak. To amplify such a weak signal, ensuring signal quality is paramount. For this purpose, the LNA cannot introduce too much noise; otherwise, the signal will degrade further, making demodulation impossible.

[0039] Most LNAs use transistors and field-effect transistors. In embodiments of this application, the LNA is a pseudo-lattice-matched high-electron-mobility transistor.(P Use HEMT).

[0040] (2) Intermodulation signals

[0041] An intermodulation signal is an intermodulation frequency signal generated when an unmodulated signal and a useful signal pass through a nonlinear device and interact with each other. Because the frequency of the intermodulation signal is very close to the frequency of the useful signal, backend filters can hardly suppress the intermodulation signal. As shown in Figure 1, when a received signal (i.e., the useful signal) and a transmitted signal leaking into the receiving link (i.e., the interference signal) pass through the LNA simultaneously, nonlinear effects can cause the frequency of the intermodulation signal generated by the two signals to sometimes be exactly equal to or close to the frequency of the received signal, resulting in the intermodulation signal passing smoothly through the receiver. Third-order intermodulation signals cause the most serious interference, known as intermodulation interference.

[0042] (3) PHEMT

[0043] PHEMTs are an improvement over high electron mobility transistors (HEMTs). PHEMTs have a double heterojunction structure, and the two-dimensional electron gas (2DEG) of a PHEMT exhibits a double-limiting effect on both sides of the potential well. Therefore, compared to HEMTs, PHEMTs have a higher electron surface density and higher electron mobility.

[0044] Figure 2A shows a typical double-δ-doped PHEMT.

[0045] (4) OIP3

[0046] The linearity of PHEMT is determined by the output third-order intercept point. (OThe OIP3 value can be expressed by the OIP3 value. A higher OIP3 value indicates higher linearity. The OIP3 value can be obtained by plotting the PHEMT radio frequency input and output curves. Specifically, two curves are drawn, as shown in Figure 3. One curve is the curve of the amplified signal power at the input frequency with respect to the input power, and the other curve is the curve of the third-order intermodulation signal with respect to the input power. In a logarithmic coordinate system, the curve of the linear amplified signal is represented as a straight line with a slope of 1, and the curve of the third-order intermodulation signal is represented as a straight line with a slope of 3. The output signal power corresponding to the intersection of these two curves is the OIP3 value.

[0047] (5) Output current

[0048] In embodiments of this application, output current is also referred to as the current output from the drain. Small output current is also simply called low current. Small output current means that the output current is less than a first threshold or less than a second threshold, where the first or second threshold may be the current density present when the PHEMT is just turned on. Alternatively, small output current means that the output current density of the PHEMT is 40-200 mA / mm or 60-100 mA / mm. The first threshold may or may not be equal to the second threshold. In embodiments of this application, an example is described in which the small output current is 60 mA / mm. In embodiments of this application, current also refers to current density.

[0049] In embodiments of this application, the thickness and materials of all layer structures within the PHEMT are designed, in particular the thickness of the epitaxial layer, the doping concentration of the doped layer, and other structures, so that the energy band structure of the channel layer of the PHEMT is tuned. Thus, when the PHEMT operates under a small output current, the conduction band energy level of the channel layer is lower than the Fermi energy level. As the gate voltage increases, the increase in electron concentration near the Fermi energy level has less effect on the electron concentration of the channel layer. This improves the linearity of the PHEMT. From the viewpoint of the conduction band structure, the conduction band gradient of the channel layer is smaller in the ON state (3).

[0050] The following describes the mechanism for adjusting the energy band structure of the channel layer.

[0051] Several major factors influence the energy band structure of the channel layer.

[0052] a: The distance between the channel layer and the gate. This distance affects the energy level of the channel layer.

[0053] b: Doping concentration of the upper / lower doped layer. The doped layer changes the degree of bending of the energy bands of the structure above it. For example, increasing the doping concentration of the upper doped layer increases the degree of bending of the energy bands of the upper barrier layer, and thus increases the energy level gradient of the upper barrier layer in the thickness direction. In another example, increasing the doping concentration of the lower doped layer increases the degree of bending of the energy bands of the channel layer, and thus increases the energy level gradient of the channel layer in the thickness direction. Therefore, reducing the concentration of the lower doped layer changes the degree of bending of the energy bands of the channel layer. small As a result, the energy level gradient of the channel layer in the thickness direction is small As a result, during operation under low output current, the conduction band energy level of the channel layer becomes lower than the Fermi energy level.

[0054] c: Ratio of doping concentrations in the upper / lower doped layers. The doping concentration in the lower doped layer is reduced to satisfy the requirement that the conduction band energy level of the channel layer be lower than the Fermi energy level when the PHEMT operates under low current. However, the total doping concentration of the upper / lower doped layers affects the carrier concentration, which impacts the device's performance. Also, higher doping concentrations result in a higher turn-on voltage for the device. Therefore, the total doping concentration should not be excessively low or excessively high.

[0055] d: Channel layer thickness. The thickness of the channel layer affects the distribution of electrons and current. A thicker channel layer avoids the accumulation of electrons beneath the channel layer when the device is operating, resulting in a more uniform distribution of electrons. This improves the linearity of the PHEMT.

[0056] Accordingly, with reference to the factors described above, embodiments of this application provide several solutions for tuning the energy band structure of the channel layer. Hence, when the PHEMT operates under low current, the conduction band energy level of the channel layer is lower than the Fermi energy level.

[0057] Solution 1: Removing the lower doped layer reduces the energy level gradient of the channel layer in the thickness direction, causing the conduction band energy level of the channel layer to be lower than the Fermi energy level during operation under low currents.

[0058] Solution 2: If the total doping concentration does not decrease, the doping concentration in the lower doping layer is decreased, or the ratio of the doping concentration in the upper doping layer to the doping concentration in the lower doping layer is increased.

[0059] Solution 3: The thickness of the channel layer is increased.

[0060] Combinations of the above solutions 1, 2, and 3, adjustments to the thickness of the upper barrier layer and / or the thickness of the upper separation layer, and combinations of at least one of the above solutions 1, 2, and 3, and similar combinations may also exist.

[0061] In the solution described above, the thickness and doping concentration of all layers within the PHEMT are adjusted so that the conduction band energy level of the channel layer is lower than the Fermi energy level during operation under low current. Thus, the linearity of the PHEMT can be improved, the linearity of the LNA formed by the PHEMT can be improved, the intermodulation signal output by the LNA can be reduced, and the signal quality can be improved.

[0062] Hereinafter, embodiments of this application will be described clearly and in detail with reference to the accompanying drawings.

[0063] Figure 4 is a schematic diagram of the cross-sectional structure of the PHEMT. The energy band structure of the channel layer is adjusted by using Solution 1, or by using a combination of Solution 1 and at least one of Solution 2 and Solution 3, which involves adjusting the thickness of the upper barrier layer and / or the thickness of the upper separation layer.

[0064] As shown in Figure 4, the PHEMT is single-δ doped and consists of a substrate 1, a buffer layer 2, a lower barrier layer 3, a channel layer 4, an upper isolation layer 5, a first doped layer 6, an upper barrier layer 7, and a cap layer 8 arranged sequentially on the substrate 1, a source 9 and a drain 10 placed on the cap layer 8, and a gate placed on the upper barrier layer 7. To 1 It includes 1. Below, we will use GaAs-based PHEMT as an example to explain the function, composition, and thickness of each layer.

[0065] Substrate 1 may be a gallium arsenide (GaAs) wafer.

[0066] The buffer layer 2 can be made of gallium arsenide (GaAs) or aluminum gallium arsenide (Al x Ga 1-x As), provided that 0 < x < 1. The buffer layer 2 can prevent defects in the substrate 1 from entering the core of the PHEMT. Generally, the Al doping concentration in the buffer layer can be gradually increased in the direction away from the substrate 1 so as to reduce the defects caused by the lattice mismatch between the substrate 1 and the lower barrier layer 3.

[0067] The lower barrier layer 3 can be made of aluminum gallium arsenide (Al x Ga 1-x As). The bandgap width of the lower barrier layer 3 is larger than that of the channel layer 4. The lower barrier layer 3 and the channel layer 4 form a heterojunction that is a negative junction. The thickness of the lower barrier layer 3 can be 10 - 50 nm or 10 - 25 nm, and can be, for example, 17 nm or 20 nm, etc.

[0068] For example, the maximum Al doping concentration in the buffer layer 2 is not more than the Al doping concentration in the lower barrier layer 3.

[0069] The channel layer 4 can be made of indium gallium arsenide (In y Ga 1-y As), provided that 0 < y < 1. For example, the value range of y can be 0.1 - 0.5. For example, y is 0.22 or 0.3.

[0070] In some embodiments, the thickness of the channel layer 4 can be greater than 8 nm or 12 nm and less than the critical thickness of the channel epitaxial layer. For example, In 0.22 Ga 0.78The critical thickness of the channel layer made of As is approximately 20 nm. The critical thickness increases as the indium content decreases. Optionally, the thickness of channel layer 4 can be 8–30 nm, 12–30 nm, or 15–20 nm, for example, 17 nm, 18 nm, 20 nm, or 24 nm. Increasing the thickness of channel layer 4 can improve the distribution of electrons and current within channel layer 4. This avoids electron accumulation below channel layer 4, reduces longitudinal current (i.e., the stacking direction of the PHEMT), and improves the linearity of the PHEMT.

[0071] For example, channel layer 4 is In 0.22 Ga 0.78 It is made of As and has a thickness of 18 nm.

[0072] The upper separation layer 5 is configured to separate the channel layer 4 from the first doped layer 6, preventing doping impurities from the first doped layer 6 from entering the channel layer 4. The upper separation layer 5 can be made of aluminum gallium arsenide and can have a thickness of 2-6 nm, for example, 4 nm or 6 nm. The upper separation layer 5 is also referred to as the first separation layer.

[0073] The first doped layer 6 can be delta-doped and is also referred to as the upper delta-doped layer. The first doped layer 6 can be silicon-doped. A thin layer of silicon is grown on the upper separation layer 5 as a doping impurity and, after ionization, provides a two-dimensional electron gas. The first doped layer 6 can be a few atoms thick, with a thickness of less than 2 nm, for example, 1 nm or less.

[0074] For example, the doping concentration of the first dope layer 6 is the sum of the doping concentrations of the two dope layers in the conventional double delta dope PHEMT, or the doping concentration is 3e12cm -2 From 5e12cm -2 , 5e12cm -2 From 6e12cm -2 , 1e12cm -2 From 3e12cm -2, 4.6e12cm -2 From 5.5 e 12 cm -2 , or 5.5e12cm -2 From 6.5 e 12 cm -2 For example, 4.5 e 12 cm -2 That is the case.

[0075] The upper barrier layer 7 is made of aluminum gallium arsenide (Al x Ga 1-x It can consist of As). The bandgap width of the upper barrier layer 7 is greater than the bandgap width of the channel layer 4. The upper barrier layer 7, the first doped layer 6, the upper isolation layer 5, and the channel layer 4 form a positive heterojunction. The thickness of the upper barrier layer 7 can be 10-30 nm or 10-25 nm, for example, 15 nm, 17 nm, or 20 nm.

[0076] The cap layer 8 is made of highly doped gallium arsenide (n + It can be made of -GaAs) and its thickness can be 5-10 nm. The cap layer 8 is configured to provide ohmic contact.

[0077] The cap layer 8 has a through hole. The gate 11 is located within the through hole and does not come into contact with the cap layer 8. Both the source 9 and drain 10 are located on the side of the cap layer 8 furthest from the upper barrier layer 7, and are situated on either side of the through hole, respectively.

[0078] Source 9, drain 10, and gate 11 are all made of conductive metal. Gate 11 is configured to provide a gate voltage to the PHEMT. When the gate voltage is higher than the turn-on voltage, source 9 and drain 10 are connected and a drain current is output.

[0079] In this embodiment of the application, the lower barrier layer 3 is directly connected to the channel layer 4, where “direct connection” means direct contact. In other words, there are no other layer structures between the lower barrier layer 3 and the channel layer 4.

[0080] Note that buffer layer 2, lower barrier layer 3, upper separation layer 5, and upper barrier layer 7 are all made of aluminum gallium arsenide (Al x Ga 1-x Al can be used, but the Al doping concentrations in these layers may be the same or different. This is not limited to this. For example, the lower barrier layer 3, the upper separation layer 5, and the upper barrier layer 7 may all be Al 0.22 Ga 0.78 Use As.

[0081] According to the single δ-doped PHEMT provided in this embodiment of this application, since the bandgap width of both the upper barrier layer 7 and the lower barrier layer 3 are greater than the bandgap width of the channel layer 4, the single δ-doped PHEMT has one doped positive junction (upper barrier layer 7 / first doped layer 6 / upper isolation layer 5 / channel layer 4) and one undoped negative junction (channel layer 4 / lower barrier layer 3). When the gate voltage is higher than the turn-on voltage, the doping impurities are ionized. Because the bandgap widths of the upper barrier layer 7 and the channel layer 4 are different, the conduction band is not continuous, and electrons move to one side of the channel layer to form a two-dimensional electron gas. The source 9 and drain 10 are connected, and a drain current is output.

[0082] In this embodiment of the application, based on the above-described adjustment mechanism for the energy band structure of the channel layer, the lower doped layer is removed, an appropriate concentration of the upper doped layer (i.e., the first doped layer 6) is selected, and appropriate thicknesses of the channel layer 4, the upper barrier layer 7, and the upper isolation layer 5 are selected. In the resulting single δ-doped PHEMT, when the output current is low, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level, or the conduction band energy level at the boundary between the channel layer 4 and the upper isolation layer 5 is lower than the Fermi energy level. Optionally, in the PHEMT, when the output current is low, the conduction band energy level of the channel layer 4 is substantially reduced in the thickness direction. In this embodiment of the application, the thickness direction is the direction from the cap layer to the substrate. See the direction shown in Figure 4. This substantial reduction may include the following two cases:

[0083] 1. The conduction band energy level of channel layer 4 decreases in the thickness direction. In other words, greater distance from the upper barrier layer indicates a lower conduction band energy level.

[0084] 2. The conduction band energy level of channel layer 4 is substantially / macroscopically decreasing in the thickness direction. In other words, in small regions microscopically separated from the upper barrier layer, a relatively high conduction band energy level is permissible.

[0085] For example, the thickness of the upper barrier layer 7 is 3-7 nm. The thickness of the upper separation layer 5 is 4 nm. The doping concentration of the first doped layer 6 is 3.0-4.5 e12 cm³. -2 The channel layer thickness is 12 nm.

[0086] For example, the thickness of the upper barrier layer 7 is 5 nm. The thickness of the upper separation layer 5 is 3-5 nm. The doping concentration of the first doped layer 6 is 3.0-4.5 e12 cm³. -2 The channel layer thickness is 8-14 nm.

[0087] Unlike the double-δ-doped PHEMTs of the prior art, this embodiment of the present application provides a single-δ-doped PHEMT. When the total doping concentration remains unchanged or does not decrease, δ-doping is performed only on the upper barrier layer 7, and the lower doped layer is removed, thereby reducing the gradient of the conduction band energy level of the channel layer 4 in the thickness direction, and as a result, the linearity of the PHEMT under small output currents can be improved without affecting the gain (i.e., the transconductance gm).

[0088] Furthermore, increasing the thickness of the channel layer 4 can improve the distribution of electrons and current within the channel layer 4. This avoids electron accumulation below the channel layer 4, reduces the current in the longitudinal direction (i.e., the stacking direction of the PHEMT), and further improves the linearity of the PHEMT.

[0089] Figure 5 shows another PHEMT according to one embodiment of this application. This PHEMT may be a double-doped PHEMT. In addition to the layer structure shown in Figure 4, this PHEMT may further include a second doped layer 12 and a lower separation layer 13.

[0090] Both the first doped layer 6 and the second doped layer 12 can be delta-doped. Thus, the first doped layer 6 is also referred to as the upper delta-doped layer 6, and the second doped layer 12 is also referred to as the lower delta-doped layer 12. Both the first doped layer 6 and the second doped layer 12 can be silicon-doped. A thin layer of silicon is grown as a doping impurity on each of the upper separation layer 5 and the lower barrier layer 3, and after ionization, provides a two-dimensional electron gas. Both the first doped layer 6 and the second doped layer 12 can be a few atoms thick, with a thickness of less than 2 nm, for example, 1 nm or less. The doping concentration of the first doped layer 6 is higher than the doping concentration of the second doped layer 12.

[0091] The lower separation layer 13 is configured to separate the second doped layer 12 from the channel layer 4, preventing doping impurities from the second doped layer 12 from entering the channel layer 4. The lower separation layer 13 can be made of gallium arsenide and may have a thickness of 2-6 nm, for example, 4 nm. The lower separation layer 13 is also referred to as the second separation layer.

[0092] Furthermore, while buffer layer 2, lower barrier layer 3, upper separation layer 5, lower separation layer 13, and upper barrier layer 7 may all be made of aluminum gallium arsenide, the doping concentrations of Al in these layers may be the same or different. This is not limited to the above.

[0093] According to the double delta-doped PHEMT provided in this embodiment of this application, since the bandgap width of both the upper barrier layer 7 and the lower barrier layer 3 are greater than the bandgap width of the channel layer 4, the double delta-doped PHEMT has one doped positive junction (upper barrier layer 7 / first doped layer 6 / upper isolation layer 5 / channel layer 4) and one doped negative junction (channel layer 4 / lower isolation layer 13 / second doped layer 12 / lower barrier layer 3). When the gate voltage is higher than the turn-on voltage, the doping impurities are ionized. Because the bandgap widths of the barrier layers and the channel layer 4 are different, the conduction band is not continuous, and electrons move to one side of the channel layer to form a two-dimensional electron gas. The source 9 and drain 10 are connected, and a drain current is output.

[0094] In some embodiments, the energy band structure of the channel layer is adjusted by using Solution 3 described above. In the PHEMT shown in Figure 5, the thickness of the channel layer 4 is greater than 12 nm and less than the critical thickness of the channel epitaxial layer (i.e., it does not exceed the migration limit of the InGaAs channel epitaxial layer). Therefore, in the double delta-doped PHEMT, when the output current is small, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level. For example, the thickness of the channel layer 4 is 8-30 nm, 12-30 nm, or 15-20 nm, for example, 17 nm, 18 nm, 20 nm, or 24 nm. The thickness or critical thickness of the channel layer 4 is related to the indium content. A lower indium content results in a greater thickness. For example, the channel layer 4 is In 0.22 Ga 0.78 It is made of As and has a thickness of 18 nm.

[0095] In the double delta-doped PHEMT described above, increasing the thickness of the channel layer 4 can improve the distribution of electrons and current within the channel layer 4. This avoids electron accumulation below the channel layer 4, reduces current in the thickness direction, and improves the linearity of the PHEMT.

[0096] In some other embodiments, the energy band structure of the channel layer is adjusted by using Solution 2 described above. Thus, in the double delta-doped PHEMT, when the output current is small, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level.

[0097] For example, the doping concentration of the first doping layer 6 is 3.5-4.5 e12 cm³. -2 Therefore, the doping concentration of the second doping layer 12 is 3-5 e11 cm³. -2 That is the case.

[0098] For example, the ratio of the doping concentration in the first doping layer 6 to the doping concentration in the second doping layer 12 is greater than a predetermined value. The predetermined value is 6 or greater, for example, 9, 10, 15, 30, 70, 100, or 150.

[0099] In another example, the doping concentration in the first doping layer 6 was 4-6 e12 cm³. -2 Therefore, the doping concentration of the second doping layer 12 is 2 e8 cm³. -2 From 3e11cm -2 , 1e6cm -2 From 1e11cm -2 , or 1e6cm -2 From 1e8cm -2 That is the case.

[0100] In another example, the doping concentration in the first doping layer 6 was 3.5-4.5 e12 cm³. -2 , 4.5-6e12cm -2 , or 4.6-5.5 e 12 cm -2 Therefore, the doping concentration of the second doping layer 12 is 2 e8 cm³. -2 From 3e11cm -2 That is the case.

[0101] In this double-δ-doped PHEMT, the doping concentration and ratio of the upper / lower δ-doped layers are adjusted to reduce the energy level gradient of the channel layer 4 caused by the second doped layer 12. Therefore, when the device operates under low current, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level. This improves the linearity of the device.

[0102] In some other embodiments, the energy band structure of the channel layer is adjusted by using solutions 2 and 3 described above. Thus, in the double-δ doped PHEMT, when the output current is small, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level. For example, the thickness of the channel layer is 18 nm. The doping concentration of the first doped layer 6 is 3.5–4.5 e12 cm².-2 The doping concentration of the second doping layer 12 is 2 e8 cm³. -2 From 3e11cm -2 Alternatively, the ratio of the doping concentration of the first doping layer 6 to the doping concentration of the second doping layer 12 is set to be greater than a predetermined value. The predetermined value is 6 or greater, for example, 9.

[0103] In a double-delta doped PHEMT, the doping concentration and ratio of the upper / lower doped layers are adjusted to reduce the energy level gradient in channel layer 4 caused by the lower doped layer. Therefore, when the device operates under low current, the conduction band energy level of channel layer 4 is lower than the Fermi energy level. This improves the linearity of the device.

[0104] In some other embodiments, the energy band structure of the channel layer is adjusted by using a combination of Solution 2 and / or Solution 3 and adjustment of the thickness of the upper barrier layer and / or upper isolation layer. Thus, in the double delta-doped PHEMT, when the output current is small, the conduction band energy level of the channel layer 4 is lower than the Fermi energy level.

[0105] For example, the thickness of the upper barrier layer 7 is 3-7 nm. The thickness of the upper separation layer 5 is 3-5 nm. The doping concentration of the first doped layer 6 is 3.0-4.5 e12 cm³. -2 The doping concentration in the second doping layer 12 is 3-5 e11 cm³. -2 The channel layer thickness is 18 nm.

[0106] In another example, the thickness of the upper barrier layer 7 is 3-7 nm. The thickness of the upper separation layer 5 is 3-5 nm. The doping concentration of the first doped layer 6 is 3.0-4.5 e12 cm³. -2 The doping concentration in the second doping layer is 2 e8 cm³. -2 From 3e11cm -2 The channel layer thickness is 14-20 nm.

[0107] In another example, the thickness of the upper barrier layer 7 is 5 nm. The thickness of the upper separation layer 5 is 4 nm. The doping concentration of the first doped layer 6 is 3.0-4.5 e12 cm³. -2 The doping concentration in the second doping layer is 2 e8 cm³. -2 From 3e11cm -2 The channel layer thickness is 14-20 nm.

[0108] Furthermore, in the above embodiment, when the PHEMT is under a small output current, the conduction band energy level of the channel layer 4 substantially decreases in the thickness direction.

[0109] In some other embodiments, each layer structure in Figure 4 or 5 may instead consist of a different material and have a different thickness, for example, a ternary, quaternary, or multi-component compound of gallium arsenide. In another example, the PHEMT is a gallium phosphorus (GaP)-based PHEMT.

[0110] In the explanation of Figures 4 and 5, the upper doped layer or upper δ-doped layer corresponds to the first doped layer 6, and the lower doped layer or lower δ-doped layer corresponds to the second doped layer 12.

[0111] Furthermore, for the sake of clarity, the layer thicknesses in Figures 4 and 5 do not correspond to the actual thickness or thickness ratio of the layers; the specific thickness range follows the thickness specified for the layers as described above.

[0112] Compared to prior art, the OIP3 value of the single delta-doped PHEMT provided in this embodiment of this application is significantly higher. When the output drain current is 60-100 mA, the OIP3 value of the single delta-doped PHEMT increases by more than 5 dBm. Specific data are shown in Figure 6. A and Figure 6B As shown in Figure 6. A and Figure 6BThis compares the simulation results of the OIP3 value of a prior art double-delta-doped PHEMT with the simulation results of the OIP3 value of a single-delta-doped PHEMT provided in this embodiment of this application. Compared with a prior art double-delta-doped PHEMT, it can be seen that the OIP3 value of the single-delta-doped PHEMT provided in this embodiment of this application increases by more than 5 dBm when the output current is 50-200 mA.

[0113] Referring to Figures 7A-7C, the principle of improving the linearity of PHEMT through single delta doping is explained below.

[0114] Figure 7A is a diagram of the energy bands of a prior art double-δ-doped PHEMT. Figure 7B is a diagram of the energy bands of a single-δ-doped PHEMT according to one embodiment of this application. Figure 7C compares the conduction band structure of a double-δ-doped PHEMT and a single-δ-doped PHEMT in the channel layer. It should be understood that the Fermi energy level increases as the gate voltage increases. Figures 7A-7C all show the Fermi energy level when the drain current (i.e., output current) is 60 mA.

[0115] Because space charge is concentrated and distributed at the δ-doping location, the energy band to the left of the δ-doping location is bent. When the output current is 60 mA, the energy band structure reveals that, as shown by the shaded region in Figure 7C, the conduction band structure of the channel layer of a single δ-doped PHEMT is close to a square, while the conduction band structure of a double δ-doped PHEMT is close to a triangle. Since the electron concentration in the channel layer is proportional to the area of ​​the polygon enclosed by the conduction band and the Fermi energy level, the square conduction band structure exhibits higher linearity than the triangular conduction band structure during the gate voltage change process.

[0116] In a single-δ-doped PHEMT, all electrons in the channel layer are supplied by the upper δ-doped layer. Therefore, to obtain the same output current, the conduction band of the channel layer of a single-δ-doped PHEMT is further below the Fermi energy level compared to the conduction band of the channel layer of a double-δ-doped PHEMT. A Fermi-Dirac distribution occurs for electrons near the Fermi energy level. Specifically, the probability of electron generation near the Fermi energy level (shown by the dashed box region in Figure 7C) is 0.5, and the probability of electron generation below the Fermi energy level is 1. Thus, the probability of electron generation near the Fermi energy level is, to some extent, nonlinear when the gate voltage changes. However, the area occupied by electrons near the Fermi energy level is a small proportion of the overall conduction band structure of the channel layer of a single-δ-doped PHEMT. Therefore, a single-δ-doped design, where the conduction band is further below the Fermi energy level, can provide higher linearity.

[0117] Referring to Figure 8, the principle of improving the linearity of PHEMT by increasing the thickness of the channel layer is explained below.

[0118] Figure 8 shows the electron concentration distribution of double delta-doped PHEMTs with channel layers of 12 nm and 18 nm thickness, respectively, under an output current of 60 mA / mm. As can be seen from Figure 8, when the PHEMT operates under an output current of 60 mA / mm, in the PHEMT with a 12 nm thick channel layer, a large number of electrons accumulate beneath the channel layer, resulting in a large z-direction component in the current within the channel layer. In comparison, in the PHEMT with an 18 nm thick channel layer, electrons are distributed more uniformly within the channel layer when the PHEMT is operating. This reduces the z-direction component of the current within the channel layer, reduces the complexity of controlling the channel current using a gate, and improves the linearity of the PHEMT.

[0119] The following describes application scenarios for PHEMT provided in the embodiments of this application.

[0120] One embodiment of this application further provides an LNA, as shown in Figure 9, which includes an input matching network, a bias circuit, a PHEMT, and an output matching network. The PHEMT may be the PHEMT shown in Figure 4 or Figure 5. The bias circuit is configured to provide a bias voltage for proper operation of the PHEMT, i.e., to set the gate, source, and drain of the PHEMT to the required potential. The input matching network is configured to achieve matching between the output impedance of the signal source and the input impedance of the LNA so that the LNA obtains maximum excitation power. The output matching network is configured to convert an external load resistance to an optimal load resistance used by the amplifier to ensure maximum output power.

[0121] One embodiment of this application further provides a receiver or transceiver, which may include an LNA as shown in Figure 9. Optionally, the receiver or transceiver may further include a duplexer, a bandpass filter, a digital-to-analog converter ( DAC ), and similar items may be included.

[0122] LNAs can be applied to radio frequency systems. As shown in Figure 10, a radio frequency system can be divided into a transmit link and a receive link. In the application scenario of this application, the low-noise amplifier LNA in the receive link of the radio frequency system can be the LNA shown in Figure 9 and is configured to amplify the signal received by the antenna.

[0123] The transmission link is for the power amplifier (PA), and the driver. Ba, at least one fill Ta, At least one Miki sa, at least one local oscillator (L O), and at least one amplifier (AThe receiving link may include an MP, a low-noise amplifier LNA, at least one filter, at least one mixer, and at least one local oscillator. (L O), and may include at least one amplifier, etc. The at least one filter may be an image rejection filter. Ta, This may include an intermediate frequency filter (IF filter) or other filters.

[0124] It should be understood that Figure 10 is merely an illustrative example. A radio frequency system may instead have other circuit configurations, and may contain fewer components than those shown in Figure 10. This is not an limitation.

[0125] This application further provides a radio frequency circuit, which includes a PHEMT as shown in Figure 4 or Figure 5, or an LNA as shown in Figure 9, and is applied to the field of wireless communication and is configured to process a signal received by an antenna and / or control the antenna to transmit a signal.

[0126] This application further provides a radio frequency chip, which is configured to process a signal received by a receiving antenna, send the signal to a processor, receive instructions from the processor, and control a transmitting antenna to transmit a signal.

[0127] This application further provides electronic equipment, which may be devices having radio frequency functions or wireless communication functions, such as mobile phones, tablet computers, e-book readers, televisions, notebook computers, digital cameras, in-vehicle devices, wearable devices, base stations, or routers. The electronic equipment may include at least one of the above-mentioned PHEMT, LNA, radio frequency system, radio frequency circuit, and radio frequency chip.

[0128] In short, the embodiments described above are intended merely to illustrate the technical solutions of this application and not to limit it. Although this application is described in detail with reference to the embodiments described above, it will be understood by those skilled in the art that modifications to the technical solutions recorded in the embodiments described above, or equivalent substitutions of some of their technical features, can still be made without departing from the scope of the technical solutions of the embodiments of this application.

Claims

1. A pseudo-lattice-matched high-electron-mobility transistor (PHEMT), Channel layer and A lower barrier layer and an upper barrier layer are arranged on both sides of the channel layer, respectively, and the lower barrier layer is connected to the channel layer. A first separation layer and a first doped layer are disposed between the channel layer and the upper barrier layer, wherein the first separation layer is configured to separate the first doped layer from the channel layer, and the first doped layer is configured to provide a two-dimensional electron gas. It has, When the output current density of the PHEMT is at a first threshold, the conduction band energy level at the boundary between the channel layer and the first isolation layer is lower than the Fermi energy level, and the first threshold is the current density present immediately after the PHEMT is turned on. When the output current density of the PHEMT is less than the first threshold, the conduction band energy level of the channel layer decreases in the thickness direction from the upper barrier layer to the lower barrier layer. PHEMT.

2. The PHEMT according to claim 1, wherein the lower barrier layer is directly connected to the channel layer.

3. The first doped layer is silicon-doped, and the doping concentration is 3 e12 cm³. －２ From 5e12cm －２ The PHEMT according to claim 2.

4. The PHEMT according to claim 1, wherein the lower barrier layer is connected to the channel layer via a second separation layer and a second doped layer, the second separation layer is configured to separate the channel layer from the second doped layer, and the second doped layer is configured to provide a two-dimensional electron gas.

5. The doping concentration of the first doped layer is 3.5 e12 cm³. －２ From 4.5 e 12 cm －２ Therefore, the doping concentration of the second doped layer is 3 e11 cm⁻¹. －２ From 5e11cm －２ The PHEMT according to claim 4.

6. The PHEMT according to claim 4, wherein the ratio of the doping concentration of the first doped layer to the doping concentration of the second doped layer is greater than a preset value, and the preset value is 6 or more.

7. The PHEMT according to claim 6, wherein the preset value is greater than 9.

8. The PHEMT according to any one of claims 5 to 7, wherein the doping concentration of the first doped layer and the doping concentration of the second doped layer enable the conduction band energy level of the channel layer to be lower than the Fermi energy level when the PHEMT is in the ON state.

9. The PHEMT according to any one of claims 1 to 7, wherein the thickness of the channel layer is 15-20 nm.

10. The PHEMT according to any one of claims 1 to 7, further comprising a cap layer, a source, a drain, and a gate, wherein the cap layer is located on the side of the upper barrier layer furthest from the channel layer and has a through hole for providing ohmic contact, the gate is located within the through hole, and the source and the drain are both located on the side of the cap layer furthest from the upper barrier layer and on either side of the through hole, respectively.

11. The PHEMT according to any one of claims 1 to 7, wherein the channel layer is made of indium gallium arsenide, and the upper barrier layer, the lower barrier layer, or the separation layer is made of aluminum gallium arsenide.

12. The PHEMT according to any one of claims 1 to 7, wherein the first threshold is one of 40 mA / mm, 60 mA / mm, 100 mA / mm, and 200 mA / mm.

13. A radio frequency chip having a PHEMT according to any one of claims 1 to 7.

14. An electronic device having a PHEMT according to any one of claims 1 to 7.

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