TW201513345A - Linear high-electron mobility transistor - Google Patents

Abstract

Embodiments of the present disclosure describe apparatuses, methods, and systems of an integrated circuit (IC) device. The IC device includes a gallium nitride (GaN) buffer layer formed on a substrate, an aluminum gallium nitride (AlGaN) layer formed on the GaN buffer layer, and an indium aluminum nitride barrier layer formed on the AlGaN layer. Other embodiments may also be described and/or claimed.

Description

Linear high electron mobility transistor

Embodiments of the present disclosure are generally directed to the field of integrated circuits, and more particularly to linear high electron mobility transistors and methods of fabrication.

Related application

The present application claims priority to U.S. Provisional Patent Application Serial No. 61/873,306, filed on Sep. 3, 2013, which is entitled "LINEAR HIGH-ELECTRON MOBILITY TRANSISTOR", The entire disclosure is hereby incorporated by reference.

A High-Electron Mobility Transistor (HEMT) typically includes a heterojunction formed between two semiconductor materials having different energy gaps. For example, high mobility charge carriers can be generated using a wide gap layer (for example, an n-type donor supply layer) and a heterojunction of a narrow gap layer. In the case of a wide band gap nitride transistor, the charges can be induced by spontaneous and piezoelectric polarization without the need to dope in the wide band gap. The current is typically confined to an ultra-narrow channel at one interface of the layers and flows between the source terminal and the drain terminal, the current being controlled by the voltage applied to a gate terminal.

Although heterostructure field effect transistors can be from ultra high frequencies (Ultra High Frequency, UHF) to millimeter wave frequencies reveal appropriate power performance; however, conventional devices may encounter difficulties in providing linear amplifier operation due to device nonlinearity. When such transistors are used in situations where linear amplification is required, external circuitry may have to be provided to compensate for the non-linear characteristics of the transistors.

An aspect of the invention is an apparatus comprising: a substrate; a gallium nitride (GaN) buffer layer formed on the substrate; an aluminum gallium nitride (AlGaN) layer formed on the GaN On the buffer layer, the AlGaN layer has an aluminum concentration of less than about 15%; and an indium aluminum nitride (InAlN) barrier layer formed on the AlGaN layer, wherein the AlGaN layer is thinner than the InAlN barrier layer.

Another aspect of the present invention is a method comprising: forming a gallium nitride (GaN) buffer layer on a substrate; forming an aluminum gallium nitride (AlGaN) layer on the GaN buffer layer, the AlGaN layer The thickness is between about 40 and 60 angstroms; an indium aluminum nitride (InAlN) barrier layer is formed over the AlGaN layer; and a gate, a source, and a drain are formed on the InAlN barrier layer.

Another aspect of the present invention is a system comprising: a transceiver for transmitting and receiving radio frequency (RF) signals; and a high electron mobility transistor (HEMT) incorporated in the transceiver Or coupling the transceiver, the HEMT includes: a substrate; a gallium nitride (GaN) buffer layer formed on the substrate; an aluminum gallium nitride (AlGaN) layer formed on the GaN buffer layer The AlGaN layer has an aluminum concentration of less than about 15%; and an indium aluminum nitride (InAlN) barrier layer formed on the AlGaN layer.

100‧‧‧Integrated circuit (IC) device

104‧‧‧Substrate

108‧‧‧Stacking

112‧‧‧GaN buffer layer

116‧‧‧AlGaN layer

120‧‧‧AlN layer

124‧‧‧Indium Nitride (InAlN) barrier layer

126‧‧‧gate insulator

128‧‧‧ gate

132‧‧‧ source

136‧‧‧汲

200‧‧‧Electrical distribution of IC devices

204‧‧‧Electronic distribution of the first IC device

208‧‧‧Electronic distribution of the second IC device

300‧‧‧Energy diagram of IC device

304‧‧‧Energy diagram of the first IC device

308‧‧‧Energy band diagram of the second IC device

400‧‧‧Electrical distribution of IC devices

404‧‧‧Response profile of the first IC device

408‧‧‧Response profile of the second IC device

500‧‧‧Energy diagram of IC device

504‧‧‧Response profile of the first IC device

508‧‧‧Response profile of the second IC device

600‧‧‧Figure of transconductance gm as a function of gate voltage

604‧‧‧ Response profile associated with a linear IC device

608‧‧‧ Response profile associated with a conventional device

800‧‧‧ system

802‧‧‧Power Amplifier (PA) Module

804‧‧‧ transceiver

806‧‧‧Antenna Switching Module (ASM)

808‧‧‧Antenna structure

810‧‧‧Power Regulator

The implementation will be easily understood by the following detailed description. example. To facilitate this description, the same element symbols represent the same structural elements. Embodiments are illustrated by way of example in the figures of the drawings, without limitation.

1 schematically illustrates a cross-sectional view of an integrated circuit (IC) device in accordance with various embodiments.

2 is an electronic distribution diagram of an IC device according to various embodiments.

3 is an energy band diagram of an IC device according to various embodiments.

4 is an electronic distribution diagram of an IC device according to various embodiments.

Figure 5 shows an energy band diagram of an IC device according to various embodiments.

Figure 6 is a diagram of a transconductance as a function of gate voltage in accordance with various embodiments.

Figure 7 is a flow diagram of a method for fabricating an integrated circuit device in accordance with various embodiments.

FIG. 8 diagrammatically illustrates an example system including an IC device in accordance with various embodiments.

Embodiments of the present disclosure provide a structural configuration, fabrication method, and system of an integrated circuit (IC) device, such as, for example, a high electron mobility transistor (HEMT).

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed description, reference should be made to the claims in the claims display. Other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the embodiments is defined by the scope of the appended claims and their equivalents.

For the purposes of this disclosure, the meaning of the terms "A and/or B" is (A), (B), Or (A and B). For the purposes of this disclosure, the meaning of the terms "A, B, and/or C" is (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

The description may use terms such as "in an embodiment" or "in an embodiment", each of which may denote one or more of the same or different embodiments. Further, the terms "including", "comprising", "having", and the like, as used in the embodiments of the present disclosure are synonymous.

The term "coupling" and its derivatives may be used in this article. "Coupled" may mean one or more of the following. "Coupled" may mean that two or more elements are in direct physical or electrical contact. However, "coupled" may also mean that two or more elements are in indirect contact with each other, but still operate cooperatively or interact with each other; and may mean that one or more other elements are coupled or connected It is considered to be between components that are coupled to each other.

In various embodiments, the phrase "a first layer formed on a second layer" may mean that the first layer is formed over the second layer, and at least a portion of the first layer may be in direct contact. (for example, direct physical and/or electrical contact) or indirect contact (for example, one or more other layers between the first layer and the second layer) at least a portion of the second layer .

FIG. 1 schematically illustrates a cross-sectional view of an IC device 100 in accordance with various embodiments. For example, the IC device 100 can be a HEMT device.

The IC device 100 can be fabricated on a substrate 104. The substrate 104 typically includes a support material on which a stack (or simply "stack 108") is deposited. In one embodiment, the substrate 104 comprises germanium (Si), tantalum carbide (SiC), aluminum oxide (Al ₂ O ₃ ) or sapphire, gallium nitride (GaN), and/or aluminum nitride (AlN). Other materials comprising suitable II-VI and III-V semiconductor material systems can also be used in the substrate 104 in other embodiments. In one embodiment, the substrate 104 can be constructed of any material or combination of materials capable of epitaxially growing a GaN buffer layer 112.

The stack 108 formed on the substrate 104 may comprise an epitaxial deposited layer composed of different material systems that form one or more heterojunction/heterostructures. The layers of stack 108 can be formed in the field. That is, the stack 108 can be formed on the substrate 104 in a fabrication facility (eg, a reaction chamber) that forms a constituent layer of the stack 108 without the need to remove the substrate 104 from the fabrication facility.

In one embodiment, the stack 108 of IC devices 100 includes a GaN buffer layer 112 formed on a substrate 104. The GaN buffer layer 112 can provide a crystal structure transition region between the substrate 104 and other layers of the stack 108 to act as a buffer or isolation layer. For example, GaN buffer layer 112 can provide stress relief between substrate 104 and other lattice mismatched materials. The GaN buffer layer 112 can be epitaxially coupled to the substrate 104. In other embodiments, a nucleation layer (eg, AlN, not shown) may be interposed between the substrate 104 and the GaN buffer layer 112.

In some embodiments, the GaN buffer layer 112 has a thickness of from about 1 to 2 microns. As used herein, the thickness of a layer refers to the size of the layer in a direction substantially perpendicular to a major surface of the substrate 104. The GaN buffer layer 112 can include other suitable materials and/or thicknesses in other embodiments. In some embodiments, the GaN buffer layer 112 may not be doped.

The stack 108 may further include: an aluminum gallium nitride (AlGaN) layer 116 formed on the GaN buffer layer 112; an AlN layer 120 formed on the AlGaN layer 116; an indium aluminum nitride (InAlN) a barrier layer 124 formed on the AlN layer 120; and a gate insulator 126 formed on the InAlN barrier layer.

The IC device 100 can further include a gate 128 formed on the gate insulator 126. The gate 128 can serve as a connection terminal of the IC device 100. The gate 128 can be directly coupled to the gate insulator 126. The gate 128 is typically constructed of a conductive material (e.g., metal). In some embodiments, the gate 128 can be nickel (Ni), platinum (Pt), iridium (Ir), molybdenum (Mo), gold (Au), and/or aluminum (Al).

The IC device 100 can further include a source 132 and a drain 136 formed on the gate insulator 126. In some embodiments, the source 132 and the drain 136 may extend through one or more layers of the stack 108 by performing an ohmic recess, for example, down to the GaN buffer layer 112. The source 132 and the drain 136 may be ohmic contacts. The source 132 and the drain 136 can be re-growth contacts that can provide a relatively low contact resistance compared to standard grown contacts. In an embodiment, the contact resistance of the source 132 and the drain 136 may be about 0.01 ohm. Mm.

The source 132 and the drain 136 may each be formed of a conductive material (eg, metal). In one embodiment, each of the source 132 and the drain 136 may comprise titanium (Ti), aluminum (Al), molybdenum (Mo), gold (Au), and/or germanium (Si). Other materials can also be used in other embodiments.

A heterojunction may be formed between the InAlN barrier layer 124 and the GaN buffer layer 112. The energy gap energy of the InAlN barrier layer 124 may be greater than the energy gap energy of the GaN buffer layer 112. The InAlN barrier layer 124 can be a wider energy gap layer that supplies mobile charge carriers, and the GaN buffer layer 112 can provide a narrower energy gap layer for the mobile charge carriers.

The AlGaN layer 116 can be positioned on the InAlN barrier layer 124 and the GaN Between the layers 112 to improve linearity. In particular, the AlGaN layer 116 can contribute to a polarization induced channel at the GaN buffer layer 112 during operation of the IC device 100 (for example, when a voltage is applied to the gate 128), thereby forming a vertical Three-Dimensional Electron Gas (3DEG) extending in the channel. For example, this may allow current (mobile charge carriers) to flow between the source 132 and the drain 136. This extended electron gas can result in a substantially constant transconductance versus gate voltage profile. As a result, the IC device 100 can be associated with a more linear operation and low amplitude modulation to amplitude modulation (AM-to-AM) distortion.

The AlN layer 120 can be used to enhance electron mobility by reducing alloy scattering caused by the rough surface of a bottom layer (for example, AlGaN layer 116).

The gate insulator 126 (when present) can serve as an insulating layer between the InAlN barrier layer 124 and the gate 128 via which the gate 128 is capacitively coupled to the InAlN barrier layer 124. This can form a Metal-Insulator-Semiconductor (MIS) structure or a metal-oxide-semiconductor structure. In various embodiments, the gate insulator 126 can help provide lower gate leakage and higher breakdown voltage. In addition to providing a low gate leakage and high breakdown voltages outside this structure may also have a relatively small gate - source capacitance variation substantially constant gain g _m reached in a wide range of gate voltage swing of An advantage, which corresponds to a relatively small amplitude modulation to phase modulation (AM-to-PM) distortion. The gate insulator 126 can be a field grown GaN or AlN grown at relatively low temperatures (for example, 500 ° C or 600 ° C), which can lead to a material having a polycrystalline structure with a very high resistivity. The gate insulator 126 may comprise GaN, AlN, Al ₂ O ₃ , lanthanum oxide (La ₂ O ₃ ), tantalum nitride, hafnium oxide, or any other suitable dielectric material.

In some embodiments, the gate insulator 126 can have a thickness of less than about 50 angstroms. For example, 18 angstroms, the thickness of the InAlN barrier layer 124 can be about 80 angstroms, the thickness of the AlN layer 120 can be about 10 angstroms, and the thickness of the AlGaN layer 116 can be about 40 to 60 angstroms.

In various embodiments, the AlGaN layer 116 can have a fixed or slowly varying aluminum content. For example, in one embodiment, the AlGaN layer 116 can have a material concentration in accordance with Al _x Ga _1-x N, where x is a value representing the relative amount of aluminum and gallium. In certain embodiments, the value of x is from about 0 to 0.15. In an embodiment having a fixed aluminum content, the AlGaN layer 116 can have a relative material concentration of Al _0.04 Ga _0.96 N throughout the thickness of the layer. In this embodiment, for example, the AlGaN layer 116 can have a thickness of about 40 angstroms. In an embodiment having a graded aluminum content, x at a portion of the AlGaN layer 116 beside the GaN buffer layer 112 may be zero and may be gradually increased to about 0.15 at a portion of the AlGaN layer 116 beside the AlN layer 120. . In this embodiment, for example, the AlGaN layer 116 can have a thickness of about 50 angstroms. Other values of x or other slowly varying structures can also be used in other embodiments.

2 is an electronic distribution diagram 200 of an IC device (eg, IC device 100) in accordance with various embodiments. In particular, diagram 200 shows an electronic distribution 204 of a first IC device and an electronic distribution 208 of a second IC device. For the purpose of measuring the graph 200, the first IC device may include a 30 angstrom gate insulator (for example, a GaN cap portion); an 80 angstrom InAlN barrier layer having a concentration of indium of 0.17; A 10 angstrom AlN layer; and a 40 angstrom AlGaN layer have an aluminum concentration of 0.04. The second IC device can be identical to the first IC device; however, the gate insulator may not be included.

3 is an energy band diagram 300 of an IC device (for example, IC device 100) in accordance with various embodiments. In particular, diagram 300 shows an energy band diagram 304 of the first IC device described above with respect to FIG. 2 and an energy band diagram 308 of the second IC device described above with respect to FIG.

The electronic distribution and energy band diagrams of Figures 2 and 3 demonstrate that the apparatus of the present invention has an extended and wider distribution of electrons in the vertical direction than conventional apparatus. This can result in improved linearity and power performance at high radio frequency (RF) input drive levels.

4 is an electronic distribution diagram 400 of an IC device (eg, IC device 100) in accordance with various embodiments. In particular, diagram 400 shows a response profile 404 of a first IC device and a response profile 408 of a second IC device. For the purpose of measuring 400, the first IC device may include a 30 angstrom gate insulator (for example, a GaN cap portion); an 80 angstrom InAlN barrier layer having a concentration of indium of 0.17; A 10 angstrom AlN layer; and a 50 angstrom AlGaN layer have a graded aluminum concentration of 0 to 0.15. The second IC device can be identical to the first IC device of FIG. 4; however, the gate insulator may not be included.

Figure 5 shows an energy band diagram 500 of an IC device (e.g., IC device 100) in accordance with various embodiments. In particular, graph 500 shows the response profile 504 of the first IC device described above with respect to FIG. 4 and the response profile 508 of the second IC device described above with respect to FIG.

Similar to the response profiles of Figures 2 and 3, the response profiles of Figures 4 and 5 demonstrate that the apparatus of the present invention has an extended and wider distribution of electrons in the vertical direction than conventional devices.

Figure 6 shows a graph 600 of transconductance gm as a function of gate voltage, in accordance with various embodiments. In particular, diagram 600 illustrates a response profile 604 that can be associated with a linear IC device (e.g., IC device 100) that is responsive to a response profile 608 that can be associated with a conventional device. As can be seen in the figure, in response to the contour 608, the response profile 604 exhibits a wider and more constant transconductance gm with respect to the gate voltage. Thus, IC device 100 can have improved device linearity and a higher saturation output power level than conventional devices.

7 is used to fabricate an IC device according to various embodiments (for example A flowchart of a method 700 of the IC device 100) of FIG. The method 700 includes, at 704, forming a buffer layer (eg, GaN buffer layer 112) on a substrate (eg, substrate 104); at 708, forming an AlGaN layer on the buffer layer (for example In other words, the AlGaN layer 116); at 712, an AlN layer (for example, the AlN layer 120) is formed on the AlGaN layer; and at 716, a barrier layer is formed on the AlN layer (for example, InAlN barrier layer 124); at 720, a gate insulator (for example, gate insulator 126) is formed on the barrier layer; and at 724, a gate, a source, and a drain are respectively formed (For example, gate 128, source 132, and drain 136). In some embodiments, the gate can be formed on the gate insulator, and the source and drain can be formed on a lower layer of the stack. In various embodiments, other layers may be formed for insertion between such layers.

According to various embodiments, one or more layers may be epitaxially deposited by the following methods: Molecular Beam Epitaxy (MBE), Atomic Layer Epitaxy (ALE), Chemical Beam Lei Chemical Beam Epitaxy (CBE), and/or Metal-Organic Chemical Vapor Deposition (MOCVD). Other suitable deposition techniques can also be used in other embodiments. The materials and/or thicknesses of the layers of the stack may be consistent with the embodiments already described in connection with IC device 100 of FIG.

The source and the drain may be formed by a re-growth process to provide an ohmic contact having a low contact resistance or a low on-resistance. In the re-growth process, material may be selectively removed (eg, etched) in the region where the source and the drain are to be formed. A highly doped material (for example, n++ material) can be deposited in regions where the layers have been selectively removed. In some embodiments, the highly doped material of the source and drain may be the same material as that used for the buffer or barrier layer. For example, in the In systems that buffer GaN, a GaN-based material that is highly doped with germanium (Si) can be epitaxially deposited in the selectively removed regions to a thickness of 400 to 700 angstroms. The highly doped material can be epitaxially deposited by MBE, ALE, CBE, MOCVD, or a suitable combination thereof. Other materials, thicknesses, or deposition techniques can also be used for this highly doped material in other embodiments. For example, one or more metals (for example, including titanium (Ti) and/or gold (Au)) may be formed at a thickness of 1000 angstroms to 1500 angstroms using a lift-off process. / deposited on the highly doped material. Other materials, thicknesses, and/or techniques can also be used with the one or more metals in other embodiments.

In some embodiments, the source and the drain can be formed by an implantation process that uses implant technology to introduce impurities (eg, germanium) for the source and the drain A highly doped material is provided. After implantation, the source and the drain are annealed at a high temperature (for example, 1100 to 1200 ° C). This re-growth process can preferably avoid high temperatures associated with post-implant annealing.

The gate can be formed on the gate insulator by depositing a conductive material on the gate insulator. The gate material can be deposited by any suitable deposition process, for example, including evaporation, Atomic Layer Deposition (ALD), and/or Chemical Vapor Deposition (CVD).

The various operations are described as a plurality of separate operations in a sequential manner in a manner that is most helpful in understanding the subject matter of the present invention; however, the order of the description should not be considered as a metaphor such operations must be sequential dependent. In particular, such operations may not be implemented in the order presented. The operations described herein can be implemented in a different order than the described embodiments. Various additional operations may be implemented and/or the operations described above may be omitted in additional embodiments.

An InAlN/GaN based device (e.g., IC device 100) can have several advantages over other conventional devices (e.g., AlGaN/GaN structures). For example, the desired lattice matching can occur by providing an indium concentration of about 17% in the InAlN barrier layer. This can reduce strain, which can result in increased reliability, higher spontaneous polarization charge density, greater energy gap discontinuities in higher electron concentrations, and higher electron saturation rates. All of this result can contribute to higher current capacity than other devices. This can be especially useful in linear power and low noise amplifiers for mobile wireless, base stations, cable TV, mmW communications, etc.

An IC device (for example, IC device 100) can be incorporated into various devices and systems. A block diagram of an example system 800 is shown in FIG. As shown, system 800 includes a Power Amplifier (PA) module 802, which in some embodiments may be a radio frequency (RF) PA module. The system 800 can include a transceiver 804 that couples the power amplifier module 802 as shown. The power amplifier module 802 can include an IC device, such as the IC device 100 described herein.

Power amplifier module 802 can receive an RF input signal RFin from transceiver 804. The power amplifier module 802 can amplify the RF input signal RFin to provide an RF output signal RFout. Both the RF input signal RFin and the RF output signal RFout can be part of a transmission link, represented by Tx-RFin and Tx-RFout, respectively, in FIG.

The RF output signal RFout can be provided to an Antenna Switch Module (ASM) 806 that performs an Over-The-Air (OTA) transmission of the RF output signal RFout through an antenna structure 808. The ASM 806 can also receive RF signals through the antenna structure 808 and couple the received RF signals Rx along a receive link to the transceiver. 804. In some embodiments, for example, the transceiver 804 can additionally/alternatively incorporate the IC device 100 into a low noise amplifier.

In various embodiments, antenna structure 808 can include one or more directional and/or omnidirectional antennas, for example, including dipole antennas, monopole antennas, patch antennas, loop antennas, microstrips Antenna, or any other type of antenna suitable for OTA transmission/reception of RF signals.

In some embodiments, system 800 can include a power conditioner 810 that additionally/alternatively includes an IC device (eg, IC device 100). The power conditioner 810 can couple and provide power to various devices of the system 800, for example, but not limited to the PA module 802 and the transceiver 804. In these embodiments, the IC device 100 can provide an effective switching device for a power switching application, the power switching application including a power conditioning application, such as, for example, alternating current (AC)-direct current (AC) Direct Current, DC) converters, DC-DC converters, DC-AC converters, and the like.

In various embodiments, system 800 can be used in particular for power amplification at high RF power and frequency. For example, system 800 can be adapted to any one or more of terrestrial and satellite communications, radar systems, and may be suitable for use in a variety of industrial and medical applications. More specifically, in various embodiments, system 800 can be one of the following: a radar device, a satellite communication device, a mobile handset, a cellular telephone base station, a broadcast radio, or a television amplifier system.

The specific embodiments have been illustrated and described herein for illustrative purposes; however, various alternatives and/or equivalent embodiments or implementations may be substituted for the same purpose. For example, it does not depart from the scope of the present disclosure. Ben Shen The request is intended to cover any variations or variations of the embodiments discussed herein. Therefore, it is obvious that the embodiments described herein are not intended to be limited only by the scope of the claims and their equivalents.

100‧‧‧Integrated circuit (IC) device

104‧‧‧Substrate

108‧‧‧Stacking

112‧‧‧GaN buffer layer

116‧‧‧AlGaN layer

120‧‧‧AlN layer

124‧‧‧Indium Nitride (InAlN) barrier layer

126‧‧‧gate insulator

128‧‧‧ gate

132‧‧‧ source

136‧‧‧汲

Claims (21)

An apparatus comprising: a substrate; a gallium nitride (GaN) buffer layer formed on the substrate; an aluminum gallium nitride (AlGaN) layer formed on the GaN buffer layer, the aluminum of the AlGaN layer a concentration of less than about 15%; and an indium aluminum nitride (InAlN) barrier layer formed on the AlGaN layer, wherein the AlGaN layer is thinner than the InAlN barrier layer. The apparatus of claim 1, further comprising: a gate insulator formed on the InAlN barrier layer. The device of claim 2, wherein the device further comprises: a gate formed on the gate insulator and capacitively coupled to the InAlN barrier layer. The device of claim 1, wherein the AlGaN layer comprises indium gallium nitride (Al _x Ga _1-x N), wherein x represents the relative amount of aluminum and gallium. The apparatus of claim 4, wherein the AlGaN layer has a fixed aluminum content and x is about 0.04. The apparatus of claim 1, wherein the aluminum concentration of the AlGaN layer is gradually changed from about 0% at a portion of the AlGaN layer positioned beside the GaN buffer layer to the side of the InAlN barrier layer About 15% of a portion of the AlGaN layer. The apparatus of claim 1, wherein the AlGaN layer has a thickness of about 40 to 60 angstroms. The device of claim 1, wherein the thickness of the AlGaN layer is about 40 Or 50 angstroms. The apparatus of claim 1, further comprising: an aluminum nitride (AlN) layer formed on the AlGaN layer, wherein the InAlN barrier layer is formed on the AlN layer. The device of claim 1, wherein the device comprises a high electron mobility transistor (HEMT). A method comprising: forming a gallium nitride (GaN) buffer layer on a substrate; forming an aluminum gallium nitride (AlGaN) layer on the GaN buffer layer, the AlGaN layer having a thickness of between about 40 and 60 angstroms Forming an indium aluminum nitride (InAlN) barrier layer on the AlGaN layer; and forming a gate, a source, and a drain on the InAlN barrier layer. The method of claim 11, further comprising: forming a gate insulator on the InAlN barrier layer. The method of claim 12, wherein forming the gate comprises forming the gate on the gate insulator. The method of claim 11, wherein the AlGaN layer comprises indium gallium nitride (Al _x Ga _1-x N), wherein x is a value between 0 and 0.15 and represents the relative of aluminum and gallium Quantity. The method of claim 14, wherein the AlGaN layer has a fixed aluminum content and x is about 0.04. The method of claim 11, wherein the forming the AlGaN layer comprises: The AlGaN layer is formed, the aluminum concentration of which is gradually changed from about 0% at a portion of the AlGaN layer positioned beside the GaN buffer layer to about 15% at a portion of the AlGaN layer beside the InAlN barrier layer. The method of claim 11, wherein the forming the AlGaN layer comprises: forming the AlGaN layer to a thickness of about 40 to 60 angstroms. A system comprising: a transceiver for transmitting and receiving radio frequency (RF) signals; and a high electron mobility transistor (HEMT) incorporated in or coupled to the transceiver The HEMT includes: a substrate; a gallium nitride (GaN) buffer layer formed on the substrate; and an aluminum gallium nitride (AlGaN) layer formed on the GaN buffer layer, the aluminum concentration of the AlGaN layer being less than about 15%; and an indium aluminum nitride (InAlN) barrier layer formed on the AlGaN layer. A system according to claim 18, further comprising: an RF power amplifier comprising the HEMT. A system according to claim 18, further comprising: a low noise power amplifier comprising the HEMT. A system according to claim 18, further comprising: a power conditioner comprising the HEMT.