TW201417278A - InGaN channel N-polar GaN HEMT profile - Google Patents

Abstract

Disclosed is an N-polar high electron mobility transistor (HEMT) device having an InGaN channel for the formation of a two dimensional electron gas (2DEG) layer. This new channel layer provides improved electron transport. It has higher electron mobility and high field velocity which enables higher frequency radio frequency (RF) performance. The device may also include a GaN cap layer deposited on top of the InGaN channel layer which provides a double confinement for the 2DEG.

Description

N-polar GaN HEMT (High Electron Mobility Transistor) profile with InGaN channels Statement of government rights

According to Government Contract No. HR0011-09-C-0132 (DARPA), the Government of the United States of America has the rights of the present invention.

The present invention relates generally to high electron mobility transistor (HEMT), and more particularly to N-polar GaN-based HEMT.

HEMT has long been manufactured using gallium arsenide (GaAs), but recently semiconductor gallium nitride (GaN) has attracted attention in the manufacture of HEMT due to its high power and high frequency performance. One of the characteristics of nitride-based semiconductors (such as GaN) is that they exhibit strong polarization due to the lack of reverse symmetry in the lattice structure and the very high electrical and electrical properties of the nitrogen atoms. As such, GaN exhibits two different faces (or polarities) depending on the orientation of the lattice structure, which are referred to as Ga-polar and N-polar.

A HEMT is a field effect transistor (FET) type in which a channel is formed not by a doped channel but by a junction between two materials having different band gaps. The junction is referred to as a heterojunction, and the channel formed by the heterojunction is referred to as a two-dimensional electron gas (2DEG). A typical N-polar GaN HEMT structure uses the GaN channel layer shown in Figure 1A. The energy band diagram of the N-polar GaN HEMT is shown in Figure 1B.

The improved performance of GaN HEMTs can be achieved by using InGaN channels. Using InGaN channels, device performance can be improved due to the inherent advantages of InGaN alloys. This includes lower electronically effective masses that provide higher electron velocities, and larger energy band offsets to barriers that provide improved carrier limitations. However, in the case of a Ga-polar HEMT, an InGaN channel of which quality is generally damaged is grown. The low growth temperature of InGaN not only reduces material quality, but also unwanted growth pauses that negatively impact device quality. This state is exacerbated by the subsequent higher temperature AlGaN barrier growth, which overheats the InGaN channel layer to increase phase separation, atomic diffusion, and further degrade the quality of the InGaN layer.

Therefore, there is a need for a GaN HEMT having an improved layer profile of InGaN channels and an epitaxial growth technique that fully exploits the inherent advantages of the InGaN alloy.

One embodiment of the invention includes an N-polar HEMT device having an InGaN channel. This novel channel layer provides improved electron transport. It has a high electron mobility and a high field speed, which makes it possible to obtain more High frequency radio frequency (RF) performance.

In one embodiment, the invention includes an N-polar Group III nitride semiconductor device having a substrate deposited on a barrier layer of the substrate on a side of the barrier layer having an N-polar orientation, and deposited on An N-polar channel layer of indium gallium nitride (InGaN) on the barrier layer. The device also has a buffer layer between the substrate and the barrier layer.

In another embodiment, the invention includes an N-polar Group III nitride semiconductor device having a substrate deposited on a barrier layer of the substrate on a side of the barrier layer having an N-polar orientation, and deposition An N-polar channel layer of indium gallium nitride (InGaN) on the barrier layer, and a cap layer deposited on the channel layer.

In another embodiment, the invention includes an N-polar HEMT made using any of the above specific examples.

In yet another embodiment, the invention includes fabricating a barrier layer having a substrate on which a barrier layer has an N-polar orientation, and an indium gallium nitride deposited on the barrier layer A method of an N-polar channel layer of (InGaN) and a semiconductor device of a cap layer randomly deposited on the channel layer.

200/300/400‧‧‧N-polar HEMT device

210/310/410/510‧‧‧Carbide (SiC) substrate

220/320/420/520‧‧‧GaN buffer layer

230‧‧‧AlGaN back barrier

240/340/440/540‧‧‧AlN barrier intermediate layer

250/350/450/550‧‧‧InGaN channel layer

260/360/460/560‧‧‧Two-dimensional electronic gas (2DEG)

330/430‧‧‧AlGaN barrier layer

370/470/570‧‧‧GaN cap layer

480‧‧‧GaN spacer

500‧‧‧ device

530‧‧‧Al _0.45 GaN barrier layer

580‧‧‧ source terminal

590‧‧‧汲 Extreme

585‧‧ ‧ gate terminal

Features of the examples of the present invention are more apparent from the description, claims, and drawings in which: FIG. 1A is a cross-sectional view of a prior art semiconductor profile of an N-polar HEMT having a GaN channel.

Figure 1B is an energy band diagram of the structure of Figure 1A.

2A is a cross-sectional view of a semiconductor profile of an N-polar HEMT having an InGaN channel.

2B is an energy band diagram of the structure of FIG. 2A.

3A is a cross-sectional view of a semiconductor profile of an N-polar HEMT having an InGaN channel with a GaN cap layer.

Figure 3B is an energy band diagram of the structure of Figure 3A.

4A is a specific embodiment of a semiconductor profile of an N-polar HEMT having an InGaN channel.

4B is a photoluminescence diagram of the InGaN channel of FIG. 4A.

Figure 5 is a cross-sectional view of a HEMT semiconductor device having gate, source and drain terminals.

InGaN channels in N-polar GaN HEMTs have higher mobility, lower effective electron mass, and higher electron velocity. In particular, the smaller electron-phonon coupling of InGaN reduces the thermal phonon scattering effect, thus further improving the electron velocity compared to the GaN channel profile. As explained above, the InGaN channel in the Ga-polar HEMT has a damaged material quality.

In a first embodiment of the invention, an N-polar HEMT device 200 having an InGaN channel is shown in Figure 2A. Device 200 includes a tantalum carbide (SiC) substrate 210. GaN, germanium, AlN, sapphire or other suitable materials may be used as an alternative to the substrate 210. If using sapphire or As is known to those skilled in the art, the device also needs to include a different nucleation layer in place of AlN to provide an N-polar surface.

The device also includes a GaN buffer layer 220. Alternatively, the buffer layer 220 made of AlGaN may be used or completely eliminated. Device 200 also includes an AlGaN back barrier 230. The buffer layer 220 or the AlGaN back barrier 230 may or may not be doped with an n-type dopant such as germanium to eliminate hole channels in the buffer layer. The AlN barrier intermediate layer 240 is optionally present depending on the application of the device. A channel layer made of InGaN is shown at 250, which forms a two-dimensional electron gas (2DEG) 260.

The epitaxial profile of the present invention is designed such that all high temperature processing (including AlGaN and AlN barrier epitaxial growth) occurs before the InGaN channel. Thus, the high quality of the temperature-sensitive InGaN layer enables a higher quality InGaN channel layer and a higher mobility InGaN channel HEMT.

In the 2DEG region, between the InGaN channel and the AlGaN or AlN barrier, a quaternary InAlGaN layer is usually formed by interdiffusion of atoms. This layer increases the scattering of the alloy and reduces electron mobility and device performance. In the present invention, an aluminum removal growth procedure is added to prevent interdiffusion of atoms and maintain a well-defined InGaN/AlGaN or InGaN/AlN interface. This improved growth procedure promotes improved electrical channel mobility.

The parameters of the InGaN channel profile of device 200 are highly selectable, depending on device parameters and application. In a preferred embodiment, the ratio of indium in the InGaN channel 250 ranges from 1% to 30%, and the thickness of the InGaN channel can range from 1 to 50 nm. The proportion of aluminum in the AlGaN back barrier 230 ranges from 20% to 100%, and the thickness of the AlGaN back barrier can be between 2 nm and 50 nm. The electron mobility of the InGaN channel HEMT 200 can be higher than 1600 cm ² /Vs.

In the case of N-polar HEMTs, InGaN channels can be grown at temperatures well above the GaN channels of the same layer, which not only improves material quality, but also avoids growth pauses near the growth layer of the channel. Due to the inverted structure of the N-polar HEMT, the high temperature AlGaN back barrier is grown before the InGaN channel, thus reducing the overall thermal budget of the InGaN channel and resulting in the formation of high quality InGaN channels.

2B shows an energy band diagram through the structure of FIG. 2A, which plots the Fermi level E _F , the conduction band energy E _{C ,} and the valence band energy E _V through each layer of the device. The 2DEG is formed at the interface between InGaN and AlN due to polarization and large band offset, and the density of the 2DEG is determined by the aluminum composition in the AlGaN back barrier and the thickness of the AlGaN, AlN, and InGaN layers.

A second specific example is shown in Figure 3A. In this particular example, similar to the apparatus 200 of FIG. 2A, the N-polar HEMT device 300 includes a substrate layer 310, a GaN buffer layer 320, an AlGaN barrier layer 330, an AlN barrier intermediate layer 340, a channel layer 350, and a 2DEG 360. Device 300 also includes a GaN cap layer 370. This specific example provides the dual limitations of 2DEG.

Like device 200 of FIG. 2A, device 300 includes a GaN buffer layer 320. Alternatively, a buffer layer 320 made of AlGaN may be used or completely eliminated. Device 300 also includes an AlGaN back barrier layer 330. The AlN barrier layer 340 is optionally present depending on the application of the device. Made of InGaN The channel layer is shown at 350, which forms a two-dimensional electron gas (2DEG) 360.

3B shows an energy band diagram through the structure of FIG. 3A, which plots the Fermi level E _F , the conduction band energy E _{C ,} and the valence band energy E _V through each layer of the device 300. 2DEG 360 is formed at the interface between InGaN and AlN. Compared to the GaN channel profile, the InGaN profile has a larger energy band offset, thus providing better electronic limitations, which results in superior device quality. The density of 2DEG 360 is determined by the aluminum composition of the AlGaN back barrier 330, the indium composition of InGaN, and the thickness of the AlGaN, AlN, and InGaN channels.

Another specific example of an N-polar HEMT device is shown in Figure 4A. In this specific example, similar to the device 300 of FIG. 3A, the N-polar HEMT device 400 includes a substrate 410, a GaN buffer layer 420, an AlGaN barrier layer 430, an AlN barrier intermediate layer 440, an InGaN channel layer 450, 2DEG 460, GaN. Cover layer 470. Device 400 also includes a GaN spacer layer 480. This particular example provides a dual limitation of 2DEG 460 at both interfaces containing GaN.

Similar to devices 200 and 300, device 400 also includes a GaN buffer layer 420. Alternatively, a buffer layer 420 made of AlGaN may be used or completely eliminated. Device 400 also includes an AlGaN barrier layer 430. The AlN barrier layer 440 is optionally present depending on the application of the device. A channel layer made of InGaN is shown at 450, which forms a two-dimensional electron gas (2DEG) 460.

The photoluminescence spectrum of the N-polar InGaN channel layer 450 is shown in Fig. 4B. As can be seen from the figure, it has a composition of up to 20% indium. InGaN grows at a channel temperature that is not possible for Ga-polarity, indicating the inherent advantages of epitaxially grown N-polar InGaN profiles.

A clear specific example of the N-polar HEMT is shown in FIG. In this specific example, the device 500 includes a SiC substrate 510, a buffer layer 520 made of 5 nm thick GaN doped with GaN, an Al _0.45 GaN barrier layer 530, an AlN barrier intermediate layer 540, an InGaN channel layer 550, and 2DEG layer 560 and GaN cap layer 570. As explained in Figures 2 through 4 above, a variety of different alternatives can be used for a particular layer. Device 500 is formed using source terminal 580, gate terminal 590, and gate terminal 585 located on the surface of GaN cap layer 570.

The apparatus of Figures 2A, 3A, 4A and 5 can be produced using a wide variety of methods. These methods include molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), and atomic layer deposition (ALD), or any deposition method suitable for nitride-based semiconductor devices.

There are numerous alternative implementations of the invention. Specific design options can be selected to control electron density and device parameters. For example, a number of different channels of the In _x Ga _1-x N form (where x is from 0 to 100%) can be used. The thickness of the InGaN channel can also vary from 1 nm to 50 nm. The device also includes a GaN heterojunction coating on top, bottom or both sides of the InGaN channel layer. Other variations include a random InGaAlN back barrier layer and a random AlGaN buffer layer.

The steps or operations described herein are merely examples. There are many variations in the steps and operations without departing from the spirit of the invention. For example, the steps can be performed in a different order, or can be added, deleted, or modified. step.

Although the example implementation of the present invention has been described and illustrated in detail, it will be apparent to those skilled in the art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention. Additions, substitutions are considered to be within the scope of the invention as defined in the following claims.

200‧‧‧N-polar HEMT device

210‧‧‧Carbide (SiC) substrate

220‧‧‧GaN buffer layer

230‧‧‧AlGaN back barrier

240‧‧‧AlN barrier intermediate layer

250‧‧‧InGaN channel layer

260‧‧‧Two-dimensional electronic gas (2DEG)

Claims (22)

An N-polar oriented Group III nitride semiconductor device comprising: a substrate; a barrier layer deposited on the substrate; and an N-polar channel of indium gallium nitride (InGaN) deposited on the barrier layer Floor. The device of claim 1, wherein the channel layer comprises between about 1% and 30% indium composition and a thickness between about 1 nm and 50 nm. The device of claim 1, wherein the barrier layer comprises AlGaN. The device of claim 3, wherein the AlGaN barrier layer comprises between about 20% and 100% aluminum composition and a thickness between about 2 nm and 50 nm. The device of claim 1, further comprising a buffer layer of gallium nitride (GaN) or aluminum gallium nitride (AlGaN). The device of claim 1, further comprising a barrier intermediate layer of aluminum nitride (AlN) interposed between the barrier layer and the channel layer. The device of claim 1, further comprising a cap layer of GaN deposited on the InGaN channel layer. The device of claim 7, wherein the cap layer is 3 nm thick. An N-polar high electron mobility transistor (HEMT) package And comprising: a substrate; a barrier layer deposited on the substrate; an N-polar channel layer of indium gallium nitride (InGaN) deposited on the barrier layer; and an N-polar cap layer deposited on the channel layer; a source deposited on top of the cap layer; a drain deposited on top of the cap layer; a gate deposited above the channel layer and interposed between the source and the drain. The device of claim 9, wherein the InGaN channel layer comprises between about 1% and 30% indium composition and a thickness between about 1 nm and 50 nm. The device of claim 9, wherein the barrier layer comprises AlGaN. The device of claim 11, wherein the AlGaN barrier layer comprises between about 20% and 100% aluminum composition and a thickness between about 2 nm and 50 nm. The device of claim 9, which additionally comprises a buffer layer of gallium nitride (GaN) or aluminum gallium nitride (AlGaN). The device of claim 13, wherein the substrate is additionally composed of tantalum carbide (SiC), and the buffer layer is deposited on the C-polar side of the substrate. The device of claim 13, wherein the substrate is blue A gemstone is formed, and the device additionally includes a nucleation layer between the substrate and the buffer layer. The device of claim 9, further comprising a barrier intermediate layer of aluminum nitride (AlN) interposed between the barrier layer and the channel layer. A method of fabricating an N-polar Group III nitride device, comprising the steps of: forming a substrate; forming a Group III nitride barrier layer on a side of the substrate layer, wherein the barrier layer is directed to an energy band thereof Selecting a gap property; and forming an N-polar InGaN channel layer on the barrier layer, wherein the channel layer has an energy band gap smaller than the barrier layer. The method of claim 17, wherein the InGaN channel layer comprises between about 1% and 30% indium composition and a thickness between about 1 nm and 50 nm. The method of claim 17, wherein the barrier layer is composed of AlGaN having an aluminum composition of between about 20% and 100%, and has a thickness of between about 2 nm and 50 nm. The method of claim 17, further comprising the step of forming a buffer layer between the substrate and the barrier layer. The method of claim 17, further comprising the step of forming a barrier intermediate layer of aluminum nitride (AlN) between the barrier layer and the channel layer. For example, the method of claim 17 of the patent scope additionally includes the following Step: forming a cap layer on the channel layer; forming a source and a drain of the HEMT on the cap layer; and forming a gate above the channel layer and between the source and the drain.