JP2010040828A - Nitride semiconductor device - Google Patents

Abstract

A nitride semiconductor device having a heterostructure having a low resistance channel (high mobility and high 2DEG concentration) and capable of being manufactured more easily than in the prior art.
A nitride semiconductor device having a laminated structure in which Al _y Ga _1-y N (AlGaN 2) and Al _x In _1-x N (AlInN 3) are deposited in this order on a substrate GaN 1. , X and y satisfy the inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are each 1 nm or more. The sum of the two is 50 nm or less, which constitutes a nitride semiconductor device.
[Selection] Figure 1

Description

  The present invention relates to a nitride semiconductor device, and more particularly to a nitride semiconductor device having a nitride semiconductor multilayer structure.

  Nitride semiconductors have wide gaps, high breakdown electric fields, high saturation electron velocities, and thermal stability, and are expected to be applied to electronic devices such as high-temperature, high-power, high-frequency transistors, etc. .

In particular, the AlGaN / GaN heterostructure induces a two-dimensional electron gas (2DEG) with a high sheet electron concentration (> 8 × 10 ¹² cm ⁻² ) and has a high electron mobility of 1000 cm ² / Vs or more. It is promising as a field effect transistor (FET) that operates at high frequency and high output.

In an AlGaN / GaN FET, the Al composition of the AlGaN barrier layer is usually 0.25. Currently, with this structure, a cut-off frequency (f _T ) of 100 GHz or higher, a maximum oscillation frequency (f _max ) of 150 GHz or higher, and an output of 10 W / mm are obtained. In the future, in order to improve these frequency characteristics and output characteristics, one means is to improve the 2DEG concentration of AlGaN / GaN and reduce the resistance.

  In AlGaN / GaN, in order to improve the 2DEG concentration, it is necessary to increase the Al composition of the AlGaN barrier layer. As the Al composition increases, the conduction band discontinuity (ΔEc) and the polarization charge increase, thereby improving the 2DEG concentration.

  However, when the Al composition is increased, the lattice irregularity with GaN increases, so the film thickness of AlGaN is limited. Further, stress due to strain is inherent in AlGaN. The critical film thickness of AlGaN is about 10 nm with an Al composition of 0.5 and about 3 nm with an Al composition of 1. There are concerns about a decrease in breakdown voltage and an increase in leakage current due to the thinning of the film thickness. In addition, there is a concern about deterioration of characteristics during the FET process due to an increase in strain stress. Thus, AlGaN / GaN FETs having a high Al composition AlGaN barrier layer are difficult to grow and produce.

AlInN / GaN heterostructure FET applications using AlInN (or AlGaInN with a high Al composition) barrier layer instead of the AlGaN barrier layer have been proposed (see Non-Patent Document 1 below). AlInN has an Al composition of about 0.83 and lattice matches with GaN. This lattice-matched Al _0.83 In _0.17 N is predicted to have a band gap of 4.8 eV, ΔEc with GaN of 1.1 eV, and a spontaneous polarization charge of 460 C / cm ² at the GaN interface. AlGaN used in the past has a band gap of 4.1 eV, ΔEc of 0.55 eV, polarization charge (sum of spontaneous and piezo) is much higher than 460 C / cm ^2, and obtains a high electron concentration without distortion. Is possible. For these reasons, research and development of AlInN (or AlGaInN with a high Al composition) / GaN heterostructure for FET applications are now being actively conducted.

However, in an AlInN (or AlGaInN with a high Al composition) / GaN heterostructure, the electron mobility is 100 cm ² / Vs, which is very low compared to AlGaN / GaN. This is because the alloy scattering of AlInN (or AlGaInN having a high Al composition) is very large and the crystal growth is difficult and it is difficult to obtain a steep interface.

For this reason, an AlInN (or AlGaInN with a high Al composition) / AlN / GaN heterostructure in which AlN is inserted at about 1 nm at the interface has been proposed. With this structure, the electron mobility is 1200 cm ² / Vs, and the 2DEG concentration is 2.6 × 10. Formation of 2DEG having a low resistance of ¹³ cm ⁻² has been reported (see Non-Patent Document 2 below). This is because the AlN intermediate layer suppresses the seepage of 2DEG into AlInN and the alloy scattering of AlInN.

Specifically, as a semiconductor structure for an FET using a nitride semiconductor material, Al _y Ga _1-y N (thickness 5 to 40 nm, 0.1 ≦ y ≦ 0.4) / GaN heterostructure, or Al _y Ga _{1 -YN} (thickness 5-40 nm, 0.1≤y≤0.4) / AlN / GaN heterostructure is conventionally used.

In addition, in order to obtain a channel having a lower strain and a lower resistance than when the above AlGaN-based barrier layer is used, Al _x In _1-x N (thickness 5 to 40 nm, 0.7 ≦ x ≦ 0.9) / AlN / GaN hetero The structure is conventionally used.
J. Kuzmik, IEEE Electron Device Lett. 22, 510 (2001) M. Gonschorek, J.-F. Carlin, E. Feltin, MA Py, and N. Grandjean, Appl. Phys. Lett. 89, 062106 (2006)

  As described above, in order to fabricate a GaN-based FET having a low resistance channel, utilization of a high Al composition AlGaN / GaN or AlInN (or AlGaInN with a high Al composition) / AlN / GaN heterostructure with little lattice mismatch It is valid. However, this structure has the following problems.

  Problem 1: It is difficult to grow an AlN intermediate layer, and the optimum growth conditions and film thickness region for obtaining a flat surface intermediate layer are very narrow. Also, since the growth temperature of AlInN (or AlGaInN with a high Al composition) is lower than that of the GaN system, the surface migration length of the growing atoms is very small, so the influence of the growth surface of AlN is very large compared to AlGaN. receive. Therefore, the area of growth conditions and structure capable of producing AlInN (or AlGaInN having a high Al composition) / AlN / GaN having a flat surface and high electron mobility is very narrow.

  Problem 2: Since AlN has a very large band gap of 6.2 eV, its electrical conductivity is very low. Therefore, since the AlN intermediate layer becomes a barrier, it is difficult to reduce the contact resistance that is essential for obtaining a high-performance FET.

  Problem 3: Compared to AlGaN, AlInN (or AlGaInN having a high Al composition) also has a large band gap, so it is difficult to obtain a low contact resistance.

  The present invention has been made in view of the above problems, and the problem to be solved by the present invention is to have a heterostructure having a low resistance channel (high mobility, high 2DEG concentration), and It is an object of the present invention to provide a nitride semiconductor device that can be manufactured more easily than the technology.

In the present invention, as described in claim 1,
A nitride semiconductor device having a laminated structure in which Al _y Ga _1-y N and Al _x In _1-x N are deposited in this order on a substrate, wherein x and y are inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1 is satisfied, the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are each 1 nm or more, and the sum of the two is 50 nm or less. The nitride semiconductor device characterized by the above is configured.

In the present invention, as described in claim 2,
A nitride semiconductor device having a laminated structure in which AlN, Al _y Ga _1-y N, and Al _x In _1-x N are deposited in this order on a substrate, wherein x and y are inequalities 0.75 ≦ x ≦ 0.9 And 0.1 ≦ y <1 is satisfied, the thickness of the AlN is not less than 0.1 nm and not more than 3 nm, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are respectively The nitride semiconductor device is characterized by being 1 nm or more and 20 nm or less.

In the present invention, as described in claim 3,
A nitride semiconductor device having a laminated structure in which Al _y Ga _1-y N and Al _x Ga _z In _1-xz N are deposited in this order on a substrate, wherein x, y, and z are inequality 0 <X <1, 0 <z <1, x + z <1 and 0.1 ≦ y <1 are satisfied, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x Ga _z In _1-xz N Constitutes a nitride semiconductor device characterized in that each has a thickness of 1 nm or more and 20 nm or less.

In the present invention, as described in claim 4,
A nitride semiconductor device having a laminated structure in which AlN, Al _y Ga _1-y N, and Al _x Ga _z In _1-xz N are deposited in this order on a substrate, wherein x, y, and z are Inequalities 0 <x <1, 0 <z <1, x + z <1 and 0.1 ≦ y <1 are satisfied, and the thickness of the AlN is 0.1 nm or more and 3 nm or less, and the Al _y Ga _1-y N The nitride semiconductor device is characterized in that the thickness and the thickness of the Al _x Ga _z In _1-xz N are each greater than or equal to 1 nm and less than or equal to 20 nm.

In the present invention, as described in claim 5,
5. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device has a source electrode, a drain electrode, and a gate electrode on the stacked structure, and operates as a field effect transistor. Constitute.

In the present invention, as described in claim 6,
5. The nitride semiconductor device according to claim 1, further comprising: a source electrode and a drain electrode in contact with the Al _y Ga _1-y N; a gate electrode on the stacked structure; The nitride semiconductor device is characterized by operating as described above.

  By using a structure in which AlGaN is inserted under AlInN (or AlGaInN with a high Al composition), it has a heterostructure having a low resistance channel (high mobility, high 2DEG concentration), and can be manufactured more easily than in the prior art. A nitride semiconductor device can be provided. The laminated structure in the nitride semiconductor device according to claims 2 and 4 is effective for solving the first problem, and the laminated structure in the nitride semiconductor device according to claims 1 and 3 is effective for solving the first and second problems. It is effective for resolution.

  In addition, the present invention has an effect that it is possible to fabricate an FET having higher transconductance, frequency characteristics, and output characteristics than a conventional FET.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a cross section of a laminated structure in an embodiment of the invention according to claim 1. As shown in the figure, a laminated structure in which AlGaN2 and AlInN3 are sequentially laminated on GaN1. More specifically, this laminated structure is formed by depositing Al _y Ga _1-y N and Al _x In _1-x N in this order on GaN as a substrate, where x and y are inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1 is satisfied, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are each 1 nm or more, and the sum of both is 50 nm or less. It is characterized by that.

  AlGaN 2 preferably has an Al composition (y) of 0.1 or more in which 2DEG is induced and an Al composition (y) of 0.4 or less with a lattice irregularity of 1% or less (in absolute value). The film thickness is preferably 1 nm or more and the critical film thickness or less covering the entire surface. The critical film thickness depends on the Al composition (y). For example, the Al composition (y) 0.3 is about 30 nm, and the Al composition (y) 0.4 is about 15 nm.

  AlInN3 preferably has an Al composition (x) in the range of 0.75 to 0.9 so that the lattice irregularity is within ± 0.1%. The film thickness is preferably 1 nm or more covering the entire surface.

  The effect of the present invention can be obtained at an arbitrary film thickness ratio between AlInN3 and AlGaN2, but the sum of the film thicknesses of AlInN3 and AlGaN2 is preferably 50 nm or less as the FET barrier layer.

  Note that when the a-axis lattice constant of AlInN is larger than that of the AlGaN layer, the AlInN / AlGaN2 layer can reduce the stress as compared with the AlGaN single layer. (y) AlGaN 2 of 0.4 or more can be used.

With this structure, it is possible to obtain a low resistance 2DEG characteristic with an electron mobility of 1000 cm ² / Vs or more and a 2DEG concentration of 2 × 10 ¹³ cm ⁻² or more.

  Also, the contact resistance of the ohmic junction is 1 Ωmm or more in the conventional AlInN / AlN / GaN structure, but can be reduced to 0.5 Ωmm or less in this structure.

FIG. 2 is a schematic diagram of a cross section of a laminated structure in an embodiment of the invention according to claim 2. As shown in the figure, a laminated structure is formed in which AlN4, AlGaN2, and AlInN3 are sequentially laminated on GaN1. More specifically, in this stacked structure, AlN, Al _y Ga _1-y N, and Al _x In _1-x N are deposited in this order on the substrate GaN, and the x and y are inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1 are satisfied, the thickness of the AlN is not less than 0.1 nm and not more than 3 nm, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are: Each is characterized by being 1 nm or more and 20 nm or less.

  The thickness of AlN4 is 0.1 nm or more and 3 nm or less, but the thickness of one atomic layer is more preferably 0.3 nm or more and the critical film thickness is 3 nm or less.

  The layer structure of AlGaN2 and AlInN3 is the same as in FIG. However, the thickness of each layer is preferably 1 nm or more so that each layer covers the entire surface, and the total thickness of both layers is preferably 50 nm or less as the thickness of the FET barrier layer. Is set to 20 nm or less.

  Note that when the a-axis lattice constant of AlInN is larger than that of the AlGaN layer, the AlInN / AlGaN2 layer can reduce the stress as compared with the AlGaN single layer. (y) AlGaN 2 of 0.4 or more can be used.

In the stacked structure shown in FIG. 2, it is possible to obtain a low resistance 2DEG characteristic with an electron mobility of 1300 cm ² / Vs or more and a 2DEG concentration of 2 × 10 ¹³ cm ⁻² or more. The measurement results of the electron mobility and 2DEG concentration in this stacked structure are shown in FIGS. 3 and 4 in comparison with the measurement results of the electron mobility and 2DEG concentration in the conventional stacked structure, respectively. In both figures, the horizontal axis represents the In composition of InAlN3, the laminated structure shown in FIG. 2 is represented by InAlN / AlGaN / AlN / GaN, and the conventional laminated structure is represented by InAlN / AlN / GaN. FIG. 3 shows that the electron mobility (black circle) in the multilayer structure of the nitride semiconductor device according to the present invention is significantly higher than the electron mobility (white circle) in the conventional multilayer structure. The usefulness of physical semiconductor devices has been clarified.

FIG. 5 is a schematic diagram of a cross section of a laminated structure in an embodiment of the invention according to claim 3. As shown in the figure, a laminated structure in which AlGaN2 and AlGaInN5 are sequentially deposited on GaN1. More specifically, this stacked structure is formed by depositing Al _y Ga _1-y N and Al _x Ga _z In _1-xz N in this order on GaN as a substrate, where x, y, and z are inequalities. 0 <x <1, 0 <z <1, x + z <1 and 0.1 ≦ y <1, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x Ga _z In _1-xz N Each is characterized by being 1 nm or more and 20 nm or less.

  AlGaN 2 preferably has an Al composition (y) of 0.1 or more in which 2DEG is induced and an Al composition (y) of 0.4 or less at which the lattice irregularity is 1% or less (in absolute value). The film thickness is preferably 1 nm or more and the critical film thickness or less covering the entire surface.

  The composition of AlGaInN5 is preferably a region where the lattice mismatch with GaN is within ± 1% and the band gap is wider than that of GaN. This region is indicated by the hatched portion in FIG. Further, the effect of the present invention becomes more effective in the region where the band gap is larger than the Al composition (x) 0.4. This region is indicated by the cross hatched portion in FIG.

  Since each layer of AlGaN2 and AlGaInN5 covers the entire surface, the thickness of each layer is preferably 1 nm or more, and the sum of the thicknesses of both layers is preferably 50 nm or less as the thickness of the FET barrier layer. The film thickness is 20 nm or less.

With this stacked structure, it is possible to obtain low resistance 2DEG characteristics with an electron mobility of 1000 cm ² / Vs or more and a 2DEG concentration of 1.8 × 10 ¹³ cm ⁻² or more.

FIG. 7 is a schematic diagram of a cross section of a laminated structure in an embodiment of the invention according to claim 4. As shown in the figure, a multilayer structure is formed in which AlN4, AlGaN2, and AlGaInN5 are sequentially deposited on GaN1. More specifically, this stacked structure is obtained by depositing AlN, Al _y Ga _1-y N, and Al _x Ga _z In _1-xz N in this order on GaN as a substrate, and the x, y and z Satisfies the inequalities 0 <x <1, 0 <z <1, x + z <1 and 0.1 ≦ y <1, the thickness of the AlN is not less than 0.1 nm and not more than 3 nm, and the Al _y Ga _1-y N And the thickness of the Al _x Ga _z In _1-xz N are 1 nm or more and 20 nm or less, respectively.

  The thickness of AlN4 is 0.1 nm or more and 3 nm or less, but the thickness of one atomic layer is more preferably 0.3 nm or more and the critical film thickness is 3 nm or less.

  AlGaN 2 preferably has an Al composition (y) of 0.1 or more in which 2DEG is induced and an Al composition (y) of 0.4 or less at which the lattice irregularity is 1% or less (in absolute value). The film thickness is preferably 1 nm or more and the critical film thickness or less covering the entire surface.

  The composition of AlGaInN5 is preferably a region having a lattice mismatch with GaN within ± 1% and a wider band gap than GaN (shaded portion in FIG. 6). Further, the effect of the present invention is more effective in a region where the band gap is larger than the Al composition (x) 0.4 (cross hatched portion in FIG. 6).

  Since each layer of AlGaN2 and AlGaInN5 covers the entire surface, the thickness of each layer is preferably 1 nm or more, and the sum of the thicknesses of both layers is preferably 50 nm or less as the thickness of the FET barrier layer. The film thickness is 20 nm or less.

  FIG. 8 is a schematic diagram of a cross-section of a nitride semiconductor device according to an embodiment of the invention according to claim 5, and a source electrode 6, a drain electrode 7, 1 shows a nitride semiconductor device having a gate electrode 8 and operating as a field effect transistor. In the case where the laminated structure shown in FIGS. 1 and 5 is used, AlN4 is not formed. As the source electrode 6 and the drain electrode 7, for example, Ti / Al / Ni / Au heat-treated, and as the gate electrode 8, for example, Ni / Au may be used.

  FIG. 9 is a schematic diagram of a cross-section of a nitride semiconductor device according to an embodiment of the invention according to claim 6, in which the source electrode 6 and the drain electrode 7 having the stacked structure shown in FIGS. Nitriding that has a source electrode 6 and a drain electrode 7 in contact with AlGaN 2 at a portion where AlInN 3 (or AlGaInN 5) in the region to be etched is etched, a gate electrode 8 on the laminated structure between both electrodes, and operates as a field effect transistor 1 shows a physical semiconductor device. In the case where the laminated structure shown in FIGS. 1 and 5 is used, AlN4 is not formed. As the source electrode 6 and the drain electrode 7, for example, Ti / Al / Ni / Au is heat-treated, and as the gate electrode 8, for example, Ni / Au may be used.

As an embodiment of the present invention, in the stacked structure shown in FIG. 2, AlInN3 is Al _0.81 In _0.19 N with a thickness of 12 nm, and AlGaN2 is Al _0.38 Ga _{0.62 with a} thickness of 5 nm. A field effect transistor is manufactured using a stacked structure of N and AlN4 having a thickness of 1 nm. As a conventional example, a 1 nm thick AlN and a 16.5 nm thick Al _0.82 In _{0 are formed} on a GaN substrate. _A field effect transistor was fabricated using a laminated structure in which _.18 N was deposited in this order, and the characteristics of both were compared. FIG. 10 shows the transistor characteristics, that is, the source-drain current (I _ds ) _-voltage (V _ds ) characteristics using the gate-source voltage V _gs as a parameter. FIG. 11 shows the relationship between the current I _gd and the gate-drain voltage V _gd . In both figures, the characteristic of the embodiment of the present invention is represented by a solid line, and the characteristic of the conventional example is represented by a broken line. In FIG. 11, the gate leakage current (solid line) in the embodiment of the present invention is one digit or more smaller than the gate leakage current (broken line) in the conventional example, and also in this respect, the nitride semiconductor device according to the present invention is useful. Sex is shown.

  In the above description, GaN is used as the substrate. However, in addition to GaN, sapphire, SiC, and Si can be used, and in this case, the same effect as described above can be obtained.

FIG. 3 is a schematic diagram of a cross section of a laminated structure in the nitride semiconductor device according to claim 1. FIG. 3 is a schematic diagram of a cross section of a laminated structure in the nitride semiconductor device according to claim 2. It is a figure which compares the measurement result of the electron mobility in the laminated structure of the nitride semiconductor device of Claim 2 with the measurement result of the electron mobility in the conventional laminated structure. It is a figure which compares the measurement result of 2DEG density | concentration in the laminated structure of the nitride semiconductor device of Claim 2 with the measurement result of 2DEG density | concentration in the conventional laminated structure. FIG. 4 is a schematic view of a cross section of a laminated structure in the nitride semiconductor device according to claim 3. In the composition diagram of AlGaInN, it is a diagram showing a composition region in which the lattice mismatch with GaN is within ± 1% and the band gap is wider than GaN. 5 is a schematic diagram of a cross section of a laminated structure in the nitride semiconductor device according to claim 4. FIG. 6 is a schematic cross-sectional view of a nitride semiconductor device according to claim 5. FIG. 7 is a schematic cross-sectional view of a nitride semiconductor device according to claim 6. FIG. It is a figure which compares the transistor characteristic of the nitride semiconductor device which concerns on this invention with the transistor characteristic of the nitride semiconductor device of a prior art example. It is a figure which compares the gate leakage current characteristic of the nitride semiconductor device which concerns on this invention with the gate leakage current characteristic of the nitride semiconductor device of a prior art example.

Explanation of symbols

  1: GaN, 2: AlGaN, 3: AlInN, 4: AlN, 5: AlGaInN, 6: source electrode, 7: drain electrode, 8: gate electrode.

Claims (6)

A nitride semiconductor device having a laminated structure in which Al _y Ga _1-y N and Al _x In _1-x N are deposited in this order on a substrate,
X and y satisfy the inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1;
The thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are each 1 nm or more, and the sum of both is 50 nm or less. . A nitride semiconductor device having a stacked structure in which AlN, Al _y Ga _1-y N, and Al _x In _1-x N are deposited in this order on a substrate,
X and y satisfy the inequalities 0.75 ≦ x ≦ 0.9 and 0.1 ≦ y <1;
The thickness of the AlN is 0.1 nm or more and 3 nm or less, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x In _1-x N are 1 nm or more and 20 nm or less, respectively. A nitride semiconductor device. A nitride semiconductor device having a laminated structure in which Al _y Ga _1-y N and Al _x Ga _z In _1-xz N are deposited in this order on a substrate,
Said x, y and z are inequalities 0 <x <1, 0 <z <1, x + z <1
And 0.1 ≦ y <1
The nitride semiconductor device, wherein the thickness of the Al _y Ga _1-y N and the thickness of the Al _x Ga _z In _1-xz N are 1 nm or more and 20 nm or less, respectively. A nitride semiconductor device having a laminated structure in which AlN, Al _y Ga _1-y N, and Al _x Ga _z In _1-xz N are deposited in this order on a substrate,
Said x, y and z are inequalities 0 <x <1, 0 <z <1, x + z <1
And 0.1 ≦ y <1
The thickness of the AlN is 0.1 nm or more and 3 nm or less, and the thickness of the Al _y Ga _1-y N and the thickness of the Al _x Ga _z In _1-xz N are 1 nm or more and 20 nm, respectively. A nitride semiconductor device comprising: The nitride semiconductor device according to any one of claims 1 to 4,
A nitride semiconductor device having a source electrode, a drain electrode, and a gate electrode on the stacked structure and operating as a field effect transistor. The nitride semiconductor device according to any one of claims 1 to 4,
A nitride semiconductor device having a source electrode and a drain electrode in contact with the Al _y Ga _1-y N, a gate electrode on the stacked structure, and operating as a field effect transistor.

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