JP2012028706A - Semiconductor device - Google Patents

Abstract

A semiconductor device capable of suppressing current collapse is provided.
The present invention relates to a channel layer made of a nitride semiconductor, an electron supply layer provided on the channel layer and having a band gap larger than that of the channel layer and made of a nitride semiconductor, and an electron supply layer. And a cap layer 18 made of a nitride semiconductor doped with Fe. According to the present invention, current collapse can be suppressed.
[Selection] Figure 2

Description

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

  A semiconductor device using a nitride semiconductor, for example, a semiconductor device such as a field effect transistor (FET) may be used as a high-frequency output amplification element. Patent Document 1 discloses an invention in which a SiN (silicon nitride) film with a controlled hydrogen content is provided on a nitride semiconductor layer.

JP-A-2005-286135

  In the conventional technique, current collapse may occur depending on the state of the surface of the nitride semiconductor layer, and the output of the semiconductor device may decrease. In view of the above problems, an object of the present invention is to provide a semiconductor device capable of suppressing a decrease in output.

  The present invention provides a channel layer made of a nitride semiconductor and the channel layer, and has a band gap larger than the channel layer, and is provided on the electron supply layer made of a nitride semiconductor and the electron supply layer. And a cap layer made of a nitride semiconductor doped with Fe. According to the present invention, current collapse can be suppressed.

In the above configuration, the cap layer may be configured to contain 1 × ^{10 10 cm -3} the Fe in the following concentrations. According to this configuration, the cap layer can be semi-insulated to suppress current collapse.

  The said structure WHEREIN: The density | concentration of the said Fe which the said cap layer contains can be set as the structure which becomes large toward the area | region far from the said electron supply layer from the area | region close to the said electron supply layer. According to this configuration, diffusion of Fe into the channel layer and the electron supply layer can be suppressed.

  In the above configuration, the electron supply layer is made of a nitride semiconductor containing Al, and the composition ratio of Al in the electron supply layer increases from a region close to the channel layer toward a region close to the cap layer. can do. According to this configuration, diffusion of Fe into the channel layer and the electron supply layer can be suppressed.

  The said structure WHEREIN: It can be set as the structure provided with the barrier layer for suppressing the spreading | diffusion of the Fe doped by the said cap layer between the said electron supply layer and the said cap layer. According to this configuration, diffusion of Fe into the channel layer and the electron supply layer can be suppressed.

  In the above configuration, a barrier layer for suppressing diffusion of Fe doped in the cap layer may be provided between the electron supply layer and the channel layer. According to this configuration, diffusion of Fe into the channel layer and the electron supply layer can be suppressed. Moreover, impurity scattering of the two-dimensional electron gas in the channel layer can be suppressed.

  The said structure WHEREIN: The said barrier layer can be set as the structure which consists of GaN or AlN. According to this configuration, diffusion of Fe into the channel layer and the electron supply layer can be suppressed.

  In the above configuration, the channel layer may be made of GaN, the electron supply layer may be made of AlGaN or InAlN, and the cap layer may be made of GaN, AlN, AlGaN, or InAlN.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor device which can suppress an output fall can be provided.

FIG. 1 is a schematic view illustrating a semiconductor device in which current collapse has occurred. FIG. 2 is a cross-sectional view illustrating a semiconductor device according to the first embodiment. FIG. 3 is a cross-sectional view illustrating a semiconductor device according to the second embodiment. FIG. 4 is a cross-sectional view illustrating a semiconductor device according to the third embodiment. FIG. 5 is a cross-sectional view illustrating a semiconductor device according to the fifth embodiment.

  First, current collapse will be described. FIG. 1 is a schematic view illustrating a semiconductor device. In FIG. 1, a part of hatching is omitted.

  As shown in FIG. 1, the semiconductor device includes a substrate 10, a nucleation layer 12, a channel layer 14, an electron supply layer 16, a cap layer 18, a source electrode 20, a drain electrode 22, and a gate electrode 24. When the source electrode 20 is grounded and a positive potential is applied to the drain electrode 22 and a negative potential is applied to the gate electrode, the two-dimensional electron gas generated in the channel layer 14 moves between the source and drain. At this time, electrons of the two-dimensional electron gas become high energy and are captured by the surface level of the cap layer 18. The drain current is reduced by trapping electrons. This phenomenon is called current collapse.

  Next, embodiments of the present invention will be described with reference to the drawings.

  Example 1 is an example in which the cap layer is doped with Fe. FIG. 2 is a cross-sectional view illustrating a semiconductor device according to the first embodiment.

As shown in FIG. 2, the semiconductor device according to the first embodiment includes a substrate 10, a nucleation layer 12, a channel layer 14, an electron supply layer 16, a cap layer 18, a source electrode 20, a drain electrode 22, and a gate electrode 24. Prepare. The substrate 10 is made of, for example, SiC (silicon carbide), Si, sapphire, or the like. The substrate 10 may be a semiconductor substrate made of GaN, ZnO (zinc oxide), or the like. The nucleation layer 12 is made of, for example, AlN (aluminum nitride) having a thickness of 300 nm. The channel layer 14 is made of, for example, i-GaN having a thickness of 1000 nm. The electron supply layer 16 is made of, for example, a thickness of _{20nm i-Al x Ga 1-} x N ( aluminum gallium nitride, x = 0.15 to 0.35). The band gap of the electron supply layer 16 is larger than the band gap of the channel layer 14. The cap layer 18 is made of, for example, n-GaN having a thickness of 5 nm. The cap layer 18 is doped with Fe having a concentration of 1 × 10 ¹⁰ cm ⁻³ or less, for example.

  The source electrode 20 and the drain electrode 22 are formed by stacking metals such as Ti / Al / Au and Ta / Al / Au from below, for example. The gate electrode 24 is formed by, for example, laminating a metal such as Ni / Al from the bottom.

Each of the nucleation layer 12, the channel layer 14, the electron supply layer 16, and the cap layer 18 is epitaxially grown by, for example, MOCVD (Metal Organic Chemical Vapor Deposition). The growth conditions are as follows, for example.
Temperature: 800-1300 ° C
Pressure: 0.1 to 1 atmosphere (0.01 to 0.1 HPa)
Carrier gas: H ₂ or N ₂ , or H ₂ and N ₂
Al material: TMA (Tri Methyl Aluminum)
Material of N: NH ₃ (ammonia)
Material of Ga: TMG (Tri Methyl Gallium)
Fe dopant: C ₁₀ H ₁₀ Fe (ferrocene)
n-type dopant: SiH ₄ (silane)
The substrate 10 is put into a furnace of an MOCVD apparatus, and materials are supplied into the furnace in order from a layer close to the substrate 10 to stack the layers. In the step of growing the cap layer 18, together with FeTMG and NH ₃ , C ₁₀ H ₁₀ Fe and SiH ₄ are also supplied into the furnace to perform Fe doping.

  Fe doped in the cap layer 18 is activated to become Fe ions. Fe ions form deep energy levels and function as trap centers. Thereby, the cap layer 18 is semi-insulated. Further, the cap layer 18 approaches a p-type due to Fe doping. Therefore, the band of the surface level of the cap layer 18 is lifted. According to the first embodiment, the influence of the surface level of the cap layer 18 is reduced and the current collapse is suppressed by the semi-insulation and the band lifting.

The amount of Fe doped is such that the cap layer 18 is sufficiently semi-insulated. In order to make the cap layer 18 semi-insulating, the concentration of Fe contained in the cap layer 18 is preferably 1 × 10 ¹⁰ cm ⁻³ or less. More preferably, the doping amount may be 1 × 10 ⁸ cm ⁻³ or less, and further 1 × 10 ⁷ cm ⁻³ or less.

  Fe easily diffuses into the nitride semiconductor. If Fe diffuses into the channel layer 14 or the electron supply layer 16, the characteristics of the semiconductor device may change. In order to suppress the diffusion of Fe, the Fe concentration of the cap layer 18 is preferably increased from a region close to the electron supply layer 16 toward a region far from the electron supply layer 16. Thereby, current collapse and diffusion of Fe are suppressed. Further, the larger the band gap of the nitride semiconductor, the more the diffusion of Fe is suppressed. For this reason, the band gap of the cap layer 18 is preferably larger than the band gap of the electron supply layer 16.

  Although the nucleation layer 12 is made of AlN, it may be made of AlGaN, for example, or a combination of AlN and AlGaN. The electron supply layer 16 is made of n-AlGaN, but may be made of i-AlGaN, InAlN (indium aluminum nitride), or the like. The cap layer 18 is made of n-GaN, but may be made of i-GaN, AlN, AlGaN, InAlN, InGaN (indium gallium nitride), or the like. Further, the nucleation layer 12, the channel layer 14, the electron supply layer 16, and the cap layer 18 may be formed of a nitride semiconductor other than those already described. A nitride semiconductor is a semiconductor containing nitrogen, such as InN (indium nitride), InGaN, InAlN, and AlInGaN (aluminum indium gallium nitride).

  Example 2 is an example in which the configuration of the electron supply layer 16 is changed. As described above, Fe is likely to diffuse into the nitride semiconductor. In Example 2, the electron supply layer 16 suppresses the diffusion of Fe. FIG. 3 is a cross-sectional view illustrating a semiconductor device according to the second embodiment. The description of the same configuration as that described above is omitted.

As shown in FIG. 3, the electron supply layer 16 is made of, for example, i-Al _x Ga _1-x N having a thickness of 20 nm, and the composition of Al from the side close to the channel layer 14 toward the side close to the cap layer 18. The ratio increases. For example, in the region 16a on the side close to the channel layer 14 of the electron supply layer 16, x = 0.15 to 0.35. On the other hand, in the region 16b on the side close to the cap layer 18 of the electron supply layer 16, x = 0.5. In FIG. 3, the region 16a and the region 16b are separated by a broken line, but this is schematically illustrated. Actually, the Fe concentration in the electron supply layer 16 continuously changes.

  According to the second embodiment, the current collapse is suppressed as in the first embodiment. AlN has a larger band gap than GaN. For this reason, AlN has a greater effect of suppressing Fe diffusion than GaN. According to the second embodiment, in the electron supply layer 16, the Al composition ratio in the region 16 a close to the cap layer 18 is made larger than the Al composition ratio in the region 16 b close to the channel layer 14, so that the electron supply layer 16 The band gap in the region near the cap layer 18 is increased. Thereby, the effect of suppressing the Fe diffusion of the electron supply layer 16 can be increased.

  The electron supply layer 16 may be configured, for example, by laminating a layer having a large Al composition ratio on a layer having a small Al composition ratio. That is, the Al composition ratio may change discretely. Further, the electron supply layer 16 may be formed of a nitride semiconductor containing Al other than AlGaN, and the Al composition ratio may be changed. That is, as described above, the electron supply layer 16 may be made of InAlN or the like in addition to AlGaN.

  Example 3 is an example in which a barrier layer is provided. FIG. 4 is a cross-sectional view illustrating a semiconductor device according to the third embodiment. The description of the same configuration as that described above is omitted.

  As shown in FIG. 4, the semiconductor device according to Example 3 includes a barrier layer 26 for suppressing the diffusion of Fe contained in the cap layer 18 between the electron supply layer 16 and the cap layer 18. The barrier layer 26 is made of i-GaN having a thickness of 2 nm, for example. The cap layer 18 is, for example, i-GaN having a thickness of 3 nm. The barrier layer 26 is formed by not doping Fe in a region near the electron supply layer 16 in the cap layer 18 of the semiconductor device according to the first embodiment.

  According to the third embodiment, the current collapse is suppressed as in the first embodiment. Further, the barrier layer 26 can suppress the diffusion of Fe into the electron supply layer 16 and the like. The barrier layer 26 may be made of, for example, i-AlN in addition to i-GaN. As described above, since AlN has a larger band gap than GaN, the effect of suppressing Fe diffusion is greater than that of GaN. Moreover, you may form the barrier layer 26 with the material which can obtain the effect of Fe diffusion suppression other than i-GaN and i-AlN. In Example 3, the cap layer 18 is made thinner than Example 1 by the thickness of the barrier layer 26. For this reason, the enlargement of a semiconductor device is suppressed. The thickness of the barrier layer 26 can be arbitrarily determined.

  Example 4 is an example in which the position of the barrier layer 26 is changed. FIG. 5 is a cross-sectional view illustrating a semiconductor device according to the fourth embodiment. The description of the same configuration as that described above is omitted.

  As shown in FIG. 4, the semiconductor device according to Example 4 includes a barrier layer 26 between the channel layer 14 and the electron supply layer 16. The barrier layer 26 is made of i-AlN having a thickness of 2 nm, for example.

  According to the fourth embodiment, the current collapse is suppressed as in the first embodiment, and the Fe diffusion is suppressed as in the second and third embodiments. Further, the two-dimensional electron gas is scattered by the impurities contained in the electron supply layer 16, and it becomes difficult for current to flow between the source and the drain. According to the fourth embodiment, since the barrier layer 26 is provided on the upper surface of the channel layer 14, it is possible to effectively suppress impurity scattering of the two-dimensional electron gas due to impurities contained in the electron supply layer 16.

  As described in the third embodiment, the cap layer 18 may not be in contact with the electron supply layer 16. Further, the cap layer 18 may not be provided on the surface of the semiconductor device, and the Fe-doped cap layer 18 may be provided above the electron supply layer 16.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Board 10
Nucleation layer 12
Channel layer 14
Electron supply layer 16
Cap layer 18
Source electrode 20
Drain electrode 22
Gate electrode 24
Barrier layer 26

Claims (8)

A channel layer made of a nitride semiconductor;
An electron supply layer provided on the channel layer, having a larger band gap than the channel layer and made of a nitride semiconductor;
And a cap layer made of a nitride semiconductor doped with Fe provided on the electron supply layer. The semiconductor device according to claim 1, wherein the cap layer contains the Fe having a concentration of 1 × 10 ¹⁰ cm ⁻³ or less.   3. The semiconductor device according to claim 1, wherein the concentration of the Fe contained in the cap layer increases from a region close to the electron supply layer toward a region far from the electron supply layer. The electron supply layer is made of a nitride semiconductor containing Al,
4. The semiconductor device according to claim 1, wherein an Al composition ratio of the electron supply layer increases from a region close to the channel layer toward a region close to the cap layer. 5.   5. The semiconductor device according to claim 1, further comprising a barrier layer for suppressing diffusion of Fe doped in the cap layer between the electron supply layer and the cap layer. 6. .   5. The semiconductor device according to claim 1, further comprising a barrier layer for suppressing diffusion of Fe doped in the cap layer between the electron supply layer and the channel layer. .   The semiconductor device according to claim 5, wherein the barrier layer is made of GaN or AlN. The channel layer is made of GaN;
The electron supply layer is made of AlGaN or InAlN,
The semiconductor device according to claim 1, wherein the cap layer is made of GaN, AlN, AlGaN, or InAlN.

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