JP2006093400A - Semiconductor laminated structure and hemt element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a HEMT element having a high electron mobility regarding the HEMT element and a semiconductor laminated structure constituting the HEMT element. <P>SOLUTION: A foundation layer 2 is formed on a substrate 1 by AlGaN having a high Al composition of a high quality, and a channel layer 3 containing In and a wide-band gap layer 5 are formed on the foundation layer 2, thus obtaining the semiconductor laminated structure 10 and further the HEMT element 20. Accordingly, the HEMT element is obtained containing the channel layer 3 comprising In and having an excellent surface flatness and a superior crystal quality. The electron mobility of the HEMT element is made better in approximately 20 to 30% at a room temperature than the HEMT element having the same channel layer and wide-band gap layer on a conventional foundation structure, and made larger in approximately 2.5 to 2.6 times at 77 K than that. In the electron mobility, the values of approximately 2,000 cm<SP>2</SP>/Vs at the room temperature and 8,500 cm<SP>2</SP>/Vs at 77 K are obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a HEMT device using a group III nitride and a semiconductor multilayer structure constituting the HEMT device.

  Group III nitride semiconductors such as GaN have a large band gap, high breakdown electric field strength, high saturation electron velocity, and high melting point. In particular, HEMT (High Electron Mobility Transistor), which is a device that takes advantage of its physical properties, has been researched and developed.

  As one of them, a semiconductor device using InN or InGaN for a channel layer is already known (see, for example, Patent Documents 1 to 3). In the semiconductor devices disclosed in Patent Documents 1 to 3, a buffer layer is provided on a base material (substrate), a barrier layer made of GaN or Ga-rich AlGaN is formed, and an InN film is further formed thereon. Alternatively, it has a structure in which a channel layer made of InGaN is formed. Alternatively, after providing a buffer layer on the base material (substrate), a barrier layer made of GaN or Ga-rich AlGaN is formed, and a layer having a large band gap such as AlN is formed thereon, and then InN or It has a structure in which a channel layer made of InGaN is formed.

JP-A-11-204778 JP 2000-196067 A Japanese Patent Laid-Open No. 11-274474

  In order to obtain a HEMT device having excellent device characteristics, it is required that the channel layer has good crystal quality. Moreover, although it is preferable that the band offset between the channel layer and the barrier layer is large, the techniques disclosed in Patent Documents 1 to 3 do not necessarily satisfy these requirements sufficiently.

  In addition, when a layer with a large band gap such as AlN is formed between the barrier layer and the channel layer, the critical film thickness that does not cause cracking of the layer is extremely small, so that it has good crystal quality and surface flatness. Layer formation is difficult.

  This invention is made | formed in view of the said subject, and it aims at providing the HEMT element with a high electron mobility.

  In order to solve the above-mentioned problem, the invention of claim 1 is a first substrate in which the molar fraction of Al element with respect to all the Group III elements contained on the predetermined substrate and contained therein is 50% or more. A base layer made of one group III nitride, a channel layer made of at least a second group III nitride containing In and formed on the base layer, and formed on the channel layer; And a wide band gap layer made of group III nitride.

The invention of claim 2 is the semiconductor multilayer structure according to claim 1, wherein the dislocation density of the underlayer is 1 × 10 ¹¹ cm ⁻² or less, and the X-ray rocking curve in the (002) plane is The full width at half maximum is 200 seconds or less.

  A third aspect of the present invention is the semiconductor multilayer structure according to the first or second aspect, wherein the protection is made of a fourth group III nitride between the channel layer and the wide band gap layer. A layer.

  According to a fourth aspect of the present invention, there is provided the semiconductor multilayer structure according to the third aspect, wherein the composition of the protective layer is substantially the same as that of the wide band gap layer.

  The invention according to claim 5 is the semiconductor multilayer structure according to any one of claims 1 to 4, wherein the moles of Al element with respect to all group III elements contained in the first group III nitride. The fraction is 80% or more.

  A sixth aspect of the present invention is the semiconductor multilayer structure according to any one of the first to fifth aspects, wherein the first group III nitride is AlN.

  The invention according to claim 7 is the semiconductor multilayer structure according to any one of claims 1 to 6, wherein the underlayer is formed at a temperature of 1100 ° C. or higher.

The invention according to claim 8 is the semiconductor multilayer structure according to any one of claims 1 to 7, characterized by having an electron mobility of 8000 cm ² / Vs or more at 77K.

The invention according to claim 9 is the semiconductor multilayer structure according to claim 8, which has an electron mobility of 1900 cm ² / Vs or more at room temperature.

  According to a tenth aspect of the present invention, a source electrode, a drain electrode, and a gate electrode are formed on the semiconductor multilayer structure according to any one of the first to ninth aspects.

  According to the first to tenth aspects of the present invention, it is possible to obtain a semiconductor multilayer structure and a HEMT device having a large band offset between the base layer acting as a barrier layer and the channel layer. Further, by using Al-rich group III nitride, the underlayer can be made highly resistant.

  In particular, according to the second aspect of the present invention, since the channel layer and the wide band gap layer are provided on the high crystal quality underlayer, the channel layer containing In and having a good crystal quality is provided, and the band offset is large. In addition, a semiconductor multilayer structure having a high electron mobility and a HEMT element are realized.

  In particular, according to the third and fourth aspects of the invention, by providing the protective layer on the channel layer, the characteristics of the semiconductor multilayer structure and the HEMT device are further improved.

<First Embodiment>
FIG. 1 is a schematic diagram showing a configuration of a semiconductor multilayer structure 10 according to a first embodiment of the present invention and a HEMT element 20 formed using the same. For convenience of illustration, the ratio of the thickness of each layer in FIG. 1 does not reflect the actual ratio.

  The semiconductor multilayer structure 10 includes a base layer 2, a channel layer 3, and a wide band gap layer 5 on a substrate (base material) 1. All of these layers are formed by a known film formation method such as MOCVD (Metal Organic Chemical Vapor Deposition).

The substrate 1 is appropriately selected according to the composition and structure of the channel layer 3 and the wide band gap layer 5 formed thereon or the formation method of each layer. For example, a substrate such as sapphire or SiC (silicon carbide) is used. Alternatively, various oxide materials such as ZnO, LiAlO ₂ , LiGaO ₂ , MgAl ₂ O ₄ , (LaSr) (AlTa) O ₃ , NdGaO ₃ , MgO, various IV group single crystals such as Si and Ge, and various IV-IV such as SiGe. A group III-V compound such as GaAs, AlN, GaN, and AlGaN, and various borides such as ZrB ₂ may be used. The thickness of the substrate 1 is not particularly limited in terms of material, but a thickness of several hundred μm to several mm is preferable for the convenience of handling.

  The underlayer 2 is formed of a group III nitride having an Al element mole fraction of 50% or more with respect to all the group III elements contained, that is, an Al-rich group III nitride. The underlayer 2 functions as a barrier layer for the channel layer 3. By using Al-rich group III nitride, the high resistance underlayer 2 can be easily obtained. Preferably, the base layer 2 can be formed with a higher resistance by using a group III nitride having a molar fraction of Al element of 80% or more, more preferably AlN. FIG. 1 illustrates the case where the underlayer is AlN (w = 1).

  When the MOCVD method is used, it is preferable to form the underlayer 2 at a temperature (base material temperature) of 1100 ° C. or higher. This is because the underlying layer 2 with good crystallinity cannot be obtained in a temperature range lower than this range. More preferably, it is formed in a temperature range of 1150 ° C. or higher to 1250 ° C. Thereby, dislocations are reduced, and the underlayer 2 with good crystal quality is formed. The upper limit of the thickness of the underlayer 2 is preferably as thick as possible from the viewpoint of suppressing the generation of pits, but the thickness is determined in consideration of other conditions such as the occurrence of cracks. The underlayer 2 is preferably formed to a thickness between 0.5 μm and 3 μm.

The underlayer 2 is preferably formed so as to have a high crystal quality for the purpose of improving the crystal quality of the channel layer 3 and the wide band gap layer 5 formed thereon. Therefore, the lower the dislocation density of the underlayer 2, the better. However, it should be at least 1 × 10 ¹¹ cm ⁻² or less. 1 × 10 ¹⁰ cm ⁻² or less is more preferable. Further, the half width of the X-ray rocking curve on the (002) plane may be 200 seconds or less, preferably 150 seconds or less, and more preferably 100 seconds or less. Since the underlayer 2 has such a crystal quality, the crystallinity of the channel layer 3 becomes even better. As a result, the channel layer 3 can be formed in a high quality state having a low dislocation density and high crystallinity, so that extremely high electron mobility is realized.

The channel layer 3 is formed by _{In 1-z Ga z N (} 0 ≦ z <1) having a composition of the group III nitride. That is, the channel layer 3 is formed of a single layer of InN (when z = 0) or InGaN mixed crystal. The channel layer 3 is formed to a thickness of about 5 nm to 50 nm.

When the MOCVD method is used, the channel layer 3 is formed in a temperature range of 400 ° C. to 900 ° C. In the case of a single layer of InN, it is more preferably formed at around 600 ° C. or lower, and the higher the Ga content ratio, the higher the temperature. For example, if In _0.1 Ga _0.9 N (when z = 0.9), it is more preferable to form the film at around 780 ° C. The reason why it is formed in such a temperature range is that if the temperature is too high, the decomposition of InN occurs and the channel layer 3 cannot be formed satisfactorily.

  In the present embodiment, the base layer 2 acting as a barrier layer is formed of AlN, and the channel layer 3 is formed of a group III nitride containing In, thereby forming the channel layer and the barrier layer. A large amount of band offset is realized.

The wide band gap layer 5 is formed of a group III nitride having a composition of Al _x In _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y <1). That is, it is formed of GaN (when x = y = 0) or a mixed crystal group III nitride. The wide band gap layer 5 is preferably formed to a thickness of about 20 nm to 30 nm as a whole from the viewpoint of securing the concentration of the two-dimensional electron gas.

When the MOCVD method is used, the wide band gap layer 5 is formed in a temperature range of 800 ° C. or higher. In the case of a single layer of GaN, it is more preferably formed at around 900 ° C., and the higher the Al content ratio, the higher the temperature. For example, if it is Al _0.25 Ga _0.75 N (when x = 0.25, y = 0), it is preferably formed at around 1080 ° C.

  The characteristics of the semiconductor multilayer structure 10 formed as described above are as follows.

When the channel layer 3 is a single layer of InN (z = 0) and the wide band gap layer 5 is a single layer of GaN (x = y = 0) (see FIG. 3A), the electron mobility is approximately 2000 cm ² / Vs at room temperature, a value of approximately 8500cm ² / Vs in the 77K is obtained. In this case, the value of the surface roughness RMS of the wide band gap layer measured by AFM (atomic force microscope) is 2 nm or less.

On the other hand, when the channel layer 3 is In _0.1 Ga _0.9 N (z = 0.9) and the wide band gap layer 5 is a single layer of Al _0.25 Ga _0.75 N (x = 0.25, y = 0) (FIG. 4 (A) refer), the electron mobility is about 1000 cm ² / Vs at room temperature, in the 77K obtained a value of 5500cm ² / Vs. In this case, the value of the surface roughness RMS of the wide band gap layer is about 0.3 nm.

  The surface roughness value indicates that the wide band gap layer 5 has excellent surface flatness. From this value, the channel layer 3 interposed between the underlayer 2 and the wide band gap layer 5 also Therefore, it is judged to have good surface flatness. And it is thought that high electron mobility is implement | achieved from the channel layer 3 having favorable crystal quality.

The HEMT element 20 is formed by forming the source electrode 6s and the drain electrode 6d by ohmic junction on the surface of the semiconductor multilayer structure 10, that is, the surface of the wide band gap layer 5, and the gate electrode 6g by Schottky junction. The source electrode 6s and the drain electrode 6d are preferably formed in a multilayer structure such as Ti / Al, Ti / Al / Ti / Au, and Ti / Al / Ni / Au. The gate electrode 6g is preferably formed of a multilayer structure such as Ni / Au, Pd / Au, and Pt / Au. Further, a protective film (not shown) made of, for example, SiO ₂ or silicon nitride may be provided on the outermost layer of the semiconductor multilayer structure 10.

  As described above, in this embodiment, the channel layer 3 containing In is formed on the base layer 2 made of AlN having a high crystal quality, so that the channel layer containing In and having a good crystal quality is formed. 3, a HEMT device having a large band offset and a high electron mobility is realized.

<Second Embodiment>
FIG. 2 is a schematic diagram showing the configuration of the semiconductor multilayer structure 110 according to the second embodiment of the present invention and the HEMT element 120 formed using the same. For convenience of illustration, the ratio of the thickness of each layer in FIG. 2 does not reflect the actual ratio.

  In the semiconductor multilayer structure 110, the base layer 2 and the channel layer 3 are provided on the substrate (base material) 1 as in the semiconductor multilayer structure 10 according to the first embodiment. However, it differs from the semiconductor multilayer structure 10 according to the first embodiment in that the protective layer 104 is provided thereon and the wide band gap layer 105 is formed. FIG. 2 illustrates the case where the underlayer is AlN.

  The formation of the foundation layer 2 and the channel layer 3 is the same as in the first embodiment. Therefore, the detailed description is abbreviate | omitted. The wide band gap layer 105 is different from the wide band gap layer 5 according to the first embodiment formed on the channel layer 3 in that it is formed on the protective layer 104. The formation method is the same as that of the wide band gap layer 5. Therefore, the description thereof is also omitted.

  Each layer constituting the semiconductor multilayer structure 110 is formed by a known film formation method such as MOCVD (Metal Organic Chemical Vapor Deposition).

  The HEMT element 120 is obtained by forming the source electrode 6s, the drain electrode 6d, and the gate electrode 6g on the surface of the semiconductor multilayer structure 110. Each electrode is formed in the same manner as that formed on the surface of the semiconductor multilayer structure 10 in the first embodiment. Therefore, the description is omitted.

  The protective layer 104 is a layer provided for the purpose of preventing the crystal quality of the surface of the channel layer 3 from being deteriorated when the wide band gap layer 105 is formed after the channel layer 3 is formed. Further, when the wide band gap layer 105 includes a layer doped with an impurity, the wide band gap layer 105 also serves as a spacer layer provided to separate the channel layer 3 and the wide band gap layer 105. The protective layer 104 is preferably formed of a group III nitride having the same composition as the wide band gap layer 105. The protective layer 4 is preferably formed to a thickness of about 0.5 to 10 nm. More preferably, the thickness is about 0.5 to 5 nm. The formation of the protective layer 4 is preferably performed by the same method as the method for forming the channel layer 3 and immediately after the formation of the channel layer 3 at the same temperature as the temperature for forming the channel layer 3. Alternatively, the temperature may be gradually increased from the formation temperature of the channel layer 3 to the formation temperature of the wide band gap layer 105.

  The characteristics of the semiconductor multilayer structure 110 formed as described above are as follows.

When the channel layer 3 is a single layer of InN (z = 0) and the protective layer 104 and the wide band gap layer 105 are a single layer of GaN (x = y = 0) (see FIG. 3B), electron transfer the degree, approximately 2100 cm ² / Vs, a value of approximately 9100cm ² / Vs in 77K obtained at room temperature. In this case, the value of the surface roughness RMS of the wide band gap layer measured by AFM (atomic force microscope) is 2 nm or less.

On the other hand, the channel layer 3 is In _0.1 Ga _0.9 N (z = 0.9), and the protective layer 104 and the wide band gap layer 105 are single layers of Al _0.25 Ga _0.75 N (x = 0.25, y = 0). for (see FIG. 4 (B)), the electron mobility is about 1100 cm ² / Vs at room temperature, in the 77K obtained a value of 6000 cm ² / Vs. In this case, the value of the surface roughness RMS of the wide band gap layer is about 0.3 nm.

  That is, also in the present embodiment, since the wide band gap layer 105 has excellent surface flatness, the channel layer 3 is also determined to have good surface flatness. In addition, when compared with the characteristic values of the semiconductor multilayer structure 10 according to the first embodiment, which differs only in the presence or absence of the protective layer 104, the electron mobility is as high as the surface roughness although the surface roughness is similar. It can be seen that the semiconductor laminated structure 110 according to the embodiment has a higher value. This is because the deterioration of the crystal quality of the channel layer 3 is suppressed by providing the protective layer 104, and good interface flatness is obtained between the channel layer 3 and the wide band gap layer 105. It is believed that there is.

  As described above, in the present embodiment, a HEMT device including In and having a channel layer 3 with good crystal quality, a large band offset, and a high electron mobility is realized. By providing the protective layer 104 on the channel layer 3, the characteristics are further improved.

  As examples of the HEMT element 20 according to the first embodiment, two types of HEMT elements having different compositions of the channel layer 3 and the wide band gap layer 5 were produced. These are shown below as Example 1a and Example 1b. As examples of the HEMT device 120 according to the second embodiment, two types of HEMT devices having different compositions of the channel layer 3 and the wide band gap layer 105 were manufactured. These are shown below as Example 2a and Example 2b.

  3 and FIG. 4 show the surface of the wide band gap layer measured with an AFM (atomic force microscope) and the electron mobility at room temperature and 77 K of the channel layer in the HEMT devices according to Examples and Comparative Examples described later. It is a figure which illustrates roughness RMS as a list.

  In addition, four HEMT elements serving as comparative examples for Examples 1a, 1b, 2a, and 2b were fabricated. FIG. 5 is a schematic diagram showing the configuration of the semiconductor multilayer structure according to Comparative Examples 1a and 1b, and FIG. 6 is a schematic diagram showing the configuration of the semiconductor multilayer structure according to Comparative Examples 2a and 2b.

Example 1a
In Example 1a, the semiconductor multilayer structure 10 according to the first embodiment was manufactured, and the HEMT device 20 using the same was manufactured.

First, in the production of the semiconductor laminated structure 10, a C-plane sapphire single crystal having a 2 inch diameter and a thickness of 330 μm was used as the substrate 1, and this was placed in a reaction vessel of a predetermined MOCVD apparatus. The MOCVD apparatus has at least H ₂ , N ₂ , TMG (trimethylgallium), TMA (trimethylaluminum), TMA (trimethylindium), a silane gas which is a supply source of Si used as an n-type dopant, and a source gas or a carrier gas; NH ₃ can be supplied into the reaction tube. The substrate 1 was heated to 1200 ° C. and subjected to thermal cleaning while the pressure in the reaction tube was set to atmospheric pressure and H ₂ was allowed to flow at an average flow rate of 1 m / sec.

After completion of the thermal cleaning, the temperature of the substrate 1 was set to 1200 ° C., NH ₃ , TMA, and H ₂ were supplied to form an AlN layer as the underlayer 2 with a thickness of 1 μm.

Thereafter, the temperature was lowered to 600 ° C., TMI and N ₂ were supplied, and an InN layer as the channel layer 3 was formed to a thickness of 10 nm.

After forming the InN layer, the temperature was raised to 900 ° C., and TMG, H _2, and N ₂ were supplied to form a GaN layer having a thickness of 25 nm as the wide band gap layer 5. Thereby, the semiconductor multilayer structure 10 was obtained.

  Subsequently, a source electrode 6s and a drain electrode 6d made of Ti / Al / Ni / Au were formed by ohmic junction, and a gate electrode 6g made of Ni / Au was formed by Schottky junction, whereby the HEMT device 20 was obtained. . These electrodes were formed by known EB vapor deposition.

  FIG. 3A shows data indicating characteristics of the HEMT element obtained in this way.

(Example 1b)
In Example 1b, a HEMT device 20 having a different composition from that of Example 1a in the channel layer 3 and the wide band gap layer 5 was produced.

The In _0.1 Ga _0.9 N layer as the channel layer 3 was formed to a thickness of 5 nm at 780 ° C. by supplying TMI, TMG and N _2, and Al _0.25 Ga _0.75 N as the wide band gap layer 5 Was formed in the same manner as in Example 1a except that TMA, TMG, N ₂ and H ₂ were supplied and formed at 1080 ° C.

  FIG. 4A is data showing characteristics of the HEMT element obtained in this way.

Example 2a
In Example 2a, the semiconductor multilayer structure 110 according to the second embodiment was manufactured, and the HEMT device 120 using the same was manufactured.

  The fabrication of the semiconductor multilayer structure 110 was performed in the same manner as in Example 1a until the formation of the InN layer as the channel layer 3.

After the formation of the InN layer, TMG, H _2, and N ₂ were supplied while maintaining the temperature at 600 ° C., thereby forming a GaN layer as the protective layer 104 with a thickness of 2 nm.

Thereafter, the temperature was raised to 900 ° C., and TMG, H _2, and N ₂ were supplied, thereby forming a GaN layer as the wide band gap layer 105 to a thickness of 23 nm. Thereby, the semiconductor multilayer structure 10 was obtained.

  Thereafter, various electrodes were formed in the same manner as in Example 1a to obtain a HEMT device 120.

  FIG. 3B is data showing characteristics of the HEMT element obtained in this way.

(Example 2b)
In Example 2b, a HEMT device 120 having a different composition from that of Example 2a in the channel layer 3 and the wide band gap layer 105 was produced.

An In _0.1 Ga _0.9 N layer as the channel layer 3 was formed to a thickness of 5 nm at 780 ° C. by supplying TMI, TMG and N _2, and Al _0.25 Ga _0.75 N as the protective layer 104, TMA, TMG, H ₂ and N ₂ were supplied and formed at 780 ° C., Al _0.25 Ga _0.75 N as the wide band gap layer 105 was supplied, and TMA, TMG, N ₂ and H ₂ were supplied. The film was formed in the same manner as in Example 2a except that the film was formed at 1080 ° C.

  FIG. 4B shows data indicating characteristics of the HEMT element obtained in this way.

(Comparative Example 1a)
In Comparative Example 1a, a semiconductor multilayer structure in the case of x = y = z = 0 in the semiconductor multilayer structure 210 shown in FIG. 5 and a HEMT element (not shown) using the semiconductor multilayer structure were manufactured.

  As the substrate 201, a C-plane sapphire single crystal was used as in Example 1a. The substrate 201 was subjected to thermal cleaning in the same manner as in Example 1.

Thereafter, after the temperature is lowered to 500 ° C., TMG, NH ₃ , H _2, and N ₂ are supplied to form a GaN layer as the buffer layer 202 with a thickness of 30 nm, and then the temperature is raised to 1180 ° C. TMG and NH ₃ were supplied to form a GaN layer having a thickness of 3 μm as the base layer 203 that acts as a barrier layer.

  After the formation of the GaN layer, the InN layer as the channel layer 204 was formed to a thickness of 10 nm, and the GaN layer as the wide band gap layer 205 was formed to a thickness of 25 nm, as in Example 1a. Thereby, the semiconductor laminated structure 210 was obtained.

  Thereafter, in the same manner as in Example 1a, various electrodes were formed to obtain a HEMT device. That is, the HEMT device obtained in this comparative example has the same structure as that of Example 1a above the channel layer, and only the underlying structure is different from Example 1a.

  FIG. 3C is data showing characteristics of the HEMT element obtained in this way.

(Comparative Example 1b)
In Comparative Example 1b, a semiconductor multilayer structure in which x = 25, y = 0, and z = 0.9 in the semiconductor multilayer structure 210 shown in FIG. 5 and a HEMT element (not shown) using the semiconductor multilayer structure were manufactured.

The formation of the base layer 203 is performed in the same manner as in Comparative Example 1a, and then, as in Example 1b, an In _0.1 Ga _0.9 N layer as the channel layer 204 is formed to a thickness of 5 nm, and the wide band gap layer 205 is formed. The Al _0.25 Ga _0.75 N layer was formed to a thickness of 25 nm. Thereby, the semiconductor laminated structure 210 was obtained.

  Thereafter, in the same manner as in Example 1a, various electrodes were formed to obtain a HEMT device. That is, the HEMT device obtained in this comparative example has the same structure as that of Example 1b above the channel layer, and only the underlying structure is different from Example 1b.

  FIG. 4C shows data indicating characteristics of the HEMT element obtained in this way.

(Comparative Example 2a)
In Comparative Example 2a, a semiconductor multilayer structure in which x = y = z = 0 in the semiconductor multilayer structure 310 shown in FIG. 6 and a HEMT element (not shown) using the semiconductor multilayer structure were manufactured.

  As the substrate 301, a C-plane sapphire single crystal was used as in Example 1a. Formation of the GaN layer as the buffer layer 302 and the GaN layer as the base layer 303 acting as a barrier layer on the substrate 301 was performed in the same manner as in Comparative Example 1a.

After the formation of the base layer 303, TMA, NH ₃ and H ₂ were supplied to form an AlN layer as a barrier layer 304 with a thickness of 5 nm at 1080 ° C.

  Thereafter, an InN layer as a channel layer 305 and a GaN layer as a wide band gap layer 306 were formed in the same manner as in Comparative Example 1a. Thereby, the semiconductor laminated structure 310 was obtained.

  Thereafter, in the same manner as in Example 1a, various electrodes were formed to obtain a HEMT device. That is, the HEMT device obtained in this comparative example has the same structure as that of Example 2a above the channel layer, and only the underlying structure is different from Example 2a.

  FIG. 3D shows data indicating characteristics of the HEMT element obtained in this way.

(Comparative Example 2b)
In Comparative Example 2b, a semiconductor multilayer structure in the case of x = 0.25, y = 0, z = 0.9 in the semiconductor multilayer structure 310 shown in FIG. 6 and a HEMT element (not shown) using the semiconductor multilayer structure were manufactured.

The formation of the barrier layer 304 is performed in the same manner as in Comparative Example 2a, and then, as in Example 1b, an In _0.1 Ga _0.9 N layer as the channel layer 305 is formed to a thickness of 5 nm, and the wide band gap layer 306 is formed. Then, an Al _0.25 Ga _0.75 N layer having a thickness of 25 nm was formed. Thereby, the semiconductor laminated structure 310 was obtained.

  Thereafter, in the same manner as in Example 1a, various electrodes were formed to obtain a HEMT device. That is, the HEMT device obtained in this comparative example has the same structure as that of Example 2b above the channel layer, and only the underlying structure is different from Example 2b.

  FIG. 4D is data showing characteristics of the HEMT element obtained in this way.

(Comparison of Example and Comparative Example)
As shown in FIGS. 3 and 4, the electron mobility in the HEMT device according to each example is improved by about 20 to 30% at room temperature as compared with the mobility of the HEMT device according to the corresponding comparative example. At 77K, it increases to about 2.5 to 2.6 times. That is, a HEMT device obtained by forming a channel layer containing In and a wide band gap layer on a base structure in which a base layer is formed of high-quality AlN on a substrate has a conventional base structure. In addition, it can be said that the device characteristics are improved as compared with the case of forming the channel layer containing In and the wide band gap layer.

  Further, regarding the surface roughness RMS in the wide band gap layer constituting the uppermost surface of the semiconductor multilayer structure, the value in the HEMT element according to each example is larger than the value of the HEMT element according to the corresponding comparative example, It is about 1/4. Thus, it is surmised that the improvement in flatness on the uppermost surface indicates that the flatness in the channel layer and the wide band gap layer is improved. It is considered that the characteristics are realized.

  At 77K, the mobility of the HEMT device according to each example is greatly improved as compared with the HEMT device according to the comparative example. AlN having a band gap larger than that of GaN is used for the base layer and the channel layer It is considered that the reason is that the carrier confinement effect is remarkably improved. In addition, the reason is that the crystal quality of the AlN layer is improved by sufficiently increasing the film thickness, and that a high resistance value is obtained compared to GaN by using AlN. Conceivable.

  In addition, the HEMT elements according to Examples 1b and 2b including the protective layer have higher electron mobility values than the HEMT elements according to Examples 1a and 2a that do not include the HEMT element. On the other hand, since the surface roughness is comparable, it is considered that the provision of the protective layer is an effect of suppressing the deterioration of the crystal quality of the channel layer 3.

  In Comparative Examples 2a and 2b, a barrier layer 304 made of AlN is provided. In the HEMT device according to Comparative Examples 2a and 2b, the mobility is slightly improved as compared with the HEMT device according to Comparative Examples 1a and 1b, but this is because the band gap of AlN is larger than that of GaN. This is thought to be due to the improved confinement effect of electrons in the layer. The surface roughness of the wide band gap layer in Comparative Examples 2a and 2b is worse than that of Comparative Examples 1a and 1b, and the critical film thickness at which cracks do not occur when AlN is formed on GaN is generally about 5 nm. Therefore, it can be said that the role of the barrier layer 304 as a barrier layer is limited. In addition, since the barrier layer 304 is extremely thin, the crystal quality is considered to be insufficient.

<Modification>
In the above-described embodiment, the wide band gap layers 5 and 105 are shown only in a mode in which they are uniformly non-doped, but may be a mode in which Si is partially doped. FIG. 7 is a diagram schematically showing an aspect in which the wide band gap layer 5 is doped with Si in the semiconductor multilayer structure 10. FIG. 7A shows a mode in which a Si-doped wide band gap layer 51 is provided at the center of the wide band gap layer 5. FIG. 7B shows a mode in which a Si-doped wide band gap layer 52 is provided in the upper part of the wide band gap layer 5. FIG. 7C shows a mode in which a Si-doped wide band gap layer 53 is provided in a lower portion of the wide band gap layer 5. Such Si doping is realized by supplying SiH ₄ gas at a predetermined timing for a predetermined time under a predetermined supply condition when the wide band gap layer 5 is formed. Although illustration is omitted, the wide band gap layer 105 can be doped with Si as in FIG.

  Alternatively, the channel layer may be doped with Si.

  When the In content ratio of the channel layer 3 is high, the buffer layer having the same composition as the channel layer is formed at a temperature lower by 100 to 150 ° C. than the formation temperature of the channel layer, for example, 350 to 550 ° C. It is also possible to form in a temperature range of

1 is a schematic diagram showing a configuration of a semiconductor multilayer structure 10 and a HEMT element 20 according to a first embodiment. It is a schematic diagram which shows the structure of the semiconductor laminated structure 110 and the HEMT element 120 which concern on 2nd Embodiment. It is a figure which illustrates the device characteristic in the HEMT element concerning each example and each comparative example. It is a figure which illustrates the device characteristic in the HEMT element concerning each example and each comparative example. It is a schematic diagram which shows the structure of the semiconductor laminated structure which concerns on the comparative examples 1a and 1b. It is a schematic diagram which shows the structure of the semiconductor laminated structure which concerns on the comparative examples 2a and 2b. FIG. 3 is a diagram schematically showing an aspect in which a wide band gap layer 5 is doped with Si in a semiconductor laminated structure 10.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Base layer 3 Channel layer 4 Protective layer 5 Wide band gap layer 6d Drain electrode 6g Gate electrode 6s Source electrode 10, 110 Semiconductor laminated structure 20, 120 HEMT element 51-53 Si doped wide band gap layer 104 Protective layer 105 Wide Band gap layer

Claims (10)

A predetermined substrate;
An underlayer composed of a first group III nitride formed on the base material and having a mole fraction of Al element with respect to all the group III elements contained in the substrate is 50% or more;
A channel layer formed on the underlayer and made of a second group III nitride containing at least In;
A wide band gap layer formed on the channel layer and made of a third group III nitride;
A semiconductor multilayer structure comprising: The semiconductor multilayer structure according to claim 1,
A semiconductor multilayer structure, wherein the dislocation density of the underlayer is 1 × 10 ¹¹ cm ⁻² or less, and the half width of the X-ray rocking curve on the (002) plane is 200 seconds or less. The semiconductor multilayer structure according to claim 1 or 2, wherein
A protective layer made of a fourth group III nitride between the channel layer and the wide band gap layer;
A semiconductor multilayer structure, further comprising: The semiconductor multilayer structure according to claim 3,
The composition of the protective layer is substantially the same as the wide band gap layer,
A semiconductor laminated structure characterized by that. A semiconductor multilayer structure according to any one of claims 1 to 4,
A semiconductor multilayer structure, wherein a mole fraction of Al element with respect to all group III elements contained in the first group III nitride is 80% or more. A semiconductor multilayer structure according to any one of claims 1 to 5,
A semiconductor multilayer structure, wherein the first group III nitride is AlN. A semiconductor multilayer structure according to any one of claims 1 to 6,
A semiconductor multilayer structure, wherein the underlayer is formed at a temperature of 1100 ° C. or higher. A semiconductor multilayer structure according to any one of claims 1 to 7,
A semiconductor stacked structure having an electron mobility of 8000 cm ² / Vs or higher at 77K. The semiconductor multilayer structure according to claim 8,
A semiconductor stacked structure having an electron mobility of 1900 cm ² / Vs or higher at room temperature. A HEMT device comprising a semiconductor stacked structure according to claim 1, wherein a source electrode, a drain electrode, and a gate electrode are formed.

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