JP2010040556A - Group iii-v compound semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group III-V compound semiconductor having high electron density and high electron mobility. <P>SOLUTION: The group III-V compound semiconductor 1 has a buffer layer 3, an electron supply layer 4, a spacer layer 5, a channel layer 6, a spacer layer 7, an electron supply layer 8 and a contact layer 9 on a semi-insulative substrate 2 using a compound semiconductor, wherein the one spacer layer is made of two layers of a GaAs spacer layer and an AlGaAs spacer layer from the channel layer side, and the other spacer layer is made of a single layer of an AlGaAs spacer layer using the channel layer 6 as a boundary. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a group III-V compound semiconductor used for an electronic device, and more particularly to a group III-V compound semiconductor capable of improving electron mobility and electron density.

  Compound semiconductors such as GaAs (gallium arsenide) and InGaAs (indium gallium arsenide) have a feature of higher electron mobility than Si (silicon) semiconductors. Taking advantage of this feature, GaAs and InGaAs are often used in devices that require high-speed operation and high-efficiency operation.

  A typical example of such a device is HEMT (High Electron Mobility Transistor). This HEMT is used for a satellite broadcast receiving antenna, a mobile phone, a wireless LAN, and the like, and can amplify a weak high-frequency signal with low noise.

  The HEMT is manufactured using a compound semiconductor composed of a contact layer, an electron supply layer, a spacer layer, a channel layer, and a buffer layer that is crystal-grown on a substrate. The contact layer is a layer for forming an electrode. The electron supply layer is doped with n-type impurities, and supplies the generated free electrons to the channel layer.

  The spacer layer has a function of preventing free electrons in the channel layer from being ion-scattered by n-type impurities in the electron supply layer. The channel layer is a layer through which free electrons flow and needs to be highly pure.

  The buffer layer has a function of preventing deterioration of device characteristics due to residual impurities on the substrate surface. The substrate is a base for single crystal growth. Crystal growth is called epitaxial growth, and a layer grown by epitaxial growth is called an epitaxial layer.

  As a type of HEMT, a channel layer in which GaAs is used as a channel layer in which electrons travel is called C-HEMT (Conventional HEMT), and a channel layer using InGaAs is called p-HEMT (Pseudomorphic HEMT).

  In addition, when focusing on the number of electron supply layers in the HEMT, the electron supply layer is a single doped type (herein referred to as S-HEMT) on the InGaAs channel and a double having an electron supply layer below the channel. It is divided into a dope type (referred to as D-HEMT here).

  The former S-HEMT has the most popular structure, and a transistor having this structure is widely used as a low-noise amplifier essential for a converter for satellite broadcasting.

  On the other hand, the latter D-HEMT has been actively researched and developed over the past few years as a high-power amplifier for digital communications, and has rapidly been put into practical use. If this thin D-HEMT wafer is used, very high power can be obtained with low distortion in a digital transistor.

  FIG. 3 is a cross-sectional structure diagram of a III-V group compound semiconductor used in a conventional double-doped p-HEMT.

  As shown in FIG. 3, a conventional III-V compound semiconductor 20 includes a substrate 21 made of GaAs, a buffer layer 22, an electron supply layer 23 made of n + AlGaAs, a spacer layer 24 made of i-AlGaAs, and i-InGaAs. The channel layer 25 is made of, the spacer layer 26 is made of i-AlGaAs, the electron supply layer 27 is made of n + AlGaAs, and the contact layer 28 is made of n + GaAs. The buffer layer 22 is formed by sequentially laminating an i-GaAs layer, an i-AlGaAs layer, an i-GaAs layer, and an i-AlGaAs layer (not shown).

  Here, n + and i− represent that the epitaxial layer is n-type and semi-insulating, respectively.

  A method for manufacturing the III-V compound semiconductor 20 will be described below.

  The substrate 21 on which the epitaxial layer is grown is set on a susceptor and heated in a growth furnace. When the source gas is supplied into the growth furnace, the source gas is decomposed by heat, and an epitaxial layer is grown on the substrate 21.

When growing i-GaAs (i-GaAs layer of the buffer layer 22), Ga source material Ga (CH ₃ ) ₃ (trimethylgallium) and As source material AsH ₃ (arsine) are supplied to the substrate 21. In addition, there is Ga (CH ₃ CH ₂ ) ₃ (triethylgallium) as another Ga raw material. Other As raw materials include As (CH ₃ ) ₃ (trimethylarsenic) and TBA (tertiary butylarsine).

_{i-Al x Ga 1-x} As ( spacer layer 24, a spacer layer 26) when grown _{in, Ga (CH 3) 3,} AsH 3, and Al raw materials of the Al (CH _{3) 3} and (trimethyl aluminum) Supply to the substrate 21. In addition, there is Al (CH ₃ CH ₂ ) ₃ (triethylaluminum) as an Al raw material. The Al _x Ga _1-x As, the ratio of Al and Ga is x: means that a 1-x.

When growing i-In _y Ga _1-y As (channel layer 25), Ga (CH ₃ ) ₃ , AsH ₃ , and In raw material In (CH ₃ ) ₃ (trimethylindium) are supplied to the substrate 21. To do. In _y Ga _1-y As means that the ratio of In to Ga is y: 1-y.

When growing n + GaAs (contact layer 28), Ga (CH ₃ ) ₃ , AsH ₃ , and n-type dopant are supplied to the substrate 21. Examples of the n-type dopant element include Si and Se (selenium). Si raw materials include SiH ₄ (monosilane) and Si ₂ H ₆ (disilane). The Se raw material includes H ₂ Se (hydrogen selenide).

When growing n + AlGaAs (electron supply layer 23, electron supply layer 27), Al (CH ₃ ) ₃ , Ga (CH ₃ ) ₃ , AsH ₃ , and Si ₂ H ₆ are supplied to the substrate 21.

  The prior art document information related to the invention of this application includes the following.

JP 2006-286755 A

  The characteristics of the HEMT device are improved as the electron mobility is higher. Generally, in order to increase the electron mobility, it is necessary to optimize the growth temperature. However, when the growth temperature is optimized, the variation in the sheet carrier concentration within the wafer surface increases.

  When the variation in the sheet carrier concentration in the wafer surface increases, the variation in the characteristics of the HEMT device increases, resulting in a decrease in yield and productivity. Further, when the sheet carrier concentration is lowered, the electron mobility can be increased, but the sheet carrier concentration cannot be changed because there is a problem that the characteristics of the HEMT device, particularly the amplification factor, changes.

  In order to solve this problem, as disclosed in Patent Document 1, an i-GaAs layer is inserted between the channel layer 25 and the spacer layers 24 and 26 of the III-V group compound semiconductor 20 of FIG. By making the layer into a two-layer structure, the electron mobility is improved.

  FIG. 4 is a cross-sectional structure diagram of a III-V group compound semiconductor disclosed in Patent Document 1.

  As shown in FIG. 4, the III-V compound semiconductor 31 is formed on a substrate 21 made of GaAs, a buffer layer 22, an electron supply layer 23 made of n + AlGaAs, a spacer layer 24 made of i-AlGaAs, and i-GaAs. A structure in which a spacer layer 29, a channel layer 25 made of i-InGaAs, a spacer layer 30 made of i-GaAs, a spacer layer 26 made of i-AlGaAs, an electron supply layer 27 made of n + AlGaAs, and a contact layer 28 made of n + GaAs are sequentially laminated. It is.

  However, in this structure, since the spacer layer is thicker than the spacer layer made of only AlGaAs, the electron density in the channel layer 25 is reduced, the pinch-off voltage is high, and the breakdown voltage is low.

  Therefore, an object of the present invention is to solve these problems and provide a III-V group compound semiconductor having a high electron density and a high electron mobility.

  The present invention has been devised to achieve the above object, and the invention of claim 1 includes a buffer layer, an electron supply layer, a spacer layer, a channel layer, a semi-insulating substrate using a compound semiconductor, In a III-V group compound semiconductor having a spacer layer, an electron supply layer, and a contact layer, one spacer layer is composed of two layers of a GaAs spacer layer and an AlGaAs spacer layer from the channel layer side with the channel layer as a boundary. The other spacer layer is a group III-V compound semiconductor composed of a single layer of an AlGaAs spacer layer.

  The invention according to claim 2 is the III-V group compound semiconductor according to claim 1, wherein the Al composition ratio of the AlGaAs spacer layer of the one spacer layer is higher than the Al composition ratio of the other spacer layer. is there.

  According to a third aspect of the present invention, in the first or second aspect, the AlGaAs spacer layer of the one spacer layer is formed such that the Al composition ratio gradually decreases toward the GaAs spacer layer on the channel layer side. It is the III-V group compound semiconductor of description.

The invention of claim 4 is a III-V group compound semiconductor having a buffer layer, an electron supply layer, a spacer layer, a channel layer, a spacer layer, an electron supply layer, and a contact layer on a semi-insulating substrate using a compound semiconductor. 2, one spacer layer is composed of two layers of an Al _x GaAs spacer layer and an Al _y GaAs spacer layer (x> y) from the channel layer side, and the other spacer layer is formed of AlGaAs. It is a III-V compound semiconductor composed of a spacer layer.

  According to the present invention, a III-V group compound semiconductor in which both electron density and electron mobility are simultaneously improved can be obtained.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional structural view of a group III-V compound semiconductor showing a preferred embodiment of the present invention. In the figure, n + and i− in the name of the epitaxial layer indicate that the epitaxial layer is n-type and semi-insulating, respectively.

  As shown in FIG. 1, a group III-V compound semiconductor 1 according to a preferred embodiment of the present invention comprises a buffer layer 3 and n + AlGaAs on a substrate 2 made of semi-insulating GaAs using a compound semiconductor. Electron supply layer 4, spacer layer 5b made of i-AlGaAs, spacer layer 5a made of i-GaAs, channel layer 6 made of i-InGaAs, spacer layer 7 made of i-AlGaAs, electron supply layer 8 made of n + AlGaAs, n + GaAs The contact layers 9 are sequentially laminated.

  At this time, the Al composition ratio of the spacer layer 5 b is preferably higher than the Al composition ratio of the spacer layer 7. This is to achieve both high electron density and high electron mobility.

  The buffer layer 3 is formed on the substrate 2 by sequentially laminating an unillustrated i-GaAs layer, i-AlGaAs layer, i-GaAs layer, and i-AlGaAs layer.

  An example of the growth method of each layer of the III-V compound semiconductor 1 will be described.

  The substrate temperature during the growth of each layer is 630 ° C., the growth furnace pressure is 6666 Pa (50 Torr), and the dilution gas is hydrogen.

Ga (CH ₃ ) ₃ and AsH ₃ may be used for growing an i-GaAs layer (i-GaAs layer of the buffer layer 3, spacer layer 5a). The flow rate of Ga (CH ₃ ) ₃ is 50 cc / min (0.05 L / min). The flow rate of AsH ₃ is 314 cc / min (0.314 L / min).

Ga (CH ₃ ) ₃ , Al (CH ₃ ) _3, and AsH ₃ may be used for the growth of the layer made of i-Al _0.23 GaAs (i-AlGaAs layer of buffer layer 3, spacer layer 5b, spacer layer 7). . Their flow rates are 23.0 cc / min (0.023 L / min), 29.6 cc / min (0.0296 L / min) and 328 cc / min (0.328 L / min), respectively.

Ga (CH ₃ ) ₃ , In (CH ₃ ) ₃ and AsH ₃ may be used for the growth of the layer (channel layer 6) made of i-In _0.20 GaAs. Their flow rates are 50 cc / min (0.05 L / min), 275.5 cc / min (0.2755 L / min) and 431 cc / min (0.431 L / min), respectively.

In addition to Ga (CH ₃ ) ₃ , Al (CH ₃ ) ₃ , and AsH ₃ used for the growth of i-Al _0.23 GaAs, the layer made of n + Al _0.23 GaAs (electron supply layer 4 and electron supply layer 8) is used. 5 ppm of Si ₂ H ₆ may be used. The flow rate of Si ₂ H ₆ is 29.2 cc / min (0.0292 L / min). The flow rate other than Si ₂ H ₆ is the same as that of the i-Al0.23 GaAs layer.

For the growth of the layer (contact layer 9) made of n + GaAs, 5 ppm of Si ₂ H ₆ may be used in addition to Ga (CH ₃ ) ₃ and AsH ₃ used for i-GaAs growth. The flow rate of Si ₂ H ₆ is 112.4 cc / min (0.1124 L / min). The flow rates other than Si ₂ H ₆ are the same as in the i-GaAs layer.

  The Al composition ratio in the growth method described above is an example and may be different.

  When an electrode is formed on the lower surface of the substrate 2 of the III-V compound semiconductor 1 and an electrode is formed on the upper surface of the contact layer 9, and the III-V compound semiconductor 11 is divided by dicing or the like, a HEMT is obtained.

  Hereinafter, the operation of the III-V compound semiconductor 1 will be described.

In general, there is a HEMT (High Electron Mobility Transistor) as a representative example of a device using a III-V group compound semiconductor. In order to improve the characteristics of this HEMT, the mobility of free electrons is reduced. It is very important to increase the electron mobility (unit: cm ² / V · s). In HEMT, n-type impurities doped in the electron supply layer emit free electrons. The emitted free electrons are stored in the channel layer. Since the channel layer has high purity, it is characterized by low scattering due to impurities and high electron mobility.

  However, since the electron supply layer is doped with n-type impurities, free electrons in the channel layer are ion-scattered. Furthermore, although it is a small amount, the n-type impurity in the electron supply layer diffuses from the electron supply layer into the spacer layer. The spacer layer serves to reduce the influence of ion scattering due to the n-type impurity in the electron supply layer, and if the n-type impurity exists in the spacer layer, it causes a decrease in electron mobility.

  Similarly, the electron density of the channel layer is important for improving the characteristics of the HEMT. In the HEMT, as described above, a spacer layer is introduced around the channel layer to prevent free electron scattering.

  However, when the spacer layer is thick, due to the large band gap difference between AlGaAs and InGaAs, electrons from the electron supply layer are difficult to be supplied to the channel layer, and electrons are not sufficiently supplied to the channel layer. This leads to a decrease in electron density in the channel layer.

  In the conventional III-V group compound semiconductor 20 or 31 shown in FIGS. 3 and 4, only AlGaAs or a spacer layer made of AlGaAs and GaAs is introduced both above and below the channel layer 25. In the -V group compound semiconductor 1, the lower spacer layer of the channel layer 6 in the figure has a two-layer structure made up of the spacer layer 5b and the spacer layer 5a, and the upper spacer layer in the figure has a single layer structure made of i-AlGaAs. Both the electron mobility and the electron density were increased.

  That is, according to the III-V group compound semiconductor 1 of the present invention, both the electron density and the electron mobility can be improved at the same time. Further, when the electron density and the electron mobility are improved, the characteristics of the HEMT device using the III-V group compound semiconductor 1 are also improved, and the satellite broadcasting receiving parabolic antenna is reduced in size and the power consumption of the mobile phone is reduced. Can be expected.

  As a modification of the III-V group compound semiconductor 1, the Al composition ratio of the spacer layer 5b may be graded so as to gradually decrease toward the spacer layer 5a on the channel layer 6 side. In addition to the effect, an effect of gently changing the band gap difference between the electron supply layer and the channel layer is also obtained.

Further, the material of the spacer layer 5a of the III-V compound semiconductor 1 is replaced with i-Al _x GaAs instead of i-GaAs, and the material of the spacer layer 5b is replaced with i-AlGaAs with Al _y GaAs (in this case x> y The same effect can be obtained.

For example, “Al _x GaAs” means Al _x Ga _1-x As. The same applies to other compounds.

  Next, a group III-V compound semiconductor showing another embodiment of the present invention will be described.

  FIG. 2 is a cross-sectional structural view of a group III-V compound semiconductor showing another embodiment of the present invention.

  As shown in FIG. 2, the group III-V compound semiconductor 10 has basically the same configuration as the group III-V compound semiconductor 1 in FIG. did.

  In the group III-V compound semiconductor 1 in FIG. 1, the lower spacer layer in the figure has a two-layer structure and the upper spacer layer in the figure has a single layer structure with the channel layer 6 as a boundary. In the group compound semiconductor 10, the upper spacer layer has a two-layer structure including, from the channel layer 6 side, a spacer layer 7a made of i-GaAs and a spacer layer 7b made of i-AlGaAs, and the lower spacer layer Was made into a single layer structure consisting of the spacer layer 5 made of i-AlGaAs.

  That is, the III-V group compound semiconductor 10 includes a buffer layer 3, an electron supply layer 4 made of n + AlGaAs, a spacer layer 5 made of i-AlGaAs, i on a substrate 2 made of semi-insulating GaAs using a compound semiconductor. A channel layer 6 made of -InGaAs, a spacer layer 7a made of i-GaAs, a spacer layer 7b made of i-AlGaAs, an electron supply layer 8 made of n + AlGaAs, and a contact layer 9 made of n + GaAs are sequentially laminated.

  In this case, the Al composition ratio of the spacer layer 7 b is preferably higher than the Al composition ratio of the spacer layer 5.

  According to the group III-V compound semiconductor 10, both the electron density and the electron mobility can be improved at the same time as in the group III-V compound semiconductor 1. The same applies to other effects.

  As a modification of the III-V compound semiconductor 10, the same effect can be obtained even when the Al composition ratio of the spacer layer 7b is gradually lowered toward the spacer layer 7a on the channel layer 6 side.

Further, the material of the spacer layer 7a of the III-V compound semiconductor 10 is replaced with i-Al _x GaAs instead of i-GaAs, and the material of the spacer layer 7b is replaced with i-AlGaAs with Al _y GaAs (in this case x> y The same effect can be obtained.

It is a sectional structure figure of a III-V group compound semiconductor which shows one embodiment of the present invention. It is a sectional structure figure of a III-V group compound semiconductor which shows other embodiments of the present invention. It is sectional structure drawing of the conventional III-V group compound semiconductor. It is sectional structure drawing of the conventional III-V group compound semiconductor.

Explanation of symbols

1 III-V group compound semiconductor 2 Substrate 3 Buffer layer 4 Electron supply layer 5 Spacer layer 6 Channel layer 7 Spacer layer 8 Electron supply layer 9 Contact layer

Claims (4)

In a III-V group compound semiconductor having a buffer layer, an electron supply layer, a spacer layer, a channel layer, a spacer layer, an electron supply layer, and a contact layer on a semi-insulating substrate using a compound semiconductor,
With the channel layer as a boundary, one spacer layer is composed of two layers of a GaAs spacer layer and an AlGaAs spacer layer from the channel layer side, and the other spacer layer is composed of a single layer of an AlGaAs spacer layer. A characteristic III-V compound semiconductor.   The III-V group compound semiconductor according to claim 1, wherein an Al composition ratio of the AlGaAs spacer layer of the one spacer layer is set higher than an Al composition ratio of the other spacer layer.   The III-V group compound according to claim 1 or 2, wherein the AlGaAs spacer layer of the one spacer layer is formed such that an Al composition ratio thereof gradually decreases toward the GaAs spacer layer on the channel layer side. semiconductor. In a III-V group compound semiconductor having a buffer layer, an electron supply layer, a spacer layer, a channel layer, a spacer layer, an electron supply layer, and a contact layer on a semi-insulating substrate using a compound semiconductor,
With the channel layer as a boundary, one spacer layer is composed of an Al _x GaAs spacer layer and an Al _y GaAs spacer layer (x> y) from the channel layer side, and the other spacer layer is an AlGaAs spacer layer. A III-V compound semiconductor comprising:

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