JPH0832052A - Compound semiconductor epitaxial wafer - Google Patents

Abstract

(57) prevents a decrease in the mobility of Abstract: OBJECTIVE HEMT of the channel layer, to provide a compound semiconductor epitaxial wafer that can prevent a decrease in amplification factor g _m. [Structure] Non-doped Ga is formed on the compound semiconductor substrate 11.
As layer 12, non-doped InGaAs layer as necessary,
Non-doped AlGaAs layer 13 or non-doped Ga
As layers are sequentially laminated to form the non-doped AlGaAs layer 13
Si-doped AlGaAs layer 14 or GaAs
The layers are laminated in this order, and the Si-doped AlGaAs layer 14 or the non-doped AlGaAs of the GaAs layer is laminated.
In a compound semiconductor epitaxial wafer in which a δ-doping layer 14a of Si is formed in the vicinity of the layer 13, the δ
The Si-doped or non-doped A is formed in the vicinity of or adjacent to at least one side of the doping layer 14a.
A compound semiconductor epitaxial wafer characterized in that an AlGaAs layer 14b or a GaAs layer in which In is added is formed in a 1GaAs layer 14 or a GaAs layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to compound semiconductor epitaxial wafers for high electron mobility transistors.

[0002]

2. Description of the Related Art High electron mobility transistors (High Elect
The RON Mobility Transistor (HEMT) is used in satellite broadcasting receivers and the like as an amplifying element having a low noise characteristic. The HEMT has a structure as shown in FIG. 3, for example, and is formed by stacking a channel layer 2, a spacer layer 3, a carrier supply layer 4, and a contact layer 5 on a GaAs substrate 1. Reference numerals 6, 7, and 8 are a source electrode, a drain electrode, and a gate electrode, respectively. FIG. 4 is a cross-sectional view of an epitaxial wafer used for forming this element. 11 is a GaAs substrate, 12 is a non-doped GaAs layer (thickness: 1 μm) to be the channel layer 2, and 13 is non-doped Al _X Ga to be the spacer layer 3. _1-X As (X: 0.
2 to 0.3) layers (thickness: 3 nm), and 14 are Si-doped n-Al _x Ga ₁ -x As (X: 0.
2 to 0.3) layer (thickness 30 nm, doping concentration 3 × 10 ¹⁸
cm ⁻³ ), 15 is Si-doped GaA to be a contact layer
It is an s layer (thickness 50 nm, doping concentration 3 × 10 ¹⁸ cm ⁻³ ).

In recent years, in order to improve the performance of this HEMT device, a method referred to as a δ-doping method or a planar-doping method is used as a method for adding impurities Si of a carrier supply layer in a planar high density. A δ-doping layer of Si is formed in the vicinity of the spacer layer of the layer,
A structure has been developed in which the thickness of the carrier supply layer is reduced and the distance between the gate electrode and the channel layer is shortened. An example of the structure of the epitaxial wafer used for this element is shown in FIG. In FIG. 5, 14a is a δ-doping layer of Si. The δ-doping layer is a layer in which impurity atoms are planarly added with a thickness of several atomic layers or less at a high density and localized in the thickness direction. In this structure, Si is added to the plane at a high density to form the δ-doping layer 14a so that sufficient electrons can be generated from the δ-doping layer 14a and sent to the channel layer 2. δ
The doping area density of Si of the doping layer 14a is usually 1 to
It is 8 × 10 ¹² cm ^-2 . The areal density of the atoms of GaAs and Al _X Ga _1-X As is 6.258 × 10.
¹⁴ cm ^-2 (Zincblend structure, lattice constant 5.6533
Å) Therefore, the amount of Si atoms in the δ doping layer 14a is
The value is about 1% with respect to the amount of Ga atoms.

Further, in order to further improve the performance of the HEMT device, In _Y Ga _{1 -Y} As having a higher electron mobility and higher electron affinity in the channel layer than GaAs is used.
A HEMT using (Y: 0.1 to 0.3) has also been developed, and this element has a P-HEMT (Pseudo-Morphic High
Electron Mobility Transistor). FIG. 6 shows an example of a cross section of an epitaxial wafer for P-HEMT formed by using the δ-doping method. Reference numeral 22 serves as a channel layer undoped _{In Z Ga 1-Z As (} Z: 0.2~
0.3) layer (thickness 10 nm). The P-HEMT having such a structure allows electrons to travel at a high mobility and a high saturation speed, and can control the amount of travel of the electrons at the gate electrode, that is, the electric current, and thus has a high frequency (> 1 GHz).
z), it is widely used as an amplification element that can be operated with a high amplification factor and low noise.

[0005]

However, the above-mentioned HEMT epitaxial wafer has the following problems. That is, 1) In order to send a sufficient amount of electrons to the channel layer and to make the thickness of the carrier supply layer smaller than that of a normal uniform-doped structure, the density of δ-doping of Si is set to 1 as described above. It is necessary to make the density as high as ~ 8 x 10 ¹² cm ^-2 . However, when such high-density doping is performed, the electron mobility of the channel layer becomes lower at the same electron density than that of normal uniform doping, depending on the growth conditions (such as growth temperature) at the time of stacking. As a result, there arises a problem that the amplification factor g _m, which is one of the indexes of the performance of the HEMT device, decreases. 2) In order to prevent this decrease in electron mobility, the thickness of the spacer layer between the carrier supply layer and the channel layer in which no impurity is added and the density of δ-doping into the carrier supply layer are appropriately controlled, and It is necessary to obtain an electron mobility equal to or higher than that of a HEMT device, but it is difficult to properly set the stacking conditions for that, and stable characteristics can be obtained. There was a problem that I could not.

As described above, the reason why the mobility of the channel layer is lowered when the δ-doping layer of Si is formed is that the Si doped at a high density in a plane diffuses to reach the channel layer and the electrons in the channel layer are diffused. It is presumed that this is due to obstruction of running. The following attempts were made to verify this guess. That is, since thermal diffusion is considered to be the cause of Si diffusion, the temperature (600 to 70) at the time of lamination of the crystal laminated by MOCVD method or MBE method.
It was kept at a growth temperature of 0 ° C.) for a long time (usually, the temperature was rapidly lowered after the lamination), and the mobility of the crystal at that time was measured. As an example, when a crystal stacked at a growth temperature of 650 ° C. was held at the same temperature for 30 minutes after the completion of stacking, the mobility of the channel layer was 30% as compared with the normal process in which the temperature was rapidly lowered after stacking. Diminished. On the other hand, the mobility of uniform-doped crystals without δ-doping was measured under the same conditions.
It decreased by 0%. From the above, it is considered that the δ-doped crystal has a larger Si diffusion amount. Therefore, it is considered that the mobility of the δ-doped crystal is lower than that of the uniform-doped crystal for the same reason, even if the crystal is not kept at the growth temperature after the growth. The cause of such a phenomenon can be considered as follows. That is, due to the difference in lattice constant between Si and AlGaAs,
The vicinity of the δ-doped layer of Si is strained, and this strain is
It is thought to promote the diffusion of The lattice constant of Si is about 5.43Å, and the lattice constant of AlAs and GaAs is about 5.65Å. Incidentally, if the surface density of δ-doping of Si is set to ˜5 × 10 ¹² cm ⁻² as described above, the amount of Si atoms becomes about 1% with respect to the amount of Ga atoms.
On the other hand, when Si is uniformly doped, for example, Si
And the uniform doping density is 3 × 10 ¹⁸ cm ⁻³ , the density of Ga atoms in the GaAs crystal is 2.2 × 10 ^22.
Since it is cm ⁻³ , the amount of Si atoms is about 0.014% with respect to the amount of Ga atoms. Therefore, when Si is δ-doped, the ratio of Si atoms to Ga atoms is 70 times as large as that in the case of uniform doping, and accordingly, the strain accompanying δ-doping of Si becomes extremely large. It is considered that this large strain increases the diffusion of Si.

[0007]

The present invention provides a compound semiconductor epitaxial wafer which solves the above-mentioned problems. A compound semiconductor substrate is provided with a non-doped GaAs layer,
Non-doped InGaAs layer, non-doped A as required
1 GaAs layers or non-doped GaAs layers are sequentially stacked, and Si-doped Al is deposited on the non-doped AlGaAs layers.
In a compound semiconductor epitaxial wafer in which a GaAs layer or a GaAs layer is laminated in this order, and a δ-doping layer of Si is formed in the vicinity of the non-doped AlGaAs layer of the Si-doped AlGaAs layer or GaAs layer, at least one side of the δ-doping layer is formed. The first invention is to form an AlGaAs layer or a GaAs layer in which In is added to the Si-doped or non-doped AlGaAs layer or the GaAs layer in the vicinity or the adjacent portion.

In addition, in the above invention, In is added.
The composition of the AlGaAs layer or GaAs layer is In_YA
l_XGa_1-XYAs or In_YGa_1-YAs
And the composition Y of In is in the range shown by the following equation.
2 It is an invention. That is, Y₀= (A_GaAs-A_si) ・ (A_InAs-A_GaAs)^-1・ Δa
_GaAs ²/ 2/1 / n 0.7Y₀≦ Y ≦ Y₀1.3 However, the lattice constants of GaAs, InAs and Si are
Each a_GaAs, A_InAs, A _siAnd Also, δ doping
The doping area density of the layer is δ, the thickness of the layer with In added is
An n-atomic layer Furthermore, in the second invention, n ≦
Setting 6 is the third invention.

[0009]

As described above, when an In-added AlGaAs layer or a GaAs layer having a thickness of several atomic layers is formed in the vicinity of (including adjacent to) at least one side of the Si δ-doped layer, the InAs lattice constant is Is about 6.06, which is larger than the lattice constants of AlAs and GaAs, so that the AlGaAs layer added with In causes strain opposite to that of the δ-doped layer of Si. Therefore, the strain in the vicinity of the δ-doped layer is relaxed and the thermal diffusion of Si is suppressed,
It is possible to prevent the mobility of the channel layer from decreasing.
Note that In is a Group 3 element like Ga and does not generate valence electrons even when added, so it does not act as an impurity for supplying electrons and does not adversely affect the channel layer.

[0010]

EXAMPLES The present invention will be described in detail below based on examples. (Embodiment 1) FIG. 1 is a sectional view of an embodiment of a compound semiconductor epitaxial wafer for HEMT according to the present invention. The reference numerals in the figure are the same as those in FIG. 5 used in the description of the conventional technique. In this embodiment, a non-doped GaAs layer (having a thickness of 1 μm) serving as a channel layer is formed on the GaAs substrate 11.
m) 12, non-doped Al _X Ga _1-X to be the spacer layer
As layer (X: 0.2 to 0.3) (thickness 3 nm) layer 13,
Si-doped n-Al _x Ga _{1 -x} A serving as a carrier supply layer
s (X: 0.2 to 0.3) layer (thickness 30 nm, doping concentration 3 × 10 ¹⁸ cm ⁻³ ) 14, Si-doped GaAs layer (thickness 50 nm, doping concentration 3 × 10 ¹⁸ ) serving as a contact layer
cm ⁻³ ) 15 are sequentially laminated. Si-doped _{n-Al X} Ga _1-X undoped As layer 14 Al _X G
In the vicinity of the a _1-x As layer 13, the Si-added surface density is 5 × 1.
A δ-doping layer 14a of 0 ¹² cm ^-2 is provided. Also, δ
In the vicinity of the doping layer 14a, non-doped Al _X Ga _1-X
In _Y Al _X Ga _1-XY with In added to the As layer 13 side
An As (X: 0.2-0.3) layer 14b is provided.

In_YAl_XGa_1-XYI of As layer 14b
The n addition amount and the thickness depend on the strain due to the δ doping layer 14a.
Set to offset only. That is, GaAs crystal and
And AlGaAs crystals have a Zincblend structure.
The areal density of atoms and Al atoms is determined by the lattice constant of GaAs crystal.
a_GaAsThen, (4 × 1/4 +1) / a_GaAs ²= 2 / a_GaAs ² Given in. The lattice constant of the AlAs crystal is Si
Or, compared with the lattice constant of InAs,
Since it is close to, it is assumed to be equal to the lattice constant of GaAs. There
Let δ be the areal density of δ-doped Si atoms.
The lattice constants of As, InAs, and Si are a_GaAs,
a_InAs, A_siDue to the δ-doping layer 14a
The distortion due to_GaAs-A_si) Δ (2 / a_GaAs ²)^-1Tona
It On the other hand, In_YAl_XGa_1-XYStrain of As layer 14b
Is approximately (a_InAs-A_GaAs)
Yn. Therefore, the In composition that cancels the strain is Y ₀When
Then, (a_GaAs-A_si) Δ (2 / a_GaAs ²)^-1= (A
_InAs-A_GaAs) Y₀n, so Y₀= (A_GaAs-A_si) ・ (A_InAs-A_GaAs)^-1・ Δa
_GaAs ²It becomes / 2 · 1 / n. By the way, n = 1, δ = 5 × 10¹²cm^-2To be
And Y₀= 0.0044. Epitaxy of this example
Channel wafer is manufactured by MOCVD method and becomes a channel layer.
When the mobility of the undoped GaAs layer 12 was measured,
There is no decrease in mobility due to fluctuations in growth conditions during stacking
Also, using this epitaxial wafer,
Gain of the HEMT device_mIs consistent and stable,
A high performance device was obtained.

(Embodiment 2) FIG. 2 is a sectional view of another embodiment of the compound semiconductor epitaxial wafer according to the present invention. The present embodiment is an improvement of the compound semiconductor epitaxial wafer for P-HEMT shown in FIG.
Its structure is as shown in FIG. 2, a non-doped and non-doped GaAs layer 12 in the embodiment Al _X Ga _1-X A
Non-doped In _Z Ga serving as a channel layer between the s layers 13
_1-Z As (Z: 0.2 to 0.3) layer (thickness 10 nm) 2
2 is inserted.

In the above embodiment, carrier supply
Si-doped n-Al to be a layer_XGa _1-XAs layer 14 is G
It may be composed of aAs. In addition, the δ doping layer 14a
In formed near_YAl_XGa_1-XYAs layer 14b
Rui In_YGa_1-YFor the As layer, the amount of In added
Is Y₀Not limited to 0.7Y₀≦ Y ≦ Y₀1.
Within the range of 3, the mobility is lowered and the amplification factor g of the element is reduced._mof
It is possible to obtain the desired effect without any deterioration or variation.
come. The thickness should be within 6 atomic layers.
The desired effect can be obtained, and it exceeds 6 atomic layers
And the effect is not remarkable, and mobility may decrease.
I started. Furthermore, In_YAl_XGa_1-XYAs layer 14b
Rui In_YGa_1-YThe As layer is the delta doping layer 14a.
Was provided on the GaAs substrate 1 side in the vicinity of the
14a may be provided on the side opposite to the GaAs substrate 1
Or on both sides of the δ-doping layer 14a
Good. However, In_YAl_XGa_1-XYAs layer 14b
Rui In_YGa_1-YThe As layer is replaced by the δ doping layer 14a
When it is provided on both sides, the total layer thickness should be within 6 atomic layers.
It

[0014]

As described above, according to the present invention, a non-doped GaAs layer, a non-doped InGaAs layer, and a non-doped AlGaA layer, if necessary, are formed on a compound semiconductor substrate.
s layers or non-doped GaAs layers are sequentially stacked, and Si-doped AlGaAs is formed on the non-doped AlGaAs layers.
A compound semiconductor epitaxial wafer in which a Si layer or a GaAs layer is laminated in this order, and a Si δ-doping layer is formed in a portion of the Si-doped AlGaAs layer or GaAs layer in the vicinity of the non-doped AlGaAs layer, in the vicinity of at least one side of the δ-doping layer. Alternatively, in the adjacent portion, the Si-doped or non-doped Al
GaAs layer or Al with In added in the GaAs layer
Since the GaAs layer or the GaAs layer is formed, thermal diffusion of Si from the δ-doped layer to the non-doped GaAs layer is suppressed, so that the mobility of the non-doped GaAs layer can be prevented from lowering. When a HEMT is manufactured using, the amplification factor g _m
It has an excellent effect of preventing the decrease of

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a compound semiconductor epitaxial wafer according to the present invention.

FIG. 2 is a sectional view of another embodiment of the compound semiconductor epitaxial wafer according to the present invention.

FIG. 3 is a sectional view of a HEMT.

FIG. 4 is a cross-sectional view of a compound semiconductor epitaxial wafer used for manufacturing a conventional HEMT.

FIG. 5 is a cross-sectional view of another compound semiconductor epitaxial wafer used for manufacturing a conventional HEMT.

FIG. 6 is a cross-sectional view of a compound semiconductor epitaxial wafer used for manufacturing a conventional P-HEMT.

[Explanation of symbols]

11 GaAs substrate 12 Non-doped GaAs layer 13 Non-doped Al _X Ga _1-X As layer 14 Si-doped n-Al _X Ga _1-X As layer 14a δ-doped layer 14b In _Y Al _X Ga _1-XY As layer 15 Si-doped GaAs layer 22 Non-doped In _Z Ga _1-Z As layer

Claims (3)

[Claims] 1. Non-doped Ga on a compound semiconductor substrate
An As layer and, if necessary, a non-doped InGaAs layer, a non-doped AlGaAs layer or a non-doped GaAs layer are sequentially laminated, and a Si-doped AlGaAs layer or a GaAs layer is laminated in this order on the non-doped AlGaAs layer, and the Si-doped AlGaAs layer or GaAs
Δ of Si in the vicinity of the non-doped AlGaAs layer of the layer
In a compound semiconductor epitaxial wafer having a doping layer formed, at least one side of the δ-doping layer is adjacent to or adjacent to one side of the δ-doping layer in the Si-doped or non-doped AlGaAs layer or GaAs layer.
A compound semiconductor epitaxial wafer having an AlGaAs layer or a GaAs layer added with n. 2. The compound semiconductor epitaxial according to claim 1, wherein the composition of the AlGaAs layer or GaAs layer to which In is added is In _Y Al _X Ga _1-XY As or In _Y Ga _1-Y As. Wafer. Here, Y ₀ = (a _GaAs −a _si ) · (a _InAs −a _GaAs ) ⁻¹ · δa
As ^{_{GaAs 2/2 · 1 / n}} , and _{0.7Y 0 ≦ Y ≦ Y 0 1.3} . However,
The lattice constants of GaAs, InAs, and Si are a
_GaAs , a _InAs , and a _si . Further, the doping surface density of the δ-doped layer is δ, and the thickness of the layer to which In is added is an n-atom layer. 3. The compound semiconductor epitaxial wafer according to claim 2, wherein n is 6 or less.