JP3136072B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a Schottky junction, such as a Schottky barrier diode, a field effect transistor, a high electron mobility transistor, and a metal-semiconductor-metal (hereinafter, referred to as MSM). The present invention relates to a highly reliable semiconductor device capable of suppressing current.

[0002]

2. Description of the Related Art Conventionally, Schottky barrier diodes (hereinafter, referred to as Schottky diodes), field effect transistors (hereinafter, referred to as MESFETs), high electron mobility transistors (hereinafter, referred to as HEMTs), metal-semiconductors A semiconductor device using a Schottky junction such as a metal light receiving element (hereinafter, referred to as MSM) is used.

For example, a HEMT includes a channel layer through which electrons travel, and an electron supply layer that supplies electrons to the channel layer. A junction between the electron supply layer and a metal electrode is a Schottky junction (the active layer in this Schottky junction is It is a device that is an electron supply layer), has a high cutoff frequency due to its high speed, and is expected to have low noise.
Used as a microwave device.

Conventionally, HEMTs using an AlGaAs layer or the like formed on a GaAs substrate as a channel layer have been used, but recently a HEMT formed on an InP substrate has been used in order to obtain a higher electron velocity. HEMTs using the InGaAs layer as a channel layer are subject to research and development. In a HEMT using an InGaAs layer as a channel layer, a material (InP, InGaAs) having a lattice constant close to that of an InP substrate is used for an electron supply layer (active layer in a Schottky junction).
s, InAlAs, etc.). Therefore,
In recent years, research on Schottky junctions using an InP substrate having a material having a lattice constant close to the active layer as an active layer has been actively conducted.

As the above-mentioned Schottky junction, for example,
There is known a structure in which an InP layer or an InGaAs layer is used as an active layer, and an InAlAs layer having a large band gap is inserted as a Schottky barrier enhancement layer (hereinafter, referred to as a barrier layer) between the active layer and a metal electrode. Usually, InP layer or InP
The Schottky junction between the GaAs layer and the metal electrode has a problem that the leakage current becomes large.
The introduction of the nAlAs barrier layer improves the Schottky barrier and suppresses the leakage current in the reverse direction.
However, even with this structure, only a Schottky barrier lower by about 0.2 eV than that of an AlGaAs-based Schottky junction is obtained.

A Schottky junction structure using an InGaAs layer as an active layer and a lattice-mismatched InGaP layer as a barrier layer (first conventional example: Journal)
of Applied Physics, September 1992, Vol. 72, No. 6, pp. 2347-2355) or a Schottky junction structure using an InAlAs layer as an active layer and a lattice-mismatched InGaP layer as a barrier layer (No. Conventional Example 2: IEEE Electron Dev
ice Letters, May 1993, Vol. 14, No. 5, pp. 259-261) are known. In these conventional examples, the lattice-mismatched InGaP barrier layer is a distorted layer having a thickness less than the critical thickness and having no transition, and has a band gap larger than that of the lattice-matched InAlAs layer. It is expected that the key barrier can be raised.

There is also known a Schottky junction structure in which an InAlAs layer is used as an active layer and a barrier layer made of a lattice-mismatched InAlP layer is inserted between the active layer and a metal electrode (IEEE Electron Device).
Letters, January 1994, Vol. 15, No. 1, 3
3-35). In this structure, since the InAlP layer having a large band gap is used as a barrier layer, the Schottky barrier can be improved.

Further, an InAlAs layer is used as an active layer, and an undoped InAlAs layer is provided between the active layer and the metal electrode.
There is known a Schottky junction structure in which a first barrier layer made of a layer and a second barrier layer made of a lattice-mismatched AlGaAs layer are inserted (fourth conventional example: JP-A-6-27565).
No. 6). The second barrier layer is provided to prevent oxidation of the InAlAs layer (first barrier layer).

[0009]

However, a Schottky diode or an ME using an InGaP layer as a barrier layer as shown in the first conventional example and the second conventional example.
In the SFET, no improvement in the Schottky barrier is observed at all, and a leak current still occurs. In addition, since the thickness of the InGaP barrier layer is small, a tunnel current may flow from the metal electrode.

In the second to fourth conventional examples, an InAlAs layer is used as an active layer. In order to lattice-match the InAlAs layer with the InP substrate, the Al composition must be 4
Must be 8%. When such an InAlAs layer having a large Al composition is used, a high-density deep level is formed inside the InAlAs layer and at an interface with another semiconductor layer, so that device characteristics are deteriorated. For example, HE
When an InAlAs layer is used for the electron supply layer of the MT, a delay occurs in the modulation of the gate potential of electrons. In addition, since InAlAs having a large Al composition is thermally unstable, there is a problem that the operation state changes with time. This problem is caused by InA as in the fourth conventional example.
Even when the 1As active layer is covered with the second barrier layer (AlGaAs layer), it poses a serious problem.

Further, the InAlP used in the third embodiment
Since the barrier layer is very thin, less than the critical thickness, a tunnel current may flow from the metal electrode through the barrier layer.

The present invention has been made in order to solve the above-mentioned problem, and is a semiconductor device using a Schottky junction, which can reduce a leak current and obtain high reliability. It is intended to provide a device.

[0013]

According to the present invention, there is provided a semiconductor device comprising:
Active consisting of an InGaAs layer formed on an InP substrate
Layer and an undoped InP layer formed in contact with the active layer
A first Schottky barrier enhancement layer made of
Undoped I formed in contact with the key barrier enhancement layer
a second Schottky barrier enhancement layer comprising an nAlP layer;
A metal electrode connected to the second Schottky barrier enhancement layer;
It is provided with.

[0014]

[0015]

The semiconductor device of the present invention comprises an active layer composed of an InP layer, and an undoped In layer formed in contact with the active layer.
A first Schottky barrier enhancement layer made of a P layer, a second Schottky barrier enhancement layer made of an undoped InAlP layer formed in contact with the first Schottky barrier enhancement layer, and a second Schottky barrier And a metal electrode in contact with the enhancement layer.

A semiconductor device according to the present invention comprises a buffer layer composed of an InP layer formed on an InP substrate and an InGaAs layer.
A first Schottky barrier enhancement layer composed of an undoped InP layer formed in contact with the electron supply layer, a channel layer composed of a layer, a spacer layer composed of an InP layer, an electron supply layer composed of an InP layer, A second Schottky barrier enhancement layer made of an undoped InAlP layer formed in contact with the first Schottky barrier enhancement layer; and a metal electrode connected to the second Schottky barrier enhancement layer. is there.

[0018]

In the semiconductor device of the present invention , an active layer having a large Al composition (such as InAlAs) is not used, and
An aAs layer or an InP layer is used. In these materials, generation of a deep level in a layer or at an interface with another semiconductor is hardly observed. For this reason, it is possible to suppress the deterioration of the device characteristics and the change over time in the operation state.

[0019] In order to use a wide an In Al P layer band gap as the barrier layer, the higher the Schottky barrier, reduces the leakage current due to thermal radiation, the withstand voltage characteristic is improved.

[0020] In the semiconductor device of the present invention, the first barrier layer made of InP layer between the second barrier layer and the active layer made of an In Al P is formed. This first barrier layer is In
Since it is the same material as the P substrate, it is possible to increase the film thickness to some extent. For this reason, a tunnel current transmitted through the barrier layer can be suppressed.

The semiconductor device of the present invention, by being provided with an In Al P barrier layer (second barrier layer), it is possible to suppress the leakage current in the gates.

[0022]

【Example】

(First Embodiment) FIG. 1 shows a sectional structure of a Schottky diode according to a first embodiment of the present invention. In FIG. 1, 1 is an n-type InP substrate, and 2 is
000 nm n-type InP buffer layer, 3 has a thickness of 100
In ₀ of _{0nm. 5 3 Ga 0. 4} 7 As active layer, an undoped In ₀ thickness of 11nm is _{6. 7 5 Al 0. 2} 5 P
The barrier layer 7 is a metal electrode.

The thickness of the InAlP barrier layer 6 is set to be equal to or less than the critical thickness in consideration of occurrence of lattice irregularity with the InP substrate 1. Therefore, a dislocation-free strained layer is obtained. The reason why this layer is undoped is that an impurity level causing a tunnel current is not generated.

FIG. 2 is an energy band structure diagram of the Schottky diode of FIG. 1 when a reverse bias is applied. Since the InAlP barrier layer 6 having a wide band gap is interposed between the InGaAs active layer 3 and the metal electrode 7, the Schottky barrier is increased, and the leakage current Ie due to thermal radiation is suppressed.

Table 1 shows characteristics of the Schottky diode having this structure (leakage current density and Schottky barrier when a voltage of 1 V is applied in the reverse direction). Here, for comparison, the characteristics in the case where an InGaP layer is used as a barrier layer (first conventional example) are also described.

[0026]

[Table 1]

As shown in Table 1, the Schottky barrier of the Schottky diode of this embodiment is high, so that the leak current can be reduced to 1/20 or less of the first conventional example.

Since the InGaAs active layer 3 is used, a deep level hardly occurs in the layer or at the interface with another semiconductor. For this reason, it is possible to suppress the deterioration of the device characteristics and the change over time in the operation state.

However, in this example, the InAlP barrier layer 6 and the I
The conduction band edge discontinuity ΔEc ₁ between the nGaAs active layer 3 and the nGaAs active layer 3 is large, and the thickness of the InAlP barrier layer 6 is small.
A tunneling current It flowing through the InAlP barrier layer 6 may be generated.

(Second Embodiment) FIG. 3 is a sectional view showing a structure of a Schottky diode according to a second embodiment of the present invention. In FIG. 3, 1 is an InP substrate, 2 is an n-type InP buffer layer having a thickness of 1000 nm, and 3 is
In ₀ of _{000nm. 5 3 Ga 0. 4} 7 As active layer, 5
Thickness 20nm undoped InP barrier layer (first barrier layer), an undoped In ₀ the thickness 6 11 _{nm. 7 5} A
l _{0. 2 5} P barrier layer (second barrier layer), 7 is a metal electrode.

This embodiment is based on the InGaAs of the first embodiment.
undoped I between the active layer 3 and the InAlP barrier layer 6
The nP barrier layer 5 is inserted, thereby suppressing a tunnel current that cannot be suppressed in the first embodiment.

FIG. 4 is an energy band structure diagram of the Schottky diode when a reverse bias is applied.
Also in this case, the thermal radiation current Ie is suppressed because the InAlP barrier layer (second barrier layer) 6 is used as in the first embodiment. Further, since the first barrier layer 5 made of the same material as the InP substrate 1 is used, the thickness of the barrier layer can be increased, and the tunnel current It can be suppressed. For this reason, the leak current can be further reduced as compared with the first embodiment.

The reason why the InP barrier layer 5 is undoped is that an impurity level causing a tunnel current is not generated.

The thickness of the InP barrier layer 5 is not limited to 20 μm, but is preferably 5 nm or more and 50 nm or less. This is because if the thickness is less than 5 nm, the tunnel current cannot be suppressed, and if the thickness is more than 50 nm, a voltage is hardly applied to the active layer 3.

(Third Embodiment) FIG. 5 is a sectional view showing a structure of a Schottky diode according to a third embodiment. 5, reference numeral 1 denotes an InP substrate;
0 nm n-type InP buffer layer, 4 has a thickness of 1000 n
m of the InP active layer 6 is an undoped I layer having a thickness of 11 nm.
_{n 0. 7 5 Al 0.} 2 5 P barrier layer, 7 is a metal electrode.

The thickness of the InAlP barrier layer 6 is set to be equal to or less than the critical thickness in consideration of occurrence of lattice irregularity with the InP substrate 1. Therefore, a dislocation-free strained layer is obtained. The reason why the InAlP barrier layer 6 is undoped is that an impurity level causing a tunnel current is not generated.

FIG. 6 is an energy band diagram of a Schottky diode according to a third embodiment of the present invention when a reverse bias is applied.

In the structure of this embodiment, the barrier layer 6 made of InAlP having a wide band gap is interposed between the InP active layer 4 and the metal electrode 7, so that a high Schottky barrier is realized and the leak current is reduced. I do.

Further, since the InP active layer 4 is used,
A deep level hardly occurs in the layer or at the interface with another semiconductor. For this reason, it is possible to suppress the deterioration of the device characteristics and the change over time in the operation state.

However, in this example, since the thickness of the InAlP barrier layer 6 is small, when the carrier concentration of the InP active layer 4 is high, the depletion layer width W of the InP active layer 4 becomes narrow, and a tunnel current It occurs. Might be.

(Fourth Embodiment) FIG. 7 shows a sectional structure of a Schottky diode according to a fourth embodiment of the present invention. In FIG. 7, 1 is an InP substrate, 2 is an n-type InP buffer layer having a thickness of 1000 nm, 4 is an InP active layer having a thickness of 1000 nm, and 5 is an undoped InP barrier layer having a thickness of 20 nm (first barrier layer). ) And 6 have a film thickness of 1
Undoped In the _{1nm 0. 7 5 Al 0.} 2 5 P barrier layer (second barrier layer), 7 is a metal electrode.

As described above, in this embodiment, the undoped InP barrier layer 5 is inserted in the structure of the third embodiment. This layer is undoped in order to prevent generation of an impurity level which causes a tunnel current.

FIG. 8 is an energy band diagram of the Schottky diode of FIG. 7 when a reverse bias is applied. As in the second embodiment, the undoped InP barrier layer 5
Is inserted, the thickness of the entire barrier layer can be increased, and the tunnel current It can be reduced even when the carrier concentration of the InP active layer 4 is high.

In the first to fourth embodiments, the InP substrate 1 is of the n-type, but is not limited to this.
It may be semi-insulating. Further, the buffer layer 2 is an n-type InP layer, but is not limited thereto.

Further, the undoped InAlP barrier layer 6
It is not limited to those having an In composition x of 75% and a film thickness of 11 nm. However, the film thickness must be equal to or less than the critical film thickness determined by the In composition x. J. W. Matthew
s et al. (Journal of Crys)
tal Growth, 1974, Vol. 27, 118
-Page 125), the In composition x
Is 75%, the critical film thickness is about 11 nm.

In the first embodiment and the second embodiment,
The n-type InGaAs layer constituting the active layer 3 is lattice-matched to the InP substrate (In composition y is 53%).
It is not limited to this. However, the film thickness must be equal to or less than the critical film thickness determined by the In composition y.

In the third and fourth embodiments, the first barrier layer 5 is formed on the epitaxial layer. However, the present invention is not limited to this, and the first barrier layer 5 may be formed directly on the InP substrate 1.

(Fifth Embodiment) FIG. 9 is a sectional view showing the structure of a HEMT according to a fifth embodiment of the present invention. In this embodiment, the Schottky junction of the fourth embodiment is replaced by HEMT.
It is applied to

In FIG. 9, 1 is an InP substrate, 2 is an InP buffer layer having a thickness of 500 nm, and 8 is a 20 nm film.
Of _{In 0. 5 3 Ga 0.} 4 7 As channel layer, 9 has a thickness of 2 nm InP spacer layer, an electron supply layer of n-type InP 10, 5 has a thickness of 20nm undoped InP barrier layer (second 1 is an undoped I film having a thickness of 11 nm.
_{n 0. 7 5 Al 0.} 2 5 P barrier layer (second barrier layer), 1
1 is a cap layer having a thickness of 2 nm; 7 is a gate electrode;
Is a source electrode, and 13 is a drain electrode.

Here, the InP electron supply layer 10, InP barrier layer 5, undoped InAlP barrier layer 6, gate electrode 7
Constitute the Schottky junction shown in the fourth embodiment. Note that the electron supply layer 10 is an active layer in a Schottky junction.

According to the structure of this embodiment, similarly to the fourth embodiment, the leak current and the tunnel current in the above-described Schottky junction are suppressed. That is, the leak current and the tunnel current in the gate electrode 7 are suppressed. Table 2 shows the experimental results of the leak current value. Here, for comparison,
The values of the leak current described in the second conventional example are also shown.

[0052]

[Table 2]

As shown in Table 2, in the HEMT of this embodiment, the leakage current at the gate electrode 7 when a voltage of -1 V is applied can be reduced to about 1/30 times that of the conventional HEMT.

As described above, in the first to fifth embodiments, the Schottky barrier diode and the HEMT have been described.
It goes without saying that a similar effect can be obtained in MESFET, MSM and the like.

[0055]

As described above, in the semiconductor device according to any one of the first to fifth aspects, since an InGaAs layer or an InP layer is used as an active layer of a Schottky junction, generation of a deep level in the semiconductor layer is prevented. Therefore, the deterioration of device characteristics and the change over time of the operation state can be suppressed, and the reliability is improved.

[0056] In order to use a wide an In Al P layer band gap as a barrier layer, reduces the leakage current due to thermal radiation, the withstand voltage characteristic is improved.

[0057] Further, by forming the first barrier layer made of InP layer between the second barrier layer and the active layer made of an In Al P, it is possible to suppress the tunnel current passing through the barrier layer .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a semiconductor device according to a first embodiment.

FIG. 2 is a diagram illustrating an energy band structure of the semiconductor device of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a structure of a semiconductor device according to a second embodiment.

FIG. 4 is a diagram illustrating an energy band structure of the semiconductor device of FIG. 3;

FIG. 5 is a cross-sectional view illustrating a structure of a semiconductor device according to a third embodiment.

FIG. 6 is a diagram illustrating an energy band structure of the semiconductor device of FIG. 5;

FIG. 7 is a cross-sectional view illustrating a structure of a semiconductor device according to a fourth embodiment.

FIG. 8 is a diagram showing an energy band structure of the semiconductor device of FIG. 7;

FIG. 9 is a sectional view showing the structure of a HEMT according to a fifth embodiment.

[Explanation of symbols]

 Reference Signs List 1 InP substrate 2 InP buffer layer 3 n-type InGaAs active layer 4 n-type InP active layer 5 undoped InP barrier layer 6 undoped InAlP barrier layer 7 gate electrode 8 undoped InGaAs channel layer 10 InP electron supply layer Ie thermal radiation current It tunnel current

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masafumi Shimizu 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-62-73675 (JP, A) JP-A-58- 141576 (JP, A) JP-A-1-119065 (JP, A) JP-A-7-263661 (JP, A) JP-A-55-95370 (JP, A) JP-A-5-74813 (JP, A) JP-A-5-160161 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29/778 H01L 21/338 H01L 29/812 H01L 29/872

Claims (3)

(57) [Claims] 1. InGaAs formed on an InP substrate
And an active layer formed in contact with the active layer.
For first Schottky barrier made of doped InP layer
An upper layer and an electrode formed in contact with the first Schottky barrier enhancement layer.
Second Schottky barrier composed of doped AlAlP layer
Connecting the wall enhancement layer and the second Schottky barrier enhancement layer
Semiconductor device comprising:
Place. 2. An active layer comprising an InP layer, and
A first undoped InP layer formed in contact with the first
A Schottky barrier enhancement layer and the first Schottky barrier
Undoped InAlP layer formed in contact with enhancement layer
A second Schottky barrier enhancement layer comprising
A metal electrode connected to the key barrier enhancement layer.
A semiconductor device, comprising: 3. An InP layer formed on an InP substrate.
Buffer layer and channel layer made of InGaAs layer
And a spacer layer composed of an InP layer and a spacer layer composed of an InP layer.
An electron supply layer and an AND formed in contact with the electron supply layer;
First Schottky barrier enhancement layer composed of an InP layer
Formed in contact with the first Schottky barrier enhancement layer
Schottky made of undoped InAlP layer
A contact between the barrier enhancement layer and the second Schottky barrier enhancement layer.
And a continuous metal electrode.
Body device.