JP2752477B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a semiconductor device, and particularly relates to a high-speed device, HET (hot electron transistor), so that a current gain can be obtained even when a voltage between a collector and a base is low to improve characteristics. And a semiconductor device in which a base layer is provided on a collector layer with a collector barrier layer interposed therebetween. The composition of at least a part of the layer on the collector barrier layer side is continuously changed from the collector barrier layer so that the magnitude of the electron affinity increases in the thickness direction from the collector barrier layer side. To be configured.

The present invention relates to a semiconductor device, and particularly to a high-speed device.
About HET.

[Prior Art] As shown in FIG. 5A, a conventional HET is formed on a subcollector layer 2 made of, for example, n-type In _0.53 Ga _0.47 As.
Collector layer 28 made of n-type In _0.53 Ga _0.47 As, i-type In _0.53
(Al _0.5 Ga _0.5 ) _0.47 As Collector barrier layer 30 of As, n-type
Base layer 8 of In _0.53 Ga _0.47 As, i-type In _0.52 Al _0.48
Emitter barrier layer 10 of As and n-type In _0.53 Ga _0.47 As
Are laminated to form a multilayer heterostructure.

The sub-collector layer 2, the base layer 8, and the emitter layer
On 12 are provided a collector electrode 14, a base electrode 16 and an emitter electrode 18, respectively.

Here, each of the base layer 8 and the collector layer 28 has n
While the type In _0.53 Ga _0.47 As is used, the collector barrier layer uses i-type In _0.53 (Al _0.5 Ga _0.5 ) _0.47 As, which has a smaller electron affinity than n-type InGaAs.
As shown in FIG. 5B, a uniform energy barrier is formed.

For this reason, electrons injected from the emitter layer 12 and reaching the collector barrier layer 30 have received many quantum mechanical reflections. Also, once electrons that have entered the collector barrier layer 30 are scattered in the barrier, there is almost no electric field in the barrier, and therefore, the electrons do not reach the collector layer 28 and do not reach the base layer 8.
Something returned, causing a decrease in current gain.

To solve this problem, the collector barrier layer 30
It is proposed to grade the energy barrier of
Specifically, by changing the composition of InAlGaAs forming the collector barrier layer 30, the barrier is graded, planar doping is performed, and the barrier is graded. Impurities are added to the collector layer 28 side of the collector barrier layer 30. Barriers are graded by doping.

However, in the case of (2), it is difficult to control the composition of InAlGaAs, in the case (2), it is difficult to control the doping amount, and in the case (2), there are problems such as formation of a kink at the bottom of the conduction band.

In addition, it is desirable to inactivate by injecting inert ions into the collector layer 28 immediately below the base electrode 16 to reduce the collector capacitance, thereby increasing the speed. _Since the band gap of _0.53 Ga _0.47 As was narrow, it was difficult to inactivate by inactive ion implantation.

[Problems to be Solved by the Invention] As described above, in the above-described conventional HET, it is difficult to control the composition, it is difficult to control the doping amount of impurities, or the band is not smoothly connected. Therefore, the barrier of the collector barrier layer cannot be formed in a graded manner, and forming a collector barrier layer that generates an electric field such that electrons are accelerated from the base to the collector is still an issue to be solved. .

In addition, since the band gap of the collector layer made of InGaAs is narrow, it is difficult to inactivate the collector layer immediately below the base electrode by ion implantation. Therefore, it is difficult to reduce the collector capacitance and increase the speed. There was a problem that is.

Accordingly, the present invention provides a semiconductor device capable of improving current characteristics by obtaining a current gain even when the voltage between the collector and the base is low, and realizing a high-speed operation by reducing the collector capacitance. With the goal.

[Means for Solving the Problem] The above object is achieved by a semiconductor device in which a base layer is provided on a collector layer via a collector barrier layer, at least a part of a region of the collector layer on the collector barrier layer side. Is continuously changed from the collector barrier layer such that the magnitude of the electron affinity increases in the thickness direction from the collector barrier layer side.

Further, in the above-described device, the present invention is achieved by a semiconductor device, wherein the composition ratio of the region of the collector layer continuously changes in a thickness direction.

Further, in the above-described device, the present invention is achieved by a semiconductor device, wherein the composition ratio of the region of the collector layer changes stepwise in the thickness direction.

Still further, in the above-described device, the present invention is achieved by a semiconductor device in which an inactive region is formed in the collector layer below a base electrode provided on the base layer by injecting inert ions.

[Operation] Since the present invention is configured as described above, the composition ratio of at least a part of the collector layer on the collector barrier layer side changes continuously or stepwise in the thickness direction. As a result, since the magnitude of the electron affinity increases in the thickness direction from the collector barrier layer side, the conduction band bottom of the collector layer is inclined without gentle kink, and at the same time, the collector barrier layer in contact with the collector layer is in contact with the collector layer. By lowering the energy level at the bottom of the conduction band, the barrier height of the collector barrier layer can be reduced from the base toward the collector.

In addition, since the graded layer such as the gradient layer or the staircase layer of the collector layer has the same composition as the composition forming the collector barrier layer, the band gap becomes large, so that the collector layer immediately below the base electrode becomes inactive. The passivation region can be formed by implanting ions, and the collector capacitance can be easily reduced.

[Examples] Hereinafter, the present invention will be specifically described based on the illustrated examples.

FIG. 1 is a cross-sectional view showing a cross section of an HET according to a first embodiment of the present invention. FIGS. 2 (a) to 2 (c) show the composition of each layer corresponding to the HET of FIG. It is a figure which shows the quantity and the energy level of the conduction band bottom.

As shown in FIG. 1, for example, n-type In _0.53 Ga _0.47 As
N-type In on the sub-collector layer 2
_0.53 consist _{(Al x Ga 1-x)} 0.47 As, the collector layer 4 having a thickness of 2000Å which x value of Al composition is varied is formed. Then, on this collector layer 4, i-type In _0.53 (Al _0.5 Ga _0.5 )
_3000Å thick collector barrier layer 6 of _0.47 As, n-type
300 mm thick base layer 8 of In _0.53 Ga _0.47 As, i-type I
n Emitter barrier layer 10 of 200 mm thick consisting of _0.52 Al _0.48 As
And an emitter layer 12 made of n-type In _0.53 Ga _0.47 As and having a thickness of 2000 ° is laminated to form a vertically stacked multilayer hetero structure.

The sub-collector layer 2, the base layer 8, and the emitter layer
On 12 are provided a collector electrode 14, a base electrode 16 and an emitter electrode 18, respectively. And base electrode 16
Immediately below the collector layer 4, there is formed an inactive region 20 into which an inactive ion such as H ⁺ (proton), B ⁺ (boron), or O ⁺ (oxygen) is implanted.

Here, the composition of each layer forming the HET in FIG.
As shown in FIG. 1A, in the subcollector layer 2, the base layer 8, and the emitter region layer 12, In _0.53
Ga _0.47 As. The composition of the collector barrier layer 6 is as follows:
In _0.53 Ga _0.47 less In _0.53 than As electron affinity (Al _0.5 Ga
_0.5 ) _0.47 As, and the composition of the emitter barrier layer 10 is In _0.52 Al _0.48 As, which has a smaller electron affinity. The collector layer 4 is In _0.53 (Al _x Ga _1-x ) _0.47 As, and the x value, which is the composition ratio of Al, is from x = 0.5 where the collector barrier layer 6 is in contact with the sub-collector layer 2. X where it touches
= 0 continuously decreasing. That is, the collector layer 4 is a gradient layer in which the Al composition ratio changes continuously.

The doping amount of, for example, Si (silicon) added to each of these layers is, as shown in FIG. 1B, 5 × 10 ¹⁸ cm ^{−3 in} the subcollector layer 2, and
1 × 10 ¹⁷ cm ^{−3 to} the base layer 8 and the emitter region layer 12
× 10 ¹⁸ cm ^-3 , each forming an n-type region. Then, the collector barrier layer 6 and the emitter barrier layer 10
Forms an i-type undoped layer not doped with Si.

The energy level of the conduction band bottom of each layer having the composition and the Si doping amount as shown in FIGS.
The energy band diagram is as shown in FIG.
In this drawing, an In _0.53 Ga _0.47 As to 1 × 10 ¹⁸ cm ^-3 of Si
Is doped, and the energy level at the bottom of the conduction band having an electron density of 1 × 10 ¹⁸ cm ⁻³ is defined as 0 eV.

Here, the barrier height of the collector barrier layer 6 in contact with the base layer 8 is In _0.53 Ga _0.47 As and In _0.53 (Al _0.5 Ga _0.5 ) _0.47
Specified by the difference in electron affinity with As, it is about 0.2 to 0.3 eV. The conduction band bottom of the collector layer 4 is In _0.53
(Al _x Ga _1-x ) 1 × 10 ¹⁷ cm ^{−3 in} the gradient layer of Al composition of _0.47 As
Fig. 2 (c)
As shown in FIG.
The slope is gentle from about 1 eV to 0 eV or less in the subcollector layer 2. At this time, no kink is formed at the bottom of the conduction band.

Therefore, the energy level of the conduction band bottom of the collector barrier layer 6 in contact with the collector layer 4 is also pushed down to around 0.1 eV, so that the conduction band bottom of the collector barrier layer 6 is inclined from the base layer 8 toward the collector layer 4. Will be.
That is, the height of the barrier of the collector barrier layer 6 is gradedly reduced from the base layer 8 to the collector layer 4.

Thus, an electric field is generated in the collector barrier layer 6 due to the graded decrease in the barrier height of the collector barrier layer 6. Therefore, from the emitter layer 12 to the emitter barrier layer 10
Are injected into the base layer 8 through the base layer 8 and reach the collector barrier layer 6, so that the electrons are hardly subjected to quantum mechanical reflection by the barrier of the collector barrier layer 6. Further, even if the electrons once entering the collector barrier layer 6 are scattered in the collector barrier layer 6, the ratio of the electrons toward the collector layer 4 is increased by the electric field of the collector barrier layer 6, and the distance between the base and the collector is increased. Even when the voltage is low, a current gain can be obtained.

An inactive region 20 into which inactive ions are implanted is formed in the collector layer 4 directly below the base electrode 16,
For example, in the conventional example shown in FIG. 5, In _0.53 Ga _0.47 As
The collector layer 28 made of
It has been difficult to form inert regions by implanting inert ions.

However, in the first embodiment, the collector layer 4
By having In _0.53 (Al _x Ga _1-x ) _0.47 As and an Al composition, as shown in FIG. 2C, the energy level at the bottom of the conduction band of the collector layer 4 becomes In _0.53 It is higher than in the case of Ga _0.47 As, and the top of the valence band is not shown here, but the band gap also becomes large. Therefore, it is possible to easily form a passivation region 20 by implanting a small amount of inert ions into the collector layer 4 having the increased band gap. The formation of the passivation region 20 makes it possible to reduce the collector capacitance and speed up the HET.

When the inert ions are implanted, they are selectively implanted into the collector layer 4 based on the LSS theory. However, some inactive ions are implanted into the base layer 8.
The doping amount of Si added to the base layer 8 in advance is
It is desirable to make the amount of doping of Si relatively larger than that of Si added.

Next, FIG. 3 shows a case where the doping amount of Si added to the collector layer 4 changes.

FIG. 3 (a) shows the composition of each layer of HET,
This is exactly the same as FIG. And FIG. 3 (b)
2 shows two cases where the doping amount of Si added to the collector layer 4 changes by ± 50% to 1.5 × 10 ¹⁷ cm ⁻³ and 0.5 × 10 ¹⁷ cm ⁻³ . In response to ± 50% increase or decrease of this doping amount,
As shown in FIG. 3 (c), the energy level at the bottom of the conduction band of the collector layer 4 also decreases or increases, but the degree of the change is slight. For this reason, the change in the conduction band bottom of the collector barrier layer 6 continuous with the collector layer 4, that is, the height of the barrier is also extremely small.

As described above, the additive is added to the collector layer 4 in which the x value of the Al composition in In _0.53 (Al _x Ga _1-x ) _0.47 As is continuously changing.
Even if there is some variation in the Si doping amount, no significant change occurs because the barrier height of the collector barrier layer 6 decreases from the base layer 8 toward the collector layer 4. That is, the method is generous with respect to the control of the doping amount. Therefore, it can be easily manufactured.

Thus, according to the first embodiment, the collector layer 4
In _0.53 (Al _x Ga _1-x ) _0.47 As, a gradient layer whose x value decreases from the collector barrier layer 6 toward the sub-collector layer 2 is formed, and the collector layer 4 is doped with Si. By doing so, the conduction band bottom of the collector layer 4 is gently inclined, and at the same time, the energy level of the conduction band bottom of the collector barrier layer 6 in contact with the collector layer 4 is lowered, so that the height of the barrier of the collector barrier layer 6 is reduced to the base layer. 8 to the collector layer 4 can be graded.

Accordingly, an electric field is generated in the collector barrier layer 6, and electrons injected from the emitter layer 12 and reaching the collector barrier layer 6 are hardly subjected to quantum mechanical reflection by the barrier of the collector barrier layer 6. Even if the entered electrons are scattered, they are pulled by the electric field of the collector barrier layer 6 and the ratio of the electrons toward the collector layer 4 increases, so that a current gain can be obtained even when the voltage between the base and the collector is low.

Further, even if the amount of Si doping added to the collector layer 4 slightly varies, a large change does not occur in the inclined barrier of the collector barrier layer 6, so that the doping amount can be easily controlled.

Furthermore, since the collector layer 4 has an Al composition, the band gap becomes large, so that a small amount of inert ions are implanted into the collector layer 4 immediately below the base electrode 16 to easily form the inactive region 20. Therefore, the collector capacitance can be reduced and HET can be speeded up.

In the first embodiment, the entire collector layer 4
In _0.53 (Al _x Ga _1-x ) _0.47 As is a graded layer in which the Al composition is graded, but this graded layer is partially provided only on the collector barrier layer 6 side of the collector layer 4 and the sub-collector The layer 2 side has the same composition as the sub-collector layer 2 and has In _0.53 Ga _0.47 As
May be formed.

Next, an HET according to a second embodiment of the present invention will be described with reference to FIG.

4 (a) to 4 (c) are diagrams respectively showing the composition of each layer of HET, the doping amount of Si, and the energy level at the bottom of the conduction band according to the second embodiment.

As in the first embodiment, a collector layer 22, a collector barrier layer 6, a base layer 8,
The emitter barrier layer 10 and the emitter layer 12 are stacked to form a vertically stacked multilayer hetero structure. Although not shown, on the sub-collector layer 2, the base layer 8, and the emitter layer 12,
Each is provided with a collector electrode, a base electrode, and an emitter electrode. The collector layer 22 directly below the base electrode
Is formed with an inert region into which inert ions are implanted.

As shown in FIG. 4A, the composition of each layer forming the HET is In _0.53 Ga _0.47 As in each of the subcollector layer 2, the base layer 8, and the emitter region layer 12. The composition of the collector barrier layer 6 is In _0.53 Ga _0.47
In _0.53 (Al _0.5 Ga _0.5 ) _0.47 As having an electron affinity smaller than As, and the composition of the emitter barrier layer 10 is In _0.52 Al _0.48 As having a smaller electron affinity.

The collector layer 22 includes a flat layer 24 made of In _0.53 Ga _0.47 As formed on the side of the sub-collector layer 2 and an n-type In layer formed on the side of the collector barrier layer 6 where the x value of the Al composition changes stepwise. And a step layer 26 made of (Al _x Ga _1-x ) _0.47 As.

The x value of In _0.53 (Al _x Ga _1-x ) _0.47 As in the step layer 26 decreases stepwise from x = 0.5 at the point in contact with the collector barrier layer 6 toward x = 0 in the flat layer 24. doing. The step layer 26 is composed of InGaAs and In
By using the pulse molecular beam method alternately for AlAs and controlling the output, Al and Ga of In _0.53 (Al _x Ga _1-x ) _0.47 As
Are formed in such a manner that the composition ratio is changed stepwise.

Also, it is added to each layer shown in FIG. 4 (b).
The doping amount of Si is exactly the same as that shown in FIG. 2 (b), and 5 × 10 ¹⁸ cm ⁻³ ,
The collector layer 22 is 1 × 10 ¹⁷ cm ⁻³ , and the base layer 8 and the emitter region layer 12 are 1 × 10 ¹⁸ cm ⁻³ , each of which forms an n-type region. The collector barrier layer 6 and the emitter barrier layer 10 form an i-type undoped layer not doped with Si.

The energy level at the bottom of the conduction band of each layer having the composition and the doping amount as shown in FIGS. 4A and 4B is as shown in the energy band diagram of FIG. 4C. Here, the energy level at the bottom of the conduction band where the electron density is 1 × 10 ¹⁸ cm ⁻³ is set to 0 eV as a reference.

The conduction band bottom in the step layer 26 of the collector layer 22 is formed by adding 1 × to the n-type In (Al _x Ga _1-x )
By doping with 10 ¹⁷ cm ^-3 of Si, as shown in FIG. 4 (c), it comes into contact with the collector barrier layer 6
It decreases stepwise from near 0.1 eV toward the flat layer 24. The bottom of the conduction band of the flat layer 24 is gently inclined toward 0 eV or less of the sub-collector layer 2 without kink.

Further, the energy level at the conduction band bottom of the collector barrier layer 6 in contact with the step layer 26 of the collector layer 22 is also pushed down to around 0.1 eV, so that in the case of the first embodiment shown in FIG. Similarly, the height of the barrier of the collector barrier layer 6 is gradedly reduced from the base layer 8 to the collector layer 22. Therefore, this collector barrier layer 6
Generates an electric field.

At this time, the fact that the conduction band bottom is stepwise lowered in the step layer 26 of the collector layer 22 does not significantly affect the electric field generated in the collector barrier layer 6.

Since the step gap layer 26 of the collector layer 22 has a large band gap as in the first embodiment, a small amount of inert ions may be implanted to form the inactive region 20. Easy.

Therefore, according to the second embodiment, instead of the gradient layer in which the x value of the Al composition of In _0.53 (Al _x Ga _1-x ) _0.47 As of the collector layer 4 in the first embodiment changes continuously. In addition, the same effect as in the first embodiment can be obtained even if the step layer 26 in which the x value changes stepwise is formed in the collector layer 22 on the collector barrier layer 6 side.

The step layer 26 is provided partially on the collector layer 22 side of the collector layer 22, but may be provided on the entire collector layer 22.

In the first and second embodiments, an InGaAs-InAlGaAs system is used as a semiconductor material. However, the semiconductor material is not limited to this and may be, for example, a GaAs-AlGaAs system or an InGaAsP system. That is, GaAs-AlAs as a sub-collector layer, a graded layer such as an emitter layer, an emitter barrier layer, a base layer, a collector barrier layer, a gradient layer or a step layer of the collector layer, or the like.
−GaAs−Al _0.3 Ga _0.7 As−Al _x Ga _1−x As (x = 0.3 to 0.0) −
GaAs and / or In _0.53 Ga _0.47 As-InAlAs-Al _0.3 Ga
_0.7 As−InP− (InP) _x (InGaAs) _1−x (x = 1.0 to 0.0)
The present invention can be applied to the case where -InGaAs or the like is used.

Although the HET in the first and second embodiments uses a single tunnel barrier layer as an emitter barrier, a resonance tunneling HE using a resonance tunnel barrier is used.
It may be T.

[Effects of the Invention] As described above, according to the present invention, the composition of at least a part of the collector layer on the collector barrier layer side continuously changes from the collector barrier layer, so that the electron affinity is reduced. Since the size increases in the thickness direction from the collector barrier layer side, the energy level at the bottom of the conduction band of the collector barrier layer in contact with the collector layer is depressed to reduce the height of the barrier of the collector barrier layer to the base layer. It can be graded down toward the collector layer, so that a current gain can be obtained even when the voltage between the base and the collector is low.

In addition, the band gap of the collector layer increases, and a small amount of inert ions can be implanted into the collector layer immediately below the base electrode to easily form an inactive region.
The collector capacitance can be reduced.

As a result, the characteristics can be improved and the speed can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an HET according to a first embodiment of the present invention, FIGS. 2 and 3 are diagrams for explaining the HET of FIG. 1, respectively, and FIG. FIG. 5 is a diagram for explaining the HET according to the second embodiment, and FIG. 5 is a diagram for explaining a conventional semiconductor device. In the figure, 2... Sub-collector layer, 4, 22, 28.
6, 30 ... collector barrier layer, 8 ... base layer, 10 ...
Emitter barrier layer, 12 Emitter layer, 14 Collector electrode, 16 Base electrode, 18 Emitter electrode, 20
Inactive region, 24: flat layer, 26: step layer.

Claims (4)

(57) [Claims] 1. A semiconductor device in which a base layer is provided on a collector layer via a collector barrier layer, wherein the composition of at least a part of the collector layer on the collector barrier layer side has a large electron affinity. The semiconductor device continuously changes from the collector barrier layer so that the thickness increases in the thickness direction from the collector barrier layer side. 2. The semiconductor device according to claim 1, wherein a composition ratio of said region of said collector layer continuously changes in a thickness direction. 3. The semiconductor device according to claim 1, wherein a composition ratio of said region of said collector layer changes stepwise in a thickness direction. 4. An apparatus according to claim 1, wherein an inert region is formed in said collector layer below a base electrode provided on said base layer by implanting inert ions. A semiconductor device characterized by the above-mentioned.