JPS63175471A - Semiconductor device - Google Patents

Abstract

PURPOSE:To make non-alloy ohmic contact by supplying sufficient tunnel current by a method wherein a single atomic doped layer is formed close to an interface between a metal and a semiconductor to augment the rate of activation of impurity atom. CONSTITUTION:The first impurity doped single atomic layer 3A is formed on the part near the surface of a semiconductor layer 2 while the second impurity doped single atomic layer 3B is formed in parallel with and inside the first impurity doped layer 3A. Resultantly, the energy level of impurity atom in a single atomic doped layer existing in the part near an interface between a metal and a semiconductor exceeds the Fermi level so that the impurity atom may be sufficiently activated even in high concentration doping process to lower the potential existing close to the interface for supplying a sufficient tunnel current. Through these procedures, non-alloy ohmic contact can be made.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor device, and particularly to a semiconductor device having an impurity doped layer that enables the formation of an ohmic electrode on a semiconductor without going through an alloying process. It is.

[Prior art] As a method of forming a low-resistance ohmic contact by flowing a tunnel current using atomic layer doping, there is a method of doping a single atomic layer in a semiconductor near the interface between a metal and a semiconductor. . An energy band diagram in this method is shown in FIG. This method has two drawbacks as shown below.

(2) First, it is necessary to increase the tunneling current passing through the triangular potential (see Figure 3) formed by the atomically doped layer and the Schottky barrier. For this purpose, the impurity in the atomically doped layer must be highly concentrated and activated. However, when atomic layer doping is performed at a high concentration, the impurity level becomes deep and the impurity is not activated sufficiently. It was not possible to obtain a voltage drop greater than the voltage corresponding to the height of the Schottky barrier, making it difficult to realize a non-alloy ohmic contact.

(2) Next, in order for a single atomic layer doping to cause a voltage drop greater than the voltage corresponding to the height of the Schottky barrier, the doped layer must be separated from the metal-semiconductor interface to some extent. (Appl, P
hys, Lett, ; 49(5), 1986.2
92), L, Kaji: At this time, the triangular potential becomes thick and the electron tunneling probability becomes low, making it difficult to realize a non-alloy ohmic contact.

The voltage drop ΔV when atomic layer doping with a sheet carrier concentration of Nc is performed at a distance d from the interface between the metal and the semiconductor is ΔV=qxdxNc/6 (1) (q is the electron charge, ε is the readout). Electricity) is given by

Here, an example will be described in which GaAs is doped with an atomic layer of St.

Si impurity is added to the atomic layer doped layer at an areal density of 5 x 10”
It has been reported that when only 20% of the cells/cm are added, only 20% of them become donors and are activated (Jpn
, J. Appl, Phys; 25° (1
986), L748), this is because the level of the Si impurity is deep and the impurity is not activated sufficiently.

FIG. 4 shows an example of a semiconductor device having one doped layer made by a conventional method. This conventional example is n-type G
After forming 200 non-doped GaAs layers 2 on an aAs substrate 1, and forming a monoatomic layer doping layer 3 containing Si impurities at an areal density of 5 x 10'' pieces/cm2,
A non-doped GaAs layer 2 is formed again, an AuGeNi ohmic contact 4 is deposited on the back surface, and an Au electrode 5 is deposited on the front surface.

Contact resistance ρ. As shown in FIG. 4, this can be measured by applying a voltage in the direction of the film thickness and measuring the current.

FIG. 5 shows the change in contact resistance ρC depending on d. When d is small, pc is high because the voltage drop due to one atomic layer doped layer is smaller than the voltage corresponding to the Schottky barrier. Furthermore, when d is increased, the triangular potential is thicker, so pc becomes higher. The formula (
In 1), d=60 [in], which corresponds to the height of the Schottky barrier. However, even in this case, ρ0 is high because the triangular potential is thick and sufficient tunnel current does not flow.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned conventional drawbacks, namely, that the activation rate of the doped layer is low and the tunnel current is small, and has a good non-alloy ohmic electrode layer. The purpose is to provide semiconductor devices.

[Means for Solving the Problems] In order to achieve such an object, the semiconductor device of the present invention includes a first impurity-doped monoatomic layer formed near the surface of the semiconductor layer and parallel to the surface. , a second impurity-doped monoatomic layer is formed inside the first impurity-doped monoatomic layer in parallel to the first layer.

[Function] In the present invention, in order to flow a sufficient tunnel current by thinning the potential formed by the monoatomic layer doped layer, the monoatomic layer doped layer is placed sufficiently close to the metal-semiconductor interface to prevent impurities from forming the monoatomic layer doped layer. The activation rate of atoms is made extremely high, and together with the next monoatomic layer doping layer, a voltage drop larger than the voltage corresponding to the height of the Schottky barrier is caused. Even though the impurity levels in the highly doped layer near the interface between the metal and the semiconductor are deep, they are all activated because they are above the Fermi level.

For this purpose, a sufficient tunneling current can be passed, making it possible to realize a non-alloy ohmic contact.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1C shows an embodiment of the present invention.

5 at the position of d=10 [people] as the first impurity doped layer.
A first layer 3A doped with a monoatomic layer of St by X 10'' pieces/crn2 is formed, and a second impurity doped layer 3B with an activation rate of 100 is formed at a position roughly at d=60CAl.
A structure was fabricated in which Si monoatomic layer doping was performed at a concentration of 5 x 10'' atoms/cI112.

When each of the first and second impurity-doped layers is composed of a plurality of atomic layers, electron emission is suppressed by interaction of impurities between the atomic layers. Therefore, both impurity-doped layers must each be a monoatomic layer. To form a monoatomic layer doped with a high concentration of impurities, MOCVD
The flow modulation MOGVD method, which is an improved method, is effective.

At this time, if the activation rate of the first impurity doped layer is 20% as in the conventional example, the voltage drop due to the first layer is ΔV,
=O, 14[V], and the voltage drop due to the second impurity doped layer is ΔV2=0,42[V], so Δv,-1-AV2<φB(0,9V), resulting in low contact resistance. ρ. cannot be obtained. However, when actually performing measurements, ρ. An extremely low contact resistance of the order of = I x 10-' [Ω·cm2] was obtained.

FIG. 2 shows the energy band of a structure in which two monoatomic layers are doped according to the present invention.

In the present invention, since electrons are emitted from the impurity level above the Fermi level, the activation rate of the first layer is substantially increased by 1, resulting in a low contact resistance. The activation rate of impurities can be increased by making the difference between the conduction band and the Fermi level relatively large at the position of The potential for electrons near the interface is thinner than the conventional triangular potential, and a sufficient tunneling current can flow.
It is possible to realize a non-alloy ohmic contact.

Rokukyu Mu Fue 1) Add the 7th doping layer to γ, 5 x 1 G"/cod", 5 x 1
0'2 pieces/cm2, and the positions of the first layer and the second layer from the semiconductor surface were changed to examine changes in resistivity. The results are shown in Table 1. The position of the first layer is from the interface 10
If there are more than 0 people apart and the second layer position is 50
If there were more than 0 people apart, it was not possible to obtain a resistivity as low as 10-6 Ω·cm2. Therefore 10-
In order to obtain a low resistivity on the order of 8 Ω cm2, the positions of the first and second layers should be 100 cm from the surface of the semiconductor.
0 people, preferably 500 or less.

Table 1 [Effects] As explained above, according to the present invention, the energy level of the impurity atoms in the monoatomic layer doped layer existing near the interface between the metal and the semiconductor is higher than the Fermi level,
Even if doping is performed at a high concentration, impurity atoms can be sufficiently activated. For this reason, the potential existing near the interface becomes extremely thin and a sufficient tunneling current can flow, making it possible to realize a non-alloy ohmic contact.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is an energy band diagram in the present invention, FIG. 3 is an energy band diagram in a conventional semiconductor device having a single doped layer, and FIG. 4 is a conventional FIG. 5 is a cross-sectional view of an example of a semiconductor device, and FIG. 5 is a diagram showing contact resistance in a conventional device. 1--.n-GaAs substrate, 2... Non-doped GaAs layer, 3A... First impurity-doped monoatomic layer, 3B... Second impurity-doped monoatomic layer.

Claims (1)

[Scope of Claims] 1) A first impurity-doped monoatomic layer is formed near the surface of the semiconductor layer in parallel with the surface, and the first impurity-doped monoatomic layer causes the first layer to be formed inside the semiconductor layer. A semiconductor device characterized in that a second impurity-doped monoatomic layer is formed in parallel with the . 2) A patent characterized in that the distance from the surface of the first impurity-doped monoatomic layer is within 100 Å, and the distance from the surface of the second impurity-doped monoatomic layer is within 500 Å. A semiconductor device according to claim 1. 3) The doping amount of the first impurity layer is an amount that causes a voltage drop smaller than a voltage corresponding to the height of a Schottky barrier formed when a metal and the semiconductor are brought into contact. A semiconductor device according to claim 1 or 2. 4) The semiconductor device according to claim 1, wherein the amount of voltage drop caused by the first and second impurity layers is larger than the voltage corresponding to the height of the Schottky barrier.