JP3032915B2 - High electron mobility transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high electron mobility transistor capable of being highly integrated and capable of shortening a manufacturing process.
ty transistor (HEMT).

At present, in a semiconductor device in which a HEMT is integrated, research and development are being conducted on a non-alloy ohmic contact which does not require a heat treatment for alloying a metal electrode in order to improve the degree of integration. However, various problems have been incidental to this, and for example, stress applied to the semiconductor layer due to its structure is one of them.

[0003]

2. Description of the Related Art FIG. 4 shows a side view of a main part of a standard HEMT for explaining a conventional example. In the figure,
21 is a semi-insulating GaAs substrate, 22 is undoped GaAs
an s channel layer; 23, an n-AlGaAs electron supply layer;
4 is an n ⁺ -InGaAs contact layer, 24A is an opening,
25 indicates a source electrode, 26 indicates a drain electrode, 27 indicates a gate electrode, and 28 indicates piezo polarization.

In this HEMT, the source electrode 25 and the drain electrode 26 are non-alloy ohmic contacts. Usually, a non-alloy ohmic contact is obtained by doping a semiconductor having a low Schottky barrier with a high concentration of impurities to form an electrode made of a high heat-resistant metal. As a semiconductor having a low Schottky barrier, an InGaAs-based semiconductor is frequently used. For example, in a HEMT using a substrate made of GaAs, the molar ratio of InAs in InGaAs is 0.15.
Of the degree is used.

[0005]

As described above, in order to obtain a non-alloy ohmic contact, the contact layer 2 on which the source electrode 25 and the drain electrode 26 are formed is formed.
No. 4 is obtained by doping a high concentration of impurities into InGaAs having a low Schottky barrier.
And it is impossible to obtain good Schottky characteristics.

Therefore, as shown in the figure, an opening 24A is formed by selectively removing the n ⁺ -InGaAs contact layer 24 in the gate region, and an underlying n-AlGaAs electron supply layer is formed in the opening 24A. 23, and a gate electrode 27 is formed thereon.

As can be seen from the above, n ⁺ -I
The formation of the opening 24A in the nGaAs contact layer 24 is an essential component for this type of HEMT. However, in such a case, a compressive stress is generated as shown by an arrow in the figure, and due to this, , Undoped GaAs
Piezo polarization 28 occurs in the channel layer 22. Thus, when the piezo polarization 28 occurs, the threshold voltage of the HEMT fluctuates.

FIG. 5 is a diagram for explaining a change in threshold voltage when piezo polarization occurs. The vertical axis shows the threshold voltage, and the horizontal axis shows the gate length. In the figure, a solid line is a characteristic line of a HEMT having a source electrode and a drain electrode which are normally alloyed so as to reach a channel layer made of GaAs, and a broken line is a non-alloy source electrode and a non-alloyed electrode formed on a contact layer made of InGaAs. A characteristic line of the HEMT in which a drain electrode is formed and a current flows in the [0,1,1] direction is shown by a dashed line. A non-alloy source electrode and a drain electrode are formed in a contact layer made of InGaAs. 1] shows characteristic lines of a HEMT in which a current flows in the direction.

As is apparent from the figure, the threshold voltage of a HEMT having a non-alloy ohmic contact fluctuates. Therefore, especially in the case of an integrated semiconductor device, the whole operation is considered to be unstable. Become.

It is an object of the present invention to reduce the stress in the vicinity of the opening even if an opening is formed in the gate region and to prevent the occurrence of piezo polarization in the channel layer.

[0011]

SUMMARY OF THE INVENTION As described above, I
Forming an opening in a contact layer made of nGaAs causes stress because the lattice constant of InGaAs is Ga.
It is derived from being larger than As.

By the way, in the HEMT, most of the channel layer functions as a buffer layer from the interface with the substrate toward the surface, and an extremely thin two-dimensional electron gas layer is formed on the buffer layer. There is an electron transit layer,
An electron supply layer is laminated on the electron transit layer. The same applies to the case where the carrier is a hole.

As described above, the difference between the lattice constant of the material of the electron supply layer and the lattice constant of the GaAs substrate depends on the lattice constant of the material constituting the contact layer and the lattice constant of the GaAs substrate. Is selected, the stress generated in the vicinity of the opening can be made zero or extremely small even if an opening is formed in the contact layer. It is possible to prevent the occurrence of piezo-polarization that causes the fluctuation of.

Therefore, in the HEMT according to the present invention, (1) the lattice constant with respect to the substrate constituent material (for example, GaAs)
Non-alloy ohmic contact layer material
Of the lattice constant of the material with respect to the substrate
The components are selected so that they are equal and the signs are opposite.
Selected carrier supply layer (eg, n-In _0.34 Ga _0.66
P-electron supply layer 3) and a non-alloy ohmic contact layer (for example, n ⁺ -In _0.15 Ga _0.85 As contact layer 4) laminated on the carrier supply layer. An opening for exposing a part of the carrier supply layer (eg, opening 4A);
A source electrode (for example, source electrode 5) and a drain electrode (for example, drain electrode 6) of a non-alloy ohmic contact formed on the alloy ohmic contact layer; A gate electrode (for example, a gate electrode 7) that is in Schottky contact with the exposed carrier supply layer, or

[0015] (2) the In (1), the GaAs substrate structure material, the lattice constant is small compared to GaAs in the carrier supply layer constituent material _{In 1-x (Ga z Al} 1-z) x
P (x> 0.516) is replaced by a non-alloy ohmic
The present invention is characterized in that In _y Ga _1-y As having a larger lattice constant than GaAs is selected as a contact layer constituent material.

[0016]

The HEMT of the present invention uses a material having a low Schottky barrier so as to favor a non-alloy ohmic contact effective for high integration, and has a high impurity concentration doped contact layer. On the other hand, when an opening for forming a gate is formed, the stress in the vicinity of the opening can be made substantially zero by the action of the carrier supply layer, and therefore, piezo polarization occurs in the channel layer. Therefore, the threshold voltage in the channel does not change.

[0017]

FIG. 1 shows an HE for explaining an embodiment of the present invention.
FIG. 3 is a sectional side view of a main part of the MT, which will be described in detail below. In the figure, 1 is a semi-insulating GaAs substrate, 2 is an undoped GaAs channel layer, 3 is n-In _0.34 Ga
_0.66 P electron supply layer, 4 is an n ⁺ -In _0.15 Ga _0.85 As contact layer, 4A is an opening, 5 is a source electrode, 6 is a drain electrode, and 7 is a gate electrode.

As described above, the substrate is made of H
In EMT, usually non-alloy ohmic
InGaAs is used as the semiconductor for the contact, and the lattice constant of InGaAs is larger than that of GaAs.
In _1-x Ga _x P whose lattice constant is smaller than that of aAs
(X> 0.516) is selected. Therefore, as seen in the above embodiment, the material of the contact layer 4 is In _y
In the case where the InAs molar ratio in Ga _1-y As is y = 0.15, its lattice constant and semi-insulating GaAs are used.
In order to make the difference between the lattice constant of the s substrate 1 and the difference between the lattice constant of the electron supply layer 3 and the lattice constant of the semi-insulating GaAs substrate 1 equal to In _1−x Ga _x P X
The value needs to be 0.66.

FIG. 2 shows the x value and I in In _1-x Ga _x P.
is a diagram showing the relationship in y value and the n _y Ga _1-y As, the vertical axis GaP molar ratio, i.e., the x value, and,
The abscissa indicates the molar ratio of InAs, that is, the y value.

FIG. 3 shows an example of I as in the above-described embodiment.
x value in n _1-x Ga _x P and In _y Ga _1-y As
5 is a diagram for explaining the variation of the threshold voltage in the HEMT in which the y value is selected in FIG. 5. As in FIG. 5, the vertical axis represents the threshold voltage, and the horizontal axis represents the gate length. It is. As is clear from the figure, the HEMT in which the current flows in the [0, 1, 1] direction or the current in the [0, 1, 1] direction is used.
In the HEMT flowing in the [-1] direction, the threshold voltage does not change.

In the HEMT of the embodiment described with reference to FIGS. 1 to 3, the carrier supply layer constituting material is In.
_1-x Ga _x was used P (x> 0.516), the actual case, in order to adjust the energy band gap, Ga _x
Is _replaced by (GazAl1 _-z ) _x , and the z value is selected as needed. In this case, the action of Ga and the action of Al may be considered substantially equal except for the width of the energy band gap. Further, the HEMT according to the present invention can be easily manufactured by using a conventionally used technique and taking ordinary steps, as long as attention is paid to the selection of the composition of the semiconductor layer.

[0022]

In the HEMT according to the present invention, the deviation of the lattice constant from the material constituting the substrate is different from the deviation of the lattice constant of the material constituting the non-alloy ohmic contact layer from the material constituting the substrate. The constituent material is formed in a carrier supply layer selected so as to be equal and opposite in sign, and in a gate region in a non-alloy ohmic contact layer laminated on the carrier supply layer to form a base. An opening for exposing a part of the carrier supply layer; a source electrode and a drain electrode of the non-alloy ohmic contact formed on the non-alloy ohmic contact layer; and an opening formed in the opening. And a gate electrode in Schottky contact with the carrier supply layer exposed in the opening.

By adopting the above-mentioned structure, a material having a low Schottky barrier is used so as to favor a non-alloy ohmic contact effective for high integration.
In addition, when an opening for forming a gate is formed in a contact layer doped with impurities at a high concentration, the stress in the vicinity of the opening can be made substantially zero by the action of the carrier supply layer. Also, no piezo polarization occurs in the channel layer, and the threshold voltage in the channel does not change.

[Brief description of the drawings]

FIG. 1 is a cutaway side view of a main part of a HEMT for explaining an embodiment of the present invention.

FIG. 2 is a graph showing x values of In _1-x Ga _x P and In _y Ga
It is a diagram showing the relationship with the y value in _1-y As.

FIG. 3 shows the x value of In _1-x Ga _x P and In _y G
FIG. 9 is a diagram for explaining a change in threshold voltage in a HEMT in which ay value in a _1-y As is selected.

FIG. 4 is a cutaway side view of a main part of a standard HEMT for explaining a conventional example.

FIG. 5 is a diagram for explaining a change in threshold voltage when piezo polarization occurs.

[Explanation of symbols]

Reference Signs List 1 semi-insulating GaAs substrate 2 undoped GaAs channel layer 3 n-In _0.34 Ga _0.66 P electron supply layer 4 n ⁺ -In _0.15 Ga _0.85 As contact layer 4A opening 5 source electrode 6 drain electrode 7 gate electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 29/778 H01L 21/338 H01L 29/812

Claims (2)

(57) [Claims] 1. The deviation of a lattice constant from a substrate constituent material is as follows:
Before non-alloy ohmic contact layer material
The deviation of the lattice constant from the material of the substrate
The components are selected such that
A carrier supply layer, and an opening formed in a gate region of the non-alloy ohmic contact layer laminated on the carrier supply layer to expose a part of the carrier supply layer as a base, A source electrode and a drain electrode of the non-alloy ohmic contact formed on the non-alloy ohmic contact layer; and a carrier supply layer formed in the opening and exposed in the opening. -A high electron mobility transistor comprising a contacting gate electrode. 2. Indium having a smaller lattice constant than GaAs as a material constituting a substrate and GaAs as a material constituting a carrier supply layer.
_{1-x (Ga z Al 1} -z) x P a (x> 0.516), the non-alloy ohmic contact layer component Ga
2. The high electron mobility transistor according to claim _{1, wherein} In _y Ga _1-y As having a larger lattice constant than As is selected.