JPH05102197A - Field-effect transistor - Google Patents

Abstract

PURPOSE:To provide an FET wherein its high-frequency characteristic is excellent, its interface state is small, it is operated stably and its heterointerface is good. CONSTITUTION:A two-dimensional electron gas is generated in a channel layer composed of Inp. An electron supply layer 5 is composed of AlxIn1-xAs in which the compositional ratio (x) of Al is 0.4 or higher and 0.6 or lower; it supplies electrons to the channel layer 3. A spacer layer 4 composed of InyGa1-yAs in which the compositional ratio (y) of In is 0.45 or higher and 0.65 or lower is formed between the channel layer 3 and the electron supply layer 5. The spacer layer 4 is provided with a tickness by which the two- dimensional electron gas is generated in the channel layer 3 by the electrons which are supplied from the electron supply layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed field effect transistor (FET) mainly used for signal frequencies in the microwave band.

[0002]

2. Description of the Related Art FE used in the signal range of microwave band
The T semiconductor material is required to have excellent high frequency characteristics. As a material of this type, In, which has an excellent electron transport property,
There are P-based semiconductor materials. Among these, InP is used for the channel layer, and In _0.52 A _0.48 lattice-matched to this InP.
High electron mobility transistors (HEMT, MODFET) using As in the electron supply layer have excellent high frequency characteristics. For details of this HEMT, refer to the following document “Electronics Letters 10th May 1990 Vol.26 No.10”.
Pp. 651-652.

[0003]

However, such a conventional AlInAs / InP hetero interface has a problem that it is difficult to obtain good interface characteristics. This is because substitution occurs between As and P between the group V elements at the hetero interface to form InPAs or InAlAsP. This phenomenon is described, for example, in 153 of the following document.
It is shown on pages 0-1532.

“Appl.Phys.Lett., Vol.58, No.14,8 April 1991” Therefore, H consisting of the conventional AlInAs / InP heterojunction
Unlike the conventional HEMT including other heterojunctions, the EMT does not have high electron mobility and does not exhibit good high frequency characteristics.

Further, since there are many interface states at the conventional AlInAs / InP hetero interface, there is a problem that the electrical characteristics change depending on whether or not the hetero interface is irradiated with light. Further, there is a problem in that the drain current has hysteresis and the operation becomes unstable.

[0006]

The present invention has been made to solve such a problem, and is a channel layer made of InP in which a two-dimensional electron gas is formed, and Al for supplying electrons to the channel layer. With an electron supply layer made of Al _x In _x-1 As having a composition ratio x of 0.4 to 0.6 and electrons supplied from the electron supply layer provided between the channel layer and the electron supply layer. A heterojunction composed of a semiconductor layer made of In _y Ga _1-y As with a composition ratio y of In having a thickness capable of forming a two-dimensional electron gas in the channel layer is 0.45 or more and 0.65 or less. The FET is formed.

[0007]

A sufficient amount of electrons are supplied from the electron supply layer to the channel layer through the semiconductor layer, the semiconductor layer has a high electron mobility and the substitution of the group V element is unlikely to occur, and the channel layer has a high saturation electron velocity. A two-dimensional electron gas is formed over both layers.

[0008]

1 is a sectional view showing the structure of a HEMT according to an embodiment of the present invention. A method of manufacturing the HEMT will be described below with reference to manufacturing process sectional views of FIG.

First, on the semi-insulating (SI) InP semiconductor substrate 1, a buffer layer 2, a channel layer 3, a spacer layer 4,
The electron supply layer 5 and the contact layer 6 are successively epitaxially grown in sequence (see FIG. 2A). This epitaxial growth is performed by molecular beam epitaxy (MBE) or metalorganic vapor phase epitaxy (OMVPE) method. The buffer layer 2 is made of undoped A _x In _1-x As or InP and has a thickness of 1 μm, the channel layer 3 is made of undoped InP and has a thickness of 150 Å, and the spacer layer 4 is made of undoped In _y Ga _{1-. y}
It is formed to a thickness of 30 Å using As as a material. The electron supply layer 5 is made of n-type A _x In _1-x As and has a thickness of 400 Å.
Is formed to a thickness of 100 angstroms using n-type In _y Ga _1-y As as a material. The electron supply layer 5 has a donor impurity concentration of 2 × 10 ¹⁸ / cm ³ , and the contact layer 6 has a donor impurity concentration of 5 × 10 ¹⁸ / cm ³ .

At this time, in the A _x In _1-x As material forming the buffer layer 2 and the electron supply layer 5, the Al composition ratio x is 0.4 or more and 0.6 or less (0.4 ≦ x ≦ 0.6)
Within the range of, the buffer layer 2 and the electron supply layer 5 are selected to have a composition ratio that lattice-matches the InP semiconductor substrate 1.
The composition ratio x is set to A _0.48 In _0.52 As. The In _y Ga _1-y As material forming the spacer layer 4 and the contact layer 6 has an In composition ratio y of 0.4.
In the range of 5 or more and 0.65 or less (0.45 ≦ y ≦ 0.65), the spacer layer 4 and the contact layer 6 are In
The composition ratio selected for lattice matching with the P semiconductor substrate 1 is In
_The composition ratio y is set to _0.53 Ga _0.47 As.

The spacer layer 4 has a thickness of 30 angstroms so that the electrons supplied from the electron supply layer 5 are sufficiently accumulated in the channel layer 3. That is, the Coulomb force of the donor ions existing in the electron supply layer 5 has a thickness sufficient to reach the two-dimensional electron gas existing in the channel layer 3. Moreover, the thickness of the spacer layer 4 is such that a sufficient spatial distance can be secured between the donor ions of the electron supply layer 5 and the two-dimensional electron gas of the channel layer 3. Further, the InGaAs material forming the spacer layer 4 has a higher electron saturation speed than A InAs forming the electron supply layer 5, and has good high frequency characteristics. Further, the electron mobility is higher than that of the InP material forming the channel layer 3.

Next, each semiconductor layer existing between the transistor formation regions is selectively removed by mesa etching to electrically isolate the elements (see FIG. 2B). Next, the source and drain electrode patterns are patterned on the contact layer 6 by using a normal photolithography technique. Then, AuGe / Ni metal is vapor-deposited on the pattern, and the pattern is lifted off. The electrode metal remaining after the lift-off is alloyed at 400 ° C. for 1 minute to form ohmic contact with the contact layer 6 to form the source electrode 7 and the drain electrode 8 (see FIG. 7C).

Next, the gate electrode is patterned by electron beam lithography or the like, and a recess is formed in the gate electrode formation region portion using this pattern as a mask (see FIG. 3D). After adjusting the recess depth so as to obtain a predetermined drain current, Ti / Pt / Au metal is deposited. After vapor deposition, the electrode pattern is lifted off to form the gate electrode 9, whereby the HEMT having the structure shown in FIG. 1 can be obtained. In FIG. 1, the same parts as those in FIG. 2 are designated by the same reference numerals.

H in such an epitaxial structure
The EMT energy band is shown in FIG. The energy band in the figure is from the left side of the figure to the electron supply layer (n-A
It corresponds to InAs) 5, spacer layer (InGaAs) 4 and channel layer (undoped InP) 3. An energy gap is formed in the spacer layer 4 and the channel layer 3, and a two-dimensional electron gas shown by hatching is formed in this energy gap. Further, an energy barrier for stopping the accumulation of the two-dimensional electron gas is formed between the electron supply layer 5 and the spacer layer 4.

That is, as described above, the spacer layer 4
Is set to a thickness at which sufficient electrons are supplied to the channel layer 3, so that the two-dimensional electron gas shown by the slanted lines is high in the spacer layer 4 made of InGaAs having a high electron mobility. It exists in both layers including the channel layer 3 made of InP having a saturated electron velocity. Also, this In
In the spacer layer 4 made of GaAs, the substitution of the group V element is relatively difficult to occur, and the substitution between As and P hardly occurs as in the conventional case. Moreover, InGaAs has excellent electrical characteristics. Therefore, according to this embodiment, AlI
By inserting the spacer layer 4 made of InGaAs at the hetero interface between nAs and InP, a heterojunction having a high electron mobility and a high saturated electron velocity possessed by the spacer layer 4 and the channel layer 3 is formed. The interface characteristics are greatly improved. As a result, a heterojunction structure exhibiting excellent high frequency characteristics is provided.

Further, in the heterojunction according to the present embodiment, the interface state is greatly reduced, so that the electrical characteristics will not change depending on the presence or absence of light incident on the heterointerface. Further, the operation does not become unstable due to the drain current hysteresis.

[0017]

As described above, according to the present invention, sufficient electrons are supplied from the electron supply layer to the channel layer through the semiconductor layer, the electron mobility is high, and the substitution of the group V element does not occur. A two-dimensional electron gas is formed over both the lei semiconductor layer and the channel layer having a high saturated electron velocity.

Therefore, the interface characteristics of the hetero interface are significantly improved, and the FET exhibits excellent high frequency characteristics. Further, since the interface state is also reduced, the electric characteristics of the FET do not change even when irradiated with light. Further, since the drain current hysteresis does not occur, the FET operates stably.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a HEMT according to an embodiment of the present invention.

2A to 2D are cross-sectional views in each step of manufacturing the HEMT shown in FIG.

FIG. 3 is an energy band diagram of a heterojunction portion of the HEMT shown in FIG.

[Explanation of symbols]

1 ... Semi-insulating semiconductor substrate (InP), 2 ... Buffer layer (undoped A _x In _1-x As or InP), 3 ...
Channel layer (undoped InP), 4 ... spacer layer (undoped _{In y Ga 1-y As)} , 5 ... electron supply layer (n-
A _x In _1-x As), 6 ... Contact layer (n-In _y
Ga _1-y As), 7 ... Source electrode, 8 ... Drain electrode,
9 ... Gate electrode.

Claims (1)

[Claims] 1. A channel layer made of InP in which a two-dimensional electron gas is formed, and A for supplying electrons to this channel layer.
Al _x In _{1-x in which} the composition ratio x of l is 0.4 or more and 0.6 or less
An electron supply layer made of As and a composition ratio of In having a thickness such that a two-dimensional electron gas is formed in the channel layer by electrons supplied between the channel layer and the electron supply layer and supplied from the electron supply layer. A field effect transistor comprising a heterojunction composed of a semiconductor layer made of In _y Ga _1-y As with y of 0.45 or more and 0.65 or less.