JP2964170B2 - Heterojunction field effect 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 heterojunction field effect semiconductor device having improved element characteristics in a high electric field region. In general, a heterojunction field-effect semiconductor device is remarkably faster than a normal field-effect semiconductor device, and is about to be widely used in a logic circuit. However, when such a field-effect semiconductor device is miniaturized, the electric field strength between the source and the drain and immediately below the gate increases, and a valley transition of electrons occurs. When this happens, the effective mass of the electrons increases rapidly and the velocity of the electrons decreases. In addition, the electrons obtained energy from the electric field diffuse widely from the traveling layer to the barrier layer (electron supply layer), and the energy band structure changes to a shape that makes it difficult to generate a two-dimensional electron gas layer. Therefore, unless the problems described above are solved, the expected performance cannot be obtained even if the field effect semiconductor device of this type is miniaturized, that is, highly integrated.

[0002]

2. Description of the Related Art FIG. 5 shows a high electron mobility transistor (h).
high electron mobility tra
3 shows a main part energy band diagram for explaining a conventional example of an nistor (HEMT). In FIG, 2 is an electron transit layer, 3 is a spacer layer, 4 the barrier layer (electron supply layer), the two-dimensional electron gas layer 5, E _V is the valence band top of, E _C is the bottom of the conduction band , L ₂ is at L valley electron transit layer 2, L ₄ is in L valley barrier layer 4, e represents the electron, respectively. The HEMT runs at high speed in the two-dimensional electron gas layer 5 where electrons e are less likely to be scattered or the like in a normal operation state.

[0003]

The HE shown in FIG.
When the MT is miniaturized, as described above, the electric field intensity between the source and the drain and immediately below the gate increases, and the electrons e are accelerated by the high electric field. Therefore, when the electron e obtains excessive energy, the transition diffusion from the Γ valley where the two-dimensional electron gas layer 5 exists to the L valley and the barrier layer 4 occurs, and the electron e transitioning to the L valley has an abrupt effective mass. And the electron velocity decreases. In such a case, the electron mobility decreases and the current-voltage characteristics show negative resistance. The high-energy electrons that have overflowed from the triangular potential to the barrier layer 4 are flattened by eliminating the bending of the energy band, so that the two-dimensional electron gas layer 5 is hardly generated, and the number of two-dimensional electrons is reduced. And the threshold voltage increases. As described above, when an excessive electric field is applied to the HEMT in an attempt to extract a large current, the accelerated electrons make a valley transition,
Alternatively, the electron velocity and the carrier concentration are reduced due to the real space transition. The present invention ensures that the carrier velocity does not increase excessively and the carrier velocity at low electric fields does not decrease even when a certain high electric field is applied.

[0004]

FIGS. 1 and 2 show an energy band diagram of a heterojunction field effect semiconductor device for explaining the principle of the present invention, and the symbols used in FIG. And the same symbol represent the same part or have the same meaning. In the figure, 22 is a carrier running layer, 23 is an intermediate intervening layer, 23A is a spacer layer constituting the intermediate intervening layer 23, 23B is an intermediate layer constituting the intermediate intervening layer 23, and 23C is an intermediate inter layer 23. Intermediate layer, 24
Is a barrier layer (carrier supply layer), and 25 is a two-dimensional carrier layer.
The gas layer, ΔE _C1, is the band discontinuity from the two-dimensional carrier gas layer 25 to the bottom of the conduction band in the spacer layer 23A, and ΔE _C2 is the band discontinuity value in the bottom of the conduction band in the intermediate layer 23B and the barrier layer 24. Band discontinuity between the bottom of the conduction band and L ₂₂
Shows in L valley carrier transit layer 22, L ₂₃ are in L valley intermediate intervening layer 23, L ₂₄ is the at L valley in the barrier layer 24, respectively. In the heterojunction field-effect semiconductor device shown in FIG. 1, the intermediate layer 23 is composed of a spacer layer 23A and an intermediate layer 23B. In the heterojunction field-effect semiconductor device shown in FIG. It is composed of a spacer layer 23A and an intermediate layer 23C. With such a configuration, an excessive increase in the carrier speed is suppressed, and a valley transition or a real space transition of the carrier can be made hard to occur, and the carrier mobility in a low electric field does not decrease.

As described above, in the heterojunction field effect semiconductor device according to the present invention, (1) an electron supply layer (for example, an n-AlGaAs barrier layer 2)
4) and a carrier traveling layer (for example, a non-doped GaAs carrier traveling layer 22), doped with impurities having a lower carrier mobility than the carrier traveling layer and a lower barrier height than the electron supply layer. intermediate layer (e.g. n-Al
The GaAs intermediate layer 23B) and a spacer layer having the same barrier height as the intermediate layer (for example, the i-AlGaAs spacer layer 2)
3A) an intermediate intermediate layer (for example, the intermediate intermediate layer 23) is provided so that the intermediate layer is opposed to the electron supply layer, or (2) between the electron supply layer and the carrier traveling layer. To carrier
Low carrier mobility and high barrier compared to the traveling layer
-Doped quantum wells with lower than that of the electron supply layer
An intermediate layer made of a door (for example, an n-GaAs intermediate layer 23C)
And barrier height (eg, band discontinuity ΔE _c1 )
Low compared to the L valley (eg L valley ₂₂ ) in the rear running layer
Intermediate layer consisting of a large spacer layer and an electron supply layer
Characterized in that it is provided so as to be opposed to .

[0006]

Operation As shown in FIG. 1, the carrier traveling layer 22
The carrier accelerated in the above transitions to the spacer layer 23A and the intermediate layer 23B when the energy exceeding the band discontinuity ΔE _C1 is obtained. The energy of the transferred carrier is reduced due to an increase in effective mass in the intermediate layer 23B, impurity scattering, alloy scattering, and the like. The increase in the effective mass in this case is small compared to the increase in the effective mass due to the transition to the L valley. The carriers that have lost some energy due to the energy relaxation in this way cannot exceed the band discontinuity value ΔE _C2 existing between the intermediate layer 23B and the barrier layer 24, and some of them again Returning to the carrier traveling layer 22, the diffusion of electrons in the real space is minimized, so that the carrier that has gained energy has a large width in the L valley L ₂₂ and the barrier layer 24 in the carrier traveling layer 22. It will not transition to the range. Moreover, as seen in Figure 2, the carrier is accelerated through the carrier transit layer 22, a quantum well bottom of the conduction band to jump over the lower spacer layer 23A than in L valley L ₂₂ in the carrier transit layer 22 In the intermediate layer 23C. For this reason, the number of carriers having higher energy than the bottom of the conduction band in the spacer layer 23A is reduced, and similarly, valley scattering and wide-range real space transition are suppressed.

[0007]

FIG. 3 is a cutaway side view for explaining an embodiment of the HEMT having the energy band structure shown in FIG. 1, and the symbols used in FIG. 1 and FIG. And the same symbol represent the same part or have the same meaning. In the figure, 21 is a substrate, 26 is an insulating film, 27 is a source electrode, 27A is an alloyed region, 28 is a drain electrode,
28A denotes an alloyed region, and 29 denotes a gate electrode.

The main data of various parts of the HEMT shown in FIG. 3 are exemplified as follows. About substrate 21 Material: Semi-insulating GaAs Carrier traveling layer 22 Material: Non-doped GaAs Thickness: 5000 [Å] Spacer layer 23A Material: i-AlGaAs thickness: 60 [Å] About intermediate layer 23B Material: n -AlGaAs impurity: Si impurity concentration: 1 ×
10 ¹⁸ [cm ^-3 ] Thickness: 100 [Å] Barrier layer (carrier supply layer) 24 Material: n-AlGaAs impurity: Si impurity concentration: 1 ×
10 ¹⁸ [cm ^-3 ] Thickness: 500 [Å] For insulating film 26 Material: SiON thickness: 2000 [Å] For source electrode 27 and drain electrode 28 Material: AuGe / Au thickness: 500 [Å] / 2000
[Å] Regarding the gate electrode 29 Material: Al thickness: 500 [Å] In the HEMT having such a configuration, a band from the two-dimensional carrier gas layer 25 to the bottom of the conduction band in the spacer layer 23A. The discontinuous value ΔE _C1 is 200 [meV],
Then, the bottom of the conduction band in the intermediate layer 23B and the barrier layer 24 are formed.
The band discontinuity ΔE _C2 between the bottom of the conduction band at
00 [meV]. The distance between the source and the drain was 2 [μm].

The HEMT shown in FIG. 3 can be easily manufactured by applying a conventionally used technique. (1) Molecular beam epitaxial growth (molecula)
By applying the r beam epitaxy (MBE) method, a non-doped GaAs carrier traveling layer 22, an i-AlGaAs spacer layer 23A, an n-AlGaAs intermediate layer 23B, and n-A are formed on a semi-insulating GaAs substrate 21.
A lGaAs barrier layer 24 is grown. In addition, the MBE method is used for metalorganic vapor deposition (metalorganic vapor deposition).
r phase epitaxy (MOVPE) method. (2) chemical vapor deposition (chemical vapor deposition)
An insulating film 26 made of SiON is formed on the barrier layer 24 by applying deposition (CVD). (3) Resists in photolithography technology
Process and Reactive Ion Etching Using CF _{4 Based} Etching Gas (reactiveion et
By applying a ching (RIE) method, the insulating film 26 is etched to form a source electrode contact window and a drain electrode contact window. (4) A vacuum deposition method and a lift-off method by dissolving and removing the photo-resist film while leaving the photo-resist film as a mask film when the insulating film 26 is etched. Depending on the application, Au
Source electrode 27 and drain electrode 2 made of Ge / Au
8 is formed. (5) An alloying heat treatment is performed at a temperature of 450 ° C. and a time of 3 minutes to form an alloyed region 27A and an alloyed region 28A. (6) Resists in photolithography technology
Process and RI using CF ₄ as etching gas
By applying the E method, the insulating film 26 is etched to form a gate electrode contact window. (7) A vacuum deposition method and a lift-off method by dissolving / removing the photo-resist film while leaving the photo-resist film, which is a mask film when etching the insulating film 26, as they are. Depending on the application, Al
Is formed.

FIG. 4 is a graph showing the currents of the embodiment shown in FIG.
FIG. 9 is a diagram showing voltage characteristics in comparison with those of a conventional example.
In the figure, the vertical axis represents the source-drain current, and the horizontal axis represents the source-drain voltage. The solid line is a characteristic line relating to one embodiment of the present invention and is measured for the HEMT having the intermediate intermediate layer 23. The dashed line is a characteristic line relating to the conventional example, and is obtained by measuring a HEMT without an intermediate intermediate layer. As can be seen from the drawing, in the embodiment of the present invention, that is, in the case of providing the intermediate intermediate layer 23, current saturation does not occur until a high electric field is obtained. Is hardly seen. Therefore, it is considered that the valley transition in the carrier traveling layer 22 was suppressed by the presence of the intermediate intermediate layer 23. If the valley transition is suppressed, it is natural that the real space transition to the barrier layer 24 having the same energy level is also suppressed.

Next, the energy energy shown in FIG.
The embodiment of the HEMT having the band structure is the same as that of the HEMT described with reference to FIG. 3 except that the intermediate layer 23C corresponding to the intermediate layer 23B is a quantum well made of GaAs having a thickness of 50 [Å]. The other components may have the same configuration. The intermediate layer 23C is made of not only GaAs but also A
AlGaAs having a low l-composition can be used.
What is necessary is just to form a quantum well. In this embodiment,
A remarkable improvement in the current-voltage characteristics is observed, and the number of conduction carriers (the number of conduction electrons) in the two-dimensional carrier gas layer 25 due to the interposition of the intermediate layer 23C as a quantum well.
Was not significantly reduced.

[0012]

In the heterojunction field effect semiconductor device according to the present invention, the forbidden band is wide and the forbidden band is narrow between the impurity-added barrier layer (carrier supply layer) and the carrier traveling layer. Further, an intermediate intermediate layer including an intermediate layer to which impurities are added and a spacer layer to which no impurities are added is provided. By adopting this configuration, the carrier traveling in the carrier traveling layer transitions to the L valley and transitions to the intermediate layer before the mobility is suddenly lowered, and the influence of alloy scattering, impurity scattering, increase of effective mass, and the like. Therefore, the carrier mobility does not decrease as much as that caused by the valley transition, and the carrier that has transitioned to the intermediate layer has minimal diffusion in the real space due to the presence of the barrier layer. And therefore,
The characteristics under a high electric field are improved as compared with the conventional one. Further, when the intermediate layer is formed of a quantum well, a larger brake can be applied to the carrier.

[Brief description of the drawings]

FIG. 1 is an energy band diagram of a heterojunction field effect semiconductor device for explaining the principle of the present invention.

FIG. 2 is an energy band diagram of a heterojunction field effect semiconductor device for explaining the principle of the present invention.

FIG. 3 is a sectional side view for explaining an embodiment of the HEMT having the energy band structure shown in FIG. 1;

FIG. 4 is a diagram showing the current-voltage characteristics of the embodiment shown in FIG. 3 in comparison with those of the conventional example.

FIG. 5 is a main part energy band diagram for explaining a conventional example of a high electron mobility transistor.

[Explanation of symbols]

Reference Signs List 22 Carrier running layer 23 Intermediate intermediate layer 23A Spacer layer constituting intermediate intermediate layer 23B Intermediate layer constituting intermediate intermediate layer 23C Intermediate layer constituting intermediate intermediate layer 23 24 Barrier layer (carrier supply layer) 25 Two-dimensional carrier Gas layer ΔE _C1 band discontinuity ΔE _C2 band discontinuity L ₂₂ L valley in carrier running layer 22 L ₂₃ L valley in intermediate intermediate layer 23 L ₂₄ L valley in barrier layer 24

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/337-21/338 H01L 27/095-27/098 H01L 29/775-29/778 H01L 29/80-29 / 812

Claims (2)

(57) [Claims] An impurity-doped medium having a lower carrier mobility and a lower barrier height than an electron supply layer between an electron supply layer and a carrier travel layer. > A heterojunction field-effect semiconductor device, characterized in that an intermediate layer composed of an intermediate layer and a spacer layer having the same barrier height as the intermediate layer is provided so that the intermediate layer faces the electron supply layer. 2. A carrier between an electron supply layer and a carrier traveling layer.
Lower carrier mobility and barrier compared to rear running layer
Height is lower than that of the electron supply layer.
Intermediate layer consisting of sub wells and barrier height are used as carrier traveling layers
Intermediate layer consisting of a spacer layer lower than the L valley in
The layer is provided such that the intermediate layer faces the electron supply layer.
A heterojunction field-effect semiconductor device characterized by the above-mentioned .