JPH04215444A - Hetero junction field effect semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the excess increase of a carrier speed even when a certain high electric field is applied and prevent the carrier speed reduction a low electric field. CONSTITUTION:A middle layer 23 constituted of an impurity doped intermediate layer 23B, which has a narrow forbidden band, and a non-doped spacer layer 23A is provided between impurity doped barrier layers 24 which have a wide forbidden band and a carrier running layer 22. Before a carrier running the carrier running layer 22 moves to an L valley L22 in high electric field, it is moved to the intermediate layer 23B so as to speed down by alloy scattering, impurity scattering, increase of effective mass, etc., and the operation of the barrier 24 suppresses the diffusion in the actual space.

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 with improved device characteristics in a high electric field region. In general, heterojunction field effect semiconductor devices are significantly faster than normal field effect semiconductor devices, and are therefore increasingly being used in logic circuits. However, when this type of field effect semiconductor device is miniaturized, the electric field strength between the source and drain and directly under the gate increases, causing electron valley transition. When this happens, the effective mass of the electron increases rapidly and the velocity of the electron decreases. Further, electrons that have obtained energy from the electric field widely diffuse 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 above-mentioned problems are solved, even if this type of field effect semiconductor device is miniaturized, ie, highly integrated, it will not be possible to obtain the expected performance.

0002

[Prior Art] Figure 5 shows a high electron mobility transistor (h
high electron mobility
This figure shows a main part energy band diagram for explaining a conventional example of a HEMT (transistor: HEMT). In the figure, 2 is an electron transit layer, 3 is a spacer layer, 4 is a barrier layer (electron supply layer), 5 is a two-dimensional electron gas layer, and EV
is the top of the valence band, EC is the bottom of the conduction band, L2 is the L valley in the electron transit layer 2, L4 is the L valley in the barrier layer 4,
e indicates an electron. In this HEMT, in a normal operating state, electrons e travel at high speed through a two-dimensional electron gas layer 5 where they are less likely to be scattered.

0003

[Problem to be solved by the invention] HE seen in Figure 5
When the MT is miniaturized, as described above, the electric field strength between the source and drain and directly under the gate increases, and the electrons e are accelerated by the high electric field. Therefore, when the electron e obtains excessive energy, it transitions and diffuses from the Γ valley where the two-dimensional electron gas layer 5 exists to the L valley and the barrier layer 4, and the effective mass of the electron e that has transitioned to the L valley rapidly increases. increases and the electron velocity decreases. When this happens, electron mobility decreases and current/voltage characteristics exhibit negative resistance. In addition, the high-energy electrons overflowing from the triangular potential to the barrier layer 4 eliminate the bending of the energy band and flatten it, making it difficult to generate the two-dimensional electron gas layer 5, and the number of two-dimensional electrons decreases. As a result, the threshold voltage becomes high. In this way, when an excessive electric field is applied to the HEMT in an attempt to extract a large current, the accelerated electrons undergo valley transition or real space transition, resulting in a decrease in electron velocity and carrier concentration. The present invention prevents the carrier velocity from increasing excessively even when a certain high electric field is applied, and prevents the carrier velocity from decreasing in a low electric field.

0004

[Means for Solving the Problems] FIGS. 1 and 2 show energy band diagrams of a heterojunction field effect semiconductor device for explaining the principle of the present invention, and the symbols used in FIG. The same symbol represents the same part or has the same meaning. In the figure, 22 is a carrier running layer, 23 is an intermediate layer, 23A is a spacer layer that constitutes the intermediate layer 23, 23B is an intermediate layer that constitutes the intermediate layer 23, and 23C is the intermediate layer 23. middle class, 24
25 is a barrier layer (carrier supply layer), and 25 is a two-dimensional carrier layer.
gas layer, ΔEC1 is the band discontinuity value from the two-dimensional carrier gas layer 25 to the bottom of the conduction band in the spacer layer 23A, and ΔEC2 is the value of the conduction between the bottom of the conduction band in the intermediate layer 23B and the barrier layer 24. band discontinuity value between the bottom of the band, L
22 indicates an L valley in the carrier traveling layer 22, L23 indicates an L valley in the intermediate intervening layer 23, and L24 indicates an L valley in the barrier layer 24, respectively. In the heterojunction field effect semiconductor device shown in FIG. 1, the intermediate intervening layer 23 is composed of a spacer layer 23A and an intermediate layer 23B, and in the heterojunction field effect semiconductor device shown in FIG.
3 is composed of a spacer layer 23A and an intermediate layer 23C. With such a configuration, an excessive increase in carrier velocity is suppressed, and carrier trough transition or
Real-space transitions can be made less likely to occur, yet carrier mobility at low electric fields is not degraded.

From the above, in the heterojunction field effect semiconductor device according to the present invention, (1) a barrier layer (for example, n-AlGaAs barrier layer 24) and a carrier transport layer (for example, non-doped GaAs carrier layer 24) are formed. Running layer 2
2) and an intermediate layer (e.g., n-AlGaAs intermediate layer 23B) in which the carrier mobility is lower than that of the carrier transport layer and the barrier height is lower than that of the barrier layer, and the intermediate layer and the barrier height are lower than that of the barrier layer. A spacer layer that is the same (e.g. i-AlGa
(2) The method is characterized in that an intermediate intervening layer (for example, intermediate intervening layer 23) consisting of an As spacer layer 23A) is provided such that the intermediate layer and the barrier layer face each other, or (2) the above (
In 1), the intermediate intervening layer consists of an impurity-doped quantum well (e.g. n-GaAs intermediate layer 23C) and the barrier height (e.g. band discontinuity value ΔEC1) is the L valley in the carrier transport layer. (For example, the L valley L22) is characterized by being composed of a lower spacer layer than the L valley L22.

[0006]

[Operation] As seen in FIG. 1, the carrier running layer 22
The carriers accelerated within the spacer layer 23A and the intermediate layer 23B transition to the spacer layer 23A and the intermediate layer 23B at the time when they obtain energy exceeding the band discontinuity value ΔEC1. The energy of the transitioned carriers is relaxed by an increase in effective mass in the intermediate layer 23B, impurity scattering, alloy scattering, etc. Note that the increase in effective mass in this case is small compared to the increase in effective mass due to transition to the L valley. The carriers that have lost a certain amount of energy due to energy relaxation in this way are transferred to the intermediate layer 23B.
Band discontinuity value ΔEC2 existing between and barrier layer 24
, and a part of the carrier travel layer 22
Since the diffusion of electrons in real space is minimized, the carriers that have obtained energy can migrate to a wide range within the L valley L22 in the carrier transport layer 22 and the barrier layer 24. will disappear. Furthermore, as seen in FIG. 2, the carriers accelerated in the carrier transit layer 22 jump over the spacer layer 23A, where the bottom of the conduction band is lower than the L valley L22 in the carrier transit layer 22, and enter the quantum well. I fall into a certain middle class 23C. For this reason, the number of carriers with energy higher than the bottom of the conduction band in the spacer layer 23A is reduced, and valley scattering and wide range real space transition are also suppressed.

[0007]

[Example] Figure 3 shows a cutaway side view of essential parts to explain an example of a HEMT having the energy band structure shown in Figure 1, and the symbols used in Figures 1 and 2 are used. The same symbol represents the same part or has 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, 2
8A indicates an alloyed region, and 29 indicates a gate electrode.

[0008] The main data of various parts in the HEMT shown in FIG. 3 are exemplified as follows. ■ Regarding the substrate 21 Material: Semi-insulating GaAs ■ Regarding the carrier transport layer 22 Material: Non-doped GaAs Thickness: 5000 [Å] ■
About the spacer layer 23A Material: i-AlGaAs Thickness: 60 [Å] ■ About the intermediate layer 23B Material: n-AlGaAs Impurity: Si Impurity concentration: 1×
1018 [cm-3] Thickness: 100 [Å] ■ Regarding the barrier layer (carrier supply layer) 24 Material: n-AlGaA
s impurity: Si impurity concentration: 1 x 1018 [cm-3]
Thickness: 500 [Å] ■ About the insulating film 26 Material: SiON Thickness: 2000 [Å] ■ About the source electrode 27 and drain electrode 28 Material: AuGe/Au Thickness: 500 [Å]/2000 [Å]
] ■ About the gate electrode 29 Material: Al Thickness: 500 [Å] In a HEMT with such a configuration, there is a band loss from the two-dimensional carrier gas layer 25 to the bottom of the conduction band in the spacer layer 23A. Continuous value ΔEC1 is 200 [meV]
, and the bottom of the conduction band in the intermediate layer 23B and the barrier layer 2
Band discontinuity value ΔEC2 between the bottom of the conduction band at 4
is 100 [meV]. Note that the distance between the source and drain was 2 [μm].

The HEMT shown in FIG. 3 can be easily manufactured by applying techniques that have been widely used in the past. (1) Molecular beam epitaxial growth
By applying the ar beam epitaxy (MBE) method, a non-doped GaAs carrier transport layer 22 and an i-AlGaA layer are formed on a semi-insulating GaAs substrate 21.
s spacer layer 23A, n-AlGaAs intermediate layer 23B,
An n-AlGaAs barrier layer 24 is grown. Furthermore, M.B.E.
The method is metalorganic vapor phase epitaxy (metalorganic vapor phase epitaxy).
vapor phase epitaxy:MOV
PE) method may be used instead. (2) Chemical vapor deposition
By applying CVD), an insulating film 26 made of SiON is formed on the barrier layer 24.
form. (3) Resist process in photolithography technology and reactive ion etching using CF4-based etching gas.
By applying the etching: RIE) method,
The insulating film 26 is etched to form a source electrode contact window and a drain electrode contact window. (4) With the photoresist film, which is the mask film used when etching the insulating film 26, remaining as it is,
By applying a vacuum evaporation method and a lift-off method that involves dissolving and removing the photoresist film, A.
A source electrode 27 and a drain electrode 28 made of uGe/Au are formed. (5) Alloying heat treatment is performed at a temperature of 450 [° C.] and a time of 3 [minutes] to form alloyed regions 27A and 28A. (6) The insulating film 26 is etched to form a gate electrode contact window by applying a resist process in photolithography technology and an RIE method using a CF4-based etching gas. (7) With the photoresist film, which is the mask film used when etching the insulating film 26, remaining as it is,
By applying a vacuum evaporation method and a lift-off method that involves dissolving and removing the photoresist film, A.
A gate electrode 29 made of L is formed.

FIG. 4 shows the current of the embodiment shown in FIG.
FIG. 3 is a diagram showing voltage characteristics in comparison with those of a conventional example. In the figure, the vertical axis shows the source-drain current, and the horizontal axis shows the source-drain voltage. The solid line is a characteristic line related to one embodiment of the present invention, which was measured for a HEMT with an intermediate intervening layer 23. The broken line is a characteristic line for the conventional example, which was obtained by measuring a HEMT without an intermediate intervening layer. As can be seen from the figure, in one embodiment of the present invention, that is, one in which the intermediate layer 23 is provided, current saturation does not occur until the electric field becomes high, and moreover, at low electric fields, there is no difference regardless of the presence or absence of the intermediate layer 23. is hardly seen. Therefore, it is considered that the existence of the intermediate intervening layer 23 suppresses the valley transition in the carrier traveling layer 22. Moreover, 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.

[0011] Next, the energy shown in Fig. 2
As an example of a HEMT having a band structure, the intermediate layer 23C corresponding to the intermediate layer 23B in the HEMT explained with reference to FIG. 3 is a quantum well made of GaAs with a thickness of 50 [Å]. The other configurations may be the same. Note that this intermediate layer 23C is made of not only GaAs but also A
AlGaAs with a low l composition can be used, in short,
It is sufficient if a quantum well is formed. Also in this example,
A significant improvement was seen in the current-voltage characteristics, and the number of conduction carriers (number of conduction electrons) in the two-dimensional carrier gas layer 25 was increased due to the interposition of the intermediate layer 23C, which is a quantum well.
No significant decrease was observed.

0012

[Effects of the Invention] In the heterojunction field effect semiconductor device according to the present invention, the forbidden band width is wide and the forbidden band width is narrow between the impurity-doped barrier layer (carrier supply layer) and the carrier transit layer. Further, an intermediate intervening layer consisting of 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 carriers traveling in the carrier traveling layer transition to the L valley and before their mobility rapidly decreases, they transition to the intermediate layer where they are affected by alloy scattering, impurity scattering, increase in effective mass, etc. Since the increase in speed is suppressed by
The carrier mobility does not decrease to the extent caused by valley transition, and the diffusion of carriers that have transitioned to the intermediate layer in real space is minimized due to the presence of the barrier layer. Therefore, compared to the conventional one, As a result, the characteristics under high electric fields are improved. Furthermore, if the intermediate layer is composed of a quantum well, an even greater brake can be applied to carriers.

[Brief explanation of the drawing]

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 side view with a main part cut away to explain an embodiment of a 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 that 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]

22 Carrier running layer 23 Intermediate intervening layer 23A Spacer layer 23B constituting intermediate intervening layer 23
Intermediate layer 23C constituting intermediate intervening layer 23 Intermediate layer 24 constituting intermediate intervening layer 23 Barrier layer (carrier supply layer) 25 Two-dimensional carrier gas layer ΔEC1 Band discontinuity value ΔEC2 Band discontinuity value L22 To carrier traveling layer 22 L valley L23 in
L valley L24 in intermediate intervening layer 23 L valley in barrier layer 24

Claims (2)

[Claims] 1. Between the barrier layer and the carrier running layer, an intermediate layer having a lower carrier mobility than the carrier running layer and a lower barrier height than the barrier layer, and an intermediate layer and a barrier height. 1. A heterojunction field effect semiconductor device comprising an intermediate intervening layer made of the same spacer layer so that the intermediate layer faces a barrier layer. [Claim 2] A claim characterized in that the intermediate intervening layer is composed of an intermediate layer made of a quantum well doped with impurities and a spacer layer whose barrier height is lower than the L valley in the carrier transit layer. Item 1. Heterojunction field effect semiconductor device.