JPH0666317B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a bipolar type semiconductor device having a quantized base and capable of operating at an extremely high speed.
By forming a carrier background tunneling prevention layer between the barrier layer and the emitter layer and, if necessary, between the collector barrier layer and the collector layer, all carriers traveling from the emitter to the collector are base. The transition is made dependent on the resonance tunneling through the sub-bands generated in the layer.

[Industrial application field]

The present invention relates to improvements in semiconductor devices that utilize transitions due to resonant tunneling of minority carriers.

[Conventional technology]

The present inventors previously provided a technology relating to a quantized base transistor (QBT) (see, for example, Japanese Patent Application No. 59-75885 and Japanese Patent Application No. 59-75886). ).

FIG. 3 is a cutaway side view showing a conventional QBT.

In the figure, 1 is a semi-insulating GaAs substrate, 2 is an n-type GaAs collector layer, 3 is an i-type AlGaAs collector / barrier layer, and 4 is a p-type.
GaAs base layer, 5 is an i-type AlGaAs emitter / barrier layer, 6
Is an n-type GaAs emitter layer, 7 is an emitter electrode, 8 is a base electrode, and 9 is a collector electrode.

The data of each part in this conventional example is illustrated as follows.

(1) About n-type GaAs collector layer 2 Thickness: 6000 [Å] Impurity: Silicon (Si) Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] (2) About i-type AlGaAs collector / barrier layer 3 Thickness: 30 [Å] (3) About p-type GaAs base layer 4 Thickness: 50 [Å] Impurity: Beryllium (Be) Impurity concentration: 1 × 10 ¹⁹ [cm ^-3 ] (4) i-type AlGaAs emitter / barrier layer 5 Thickness: 30 [Å] (5) About n-type GaAs emitter layer 6 Thickness: 4000 [Å] Impurity: Si Impurity concentration: 1 x 10 ¹⁸ [cm ^-3 ] (6) Emitter electrode 7 Material: Gold (Au) / Germanium (Ge) / Au (7) About base electrode 8 Material: Au / Zinc (Zn) / Au (8) About collector electrode 9 Material: Same as emitter electrode 7 The energy band diagram of the conventional example is shown.

In the figure, the bottom of the conduction band E _C , E _F is the Fermi level,
E _V is the top of the valence band, E ₁ and E ₂ are energy sub-bands, E is the emitter, EB is the emitter barrier, B is the base, CB is the collector barrier, C is the collector, Z is the carrier (here Indicates the direction in which electrons) go from the emitter E to the collector C.

Now, in this QBT, the base B sandwiched between the emitter-barrier EB and the collector-barrier CB is substantially two-dimensional, and the movement of the carrier in the Z direction is sufficiently quantized. It is set thin.

When the base B is thinned in this way, it is in a state like a potential well, in which carriers from the emitter E to the collector C, that is, carriers in the Z direction, have a certain energy level. A state where only the rank can be taken is realized. That is, with the quantization, the base B has energy sub-bands E ₁ , E _2, ...
.. is generated.

Appropriate voltage is applied between the emitter E and the base B and between the collector C and the base B of this QBT, and, for example, carriers having the same energy as the energy sub-band E ₁ are injected from the emitter E in the Z direction. Then, the carrier reaches the collector C with a transmittance of 1, that is, complete transmission.

In the case of QBT, the process in which the carrier reaches the collector C from the emitter E does not depend on the conventional traveling,
It is extremely fast because it is a transition through two potential barriers by the tunnel effect, which is so-called resonant tunneling.

[Problems to be solved by the invention]

As explained above, in QBT, when the energy sub-band and the bottom of the conduction band at the emitter are aligned, the carriers resonantly tunnel from the emitter to the collector through the energy sub-band. However, since the base is extremely thin, the occurrence of bag ground tunneling that occurs through the energy band gap, rather than the carrier transition in the above-described form, cannot be avoided, and If more carriers reach the collector due to this background tunneling, it becomes difficult to obtain a sharp negative resistance in the case of only resonant tunneling.

In addition to the above, the base of the QBT is extremely thin, which may cause depletion of the base layer when contacting the base electrode. Can't act on.

The present invention makes it possible for all carriers going from the emitter to the collector to make a transition depending on resonance tunneling with a very simple modification to the structure of the QBT, and the base electrode works well as an ohmic contact electrode. To be able to.

[Means for solving problems]

In a semiconductor device according to the present invention, an energy sub-band (for example, energy sub-band E ₁ , E _2, ...) Is generated for a minority carrier, and a base layer (for example, base layer 15), Layer energy band
An emitter barrier layer (e.g., emitter barrier layer 16) that has a thickness that is wider than the gap and is thick enough to cause tunneling effects, and a thickness and an impurity concentration that can be fully depleted during operation. Layers that prevent background tunneling of the carrier (eg, back
An emitter layer (for example, an emitter layer 20) facing the base layer via a ground tunneling prevention layer 17),
A collector barrier layer having a width larger than the energy band gap of the base layer and having a thickness capable of causing a tunnel effect (for example, collector barrier layer 1
4) and optionally via a layer that has a layer thickness and impurity concentration that can be fully depleted during operation to prevent carrier background tunneling (eg background tunneling prevention layer 13). A collector layer (for example, collector layer 12) facing the base layer is provided.

[Action]

According to the above structure, even if the base layer is formed so thin as to quantize the carrier movement from the emitter to the collector, the carriers tunnel the energy band gap, that is, Background tunneling is prevented and its operation is extremely fast, since all carriers transition from emitter to collector due to resonant tunneling through the energy sub-band, and also background Since the tunneling prevention layer is present,
Even if the base layer is thin, it does not cause defects such as depletion of the base layer and formation of a good ohmic contact with the base electrode.

〔Example〕

FIGS. 1 (A) to 1 (C) are sectional side views of a main part of a semiconductor device in a process key point for explaining a case of manufacturing an embodiment of the present invention. Hereinafter, these figures will be referred to. I will explain.

See Fig. 1 (A) (1) Molecular beam epitaxial growth
pitaxy: MBE method is applied, the collector layer 12 and the background tunneling prevention layer on the semi-insulating GaAs substrate 11.
13, collector barrier layer 14, base layer 15, emitter barrier layer 16, background tunneling prevention layer 1
7, depletion promoting layer 18, graded layer 19, emitter layer 20
Grow. In addition to the MBE method, metalorganic chemical vapor deposition (metalorganics chemical vapor deposition) is used to grow these semiconductor layers.
A chemical vapor deposition (MOCVD) method can also be applied.

The data of each semiconductor layer are as follows.

About collector layer 12 Material: n-type GaAs Thickness: 6000 [Å] Impurity: Si Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] About background tunneling prevention layer 13 Material: p-type GaAs Thickness: 50 [ Å] Impurity: Be Impurity concentration: 5 × 10 ¹⁸ [cm ^-3 ] About collector / barrier layer 14 Material: i-type AlGaAs Thickness: 30 [Å] Base layer 15 Material: p-type GaAs Thickness: 50 [Å ] Impurity: Be Impurity concentration: 1 × 10 ¹⁹ [cm ^-3 ] Emitter / barrier layer 16 Material: i-layer AlGaAs Thickness: 30 [Å] Back-ground tunneling prevention layer 17 Material: p-type GaAs thickness : 50 [Å] Impurity: Be Impurity concentration: 5 × 10 ¹⁸ [cm ^-3 ] About depletion promoting layer 18 Material: n-type AlGaAs x value: 0.3 Thickness: 200 to 300− (thickness of graded layer 19 ) [Å] impurity: Si impurity concentration: about 1 × 10 ¹⁸ [cm ^-3] graded layer 19 material: i-type AlGaAs x value: 0.3 to 0 (the direction of the emitter layer 20) thickness: 200 300- (thickness of depletion promoting layer 18) [Å] For the emitter layer 20 material: n-type GaAs having a thickness of 4000 [Å] impurity: Si impurity concentration: 1 × 10 ¹⁸ [cm ^-3] Incidentally, back The film thickness and the impurity concentration in the ground tunneling prevention layer 13 depend on the action of the collector layer 12, and the background tunneling prevention layer 17
It is assumed that the film thickness and the impurity concentration in the depletion promoting layer 18 and the graded layer 19 are selected so that the depletion promoting layer 18 and the graded layer 19 completely deplete.
The graded layer 19 and the like have a layer thickness and an impurity concentration sufficient to deplete the background tunneling prevention layer 17, and the background tunneling prevention layer 17 is completely depleted below the emitter electrode. I am trying to change.

See FIG. 1B. (2) A photoresist film (not shown) having a window for forming an emitter electrode is formed by applying a resist process in a normal photolithography technique. Then, an emitter electrode material film is formed by applying a vapor deposition method, and then the photoresist film is dissolved and removed.

By this step, the emitter electrode material film on the photoresist film is patterned by lift-off method,
The emitter electrode 21 is formed. In addition, the emitter electrode 21 may be formed by an appropriate technique such as a reactive ion etching (RIE) method instead of the lift-off method.

Examples of various data regarding the emitter electrode 21 are as follows.

Material: Au ・ Ge / Au / Titanium (Ti) Thickness: 200 [Å] / 1000 [Å] / 500 [Å] (3) Selective dry, where the etchant is a gas whose main component is CCl ₂ F ₂ By applying the etching method,
The emitter layer 20 is etched using the emitter electrode 21 as a mask.

When the selective dry etching method is applied, the etching of the emitter layer 20 is stopped at the surface of the underlying i-type AlGaAs graded layer 19 containing Al appropriately.

See FIG. 1 (C). (4) After applying a resist process in a normal photolithography technique to form a photo resist film having a window for forming a base electrode, an etchant KI: I ₂ : H ₂ O = 10 [g]: 7.6 [g]: 200 [g]
By patterning and etching the graded layer 19 and the depletion promoting layer 18, a base electrode contact window 22 is formed by applying a selective wet etching method using a mixed liquid of HCl and HCl.

(5) A base electrode material film is formed by applying a vapor deposition method, and then the photoresist film is dissolved and removed.

Through this step, the base electrode material film is patterned by the lift-off method to form the base electrode 23.

As described above, the base electrode 23 is configured to directly contact the background tunneling prevention layer 17, and the base layer 15 is not depleted.
The cotact property of is improved. Incidentally, since the emitter / barrier layer 16 is extremely thin, there is no problem.

Examples of various data regarding the base electrode 23 are as follows.

Material: Ti / Platinum (Pt) / Au Thickness: 300 [Å] / 500 [Å] / 2200 [Å] The base electrode 23 is not limited to the above-mentioned embodiment, and Au / Zn / Au may be used.

(6) After forming a photoresist film having a collector electrode forming window by applying a resist process in a normal photolithography technique, for example, hydrofluoric acid (HF) is used as a main component By applying a wet etching method using an etchant, selective etching is performed to a depth from the surface of the graded layer 19 to the surface of the collector layer 12 to expose the region where the collector electrode contacts. Let

(7) A collector electrode material film is formed by applying a vapor deposition method, and then the photoresist film is dissolved and removed.

Through this step, the collector electrode material film is patterned by the lift-off method to form the collector electrode 24.

Examples of various data regarding the collector electrode 24 are as follows.

Material: Au / Ge / Au Thickness: 200 [Å] / 2800 [Å] FIG. 2 is an energy band diagram of a semiconductor device obtained through the steps described in FIGS. 1 (A) to 1 (C). The same symbols as those used in FIGS. 1 and 4 indicate the same parts or have the same meanings.

In the figure, the bending of the energy band indicated by the arrow is due to the presence of the p-type GaAs background tunneling prevention layers 13 and 17.

In this way, when the energy band is bent, a thick barrier due to the bending is present. Therefore, no matter how thin the base B is formed, the carrier is in the energy band band.
It becomes impossible to tunnel through the gap, so that the only carriers going from the emitter E to the collector C are those that transit due to resonant tunneling through the energy sub-bands E ₁ , E _2, ... Becomes

Although the npn type has been described in the above embodiments, the carrier to be handled is an electron, but the present invention can be similarly applied to the pnp type, in which case the conductivity types of the respective semiconductor layers are opposite. The carriers to be handled are, of course, holes. In addition, as another embodiment,
The background tunneling prevention layer 13 may be omitted, and the same effect is obtained in this case as well.

〔The invention's effect〕

In the semiconductor device according to the present invention, a base layer in which a sub band for minority carriers can be generated, and a base layer having a width wider than the energy band gap of the base layer and having a thickness enough to cause a tunnel effect are provided. An emitter barrier layer having a layer thickness and an impurity concentration that can be fully depleted during operation to counteract the base layer through a layer that prevents background tunneling of carriers; and the base layer. And a collector layer facing the base layer via a collector barrier layer having a thickness wider than the energy band gap of the collector layer and having a thickness enough to cause a tunnel effect. .

Due to such a structure, no matter how thin the base layer is formed, the carrier is tunneled through the energy band gap and the background background.
The occurrence of tunneling is suppressed, and the carrier from the emitter to the collector almost depends on the transition due to resonant tunneling, so that a very sharp negative resistance is obtained and the high speed operation performance is improved.

In addition, the base electrode is a background
Since it contacts the tunneling prevention layer, even if the base layer is thinly formed, the base layer is depleted due to the contact of the base electrode, and good ohmic contact performance is lost. Does not occur.

Furthermore, from the viewpoint of manufacturing, as a result, the layer thickness of the semiconductor layer with which the base electrode is to be contacted is increased, which increases the manufacturing margin.

[Brief description of drawings]

FIGS. 1 (A) to 1 (C) are side views of a main part of a semiconductor device at a process step for explaining a case of manufacturing an embodiment of the present invention, and FIG. 2 is described with reference to FIG. The energy band diagram of the semiconductor device obtained by the process, FIG. 3 is a side view of a main part of the conventional example, and FIG. 4 is the energy band diagram of the conventional example shown in FIG. ing. In the figure, 11 is the substrate, 12 is the collector layer, 13 is the background tunneling prevention layer on the collector side, 14 is the collector barrier layer, 15 is the base layer, 16 is the emitter barrier layer, and 17 is the emitter side. Background tunneling prevention layer, 18 is a depletion promoting layer, 19 is a graded layer,
20 is an emitter layer, 21 is an emitter electrode, 23 is a base electrode,
24 shows collector electrodes, respectively.

Claims (1)

[Claims] 1. A base layer in which a sub-band for minority carriers can be generated, and an emitter having a width wider than the energy band gap of the base layer and having a thickness capable of causing a tunnel effect. The barrier layer and an emitter layer facing the base layer through a layer thickness and an impurity concentration that can be fully depleted during operation to prevent carrier background tunneling; and the energy of the base layer. A semiconductor layer having a width larger than the band gap and having a thickness sufficient to cause a tunnel effect, the collector layer facing the base layer. .