JPH0337735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a bipolar type semiconductor device (quantized base transistor: QBT) which has an operating principle completely different from conventional devices and can operate at ultra high speed.

Prior Art and Problems Generally, the operating principle of a bipolar semiconductor device is well known, but its outline will be explained next with reference to FIG.

FIG. 1 is an energy band diagram when a conventional npn type bipolar semiconductor device is in a thermal equilibrium state.

In the figure, E is the emitter, B is the base, C is the collector, E _F is the Fermi level, _EV is the valence band, E _C is the conduction band, and n and p are the conductivity types, respectively.

The basic operating principle of such a bipolar semiconductor device is as follows.

Now, when a forward voltage is applied between emitter E and base B, electrons injected from emitter E to base B travel through base B by diffusion etc.
The signal has been transmitted from emitter E to collector C by reaching .

Therefore, the operating speed of this bipolar semiconductor device is ultimately determined by the time required for electrons to travel from emitter E to collector C by thermal diffusion, that is,
This means that the travel time is regulated by heat diffusion.

In order to overcome the problem that the operating speed of bipolar semiconductor devices is limited by the transit time of electrons due to thermal diffusion, attempts have been made to utilize the resonance tunneling phenomenon of electrons.
The invention is disclosed in Publication No. 3277 or Japanese Patent Application Laid-open No. 105785/1985.

However, in the invention disclosed therein, the basic operating principles of resonant tunneling transistors have not been sufficiently investigated, and therefore the basic functions of a transistor, such as current amplification and power amplification, cannot be performed, and the transistor action is It has become something lacking.

That is, in all of the above-mentioned publications, there is a valley layer (base) sandwiched between barrier layers (emitter and collector).
A transistor is disclosed which is said to operate by resonant tunneling phenomena.

However, in that transistor, the emitter, base, and collector are all of the same conductivity type, for example n, n, n, or even if metal is used for the emitter, the base and collector are of the same conductivity type. .

Therefore, when a positive voltage is applied between the collector and base to operate this transistor, since the base and collector are of the same conductivity type, electrons tunnel from the base to the collector without relying on the resonant tunneling phenomenon. Reactive current will flow. Moreover, this reactive current is larger than the resonant tunneling current from the emitter, which should be normal as a resonant tunneling transistor. The reason for this is that the only tunneling barrier against this reactive current is the collector barrier.

The reactive current from the base to the collector mentioned above is
Naturally, this makes current amplification of the transistor impossible.

Purpose of the Invention The present invention not only enables high-speed operation without being constrained by the travel time due to thermal diffusion of the carrier, but also has basic functions as a transistor such as current amplification and power amplification. Furthermore, the present invention provides a semiconductor device that can be provided with various features as required.

Structure of the Invention In the semiconductor device according to the present invention, 1. a base of one conductivity type (for example, p-type base B) in which sub-bands (for example, sub-bands E ₁ , E ₂ . . . ) for minority carriers can be generated; , the energy is transferred from the base of one conductivity type.
An emitter of the opposite conductivity type is in contact with the base of the one conductivity type via an emitter potential barrier (for example, an emitter potential barrier PB _E ) having a large band gap and a thickness sufficient to cause a tunnel effect. (e.g. n-type emitter E) and a collector potential barrier (e.g. collector
a collector of an opposite conductivity type (for example, an n-type collector _C ) that is in contact with the base of one conductivity type via a potential barrier PB C ), and an emitter is connected to the minority carrier generated at the base via a sub-band. 2. a base of one conductivity type in which a sub-band for the minority carrier can be generated; an emitter made of metal (such as Al) that is in contact with the base of the one conductivity type through an emitter potential barrier having a large band gap and a thickness sufficient to cause a tunnel effect; a collector of the opposite conductivity type that is in contact with the base of the one conductivity type via a collector potential barrier having a larger energy band gap than the base of the base and having a thickness sufficient to cause a tunnel effect; The structure is characterized in that the minority carrier generated at the base undergoes resonant tunneling transition from the emitter to the collector via a sub-band for the minority carrier.

Since the operating principle of the semiconductor device of the present invention having such a configuration is completely different from that of conventional bipolar semiconductor devices, it will be explained next.

FIG. 2 shows an energy band diagram when a semiconductor device according to an embodiment of the present invention is in a thermal equilibrium state, and the same portions as those explained in connection with FIG. 1 are indicated by the same symbols.

In the figure, PB _E is the emitter potential.
barrier, PB _C is the collector potential barrier, E ₁ , E ₂ ... E _o ... is the sub band, L _B is the width (thickness) of base B, Z is from emitter E to collector C
Each shows the direction to go.

Now, the base B sandwiched between the emitter potential barrier PB _E and the collector potential barrier PB _C is substantially two-dimensional, and to the extent that the movement of electrons (carriers) in the Z direction is quantized. The thickness is set to be sufficiently thin, for example, about 50 [Å].

When the base B is formed thin in this way, the base B is in a state like a potential well, in which electrons traveling from the emitter E to the collector C, that is, electrons traveling in the Z direction, are A state is realized in which only energy levels can be assumed. That is, along with the quantization, the base B
sub-bands E ₁ , E ₂ . . . E _{o .} . . are formed.

The energy level E _o of the sub-band is approximately:
That is, when the potential barrier is infinite, E _o = πζ ² n ² /2m ^* L _B ² ζ = h/2π h: blank constant n = energy quantum number m ^* = effective mass of electron ) L _B = given by base width.

Now, in such a semiconductor device, when a forward voltage is applied between the emitter E and the base B,
The energy band diagram in that case changes as seen in FIG.

In FIG. 3, the same parts as those explained in connection with FIG. 2 are indicated by the same symbols.

In the figure, V _EB is the emitter-base voltage,
V _CB is the collector-base voltage, DB is the DeBloglie wave, and the emitter potential barrier PB _E and the collector
The thickness of each potential barrier PB _C is selected to allow electron tunneling.

When voltage is applied as shown,
For example, when electrons with the same energy as energy level _E1 are injected from emitter E in the Z direction,
The electrons reach the collector C with a transmittance of 1, that is, complete transmission, as seen in the de Broglie wave DB.

The process in which these electrons reach collector C from emitter E does not rely on conventional travel, but rather a transition that relies on so-called resonant tunneling, in which they pass through two potential barriers due to the tunnel effect. It is extremely fast.

When operating this semiconductor device as a transistor, it is only necessary to realize energy band alignment using the emitter-base voltage V _EB , and in principle, the base current is not essential for operation.

Therefore, although the input voltage is zero in direct current terms, a displacement current flows to charge the capacitance between the emitter and base, so this becomes a constant current through the circuit, and an ohmic current flows through the emitter and base. AC power is generated due to the resulting Joule loss.

Generally, the output power is determined by the collector current and the collector current.
Since this is the product of the base-to-base voltage V _CB , this semiconductor device has the function of an amplifier.

In addition, if the base-emitter voltage V _EB is increased so that the conduction band E _C of the emitter is aligned between the energy levels E ₁ and E ₂ , the electron transmittance becomes zero. That is, it becomes a state of complete reflection, and the collector current also becomes zero.

Furthermore, when the base-emitter voltage V _EB is increased and, for example, the energy level E ₂ and the conduction band E _C are aligned, complete transmission becomes possible again and a collector current is generated.

Here, the amplification function in the semiconductor device of the present invention will be explained in more detail.

In the semiconductor device of the present invention, the emitter base
The conductivity type of the collector is “n・p・n” or “p・
If the energy band diagram shown in Figure 3 is related to an npn transistor, then When operated by applying an appropriate positive voltage to the collector, electrons (minority carrier in the base) resonantly tunnel from the emitter to the collector. At this time, since there are only holes as major carriers in the base, there is no tunneling to the collector side when a positive voltage is applied to the collector, and therefore no reactive current flows, so it is amplified as a transistor. It can exert its effect.

In this way, the semiconductor device of the present invention, that is,
In addition to its rare high speed, QBT has strong nonlinearity and diverse functions not found in conventional semiconductor devices.

In order to further clarify the above point, Figure 4 shows
FIG. 2 is a diagram comparing and showing the transfer characteristics of a QBT and a conventional bipolar transistor.

In the figure, the vertical axis shows the collector current I _C and the horizontal axis shows the emitter-base voltage V _EB .
A is the characteristic line of the QBT, B is the characteristic line of the conventional bipolar transistor, V ₁ and V ₂ are the emitter-base voltages for aligning the conduction band E _C to the energy levels E ₁ and E _2, respectively. V _EB are shown respectively.

As can be seen from the figure, in a conventional bipolar transistor, the emitter-base voltage V _EB only increases monotonically, but in the QBT, the emitter-base voltage V _EB is V ₁ and V ₂ . Only when a pulsed collector current I _C is generated, this collector current I _C exhibits an extremely nonlinear dependence on the emitter-base voltage V _EB . This characteristic transfer characteristic is effective not only for ordinary binary logic circuits but also for realizing advanced logic circuits such as multivalued logic circuits.Example of the Invention Figure 5 shows a cutaway of a main part of an embodiment of the present invention. It represents a side view.

In the figure, 1 is a semi-insulating GaAs substrate, 2 is a collector, 3 is a collector potential barrier,
4 is a base, 5 is an emitter/potential barrier, 6 is an emitter, 7 is a gold/germanium/gold (Au/Ge/Au) ohmic collector electrode, 8
9 indicates the base electrode of the gold/zinc/gold (Au/Zn/Au) ohmic, and 9 indicates the emitter electrode of the Au/Ge/Au ohmic, respectively.

An example of the material structure, etc. in this embodiment is as follows.

Emitter semiconductor: n-type GaAs Dopant concentration: 4×10 ¹⁸ [cm ^-3 ] Dopant: Si Thickness: 1 [μm] Emitter potential barrier semiconductor: p-type Al _0.3 Ga _0.7 As Dopant concentration: 2×10 ¹⁹ [cm ^-3 ] Dopant: Be Thickness: 20 [Å] Base semiconductor: p-type GaAs Dopant concentration: 2×10 ¹⁹ [cm ^-3 ] Dopant: Be Thickness: 50 [Å] Collector potential barrier semiconductor: p-type Al _0.3 Ga _0.7 As Dopant concentration: 2×10 ¹⁹ [cm ^-3 ] Dopant: Be Thickness: 20 [Å] Collector semiconductor: n-type GaAs Dopant concentration: 4×10 ¹⁷ [cm ^-3 ] Dopant: Si Thickness: 1 [μm] ] Note that the emitter potential barrier and collector potential barrier are p-type, but this is a consideration to prevent the thin base from being filled with a depletion layer extending from the pn junction. For example, increase the dopant concentration of the emitter by 2×
10 ¹⁷ [cm ^-3 ], and if the collector dopant concentration is set to about 2×10 ¹⁵ [cm ^-3 ], the depletion layer will extend to the emitter side or collector side, so even if an i-layer is used, good.

An outline of the process applied when manufacturing this example will be explained.

(a) First, by applying, for example, the molecular beam epitaxy (MBE) method, n is grown on a semi-insulating GaAs substrate 1.
A type GaAs collector 2, a p-type Al _0.3 Ga _0.7 As collector potential barrier 3, a p-type GaAs base 4, a p-type Al _0.3 Ga _0.7 As emitter potential barrier 5, and an n-type GaAs emitter 6 are grown in this order. The n-type GaAs emitter 6 is formed to be sufficiently thick, for example, approximately 1 [μm], so as not to cause penetration when the emitter electrode is later heat-treated for alloying.
If the GaAs emitter 6 is made to have a sufficiently high concentration, the heat treatment described above becomes unnecessary, and therefore it is possible to make it thin.

(b) Perform mesa etching for isolation between elements using, for example, a hydrofluoric acid (HF)-based etching solution. This mesa etching is a semi-insulating GaAs
Continue until substrate 1 is reached.

(c) Form a base pattern photoresist film (not shown) and use the photoresist film as a mask to perform mesa etching until it reaches the n-type GaAs collector 2 using a hydrofluoric acid etching solution. The collector potential barrier 3, the base 4, the emitter potential barrier 5, and the emitter 6 are selectively removed.

(d) Form a photoresist film (not shown) having openings where the emitter electrode and collector electrode are to be formed.

(e) By applying the vapor deposition method, Au/Ge/
An Au film is formed, and then, in order to pattern it by lift-off, the photoresist film is dissolved and removed, and then an alloying process is performed to form a collector electrode 7 and an emitter electrode 9. .

(f) forming a photoresist film (not shown) having a pattern for forming the base electrode 8;
The emitter 6 is selectively removed by dry etching using a CCl ₂ F ₂ based etchant.

(g) By applying the vapor deposition method, Au・Zn/Au
In order to form a film and then pattern it by lift-off, the photoresist film formed in step (f) is dissolved and removed, and then an alloying process is performed to form the base electrode 8. Form and complete.

The embodiments described above are based on the above-mentioned "Structure of the Invention".
It goes without saying that it operates in accordance with the operating principle explained in .

Incidentally, in the semiconductor device of the present invention, the essential items are (1) formation of a sub-band for the minority carrier in the base, (2) formation of an emitter potential barrier with a thickness that can cause a tunnel effect, and This is the formation of a collector potential barrier, and therefore, the material composition etc. need only satisfy the matters (1) and (2) above, and are not limited to the above embodiments. Further, the base does not have to be p-type as in the above embodiments, but may be n-type. Of course, in that case, the conductivity type of the emitter and collector will be p-type.

FIGS. 6 and 7 are diagrams showing electrical characteristics obtained by the embodiment having the semiconductor heterojunction described above.

Figure 6 shows the base-grounded collector characteristics of QBT.

In the figure, the vertical axis represents the collector current I _C , the horizontal axis represents the collector-base voltage V _CB , and the parameter is the emitter current I _E. Incidentally, the temperature T at the time this data was obtained was 77 [K].

Figure 7 shows the transfer characteristics of QBT.

In the figure, the vertical axis shows the collector current I _C and the horizontal axis shows the emitter-base voltage V _EB .
The temperature T in this case was also 77 [K].

The dimensions of the QBT from which these data were obtained are as follows: Emitter electrode width: 1 [μm], emitter electrode length: 50 [μm], emitter-base electrode spacing:
It was 1 [μm].

As can be seen from Figure 6, if the emitter current I _E is 0, the collector current I _C is also almost 0, and it is understood that the emitter current I _E ≒ collector current I _C , and the base current is extremely small. Ru.

This means that the current amplification factor β is large.

Next, various embodiments different from the above-mentioned embodiments will be presented.

A Case of multiple embodiments with semiconductor heterojunction Part 1 Emitter: Ge Emitter potential barrier: GaAs Base: Ge Collector potential barrier: GaAs Collector: Ge Part 2 Emitter: Si _{1-X Ge}・Barrier: Si Base: Si _{1-X Ge X Collector} Potential Barrier: Si _Collector : Si _{1-X Ge}
Ga _1-y As Base: Al _Z Ga _1-Z As Collector Potential Barrier: Al _v
Ga _1-v As Collector: Al _u Ga _1-u As Part 4 Emitter: InSb Emitter potential barrier: CdTe Base: InSb Collector potential barrier: CdTe Collector: InSb Part 5 Emitter: InAs Emitter potential barrier: GaSb Base: InAs Collector Potential Barrier: GaSb Collector: InAs In addition to the materials presented above, select materials that satisfy the conditions that there is a difference in energy gap and that the lattice constants are similar. I can do it.

The present invention is not limited to the above-mentioned junction using a semiconductor, but can also be made of a semiconductor and an insulator, or the emitter may be made of pure metal as long as it can supply a carrier. be.

Next, various embodiments will be shown and explained.

B In case of semiconductor/insulator junction system example Emitter semiconductor: n-type Si Dopant concentration: 10 ¹⁹ [cm ^-3 ] Dopant: As Thickness: 1 [μm] Emitter potential barrier material: SiO ₂ Thickness: 20 [ Å] Base semiconductor: p-type Si Dopant concentration: 4×10 ¹⁹ [cm ^-3 ] Dopant: B Thickness: 50 [Å] Collector potential barrier material: SiO ₂ Thickness: 20 [Å] Collector semiconductor: n-type Si Dopant concentration: 5×10 ¹⁸ [cm ^-3 ] Dopant: As Thickness: 1 [μm] To manufacture a semiconductor device of this semiconductor/insulator system, (a) By applying the MBE method, An n-type Si collector is formed.

(b) A collector potential barrier made of SiO ₂ is formed by transferring the Si substrate to a plasma oxidation chamber and performing plasma oxidation without taking it out into the air.

The pressure inside the oxidation chamber at this time is 10 ^-3
[Torr], the energy may be set to 100 [W].

During the formation of the collector potential barrier made of SiO ₂ by oxidation, for example, by applying the ellipsometry method used to measure the thickness of the oxide film when manufacturing Josephson devices, it is possible to The thickness of the collector potential barrier is measured (in-situ), and oxidation is performed to the set value.

(c) By applying the MBE method again, p-type
Forms a Si base.

In this case, Si becomes polycrystalline or amorphous, but it is easy to convert it into a single crystal using techniques such as electron beam annealing and laser annealing.

(d) After this, the emitter potential barrier and emitter are formed through the same process as above.

(e) To pattern each of the semiconductors or insulators, and to form and complete the required electrodes, a normal manufacturing process for bipolar semiconductor devices may be applied.

C For embodiments with metal emitters Emitter material: Al Thickness: 1 [μm] Emitter potential barrier material: SiO ₂ thickness: 20 [Å] Base semiconductor: p-type Si Dopant concentration: 4×10 ¹⁹ [cm ^{- 3} ] Dopant: B Thickness: 50 [Å] Collector potential barrier material: SiO ₂ Thickness: 20 [Å] Collector semiconductor: n-type Si Dopant concentration: 5×10 ¹⁸ [cm ^-3 ] Dopant: As Thickness: 1 [μm] FIG. 8 represents an energy band diagram of an embodiment having a metal emitter, in which the same parts as those described with respect to FIGS. 1 to 3 are designated with the same symbols. Note that for the sake of simplicity, the bending of the band is omitted from the illustration.

In the figure, emitter potential barrier
PB _E and collector potential barrier PB _C are
Needless to say, it is composed of SiO ₂ .

The structure of this embodiment has the advantage that the series resistance of the emitter can be reduced and that it is easy to form fine emitters.

Moreover, the manufacturing process of this example is
The process is almost the same as in the case of manufacturing "Embodiment of Semiconductor/Insulator Bonding".

Effects of the Invention The semiconductor device according to the present invention has the following features: 1. A base of one conductivity type in which a sub-band for minority carriers can be formed, and an energy band gap larger than that of the base of one conductivity type. an emitter of an opposite conductivity type that is in contact with the base of the one conductivity type through an emitter potential barrier having a thickness sufficient to cause a tunnel effect; and an emitter of an opposite conductivity type that has a larger energy band gap than the base of the one conductivity type a collector of an opposite conductivity type that is in contact with the base of the one conductivity type through a collector potential barrier having a thickness that is thick enough to cause a tunnel effect;
or 2. a base of one conductivity type in which a sub-band for the minority carrier can be generated; an emitter made of metal that is in contact with the base of the one conductivity type via an emitter potential barrier that has a larger energy band gap than the base of the one conductivity type and is thick enough to cause a tunnel effect; a collector of the opposite conductivity type that is in contact with the base of the one conductivity type via a collector potential barrier having a larger energy band gap than the base of the one conductivity type and having a thickness sufficient to cause a tunnel effect; and minority groups generated on the above base.
The configuration is characterized by a resonant tunneling transition of the minority carrier from the emitter to the collector via a sub-band for the carrier.

By adopting this configuration, if the carrier is an electron, when the energy level of the electron injected from the emitter to the base is aligned with the energy level of the sub-band in the base, the electron The electrons can reach the collector through complete transmission, and if the alignment described above cannot be achieved, the electrons will be completely reflected and will not reach the collector.

By the way, the movement of electrons when the alignment is achieved is a transition based on so-called resonance tunneling, which passes through the emitter potential barrier and the collector potential barrier due to the tunnel effect. Unlike the way electrons travel, it is extremely fast.

Further, as is clear from the above description, the collector current is turned on or off depending on whether the alignment is achieved or not. Since this alignment depends on the voltage between the base and emitter, the collector current turns on and off depending on the voltage, and moreover, the alignment can be taken not at one point but at multiple points. Therefore, by applying various base-emitter voltages having different values in a pulsed manner, a collector current flows in a pulsed manner each time alignment is achieved.

Furthermore, as is natural for a device called a transistor, it also has an amplification function, which is its basic function.

Therefore, advanced logic circuits such as ultra-high-speed binary logic circuits and multi-value logic circuits can be easily realized by utilizing such basic functions and the unique transfer characteristics described above.

[Brief explanation of drawings]

Fig. 1 is an energy band diagram of a conventional npn bipolar semiconductor device, Fig. 2 is an energy band diagram of the semiconductor device of the present invention when it is in thermal equilibrium, and Fig. 3 is an energy band diagram of the semiconductor device of the present invention. An energy band diagram when the device is in operation, FIG. 4 is a diagram comparing the transfer characteristics of the semiconductor device of the present invention and a conventional example, and FIG. 5 is a diagram showing the main points of one embodiment of the present invention. 6 is a diagram showing the base ground collector characteristics of an embodiment of the present invention, FIG. 7 is a diagram showing the transfer characteristics of an embodiment of the present invention, and FIG. 8 is a diagram showing the transmission characteristics of an embodiment of the present invention. Each of the other embodiments represents an energy band diagram when the other embodiments are in thermal equilibrium. In the figure, 1 is a semi-insulating GaAs substrate, 2 is a collector, 3 is a collector potential barrier,
4 is a base, 5 is an emitter potential barrier, 6 is an emitter, 7 is a collector electrode, 8 is a base electrode, and 9 is an emitter electrode.

Claims (1)

[Scope of Claims] 1. A base of one conductivity type in which a sub-band for a minority carrier can be generated;
an emitter of an opposite conductivity type that is in contact with the base of the one conductivity type through an emitter potential barrier having a large gap and a thickness sufficient to cause a tunnel effect;・
a collector of the opposite conductivity type that is in contact with the base of the one conductivity type through a collector potential barrier having a large gap and a thickness that can cause a tunnel effect, and a collector of the opposite conductivity type that is formed on the base; A semiconductor device characterized in that the minority carrier undergoes a resonant tunneling transition from the emitter to the collector via a sub-band for the carrier. 2. A base of one conductivity type in which a sub-band for the minority carrier can be generated, and an energy band
an emitter made of metal that is in contact with the base of one conductivity type via an emitter potential barrier having a large gap and a thickness that can cause a tunnel effect;
a collector of the opposite conductivity type that is in contact with the base of the one conductivity type through a collector potential barrier having a large gap and a thickness that can cause a tunnel effect, and a collector of the opposite conductivity type that is formed on the base; A semiconductor device characterized in that the minority carrier undergoes a resonant tunneling transition from the emitter to the collector via a sub-band for the carrier.