JPH04103171A - Resonant tunneling bipolar transistor - Google Patents

Abstract

PURPOSE:To enable a bistable state to be obtained without using an outer load resistor and to obtain a memory cell of high integration by a method wherein the resonant level of base majority carriers is formed but that of base minority carrier is not formed in a quantum well. CONSTITUTION:In a quantum well layer 6a, a resonant level 9a is formed in a valence band, but a resonant level is not present in a conduction band. The above quantum well can be realized by the combination of a barrier layer 5a of InGaAlAs with an InP well layer 6a or the combination of a barrier layer 5a of ZnSSe with a well layer of GaAs. There is a differential negative resistance region in a relation between a base.emitter voltage VBE and a base current IB, if a proper base current IB is selected, a collector current IC can be set in a bistable state where IC is set to a value of either H or L. When a collector current IC is set to a stable value of either H or L, a load resistor is not required. Therefore, a memory cell can be integrated high in density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device having differential negative resistance characteristics, and in particular to a resonant tunneling bibolar transistor.

BACKGROUND OF THE INVENTION Referring to FIG. 5A, a conventional resonant tunneling bibolar transistor (RTBT) is shown in cross-section.

This RTBT has a p-type emitter layer 1. p-type base layer 3. and a p-type collector layer 7. The base layer 3 includes a quantum well layer 6 sandwiched between two barrier layers 5. Emitter layer 1. The base layer 3 and the collector layer 7 are connected to the emitter electrode 8a, the base electrode 8b, and the collector electrode 8C, respectively.

Referring to FIG. 5B, the energy band structure in the RTBT of FIG. 5A is shown. In this energy band structure, an electron resonance energy level 9 exists in the quantum well 6 included in the base 3, but a hole resonance energy level does not exist.

The RTBT shown in FIG. 5A can be operated with a common emitter like a normal bipolar transistor. now,
If we consider the case where we keep the collector-emitter voltage VCE constant and increase the base-emitter voltage By recombining with holes, the base current becomes a base current a.

However, the electrons that did not recombine with the holes in base 3 are
As the base-emitter voltage V[IE increases, it approaches the resonance level 9 and, with the help of thermal energy, the barrier layer 5
Then, it passes through the quantum well layer 6 and reaches the collector 7 .

This flow of electrons is indicated by arrow 10 in FIG. 5B. Since the number of electrons injected into the base 3 increases with the base-emitter voltage VBE, the base current I and the collector current Ic increase with the base-emitter voltage VEIE.

However, as shown in FIG. 5C, if the base-emitter voltage vIIVE is further increased, the energy level of the conductive band at the base-emitter junction becomes flat and higher than the resonance level 9. Therefore, as the base-emitter voltage V[IE increases, the deviation between the energy level of electrons injected from the emitter 1 to the base 3 and the resonance level 9 increases, and the deviation from the resonance state becomes larger. As a result, the collector current l. decreases, and the differential negative resistance of RTBT appears. However, since the base current IB is determined by the number of holes injected from the base 3 to the emitter 1, the Hass current I still increases with increasing base-emitter voltage V[IE.

Figures 5D, 5E, and 5F show the R
It is a graph showing the characteristics of TBT. FIG. 5D shows the relationship between base-emitter voltage vaE and base current III. Figure 5E shows the relationship between base-emitter voltage VBE and collector current Ic, which is (dlo/dV
There is a region of negative differential resistance where E) is zero.

From the relationship between Figures 5D and 5E, the base current (input) Ia and collector current (output) Ic shown in Figure 5F are
The following relationship is obtained. Also in this FIG. 5F, input 1.
There is a region where the output decreases by 1°, contrary to the increase in .

RTBTs having the above characteristics can be applied to memory cells. A memory cell is required to be capable of assuming at least two different stable states. In FIG. 5E, the dashed curve represents the load straight line. That is, if an appropriate load is selected, the load line intersects the collector current curve at three points H, X, and
These intersection points H, X, and L are the operating points of RTBT.

Therefore, the collector current value can take three values, but the collector current value at the intermediate point X is unstable,
There are two stable operating points: H and L.

That is, it can be seen that the RTBT shown in FIG. 5A can take a bistable state, which is two different stable collector current states, by applying an appropriate load resistance, and can be used as a memory cell.

C Problems to be Solved by the Invention] The conventional RTBT has a collector current I as an output. has a differential negative resistance, so an external load resistor is required to obtain two different stable operating states for use in memory cells. Such an external load resistance is not preferable for achieving high integration of memory cells, and there is also a problem that the characteristics of the memory cell are affected by the load resistance.

In view of the problem of the prior art, the object of the present invention is to
An object of the present invention is to provide an RTBT that can be applied to a memory cell without an external load resistance.

[Means for Solving the Problems] A resonant tunneling bipolar transistor according to the present invention includes an emitter layer of a first conductivity type, a base layer of a second conductivity type, and a collector layer of a first conductivity type. One of the layers includes a quantum well layer sandwiched between two barrier layers, and a resonance level of majority carriers of the second conductivity type is formed in the quantum well layer, but a resonance level of minority carriers is formed in the quantum well layer. It is characterized by the fact that no levels are formed.

[Operation] In the RTBT according to the present invention, a resonance level of majority carriers in the base is formed in the quantum well, but a resonance level of minority carriers in the base is not formed, so that the input base current 1. can have differential negative resistance characteristics. Therefore, the RTBT according to the present invention can obtain a bistable state without using an external load resistor, and enables high integration of memory cells.

[Embodiment] Referring to FIG. 1A, a cross-sectional view of a pnp type RTBT according to an embodiment of the present invention is shown. RTB in Figure 1A
T is similar to that of FIG. 5A, but the energy structure of the barrier layer 5a and quantum well layer 6a is different.

Referring to FIG. 1B, the energy band structure in the RTBT of FIG. 1A is shown. Is a resonance level 9a formed in the valence band in the quantum well layer 6a?
There are no resonance levels in the conduction band. Such a quantum well! A combination of an nGaAlAs barrier layer 5a and an InP well layer 6a, or a ZnSSe barrier layer 5a
This can be realized by a combination of and the GaAs well layer 6a.

In the RTBT shown in the mlA diagram, the emitter-base junction and the base-collector junction may be configured as either a homojunction or a heterojunction, but the emitter-base junction is a homojunction to improve hole flow. It is preferable to configure The base electrode 8b is formed in ohmic contact with the portion of the base layer 3 closer to the collector in order to allow holes to tunnel through the barrier layer 5a and the well layer 6a.

In the RTBT of FIG. 1A, the base-emitter voltage V
If aE is increased from 0, the forward bias of the base-emitter junction increases. As understood from Figure 1B,
Some of the electrons 10 injected from the emitter 1 to the base 3 are scattered and become the base current ra, but most of them are the collector current (2). becomes. Therefore, as the base-emitter voltage VaE increases, the collector current! . increases. On the other hand, holes injected from the portion of the base layer 3 closer to the collector approach the resonance level 9a as the base-emitter voltage VEIE increases, and with the help of thermal energy, the holes inject into the barrier layer 5a and the quantum well layer 6a. and reaches emitter 1. This flow of holes is indicated by a dashed arrow 11. Therefore, the base-emitter voltage VBE
As the base current IB increases, the base current IB increases.

However, as shown in FIG. 1C, if the base-emitter voltage VBE is further increased, the holes move away from the resonance level 9a and the deviation from the resonance state increases. As a result, the number of holes injected from the base 3 to the emitter 1 decreases, and a differential negative resistance appears in the base current 1B. However, since there is no resonance level in the conduction band, the collector current l. continues to increase monotonically as the base-emitter voltage VEIE increases.

FIGS. 1D, 1E, and 1F are graphs showing the characteristics of the RTBT shown in FIG. 1A as described above. FIG. 1D shows the relationship between the base-emitter voltage VBE and the base current IB, and there exists a differential negative resistance region where (dII11/dVBE)<O. Figure 1E shows
It represents the relationship between base-emitter voltage V[IE and collector current IC.

From the relationship between FIG. 1D and FIG. 1E, the relationship between the base current (input) Ia and collector current (output) Ic shown in FIG. 1F can be obtained.

As can be seen from FIG. 1F, if an appropriate base current I is selected, the collector current IC can be in a bistable state taking two different stable values H and L. However, the collector current I. When taking these two stable different values H and L, no load resistance is required. Also, 1st A
The RTBT shown in the figure has the same basic structure as a normal bipolar transistor, so it can exhibit an amplification effect.

It will be understood that in the embodiment of FIG. 1A, the portion of the base layer 3 between the emitter layer 1 and the barrier layer 5a may be omitted.

In addition, in the embodiment shown in FIG. 1A, a quantum well 6a is provided in the base 3.
Although the case where a quantum well 6a is provided in the emitter 1 has been described, a quantum well 6a may be formed in the emitter 1 as shown in FIG. 2A. FIG. 2B shows the energy band structure in the RTBT of FIG. 2A.

Furthermore, although npn type RTBTs have been described in the above embodiments, it will be understood that the present invention can also be applied to pnp type RTBTs. The present invention can be applied to a pnp type RTB.
As an example applied to T, FIG. 2C shows the energy band structure in an RTBT that has a similar structure to FIG. 2A or is of the pnp type. In this case, resonance level 9
a is formed in a conductive band.

Furthermore, in the above embodiment, an electric signal is used as an input signal to the base 3, but the base 3
Optical signals can also be used as human input signals. 3rd A
The figure shows an RTBT that inputs an optical signal 2 to the base 3 via the emitter layer 1, and FIG. 3B shows an RTBT that inputs the optical signal 12 directly to the base 3. These RTBTs can be applied in opto-electrical memory cells involving conversion between optical and electrical signals. Moreover, by monolithically integrating these RTBTs and light emitting diodes or semiconductor radars, it becomes possible to form optical-optical memory cells.

Furthermore, in the above embodiments, we have described the case where only the first resonance level is formed in the quantum well, but by also utilizing higher-order resonance levels, it is possible to create multiple stable states and multiple bistable states. You can also get the status. Figures 4A and 4B illustrate the characteristics of an RTBT that can give rise to multiple stable states.

FIG. 4A shows the relationship between the base-to-emitter voltage VaE and the base current 16, and FIG. 4B shows the relationship between the base current I and the collector current.

As can be seen from FIG. 4B, three stable states H, M, and L can be obtained by selecting an appropriate base current. Similarly, Figures 4C and 4D illustrate the characteristics of an RTBT that can produce multiple bistable states. Figure 4C shows the base-emitter voltage VINE and the base current I.
FIG. 4D shows the relationship between base current I and collector current IC. As can be seen from FIG. 4D, such an RTBT can assume multiple bistable states.

Whether an RTBT can have multiple stable states or multiple bistable states is determined depending on the ratio of the other base currents to the base currents passing through the resonance level. That is, when the current passing through the resonance level forms the majority of the base current flow 6, the RTBT can be in a multi-stable state, and when there is a large amount of current other than the resonance level passing through the base current, the RTBT Multiple bistable states are possible.

[Effects of the Invention] As described above, according to the present invention, the resonance level of the majority carriers in the base is formed in the quantum well, but the resonance level of the minority carriers in the base is not formed, so that the external load resistance It is possible to provide an RTBT that can obtain a bistable state without using. Therefore, when the RTBT according to the present invention is applied to a memory cell, the conventional R
It is possible to achieve higher integration than TBT.

[Brief explanation of the drawing]

FIG. 1A is a cross-sectional view of an RTBT according to an embodiment of the present invention. FIG. 1B and FIG. 1C are diagrams showing the energy band structure in the RTBT of FIG. 1A. Figures 1D, 1E, and 1F represent R of Figure 1A.
It is a figure showing the characteristic of TBT. FIG. 2A shows an RTBT according to another embodiment of the invention.
FIG. FIG. 2B is a diagram showing the energy band structure in the RTBT of FIG. 2A. FIG. 2C shows p
FIG. 3 is a diagram showing an energy band structure in an np type RTBT. FIGS. 3A and 3B are cross-sectional views showing RTBTs according to still other embodiments of the present invention. Figures 4A and 4B show an RTBT that can have multiple stable states.
FIG. Figures 4C and 4D show that R can have multiple bistable states.
It is a figure showing the characteristic of TBT. In the figure, 1 is an emitter, 3 is a base, 5a is a barrier layer, 5a is a quantum well layer, 7 is a collector, 8a is an emitter electrode, 8b is a base electrode, 8c is a collector electrode, 9a is a resonance level, and 10 is an electron , 11 is a hole flow, and 12 is an optical signal. In each figure, the same reference numerals indicate the same contents or corresponding parts.

Claims (1)

[Claims] An emitter layer of a first conductivity type, a base layer of a second conductivity type,
In a bipolar transistor including a collector layer of a first conductivity type, one of the base layer and the emitter layer includes a quantum well layer sandwiched between two barrier layers, and the quantum well layer includes a quantum well layer sandwiched between two barrier layers. A resonant tunneling bipolar transistor characterized in that a resonance level of majority carriers of a second conductivity type is formed but a resonance level of minority carriers is not generated.