JPS61131491A - Bipolar transistor - Google Patents

Abstract

PURPOSE:To much effectively perform a light coupling as compared with the conventional one by forming a structure that the compositions of the second collector region of a collector layer and a base layer are altered to form the energy gap of the second collector region smaller than that of the base layer. CONSTITUTION:A collector layer 2 is formed of collector regions 2a, 2b, and the composition of a crystal is set to become the relationships of Eg4>Eg3<Eg2 and Eg3>Ebg2 in the magnitude relationship between the energy gaps Eg2 and Eg4 among collector layer 2(2a, 2b), a base layer 3 and an emitter layer 4. In case of Eg4>Eg3, the improvements in the current injection efficiency by wide gap emitter and light input/output efficiency of upper emitter layer 4 side are performed. Eg3<Eg2 is satisfied to enhance the emitting intensity. Further, since Eg4>Eg3<Eag2 is satisfied, a laser operation can be executed. Since Eg3>Eg2 is satisfied, there is high sensitivity photoreceiving wavelength band from the wavelength of emitting light to longer wavelength for the external incident light.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a bipolar transistor, and particularly to a bipolar transistor using a compound semiconductor, which has the functions of emitting light, receiving light, and amplifying current using one transistor.

, (Prior art) □ Conventionally, as a bipolar transistor using this type of compound semiconductor, there has been a bipolar transistor disclosed in Japanese Patent Application Laid-Open No. 57-9858 filed by the present applicant.
There are some proposed in No. 8 and No. 57-111786.5. FIG. 4 schematically shows an example of the construction of a bipolar type light emitting/receiving transistor that has been proposed so far. , an npn type transistor 2 formed by laminating an n type emitter layer 4 and an n type contact layer 5 as semiconductor crystal layers. A portion of this contact layer 5 is removed by etching to leave a portion that does not interfere with the incidence and emission of light as a contact layer 5, and the remaining contact layer 5, emitter layer 4, and base layer 3 are coated with, for example, A structure is obtained in which p-type regions 6, 7, and 8 are formed by inverting a portion of each layer 5, 4, and 3 to p-type by performing p-type impurity diffusion. Reference numeral 9 denotes an ohmic collector electrode provided on the lower surface of the substrate so as not to interfere with the incidence and emission of light; 10 refers to an ohmic emitter electrode provided on the contact layer 5; and 11
is an ohmic base electrode provided on the p-type region 6. The relationship between the energy gap (forbidden band width) of each layer of a conventional transistor having such a structure is shown in FIG.
In FIG. 5, the horizontal axis shows the layer thickness from the contact layer 5 side, and the vertical axis shows the relative size of the energy gap. As is clear from this figure, the substrate 1, the collector layer 2, the base layer 3, the contact layer 4
and each energy gap Es□ of p-type region 6
E12*Ey3, Ej51 and Ey6 have the same or almost the same size, but the energy gap E4 of the emitter layer 4 is set larger than that of these other layers l, 2.3.5.6, thereby The aim was to increase the current amplification factor.

(Problem to be Solved by the Invention) However, if the energy gap E4 of the emitter layer 4 is made larger than that of other layers, the amplification factor can be improved, but the emission wavelength and high sensitivity There was a drawback that the matching with the receiving wavelength region deteriorated. Figure 6 is a characteristic curve diagram showing the relationship between wavelength (horizontal axis), emission intensity, and light-receiving sensitivity (vertical axis) of such a conventional transistor, and curve A in the figure shows the spectrum in the region of high light-receiving sensitivity. As shown, curve B shows the spectrum of emission intensity. As is clear from this figure, the wavelength region with high light-receiving sensitivity and the emission wavelength region are different from each other, so we tried to use multiple transistors of the same type to transmit and receive light between these transistors. Then, as mentioned above, wavelength matching is poor, and it is therefore extremely difficult to achieve good optical coupling between transistors.

It is an object of the present invention to eliminate the drawbacks of the conventional bipolar transistors mentioned above, to have the functions of light emission, light reception, and current amplification using -2 transistors, to match the light emission wavelength and light reception sensitivity wavelength, and to be able to emit light. It is an object of the present invention to provide a bipolar transistor having a structure in which the strength is increased and the amplification factor is increased.

(Means for Solving the Problems) In order to achieve the object of the present invention, according to the present invention, a collector layer 2, a base layer 3, and an emitter layer 4 are formed on a substrate.
In the bipolar transistor using a compound semiconductor, the collector layer 2 is formed of a first collector region 2a on the base layer 3 side and a second collector region 2b adjacent to the first collector region 2a. Energy gap EayzI of one collector region 2a = larger than the energy gap Ey3 of the above-mentioned base layer 3 and energy gap IEb of the above-mentioned second collector region 2b
>2 is the energy gap Ej3 of the base layer 3 mentioned above.
Further, in carrying out the present invention, it is preferable that the energy gap Eff+ of the substrate 1 is made larger than the energy gap Ebtz of the second collector region 2b.

(Function) In this way, if E$3<Ha, 2 is set, when electrons are injected from the emitter layer 4 or the collector layer 2 into the base layer 3 in the case of diode operation without transistor operation, these Injected electrons and holes can be confined within the base region 3 and prevented from being extracted from the base layer 3. Therefore, it is possible to perform strong light emission or laser oscillation, especially in the lateral direction, and therefore, the characteristics of lateral optical coupling are improved.

Furthermore, since it is configured so that Eb $ 2 < Egs, the highly sensitive light receiving wavelength region of this transistor is approximately λ3("K/E7g) <In &2 (=N/Eb
2z (however, is a constant of about 1240 nm/eV), and the emission wave penetration 3 can be made smaller than the long wavelength end entry b2 of the absorption wavelength band in the collector layer 2. Therefore, the wavelength matching of emission and light reception is Good characteristics can be obtained.

In addition, by setting Es+ > EbtJ2, more efficient light receiving characteristics can be obtained when light enters from the substrate side, and the light can be efficiently emitted from the emitter side or from the side, resulting in unidirectional light emission. A light receiving transistor can be obtained.

(Embodiment) An embodiment of the bipolar transistor of the present invention will be described below with reference to the drawings.

The layer structure of the transistor in this embodiment is schematically shown in FIG. 2. In this figure, the same components as those shown in FIG. 4 are designated by the same reference numerals. In the case of the transistor shown in FIG. The relationship between the energy gap sizes of contact layers 5 and 6 is different from the conventional one. In this case as well, the collector layer 2 and the emitter layer 4
An example in which the conductivity type is n-type and the base layer 3 is p-type will be explained, but it is also possible to have a structure in which the conductivity types are reversed, or the collector layer 2 and the emitter layer 4 may be exchanged and the substrate l is used as the emitter layer 4. It is also possible to have a structure in which the contact Fj5 is made to function as a contact layer and the contact Fj5 is removed.

In this structure, the n-type semiconductor crystal substrate l is generally n
It is formed of a material having similar crystallographic and electrical properties to the type layers 2a, 2b, 3.4, and 5. For example, when the collector layer 2 is made of n-type GaAs, the substrate l
The collector layer 2 may be made of n-type GaAs or n-type Si% n-type Ge. Also, since this collector layer 2 also serves as a connection with the electrode 9°, it is preferable that it has high electrical conductivity, and from the viewpoint of high frequency characteristics. are also desirable, and each of these 112a, 2b
, 3.4 and 5 are also semiconductor crystals. The most important active layer in this transistor structure is the collector layer 2.
(2a, 2b).

They are a base layer 3 and an emitter layer 4.

If each layer of this transistor is formed of a compound semiconductor with high luminous efficiency, this transistor can operate not only as a light-receiving transistor but also as a light-emitting transistor. The input and output of light is possible from the top, bottom, or sideways, and these input and output lights are shown in 12.1 in the figure.
3 and 14, respectively.

In such a transistor structure, 1.2(
2a, 2b), 3.4, 5 and 6 are shown in FIG. 1, and will be explained.

The essentially most important energy gap relationship in this invention is the magnitude relationship between the energy gaps E2□ to Era between the collector layer 2 (2a, 2b), the base layer 3, and the emitter layer 4. As shown in Figure 1, in this invention, Ey. 〉E23<Ea2z and E)3>Eb
The composition of the crystal is set so that the relationship is y2.

Et. In the case of E73, as is generally well known, it is possible to improve the current injection efficiency due to the wide gap emitter and the light input/output efficiency on the upper emitter layer 4 side. Electrons injected from the wide-gap n-type emitter layer 4 are injected into the p-type base layer 3, and part of them recombines with holes to emit light, so the base layer 3 is the main light-emitting layer of this transistor. . Furthermore, the emitter layer 4 may also emit light due to reverse injection of holes.

E) By setting s<Eayz, electrons are temporarily transferred to the emitter layer 4 or the collector layer 2, especially when the collector is open or the collector is in a negative bias state, that is, when there is no transistor action and a diode action is performed. After being injected into the base layer 3, these injected electrons and holes can be confined within the base layer 3 so that they do not escape from the base layer 3. Therefore, the luminous intensity can be increased.

Furthermore, since Ep4 > Et3 < IEa y 2.

The refractive index of the emitter layer 4 and the collector region 2a is often smaller than the refractive index of the base region 3, and in order to control this and increase the lateral light emission 14, the lateral light intensity increases and the laser operation It becomes possible to perform the following.

Since jf Et3 > Eb 92, the highly sensitive light receiving wavelength band of the transistor is approximately λa (=to/EtJa
) or enter 42 (=ni/Ea)2 ) <enter 3 (=
K / Eya )kuλh 2 (-K/Eb22
) (However, K is a constant, approximately 1240n/eV
), therefore, the wavelength λ3 of one light in the base layer 3 can be made smaller than the long wavelength end λb2 of the absorption wavelength band in the collector layer 2. Therefore, this transistor has a characteristic of having a highly sensitive light-receiving wavelength band to a wavelength longer than the wavelength of the output light with respect to externally incident light 12, 13, and 14 from above, below, and lateral directions. FIG. 3 shows spectral characteristics showing the relationship between wavelength, emission intensity, and light receiving sensitivity of a transistor having such an energy gap relationship.

In the figure, wavelength is plotted on the horizontal axis, and emission intensity and light reception sensitivity are plotted on the vertical axis. Curve C is a reception spectrum curve, and curved line is an emission spectrum curve. As is clear from FIG. 2, since the emission wavelength band of the transistor of the present invention falls within the light-receiving sensitivity wavelength band, wavelength matching between emission and reception can be achieved reliably and well.

By the way, there are many possible combinations of semiconductor crystals with energy gaps having the above-mentioned relationships for each of these layers 2 (2a, 2b), 3, and 4. For example, the material may be AQGaAs or rnGa.
Other ternary semiconductors such as As, InP', etc. can be used. Furthermore, in the case of A9xGat-xAs,
The compositional relationship can be set so as to satisfy the relationship of X>0 for the first collector region 2a. In the case of No. 9, it is advantageous to introduce p-type impurities into the base layer 3, which has good luminous efficiency, by liquid phase growth.

Next, the energy gap Es1 of the substrate 1 will be explained. The energy gap Ey1 of the substrate 1 can be first set so that Eb, 2≧Ejt. In this way, the substrate l acts as a light absorption layer.

Alternatively, it is also possible to set the relationship Efft > IEb tJz. In this case, more efficient light receiving characteristics can be obtained when light is incident from the lower substrate side (indicated by 13). Therefore, it is possible to form a bidirectional light-emitting/light-receiving transistor that enters light from the substrate l side and effectively emits light from the upper emitter 4 side (indicated by 12) or laterally (indicated by 14).

Although detailed explanation is omitted, Et3 as described above
> When the energy gap between the base layer 3 and the second collector region 2b is set so as to have a relationship of Since the light is absorbed and an effective light-receiving current is generated between the base and the collector, it becomes a kind of positive feedback phenomenon, and therefore, in this case, the effect of increasing the current amplification factor can be obtained.

Further, each layer may be formed to have a uniform composition and a uniform energy gap within the layer, or it is not necessary to do so, and the above-mentioned energy gap relationship E, 4 > Ey3 < Ea F 2 and E33
> There may be non-uniformity within the layer within the range that satisfies Eb ti 2. Such non-uniformity can be actively used to create a gradient in the ice-lugian gap within the layer, and this gradient can be It can be used to detect carrier drift effects, light absorption effects,
Alternatively, effective bacteria can be utilized as necessary, such as phylum with a reduced interface unit.

It is clear that the invention is not limited to the embodiments described above.

For example, as long as it satisfies the condition that the energy gap of the collector layer 2 is smaller than the energy gap of the base layer 3, any type of compound semiconductor material can be used, and its composition can be set arbitrarily. I can do it.

For example, as already explained, this bipolar transistor can be configured as a pnp type transistor, and the stacking order on the substrate l is 2': the transmitter layer 4, the base layer 3, the second collector region 2b, and the first collector region. Area 2
It is also possible to adopt a structure as shown in a, or the conductivity type of each layer may be reversed from that of the above-described embodiment.

Furthermore, for example, the ohmic electrode 10 may be brought into direct contact with the emitter layer 4 without providing the contact layer 5, and furthermore, instead of providing a region 6.7.8 of one conductivity type, e.g. p-type, the emitter layer The ohmic electrode 11 may be brought into direct contact with a portion of the base layer 3 by making electrode holes or grooves at 4° by etching or other means.

It is also easy to infer that this bipolar transistor can be configured as an integrated circuit, for example,
It is also possible to use an insulating substrate as the substrate 1 and take out the electrodes from the collector layer 2 using a separate method, or to provide a separate insulating substrate below the substrate 1. The structure of the lever substrate 1 may be grown by an epitaxial growth method. In this way, a monolithic light-emitting/light-receiving integrated circuit can be constructed by forming a large number of bipolar transistors on the same substrate. I can do it.

In addition, in the transistor of this invention, the emitter base and collector layer have a so-called double heterostructure, so by performing a large current operation in the lateral direction, laser oscillation is facilitated, and lateral coupling is made stronger. It is also possible.

(Effects of the Invention) As is clear from the above description, according to the bipolar transistor of the present invention, the compositions of the second collector region of the collector layer and the base layer are changed.

Since the structure is such that the energy gap of the second corfta region is smaller than the energy gap of the base layer, the wavelength of light emitted from the base region falls within the high-sensitivity light reception wavelength band of the collector layer.

This makes it possible to reliably and better match the emission wavelength and the high-sensitivity reception wavelength range, and therefore, even when transmitting and receiving light between these transistors, optical coupling is better than before. It can be done very effectively.

The composition of the first collector region of the collector layer and the base layer are changed to make the energy gap of the first collector region larger than the energy gap of the base layer, so that the electrons and electrons injected into the base layer are Holes are easily confined effectively, and therefore, more powerful light emission and laser oscillation, particularly in the lateral direction, can be performed, and the characteristics of lateral optical coupling are significantly improved compared to conventional ones.

Further, when the energy gap of the substrate is made larger than the energy gap of the collector layer, a unidirectional light-emitting/light-receiving transistor can be obtained.

The bipolar transistor of the present invention has a characteristic of good wavelength matching of light emission and light reception, and the light emission intensity is significantly stronger than that of the conventional one, making it suitable for use as a single optical element in optical communications and optical control devices. It is particularly suitable to apply this bipolar transistor to optical integrated circuits as well.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the energy gap sizes of each layer of the bipolar transistor of this invention, Figure 2 is a cross-sectional view schematically showing the structure of Hatsue's bipolar transistor, and Figure 3 is FIG. 4 is a sectional view for explaining the structure of a conventional bipolar transistor; FIG. 5 is a diagram similar to FIG. 1 of a conventional bipolar transistor. FIG. 6 is a spectral curve diagram similar to FIG. 3 of a conventional bipolar transistor. l...n-type substrate, 2...n-type collector layer□ 2a...first collector region, 2b...second collector region 3...p-type base layer, 4-n-type emitter layer 5... Contact layer, 6.7.8... P-type region 9... Ohmic collector electrode lO... Ohmic, emission-saving electrode 11... Ohmic base electrode 12.13.14. ...Light emitted and received. Patent applicant Oki Electric Industry Co., Ltd.
- yy'zi°VKoroi 1 Gin e-, cS4 \ Figure 5 Shofue 6 Figure Wave Procedures Amendment February 25, 1981

Claims (1)

[Claims] 1. In a bipolar transistor using a compound semiconductor, which includes a collector layer, a base layer, and an emitter layer on a substrate, the collector layer is connected to a first collector region on the base layer side and the first collector region. and a second collector region adjacent to the base layer, and the energy gap of the first collector region is larger than the energy gap of the base layer, and the energy gap of the second collector region is smaller than the energy gap of the base layer. A bipolar transistor characterized by: 2. The bipolar transistor according to claim 1, wherein the energy gap of the substrate is larger than the energy gap of the second collector region.