JP2743417B2 - Heterojunction bipolar transistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heterojunction bipolar transistor.

2. Description of the Related Art Trends in semiconductor devices include high-density integration, high speed, and high frequency. Recently, a heterojunction bipolar transistor using a gallium arsenide system having higher electron mobility than silicon has attracted attention as a high-frequency device. In a heterojunction bipolar transistor, a semiconductor having a larger bandgap than a base semiconductor is used as an emitter, and a heterojunction is formed between the emitter and the base. As a result, carrier injection from the base side to the emitter side is reduced, and there is an advantage that a sufficient current amplification factor can be obtained even if the base is thin and has a high concentration for high frequency operation. In the conventional heterojunction bipolar transistor, the conductor is inclined from the emitter side by changing the mixed crystal ratio of the semiconductor in the base, electrons are accelerated by the electric field formed by this, and the transit time of the base is reduced. Was being planned. This is called a tilt base. Further, the inclined base suppresses electrons flowing from the emitter to the external base due to scattering, and improves the current amplification factor of the transistor. FIG. 3 shows the structure of the aluminum gallium arsenide-based npn-type heterojunction bipolar transistor having the inclined base, and FIG. 4 shows the state of the conduction band from the emitter to the collector when the transistor operates.

As shown in FIG. 3, a collector contact region 2 containing an n-type impurity at a high concentration, a collector region 3 containing an n-type impurity, and a base region 4 containing a p-type impurity at a high concentration on a semiconductor substrate 1. An emitter region 5 containing an n-type impurity and an emitter contact region 6 containing a high concentration of an n-type impurity, which are formed of a semiconductor having a forbidden band width larger than that of a base region to form a heterojunction, are sequentially formed; An external base region 12 in which p-type impurities are ion-implanted to reduce resistance is formed, and an insulating region 11 in which carriers are reduced by ion implantation to reduce stray capacitance is formed in a collector layer immediately below the external base region 12. Is formed with an element isolation region 13 insulated by ion implantation. On the collector contact region 2, the external base region 12, and the emitter contact region 6, a collector electrode 7, a base electrode 8, and an emitter electrode 9, which are in ohmic contact, respectively, are formed. At this time, as shown in FIG. 4, in the base region 4, the region base is formed by gradually changing the composition ratio of aluminum gallium arsenide from the end of the emitter region 5.
For example, Proceedings of the International Conference on Solid State Devices and Materials 34
3 (1984).

However, in the above configuration, the base electrode on the external base region having the same composition as that of the base region is formed on the emitter side having a large aluminum composition ratio, that is, a large forbidden band width. Therefore, a sufficiently low contact resistance cannot be obtained, which leads to an increase in base resistance which adversely affects high frequency characteristics. Further, since the composition of aluminum is gradually changed in the base region, the cue of the base cannot be performed by selective etching of aluminum gallium arsenide and gallium arsenide, thereby complicating the manufacturing process.

The present invention significantly improves the above-mentioned problems, and provides the advantage of a tilt base and a sufficiently low contact resistance.
It is another object of the present invention to provide a hetero-junction bipolar transistor capable of searching for a base by selective etching.

Means for Solving the Problems To solve the above problems, the heterojunction bipolar transistor of the present invention has a conduction band in the base, a region where electron energy is gradually reduced from the emitter side, and a steeply reduced region. , A flat region, a steeply increasing interface, and a gradually decreasing region on the collector side.

The heterojunction bipolar transistor having the above configuration can obtain a lower contact resistance of the base electrode while having almost the same current amplification factor and base transit time as compared with the heterojunction bipolar transistor having the conventional configuration. This greatly contributes to increasing the frequency of the heterojunction bipolar transistor. In addition, since the base can be located by selective etching, the manufacturing process can be simplified.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view showing the structure of an aluminum gallium arsenide-based npn-type heterojunction bipolar transistor according to an embodiment of the present invention. FIG. 2 is a structural diagram showing the state of the conductor from the emitter to the collector during the operation of the transistor. First, as shown in FIG. 1, a collector contact region 22 containing an n-type impurity at a high concentration and a collector region 23 containing an n-type impurity are formed on a gallium arsenide semi-insulating substrate 21, respectively. ing. A first base region 41 containing a high concentration of p-type impurities is a mixed crystal of aluminum gallium arsenide, and the composition ratio of aluminum from the collector region 23 side is 0 to 0.
While gradually increasing to 05, the second base regions 42 containing p-type impurities at a high concentration are formed of gallium arsenide, respectively. Further, a third base region 43 containing a p-type impurity at a high concentration is formed by a mixed crystal of aluminum gallium arsenide while the composition ratio of aluminum is gradually increased from 0.15 to 0.2 from the second base region 42 side. ing. Further, the emitter region 25 containing an n-type impurity is
A mixed crystal of aluminum gallium arsenide was used to set the composition ratio of aluminum to 0.3, and emitter contact regions 26 containing n-type impurities at a high concentration were respectively formed of gallium arsenide, and p-type impurities for reducing resistance were ion-implanted. The external base region 32 is formed so as to be drawn out from the second base region. In the collector layer immediately below the external base region 32, an insulating region 31 in which carriers are reduced by ion implantation to reduce stray capacitance is formed, and an element isolation region 33 insulated by ion implantation is formed in the periphery. . On the collector contact region 32, the external base region 32, and the emitter contact region 26, a collector electrode 27, a base electrode 28, and an emitter electrode 29 that are in ohmic contact are formed, respectively.

Thereby, as shown in FIG. 2, the conductor in the base has a region where the electron energy gradually decreases, that is, the third base region 43, and an interface where the conductor decreases sharply, that is, the third base region 43. A junction between the second base region 42 and a flattened region, that is, a second base region 42 is formed, and further, a steeply increasing interface, that is, a junction between the second base region 42 and the first base region 41 Part and the area that gradually gets smaller,
That is, the first base region 41 is formed. At this time, electrons injected from the emitter side are accelerated by the electric field in the third base region 43, and the third base region 43 and the second base region 42
Hot electrons at the junction. Since the hot electrons are dominated by the velocity component in the direction of the collector, scattering in the direction of the external base or the like is suppressed, and the hot electrons are injected into the first base region 41 at a stretch, and furthermore, the first base region 41
It is accelerated again by the electric field inside and reaches the collector region 23.
Therefore, the base current can be formed with a gallium arsenide layer having a lower contact resistance while maintaining the high current amplification factor and the fast base transit time, which are the advantages of the tilted base.

The second base region in the above structure may be formed of a mixed crystal of indium gallium arsenide having a smaller forbidden band width and a semiconductor having an indium composition of 0 to 1. Further, the composition ratio of the mixed crystal in the emitter region, the third base region, the second base region and the first base region can be freely designed,
Aluminum gallium arsenide with an aluminum content of 0.5 or more is not practical because of severe oxidation.

Effect of the Invention As described above, the heterojunction bipolar transistor having the configuration of the present invention has almost the same current amplification factor and base transit time as compared with the heterojunction bipolar transistor having the conventional configuration. A low base electrode contact resistance can be obtained, which means that
It greatly contributes to higher frequency of heterojunction bipolar transistor. In addition, since the base can be located by selective etching, the manufacturing process can be simplified.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a heterojunction bipolar transistor according to an embodiment of the present invention, FIG. 2 is a structural view showing the conduction band of the transistor of FIG. 1, and FIG. Sectional view showing the configuration,
FIG. 4 is a structural diagram showing a conduction band of the transistor of FIG. 21 ... semi-insulating substrate, 22 ... collector contact area,
23 ... collector region, 25 ... emitter region, 26 ... emitter contact region, 27 ... collector electrode, 28 ... base electrode, 29 ... emitter electrode, 31 ... insulating region, 32 ...
External base region, 33: device isolation region, 41: first base region, 42: second base region, 43: third base region.

Claims (3)

(57) [Claims] 1. A heterojunction bipolar transistor in which a semiconductor having a larger forbidden band width than a semiconductor used for a base is used for an emitter.
With respect to the electron energy, it is necessary to have a region that gradually decreases from the emitter side, an interface that sharply decreases, a region that becomes flat, an interface that sharply increases, and a region that gradually decreases on the collector side. Characteristic heterojunction bipolar transistor. 2. The heterojunction bipolar transistor according to claim 1, wherein the base electrode is formed on a region in the base where the conductor is flat. 3. A semiconductor having a mixed crystal of aluminum gallium arsenide and a composition ratio of aluminum of 0 to 0.5 as an emitter.
3. The heterojunction bipolar transistor according to claim 2, wherein a semiconductor in which the indium composition ratio of indium is 0 to 1 is used as a region where the conduction band in the base is flat.