JP4774137B2 - Hetero bipolar semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hetero-bipolar semiconductor device improved so as to be capable of low voltage operation.
[0002]
Currently, mobile phones are rapidly spreading, and one of the reasons is the low price and large size of mobile phone terminals.
[0003]
In general, a GaAs FET (Field Effect Transistor) has been widely used as an output stage transistor in a mobile phone terminal. However, in recent years, it operates with a single power source, has high efficiency, and has low distortion characteristics. Bipolar transistors (HBT) tend to be used.
[0004]
Many of the reasons for downsizing mobile phone terminals are due to the high efficiency of the battery and the reduction in the number of amplification stages. For example, in the initial stage, the output voltage of the battery required 7.2 [V]. However, it gradually decreased and now it is 3.6 [V].
[0005]
In the future, when the power supply voltage is further lowered, a transistor that operates efficiently even at a low voltage is required, and HBT is attracting attention in that respect.
[0006]
In the HBT, the largest factor that determines the lower limit of the operating voltage is the base-emitter voltage V _be .
[0007]
For example, the base-emitter voltage V _be of an npn type HBT is mainly the maximum potential energy (upper end of the valence band) in the valence band of the base layer and the minimum potential energy (conduction) in the conduction band of the energy layer. It is determined by the difference from the lower end of the belt.
[0008]
Accordingly, if a material having a small energy band gap is used as the material of the base layer, the base-emitter voltage V _be can _be reduced. If the lattice constants of the two are greatly different from each other, a transition occurs in the base layer and the characteristics of the HBT are deteriorated.
[0009]
By the way, GaInNAs has recently attracted attention as a semiconductor material lattice-matched to GaAs and having a smaller energy band gap than GaAs.
[0010]
In GaInNAs, it is said that the energy band gap can be significantly reduced while lattice matching with GaAs by appropriately adjusting the amounts of In and N.
[0011]
However, in GaInNAs, when the amounts of In and N are increased, the position of the valence band hardly moves and the position of the conduction band is greatly lowered as compared with GaAs.
[0012]
Therefore, when GaInNAs is used for the base layer of the HBT, the energy band gap is reduced, but the base-emitter voltage V _be is not lowered. Incidentally, in order to lower the base-emitter voltage V _be , it is necessary to raise the upper end of the valence band.
[0013]
[Problems to be solved by the invention]
In the present invention, an appropriate material lattice-matched to GaAs is used as a material constituting the base layer in the HBT, and the base-emitter voltage V _be can _be sufficiently reduced.
[0014]
[Means for Solving the Problems]
In the present invention, GaAs NSb lattice-matched with GaAs is basically adopted as a material constituting the base layer in the HBT.
[0015]
In general, GaAs NSb substantially lattice-matched to GaAs contains the ratio of N and Sb while maintaining a pair ratio, and the energy band gap decreases as the ratio of both increases.
[0016]
Normally, the lower end of the conduction band is lowered as N increases, but Sb is also added at the same time, so the upper end of the valence band rises according to the ratio of Sb. As a result, the increase in N and Sb leads to HBT. In this case, the base-emitter voltage V _be becomes smaller.
[0017]
By the way, in the present invention, GaAsNSb containing a controlled amount of N and Sb is basically used as a material for the base layer of the HBT. However, it has been conventionally performed to add N or Sb to a compound semiconductor. It is.
[0018]
Here, although it cannot be a conventional technique related to the present invention, it is not useless to confirm the patentability of the present invention to list related known techniques. Explained.
[0019]
(1) Invention of Japanese Patent Application No. 10-118466 This invention discloses that carbon-doped InGaAs or carbon-doped GaAsSb is used for the base layer of HBT, and that carbon-doped GaAsSb or carbon-doped GaInAsSb is used for the base leading layer. However, there is no disclosure or suggestion of using GaAsNSb as in the present invention and controlling the composition ratio of N and Sb.
[0020]
(2) Invention of Japanese Patent Application Laid-Open No. 10-12905 Although it is disclosed that GaNAsSb is used for the p-type semiconductor layer or the n-type semiconductor layer in the solar cell, the energy band gap is narrowed and the valence band is disclosed. There is no disclosure or suggestion of controlling the composition ratio of N and Sb with the recognition that the upper end of the substrate is raised.
[0021]
(3) Invention of Japanese Patent Laid-Open No. 7-162097 Although it is disclosed that GaAsNSb is used for the active layer of a laser diode, the energy band gap is narrowed and the upper end of the valence band is raised. There is no disclosure or suggestion of controlling the composition ratio of N and Sb with recognition.
[0022]
(4) Invention of Japanese Patent Laid-Open No. 8-195522 Although it is disclosed that GaAsNSb is used for the active layer of a laser diode, the energy band gap is narrowed while the upper end of the valence band is raised. There is no disclosure or suggestion of controlling the composition ratio of N and Sb with recognition.
[0024]
In the hetero-bipolar semiconductor device according to the present invention,
(1)
That the composition of GaAs to GaAsNSb is interposed therebetween composition gradient layer that changes slowly (for example i-GaAsNSb composition gradient layer 5) between the base layer made of GaAsNSb that lattice matching with the collector layer and the GaAs of GaAs Or
[0025]
(2)
In (1) , the GaAs NSb layer is doped with carbon.
[0026]
By adopting the above means, the energy band gap in the base layer of the HBT becomes narrow and the upper end of the valence band rises, so that the base-emitter voltage V _be can _be reduced, Therefore, the HBT can operate at a low voltage, and for example, a mobile phone terminal can be further downsized.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cut-away side view of an essential part showing an HBT for explaining an embodiment of the present invention.
[0028]
In the figure, 1 is a substrate, 2 is a buffer layer, 3 is a sub-collector layer, 4 is a collector layer, 5 is a composition gradient layer, 6 is a base layer, 7 is an emitter layer, and 8 and 9 are emitter contact layers. Reference numeral 10 denotes an emitter electrode, 11 denotes a base electrode, and 12 denotes a collector electrode.
[0029]
Examples of main data for each element are as follows.
(1) About substrate 1 Material: GaAs
(2) Buffer layer 2 Material: i-GaAs
Thickness: 100 [nm]
(3) Sub-collector layer 3 Material: n-GaAs
Impurity concentration: 4 × 10 ¹⁸ [cm ^-3 ]
Thickness: 500 [nm]
(4) About collector layer 4 Material: i-GaAs
Thickness: 1000 [nm]
(5) About the composition gradient layer 5: Material: i-GaAs NSb
(The composition is changed so that GaAs → GaAsNSb from the collector layer 4 side toward the base layer 6)
Thickness: 50 [nm]
(6) Material for base layer 6: p-GaAs NSb
Impurity concentration: 4 × 10 ¹⁹ [cm ⁻³ ]
Thickness: 100 [nm]
(7) Material for emitter layer 7: n-InGaP
Impurity concentration: 4 × 10 ¹⁷ [cm ⁻³ ]
Thickness: 50 [nm]
(8) Material for emitter contact layer 8: n-GaAs
Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ]
Thickness: 300 [nm]
(9) Material for emitter contact layer 9: n-InGaAs
Impurity concentration: 3 × 10 ¹⁹
Thickness: 100 [nm]
(10) Emitter electrode 10 Material: WSi
(11) About the base electrode 11 Material: Pt (base layer 6 side) / Ti / Au (surface side)
(12) About collector electrode 12 Material: Ni (sub-collector layer 3 side) / Au / Ge (surface side)
[0030]
The HBT can be easily manufactured by applying conventional techniques, and the process will be briefly described below.
[0031]
(1) The buffer layer 2, the sub-collector layer 3, the collector layer 4, the composition gradient layer 5, the base layer 6, the emitter layer 7 and the emitter contact layer 7 are applied by applying the MOCVD (Metalorganic Chemical Vapor Deposition) method. The emitter contact layer 8 and the emitter contact layer 9 are grown.
[0032]
(2) An emitter electrode 10 is formed on the emitter contact layer 9.
[0033]
(3) Etching is performed from the surface of the emitter contact layer 9 to the surface of the base layer 6 to expose the base electrode contact portion.
[0034]
(4) The base electrode 11 is formed on the base electrode contact portion.
[0035]
(5) Etching from the surface of the emitter contact layer 9 to the surface of the sub-collector layer 3 is performed to expose the collector electrode contact portion.
[0036]
(6) The collector electrode 12 is formed in the collector electrode contact portion. Thereafter, the HBT is completed through a normal wiring process.
[0037]
FIG. 2 is an energy band diagram of the HBT shown in FIG. 1, and the symbols used in FIG. 1 represent the same parts or have the same meaning.
[0038]
In the figure, the solid line shows the energy band of the HBT according to the prior art using GaAs for the base layer, and in the base layer and its vicinity, the energy energy represented by the broken line connected to the solid line. The band relates to an HBT according to the present invention in which GaAs NSb, specifically GaAs _0.685 N _0.075 Sb _0.24, is used for the base layer.
[0039]
When GaAsNSb is used for the base layer 6, the lower end of the conduction band is lowered, and if the structure is in contact with the collector layer 4, it rapidly rises at the interface as shown by the one-dot chain line in the figure.・ The conduction band discontinuity between collectors becomes large, and the base layer becomes like a well.
[0040]
Therefore, there is a concern that electrons emitted from the emitter layer 7 are trapped by the discontinuity and the recombination current increases. Therefore, in the HBT according to the present embodiment, the base layer 6 made of p-GaAs NSb and An i-GaAs NSb composition gradient layer 5 that is graded from GaAs to GaAs NSb is interposed between the collector layer 4 made of i-GaAs.
[0041]
By adopting this configuration, the lower end of the conduction band in the energy band becomes a state where it slowly falls gradually from the base layer 6 toward the collector layer 4 as shown by the broken line in the figure, The electrons emitted from the layer 7 are not trapped.
[0042]
FIG. 3 is a diagram for explaining the composition dependence of potential energy in GaAsNSb.
[0043]
In the HBT shown in FIG. 1, the base layer 6 is formed using GaAsNSb having a composition lattice-matched to the substrate 1 made of GaAs, and the composition ratio of Sb and N is increased in the GaAsNSb. It shows how the potential energy at the top of the valence band and the bottom of the conduction band sometimes change.
[0044]
In GaAs NSb, when the Sb composition is 24% and the N composition is 7.5%, the upper end of the valence band is 180 [meV] higher than that of GaAs. , in the base-emitter voltage V _be the HBT of the GaAsNSb with this composition as the base layer is smaller by 180 as compared with the case of GaAs [meV].
[0045]
In the above-described HBT, carbon having a low diffusion rate is used as an acceptor raw material in the p-GaAs NSb base layer 6, so that the movement of the acceptor can be suppressed even when a current is passed.
[0046]
The present invention is not limited to the embodiment described above, and many modifications can be realized without departing from the scope described in the claims. For example, in the embodiment, the base layer As the GaAs NSb constituting 6, those having a composition of Sb: 24 [%] and N: 7.5 [%] are mentioned, but the Sb composition is selected in the range of 15 [%] to 30 [%]. Therefore, it is possible to push up the lower end of the valence band by 100 [meV] to 250 [meV].
[0047]
【The invention's effect】
In the hetero bipolar semiconductor device according to the present invention comprises a base layer comprising a layer of a GaAsNSb to lattice matched to GaAs.
[0048]
By adopting the above configuration, the energy band gap in the base layer of the HBT becomes narrow and the upper end of the valence band rises, so that the base-emitter voltage V _be can _be reduced, Therefore, the HBT can operate at a low voltage, and for example, a mobile phone terminal can be further downsized.
[Brief description of the drawings]
FIG. 1 is a cut-away side view of an essential part showing an HBT for explaining an embodiment in the present invention.
2 is an energy band diagram of the HBT shown in FIG.
FIG. 3 is a diagram for explaining the composition dependence of potential energy in GaAsNSb.
[Explanation of symbols]
Reference Signs List 1 substrate 2 buffer layer 3 sub-collector layer 4 collector layer 5 composition gradient layer 6 base layer 7 emitter layers 8 and 9 emitter contact layer 10 emitter electrode 11 base electrode 12 collector electrode

Claims (2)

A hetero-bipolar, characterized in that a composition gradient layer whose composition changes slowly from GaAs to GaAsNSb is interposed between a collector layer made of GaAs and a base layer made of GaAsNSb lattice-matched to GaAs. Semiconductor device. The hetero-bipolar semiconductor device according to claim 1, wherein the GaAs NSb layer is doped with carbon .

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