CN110610991A - Epitaxial structures and low on-voltage transistors - Google Patents

Abstract

The present application provides an epitaxial structure and a low on-voltage transistor, and relates to the technical fields of semiconductors and communications. The low on-voltage transistor includes an epitaxial structure. The epitaxial structure includes a composite base electrode layer and an emitter layer. The composite base electrode layer includes a first base electrode layer and a second base electrode layer made based on the first base electrode layer; wherein, the material of the first base electrode layer includes GaAs, and the material of the second base electrode layer Including In _x Ga _1‑x As. The composite base electrode layer can reduce the energy gap of the base electrode layer, so that the peak effect of the conduction band between the base electrode layer and the emitter layer can be reduced. When used in transistors, it can reduce the on-voltage and power consumption; in the second base electrode It is easier to use Pt on the layer to form an ohmic contact layer, and the thickness of Pt can be reduced, so that the amount of Pt driven into the composite base electrode layer is reduced, so that the interface recombination current of the device is reduced, and the reliability test of the device is more stable. reliable.

Description

Epitaxial structures and low on-voltage transistors

technical field

The present application relates to the field of semiconductor and communication technologies, and in particular, to an epitaxial structure and a low on-voltage transistor.

Background technique

In power amplifiers currently used in 3G or 4G, additional power efficiency (power added efficiency, "PAE" for short) is a very important parameter. PAE is defined as the ratio of the difference between the output power Pout and the input power Pin to the DC input power Pdc, namely: (Pout-Pin)/Pdc. PAE is a pointer indicating the efficiency quality of the PA, and the larger the value is, the more the power consumption of the power amplifier can be suppressed. In order to improve the DC power consumption, the on-voltage (Von), the knee voltage (“Vk” for short) and the offset voltage (“Voff” for short) are reduced. However, the on-voltage of the transistor used in the existing power amplifier is too large, and it is difficult to reduce it, resulting in a large power consumption of the device.

Therefore, designing a transistor that can be applied to a low turn-on voltage and reduce power consumption is a technical problem that needs to be solved urgently at present.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present application is to provide an epitaxial structure and a low on-voltage transistor to improve the above problems.

The embodiment of the present application provides an epitaxial structure, including:

a composite base electrode layer, comprising a first base electrode layer and a second base electrode layer fabricated based on the first base electrode layer;

An emitter layer made based on the second base electrode layer;

Wherein, the material of the first base electrode layer includes GaAs, and the material of the second base electrode layer includes _{InxGa1 - xAs} .

In the In _x Ga _1-x As of the epitaxial structure of the above embodiment, the value of x remains unchanged.

In the epitaxial structure of the above embodiment, x=0.25.

In the second base electrode layer of the epitaxial structure of the above embodiment, the composition of In is 25%.

In the In _x Ga _1-x As of the epitaxial structure of the above embodiment, the value of x increases gradually in the direction close to the emitter layer.

In the epitaxial structure of the above embodiment, the value of x is gradually increased from 0.05 to 0.25.

In the second base electrode layer of the epitaxial structure of the above embodiment, the composition of In ranges from 5% to 25%.

In the epitaxial structure of the above embodiment, the thickness of the second base electrode layer is 5 nm or less than the critical thickness.

In the epitaxial structure of the above embodiment, the material of the emitter layer includes InGaP.

Embodiments of the present application further provide a low on-voltage transistor including the epitaxial structure.

The beneficial effects of the epitaxial structure and the low on-voltage transistor provided by the embodiments of the present application:

1. A second base electrode layer is added between the first base electrode layer and the emitter layer, the material of the second base electrode layer includes InxGa1 _{- xAs} , InxGa1 _{- xAs} has the advantage of low energy gap, It can reduce the energy gap of the base electrode layer and reduce the peak effect of the conduction band between the base electrode layer and the emitter layer. When used in transistors, it can reduce the on-voltage and power consumption;

2. Because In _x Ga _1-x As has the advantage of low energy gap, it is easier to use Pt to form an ohmic contact layer on the second base electrode layer, which can reduce the thickness of Pt and reduce the amount of Pt driven into the composite base electrode layer. , so that the interface recombination current is reduced in the device, and the reliability test of the device is more stable and reliable.

In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the preferred embodiments are exemplified below, and are described in detail as follows in conjunction with the accompanying drawings.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present application more clearly, the following drawings will briefly introduce the drawings that need to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore do not It should be regarded as a limitation of the scope, and for those of ordinary skill in the art, other related drawings can also be obtained according to these drawings without any creative effort.

FIG. 1 is a schematic diagram of an epitaxial structure provided by a first embodiment of the present application.

FIG. 2 is a flow chart of a method for fabricating the epitaxial structure in FIG. 1 .

FIG. 3 is a schematic diagram of a low on-voltage transistor provided by a third embodiment of the present application.

Icon: 100-epitaxial structure; 1-composite base electrode layer; 11-first base electrode layer; 12-second base electrode layer; 2-emitter layer; 3-substrate; 4-secondary collector layer; 5- Collector layer; 6-cap layer; 7-emitter metal contact layer; 8-base electrode metal contact layer; 9-collector metal contact layer.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments It is only a part of the embodiments of the present application, but not all of the embodiments. The components of the embodiments of the present application generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

Thus, the following detailed description of the embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application as claimed, but is merely representative of selected embodiments of the application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

In the GaAs-based single heterojunction transistor device, the material of the base electrode layer is gallium arsenide (GaAs), and the material of the emitter layer is indium gallium phosphide (InGaP). The energy gap difference (ΔEc) between the base electrode layer and the emitter layer is obvious, and the conduction band spiking effect between the base electrode layer and the emitter layer is obvious, and there is a larger forward conduction voltage. The energy gap difference between the base electrode layer and the collector layer under the homogeneous material is ΔEc=0, so the base-emitter turn-on voltage (Vbe,on) will be larger than that between the base-collector electrodes, making the The device offset voltage (Voff) is too large.

And platinum metal (Pt metal) is an important material formed by the metal ohmic contact layer (Base Ohmic contact) on the base electrode. During the thermal annealing process of platinum metal to form ohmic contact, because platinum metal reacts with the GaAs-based electrode layer, it is easy to make the base current (base current) generate a higher interface recombination current (interface recombination current), Affects the reliability test results of the device.

The embodiments of the present application provide an epitaxial structure and a low on-voltage transistor, which can not only reduce the compensation voltage of the device, but also make the reliability test result of the device more reliable.

first embodiment

Referring to FIG. 1 , this embodiment provides an epitaxial structure 100 including a composite-based electrode layer 1 and an emitter layer 2 fabricated based on the composite-based electrode layer 1 .

The composite base electrode layer 1 is a double-layer material structure, including a first base electrode layer 11 and a second base electrode layer 12 made based on the first base electrode layer 11 . The material of the first base electrode layer 11 includes GaAs, and the material of the second base electrode layer 12 includes InxGa1 _{- xAs} . Compared with GaAs, In _x Ga _1-x As is a material with a lower energy gap. When used in transistors, it can improve the influence of the conduction band spiking effect, reduce the on-voltage of the transistor, and reduce power consumption.

In the second base electrode layer 12, in the direction close to the emitter layer 2, the In content _is equal, that is to say, the second base electrode layer 12 in FIG. In _1-x As, the value of x remains unchanged.

In In _x Ga _1-x As, there are various options for the value of x, and the selectable range is 0.2 to 0.3. In this embodiment, the value of x is selected as 0.25. That is to say, in the second base electrode layer 12, the composition range of In can be any fixed value from 20% to 30%. In this embodiment, the composition of In is selected to be 25%.

The emitter layer 2 is a single-layer material structure. The material of the emitter layer 2 includes GaInP. The In content in the emitter layer 2 is a fixed composition suitable for the GaAs-based electrode layer.

Referring to FIG. 2, the present embodiment also provides a method for fabricating the above-mentioned epitaxial structure 100, including the following steps:

S1: Fabrication of the first base electrode layer 11

The material of the first base electrode layer 11 is GaAs. During the formation of the first base electrode layer 11 , the layer is grown at a suitable mole ratio according to material growth requirements.

S2: Making the second base electrode layer 12

The material of the second base electrode layer 12 is InxGa1 _{- xAs} . In the process of forming the second base electrode layer 12, the value of x is selected to be 0.25, so that the molar ratio of In and the molar ratio of Ga are adjusted proportionally, and the second base electrode layer of suitable high quality is gradually formed by accumulation. 12.

The thickness of the second base electrode layer 12 may be designed to be 5 nm or less than the critical thickness under this composition (x=0.25). The critical thickness refers to the maximum film thickness that a single crystal material can grow without the lattice mismatch of the epitaxial layer. According to theoretical calculation, in InxGa1 _{- xAs} , when x=0.25, the critical thickness of the second base electrode layer 12 is about 40A, but with the current advancement of epitaxy technology, the critical thickness can be grown to 75A.

S3: Making Emitter Layer 2

The emitter layer 2 is designed as a single-layer material structure, and the material of the emitter layer 2 is InGaP. During the formation process of the emitter layer 2, the layer is grown at a suitable molar rate according to the material growth requirements. In the second base electrode layer The emitter layer 2 is formed by gradually accumulating on the 12 .

The beneficial effects of the epitaxial structure 100 and the preparation method thereof provided by this embodiment:

1. A second base electrode layer 12 is added between the first base electrode layer 11 and the emitter layer 2. The material of the second base electrode layer 12 includes InxGa1 _{- xAs} , and InxGa1 _{- xAs} has a low energy The advantage of the gap can improve the conduction band peak effect between the second base electrode layer 12 and the emitter layer 2, and when used in a transistor, it can reduce the on-voltage and power consumption;

2. Because In _x Ga _1-x As has the advantage of a low energy gap, it is easier to use Pt to form an ohmic contact layer on the second base electrode layer 12 , and the thickness of Pt can be reduced so that Pt is driven into the composite base electrode layer 1 . reduce the amount of interfacial recombination current generated by the device, and make the reliability test of the device more stable and reliable;

3. The preparation method only needs to correspondingly adjust the molar fraction of the raw material, the preparation method is convenient and the cost is low.

Second Embodiment

This embodiment provides an epitaxial structure 100 , which is different from the epitaxial structure 100 provided by the first embodiment in that the composition of In in the second base electrode layer 12 is different.

The epitaxial structure 100 includes a composite base electrode layer 1 and an emitter layer 2 . The composite base electrode layer 1 is a double-layer material structure, including a first base electrode layer 11 and a second base electrode layer 12 made based on the first base electrode layer 11 . The first base electrode layer 11 and the emitter layer 2 are the same as those in the first embodiment, and will not be repeated here.

In the direction of the In _x Ga _1-x As in the second base electrode layer 12 , the value of x increases gradually in the direction close to the emitter layer 2 . That is to say, in the second base electrode layer 12 in FIG. 1 , the In content gradually increases as the thickness increases, and the increasing speed can maintain a linear relationship with the thickness, or the size relationship can be flexibly designed according to performance requirements, as long as the In content increases with the thickness. As the height increases, there is an increasing trend, which should belong to the scope of protection claimed in this application.

Gradually increasing the In content can improve the carrier mobility of electrons and keep the resistance value at a low level. When used in transistors, it can ensure good frequency characteristics of the transistors. At the same time, the peak of the conduction band between the second base electrode layer 12 and the emitter layer 2 decreases as the In content gradually increases, which further reduces the turn-on voltage of the transistor.

Specifically, in the direction close to the emitter layer 2 of In _x Ga _1-x As in the second base electrode layer 12 , the value of x can be selected to gradually increase from 0.05 to 0.25. That is, in the second base electrode layer 12, the composition range of In is 5% to 25%.

In the process of preparing the second base electrode layer 12 on the first base electrode layer 11, the molar ratio of In and the molar ratio of Ga are firstly modulated in proportion, wherein the molar ratio of In will gradually increase, The molar fraction of Ga gradually decreases. Therefore, from bottom to top in the second base electrode layer 12 , the In content gradually increases, the Ga content gradually decreases, and the As content remains unchanged.

In addition to the beneficial effects of the first embodiment, the epitaxial structure 100 and the preparation method thereof provided in this embodiment can also improve the carrier mobility of electrons, keep the resistance at a low level, and are used in transistors. The frequency characteristic of the transistor can be guaranteed to be good. At the same time, the peak of the conduction band between the second base electrode layer 12 and the emitter layer 2 decreases as the In content gradually increases, which further reduces the turn-on voltage of the transistor.

Third Embodiment

This embodiment provides an epitaxial structure 100 , which is further designed to be an epitaxial structure 100 suitable for HBT (heterojunction bipolar transistor) based on the epitaxial structure 100 provided in the first embodiment or the second embodiment.

Referring to FIG. 3 , the epitaxial structure 100 includes a substrate 3 , a sub-collector layer 4 , a collector layer 5 , a composite base electrode layer 1 , an emitter layer 2 and a cap layer 6 , which are sequentially grown from bottom to top. Among them, the composite base electrode layer 1 and the emitter layer 2 adopt the structures in the first embodiment or the second embodiment.

In addition, an emitter metal contact layer 7 is arranged above the emitter layer 2 , and the emitter metal contact layer 7 covers the cap layer 6 and is in ohmic contact with the emitter layer 2 , wherein the cap layer 6 is etched with a supply for The through hole through which the emitter metal contact layer 7 passes. The composite base electrode layer 1 is provided with a base electrode metal contact layer 8 , and the base electrode metal contact layer 8 is in ohmic contact with the composite base electrode layer 1 . A collector metal contact layer 9 is provided on the sub-collector layer 4 , and the collector metal contact layer 9 is in ohmic contact with the sub-collector layer 4 .

The materials of the substrate 3 , the sub-collector layer 4 , the collector layer 5 and the cap layer 6 can be GaAs. In the base electrode metal contact layer 8, Pt, Ti, and Au may be stacked in order from bottom to top. In the second base electrode layer 12, in the direction close to the emitter layer 2, the In content is equal or gradually increased, which can make it easier to use Pt to form an ohmic contact layer on the second base electrode layer 12, which can be thinned The thickness of Pt reduces the amount of Pt driven into the composite base electrode layer 1 , thereby reducing the generation of interfacial composite current in the device, and making the reliability test of the device more stable and reliable.

In this application, only the example of applying the epitaxial structure 100 to HBT is introduced in detail. Of course, the epitaxial structure 100 provided in this application can also be applied to transistors of other structural forms. The composite base electrode layer 1 should all belong to the scope of protection claimed in this application.

The epitaxial structure 100 and the low-on-voltage transistor provided in this application can also be used in power amplifiers, and power amplifiers or other electrical appliances using the epitaxial structure 100 and the low-on-voltage transistor provided in this application should belong to this application. Scope of protection claimed.

It should be noted that the values mentioned in this application, including the values of components and thicknesses, are only relatively reliable values obtained by the applicant through experiments and calculations, rather than strictly limiting the corresponding parameters. are these values. Those skilled in the art may perform further experiments on the basis of the scheme of the present application to obtain other values with similar effects. These values do not depart from the core of the present application, and should also belong to the scope of protection claimed in the present application.

In the above-mentioned embodiments of the present application, the composite base electrode layer 1 is a double-layer material structure. According to the principle of the present application, the composite base electrode layer 1 can also be designed with a larger number of layer structures, which can also play the role of the composite base electrode in the present application. Therefore, in other embodiments, the number of layer structures may not be limited.

The epitaxial structure 100 and the low on-voltage transistor provided by the above-mentioned embodiments of the present application use low-energy-gap materials, which can reduce the on-voltage of the transistor and reduce power consumption; at the same time, the In content in the second base electrode layer 12 gradually increases from bottom to top , which can improve the carrier mobility of electrons, keep the resistance at a low level, and ensure good frequency characteristics of the transistor. In addition, in the preparation process, it is only necessary to adjust the discharge speed of the raw materials, the preparation method is simple, and the cost is low.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (10)

1. An epitaxial structure, comprising:

a composite base electrode layer (1) including a first base electrode layer (11) and a second base electrode layer (12) fabricated on the basis of the first base electrode layer (11);

an emitter layer (2) fabricated on the basis of the second base electrode layer (12);

wherein the material of the first base electrode layer (11) comprises GaAs, and the material of the second base electrode layer (12) comprises In_xGa_1-xAs。

2. The epitaxial structure of claim 1, wherein the In_xGa_1-xIn As, the value of x remains unchanged.

3. The epitaxial structure of claim 2 wherein x is 0.25.

4. Epitaxial structure according to claim 2, characterized In that the In composition In the second base electrode layer (12) is 25%.

5. The epitaxial structure of claim 1, wherein the In_xGa_1-xAs, the value of x gradually increases in the direction of approaching the emitter layer (2).

6. Epitaxial structure according to claim 3, characterized in that the value of x increases gradually from 0.05 to 0.25.

7. Epitaxial structure according to claim 2, characterized In that the composition of In the second base electrode layer (12) ranges from 5% to 25%.

8. Epitaxial structure according to claim 1, characterized in that the thickness of the second base electrode layer (12) is 5nm or less than a critical thickness.

9. Epitaxial structure according to claim 1, characterized in that the material of the emitter layer (2) comprises InGaP.

10. A low on-voltage transistor comprising an epitaxial structure according to any of claims 1 to 9.