# US 10,312,324 B2 · Epitaxial wafer for hetero-junction bipolar transistor and hetero-junction bipolar transistor

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- Number: US 10,312,324 B2
- Document ID: US10312324B2
- Status: Granted
- Kind: B2
- Application number: 15/561,345
- Filed: 2016-01-12
- Published: 2018-03-01
- Granted: 2019-06-04
- Earliest claimed: 2015-03-26
- Assignees: Sumitomo Chemical Company, Limited
- Applicants: Sumitomo Chemical Company, Limited
- Inventors: Takeshi Meguro; Shinjiro Fujio
- Web page: https://patentgrep.com/patent/US10312324B2

## CPC

- H10D 62/137: {Collector regions of BJTs}
- H10D 10/021: {of heterojunction BJTs [HBT]}
- H10D 10/821: {Vertical heterojunction BJTs}
- H10D 62/854: further characterised by the dopants
- H10D 62/85: being Group III-V materials, e.g. GaAs
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

An epitaxial wafer for a heterojunction bipolar transistor and a heterojunction bipolar transistor capable of reducing the resistance of the sub-collector layer without reducing the current amplification factor are provided. In an epitaxial wafer for a heterojunction bipolar transistor including a sub-collector layer made of n-type GaAs, the sub-collector layer contains n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site and n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site.

## Claims

### Claim 1

An epitaxial wafer for a heterojunction bipolar transistor comprising:
a sub-collector layer made of n-type GaAs, the sub-collector layer containing n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site and n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site,
wherein in the sub-collector layer, a sum ((A)+(B)) of a concentration (A) of the n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site and a concentration (B) of the n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site is equal to or greater than 3×1018 cm−3 and equal to or less than 1×1019 cm−3.

### Claim 2

A heterojunction bipolar transistor comprising:
a sub-collector layer made of n-type GaAs, the sub-collector layer containing n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site and n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site,
wherein in the sub-collector layer, a sum ((A)+(B)) of a concentration (A) of the n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site and a concentration (B) of the n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site is equal to or greater than 3×1018 cm−3 and equal to or less than 1×1019 cm−3.

### Claim 3 (depends on 1)

The epitaxial wafer for a heterojunction bipolar transistor according to claim 1, wherein in the sub-collector layer, a ratio ((A)/(B)) of a concentration (A) of the n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site to a concentration (B) of the n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site is equal to or greater than 2 and equal to or less than 5.

### Claim 4 (depends on 2)

The heterojunction bipolar transistor according to claim 2, wherein in the sub-collector layer, a ratio ((A)/(B)) of a concentration (A) of the n-type impurities having a covalent radius that is smaller than the covalent radius of the substitution site to a concentration (B) of the n-type impurities having a covalent radius that is larger than the covalent radius of the substitution site is equal to or greater than 2 and equal to or less than 5.