Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Bipolar transistor
Reexamination Certificate
2000-11-14
2002-10-08
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Bipolar transistor
C257S197000
Reexamination Certificate
active
06462362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heterojunction bipolar transistor and a fabricating method thereof, and in particular, to those used for microwave devices (such as mobile telephone units) and optical communication signal processing circuits.
2. Prior Arts
FIG. 1
is a sectional view showing the structure of a heterojunction bipolar transistor (hereinafter referred. to as HBT) disclosed in “Extended Abstracts of the 1992 International Conference on Solid State Devices and Materials, pages 316-318 and “Electronic Letters”, Vol. 28, No. 25, pages 2308-2309. As shown in
FIG. 1
, in the HBT according to the first prior art reference, a sub-collector layer
52
is grown on a substrate
51
. A collector layer
53
is grown on the sub-collector layer
52
. A base layer
54
is grown on the collector layer
53
. A part of the base layer
54
is coated with a very thin emitter layer
55
. The thickness of the emitter layer
55
is around 30 nm. An emitter contact layer
56
is grown on the emitter layer
55
.
A base electrode
61
is formed on an alloyed region
63
. The alloyed region
63
is formed by heat treating the emitter layer
55
. The base electrode
61
and the base layer
54
are ohmic contacted through the alloyed region
63
. A part of the emitter layer
55
without being covered by the emitter contact layer is depleted and acts as guard-ring. Tile guard-ring
70
is depleted by pinning the Fermi level on front surface of a semiconductor so as prevent carriers from being recombined in the vicinity of the front surface of the base layer
54
.
An emitter electrode
62
is formed on the emitter contact layer
56
. An insulator film
80
is formed so that the insulator film
80
coats the guard-ring
70
, the base electrode
61
, the base layer
54
, and the sub-collector layer
52
.
However, in the HBT shown in
FIG. 1
, since the thickness of the emitter layer
55
is around 30 nm, even if the alloyed region
63
is formed, the contact resistance between the base layer
54
and the base electrode
61
becomes large. Thus, the high frequency characteristic of the HBT deteriorates.
As a second prior art reference that solves such a disadvantage, an HBT that does not have an alloyed region
63
is disclosed in JPA 10-303214.
FIG. 2
is a sectional view showing the structure of the HBT described in the publication as the second prior art reference. For simplicity, in
FIG. 2
, similar portions to those in
FIG. 1
are denoted by similar reference numerals. In the HBT shown in
FIG. 2
, a base electrode
61
is formed so that the base electrode
61
contacts to a base layer
54
and a part of a guard-ring
70
. Thus, the base electrode
61
and the base layer
54
are contacted without need to use an alloyed region
63
. As a result, since the contact resistance between the base layer
54
and the base electrode
61
becomes small, the high frequency characteristic of the HBT can be suppressed from deteriorating.
However, in the HBT shown in
FIG. 2
, since the base electrode
61
is contacted to the guard-ring
70
, when the HBT is driven, the surface potential of the guard-ring
70
varies. Thus, a part of the guard-ring
70
is not depleted, but becomes a neutral region. Consequently, a PN junction between the guard-ring
70
and the base layer
54
causes carriers to be recombined. As a result, since a leak current flows between the base and the emitter of the HBT, the current gain decreases.
On the other hand, when the base electrode
61
is not contacted to the guard-ring
70
, carriers are recombined in the vicinity of the front surface of the base layer
54
and an edge portion
70
a
of the guard-ring
70
. As a result, a leak current flows.
SUMMARY OF THE INVENTION
In order to overcome the aforementioned disadvantages, the present invention has been made and accordingly, has an object to provide an HBT and its fabricating method in which a contact resistance between the base layer and the base electrode is small and a leak current between the base and the emitter is suppressed.
According to an aspect of the present invention, there is provided a bipolar transistor, comprising: a collector layer of first conduction type; a base layer of second conduction type, formed on the collector layer; a prevention layer, formed on the base layer, for preventing carrier recombination; an emitter layer of first conduction type, formed on a first part of the prevention layer; and a base electrode, formed on a second part separated from the first part of the prevention layer.
The bipolar transistor may further comprise: a guard ring, formed on an outer periphery of the emitter layer and on the prevention layer.
The bipolar transistor may further comprise: an emitter electrode, formed on the emitter layer.
The bipolar transistor may further comprise: an emitter contact layer, formed between the emitter layer and the emitter electrode.
The bipolar transistor may further comprise: a sub-collector layer of first conduction type, formed below the collector layer.
The bipolar transistor may further comprise: a collector electrode, connected to the sub-collector layer.
The bipolar transistor may further comprise: an insulation side wall, formed on the guard-ring, for defining the size of the guard-ring.
The bipolar transistor may further comprise: an alloyed region, piercing the prevention layer, formed between the base layer and the base electrode.
The bipolar transistor may further comprise: a diffused region, piercing the prevention layer, formed between the base layer and the base electrode.
In the bipolar transistor, the emitter layer may be a III-V group compound semiconductor.
In the bipolar transistor, a V group element of the III-V group compound semiconductor may be phosphorus.
In the bipolar transistor, the III-V group compound semiconductor may be selected from a group consisting of InGaP, InGaAsP, InGaAlP, InGaAlAsP, AlGaP, AlGaAsP, GaP, GasP, and InP.
In the bipolar transistor, the emitter layer may have a laminate structure.
In the bipolar transistor, the laminate structure may have a sloped-composition layer between two adjacent layers.
In the bipolar transistor, the base layer may be a III-V group compound semiconductor.
In the bipolar transistor, a V group element of the III-V group compound semiconductor may be arsenic.
In the bipolar transistor, the III-V group compound semiconductor may be selected from a group consisting of GaAs, AlGaAs, InGaAs, InGaAs, InAlGaAs, and InAlAs.
In the bipolar transistor, the base layer may have a laminate structure.
In the bipolar transistor, the laminate structure may have a sloped-composition layer between two adjacent layers.
In the bipolar transistor, the prevention layer may be of first conduction type.
In the bipolar transistor, a potential gap of the prevention layer may be larger than a potential gap of the base layer so that the potential gap of the prevention layer functions as a potential barrier for majority carriers of the base layer.
In the bipolar transistor, when the bipolar transistor is driven, a portion of the prevention layer which is not coated with the emitter layer may be fully depleted.
In the bipolar transistor, when the bipolar transistor is driven, a portion of the prevention layer which is not coated with the emitter layer or the guard-ring layer may be fully depleted.
In the bipolar transistor, a potential barrier of the prevention layer for majority carriers of the emitter layer may be 100 meV or less.
In the bipolar transistor, the prevention layer may have a laminate structure.
In the bipolar transistor, the laminate structure may have a sloped-composition layer between two adjacent layers.
In the bipolar transistor, the alloyed region may contain palladium or platinum.
In the bipolar transistor, the diffusion region may be doped with at least one of zinc, beryllium, carbon, magnesium, and manganese.
In the bipolar transistor, the highest portion of the prevention layer may have an etching resistance against an etchant of the emitter layer.
In the bip
McGinn & Gibb PLLC
Nadav Ori
Thomas Tom
LandOfFree
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