US 5,206,524 AGranted

Heterostructure bipolar transistor

AssigneeAT&T Bell Laboratories

InventorsYoung-Kai Chen, Anthony F. J. Levi, Richard N. Nottenburg, Morton Panish

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Abstract

Improved heterojunction bipolar transistor (HBT) are disclosed. Inventive devices can attain high cut-off frequency (f.sub.T), exemplarily 80 GHz or higher, and high DC current gain (.beta.), exemplarily 25 or higher. The devices exhibit lateral scaling, permitting reduction in emitter stripe width without unacceptable decrease in .beta.. Exemplarily the stripe width is 1 .mu.m or less. The inventive HBTs are hot electron devices, with the hot electrons in the base region being spatially confined such that relatively few electrons reach the surface of the extrinsic base region. The relatively low bulk and surface recombination rate in the base of inventive HBTs is an important aspect of the invention and makes possible devices having relatively high .beta. and low power consumption. Appropriate choice of base material, namely, a semiconductor material having relatively low intrinsic surface recombination velocity, can result in further reduction of surface recombination, as can, for instance, the use of an appropriate non-alloyed metal base contact. Appropriate choice of collector material can result in improved ballistic transport through the collector depletion region, and novel selection criteria are disclosed. InP, InAs, and In.sub.0.53 Ga.sub.0.47 As are exemplary materials that meet these criteria. Use of a highly doped collector contact region, with dopant level within a relatively narrow concentration range, can also lead to improved device behavior, as can the use of a compound emitter that comprises one or more appropriately placed thin undoped heteroepitaxial layers.

A heterostructure bipolar transistor comprising a collector region, a base region, and an emitter region, and further comprising means for making electrical contact with the emitter, base, and collector regions, respectively;

the transistor being of the type wherein, under normal emitter/base forward bias conditions, hot electrons are injected into the base region from the emitter region;
associated with the transistor being structural features including a width W of the emitter region, a base region thickness, a base region dopant concentration, and a base region surface that comprises, in addition to a portion that is overlain by the emitter region (this portion to be referred to as the "intrinsic" base region surface), a further portion that is adjacent to the emitter region and is not overlain by the emitter region, the further portion to be referred to as the "extrinsic" base region surface;
wherein
a) the emitter and collector regions comprise n-type III-V semiconductor material and the base region comprises p-type III-V semiconductor material;
b) the width W is at most 1 .mu.m, the base region thickness is less than 100 nm, and at least a portion of the base region has a dopant concentration of at least 2.times.10.sup.19 /cm.sup.3 ;
characterized in that
c) the emitter region comprises at least a first and a second semiconductor material, associated with each of the first and second materials being a valence band edge and a conduction band edge, the second material having a bandgap that is wider than the bandgap of the first material, with the offset between the first and second material valence band edge being greater than half the difference between said bandgaps, a layer of the second material being epitaxial with the first material and being situated relatively close to the emitter region/base region interface and being substantially undoped, with the second material layer thickness selected to substantially prevent tunneling of holes from the base region into the emitter under normal emitter/base forward bias conditions.

4 more elements

Facts

Application

07/721,913Filed 20 Jun 1991 · continuation

Priority

28 Sep 1988

Granted

27 Apr 1993

Term ends

Not estimatedThe source records don’t support an estimate.

Classification4 codes

H10D 10/821
Heterojunction BJTs: vertical heterojunction BJTs
H10D 62/165
Semiconductor regions connected to electrodes carrying current to be rectified, amplified or switched, e.g. source or drain regions: tunnel injectors
H10D 62/824
Heterojunctions: comprising only Group III-V materials heterojunctions, e.g. GaN/AlGaN heterojunctions
H10D
Inorganic electric semiconductor devices

Abstract

Claims8