GB2128026A - Transistors - Google Patents
Transistors Download PDFInfo
- Publication number
- GB2128026A GB2128026A GB08324869A GB8324869A GB2128026A GB 2128026 A GB2128026 A GB 2128026A GB 08324869 A GB08324869 A GB 08324869A GB 8324869 A GB8324869 A GB 8324869A GB 2128026 A GB2128026 A GB 2128026A
- Authority
- GB
- United Kingdom
- Prior art keywords
- base
- collector
- emitter
- regions
- region
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000004065 semiconductor Substances 0.000 claims abstract description 9
- 239000002784 hot electron Substances 0.000 claims abstract description 6
- 239000000463 material Substances 0.000 claims abstract description 6
- 239000004411 aluminium Substances 0.000 claims description 9
- 229910052782 aluminium Inorganic materials 0.000 claims description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 9
- 239000000758 substrate Substances 0.000 claims description 9
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 claims description 6
- 229910001218 Gallium arsenide Inorganic materials 0.000 claims description 6
- 229910000980 Aluminium gallium arsenide Inorganic materials 0.000 claims description 4
- 239000000969 carrier Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 2
- 241000024192 Aloa Species 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005513 bias potential Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/7606—Transistor-like structures, e.g. hot electron transistor [HET]; metal base transistor [MBT]
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Bipolar Transistors (AREA)
Abstract
A hot electron transistor comprises emitter (11), base (5) and collector (3) regions consisting of n-type semiconductor materials having energy band- gaps such that there is a conduction band edge discontinuity ( DELTA Eeb) between the base (5) and emitter (11) regions which is larger than the conduction band edge discontinuity ( DELTA Ecb) between the base (5) and collector (3) regions. A corresponding hot hole transistor is also envisaged. <IMAGE>
Description
SPECIFICATION
Transistors
This invention relates to transistors.
More particularly the invention relates to socalled hot carrier transistors, that is to say transistors wherein current carriers are injected into the base region of the transistor from the emitter region and travel through the base region to the collector region ballistically. By contrast, in a conventional junction transistor carriers diffuse from one region to another under the influence of applied bias potentials.
A known form of hot carrier transistor comprises a very thin metal base region between semiconductor emitter and collector regions. However, the different electronic structure of the semiconductor and metal regions gives rise to poor interface quality with a resultant high quantum mechanical reflection coefficient at the metal-semiconductor interfaces and hence, low current gain.
It is an object of the invention to provide an improved form of hot carrier transistor.
Accordingly, the present invention provides a hot electron transistor which comprises emitter, base and collector regions consisting of n-type conductivity semiconductor materials having energy bandgaps such that there is a conduction band edge discontinuity between the base and emitter regions which is larger than the conduction band edge discontinuity between the base and collector regions.
The invention also provides a hot hole transistor which comprises emitter, base and collector regions consisting of p-type conductivity semiconductor materials having energy bandgaps such that there is a valence band edge discontinuity between the base and emitter regions which is larger than the valence band edge discontinuity between the base and collector regions.
In one particular embodiment of the invention the emitter and collector regions consist of aluminium-gallium arsenide of the form AIxGa1 XAs doped to have n-type conductivity and the base region consists of gallium arsenide the collector region having a lower aluminium content than the emitter region.
Preferably the aluminium content of the collector region falls in a direction away from the base-collector interface to a value substantially equal to the aluminium content in a gallium arsenide substrate carrying the transistor.
One transistor in accordance with the invention will now be descirbed, by way of example with reference to the accompanying drawings in which:
Figure 1 is a diagrammatic sectional view of the transistor; and
Figure 2 is a diagram illustrating the variation of the energy bandgap through the thickness of the transistor.
Referring to Figure 1 the transistor incorporates gallium arsenide substrate 1 having a high n-type doping level.
On a main face the substrate 1 carries a first layer 3 consisting of aluminium-gallium arsenide and having an n-type doping level lower than the substrate 1. The aluminium content of the layer falls from a maximum value at its face remote from the substrate 1 to zero at its face adjacent the substrate 1.
On the layer 3 there is formed a second layer 5 of gallium arsenide having an n-type doping level higher than the layer 3.
On the exposed surface of the layer 5 there are two narrow spaced parallel metal strips 7 and 9, and centrally between the strips 7 and 9 there is a strip 11 of similar width consisting of aluminium-gallium arsenide having throughout a higher aluminium content than the maximum aluminium content of the layer 3, and an n-type doping level between that of the layers 3 and 5. On its face remote from the layer 5 the strip 11 carries a contact strip 13.
The strip 11, layer 5 and layer 3 respectively constitute the emitter, base and collector regions of the transistor, the strip 13 serves as an emitter contact and the strips 7 and 9 as base contacts, the collector contact being constituted by an area of metallisation (not shown) on a surface of the substrate 1.
In the transistor the variation of the conduction band minimum energy level and the valence band maximum energy level through the thickness of the transistor are as indicated by lines Ec and Ev respectively in Figure 2. Thus, at the emitter-base interface there is an energy level drop of hEeb and at the base-collector interface an energy level increase of herb, smaller than AEeb. Hence, in operation, with the emitter region negatively biassed with respect to the base region and the collector region positively biassed with respect to the base region, electrons will be injected from the emitter region into the base region 5 with an energy AE0b above the base region conduction band edge and will travel semiballistically towards the collector region.Those electrons having an energy greater than AECb when they reach the collector-base interface will enter the collector region 3, the rest appearing as base current.
For values of AEeb above 0.34 eV, electrons are transferred directly into the upper valleys of the conduction band and the device becomes inefficient.
AE0b is preferably made greater than 0.2 eV for operation at normal temperatures to limit thermionic emission from base to collector.
A value for AEeb between these two limits is therefore chosen to be for example 0.3 eV. The initial electron velocity in the (100) direction in the base region will then approach 108 ##cms/s with a mean free path of about 1500 A . With a value of AEcb less than hEeb by 0.05 eV, i.e. 0.25 eV, a high percentage of electrons, in the region of 85%, will reach the collector region 3 for base region thicknesses of 0.45 lim. Athickness of 0.2 lim for the base region 5 is thus quite acceptable giving operation for frequencies up to 200 G Hz.
Values of 0.3 eV and 0.25 eV respectively for AE0b and hECb are obtained with the emitter and collector regions having compositions adjacent their respective interfaces with the base region of Aloa Ga0 7 As and Al0.25 GaO 7s As respectively.
Further requirements for microwave operation are low base resistance and low emitter and collector charging times. This dictates a high base region doping e.g. 1019 atoms per cc and a small emitter width, e.g. 1 um.
The emitter region 11 suitably has a doping level of 3 x 1017 atoms per cc and a thickness of 0.05 ,am.
The collector region 3 suitably has a doping level of 3x 1015 atoms per cc and a thickness of 0.3 ,um, the collector depletion region being required to be sufficiently wide to prevent breakdown.
The strips 7 and 9 are suitably of width 1 Fm and at spacings of 1 m from the emitter region strip 11.
It will be understood that the grading of the composition of the collector region alloy is to avoid a conduction band edge discontinuity at the collector-substrate interface.
It will be appreciated that with a transistor according to the invention satisfactory operation at very high frequencies may be expected, not only because of short base region transit time, but also because there are no minority carrier storage or diffusion effects.
It will be further appreciated that while carrier reflection at the emitter-base and collector-base interfaces will affect performance of the device, since the crystal structures on either side of each interface are similar, such reflection will not be large enough to impair operation of the device seriously.
Whilst in the transistor described above, by way of example, the current carriers are electrons, in other transistors in accordance with the invention the current carriers may be holes. The emitter base and collector regions will then consist of p-type conductivity semiconductor materials chosen to provide appropriate discontinuities in the valence band edge.
Claims (6)
1. A hot electron transistor comprising emitter, base and collector regions consisting of n-type conductivity semiconductor materials having energy bandgaps such that there is a conduction band edge discontinuity between the base and emitter regions which is larger than the conduction band edge discontinuity between the base and collector regions.
2. A hot electron transistor according to Claim 1 wherein the emitter and collector regions consist of aluminium-gallium arsenide of the form AI,Ga,.,As doped to have n-type conductivity and the base region consists of gallium arsenide, the collector region having a lower aluminium content than the emitter region.
3. A hot electron transistor according to Claim 2 wherein the aluminium content of the collector region falls in a direction away from the base-collector interface to a value substantially equal to the aluminium content in a gallium arsenide substrate carrying the transistor.
4. A hot electron transistor substantially as hereinbefore described with reference to the accompanying Figures.
5. A hot hole transistor comprising emitter, base and collector regions consisting of p-type conductivity semiconductor materials having energy bandgaps such that there is a valence band edge discontinuity between the base and emitter regions which is larger than the valence band edge discontinuity between the base and collector regions.
6. A hot hole transistor substantially as hereinbefore described.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08324869A GB2128026B (en) | 1982-10-01 | 1983-09-16 | Transistors |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8228096 | 1982-10-01 | ||
| GB08324869A GB2128026B (en) | 1982-10-01 | 1983-09-16 | Transistors |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8324869D0 GB8324869D0 (en) | 1983-10-19 |
| GB2128026A true GB2128026A (en) | 1984-04-18 |
| GB2128026B GB2128026B (en) | 1986-03-26 |
Family
ID=26284004
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08324869A Expired GB2128026B (en) | 1982-10-01 | 1983-09-16 | Transistors |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2128026B (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0092645A2 (en) * | 1982-04-26 | 1983-11-02 | International Business Machines Corporation | Transistor and circuit including a transistor |
| FR2556504A1 (en) * | 1983-12-12 | 1985-06-14 | Gen Electric Co Plc | SEMICONDUCTOR SWITCHING DEVICE |
| US4926221A (en) * | 1988-09-07 | 1990-05-15 | At&T Bell Laboratories | Bipolar hot electron transistor |
| US5206524A (en) * | 1988-09-28 | 1993-04-27 | At&T Bell Laboratories | Heterostructure bipolar transistor |
| GB2261112A (en) * | 1991-10-30 | 1993-05-05 | Hitachi Europ Ltd | Electronic device with phase selection |
| US5543749A (en) * | 1986-03-13 | 1996-08-06 | Fujitsu Limited | Resonant tunneling transistor |
-
1983
- 1983-09-16 GB GB08324869A patent/GB2128026B/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0092645A2 (en) * | 1982-04-26 | 1983-11-02 | International Business Machines Corporation | Transistor and circuit including a transistor |
| EP0092645A3 (en) * | 1982-04-26 | 1986-10-01 | International Business Machines Corporation | Transistor and circuit including a transistor |
| FR2556504A1 (en) * | 1983-12-12 | 1985-06-14 | Gen Electric Co Plc | SEMICONDUCTOR SWITCHING DEVICE |
| US5543749A (en) * | 1986-03-13 | 1996-08-06 | Fujitsu Limited | Resonant tunneling transistor |
| US4926221A (en) * | 1988-09-07 | 1990-05-15 | At&T Bell Laboratories | Bipolar hot electron transistor |
| US5206524A (en) * | 1988-09-28 | 1993-04-27 | At&T Bell Laboratories | Heterostructure bipolar transistor |
| GB2261112A (en) * | 1991-10-30 | 1993-05-05 | Hitachi Europ Ltd | Electronic device with phase selection |
| GB2261112B (en) * | 1991-10-30 | 1995-06-28 | Hitachi Europ Ltd | Charge carrier source |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8324869D0 (en) | 1983-10-19 |
| GB2128026B (en) | 1986-03-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19930916 |