EP0005059A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
A semiconductor device having a layered structure and a method of making it
Assignee: AT&T Inc
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Filing: 1979-04-20
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Granted: —
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Expires: 1999-04-20
Abstract
Abstract In known semiconductor devices, carrier mobility is limited to a considerable extent by impurity scattering. If the impurity concentration is reduced, so is the carrier concentration and hence the conductivity. In this invention a layered structure is employed in which wide-bandgap layers alternate with narrow-bandgap layers. The wide-bandgap layers are doped (22) to provide the charge carriers (26) which, however, are transferred (30) to the narrow-bandgap layers where they are essentially confined by band steps (ΔE c ) at the interfaces between layers. Thus the charge carriers are segregated from the impurities which provide them and the dilemma is avoided. Mobilities well above the theoretical maximum can be achieved in this way. The layered structure can be made using molecular beam epitaxy.
Inventors
- 👤 Raymond Dingle
- 👤 Arthur Charles Gossard
- 👤 Horst Ludwig Stormer
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 16:23
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/40; H10D30/47; H10D30/471; H10D30/473; H10D30/4732; H10D62/00; H10D62/80; H10D62/81; H10D62/815; H10D62/8161; H10D62/8162; H10D62/8164; H10P; H10P14/00; H10P14/20; H10P14/32; H10P14/3202; H10P14/3214; H10P14/3218; H10P14/3221; H10P14/3222; H10P14/3242; H10P14/3244; H10P14/3251; H10P14/3252; H10P14/34; H10P14/3402; H10P14/3414; H10P14/3418; H10P14/3421; H10P14/3422; H10P14/3438; H10P14/3441
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
94 words
A semiconductor device having a layered structure (10) characterised in that the layered structure includes a layer (14) of material having a comparatively wide bandgap forming a lattice-matched heterojunction (16) with a layer (12) of material having a comparatively narrow bandgap, the wide-bandgap layer is doped so that the product of impurity concentration times thickness for the wide-bandgap layer is greater than the product of impurity concentration times thickness for the narrow-bandgap layer, and charge carriers of the type provided by the doping of the wide-bandgap layer are essentially confined to the narrow-bandgap layer.
Claim 2
Dependent Claim
94 words
A semiconductor device having a layered structure (10) characterised in that the layered structure includes a layer (14) of material having a comparatively wide bandgap forming a lattice-matched heterojunction (16) with a layer (12) of material having a comparatively narrow bandgap, the wide-bandgap layer is doped so that the product of impurity concentration times thickness for the wide-bandgap layer is greater than the product of impurity concentration times thickness for the narrow-bandgap layer, and charge carriers of the type provided by the doping of the wide-bandgap layer are essentially confined to the narrow-bandgap layer.
Claim 3
Dependent Claim
127 words
A semiconductor device having a layer structure (10) characterised in that the layer structure comprises layers (14) of a material having a comparatively wide bandgap interleaved with layers (12) of material having a comparatively narrow bandgap, the said materials are substantially lattice-matched so as to form heterojunctions at the interfaces (16) between adjacent layers, the wide-bandgap layers (14) are so doped that the product of impurity concentration times thickness for each wide-bandgap layer is greater than the products of impurity concentration times thickness for the adjacent narrow-bandgap layers, and there are conduction or valence band steps (ΔE c ) at the interfaces (16) between adjacent layers effective to essentially confine the charge-carriers of the type provided by the doping of the wide-bandgap layers to the narrow-bandgap layers.
Claim 4
Dependent Claim
127 words
A semiconductor device having a layer structure (10) characterised in that the layer structure comprises layers (14) of a material having a comparatively wide bandgap interleaved with layers (12) of material having a comparatively narrow bandgap, the said materials are substantially lattice-matched so as to form heterojunctions at the interfaces (16) between adjacent layers, the wide-bandgap layers (14) are so doped that the product of impurity concentration times thickness for each wide-bandgap layer is greater than the products of impurity concentration times thickness for the adjacent narrow-bandgap layers, and there are conduction or valence band steps (ΔE c ) at the interfaces (16) between adjacent layers effective to essentially confine the charge-carriers of the type provided by the doping of the wide-bandgap layers to the narrow-bandgap layers.
Claim 5
Dependent Claim
33 words
A device as claimed in claim 2 wherein the wide-bandgap layers are doped only in a central portion (14.2) thereof so as to leave thin, substantially undoped buffer zones (14.1) adjacent the heterojunctions.
Claim 6
Dependent Claim
20 words
A device as claimed in claim 3 wherein the buffer zones are between about 10 and 60 Angstrom units thick.
Claim 7
Independent Claim
27 words
A device as claimed in any of claims 1 to 4 wherein the narrow-bandgap layers have impurity concentrations not greater than about 10 14 /cm 3 .
Claim 8
Dependent Claim
23 words
A device as claimed in claim 5 wherein the wide-bandgap layers have an impurity concentration of at least 10 16 /cm 3 .
Claim 9
Dependent Claim
39 words
A device as claimed in claim 6 wherein the narrow-bandgap layers are of Al y Ga 1-y As and the wide-bandgap layers are of n-type Al x Ga 1-x As, 0 ≤ y , x - y > 0.02.
Claim 10
Dependent Claim
19 words
A device as claimed in claim 7 wherein y - 0 and x is between about 0.2 and 0.35.
Claim 11
Dependent Claim
25 words
A device as claimed in claim 7 or claim 8 wherein the layers each have a thickness in the range 100 to 400 Angstrom units.
Claim 12
Independent Claim
58 words
A device as claimed in any of claims 7 to 9 wherein the Al x Ga 1-x As layers are doped n-type in the range of about 10 16 to about 10 18 /cm 3 , and including means (15) for cooling the layer structure so as to increase electron mobility therein compared with that at room temperature.
Claim 13
Dependent Claim
43 words
A device as claimed in claim 10 wherein the cooling means includes cryogenic apparatus for cooling the layer structure below approximately 50°K so as to increase the electron mobility therein to at least about 16,000 c m 2 V- 1 sec -1 .
Claim 14
Independent Claim
40 words
A device as claimed in any of the preceding claims including means (104, 106) arranged to facilitate .passing an electric current through the layer structure so that the current flow in the layer structure is generally parallel to the layers.
Claim 15
Dependent Claim
42 words
A device as claimed in claim 11 wherein the facilitating means comprises a source (104) and a drain (106) of a field-effect transistor, and wherein a gate electrode (114) is closely adjacent to the layer structure for controlling the said current flow.
Claim 16
Independent Claim
37 words
A method of making a device as claimed in any of the preceding claims wherein the layers are grown by molecular beam epitaxy in an ultra high vacuum chamber. the layers being grown on a semiconductor substrate.
Claim 17
Dependent Claim
65 words
A method as claimed in claim 14 wherein the chamber includes an oven carrying a dopant source which is used to generate a donor beam for doping the wide-bandgap layer or layers and which is shuttered closed during the growth of the narrow-bandgap layer or layers so that any impurities incorporated in the narrow-bandgap layer or layers are primarily from background contamination in the chamber.
References Cited (Backward Citations)
No citation records indexed.
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