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Low Source Resistance Modulation Doped Field-Effect Transistor Device

IP.com Disclosure Number: IPCOM000035720D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 111K

Publishing Venue

IBM

Related People

Heiblum, M: AUTHOR [+2]

Abstract

A reduced series resistance modulation doped field-effect transistor (MODFET) structure is provided with two channels of 2D electron gases, both in parallel. This reduces the series resistance by at least a factor of two. The layered structure is described in Fig. 1. It is fabricated by growth by normal molecular beam epitaxy (MBE).

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Low Source Resistance Modulation Doped Field-Effect Transistor Device

A reduced series resistance modulation doped field-effect transistor (MODFET) structure is provided with two channels of 2D electron gases, both in parallel. This reduces the series resistance by at least a factor of two. The layered structure is described in Fig. 1. It is fabricated by growth by normal molecular beam epitaxy (MBE).

In the structure of Fig. 1, two high conductivity channels are formed on both sides of the doped AlGaAs. The lower one has a higher mobility, such as at 77K, of the order of 100,000 cm2/V sec. The upper one has usually a lower mobility, such as at 77K, of the order of 40,000 cm2/V sec. The top GaAs layer is intentionally left undoped to a depth of about 300 Angstroms, facilitating the conditions for the high mobility electron gas. In the fabrication of the MODFET device, a gate is then recessed in as shown in Fig. 2.

The 20 Angstrom AlAs layer will serve as a stop layer for reactive ion etching (RIE), so that the gate can be placed accurately above the AlGaAs. The gate is recessed so that N 200 Angstroms of n+:GaAs is left and the surface depletion layer does not pinch-off the high conductivity 2D gas. In the alternative, the 20 Angstroms of AlAs may be eliminated and a reactive ion etch will stop at the AlGaAs. Further, if the AlGaAs is only 200 Angstroms, an enhancement type device will be fabricated. Still further, if the AlGaAs is N 400 Angstroms, a depletion ty...