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Novel Selectively Doped High Current THETA Device

IP.com Disclosure Number: IPCOM000036210D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Heiblum, M: AUTHOR [+2]

Abstract

Disclosed is a method to selectively dope the base of a hot electron device. Since a very thin base is necessary in order to achieve a high gain ballistic hot electron device, most devices suffer from a high base resistance that degrades their speed performance. It was previously proposed to generate a quasi two-dimensional electron gas (2DEG) in the base, and avoid doping it with impurities, by doping the collector barrier (AlGaAs) with donors, which will supply the electrons for 2DEG [*]. Due to the high mobility of the electrons in 2DEG, the base resistance is expected to be low enough for device applications. Attempts to do this failed since the barrier became very leaky after the introduction of impurities in it.

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Novel Selectively Doped High Current THETA Device

Disclosed is a method to selectively dope the base of a hot electron device. Since a very thin base is necessary in order to achieve a high gain ballistic hot electron device, most devices suffer from a high base resistance that degrades their speed performance. It was previously proposed to generate a quasi two- dimensional electron gas (2DEG) in the base, and avoid doping it with impurities, by doping the collector barrier (AlGaAs) with donors, which will supply the electrons for 2DEG [*]. Due to the high mobility of the electrons in 2DEG, the base resistance is expected to be low enough for device applications. Attempts to do this failed since the barrier became very leaky after the introduction of impurities in it.

By doping a modified emitter barrier which is also made of AlGaAs, one can achieve a similar effect. If the emitter will be made of uniform or step graded heavily doped AlGaAs with a thin undoped AlGaAs spacer to separate the doping from the GaAs layer, electrons will spill over into the adjacent GaAs layer (base), and form there the 2DEG (see the figure). Upon biasing negatively the emitter with respect to base, electrons will be injected via tunnelling through the tip of the emitter barrier (be it a graded AlGaAs, the higher AlAs mole fraction spacer or else) and traverse the base ballistically.

To reduce the risk of depletion of the base upon biasing the emitter negatively, a planar-doping sheet...