Browse Prior Art Database

Heterojunction FET

IP.com Disclosure Number: IPCOM000061110D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Harder, C: AUTHOR

Abstract

A heterojunction field-effect transistor (HJFET) is proposed having an n GaAs channel and a p+In(x)Ga(1-x)As gate, causing the bandgap of the heavily doped gate to be narrower than the bandgap of the channel. Compared with an ordinary junction FET, the disclosed HJFET has a large gate turn-on voltage, permitting higher voltage swing operations. Also, its gate can be used as a voltage clamp since the injection of minority carriers is reduced. A cross-section of the transistor is shown in the figure.""The n GaAs channel is formed on an i GaAs substrate.

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Heterojunction FET

A heterojunction field-effect transistor (HJFET) is proposed having an n GaAs channel and a p+In(x)Ga(1-x)As gate, causing the bandgap of the heavily doped gate to be narrower than the bandgap of the channel. Compared with an ordinary junction FET, the disclosed HJFET has a large gate turn-on voltage, permitting higher voltage swing operations. Also, its gate can be used as a voltage clamp since the injection of minority carriers is reduced. A cross-section of the transistor is shown in the figure.""The n GaAs channel is formed on an i GaAs substrate. The gate consists of p+In(x)Ga(1-x)As, in which x is very small, just sufficiently large that most of the gate current is due to the current In of electrons from the channel into the gate and only a small fraction is due to the current Ip of holes from the gate into the channel, if the gate is forward biased. A rough estimate of the necessary difference in bandgap dEg between gate and channel material can be derived from

(Image Omitted)

where B is the injection ratio In/Ip, Pg and Nch are the carrier concentrations of holes in the gate and electrons in the channel, respectively, and Vpch and Vng are the effective minority carrier velocities for electrons in the gate and holes in the channel. With a doping ratio of Pg/Nch = 5, an effective ratio of velocities Vpch/Vng = 1/20 and an injection ratio B = 100, a dEg = 80 meV is needed at room temperature. This can be achieved with an In fraction of x =...