24.3 Field-Effect Transistors
705
(c)
In Ga As
E C
E V
F p
F n
F n
emitter
base
collector
Fig. 24.13 Microscopic image of an InGaP/GaAs HBT with two 5-nm InGaAs/GaAs QWs in the 30-nm wide base at a
zero base current and b at 1 mA base current in the common emitter configuration with Si CCD image of light emission.
c Schematic band diagram of a HBT with a single InGaAs/GaAs quantum well in the base. Parts a, b from [2057], part
c adapted from [2057]
(a)
ohmic
drain
contact
ohmic
source
contact
depletion
region
+
+ V D
V G
L
a
a
z
n-type
h
b
(b)
p-type
n
+
n
+
L
channel
source
drain
gate
d
V D
V G
-V BS
oxide
Fig. 24.14 a Shockley’s model of a JFET. The dashed line represents the middle of the symmetric channel of total
thickness 2a. The light grey area is the depletion layer with thickness h. The gate length is L. The dark grey areas are
ohmic metal contacts. Based on [109]. b Scheme of a MOSFET with channel length L and oxide thickness d. The dark
grey areas are ohmic metal contacts. Adapted from [574]
In a MESFET, a metal–semiconductor diode (Schottky diode) is used as rectifying contact instead
of a pn-diode. Otherwise, the principle is the same as that of the JFET. After the proposal by Mead in
1966 [135], the first (epitaxial) GaAs MESFET was realized by Hooper and Lehrer in 1967 [138]. The
MESFET offers some advantages, such as the fabrication of the metal gate at lower temperature than
necessary for the (diffusion or epitaxy of the) pn-diode, lower resistance, good thermal contact.
In a MISFET, the gate diode is a metal–insulator–semiconductor diode (Fig. 24.14b). If the insulator
is an oxide, the related FET is a MOSFET. When the gate is put at a positive voltage (for a p-channel), an
inversion layer is formed close to the insulator–semiconductor interface. This layer is an n-conducting
channel allowing conduction between the two oppositely biased pn-diodes. It can carry a high current.
The MOSFET was theoretically envisioned early by Lilienfeld in 1925 [55] and realized only in 1960
by Kahng and Atalla [121].
705
(c)
In Ga As
E C
E V
F p
F n
F n
emitter
base
collector
Fig. 24.13 Microscopic image of an InGaP/GaAs HBT with two 5-nm InGaAs/GaAs QWs in the 30-nm wide base at a
zero base current and b at 1 mA base current in the common emitter configuration with Si CCD image of light emission.
c Schematic band diagram of a HBT with a single InGaAs/GaAs quantum well in the base. Parts a, b from [2057], part
c adapted from [2057]
(a)
ohmic
drain
contact
ohmic
source
contact
depletion
region
+
+ V D
V G
L
a
a
z
n-type
h
b
(b)
p-type
n
+
n
+
L
channel
source
drain
gate
d
V D
V G
-V BS
oxide
Fig. 24.14 a Shockley’s model of a JFET. The dashed line represents the middle of the symmetric channel of total
thickness 2a. The light grey area is the depletion layer with thickness h. The gate length is L. The dark grey areas are
ohmic metal contacts. Based on [109]. b Scheme of a MOSFET with channel length L and oxide thickness d. The dark
grey areas are ohmic metal contacts. Adapted from [574]
In a MESFET, a metal–semiconductor diode (Schottky diode) is used as rectifying contact instead
of a pn-diode. Otherwise, the principle is the same as that of the JFET. After the proposal by Mead in
1966 [135], the first (epitaxial) GaAs MESFET was realized by Hooper and Lehrer in 1967 [138]. The
MESFET offers some advantages, such as the fabrication of the metal gate at lower temperature than
necessary for the (diffusion or epitaxy of the) pn-diode, lower resistance, good thermal contact.
In a MISFET, the gate diode is a metal–insulator–semiconductor diode (Fig. 24.14b). If the insulator
is an oxide, the related FET is a MOSFET. When the gate is put at a positive voltage (for a p-channel), an
inversion layer is formed close to the insulator–semiconductor interface. This layer is an n-conducting
channel allowing conduction between the two oppositely biased pn-diodes. It can carry a high current.
The MOSFET was theoretically envisioned early by Lilienfeld in 1925 [55] and realized only in 1960
by Kahng and Atalla [121].