Gunn effect

The Gunn effect [ ˈgʌn- ] is a physical effect that occurs in some semiconductor materials at high electrical field strengths and causes a negative differential resistance .

The effect was discovered by John Battiscombe Gunn in 1963 when he made electrical contact with gallium arsenide (GaAs) or indium phosphide (InP) with an ohmic contact, exposed them to high electrical field strengths and, from a critical value, noticed a high-frequency oscillation in the measured electrical current. The effect was theoretically predicted in advance by BK Ridley, TB Watkins and C. Hilsum and is therefore also called the RWH mechanism. H. Kromer explained it as an electron transfer process.

The effect in the applied Gunn diode in waveguides for microwaves to be generated.

description

Simplified band structure of GaAs at 300 K.

In order for the Gunn effect to occur in a semiconductor, one of the energy bands responsible for conducting electrical current must have a relative minimum ( electron transport ) or maximum ( defect electron transport ), the energy of which differs only slightly from the absolute minimum or maximum.

Electrons that have been excited from the valence band into the conduction band , for example , are first in the absolute minimum of the conduction band. As a result, the flow of current through the semiconductor first increases with increasing voltage . When these electrons reach an energy in an electric field that is in the range of the energy difference between the absolute and relative minimum (for GaAs 0.29 eV ), they are scattered into the relative minimum in interaction with optical phonons . Since the effective mass of the electrons is inversely proportional to the curvature of the band, the electrons in the side valley have a higher effective mass and thus a lower average mobility . Therefore the current decreases again when the voltage rises, i.e. That is, a negative differential resistance is established.

Individual evidence

^ JB Gunn: Microwave oscillations of current in III – V semiconductors . In: Solid State Communications . tape 1 , no. 4 , September 1963, p. 88-91 , doi : 10.1016 / 0038-1098 (63) 90041-3 .
↑ ^a ^b ^c J. Auth, F. Kugler, HW Mittenzwei: Gunn effect . In: Manfred von Ardenne (ed.): Effects of physics and their applications . Harri Deutsch Verlag, 2005, ISBN 978-3-8171-1682-9 , pp. 394-401 .

[1] JB Gunn: Microwave oscillations of current in III – V semiconductors . In: Solid State Communications . tape 1 , no. 4 , September 1963, p. 88-91 , doi : 10.1016 / 0038-1098 (63) 90041-3 .

[AuthKuglerMittenzwei-2] J. Auth, F. Kugler, HW Mittenzwei: Gunn effect . In: Manfred von Ardenne (ed.): Effects of physics and their applications . Harri Deutsch Verlag, 2005, ISBN 978-3-8171-1682-9 , pp. 394-401 .