The effect of reflecting contacts on high-field transport

The effect of reflecting contacts on high-field transport is investigated by detailed Monte Carlo simulations of electron transport in an n
^-
GaAs region that terminates in an n
⁺
GaAs/metal contact. We determine that the average electron velocity in the n
^-
region of the device decreases rapidly (because of reflections at the contact) as the doping concentration in the n
⁺
contact region decreases. We study the n
⁺
concentration range of 2 × 10
¹⁸
cm
^-3
to 1 × 10
¹⁹
cm
^-3
The probability of reflection at the contact is found to depend sensitively on the energy and momentum of the electrons impinging on the contact region as long as transport at the contact is dominantly by tunneling. The dependence is weaker for transport through the contact by thermionic emission. The velocity degradation due to electrons reflected at the contact is less severe for high electric fields with the electrons transferred to the upper valleys.