Influences of surface charges and gap width between p-type and n-type semiconductors on charge pumping

Abstract

It has been reported that charges can be pumped out of an intermittently contacted p-n (or Schottky) junction, accompanied with mechanical to electric power conversion [1]. The amount of charge measured in the circuit, however, was observed to be 3–4 orders of magnitudes smaller than the space charge in the depletion regions of an ideal p-n (or Schottky) junction formed with the corresponding semiconductors (or metals). In this work, charge pumping between p -type and n -type silicon is investigated using the first principles calculation with non-equilibrium Green function. We find that a large density of states is formed during silicon surface relaxation and they are further changed during hydrogenated process. The surface charges result in a surface potential barrier, which has a negative impact on electron and hole transfer between the contacted silicon surfaces. In addition, it is also found that the total charges in the depletion regions depend very sensitively on the air gap between the two silicon electrodes. More than 68% of the charges can be pumped out with a gap of 30 Å . These results suggest that intermittently contacted p-n junction could function as an efficient electric generator or mechanical sensor if the surface states and gap width are well controlled. • A large density of states are formed during silicon surface relaxation and hydrogenated process. • The surface charges result in a surface potential barrier, which has a negative impact on electron and hole transfer between two electrodes. • The total charges in the depletion regions depend very sensitively on the air gap between two electrodes. • Intermittently contacted p-n junction could function as a ultrahigh frequency electric generator or mechanical sensor.