Charge Transport in Amorphous Silicon Nitride

Charge transport in amorphous silicon nitride (Si 3 N 4 ) is studied experimentally in a wide range of electric fields and temperatures. The experimental data are compared with the results of numerical calculations. To describe the ionization of deep centers (traps) in Si 3 N 4 , the Frenkel effect is used with the account for thermally assisted tunneling and the multiphonon mechanism. It is shown that the Frenkel effect with allowance for thermally assisted tunneling formally describes the experiment. However, an anomalously small frequency factor (10 9 s –1 ) and a large effective tunneling mass (3 m 0 ) must be used in calculations in this case. A satisfactory agreement between the results of experiments and calculations was attained using the theory of multiphonon ionization of traps with the following parameters: W_T^e,h = 1.6 eV, W_opt^e,h = 3.2 eV, W_ph^e,h = 0.064 eV, m_e,h^* = 0.6 m 0 , and N e , h = 6 × 10 18 cm –3 , which correspond to the thermal energy, optical energy, phonon energy, tunneling effective mass, and concentrations of electron and hole traps, respectively.