Monte Carlo Investigation of Size-Dependent Impact Ionization Properties in InP Under Submicron Scale

The impact ionization properties in InP have been studied by using an ensemble Monte Carlo (EMC) method. In our EMC model, analytical model which contains three conduction bands and three valance bands is adopted to describe the band structure. The electron and hole impact ionization rate is fitted to the available measurement in the wide range of electric field by using Keldysh formula. The steady properties of InP are presented and analyzed. Particularly, the impact ionization behaviors in InP under submicron scale are discussed in detail. It is found that the impact ionization coefficient is not only a function of the applied electric filed but also behaves a size-dependent property when the size is down to submicron scale. We also find that, the size-dependent impact ionization effect which results from the dead space effect and the confined size, can help to prevent the carriers from impact ionization. Finally, the ratio of the electron impact ionization coefficient and the hole impact ionization coefficient is further studied. By taking the size-dependent impact ionization effect into consideration, this ratio is no longer holding as a constant but changing with the size of the devices under the specific electric field. As the size scaling down, the ratio will tend to deviate from one unit, which may contribute to a new look at the noise theory of APD devices.