Investigation of impact ionization in thin GaAs diodes

The electron and hole multiplication coefficients, M(e) and M(h), respectively, have been measured in thin GaAs homojunction PIN and NIP diodes and from conventional ionization analysis the effective electron and hole ionization coefficients, alpha and beta, respectively, have been determined. The nominal intrinsic region thickness omega of these structures ranges from 1.0 mu m down to 25 nm. In the thicker structures, bulk-like behavior is observed; however, in the thinner structures, significant differences are found. As the i-regions become thinner and the electric fields increase, the M(e)/M(h) ratio is seen to approach unity. The experimental results are modeled and interpreted using a semianalytical solution of the Boltzmann equation. In thin (omega less than or equal to 0.1 mu m) devices the dead space effect reduces effective ionization coefficients below their bulk values at low values of carrier multiplication. However, overshoot effects compensate for this at extremely high fields (greater than or equal to 1 x 10(3) kV/cm).