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, α and β, respectively, have been determined. The nominal intrinsic region thickness w of these structures ranges from 1.0 μm 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 (w⩽0.1 μm) 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 (⩾1×10³ kV/cm)