Impact ionization in GaAs metal–semiconductor field‐effect transistors with a lightly doped drain structure and an Al0.2Ga0.8As/GaAs heterobuffer layer

Kink effects (abrupt increases in drain current) were observed with an abrupt increase of gate current (IG), substrate current (Isub), substrate potential (Vsub), and photoemission intensity (Iphoto) in GaAs metal–semiconductor field‐effect transistors (MESFETs) with a lightly doped drain (LDD) structure and an Al0.2Ga0.8As/GaAs heterobuffer layer. The kink drain voltage (VKD) increases as substrate temperature increases. Since impact ionization has a negative coefficient for increase of temperature, the increase of VKD indicates that impact ionization occurs at VKD. VKD also increases as VG becomes more negative and as the ratio of the dose of the silicon ions is reduced in the LDD region. Thus it is confirmed that impact ionization occurs at the drain side along the channel current path because those changes of VG and dose ratio reduce the electric field at the drain‐side channel. In addition, impact ionization coefficients were calculated from IG and Isub based on the method proposed by Hui et al. Both...