On the frequency dependent drain conductance of ion-implanted GaAs MESFETs

The effect of MESFET structure on the frequency dispersion of drain conductance (g_d) was examined, It was found that a shorter gate length, lower buried p-layer concentration, lower sheet resistance of n⁺ layer, and thinner active layer thickness are effective in suppressing the frequency dependent g_d. These phenomena are explained by the presence of deep traps in the depletion layer between the semi-insulating substate and active layer. We also show that the cross-point change of eye-pattern for density of input signal in logic ICs is due to frequency dependent g_d The cross-point change between mark ratio of 1/8 and 7/8 shows a linear relationship with gd_RF/gd_dc (the ratio of the drain conductance at RF and dc input), These results indicate that an optimized device structure with g_d small frequency dispersion can be used to realize high-speed and high quality logic ICs.