Nonlinear Electron Transport Mobility in GaAs/Al x Ga1-x As Square - Parabolic Double Quantum Well MODFET Structure

We study doping dependence nonlinear electron transport mobility $\mu _{t}$ in a GaAslAlxGal-x4s double quantum well MODFET structure. We consider square (parabolic) well towards the substrate (surface) side of the structure. The side barrier towards the substrate (surface) is modulation delta doped with Si of doping concentration $Nd_{sub}(Nd_{sur})$. We analyze $\mu _{t}$ as function of $Nd_{sub}$ (keeping $Nd_{sur}$ constant) by considering different scattering mechanisms such as: ionized impurity (Imp-), alloy disorder (Al-) and interface roughness $(Ir-)$. We show that $\mu _{t}$ is mainly decided by $\mu i^{mp}$ whereas $\mu i^{r}$ reduces the overall $\mu _{t}$. We also show that nonlinear $\mu _{t}$ can be achieved during double subband occupancy and attain minimum at the anticrossing of subband states which occur for $Nd_{sub} \lt Nd_{sur}$. There is also a sudden enhancement $of\mu _{t}$ due to the cease of intersubband effects at $(Nd_{sub})_{trans}$ where double to single subband occupancy takes place. It is gratifying to show that increasing well width $w$ enhances $\mu _{t}$ as well as transition from double to single occur for higher value of $(Nd_{sub})_{trms}$. Our results can be utilized for the analysis of improvement of channel conductivity of double quantum well MODFET structure.