Ensemble Monte Carlo characterization of graded Al_xGa _1-xAs heterojunction barriers

Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded Al_xGa_1-xAs heterojunction barriers using a self-consistent ensemble Monte Carlo method. In this paper, we consider barriers with two doping levels, 1×10¹⁵ cm^-3 and 1×10¹⁷ cm^-3, and two barrier heights, 100 and 265 meV. The 100-meV barrier resulted in small rectification at room temperature whereas the higher barrier exhibited considerable rectification. In both cases the structure with the lower doped barrier has resulted in a smaller current in both forward and reverse regions due to space-charge effects. The energy and momentum distribution functions deviate from a Maxwellian distribution inside the barrier region and in general show two peaks: one is comprised mainly of electrons near equilibrium and the second arises mainly from ballistic electrons. The higher doped structure resulted in a faster electron relaxation toward equilibrium as a function of position because the electric field decreases rapidly in the barrier region.