Real-space electron transfer by thermionic emission in GaAsAlxGa1−xAs heterostructures: Analytical model for large layer widths

Calculations are presented for negative differential resistance (NDR) and switching in layered GaAsAl_xGa_1?xAs heterostructures with a high electric field parallel to the interface. The mechanism is based on thermionic emission of hot electrons from the GaAs layers into the Al_xGa_1?xAs layers. An analytical model is obtained in the limit of relatively large layer widths (400 Å or wider). The method of moments is employed to solve the Boltzmann equation, assuming a position-dependent electron temperature and Quasi-Fermi level in the Al_xGa_1?xAs layers, and a position-independent electron temperature and Quasi-Fermi level in the narrower GaAs layer. Thermal conduction of hot electrons from the GaAs layer into the Al_xGa_1?xAs layers is taken into account. The results of the calculations show that the threshold electric field for the onset of NDR and the peak-to-valley ratio can be controlled to a large extent by adjusting the mobility of the Al_xGa_1?xAs layer, the layer dimensions, and the potential barrier (Al mole fraction in the Al_xGa_1?xAs).