Self-consistent Monte Carlo study of high-field carrier transport in graded heterostructures

Hot-electron transport over graded AlxGa1−xAs heterostructures is investigated using the self-consistent ensemble Monte Carlo method. A new formulation of the carrier transport based on a semiclassical limit of a position-dependent k⋅p two-valley Γ-L energy-band model and the phonon spectra has been developed. Quantum mechanical reflection, and ohmic contacts preserving the stochastic nature of carriers at device boundaries have been included. Using this formalism, nonequilibrium hot-carrier transport for the compositionally graded barrier diode and the heterojunction ballistic launchers is examined. Results show that transport across compositionally graded semiconductors structures cannot be described with thermionic drift diffusion. Heterostructure launchers are shown to generate a ballistic electron fraction as high as 15% and 40% of the total electron population for 300 and 77 K, respectively, but simultaneously reduce macroscopic average currents and carrier velocities. The decay length of the ballistic electron fraction is less than 200 nm for temperatures as low as 77 K. The width of the ballistic peak in the electron distribution is 60 meV and the contribution of the ballistic electrons to the total current as large as 78% at 77 K for an applied voltage of 1 V.