High-order spherical harmonics solution of the Boltzmann equation and noise modeling

The spherical harmonics expansion is a deterministic alternative to the Monte Carlo method for solving the Boltzmann equation. With the spherical harmonics expansion solver it is possible to obtain truly stationary solutions of the Boltzmann equation. Rare events (e.g. small currents or slow processes) cause no problems. Small-signal and noise analysis can be performed directly in the frequency domain and more information can be obtained from the spherical harmonics expansion solver than from the Monte Carlo method. In order to obtain accurate results, it is necessary to consider a sufficient number of spherical harmonics in the simulations, especially if transport is quasi-ballistic.