Numerical modelling of hot electron transport in Schottky-diodes and heterojunction structures

Doktorsavhandling, 1991

A one-dimensional drift-diffusion model, including energy balance equations, is used to model Schottky-diodes and heterojunction structures. The set of equations are solved simultaneously with a finite-difference iterative scheme. The flux of energy across the metal-semiconductor interface is set equal to the energy transport caused by the net-flow of charged carriers arising from the electric current. This boundary condition allows the carrier temperature in the semiconductor at the Schottky contact to differ from the lattice temperature. The model has been used to investigate dc-properties (IV, CV) of strongly forward biased Schottky-diodes on n-GaAs. The modelled IV of four different diodes are compared with measured IV curves. The inclusion of hot electron transport is essential to obtain good agreement between modelled and measured IV characteristics for diodes with short epitaxial layers. The effects of image force lowering and thermionic-field emission are modelled with a field-dependent barrier height. The differential capacitance is determined from the change of electric charge in the semiconductor for an incremental voltage change. The numerically simulated capacitance increases with forward voltage to a finite value, and then it starts to decrease. The computer program is extended to model heterojunctions by including position dependent material parameters. The simulated IV characteristic of a forward biased graded heterojunction diode is in good agreement with published Monte Carlo results of a similar device.