Incoherent processes due to phonons, interface roughness and disorder had been suspected to be the primary source of the valley current of resonant tunneling diodes (RTDs) at the beginning of the NEMO1D project in 1994. The modeling tool NEMO was created at Texas Instruments to fundamentally understand the valley current in RTDs. With the common understanding that scattering is the source of the valley current and with the early successes in NEGF significant resources were invested to model incoherent scattering. A full NEGF transport model implemented in NEMO1D enabled an analysis of various scattering mechanisms. Important incoherent scattering mechanisms that affect the operation of a GaAs/AlGaAs RTD are alloy disorder, interface roughness, acoustic and polar optical phonon scattering. A thorough analysis of each of these scattering mechanisms has shown that the effects of alloy and acoustic phonon scattering are small compared to those of interface roughness and polar optical phonon scattering. It is found from the analysis performed with NEMO1D tool that incoherent scattering affects the valley current of the RTD particularly at low temperatures. These scattering effects are, however not strong enough to explain the valley current in high performance, high temperature devices. Two other key elements are needed to explain the valley current in RTDs: 1) scattering in the contact/emitter and 2) the proper modeling of excited states through full band material representations.
This presentation provides an overview of the physical scattering mechanisms and tries to convey some intuition of what is to be expected from these scattering mechanisms. Quantitative agreement of NEMO1D simulations with experimental data at low temperatures proves that NEMO1D indeed models the critical scattering mechanisms inside the central RTD properly. Experimental data for the same device at room temperature that scattering is not enough to expain the valley current at room temperature.
- Overview scattering mechanisms inside a resonant tunneling diode, polar optical phonons, acoustic phonons, interface roughness, and alloy disorder.
- Demonstrate that NEMO1D can model scattering quantitatively at low temperatures and match experimental data.
- Demonstrate that scattering is not enough to explain room temperature data.
Università di Pisa, Pisa, Italy