Simulation of Transport in Type-II Superlattice Avalanche Photodiodes

Improvements in semiconductor technology have allowed for growing commercial and institutional use of photodiodes as photodetectors due to their compact size, high reliability, and low cost. Of particular interest are low-excess noise avalanche photodiodes (APDs) which have increased sensitivity as a result of avalanche gain. The desire for APDs for short-wavelength (1-2 micron) and mid-wavelength (2-5 micron) photodetection is driven by applications which include fiber-optic communication, gas detection and monitoring, thermal imaging, and 3D light detection and ranging (LiDAR). We design and assess APDs fabricated from band-engineered InAlAs/InAsSb type-II superlattices which are nanostructures that permit the tuning of APD properties via electronic structure design. Complementary to the experimental growth, characterization, and fabrication of novel semiconductor material systems and devices are theoretical tools to design and simulate electronic devices. The design of type-II superlattices begins with a detailed calculation of the electronic band structure and carrier scattering rates. In this thesis, we consider the next step and report on the development of microscopic transport simulation methods used to devise band-engineering strategies which enable the design of type-II superlattices for use as high-performance APDs. The result is an ensemble Monte Carlo algorithm suitable for the simulation of Boltzmann transport within the full zone electronic structure of type-II superlattices. Within the uniform field model we demonstrate orders-of-magnitude improvement of the hole-to-electron impact ionization ratio---a key metric in the determination of APD performance---for InAlAs/InAsSb superlattices as compared with bulk InAs. We associate superlattice design features like miniband widths and the placement of Brillouin zone boundaries with electron and hole impact ionization coefficients and hence device properties like excess noise and bandwidth. This analysis reveals the InAlAs/InAsSb type-II superlattice as a platform for high-performance low-excess noise APDs in the short-wavelength infrared band. Finally, we report on the development of a self-consistent ensemble Monte Carlo-Poisson solver algorithm suitable for the simulation of type-II superlattice APD devices and demonstrate the direct simulation of avalanche breakdown.