Novel devices employing epitaxial wide bandgap semiconductors: Physics, electronics and materials characterization

This thesis describes the developments of novel semiconductor devices based on epitaxial wide band gap semiconductors GaN and ZnS. It consists of three major topics, structural characterization and kinetic growth modeling of the GaNAs/GaAs superlattices, structural and optical characterization and solid phase recrystallization of ZnS thin films grown on GaN and sapphire substrates, and design and fabrication of GaN high power devices as well as measurement of fundamental electronic properties of GaN.; The set of GaNAs/GaAs superlattices grown by MBE was analyzed by high resolution X-ray diffraction and cross-sectional transmission electron microscopy. The activation energies for nitrogen desorption and nitrogen to arsenic segregation were found through simple kinetic model, which is in fine agreement with experimentally obtained results.; Zinc sulfide/Gallium nitride heterostructures are interesting for blue and green light emitters. Zinc sulfide thin films were characterized by photoluminescence and X-ray diffraction. Electroluminescence of fabricated ZnS/GaN heterostructures was found to be centered around 390 nm. Since as grown films suffered from crystalline imperfections, the ZnS thin films on sapphire were recrystallized, by annealing at temperatures above 900 C at high sulfur overpressure. The structural properties of samples significantly improved after recrystallization.; The minority carrier diffusion lengths and lifetimes were measured for minority carriers in GaN. The experimentally observed diffusion lengths were in the 0.25 μm range for MOCVD and MBE grown samples, and 1 μm in the case of HVPE grown sample. The size of the defect-free regions surrounded by linear dislocations is found to be of the order of measured diffusion length, in qualitative agreement with minority carrier recombination at linear dislocations.; The design rules for nitride based Schottky rectifiers and thyristors are presented. The critical field for electric breakdown and minority carrier recombination lifetimes are found to be important design parameters. The Schottky rectifiers were fabricated on thick GaN layers grown by HVPE and had a standoff voltages in the 450 V to 750 V range, depending on the thickness of the GaN film and contact geometry. The lower limit of the critical field for electric breakdown in GaN was found to be (2.5 ± 0.5) MV/cm.