Investigation of self-heating and macroscopic built-in polarization effects on the performance of III-V nitride devices

The effect of hot phonons and the influence of macroscopic polarization-induced built-in fields on the performance of III-V nitride devices are investigated. Self-heating due to hot phonons is analyzed in AlGaN/GaN high electron mobility transistors (HEMTs), and the effect of macroscopic polarization charges on the operation of blue and green InGaN-based quantum well lasers is presented.;AlGaN/GaN HEMTs are extensively used in high power applications. Under typical operating conditions, highly energetic electrons internal to the device lose their excess energy primarily through the emission of dispersionless longitudinal optical (LO) phonons, which eventually decay into acoustic phonons. Acoustic phonons transport the thermal energy primarily toward the substrate. This thermal transport by acoustic phonons in the diffusive limit is modeled using a two-dimensional lattice heat equation.;InGaN-based devices are in great demand for blue and green lasers. To characterize these laser structures, the two-dimensional quantum well laser simulator MINILASE is extended to include nitride bandstructure and material models. A six-band k.p theory for strained wurtzite materials is used to compute the valence subbands. Spontaneous and piezoelectric polarization charges at the interfaces are included in the calculations, and their effects on the device performance are described. Additionally, k.p Hamiltonian for crystal growth directions that minimize the polarization-induced built-in fields are modeled, and valence band dispersions for the non-polar planes are calculated.;Finally, a design parameter subspace is explored to suggest epitaxial layer structures which maximize gain spectral density at a target wavelength for green InxGa1-xN-based single quantum well active regions. The dependence of the fundamental optical transition energy on the thickness and composition of barriers and wells is discussed, and the sensitivity of gain spectral density to design parameters, including the choice of buffer layer material, is investigated.