The III-Nitride alloys span the entire visible spectrum and offer applications to LEDs, lasers, solar cells and power electronics. A detailed understanding of heterojunction growth is required for achieving high performance devices especially due to the large lattice mismatch in this alloy system. The wurtzite crystal system also lacks an inversion center which provides a polarization-induced electric field along the c direction that can be exploited in device design or reduced by growth on other substrate orientations.

We present results on the growth of InGaN films by Ammonia MBE on polar gallium nitride substrates as well as on nonpolar and semipolar orientations. We show results from coloaded growth conditions and investigate the effect of substrate temperature, growth rate, and ammonia flow on indium incorporation and impurity uptake. We then present solar cell results from a high indium uptake semipolar orientation with fields in a favorable direction for a p-i-n device. We also investigate and understand the effect of relaxation via basal plane slip and unintentional impurity incorporation on device performance.

Results are then be presented on electron transport through c plane InGaN/GaN multiple quantum well (MQW) active regions grown by NH3 MBE which have direct relevance to transport in MQW solar cells and LEDs. The presence of indium fluctuations in InGaN has been suspected and debated in the literature for some time, but there is still much that is not well understood. We present Atom Probe Tomography (APT) analysis of the quantum wells to explicitly examine the magnitude and length scale of these observed local alloy fluctuations. The discrepancy in current-voltage behavior between experiment and modeling using traditional 1D simulation software will be discussed. A 2D/3D drift-diffusion Schrodinger-Poisson solver developed by collaborators was used to input alloy fluctuation parameters to elucidate their direct effect on barrier heights and on transport behavior in these devices.