Mode dynamics of high power (InAl)GaN based laser diodes grown on bulk GaN substrate

Time resolved scanning near-field optical microscopy was employed to study spatial and temporal dynamics of III-nitride-system-based blue light emitting laser diodes with a ridge width of 20 mu m deposited on high pressure grown bulk GaN substrate. Devices were driven in a pulse regime with a current pulse length of 500 ns. Temperature effects and fluctuation in carrier concentration resulted in a complicated dynamic picture of the photon field evolution. The guided modes did not reach a stable form during a driving pulse. Due to a large antiguiding factor which is characteristic for nitride compounds, filamentation processes were clearly observable leading to the formation of up to four filaments across the ridge, each about 3 mu m. Analysis of spatial and temporal evolution of the guided mode revealed strong light leakage into the highly absorptive substrate. Separation between the adjacent cavity modes equals to 0.57 nm which corresponds to the cavity length of 50 mu m being very close to the thickness of GaN substrate. Detection of near-field-to-far-field evolution evidenced a considerable beam steering as a result of temperature and carrier induced refractive index changes. (c) 2007 American Institute of Physics.