In this work several aspects concerning (In Al Ga)N laser diodes with high spectral purity
designed for applications in spectroscopy were studied. A complete fabrication process for
ridgewaveguide laser diodes on GaN substrate was developed. The lateral size of the ridge
waveguides was as narrow as 1.5 ¿m: this is necessary in order to achieve lateral single-mode
lasing in (In Al Ga)N laser diodes. A peculiar property of (In Al Ga)N laser diodes is that
when the ridge is narrow the threshold current strongly depends on the ridge etch depth. This
phenomenon was investigated by fabricating laser diodes with different etch depths. For ridge
widths below 2 ¿m the threshold current of shallow-ridge devices was found to be more than two
times larger than that of comparable deep-ridge devices. Moreover in the lateral far-field
patterns of shallow-ridge laser diodes side-lobes were observed which would support the
hypothesis of strong index-antiguiding. The antiguiding factor at threshold was experimentally
determined to be about 10 which is among the largest values ever published for (In Al Ga)N
laser diodes. The devices were further studied by simulation and the results confirmed that
the carrier-induced index change in the quantum wells can compensate the lateral index step if
the ridge is shallow. This in turn reduces the lateral optical confi nement which increases
the threshold current and generates side lobes in the far-fi eld patterns. Based on this
research blue and violet laser diodes suitable for packaging in TO cans and continuous-wave
(CW) operation exceeding 50 mW were fabricated. An external cavity diode laser (ECDL) was also
realized which could be tuned over the spectral range 435 nm ¿ 444 nm and provided a peak
emission power of more than 27 mW CW at 439 nm. As an alternative approach to obtain a narrow
spectral linewidth the feasibility of monolithically integrated Bragg-gratings was studied.
