Recent studies demonstrated that degradation of InGaN-based laser diodes is due to an increase in non-radiative
recombination rate within the active layer of the devices, due to the generation of defects.
The aim of this paper is to show - by DLTS - that the degradation of InGaN-based laser diodes is strongly correlated to
the increase in the concentration of a deep level located within the active region. The activation energy of the detected
deep level is 0.35-0.45 eV. Hypothesis on the nature of this deep level are presented in the paper.
With this paper we describe recent results on the physical mechanisms responsible for the gradual degradation
of GaN-based laser diodes and Light-Emitting Diodes (LEDs). The results described in the following were obtained by
means of an extensive electrical and optical characterization of laser diodes and LEDs submitted to accelerated stress
conditions. The experimental evidence described within this paper demonstrate that: (i) during stress, the threshold
current of laser diodes can significantly increase, possibly due to a diffusion-related process; (ii) slope efficiency of laser
diodes does not significantly change as a consequence of stress; (iii) LED samples - with the same epitaxial structure of
laser diodes - show a significant decrease in optical power during stress time; degradation is more prominent at low
measuring current levels, suggesting that it is due to the increase in non-radiative recombination; (iv) the worsening of
the optical characteristics of LEDs and laser diodes is significantly correlated to the increase in the defect-related current
components. Results described within this paper strongly support the hypothesis that the degradation of laser diodes and
LEDs submitted to stress at high current densities (>4 kA/cm2) is due to the increase in the concentration of defects
within the active layer of the devices, activated by the high flux of accelerated carriers through the quantum-well region.
High-power (>100mW) 820 nm-band distributed Bragg reflector (DBR) laser diodes (LDs) with stable fundamental transverse mode operation and continuous wavelength tuning characteristics have been developed. To obtain high-power LDs with a stable fundamental transverse mode in 820 nm wavelength range, an AlGaAs narrow stripe (2.0 micrometers ) real refractive-index-guided self-aligned (RISA) structure is utilized. In the RISA structure, the index step between inside and outside the stripe region ((Delta) n) can be precisely controlled in the order of 10-3). To maintain a stable fundamental transverse mode up to an output power over 100 mW, (Delta) n is designed to be 4x10-3. Higher-order transverse modes are effectively suppressed by a narrow stripe geometry. Further, to achieve continuous wavelength tuning capability, the three-section LD structure, which consists of the active (700micrometers ), phase control (300micrometers ), and DBR(500micrometers ) sections, is incorporated. Our DBR LDs show a maximum output power over 200mW with a stable fundamental transverse mode, and wavelength tuning characteristics ((Delta) (lambda) ~2nm) under 100 mW CW operation.