InGaAsP/GaAs0.7P0.3 stripe geometry DH visible laser diodes having a p-type cap layer are fabricated. The advantage of the use of GaAs0.7P0.3 substrate instead of GaAs0.6P0.4 is discussed in terms of the injected carrier distribution ratio in direct valley (Γ) to X and L valleys. The fabricated diodes operate at room temperature under pulsed-condition. Minimum threshold current density is 4.5 kA/cm2 at a lasing wavelength of 663.0 nm.

Dislocation properties in InGaN/GaN Quantum Wells and GaN grown on bulk GaN and sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were characterized using cathodoluminescnece (CL), transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL). It was clearly demonstrated that dislocations act as nonradiative recombination centers in both n-type (undoped and Si-doped) GaN and InGaN layers. Furthermore the very short-minority carrier diffusion length was a key parameter to explain the high light emission efficiency in GaN-based light emitting diodes (LEDs) prepared on sapphire substrates. On the other side band-tail states were detected in the heteroepitaxial InGaN layers only by temperature dependence PL measurement. Additionally InGaN phase separation, which consists of few micron domains, has been produced under growth conditions which favors the spiral growth. These results indicate that the dislocations in the InGaN layers act as triggering centers for the InGaN phase separation which cause both a compositional fluctuation and the formation of few micron phase separated domains. The homoepitaxial InGaN layers showed however quite normal behaviors for all characterizations.

In this paper, we report the calculations of the quantum efficiencies of new types of photodiodes that have the ability to demultiplex the incident light beam into two or three independent outputs according to its wavelength, and determine the diode parameters that give maximum efficiency and low crosstalk. Two types of diodes were fabricated with LPE grown InGaAsP/InP quaternary system which is one of the most useful materials in the 1.01.7 µm low-loss spectral window of optical fiber. One diode divides the input light beam into two outputs and the other does in three outputs. The experimentally obtained spectral responses of the diodes were in good agreement with the calculated ones. The fabricated diodes exhibited nearly 100% internal quantum efficiency and crosstalks of 34 dB at λ1.0 µm and below 50 dB at λ1.35 µm, respectively, where the efficiencies of two outputs take their maximum values.

Excitonic optical properties of GaN homoepitaxial layers have been studied by means of magneto-luminescence and time-resolved luminescence spectroscopy. The luminescence lines due to the radiative recombination of excitons bound to neutral donors and acceptors have been measured under magnetic field up to 8 T, which was aligned perpendicular and parallel to the hexagonal c-axis. Under the magnetic field aligned perpendicular to the hexagonal c-axis, both the donor- and acceptor-bound-exciton lines clearly split into two components, which originated from the Zeeman splitting. The effective g-factors for both the donor- and acceptor-bound excitons were estimated to be 2.02 and 2.47, respectively. Under the magnetic field aligned parallel to the hexagonal c-axis, slight broadening of the bound-exciton lines was observed and the Zeeman splitting was too small to be detected. On the other hand, the diamagnetic shift for both the donor- and acceptor-bound-exciton luminescence lines was observed under the magnetic field aligned both perpendicular and parallel to the hexagonal c-axis. It was found that the diamagnetic shift of the donor-bound exciton was smaller than that of the acceptor-bound exciton. Furthermore, recombination dynamics of excitonic transitions was measured under high-density excitation. An excitation-density-dependent transition of the dominant radiative recombination process from donor-bound excitons to biexcitons was clearly observed in the temporal behavior. In addition, double-exponential decay of biexciton luminescence was observed, which is one of the characteristics of biexciton luminescence at high excitation densities.