Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN quantum wells, low-excitation photoluminescence peak energy increased moderately with decreasing well thickness L and the PL lifetime did not strongly depend on L. The results clearly indicated that the piezoelectric field was not acting on the transition process. The TRPL signal was well fitted as a stretched exponential decay from 10 to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures such as In clusters. The localized states were considered to have two-dimensional density of states at 300 K (quantum disk size), since the radiative lifetime increased with increasing temperature above 150 K.

Cubic AlxGa1−xN alloy layers have been successfully grown for x=0−1 by gas-source molecular beam epitaxy on cubic-SiC/Si substrates, and the compositional dependence of the transverse-optic (TO) and longitudinal-optic (LO) phonon modes has been studied by Raman scattering. The LO-mode frequency of mixed crystals shows a systematic variation from the pure cubic AlN phase to the cubic GaN phase (one-mode type). On the contrary, there are two branches for the TO mode varying slowly in frequency with the composition (two-mode type). This behavior is explained within a random-element-isodisplacement model including the effect of polarization field. Our result indicates a strong polarization field acting on the cation-nitrogen bonds.

Erratum: "Evidence of localization effects in InGaN single-quantum-well ultraviolet light-emitting diodes" [Appl.An InGaN multiple-quantum-well laser diode wafer that lased at around 400 nm was shown to have the InN mole fraction, x, of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift ͑SS͒ of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E 0 , was estimated to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells was estimated to be as small as 300 kV/cm, SS was considered to originate from effective band-gap inhomogeneity. Because the well thickness fluctuation was insufficient to reproduce SS or E 0 and bulk cubic In 0.02 Ga 0.98 N that does not suffer any polarization field or thickness fluctuation effect exhibited a SS of 140 meV at 77 K, the exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clustering in InGaN material. The spontaneous emission from the InGaN wells was thus assigned as being due to the recombination of excitons localized at the exponential tail-type potential minima in the density of states. The upper bound of the lateral localization size has been estimated to be 50 nm. Such shallow and low density localized states are leveled by injecting high density carriers under the lasing conditions.

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