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We investigated lateral charge carrier transport in indium gallium nitride InGaN/GaN multi-quantum wells for two different samples, one sample emitting green light at about 510 nm and the other emitting cyan light at about 470 nm. For the cyan light emitting sample we found a diffusion constant of 1.2 cm2/s and for the green light emitting sample 0.25 cm2/s. The large difference in diffusion constant is due to a higher point defect density in the green light emitting quantum wells (QWs) as high indium incorporation tends to reduce material quality.

Optical properties induced by two major effects, potential fluctuation and piezoelectric fields, have been assessed to interpret the emission mechanism in low-dimensional nitride semiconductors because the former leads to the exciton/carrier localization, and the latter to the quantum confined Stark effect (QCSE). Degenerated white-light pump-and-probe spectroscopy has been employed to assess which factor plays an important role in the series of In x Ga 1-x N multiple quantum well (MQW) structures whose well widths are 3 nm, 5 nm and 10 nm. Moreover, photoluminescence (PL) mapping with scanning near-field optical microscopy (SNOM) has revealed the dense distribution of island-like structures, the size of which ranges from 20 nm to 70 nm in a 3 nm-thick In x Ga 1-x N single quantum well (SQW) structure emitting at blue spectral region.

Carrier dynamics in GaN and InGaN/GaN SQW structures were observed by using the transient grating (TG) method with sub-picosecond pulsed laser at room temperature. The diffusion coefficients (D) of photo-created carriers were estimated by the decay rate time of TG signals and the photoluminescence (PL) lifetime. It was found that D depends on the emission wavelength (In composition). The relationship between the emission efficiencies and carrier diffusion was considered in terms of the spatial inhomogeneity of In composition.

Spatial distribution of photoluminescence (PL) spectra has been assessed in an InGaN single quantum well (SQW) structure by means of fluorescence microscopy and scanning near-field optical microscopy (SNOM) under illumination-collection mode. The PL intensity of fluorescence image is uniform at 77 K, but the dark spot areas were extended with increasing temperature. The near-field PL images revealed the variation of both peak energy and intensity in PL spectra according to the probing location with the scale less than a few hundreds nm.