Radiative and nonradiative recombination dynamics in strained cubic $\mathrm{(c-)}$ ${\mathrm{In}}_{\mathrm{0.1}}{\mathrm{Ga}}_{\mathrm{0.9}}\mathrm{N}\mathrm{/c-}\mathrm{GaN}$ 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 $\mathrm{L.}$ 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.

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 (SS) of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E0, 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 E0 and bulk cubic In0.02Ga0.98N 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.

The energy band diagrams of NiO-based solar cell structures that use various n-type oxide semiconductors such as ZnO, Mg_0.3Zn_0.7O, Zn_0.5Sn_0.5O, In₂O₃:Sn (ITO), SnO₂, and TiO₂ were evaluated by photoelectron yield spectroscopy. The valence band discontinuities were estimated to be 1.6 eV for ZnO/NiO and Mg_0.3Zn_0.7O/NiO, 1.7 eV for Zn_0.5Sn_0.5O/NiO and ITO/NiO, and 1.8 eV for SnO₂/NiO and TiO₂/NiO heterojunctions. By using the valence band discontinuity values and corresponding energy bandgaps of the layers, energy band diagrams were developed. Judging from the band diagram, an appropriate solar cell consisting of p-type NiO and n-type ZnO layers was deposited on ITO, and a slight but noticeable photovoltaic effect was obtained with an open circuit voltage (V_oc) of 0.96 V, short circuit current density (J_sc) of 2.2 μA/cm², and fill factor of 0.44.