Masanobu Ando

Photoluminescence from exciton-exciton scattering in a lightly alloyed InGaN thin film under intense excitation conditions

We have investigated the photoluminescence properties of a lightly alloyed In0.02Ga0.98N thin film at 10 K under intense excitation conditions. A photoluminescence band (P band) peculiar to the intense excitation condition has been clearly observed. The excitation-power dependence of the P-band intensity exhibits an almost quadratic behavior, accompanied by a threshold-like appearance. The threshold-excitation power for the P band is very low: ∼3kW∕cm2. At the threshold excitation power, the energy of the P band is lower than the energy of the n=1 A free exciton by the energy difference between the n=1 and n=2 exciton states. The results described above indicate that the P band originates from exciton-exciton scattering. Furthermore, we have confirmed the existence of optical gain leading to stimulated emission in the energy region of the P band by using transmission-type pump-probe spectroscopy.

Miniband structures and effective masses of GaAs/AlAs superlattices with ultra-thin AlAs layers

Abstract We report the photoreflectance study of miniband structures of (GaAs)10/(AlAs) superlattices with m = 1,2 and 4 monolayers. We clearly observe the optical transitions at the mini-Brillouin-zone center (Γ point) and the edge (π point). The observed transition energies are well explained by the calculation in the framework of an effective-mass approximation even in the m = 1 superlattice. Moreover, we detect Franz-Keldysh oscillations originating from the transitions at the Γ and π points in the m = 1 superlattice and discuss the miniband masses estimated from the oscillation profiles, comparing with those theoretically derived from the miniband structures.

Photoluminescence and optical gain due to exciton-electron scattering in a high quality GaN thin film

We have investigated photoluminescence (PL) properties of a high quality GaN thin film grown by metal organic vapor phase epitaxy under intense excitation conditions in a high temperature regime from 120K to room temperature. It is found that a PL band peculiar to intense excitation conditions appears with a threshold-like behavior. The energy spacing between the PL band at the threshold excitation power and the A exciton is proportional to temperature. The extrapolation of the linear dependence results in zero value of the energy spacing at absolute zero temperature. These PL profiles are specific to an emission process originating from exciton-electron scattering. Furthermore, we have demonstrated that the exciton-electron scattering process produces optical gain at room temperature from measurements of PL with a variable stripe-length method.

Photoluminescence from the Barrier-X State in GaAs/InAlAs Strained Superlattices under Applied-Bias Voltages

We have studied the photoluminescence properties of GaAs/InAlAs strained superlattices as a function of applied-bias voltage. We have detected the appearance of the photoluminescence from the first X-electron state confined in the InAlAs barriers, resulting from the Γ–X electron resonance induced by the applied bias. From the calculations of the energies of the Γ and X states based on an effective-mass approximation including strain effects, it is demonstrated that the above PL is applicable to probe the barrier-X state.