Xiangmeng Lu

Effect of cavity-layer thicknesses on two-color emission in coupled multilayer cavities with InAs quantum dots

A GaAs/AlAs coupled multilayer cavity structure was grown on a (001) GaAs substrate. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode light. The bottom cavity layer was grown with lateral thickness variation in the wafer to investigate the effects of the thickness difference between the two cavity layers quantitatively. The frequency difference was minimum, and the intensity ratio of the two-color emission was unity when the optical thicknesses of the two cavity layers were the same. The emission intensity ratio was explained in terms of the electric fields at the top cavity region containing the QDs.

Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

We fabricated the two color surface emitting device of a coupled cavity structure which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on a (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer-bonding of them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although lasing was not observed.

Two-color surface-emitting lasers using a semiconductor coupled multilayer cavity

Two-color surface-emitting lasers were demonstrated, employing a GaAs/AlGaAs coupled multilayer cavity composed of two cavity layers and three distributed Bragg reflector (DBR) multilayers. InGaAs multiple quantum wells (MQWs) with two different well widths were introduced only in the upper cavity, sandwiched between p-type and n-type DBRs. This current-injection type device exhibited two-color lasing in the near-infrared region under room temperature pulsed conditions. This two-color lasing was obtained when the lower cavity had an optimal thickness relative to the upper cavity thickness and the MQW emission properties.

Size Distribution and Scaling Behavior of InAlAs/AlGaAs Quantum Dots Grown on GaAs by Molecular Beam Epitaxy

We studied the size distribution and scaling behavior of self-assembled InAlAs/AlGaAs quantum dots (QDs) grown on GaAs in the Stranski–Krastanow (SK) mode by molecular beam epitaxy (MBE) at 480 and 510 °C as a function of InAlAs coverage. A scaling function of the volume was found for the first time in ternary alloy QDs. The function was similar to that of InAs/GaAs QDs, which agreed with the scaling function for a two-dimensional submonolayer homoepitaxy simulation with a critical island size of i = 1. However, a characteristic of i = 0 was also found as a tail in a large volume.

Sublattice reversal in GaAs/Ge/GaAs heterostructures grown on (113)B GaAs substrates

GaAs/Ge/GaAs heterostructures were grown on high-index (113)B GaAs substrates by molecular beam epitaxy. Sublattice reversal in GaAs/Ge/GaAs was identified by comparing the anisotropic etching profile of the epitaxial sample with that for reference (113)A and (113)B GaAs substrates. The shape of the resulting mesa for the lower GaAs layer was similar to that for the reference (113)B GaAs substrate, whereas that for the upper GaAs layer was similar to that for the reference (113)A GaAs substrate. An atomic-resolution analysis was also conducted by mapping using energy-dispersive X-ray spectroscopy, whereby the sublattice reversal was directly observed through the atomic arrangements.

Current-injection two-color lasing in a wafer-bonded coupled multilayer cavity with InGaAs multiple quantum wells

Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

GaAs/AlAs triple-coupled cavity with InAs quantum dots for ultrafast wavelength conversion devices

We grew the GaAs/AlAs triple-coupled multilayer cavity structure with InAs QDs, which were embedded in topside GaAs cavity. The frequency separations of the cavity modes depending on the cavity layer thickness were measured using reflection spectra. Three reflection dips around telecommunication wavelength of 1.5 μm were due to the cavity modes and equivalent frequency separation between two adjacent modes was obtained. Time-resolved four-wave mixing (FWM) signals from the triple-coupled cavity were measured using femtosecond laser system. The wavelength-converted FWM signal of was clearly observed when the triple-coupled cavity sample was excited by spectrally shaped laser pulses.

Two-color lasing from a GaAs/AlGaAs coupled multilayer cavity by current injection

Two-color lasing at the room temperature has been demonstrated by current injection into a GaAs/AlGaAs coupled multilayer cavity. By introducing InGaAs quantum wells in the topside cavity layer, we observed two-color lasing in the near-infrared region (972.3 and 981.9 nm) with the frequency difference of 3.0 THz. A novel type of terahertz emitting device based on difference-frequency generation of the two modes is expected when the other side cavity is allowed to have the second-order nonlinearity.