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We report on the intense terahertz emission from InAs/GaAs quantum dot (QD) structures grown by molecular beam epitaxy. Results reveal that the QD sample emission was as high as 70% of that of a p-type InAs wafer, the most intense semiconductor emitter to date. Excitation wavelength studies showed that the emission was due to absorption in strained undoped GaAs, and corresponds to a two order-of-magnitude enhancement. Moreover, it was found that multilayer QDs emit more strongly compared with a single layer QD sample. At present, we ascribe the intense radiation to huge strain fields at the InAs/GaAs interface.

We report a detailed study on the valence band splitting in epitaxial lift-off (ELO) GaAs film bonded to silicon. The GaAs film used in this study was grown by molecular beam epitaxy on epiready GaAs (100) substrate. Variable temperature photoluminescence and reflectivity spectra were obtained for the as-grown film, the freestanding ELO film, and the ELO GaAs film bonded to silicon. The PL spectra for the GaAs film on Si showed the removal of the valence band degeneracy with the light hole and heavy hole transitions separated by 4.2meV at 10K and decreased monotonously to 1.6meV at 230K. No similar splitting was observed for the as-grown and freestanding films. The strain and stress were calculated at ε=(1.2±0.04)×10−3 and X=0.8±0.05kbar, respectively, at 10K and ε=(2.3±0.04)×10−4 and X=0.3±0.05kbar at 230K. The temperature dependence of the heavy hole–light hole separation energy indicated a strain-induced effect caused by the difference in the coefficient of thermal expansion between GaAs and Si. This shows the efficiency of using ELO techniques on dissimilar materials for strain related spectroscopy.

Influences of the spacer layer growth temperature on multilayer InAs ∕ GaAs quantum dot structures

We report the effect of changing the polarity of a magnetic field parallel to the surface plane of GaAs/AlGaAs modulation-doped heterostructures (MDHs) with various spacer thicknesses on the terahertz radiation power and its spectral characteristics. Results show that flipping the direction of the transverse 1 T magnetic field modifies the extent of field-induced terahertz radiation enhancement. The observations are analyzed in the context of junction electric field strength, carrier confinement and mobility, and the AlGaAs/GaAs interface roughness. This terahertz method may prove as an efficient tool to qualitatively evaluate the characteristics of MDH layers.