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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.

The carrier lifetimes and electron mobility values were estimated for 2 μm thick GaAs films grown on Si (100) substrates by means of optical pump terahertz probe (OPTP) technique. The GaAs/Si films measured were epitaxial grown at different substrate temperatures (T S =520 °C or T S =630 °C). From x-ray diffraction measurements and Raman spectroscopy, the GaAs/Si films were shown to experience minimum strain at room temperature, and crystal misorientation in the (111) or (110) direction. With no measureable photoluminescence at room temperature, carrier lifetimes were measured via OPTP and found to be ∼20 and ∼35 ps for a fluence of ∼4 μJ cm −2 , which is in the same order of magnitude as a reference bulk GaAs grown on SI-GaAs (T S =630 °C) having a lifetime of ∼70 ps. From OPTP photoconductivity measurements, the estimated GaAs/Si films' electron mobility are ∼2900 cm 2 V −1 s −1 (T S =520 °C) and ∼3500 cm 2 V −1 s −1 (T S =630 °C) at a pump-probe delay time of Δt=50 ps, in which the bulk GaAs electron mobility is ∼5200 cm 2 V −1 s −1 .

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