Terahertz (THz) emission increase is observed for GaAs thin lms that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (T s = 320ºC, 520ºC and 630ºC). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at T s = 600ºC.Re ection high energy electron diffraction con rms the layer-by-layer growth mode of the GaAs on Si. Xray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz timedomain spectroscopy is performed in re ection and transmission excitation geometries. At T s = 320ºC, the low crystallinity of GaAs on Si makes it an inferior THz emitter in re ection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher T s , the GaAs on Si thin lms emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identi ed from scanning electron microscopy and Raman spectroscopy. An intense THz emission in re ection and transmission excitation geometries is observed for the GaAs on Si grown at T s = 520ºC, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most e cient in both excitation geometries. The results are signi cant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices.
Relevance SummaryDemonstration of GaAs integration on exact n-type undoped Si(100) by MBE using a two-layer LTG-GaAs buffer system. The buffer system allows for a controlled growth of relatively high-quality GaAs layers at different substrate temperatures as con rmed by in-situ RHEED, SEM, XRD diffraction and Raman spectroscopy. Utilization of Si substrates, which has a lower absorption in the THz region, to establish a GaAsbased THz emitter that is more effective in both re ection and transmission excitation geometries.The GaAs on Si material system will constitute a cost-effective THz photoconductive antenna device and likewise provide an improved refractive index matching with a Si lens mount.Con rmation of THz emission enhancement in GaAs on Si heterostructure, which is not solely dependent on high crystallinity but also on the presence of structural defects such as APBs.Validation of the reduced THz absorption losses in GaAs on Si structures advantageous for THz measurements in transmission excitation geometry.Establishment of GaAs on Si as a more effective material system even with the presence of structural defects over LTG-GaAs homostructure in the generation of THz radiation in both re ection and transmission excitation geometries.
