Abstract:We report the terahertz emission spectroscopy (TES) and photoluminescence (PL) spectroscopy results for a semi-insulating (SI) GaN film in comparison with those for unintentionally doped (UID) and magnesium (Mg)-doped ones. The TES and PL results showed notable slow changes on a time scale of approximately 10 s for the SI and UID GaN films, but not for the Mg-doped GaN film upon femtosecond ultraviolet laser illumination. The origin of the slow responses of the TES and PL spectra was studied by observing them … Show more
“…S4 in the supplementary information. The results indicate that the H-terminated surface is quite stable under laser illumination and the decline tendency of the amplitude with illumination time increases is due to the long-time dissociation of the hydrogen from the surface 38 . Fig.…”
Advances in modern semiconductor integrated circuits have always demanded faster and more sensitive analytical methods on a large-scale wafer. The surface of wafers is fundamentally essential to start building circuits, and quantitative measures of the surface potential, defects, contamination, passivation quality, and uniformity are subject to inspection. The present study provides a new approach to access those by means of terahertz (THz) emission spectroscopy. Upon femtosecond laser illumination, THz radiation, which is sensitive to the surface electric fields of the wafer, is generated. Here, we systematically research the THz emission properties of silicon surfaces under different surface conditions, such as the initial surface with a native oxide layer, a fluorine-terminated surface, and a hydrogen-terminated surface. Meanwhile, a strong doping concentration dependence of the THz emission amplitude from the silicon surface has been revealed in different surface conditions, which implies a semiquantitative connection between the THz emission and the surface band bending with the surface dipoles. Laser-induced THz emission spectroscopy is a promising method for evaluating local surface properties on a wafer scale.
“…S4 in the supplementary information. The results indicate that the H-terminated surface is quite stable under laser illumination and the decline tendency of the amplitude with illumination time increases is due to the long-time dissociation of the hydrogen from the surface 38 . Fig.…”
Advances in modern semiconductor integrated circuits have always demanded faster and more sensitive analytical methods on a large-scale wafer. The surface of wafers is fundamentally essential to start building circuits, and quantitative measures of the surface potential, defects, contamination, passivation quality, and uniformity are subject to inspection. The present study provides a new approach to access those by means of terahertz (THz) emission spectroscopy. Upon femtosecond laser illumination, THz radiation, which is sensitive to the surface electric fields of the wafer, is generated. Here, we systematically research the THz emission properties of silicon surfaces under different surface conditions, such as the initial surface with a native oxide layer, a fluorine-terminated surface, and a hydrogen-terminated surface. Meanwhile, a strong doping concentration dependence of the THz emission amplitude from the silicon surface has been revealed in different surface conditions, which implies a semiquantitative connection between the THz emission and the surface band bending with the surface dipoles. Laser-induced THz emission spectroscopy is a promising method for evaluating local surface properties on a wafer scale.
“…We have applied TES and LTEM to Si-based materials and devices and proven that one can estimate various parameters, such as surface potential, work function, impurity doping density, defects density in passivation layers, surface state density, and so on, semi-quantitatively and non-contactly by just observing the THz radiation [8][9][10][11][12][13][14][15][16][17]. In the present work, we review the TES and LTEM application to wide bandgap semiconductors [18][19][20][21][22][23][24].…”
The time-domain waveforms of terahertz (THz) emission spectroscopy (TES) can tell us the ultrafast nature of the material photoresponse, and TES is becoming an essential tool to explore the advanced material functionalities and disclose the dynamics of the photocarriers. However, universal applications can not be reached without understanding physics in more detail over the broad dimensional range in the time-domain. We have applied TES and LTEM to Si-based materials and devices and proven that one can estimate various parameters, such as surface potential, work function, impurity doping density, defects density in passivation layers, surface state density, and so on, semi-quantitatively and non-contactly by just observing the THz radiation. In the present work, we review the TES application to wide bandgap semiconductors.
Eu-doped Gallium nitride (GaN) is a promising candidate for GaN-based red light-emitting diodes, which are needed for future micro-display technologies. Introducing a superlattice structure comprised of alternating undoped and Eu-doped GaN layers has been observed to lead to an order-of-magnitude increase in output power; however, the underlying mechanism remains unknown. Here, we explore the optical and electrical properties of these superlattice structures utilizing terahertz emission spectroscopy. We find that ~0.1% Eu doping reduces the bandgap of GaN by ~40 meV and increases the index of refraction by ~20%, which would result in potential barriers and carrier confinement within a superlattice structure. To confirm the presence of these potential barriers, we explored the temperature dependence of the terahertz emission, which was used to estimate the barrier potentials. The result revealed that even a dilutely doped superlattice structure induces significant confinement for carriers, enhancing carrier recombination within the Eu-doped regions. Such an enhancement would improve the external quantum efficiency in the Eu-doped devices. We argue that the benefits of the superlattice structure are not limited to Eu-doped GaN, which provides a roadmap for enhanced optoelectronic functionalities in all rare-earth-doped semiconductor systems.
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