Cyril Sadia

GaAs films on Si substrates were grown via Molecular Beam Epitaxy (MBE). The effect of pre-growth heat treatment of the Si substrate on the grown GaAs layer was investigated. Photoluminescence (PL) at T = 11K shows that the GaAs/Si band edge emission was redshifted by 23 meV as compared to as-grown GaAs indicating that the films are strained. The PL intensity of the GaAs/Si sample substrate treated at 720°C showed a remarkably higher PL intensity compared to the sample substrate treated at 610°C, indicating that heat treatment at higher temperature yields a GaAs thin film with better optical qualities.

This study investigates the enhancement of terahertz (THz) emission from textured semi-insulating gallium arsenide (GaAs) (100). Wafers were etched at different etching times to texturize the surface. Reflectance spectroscopy was used to examine the texturization. The THz emission of the sample was investigated using THz time domain spectroscopy. An enhanced THz emission was observed for the sample etched for 30 minutes. Azimuthal angle dependence of the terahertz emission suggests no change in the orientation of the crystal GaAs. Small angle x-ray diffractrometry confirms the crystallinity of the surface is preserved.

Terahertz (THz) emission from GaAs/p-GaSb and p-InAs/n-GaSb semiconductor structures under a 1.55 μm femtosecond laser excitation is reported. The influence of the GaAs thin film on a p-GaSb substrate is investigated. Results show intense THz emission from GaAs/p-GaSb as compared to bare p-GaSb that could be attributed to the built-in field at the interface of the sample. The GaAs/p-GaSb sample was also compared with bulk p-InAs and p-InAs/n-GaSb emitters.

We investigate the terahertz (THz) mechanism in GaAs films deposited on Si substrates (GaAs/Si). THz radiation is observed from femtosecond laser-excited GaAs/Si in the reflection geometry. In particular, SI-GaAs/Si exhibits the strongest emission compared to the other GaAs-based samples and comparable to bulk p-InAs which is the currently-accepted strongest THz emitter. The GaAs/Si films have no significant azimuthal angle dependence of THz signal amplitude. Pump excitation power experiments show that SI-GaAs/Si has a higher saturation value than p-InAs due to the laser's deeper penetration depth in GaAs as compared to that of p-InAs. In addition, the type of doping could greatly affect the THz emission properties of the GaAs/Si film. This enhancement in THz radiation in GaAs/Si could be attributed to surge current by the acceleration of photo-generated carriers in the surface field and not to nonlinear optical rectification effect.

InAs (p-doped) is grown on a GaAs-buffered GaSb substrate via molecular beam epitaxy. The heterostructure is tested as an emitter in a terahertz time-domain spectroscopy system with a 1550-nm-wavelength femtosecond laser. We achieve an enhancement in the terahertz radiation intensity of approximately twice compared to that of bulk p-InAs. Pump power dependence of the THz signal (800-nm femtosecond laser excitation) show similar trend in the saturation fluence of the samples. Azimuthal-angle measurements reveal surge current mechanism via photo-Dember effect.

We report the molecular beam epitaxy growth of high-quality p-InAs thin films evaluated in the context of 1.55 μm femtosecond laser-excited THz emission efficiency. The presence of p-InAs is confirmed via scanning electron microscopy and X-ray diffraction. Using a GaAs buffer layer, the epitaxial growth of p-InAs layers was successfully achieved. Initiating GaAs deposition by growth interruption, we find that GaAs adheres to the GaSb substrate and provides a quasi-planar surface for the subsequent layers. We also find a significant enhancement in the THz radiation intensity of p-InAs films that is approximately twice compared to that of bulk p-InAs for 1.55 μm wavelength.

Copyright 2018 Elsevier

We demonstrate molecular beam epitaxy growth of p-InAs layers on GaAs-buffered GaSb that may be suitable for terahertz applications. GaAs buffer deposition is initiated by applying growth interruption. Reflection high-energy electron diffraction shows that GaAs growth proceeds to a quasi-two-dimensional growth mode. The scheme allows growth of a p-InAs layer 600 nm to 1.0 µm thick. Growth performed without GaAs and growth interruption resulted in decomposition of the p-InAs. When the scheme is used, the ensuing p-InAs first follows quasi-two-dimensional growth before favoring faceted islanding. Under 800-nm-wavelength femtosecond laser excitation, the p-InAs layer generates terahertz signals 70% of that of bulk p-InAs.

Copyright 2015 The Japan Society of Applied Physics

Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75\% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope (SEM) images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

We report on the terahertz (THz) emission from n-GaAs/p-GaSb and /p-InAs/n-GaSb structures using a 1.55 μm femtosecond laser excitation. The effect of the n-GaAs thin film on a p-GaSb substrate is investigated. Significant THz emission from n-GaAs/p-GaSb compared to bare p-GaSb is observed and could be attributed to the built-in field at the interface of the sample. The comparison with a bulk p-InAs and p-InAs/n-GaSb indicates n-GaAs/p-GaSb is a strong THz emitter comparable with those InAs-based emitters.