Articles you may be interested inElectrical properties and deep traps spectra of N-polar and Ga-polar AlGaN films grown by molecular beam epitaxy in a wide composition range J. Appl. Phys. 105, 113712 (2009); 10.1063/1.3143012In-plane self-arrangement of high-density InAs quantum dots on GaAsSb ∕ GaAs ( 001 ) by molecular beam epitaxy
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.
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. IntroductionFemtosecond laser excitation of semiconductor surfaces produces electromagnetic (EM) waves that extend into the terahertz (THz) frequency and can be used for applications like THz time-domain spectroscopy (THz-TDS) [1,], imaging [2], and non-contact detection of harmful or illegal materials [3]. To be more useful inside and outside the laboratory environment, these applications require compact THz systems. In such case, a fiber laser is a good laser source owing to its portability, size, and ease of use. In addition, it is also crucial to further investigate THz emitters that can easily be incorporated into these systems and bulk/unbiased semiconductors are such emitters.Bulk semiconductor as a THz emitter was first discovered by Zhang et al. [4]. They showed that THz waves are radiated in the inward and outward directions of a semiconductor upon illumination of subpicosecond laser pulses. THz emission mechanism from bulk semiconductors is typically separated into two processes. One process is described by nonlinear optics. This process is the dominant THz emission mechanism at high excitation fluences [5], and is just the optical rectification of the pump laser at the semiconductor surface [6]. The second process involves the acceleration or diffusion of photo-excited carriers that produce a current surge [7], without any external voltage bias field. The current surge process is dominant at low excitation fluences and can be explained either by the acceleration of photo-carriers through the surface field effect [8], and the photo-Dember effect owing to the large difference in the mobility of electrons and holes in the diffusion process [9]. The surface field effect drives the electrons and holes in opposite directions, thus creating a transient electric dipole along the direction normal to the excited surface that emits THz radiation. This effect is responsible for the THz emission from wide bandgap III-V semiconductors like gallium arsenide (GaAs). In the photo-Dember effect, the electrons and holes are diffuse in the same direction. However, the large difference in their mobilities and diffusion coefficients produces a very large spatial gradient that causes an electric dipole to exist in the direction perpendicular to the excited surface. The main THz emission mechanism in narrow bandgap III-V semiconductors like indium arsenide (InAs) is the photo-Dember effect [10].GaAs and InAs are considered to have some of the best THz emission efficiencies of the bulk semiconductors. The reason for this is ...
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