Subpicosecond electron-hole recombination time and terahertz-bandwidth photoresponse in freestanding GaAs epitaxial mesoscopic structures

Abstract

We present the ultrafast (THz-bandwidth) photoresponse from GaAs single-crystal mesoscopic structures, such as freestanding whiskers and platelets fabricated by the top-down technique, transferred onto a substrate of choice, and incorporated into a coplanar strip line. We recorded electrical transients as short as ∼600 fs from an individual whisker photodetector. Analysis of the frequency spectrum of the photoresponse electrical signal showed that, intrinsically, our device was characterized by an ∼150-fs carrier lifetime and an overall 320-fs response. The corresponding 3-dB frequency bandwidth was 1.3 THz—the highest bandwidth ever reported for a GaAs-based photodetector. Simultaneously, as high-quality, epitaxially grown crystals, our GaAs structures exhibited mobility values as high as ∼7300 cm2/V·s, extremely low dark currents, and ∼7% intrinsic detection efficiency, which, together with their experimentally measured photoresponse repetition time of ∼1 ps, makes them uniquely suitable for terahertz-frequency optoelectronic applications, ranging from ultrafast photon detectors and counters to THz-bandwidth optical-to-electrical transducers and photomixers.

Generation of THz transients by photoexcited single-crystal GaAs meso-structures

“…Figure 3 shows both the one-color (800-nm/ 800-nm) and two-color (400-nm/800-nm) optical pumpprobe time-resolved photoresponse normalized reflectivity change DR/R transients, denoted as the solid and dotdashed lines, respectively. For 800-nm excitation, the DR/R signal has a full-width-at-half-maximum (FWHM) of 310 fs and fall time of 290 fs, which agrees very well with our characterization of the intrinsic photoresponse of a freestanding whisker meso-structure [10]. The latter indicates that the demonstrated THz-bandwidth optoelectronic performance of our both whisker-and platelet-type devices is the material, rather than geometry limited.…”

“…It is well known that in LT-GaAs, structure defects, and As precipitates are responsible for carrier trapping-the key mechanism responsible for the LT-GaAs ultrafast response. Our devices, however, have been made of high-quality, singlecrystal GaAs with l as high as *7,300 cm 2 /V s [10]. More research in this aspect is clearly needed, including, possibly, extensive Monte Carlo simulations of the carrier transport in GaAs with the various levels of carrier trapping.…”

“…Independently, during the last decade, there has been an explosive growth of interest in novel devices, based on nanometer-sized structures [8,9]. Most recently, we have demonstrated THz response from a single-crystal GaAs meso-whisker, as well as presented its ultra-high-speed photodetector operation with a repetition rate of above 1 THz [10].…”

Ultrafast transient responses of optical wireless communication detectors

“…Photoconductive (PC) detectors are important elements for ultrafast optoelectronic switching, as picosecond response times and terahertz bandwidths can be achieved with these fundamental semiconductor switches [1][2][3][4]. Excellent performance characteristics are achieved by PC detectors in optical fiber implementations, in particular, as such systems can be implemented over well-restricted spectral windows (typically 1500-1600 nm) with simple fiberdetector coupling [5].…”

Direct electro-optical pumping for hybrid CdSe nanocrystal/III-nitride based nano-light-emitting diodes

“…During the last decades, rapid progress in the development of nanostructures brought about new insights into applied physics resulting in a number of new applications for electronics, 1-4 medicine, [5][6][7] optics or even main stream electronics. 8,9 However it has become more and more challenging on the one hand to connect nanoscale structures to the "real world" and on the other hand to characterize them. There are numerous reasons.…”