Abrupt dependence of ultrafast extrinsic photoconductivity on Er fraction in GaAs:Er

Abstract

We present a study of room-temperature, ultrafast photoconductivity associated with a strong, subbandgap, resonant absorption around k ¼ 1550 nm in three MBE-grown GaAs epitaxial layers heavily doped with Er at concentrations of %2.9 Â 10 18 (control sample), 4.4 Â 10 20 , and 8.8 Â 10 20 cm À3 , respectively. Transmission-electron microscopy reveals lack of nanoparticles in the control sample, but abundant in the other two samples in the 1.0-to-3.0-nm-diameter range, which is consistent with the previously known results. We measure very high photoelectron (Hall) mobility (2.57 Â 10 3 cm 2 /V-s) and terahertz power (46 lW average) in the 4.4 Â 10 20 sample, but then, an abrupt decay in these properties as well as the dark resistivity is seen as the Er doping is increased just 2 times. The Er doping has little effect on the picosecond-scale, 1550-nm photocarrier lifetime.

Continuous-wave 1550 nm operated terahertz system using ErAs:In(Al)GaAs photo-conductors with 52 dB dynamic range at 1 THz

“…This typically requires interband absorption and therefore materials with a band gap smaller than 0.8 eV for operation with telecom lasers [6,[10][11][12]. There are, however, a few examples in the literature where absorption via trap states located in the center of band gap allows for absorption of photons with approximately half the band gap energy [13]. This usually leads to somewhat lower absorption coefficients but may still be useful for Terahertz generation and detection if sufficient laser power is available.…”

“…Material grown by molecular beam epitaxy seems to be better suited [19]. An approach that leads to high device resistance and short carrier lifetime at the same time is extrinsic photoconductivity in ErAs:GaAs, where ErAs forms a miniband in the band gap of GaAs [13]. While pulsed operation of such devices has yet been reported, there are no CW results in the literature so far.…”

High power generation of THz from 1550-nm photoconductive emitters

“…It was also supported by photoconductivity and photo-Hall measurements, the latter proving that the photocarriers are indeed electrons. Finally, the photoelectron lifetime was determined to be approximately 1.7 ps by pump-probe experiments [16]. Thus, the material had good merits for ultrafast photoconductive devices.…”

“…1) [14,15]. For example, 1550nm-driven GaAs:Er based PC devices were demonstrated to produce ~46 µW THz power, with a power conversion efficiency of 0.075% [16]. In this work we extend the GaAs:Er extrinsic-PC device performance further through the design and characterization of a spiral-antenna and a slot-antenna PC switch (Fig.…”

“…The growth was performed at 600°C, with simultaneous deposition of gallium and erbium atoms. At such high density, Er incorporates into GaAs in the form of ErAs quantum dots (with mean diameter ~1.2 nm) as shown by Transmission Electron Microscopy (TEM) [16]. From the TEM images, a very low level of defects is visible other than the ErAs quantum dot formation.…”