Characterisation of InAs:GaAs quantum dot-based photoconductive THz antennas (original) (raw)

Quantum-dot based ultrafast photoconductive antennae for efficient THz radiation

SPIE Proceedings, 2016

Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pumped at very high optical intensities of higher than 1 W optical mean power, i.e. about 50 times higher than the conventional LT-GaAs based antennae. Apart from high thermal tolerance, defect-free GaAs crystal layers in an InAs:GaAs quantum dot structure allow high carrier mobility and ultrashort photocarrier lifetimes simultaneously. Thus, they combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. By changing quantum dot size, composition, density of dots and number of quantum dot layers, the optoelectronic properties of the overall structure can be set over a reasonable range-compact semiconductor pump lasers that operate at wavelengths in the region of 1.0 µm to 1.3 µm can be used. InAs:GaAs quantum dot-based antennae samples show no saturation in pulsed THz generation for all average pump powers up to 1 W focussed into 30 µm spot. Generated THz power is superlinearly proportional to laser pump power. The generated THz spectrum depends on antenna design and can cover from 150 GHz up to 1.5 THz.

Operation of quantum dot based terahertz photoconductive antennas under extreme pumping conditions

Applied Physics Letters

Photoconductive antennas deposited onto GaAs substrates that incorporate InAs quantum dots have been recently shown to efficiently generate both pulsed and CW terahertz radiation. In this Letter, we determine the operational limits of these antennas and demonstrate their extreme thermal breakdown tolerance. Implanted quantum dots serve as free carrier capture sites, thus acting as lifetime shorteners, similar to defects in low-temperature grown substrates. However, unlike the latter, defect-free quantum-dot structures possess perfect lattice quality, thus not compromising high carrier mobility and pump intensity stealth. Single gap design quantum dot based photoconductive antennas are shown to operate under up to 1 W of average pump power ($1:6 mJ cm À2 energy density), which is more than 20 times higher than the pumping limit of low-temperature grown GaAs based substrates. Conversion efficiency of the quantum dot based photoconductive antennas does not saturate up to 0.75 W of pump power ($1:1 mJ cm À2 energy density). Such a thermal tolerance suggests a glowy prospect for the proposed antennas as a perspective candidate for intracavity optical-to-terahertz converters.

Quantum dot photoconductive antenna-based compact setups for terahertz spectroscopy and imaging

Terahertz Emitters, Receivers, and Applications XI, 2020

We present the overview of the results on the development of compact THz setups based on the quantum dot photoconductive antennas obtained during the past five years. We demonstrate the potential of the InAs/GaAs Quantum-Dot based setups to become an efficient approach to compact, room-temperature operating CW and pulsed terahertz setups for spectroscopy and imaging. We describe the photoelectronic processes in quantum dot substrates and reveal the role of quantum dots in free carrier lifetimes and the formation of the ultrafast photocurrent. We demonstrate the operation mode of the proposed antennas in pulsed and CW regimes under resonant (carriers are excited only inside the quantum dots) and off-resonant (carriers are excited in the bulk volume of the substrate) pumps with compact quantum dot semiconductor lasers. The results allow suggesting the quantum dot based setups as a new approach to field condition compact THz sources for imaging and spectroscopy.

Terahertz emission characteristics of ErAs:InGaAs-based photoconductive antennas excited at 1.55 μm

Applied Physics Letters, 2010

We characterize ErAs: In 0.53 Ga 0.47 As superlattices as substrates for photoconductive terahertz emitters excited at 1.55 m. The bandwidth of the emitted radiation is studied as a function of the superlattice period ͑or equivalently the electron lifetime͒ and the applied bias field. The results show that a variation in the electron lifetime from 0.2 to 6.3 ps does not considerably influence the bandwidth of the emitted radiation. However, the bandwidth increases linearly from 2.6 to 3.0 THz as the applied bias field is increased from 7 to 30 kV/cm. At higher bias fields, saturation is observed. The largest measured bandwidth is 3.1 THz.

THz generation using 800 to 1550 nm excitation of photoconductors

2009

We demonstrate the efficient generation of terahertz (THz) radiation from Fe-doped InGaAs-based photoconductive antennas. We present time-domain data showing generation of pulsed THz radiation from antennas fabricated on two different wafers, optimized to maximize the near-infrared-to-THz conversion efficiency. Detection was performed using both (110) ZnTe and GaP crystals, with pump and probe wavelengths being adjusted from 800 nm to 1550 nm using a cavity-tuned OPO pumped by a pulsed near-infrared Ti:Sapphire laser.

Critical comparison of GaAs and InGaAs THz photoconductors

Terahertz Technology and Applications V, 2012

Ultrafast photoconductors have been an enabling device technology in the THz field during the past decade. And their implementation is now worldwide in time-and frequency-domains systems of various types. While the technological push is towards InGaAs or similar photoconductors operating at 1550 nm, the GaAs-based devices operating around 800 nm still provide superior performance and robustness in most cases. This paper contrasts the GaAs and 1550-nm devices in terms of materials design and solid-state metrics such as electron-hole lifetime, carrier mobility, and resistivity. It also summarizes the main materials developed over the past 20 years.

Quantum dot materials for terahertz generation applications

Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual-wavelength continuous wave laser systems, though some limitations , such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot-based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-of-concept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.