Abstract
We report on large-area photoconductive terahertz (THz) emitters with a low-temperature-grown GaAs (LT-GaAs) active layer fabricated on quartz substrates using a lift-off transfer process. These devices are compared to the same LT-GaAs emitters when fabricated on the growth substrate. We find that the transferred devices show higher optical-to-THz conversion efficiencies and significantly larger breakdown fields, which we attribute to reduced parasitic current in the substrate. Through these improvements, we demonstrate a factor of ~8 increase in emitted THz field strength at the maximum operating voltage. In addition we find improved performance when these devices are used for photoconductive detection, which we explain through a combination of reduced parasitic substrate currents and reduced space-charge build-up in the device.
Highlights
Photoconductive (PC) switches [1], triggered by femtosecond lasers are widely used for both the generation and detection of free-space terahertz (THz) radiation [2,3,4]
The typical resistance values for LT-GaAs devices on an SI-GaAs substrate (LoG), LT-GaAs devices on a quartz substrate (LoQ) and bulk SI-GaAs emitters were obtained from current-voltage (I-V) measurements, and are summarised in Table 1 for both light and dark conditions
We attribute this greater value to the absence of an additional current path through the SI-GaAs substrate and the reduced area of lowtemperature-grown GaAs (LT-GaAs) used in fabrication
Summary
Photoconductive (PC) switches [1], triggered by femtosecond lasers are widely used for both the generation and detection of free-space terahertz (THz) radiation [2,3,4]. When exciting at 800 nm, the best-performing material for PC switches is low-temperaturegrown gallium arsenide (LT-GaAs) which incorporates excess arsenic trapping sites to ensure a very short carrier lifetime, typically ∼300 fs [9, 10] It exhibits very high breakdown fields (500 kV cm−1) [11], relatively good mobility and high dark resistance, compared with semi-insulating (SI)-GaAs or silicon-on-sapphire [3]. Three examples of free-space THz radiation emission have been demonstrated using LT-GaAs bonded with sapphire [15,16,17], as well as one instance of LT-GaAs bonded with Si and MgO for on-chip applications [18] These did not provide a comprehensive comparison between lift-off-transfer (LOT) devices and devices fabricated ‘as-grown’ on the SI-GaAs substrate, the latter of which are very widely used. In addition we find improved performance when these devices are used for photoconductive detection, which we explain through a combination of reduced parasitic substrate currents and reduced space-charge build-up in the device
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
