Traveling-wave photomixers fabricated on high energy nitrogen-ion-implanted GaAs

Abstract

The authors report on fabrication and measurement of traveling-wave photomixers based on high energy and low dose nitrogen-ion-implanted GaAs. They used 3MeV energy to implant N+ ions into GaAs substrates with an ion concentration dose of 3×1012cm−2. The N+-implanted GaAs photomixers exhibit improvements in the output power in comparison with their counterparts, photomixers fabricated on low-temperature-grown GaAs. The maximal output power was 2.64μW at 850GHz. No saturation of the output power with increased bias voltage and optical input power was observed. These characteristics make N+-implanted GaAs the material of choice for efficient high power sources of terahertz radiation.

Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy

“…Therefore, commonly used semiconductors for THz generation are defect-rich to reduce the fall time of the transient current. Examples include low-temperature grown or ion-implanted GaAs and silicon (McIntosh et al, 1995;Shan and Heinz, 2004;Krotkus and Coutaz, 2005;Mikulics et al, 2006). Following the pioneering work of Auston (1983), Grischkowsky (1993), and their coworkers, researchers optimized ultrafast photoconductive switches in the past two decades to permit generation and field-resolved detection of electromagnetic transients up to $5 THz.…”

Losses from long-living photoelectrons in terahertz-generating continuous-wave photomixers

“…[4][5][6] Using this technique, we applied 400 mW to our mixers, limited by our optical amplifier, typically illuminating an interdigitated stripline area of 2 lm  150 lm (FWHM). 5,7,8 These intensities were comparable with those of lumped-element mixers, but typically stronger saturation was observed, with two contributions: the sub-linear behavior of the DC photocurrent I ph (P NIR ) with input power (responsivity), explained by thermal effects; and a saturation in addition to the square law dependence of the THz-power on the DC photocurrent, P THz (I ph ). This second contribution varied significantly between mixers of different materials and layer structures.…”

“…Moreover, no re-absorption could be found in 3 MeV ion-implanted samples. 7,17 To illustrate the magnitude of this effect, for example, we have computed the total THz power losses due to reabsorption from our measured A coefficient at 700 GHz for the thick LT-GaAs sample. The reduction in output power at 400 mW is 55% and the reduction at 1000 mW would be 86%.…”

“…This could then explain why high-energy ion-implanted GaAs-mixers retain a square-law dependence of the output power up to higher input powers than LT-GaAs layer on SI-GaAs based mixers, resulting in an observed factor of three at 400 mW. 7 In conclusion, this proposed loss due to reabsorption by long-living photoelectrons can result in large losses at high input powers, and due to the argued independence from scale length this would also be valid for lumped-element devices. The solution would be using non-NIR-absorbing substrates (e.g., transferring LT-GaAs to other substrates) or achieving ultra-short lifetimes also in the substrate (high-energy ion implantation).…”

Comparison of continuous-wave terahertz wave generation and bias-field-dependent saturation in GaAs:O and LT-GaAs antennas

“…Of all the semiconductor materials that have been studied, GaAs grown by molecular beam epitaxy at low substrate temperatures (LT-GaAs) exhibits favorable characteristics, such as high dark resistivity, high breakdown field strength, ultrashort carrier lifetime, and relatively high carrier mobility simultaneously [5,6]. On the other hand, GaAs wafers implanted with ions such as As + , H + , N + , and O + have also been investigated quite extensively for making photoexcited THz antennas [7][8][9][10][11]. Kang et al [12] and Lederer et al [13] have respectively reported subpicosecond carrier trapping time in oxygen-doped GaAs epilayer and subpicosecond response time in oxygen-implanted GaAs.…”