The fabrication and characterization of terahertz wave photoconductive dipole antennas on oxygen ion implanted gallium arsenide.

摘要

In the recent decade, lots of funds are provided to investigate terahertz (THz) wave and its applications in Fundamental Physics, Homeland Security, Biomedical, Astronomy and THz Communication. The main reason is that terahertz wave has some advantages of microwave, like the relatively long wavelength and transparency to some materials, and also some advantages of light, such as good directionality and high capacity for information transmission.;Lately, oxygen ion implanted GaAs (GaAs:O) has caught a lot of attention and been studied as an alternative material to Low Temperature Grown (LTG) GaAs material (which is commonly used to generate terahertz wave by photoconductive method) for its good performances in THz wave generation. GaAs:O has a reasonably high resistivity and ultra-short carrier lifetime close to those of LTG GaAs material. The preparation of GaAs:O is easy to control and reproduce compared with LTG GaAs material. A higher saturation level of both pumping and bias field of GaAs:O THz wave emitter is observed, which will lead to a higher output power of THz wave.;In this work, the GaAs:O materials are further studied. The preparation conditions of GaAs:O materials are optimized by adjusting the implant process and annealing temperature. The performance of devices made from GaAs:O in terms of THz wave generation is investigated under both pulsed and continuous-wave (CW) modes. The saturation behaviors and screening effects are also studied in this work.;The main results and original contribution of this research are summarized as follows: (1) Material. (a) A uniform defect distribution was obtained in oxygen ion implanted GaAs materials by a multi-implantation process followed by Rapid Thermal Annealing (RTA). (b) A dark resistance higher than 106 Ohm/square was obtained after RTA in GaAs:O. An ultra-short carrier lifetime (around 0.35ps) was achieved with high implant dosage and a suitable annealing temperature. (c) Compared with the LTG GaAs tested in this work, GaAs:O has a relatively higher saturation threshold, which allows it to generate higher CW THz power than this type LTG GaAs. (2) Photoconductive devices. (a) For high-dose GaAs:O based PC antenna, under the pulsed generation mode, around 31microW average power was achieved under the condition of 35mW pumping power and 70V DC bias. Under the CW generation mode, 0.35 THz single frequency wave is generated at the level of tens of nW, which is around 2∼3 orders smaller than that under pulsed generation mode. (b) For low-dose GaAs:O based PC antenna, about 48microW average power was achieved under pulsed generation mode, which is the highest power ever reported to our knowledge by such kind of devices. An analysis of the power saturation behavior suggests that power levels at ∼200microW may be achievable in GaAs:O materials. CW THz wave at microW level was also achieved from this device at 0.358THz under 180mW pump power and 80V bias voltage. (c) The THz spectra of some GaAs:O devices are similar to that of LTG GaAs, which suggests GaAs:O can yield as good THz spectra as the LTG GaAs sample tested in this work. (3) Device modeling. (a) Screening effect in the PC antenna, especially under CW background illumination, has been studied experimentally and theoretically. A simple empirical model has been proposed to explain the mechanism of the screening effect. (b) We propose an enhanced theoretical model of CW THz generation which can adequately explain the bias-dependent saturation behavior of the PC antenna, as evidenced by the good matching of simulation results and experimental data.