Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission

We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both experimentally and using a three-dimensional carrier dynamics simulation. A uniform density of vacancies was formed over the optical absorption depth of bulk GaAs samples by performing multi-energy implantations of arsenic ions (1 and 2.4MeV) and subsequent thermal annealing. In a series of THz emission experiments the frequency of peak THz power was found to increase significantly from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to 10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast carrier dynamics to reproduce and explain these results. The effect of the ion-induced damage was included in the simulation by considering carrier scattering at neutral and charged impurities, as well as carrier trapping at defect sites. Higher vacancy concentrations and shorter carrier trapping times both contributed to shorter simulated THz pulses, the latter being more important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure

Acceptor-like deep level defects in ion-implanted ZnO

N-type ZnO samples have been implanted with MeV Zn⁺ ions at room temperature to doses between 1×10⁸ and 2×10¹⁰cm⁻², and the defect evolution has been studied by capacitance-voltage and deep level transient spectroscopy measurements. The results show a dose dependent compensation by acceptor-like defects along the implantation depth profile, and at least four ion-induced deep-level defects arise, where two levels with energy positions of 1.06 and 1.2 eV below the conduction band increase linearly with ion dose and are attributed to intrinsic defects. Moreover, a re-distribution of defects as a function of depth is observed already at temperatures below 400 K.This work was supported by the Norwegian Research Council through the Frienergi program and the Australian Research Council through the Discovery projects program

Hidden Order in Crackling Noise during Peeling of an Adhesive Tape

We address the long standing problem of recovering dynamical information from noisy acoustic emission signals arising from peeling of an adhesive tape subject to constant traction velocity. Using phase space reconstruction procedure we demonstrate the deterministic chaotic dynamics by establishing the existence of correlation dimension as also a positive Lyapunov exponent in a mid range of traction velocities. The results are explained on the basis of the model that also emphasizes the deterministic origin of acoustic emission by clarifying its connection to sticks-slip dynamics.Comment: 5 pages, 10 figure

Polarisation-sensitive terahertz detection by multicontact photoconductive receivers

We have developed a terahertz radiation detector that measures both the amplitude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.Comment: 3 pages, 3 figure

IoT enabled communication device with mixer less low complex QPSK based transmitter architecture for low frequency applications

echnological development in the area of wireless communications lead to the requirement of tight integration of both the digital and analog functional units. Integrating mixers is a challenging task, especially in mixed signal design. IoT communication devices require low design complexity as we expect millions of devices connected. In this paper we propose a mixer less low complex QPSK based transmitter architecture targeting low frequency applications which reduced the complexity in transmitter design. A prototype has been developed using Bipolar Junction Transistors (BJTs) and FPGA as the base band controller. The design can easily be adapted to MOSFET technology and modulation is achieved without the need of generating the carrier externally. The prototype developed was tested successfully by generating frequencies of range varying from 1 KHz to 120 MHz. The proposed architecture can also be used for any other digital modulation scheme such as BPSK, FSK etc

Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs

The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy measurements, coupled with Monte Carlo simulations of THz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump THz-probe spectroscopy, and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, we have demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch THz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast THz photonic devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter

Ultrafast trapping times in ion implanted InP

As⁺ and P⁺implantation was performed on semi-insulating (SI) and p-type InP samples for the purpose of creating a material suitable for ultrafast optoelectronic applications. SI InP samples were implanted with a dose of 1×10¹⁶ cm⁻² and p-type InP was implanted with doses between 1×10¹² and 1×10¹⁶ cm⁻². Subsequently, rapid thermal annealing at temperatures between 400 and 700 °C was performed for 30 sec. Hall-effect measurements, double-crystal x-ray diffraction, and time-resolved femtosecond differential reflectivity showed that, for the highest-annealing temperatures, the implanted SI InP samples exhibited high mobility, low resistivity, short response times, and minimal structural damage. Similar measurements on implantedp-type InP showed that the fast response time, high mobility, and good structural recovery could be retained while increasing the resistivity

Synthesis of functionalized tricyclo[5.3.1.02,6]undecadienones

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Separation of vacancy and interstitial depth profiles in ion-implanted silicon: Experimental observation

An experimental concept of studying shifts between concentration-versus-depth profiles of vacancy and interstitial-type defects in ion-implanted silicon is demonstrated. This concept is based on deep level transient spectroscopy measurements where the filling pulse width is varied. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the substitutional carbon–interstitial carbon pair, are obtained at the same sample temperature and can be recorded with a high relative depth resolution. For 6 MeV ₁₁B ions, the peak of the interstitial profile is displaced by ∼0.5 μm towards larger depths compared to that of the vacancy profile, which is primarily attributed to the preferential forward momentum of recoiling Si atoms.Financial support was kindly provided by the Swedish Research Council for Engineering Sciences (TFR), the Swedish Foundation for International Cooperation in Research and Higher Education (STINT), and the EU Commission, Contract No. ERBFMRXCT980208 (ENDEASD—TMR network)