GaAs Photoconductive Switches Research Articles

Carrier Transport and Pulse Compression of an Opposed-Contact GaAs Photoconductive Switch at Low-Energy Optical Excitation

Carrier Transport and Pulse Compression of an Opposed-Contact GaAs Photoconductive Switch at Low-Energy Optical Excitation

Evolution of Current Filament With Electron-Hole Plasma in High-Gain GaAs Photoconductive Switches With Opposed Electrodes

Evolution of Current Filament With Electron-Hole Plasma in High-Gain GaAs Photoconductive Switches With Opposed Electrodes

Photoexcited carrier dynamics in a GaAs photoconductive switch under nJ excitation

In this article, the bunched transport of photoexcited carriers in a GaAs photoconductive semiconductor switch (PCSS) with interdigitated electrodes is investigated under femtosecond laser excitation. Continuous outputs featuring high gain are obtained for single shots and at 1 kHz by varying the optical excitation energy. An ensemble three-valley Monte Carlo simulation is utilized to investigate the transient characteristics and the dynamic process of photoexcited carriers. It demonstrates that the presence of a plasma channel can be attributed to the bunching of high-density electron–hole pairs, which are transported in the form of a high-density filamentary current. The results provide a picture of the evolution of photoexcited carriers during transient switching. A photoinduced heat effect is analyzed, which reveals the related failure mechanism of GaAs PCSS at various repetition rates.

Coherent GHz lattice and magnetization excitations in thin epitaxial Ag/Fe/Cr/Fe films

We excited an epitaxial magnetic Ag/Fe/Cr/Fe multilayer nonthermally and nonoptically with very short (1 ps) electromagnetic pulses. We detected the synchronous phononic-magnetic response by time-resolved magneto-optical Kerr effect measurements. The Ag/Fe/Cr/Fe multilayer was patterned into a coplanar waveguide transmission line, and the electromagnetic pulses were generated by pulsed-laser illumination of an integrated GaAs photoconductive switch (PCS). The detected magnetic excitations comprise up to four narrow-band high-order modes with the highest frequency reaching 30 GHz. The mode frequencies are independent of both temperature in the range from 16 to 300 K and the applied external magnetic field up to 120 mT. Our analysis shows that the origin of the rigidity of these high-frequency modes is the strong coupling of the magnetic subsystem with the lattice of the Ag/Fe/Cr/Fe multilayer. The exciting electromagnetic pulse generated by the PCS induces, via magnetoelastic coupling, long-lived (ns) standing GHz acoustic waves normal to the Ag/Fe/Cr/Fe film plane. These lattice oscillations in turn couple back and drive the magnetization oscillations via the magnetoelastic coupling. The temperature and field dependence of the damping of the oscillations can be described by inelastic phonon-phonon and phonon-magnon scattering. Our study opens up a possibility of using coherent lattice and magnetization dynamics in ferromagnetic films for spintronic devices at GHz clock rates.

Colloidal upconversion nanocrystals enable low-temperature-grown GaAs photoconductive switch operating at λ = 1.55 μm

Microwave photoconductive switches, allowing an optical control on the magnitude and phase of the microwave signals to be transmitted, are important components for many optoelectronic applications. In recent years, there are significant demands to develop photoconductive switches functional in the short-wave-infrared spectrum window (e.g. λ = 1.3–1.55 μm) but most state-of-the-art semiconductors for photoconductive switches cannot achieve this goal. In this work, we propose a novel approach, by the use of solution-processed colloidal upconversion nanocrystals deposited directly onto low-temperature-grown gallium arsenide (LT-GaAs), to achieve microwave photoconductive switches functional at λ = 1.55 μm illumination. Hybrid upconversion Er3+-doped NaYF4 nanocrystal/LT-GaAs photoconductive switch was fabricated. Under a continuous wave λ = 1.55 μm laser illumination (power density ∼ 12.9 mW μm−2), thanks to the upconversion energy transfer from the nanocrystals, a more than 2-fold larger value in decibel was measured for the ON/OFF ratio on the hybrid nanocrystal/LT-GaAs device by comparison to the control device without upconversion nanoparticles. A maximum ON/OFF ratio reaching 20.6 dB was measured on the nanocrystal/LT-GaAs hybrid device at an input signal frequency of 20 MHz.

不同激光能量涨落对GaAs光电导开关时间抖动的影响

不同激光能量涨落对GaAs光电导开关时间抖动的影响

Study of photoexcited-carrier dynamics in GaAs photoconductive switches using dynamic terahertz emission microscopy

We propose dynamic terahertz (THz) emission microscopy (DTEM) to visualize temporal–spatial dynamics of photoexcited carriers in electronic materials. DTEM utilizes THz pulses emitted from a sample by probe pulses irradiated after pump pulse irradiation to perform time-resolved two-dimensional mapping of the THz pulse emission, reflecting various carrier dynamics. Using this microscopy, we investigated carrier dynamics in the gap region of low-temperature-grown GaAs and semi-insulating GaAs photoconductive switches of the identical-dipole type. The observed DTEM images are well explained by the change in the electric potential distribution between the electrodes caused by the screening effect of the photoexcited electron-hole pairs.

The Jitter Time of GaAs Photoconductive Switch Triggered by 532- and 1064-nm Laser Pulse

A jitter time test of GaAs photoconductive semiconductor switch (PCSS) with excitation laser wavelength of 1064 and 532 nm is presented. When the laser pulse energy increases from 10.0 to 165.0 $\mu \text{J}$ with 8-ns laser pulse width, the corresponding jitter time decreases from 96.4 to 86.6 ps at 1064 nm and 71.6 to 63.3 ps at 532 nm, respectively. All measurements are carried out at a constant electrode gap size of 2 mm. The analysis indicates that the jitter time is proportional to the laser absorption depth in GaAs PCSS. These findings are important for decreasing the jitter time in X-ray streak camera and other accurate synchronization systems.

A Method to Maximize the Amplitude of Generated Terahertz Pulse From LT GaAs Photoconductive Semiconductor Switch

The substrate characteristics of GaAs photoconductive switch has been studied in order to determine the conditions required to generate maximum terahertz pulse amplitude in the device. In particular, the substrate material characteristics, such as trap density, capture cross sections, trap occupancy that determine fields, recombination rate, and photogeneration that influence the pulse rise-time in a low temperature grown gallium arsenide semiinsulating material, are studied. Results show that maximum pulse amplitude occurs when the carriers of both polarities contribute to the terminal currents, and the voltage at this point is referred to as the dual injection voltage (DIV). DIV for a given device is directly dependent on the substrate properties as well as the proximity of the electrodes.

Research progress on avalanche multiplication GaAs photoconductive terahertz emitter

GaAs photoconductive switch illuminated by a femto-second laser has been widely used in a terabertz (THz) time domain spectroscopy system as a THz wave emission antenna. Now, all of the GaAs photoconductive switches are used in linear mode. However, when the GaAs photoconductive switch operates in an avalanche multiplication mode, the power capacity of output ultrafast electric pulse is much higher than that in a linear mode. So far, nobody has proposed the idea of generating THz waves by using the GaAs photoconductive switches in the avalanche multiplication mode. In this paper, we report the feasibility and research progress of using the GaAs photoconductive switches in the avalanche multiplication mode as the THz sources. By theoretical analysis and experimental research, some results are obtained experimentally as follows. 1) The GaAs photoconductive antenna can operate in an avalanche multiplication mode when illuminated by a femto-second laser pulse with an energy on the order of nJ. 2) The maintaining time of the avalanche multiplication mode, i.e, lock-on period, can be reduced by the quenching mode of photo-activated charge domain. These results lay the foundation for generating the high intensity THz emission by the GaAs photoconductive antenna with the avalanche multiplication mechanism.

Impact of Current Filaments on the Material and Output Characteristics of GaAs Photoconductive Switches

The current filament phenomena in high gain gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) always draw a significant influence on the lifetime of the devices. This paper presents a study on the influence of the current filament over the material properties and output characteristics of the GaAs PCSS. The working principle of the current filaments has been analyzed and it is shown that the performance of GaAs PCSS degrades due to the heating effects of the current filaments. It is observed that the heating effect of current filament reduces the dark resistivity of the GaAs material; furthermore, it gradually damages electrode of PCSS, leading to the breakdown of PCSS. This paper presents the relationship between the turn-ON process and damage of the PCSS.

Research on Flashover Characteristics and the Physical Mechanism of High-Gain GaAs Photoconductive Switches

We have presented surface flashover characteristics of high-gain GaAs photoconductive semiconductor switch (PCSS) under the different output current. Under the low output current, the recorded flashover spectrum was different from the spark discharge spectrum of air. Based on the analysis of current waveform and the flashover spectrum, the physical mechanism of the flashover phenomena was discussed. Under the high output current, the recorded time waveform of flashover was periodic oscillation. This phenomenon was analyzed based on pinch effect. Finally, the mechanism of the surface flashover led to the damage of GaAs PCSS, which was demonstrated and analyzed.

Picosecond Joule heating in photoconductive switch electrodes

We present experimental observations of picosecond Joule heating inside the gold metallization of ErAs:GaAs photoconductive switches. Femtosecond laser time-domain thermoreflectance is employed to resolve the fast thermal dynamics in the central switch electrode during generation and transmission of rf electrical pulses. Sharp features in the thermoreflectance signal scaling quadratically with the bias/pulse voltage reveal Joule heating with durations $\ensuremath{\le}$5 ps inside the gold metal. The temporal shape and rise time of the signals is in excellent agreement with the theoretical pulse wave form and subpicosecond carrier lifetime of the active medium. Probing different locations on the electrode shows the propagation, attenuation, and dispersion of the electrical pulses along the coplanar waveguide structure. Overall, the presented photothermal experiments demonstrate great potential to reveal the internal dynamics of photoconductive switches, characterize transmission lines, and study ultrafast heating in metals.

Influence of the incident laser pulse energy on jitter time of GaAs photoconductive semiconductor switches

We have experimentally investigated the jitter time of a GaAs photoconductive switch (PCSS) when it is triggered by a laser pulse with 30 ns pulse width and 1064 nm wavelength. It is found that the jitter time decreases as the incident laser pulse energy increases from 0.40 to 1.6 mJ. In addition, a theoretical analysis indicates that the jitter time is proportional to relative deviation of the laser pulse energy. This work provides a path to improve the performance of the PCSS, which is used in applications such as a high time precision synchronous control system and ultrawide-band radiation source.

A Novel Test Method for Ultrafast Pulse Response Characteristics of ZnO Varistor Ceramics

A ZnO varistors in series connected with a semi‐insulating GaAs photoconductive switches (SI‐GaAs PCSS's), a test method for ultrafast pulse response characteristics of ZnO varistor ceramics with DC bias was presented for the first time. The DC voltage distribution of the PCSS's and the varistors was measured in a dark state and the pulse response characteristics of the ZnO varistor ceramics was examined by a nanosecond laser pulse illuminating the PCSS's. The results indicate that the electric pulse output from the varistors includes capacitive current and conduction current and there is a time delay between their peaks. It is revealed that ZnO varistors has a nonlinear conductivity for the nanosecond electric impulse excitation and the barrier capacitance decay constant of the ceramics sample is 105 ns, which is explained through the analysis of examining the material structure and the conductive mechanisms.

Microwave On/Off Ratio Enhancement of GaAs Photoconductive Switches at Nanometer Scale

This paper reports on performances enhancement of photoconductive switches in term of On/Off ratio and insertion losses. The optimization parameters on which the research has been focused are gap dimensions reduction to nanometer scale. The device characterization results up to a microwave frequency of 40 GHz and under CW illumination at a wavelength of 800 nm are presented. On/Off ratio reveals a value of 13 dB at 20 GHz under 100 mW optical power.

Infrared Inhibition of Flashover in Photoconductive Semiconductor Switch in High Electric Field

Semi-insulating GaAs photoconductive switches hold great potential for use in high-voltage switching applications. However, the utility is restricted by surface flashover, which resulted in breakdown in previous experiments. In this letter, we designed a configuration based on infrared inhibition to suppress the surface flashover in high-voltage operation. Bias voltage can be up to 32 kV with a 0.9-kA switching current. Results show that transport of photo-activated charge domain is interrupted by the formation of new domains due to second laser trigger.

THz generation using extrinsic photoconductivity at 1550 nm

1550-nm pulses from a fiber-mode-locked laser are used to drive an ErAs:GaAs photoconductive switch, resulting in easily measured THz radiation with average broadband (~0.1 to 1.0 THz) power of ≈0.1 mW. The new THz switching mechanism is attributed to fast extrinsic photoconductivity that generates photocarriers (probably electrons) from the ErAs nanoparticles embedded in the material with a lifetime of ~0.45 ps (354 GHz bandwidth). This is the first known demonstration of useful THz power generation by extrinsic photoconductivity.

Peculiar Transmission Characteristics of the Large Gap Semi-Insulating GaAs Photoconductive Switch

Unique experimental phenomena are discovered in a large gap semiinsulating (SI) GaAs photoconductive semiconductor switch (PCSS) and the peculiar transmission characteristics are exhibited in the experiment. The transmission characteristics for the large gap SI-GaAs PCSS are entirely different from the commonly designed PCSS. By analyzing the differences of the transmission characteristics between the common and the large gap SI-GaAs PCSS, a detailed statistical analysis and theoretical explanations are expounded. The large gap SI-GaAs PCSS works in the overvoltage relaxation limit space charge accumulation (LSA) mode when the conditions of 5 × 104 s · cm−3 ≤ n0/f ≤ 3 × 105 s·cm−3 and n0L ≥ 1013 cm−2 must be met in the switch, with n0 being carrier concentration and f the frequency. The large gap SI-GaAs PCSS we developed has not shown the nonlinear (lock-in) behavior at high bias voltage, so the withstand voltage and service life for PCSS are improved.

Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch.