Results of experiments of the 4 mm gap semi-insulating(SI) GaAs photoconductive switch triggered by 1064 nm, 1.0 mJ pulse laser showed the nonlinear mode when the bias field was 3800 V. Under the same bias electric field and trigger light energy conditions, the switch outputs stably nonlinear electrical pulses, and the switch surface injury mark is caused by filamentation after 1500 times triggering. Analysis shows that under given conditions of trigger energy and electric field, two transient thermal effects occur in the switch chip, namely the thermal relaxation and photoactivated charge domain-phonon drag, respectively. Thermal relaxation time is shortened to the order of picoseconds or subpicoseconds, thermal relaxation process leads to the thermal conduction relaxation. When photoactivated charge domain moves at 107cm/s speed from cathode to anode, switch chip transient temperature makes relaxation oscillations owing to these effects, and the rapid increase of temperature in the chip is constrained. Photoactivated charge domain-phonon drag effect transmits in the direction of the dislocation movement, the temperature in mobile region increases when the flow of thermal energy carried by the phonons was concentrated in the movement plane, the injury of filamentation is produced by superposition and cumulation of mobile tracks.
Femtosecond streak camera is currently the only diagnostic device with a femtosecond time resolution. Scanning circuit with bilateral symmetrical output is an important part of femtosecond streak camera. To achieve better performance of the streak camera, high requirements are placed on the output of scanning circuit. Owing to the excellent feature of litter time jitter and fast response speed, a GaAs photoconductive semiconductor switch (PCSS) has become a core device in the scanning circuit. Investigating the positive and negative symmetric pulses with fast rising edgeof GaAs PCSS is of great significance to improving the time resolution of femtosecond streak camera. In this paper, a laser with a pulse width of 60 fs was used to trigger a GaAs PCSS with an electrode gap of 3.5 mm. Under different storage capacitors and bias voltages, the positive and negative symmetric pulses withthe fastest rise time of 149 ps and the highest voltage transmission efficiency of 92.9% were obtained. The test results meet the design requirements of streak camera to realize femtosecond time resolution. Through the comparative analysis of the experimental values, it is concluded that the storage capacitor can affect the efficiency and rise time of the output electrical pulse in the same trigger laser pulse. By calculating the multiplication rate of carriers in combination with the output electrical pulse waveform, it is concluded that the GaAs PCSS operates in linear mode. According to the working characteristics of the linear mode and the energy storage characteristics of the capacitor, the analysis indicates that, when the characteristics of the trigger laser pulse are the same, the transmission efficiency and rise time of the output electric pulse voltage increase with the increase in storage capacitor, which is consistent with the experimental results. This study has a certain guiding significance for the better application of GaAs PCSS in femtosecond streak camera, which also has a certain propelling effect on improving the time resolution of femtosecond streak camera.
The 4 mm gap and 5 ns pulse width semi-insulating GaAs photoconductive switches were triggered by 532 nm laser pulse with gradual increase of bias voltage from 500 V in steps of 50 V until the emergence of nonlinear electrical pulse. The expermental results showed that the linear and nonlinear electrical pulse waveforms had smaller amplitude and varying degrees of oscillation reduction after going through a main pulse. Then the microscopic state and transport process of carriers (hot-electron) in the switch material were studied in detail using the quantum theory. It was found that in the DC bias electric field, when the relaxation time of the hot-electrons in the electron-electron and electron-phonon interaction process is longer than the carrier life, the photoconductivity oscillation can be caused by the change of mobility in the process of optoelectronic transport, which is the main cause for the output electrical pulse to show oscillations.
Semi-insulating GaAs photoconductive semiconductor switch (PCSS) with withstand voltage of 32 kV and peak current of 3.7 kA has been developed. The breakdown mechanism of the PCSS is analyzed. It is shown that the breakdown of PCSS fabricated from indirect band-gap semiconductors is determined mainly by limited conduction of trap filling, but for PCSS's fabricated from materials that exhibit the transferred-electron effect, such as GaAs, breakdown of the PCSS is caused mainly by the negative-resistance-induced electric field enhancement at the anode boundary. Based on the Gunn effect electronics, the breakdown voltage of the semi-insulating GaAs PCSS is calculated, and the calculated results agree with the experimental results.
Time precision switching is crucial to a high-precision synchronization control system with several synchronized sources. Compared with the other high-power switches, a GaAs photoconductive semiconductor switch (PCSS) with a litter time jitter has been widely used in a precision synchronization control system. There is little work on the time jitter of a GaAs PCSS. In this paper, a formula of GaAs PCSS time jitter is derived by the qualitative theoretical derivation through using the probability distribution of the output electrical pulse and the corresponding relation between the time and electrical waveform of GaAs PCSS, and combining the carrier transport process. In experiment, a neodymium-doped yttrium aluminum garnet nanosecond laser beam is split by a semipermeable half mirror into two optical beams, and then these two beams simultaneously trigger two identical GaAs PCSSs in two parallel circuits. As the energy of a triggering laser pulse is fixed at 0.35 mJ, four different laser pulse widths, namely 30 ns, 22 ns, 16 ns and 11 ns, respectively, are used to trigger the GaAs PCSSs. The bias voltage changes from 0.1 kV to 1 kV in steps of 0.1 kV, and it is used in the above-mentioned experiment. The PCSSs are triggered 20 times at each of the bias voltage values. The time jitter of the GaAs PCSS with a 3-mm gap can be measured. By analyzing the experimental data, we conclude that the time jitter of the GaAs PCSS decreases with the triggering laser pulse width decreasing under the condition of different bias voltage. In the linear mode, the GaAs PCSS illuminated by a photon with a proper wavelength creates an electron-hole pair. The characteristic of the triggering laser pulse determines that of the output electrical pulse. With the energy of triggering laser pulse fixed, the fluctuation of electrical pulse increases fast with its pulse width decreasing. Moreover, according to the derived formula for a time jitter, the GaAs PCSS time jitter decreases with triggering laser pulse width narrowing, under the different externally applied bias voltages. It is demonstrated that the theoretical and experimental results of the relationship between the triggering laser pulse width and the GaAs PCSS time jitter are consistent. The obtained results provide a basis for further reducing the GaAs PCSS time jitter, which is important for a next-generation fusion research facility and laser trigger antenna array of generating short pulse sequence.
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