GaAs Photoconductive Semiconductor Switches Research Articles

Nanostructure enabled lower on-state resistance and longer lock-on time GaAs photoconductive semiconductor switches.

We report a new, to the best of our knowledge, type of SI-GaAs photoconductive semiconductor switch (PCSS) with nanostructures. Since light can enter from both the top and side surfaces of nanostructures, the effective penetration depth is significantly increased. Lower on-state resistance and a longer lock-on time have been achieved in the nonlinear mode with this design, as well as a lower triggering fluence in the linear mode. This could be highly useful for a variety of applications that require lower on-state resistance and/or longer lock-on time such as pulsed power systems and firing set switches.

Breakdown Behavior of GaAs PCSS with a Backside-Light-Triggered Coplanar Electrode Structure

The competitive relationship between the surface flashover of the coplanar electrodes and the body current channel was investigated. Breakdown behavior of GaAs photo-conductive semiconductor switch (PCSS) with a backside-light-receiving coplanar electrode structure was studied in this paper. GaAs PCSS was triggered by the laser pulse with an extrinsic absorption wavelength of 1064 nm. Special insulating construction was designed for GaAs PCSS, while the surface of the electrodes was encapsulated with transparent insulating adhesive. Our first set of experiments was at a bias voltage of 8 kV, and the surface flashover breakdown of GaAs PCSS was observed with 10 Hz triggering laser pulse. In the second experiment, at a bias voltage of 6 kV, the body current channel breakdown appeared on the backside of the GaAs PCSS. Compared with these results, the existence of a competitive relationship between the surface flashover breakdown and the body current channel breakdown of the GaAs PCSS was confirmed. When the bias voltage is set within a certain range (just reaching avalanche mode), GaAs PCSS with a backside-light-receiving coplanar electrode structure will undergo the body current channel breakdown. This finding is also consistent with the simulation results.

Performance Investigation of Bulk Photoconductive Semiconductor Switch Based on Reversely Biased p+-i-n+ Structure

We present an investigation of a low-energy-triggered bulk gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS) that is characterized by powerful avalanche domains. The performance of the switch is investigated using a reversely biased p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -i-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> structure with 0.625-mm thickness, and the 8.0-kV, 170-ps bulk PCSS that is triggered by a 905-nm laser at the energy of 5.7 nJ is achieved. In the low-energy-triggered mode, it is found experimentally that the reduction of required energy for switching operation is not always kept by the continuous increase of the bias field in the bulk PCSS due to Franz-Keldysh effect. We also analyze the triggering efficiency depending on the laser wavelength numerically, and results indicate that the earlier formation of the powerful avalanche domains is realized by the increased wavelength, which causes lower laser energy for switching operation. Moreover, the prestudy of high-power microwave (HPM) applications is also introduced utilizing bulk PCSS, and we constructed the basic units for ultrawide-band (UWB) pulse and HPM-driven pulse.

Optical testing method analysis of carrier transport in GaAs PCSS

Measurement of the carrier transport in the GaAs photoconductive semiconductor switch (PCSS) is important for the study of the GaAs PCSS current filament and the design of improved GaAs PCSS devices. In this study, an optical testing method was proposed for the measurement of the time-dependent carrier density distribution in the GaAs PCSS. The measured electron density curves show that the carrier density distribution between the two electrodes is nonuniform for Δt = 0, and as Δt increase from 0.6 ns to 6 ns, a large number of carriers concentrate near the anode of the GaAs PCSS. These phenomena are analyzed in detail and the measured curves are found to be in good agreement with the simulation results.

A 80 kV gas switch triggered by a 17 μJ fiber-optic laser.

A gas switch triggered by μJ laser pulses was developed. The switch employed a 10 mm-gap GaAs photoconductive semiconductor switch (PCSS) mounted in parallel with one of its two gaps. The dark current-voltage characteristic of the PCSS was obtained, and the gas switch characteristics at different bias voltages were experimentally investigated. The results indicate that the switch can be triggered reliably by using a 17 µJ laser pulse, and the jitter is less than 3 ns at the bias voltage of 80 kV and 60% of the self-breakdown voltage.

998 Multiplication Rate of GaAs Avalanche Semiconductor Switch Triggered by 0.567 nJ

In this paper, the results show that the avalanche mode of GaAs photoconductive semiconductor switches (PCSS) requires only a low trigger optical energy of 0.567 nJ to achieve. At the bias electric field is 94 kV/cm, a trigger optical energy with sub-Nano Joule is used to trigger the PCSS, and the multiplication rate can be as high as 988. We have presented avalanche delay characteristics under the different bias electric voltage, and the physical mechanism of the avalanche delay time is analyzed. This article shows a high multiplication rate ultrafast pulse source with low-energy triggering.

Anode Failure Mechanism of GaAs Photoconductive Semiconductor Switch Triggered by Laser Diode

This paper presents an experimental study on the failure mechanism of high-current gallium arsenide photoconductive semiconductor switches (GaAs PCSSs) triggered by the laser diode. We propose a Blumlein pulse forming line to test the GaAs PCSS. The result shows that the damage of GaAs PCSS almost occurs at the anode under the circumstances that either anode or cathode is illuminated, since the highest amplitude of Gunn oscillation always occurs on the anode. We speculate that the failure of high-current GaAs PCSS is attributed to the Gunn effect according to the statistics about failure factors of GaAs PCSS. We use a scanning electron microscope to semiquantitatively analyze the compositions of the erosions microball or granules, which are gallium and arsenium. The result proves our speculation.

Transient Characteristics of Interdigitated GaAs Photoconductive Semiconductor Switch at 1-kHz Excitation

To explore the stability of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) with avalanche multiplication mechanism, an interdigitated electrode structure is presented at 1-kHz excitation by a femtosecond laser. The influences of optical excitation and bias electric field on switching characteristics are investigated. The transient current density and the distribution of electric field are demonstrated by the Monte Carlo simulation. The repetitive switching indicates that the avalanche multiplication mechanism could persist stably at 1-kHz repetition rate operation with this specific electrode structure.

Research on Time Jitter of GaAs Photoconductive Semiconductor Switches in the Negative Differential Mobility Region

Time jitter of GaAs photoconductive semiconductor switches (PCSS) is investigated at an optical excitation of 1053-nm wavelength and 500-ps pulse duration. The experimental results indicate that the time jitter of the GaAs PCSS exhibits a nonmonotonic variation in the negative differential mobility (NDM) region. All of these time jitters are lower than 4% of the rise time of the switching waveform. The optimum time jitter of ~15 ps is achieved at the onset of the NDM region. The theoretical relationship between the optical excitation parameters, the bias electric field, and the time jitter of the GaAs PCSS is built up. The nonmonotonic behavior of the time jitter with electric field is attributed to the instability of the relative fluctuation of drift velocity caused by inter-valley transition of carriers in GaAs.

Positive and Negative Symmetric Pulses with Fast Rising Edge Generated from a GaAs Photoconductive Semiconductor Switch

In this paper, the positive and negative symmetric pulses with a fast rising edge were generated by a GaAs photoconductive semiconductor switch (PCSS). When the GaAs PCSS was biased at 2.0 kV and triggered by a femtosecond laser pulse with a pulse energy of 97.5 J, the peak voltages of the positive and negative pulses were 1.313 kV and 1.329 kV, respectively, and the rise times were 174 ps and 164 ps, respectively. Moreover, the GaAs PCSS presents good stability. The experimental results show that GaAs PCSSs can meet the requirement of a femtosecond streak camera.

Effect of capacitance on positive and negative symmetric pulse with fast rising edge based on GaAsphotoconductive semiconductor switch

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.

Ruby fluorescence-enabled ultralong lock-on time high-gain gallium arsenic photoconductive semiconductor switch.

We report a new type of photoconductive semiconductor switch (PCSS), consisting of a semi-insulating gallium arsenic (GaAs) substrate and a front-bonded ruby crystal. The 532nm laser pulses from an Nd-YAG laser incident on the front surface of the ruby crystal. A portion of the laser pulse passes through the crystal and reaches the GaAs substrate, and the remaining portion of the laser pulse is absorbed by the ruby crystal. This results in the emission of 694nm fluorescent light. Furthermore, a portion of emitted fluorescent light also reaches the GaAs substrate. The high-fluence 532nm short laser pulse with a pulse width around several nanoseconds is used to trigger the PCSS entering the high-gain nonlinear mode, whereas the low-fluence long-lifetime (on the order of a millisecond) 694nm fluorescent light is used to maintain the lock-on time. Thus, an ultralong lock-on time on the order of millisecond is achieved, which is 3 orders of magnitude longer than a typical lock-on time of high-gain GaAs PCSS.

Optical absorption mechanism of GaAs photoconductive semiconductor switch

The output charges of linear and nonlinear semi-insulating GaAs photoconductive semiconductor switches (PCSSs) triggered by a 1064 nm nanosecond pulse laser with an energy of millijoule level are measured under different bias voltages. On the basis of the operation mechanism of the linear PCSS, the photogenerated carrier densities of the PCSS are measured. From the results of the comparison between the measured values and the values determined by different absorption mechanisms, the absorption mechanism of the switch is analyzed. As an important parameter of the avalanching charge domain, the effect of the photogenerated carrier density on the output performance of GaAs PCSSs is discussed.

Photoconductive semiconductor switch-based triggering with 1 ns jitter for trigatron

Synchronization for multiple-pulse at nanosecond range shows a great value on the power multiplication and synchronous electric fields applications. Nanosecond or sub-ns jitter synchronization is essential for the improved working efficiency of the large amounts of pulse modules and accurate requirements for the power coherent combining applications. This paper presents a trigger generator based on a laser diode-triggered GaAs photoconductive semiconductor switch (PCSS) with low jitter and compact size characteristics. It avoids the high currents that are harmful to high-gain mode PCSSs. In the trigger circuit, a 200 pF capacitor is charged by a microsecond-scale 18 kV pulse and then discharged via the high-gain mode GaAs PCSS to trigger the high-power trigatron switch. When triggered by the ∼10 ns pulse generated by the PCSS, the DC-charged trigatron can operate in the 20–35 kV range with 10 ns rise time and 1 ns delay-time jitter.

Investigation on the surface flashover of high gain SI‐GaAs PCSS

AbstractThe GaAs photoconductive semiconductor switch (PCSS) is generally recognized currently as a leading power electronic device for its unique advantages. A major limitation of PCSS has been its surprisingly low voltage threshold for the surface flashover found when PCSS works at the high gain mode. In this paper, the surface flashover of high gain PCSS is studied by experiments. We propose that the non‐uniform distribution of the surface field that resulted from the photo‐activated charge domain (PACD) and the gas desorption is the key cause of such reducing of the SF field. SF6 ambient dielectric is efficient in increasing the surface field, and the experiment results show that the PCSS we developed could resist a voltage as high as 20 kV/cm when the ambient dielectric is 3 atmospheric SF6. This conclusion has the practical application of significance to improve the performance of the high gain PCSS, which is severely limited by the premature breakdown effects.

Time jitter characteristics of GaAs photoconductive semiconductor switch in linear mode

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.

The Role of the Photo-Generated Carrier in Surface Flashover of the GaAs Photoconductive Semiconductor Switch

The development of Gallium arsenide photoconductive semiconductor switch has been hampered by the surface flashover. The surface flashover threshold with the laser excitation is far lower than the one without the laser excitation. In this paper, the phenomena of surface flashover, including the infrared video, flashover spectrum, and the voltage waveforms are presented to research their work mechanism. The dynamic development process of surface flashover is divided into four typical states. Based on the 1-D time domain finite element method, the role of the photo-generated carrier in the surface flashover is analyzed. Our results suggest that the photo-activated charge domain (PACD) will enhance the local electric field and result in the surface flashover occurrence between the electrodes and semiconductors. So the atoms of GaAs semiconductors and electrodes are involved in the surface flashover. According to the PACD theory, the experimental phenomena can be explained reasonably.

A New Phenomenon in Semi-Insulating 4H-SiC Photoconductive Semiconductor Switches

A new oscillational phenomenon has been found in high-biased semi-insulating (SI) 4H-SiC photoconductive semiconductor switches (PCSSs) with high densities of vanadium and nitrogen dopants, and this oscillational phenomenon has no relationship with the laser wavelength, bias voltage, the charge capacitor, and the shape/size of the 4H-SiC PCSS. This paper shows that the photo activated charge domain theory in SI GaAs PCSS may explain this phenomenon. Due to the high densities of vanadium and nitrogen dopants, the intervalley scattering may occur in the 4H-SiC PCSS, and the space charge field region will appear in the 4H-SiC PCSS for the electrons accumulation. This region looks upon an equivalent capacitor, when the accumulation of the electrons is over, the equivalent capacitor will discharge, and the oscillational phenomenon appears.

Solid-State Nanosecond Pulse Generator Using Photoconductive Semiconductor Switch and Helical Pulse Forming Line

A solid-state pulse generator module using two helical pulse forming lines (HPFLs) and a photoconductive semiconductor switch (PCSS) is presented. Two solid-state HPFLs are stacked as one stage Blumlein line. The HPFL is made of Al2O3 ceramic, which can hold-off voltages larger than 40 kV at microseconds-charging-time range. To achieve the goal of the synchronization for future power combining, the GaAs PCSS is adopted in the module. The GaAs PCSS is operated in the high-gain mode with a compact laser diode triggering, aiming to take advantage of the low-jitter and compactness. In tests, sub-ns jitter characteristic of GaAs PCSS has been obtained under different electrical conditions, and GaAs PCSS in the high-gain mode shows an attractive synchronous characteristic. By changing the angle between the two HPFLs of the module, we prove that the electromagnetic coupling effect is quite weak between the two lines. Based on the low-jitter characteristics of the GaAs PCSS, the jitter of delay time between command signal (3 V) and output pulse of the module is 612 ps among 30 times consecutive group tests. The module can deliver a high power pulse with 50-ns pulse duration and 18.5-kV peak voltage value on the matching resistive load ( $67~\Omega )$ .

Comparison on the Synchronization of Two Parallel GaAs Photoconductive Semiconductor Switches Excited by Laser Diodes

In this letter, the synchronization of GaAs photoconductive semiconductor switches in two electrically driven configurations for laser diodes excitation is investigated. Comparisons on the synchronization are carried out by varying the bias electric field and optical excitation energy. The optimum synchronization of 296 ps is achieved at 1.2 kV with optical excitation energy of 1.9 μJ. The results demonstrate the relationship between the synchronization and transient carriers' population ratio among the intervalley.