Photoconductive Semiconductor Switches Research Articles

Application of an Al-doped zinc oxide subcontact layer on vanadium-compensated 6H–SiC photoconductive switches**Project supported by the Innovation Program of the Shanghai Institute of Ceramics (Grant No. Y39ZC1110G), the Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10), the Industry–Academic Joint Technological Innovations Fund Project of Jiangsu Province, China (Grant No. BY2011119), the Natural Science Foundation of Shanghai (Grant

Al-doped ZnO thin film (AZO) is used as a subcontact layer in 6H–SiC photoconductive semiconductor switches (PCSSs) to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the on-state resistance of lateral PCSS with an n+-AZO subcontact layer is 14.7% lower than that of PCSS without an n+-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials.

Plasma Etching of n-Type 4H-SiC for Photoconductive Semiconductor Switch Applications

Photoconductive semiconductor switches (PCSS) fabricated on high-purity semi-insulating 4H-SiC substrates (000\( \bar{1} \)) are capable of switching high currents in compact packages with long device lifetimes. A heavily doped n-type SiC epitaxial layer of appropriate thickness is required to form low-resistance ohmic contacts with these devices. In addition, to enhance the performance of the PCSSs, the SiC surface between the ohmic contacts must be extremely smooth. We report a chlorine-based, inductively coupled plasma reactive ion-etching process yielding n-type SiC epitaxial layers with the required smoothness. The rate of etching and post-etching surface morphology were dependent on plasma conditions. We found that the surface smoothness of epitaxial layers can be improved by including BCl3 in the argon–chlorine mixture. The optimum etching process yielded very smooth surfaces (∼0.3 nm RMS) at a relatively high rate of etching of ∼220 nm/min. This new fabrication approach significantly reduced the on-state resistance of the PCSS device and improved its durability of operation.

Research on synchronization of 15 parallel high gain photoconductive semiconductor switches triggered by high power pulse laser diodes

The synchronization of 15 parallel high gain gallium arsenide photoconductive semiconductor switches (GaAs PCSS) has been researched aiming to get higher output voltage. Each PCSS is triggered independently by a high power pulse laser diode. The pulse width, energy, peak power, and central wavelength of the laser pulse are approximately 18 ns, 360 μJ, 20 kW, and 905 nm, respectively. In the stacked Blumlein transmission lines structure, the synchronous conduction of 15 parallel GaAs PCSSs has been achieved by offering optimized bias voltage and laser parameters. The method of synchronization calculation is given, and the synchronization of the 15 parallel GaAs PCSSs is measured as 775 ps. Furthermore, influences of the bias voltage, laser parameters on the synchronization are analyzed. In the output terminal, superimposed by the output voltages of 15 Blumlein transmission lines, the total output voltage reaches up to 328 kV, which is the highest output voltage of GaAs PCSSs that has been reported so far.

An Ultrawideband to Dual-Band Switchable Antenna Design for Wireless Communication Applications

A switchable planar monopole antenna operating in ultrawide band (UWB)and dual-band mode is demonstrated. The switching is triggered with a photoconductive semiconductor switch triggered by light emitting diode. In the switched-off state, the antenna operates in the dual-band/UWB mode, while in the switch-on state the configuration converts to a dual-band antenna due to the extended ground plane. The measured and simulated results show that the dual-band/UWB mode entirely covers the UWB frequency band and the 2.4 GHz wireless local area network WLAN, while the dual-band mode represents a dual-band antenna operating at WiMAX and X-band Satellite communication bands.

激光触发能量对横向结构4H-SiC光导开关导通电阻的影响

激光触发能量对横向结构4H-SiC光导开关导通电阻的影响

Large Current GaAs PCSS Triggered by a Laser Diode

We have fabricated a 2-mm gap semi-insulating GaAs photoconductive semiconductor switch (PCSS), and obtained a 1.45-kA large current under a bias voltage of 6 kV when the PCSS was triggered by a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> J commercial laser diode. An RLC transient circuit model was employed to get the electrical properties of the PCSS in the transient discharge process. The reason for the switch exiting from nonlinear operating mode was that the electric field across the switch dropped below the lock-on field. This letter shows the attractive prospect of a low-cost compact high-power pulse source with the GaAs PCSS.

Investigation of GaAs PCSS Triggered by Laser Pulses With Different Parameters

Photoconductive semiconductor switch (PCSS) has many advantages, such as low time jitter, fast response, high repetition rate, compact size, easy integration, and so on. It has extensive applications in the field of pulse power. The laser pulse adopted to trigger the PCSS exerts significant influences to its output characteristics. The parameters to characterize a laser pulse include rise time, pulsewidth, laser energy, wavelength, and so on. In this paper, a new concept of laser power is proposed and the influences that laser pulse exerts to the PCSSs output characteristics are studied. A laser diode that emits laser pulse with a dominant wavelength of 905 ns is employed to trigger a semi-insulating GaAs PCSS, which is vertical structure. Laser energy is fixed to 6.4 μJ by synchronous adjustment of both laser pulsewidth and laser power. Thus, the influences of triggering laser power to the PCSS are studied. The rise times of triggering laser pulses include 10 and 80 ns. The experiment results show that the influences that laser power exerts to the PCSS vary when the rise time of laser pulses differs.

Development of all-solid-state flash x-ray generator with photoconductive semiconductor switches.

A compact, low-jitter, and high repetitive rate all-solid-state flash x-ray generator making use of photo conductive semiconductor switches was developed recently for the diagnostic purpose of some hydrokinetical experiments. The generator consisted of twelve stages of Blumlein pulse forming networks, and an industrial cold cathode diode was used to generate intense x-ray radiations with photon energy up to 220 keV. Test experiments showed that the generator could produce >1 kA electron beam currents and x-ray pulses with ~40 ns duration under 100 Hz repetitive rates at least (limited by the triggering laser on hand), also found was that the delay time of the cathode explosive emission is crucial to the energy transfer efficiency of the whole system. In addition, factors affecting the diode impedance, how the switching synchronization and diode impedance determining the allowable operation voltage were discussed.

Effect of BCl3 in chlorine-based plasma on etching 4H-SiC for photoconductive semiconductor switch applications

Inductively coupled plasma reactive ion etching (ICP-RIE) of n-type SiC epitaxial layers grown on (0001¯) 4H-SiC semi-insulating substrates has been investigated using chlorine-based plasma. The etch rate and postetching surface morphology have been studied as functions of the plasma composition, ICP power, RIE power, and process pressure. The authors found that the surface smoothness of the epitaxial layer was increased by introducing BCl3 into Cl2/Ar plasma. An optimized process has been developed yielding etch rates of ∼220 nm/min and very smooth surfaces with root mean square roughness of ∼0.3 nm. The spatial-frequency dependence of the one dimensional power spectral density was interpreted using the surface height function h(x) including a low-frequency range, which exhibits saturation and a high-frequency range, which exhibits scaling properties. Through this etching process, the effects of subcontact doping on 4H-SiC photoconductive semiconductor switch (PCSS) performance were investigated. A PCSS was fabricated using this etching process with a 1 μm heavily doped (1.6 × 1018 cm−3 n-type) epitaxial layer beneath the device contacts and compared with a PCSS fabricated with a subcontact doped layer created through laser enhanced diffusion (∼50 nm depth, 2.0 × 1018 cm−3 n-type). The PCSS with the epitaxial layer demonstrated on average a 30% reduction in minimum on-state resistance, and eliminated cracking of the bulk material when switching currents ≤38 A.

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.

Carrier Injection in High Gain GaAs Photoconductive Semiconductor Switches

The carrier injection in high gain semi-insulating GaAs photoconductive semiconductor switches (PCSS) is studied. A great quantity of carrier generation in the insulating region of the GaAs PCSS depends upon photo-ionization and impact ionization. The impact ionization avalanche carrier generation exists in the electron avalanche domains (EAD). The EAD is closely related to the growing domains associated with carrier injection. Carriers are injected either at the contacts (Cathode and Anode) or at the tip of the current filaments which works as a “contact reaching further into the gap”. Carrier injection plays an important role for the EAD formation.

Electron Avalanche Domains in High Gain Semi-Insulating GaAs Photoconductive Semiconductor Switches

The electron avalanche domains (EAD) in high gain semi-insulating (SI) GaAs photoconductive semiconductor switches (PCSS) are analyzed. The EAD are closely related to the growing domains associated with carrier injection. The EAD formation requires high carrier density and high field impact ionization. The avalanche carrier generation in the EAD can cause and complete the localized direct transform from theN-shaped current-voltage (I-V) characteristics toS-shapedI-Vcharacteristics. Then a transition from the EAD to current filament mechanisms can occur. The EAD ideas can explain the branch and the bend of the filaments during the formation and propagation of the filaments.

Photoionization in GaAs Photoconductive Semiconductor Switches

The density distribution characteristics of non-equilibrium carrier from spontaneous emission ahead of the tip of the current filaments in high gain semi-insulating GaAs photoconductive semiconductor switches are analyzed. The results show that the ratio of volume to area of the current filament and the average carrier density in the current filaments are two key factors that affect the photoionization effects of the current filaments. The reabsorption of wavelengths λ ≤ 876 nm radiations plays a dominant role in producing the maximum carrier density. The maximum density of photo-generated carrier is approximately 1~3 orders of magnitude lower than the average density of excess carrier inside the current filaments.

Influence of different illumination profiles on the on-state resistances of silicon carbide photoconductive semiconductor switches.

Characteristics of a silicon-carbide (SiC) photoconductive switch under different illumination profiles are presented. We triggered a V-doped semi-insulated 6H-SiC switch with lateral geometry using a laser beam of 532-nm wavelength. Photoconductivity tests for different spot profiles and locations show that such switches achieve a minimum on-state resistance when the switching gap is illuminated. The differences between on-state resistances are small for various partial illuminations of the switching gap. Semiconductor modeling is used to simulate the electric field and current profiles for different partial illuminations. The simulation results show poor on-state switch performance when partially illuminated. Based on these results, a more revealing circuit model for the switch matches well with experimental results for partial illuminations.

Fabrication and properties of V-doped semi-insulating 6H-SiC photoconductive semiconductor switch

High power photoconductive semiconductor switches (PCSSs) were fabricated on V-doped semi-insulating 6H-SiC single crystal. The 6H-SiC PCSS were measured by applying a bias voltage from 1 kV to 14 kV. The triggered laser was a 355 nm pulse laser with an energy density of 150 J/mm2. The peak photocurrent shows an increasing trend with improving the applied voltage. The peak photocurrent running through the PCSS and the calculated on-state resistance are 185 A and about 22 respectively when the applied voltage reaches 14 kV, and the corresponding peak power is 2.59 MW.

A Method for Generating High-Current, Ultrashort, and Square-Wave Pulses Based on a Photoconductive Switch Operating in the Quenched High-Gain Mode

The quenched high-gain mode of semi-insulation photoconductive semiconductor switch (PCSS) is a new operating mode. It has many advantages over the traditional modes, such as ultrafast rise time (mainly determined by the laser), high power, short pulsewidth, ultrafast fall time (mainly determined by the carrier lifetime), and so on, making it possible to generate high-power ultrashort pulses. To approximate square waveforms, a method for controlling PCSS is presented in this paper. First, a physical model of PCSS is established, which depends on the electronic negative differential mobility, the high-voltage impact ionization, the characteristic of luminous current filament, and the continuity equation of current. Second, constraint equations of circuit parameters are deduced to hold the dynamic balance of the tendency of current to increase or decrease for obtaining the flat top of output pulses. Finally, the control circuits of GaAs:EL2 PCSS operating in the quenched high-gain mode are designed, the parameters of which are the solutions to the constraint equations. The experimental results demonstrate that the method can generate square-wave pulses of kiloampere amplitude and about 50-ns pulsewidth on a subohm load.

Investigation of electric field threshold of GaAs photoconductive semiconductor switch triggered by 1.6 μJ laser diode

A 3-mm-gapped GaAs photoconductive semiconductor switch is triggered by a 1.6 μJ laser diode. Effects of the rectangular spot's layout and the triggering position on the electric field threshold of nonlinear mode are investigated. As the illuminated position moves from the cathode to the anode, the effective illumination optical energy varies. In that case, when the rectangular spot is perpendicular to two electrodes the electric field threshold increases linearly. And when the rectangular spot is parallel to the electrodes, the electric field threshold exhibits an asymmetric parabola-like curve.

介质壁加速器用固态脉冲形成线设计与实验

The solid-state pulse forming lines (PFL) of CaO-TiO2-Al2O3 composite ceramic are designed and manufactured for the dielectric wall accelerator. The PFLs geometric parameters are 300 mm long, 15 mm wide, 1mm thick of ceramic dielectric and 280 mm long, 2 mm wide of silver electrode. The electrical parameters are 23.5 relative dielectric constant, about 26 characteristic impedance, 4.5 ns characteristic time, 20 kV/mm and 25 kV/mm breakdown field strength for DC and pulsed high voltage. The solid-state PFLs design gives consideration to operating requirement of photoconductive semiconductor switches (PCSS), design parameters of high gradient insulator, charged particle beams transport and accelerators structural design. Combined with the PCSS, the experimental research of solid-state Blumlein PFL is performed. The solid-state Blumlein PFL could output about 23 kV pulsed voltage on the load under about 25 kV pulsed voltage.

光导开关非线性导通时的载流子累加效应收

光导开关非线性导通时的载流子累加效应收