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Modeling and Simulation of a High Power Photoconductive Semiconductor Switch (PCSS)

Hemmat, Zahra | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46222 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Faez, Rahim
  7. Abstract:
  8. There are a wide variety of light-triggered switches. Photoconductive semiconductor switches (PCSSs) have been investigated intensively for many applications owing to their unique advantages over other switches. The advantages of PCSSs make them a perfect choice for many important applications where high switching accuracy and high-power capability are required. Photoconductive switches are fabricated from a variety of semiconductors, including silicon carbide (SiC), gallium arsenide (GaAs) and gallium nitride (GaN). In Photoconductive semiconductor switches (PCSSs) the switching mechanism is initiated by optical illumination and laser source controls the flow of current. In the off or blocking state, the device behaves similar to an insulator, with low current leakage at high blocking voltages. In the on or conducting state, the bulk semiconductor absorbs light of a suitable wavelength and the conductivity of the device is dramatically increased. Wide Band-gap, high critical field strength and high-saturated electron velocity are the characteristics of 4H-SiC and GaN. These material properties make semi insulating 4H-SiC and GaN attractive semiconductor materials for the photoconductive semiconductor switch (PCSS) application.
    By means of three-dimensional device simulator, the 4H-SiC PCSS device is designed in a newly proposed rear-illuminated, radial switch structure. In this modeling with SILVACO Atlas tools defect traps are used for Semi-Insulating Compensations. In the first phase of simulation radial structure is compared with non-radial structure. Radial structure extends the blocking voltage by reducing the peak electric field near the anode. Then photocurrent profiles have been investigated. The results show that minimum switch resistance decrease with increase of laser energy and the resistance decrease with decrease of semiconductor thickness. Also increase of wavelength will increase the photon’s penetration depth that leads to increase of peak photocurrent. Simulation results of 4H-SiC are in agreement with the experimental results.
    In the second phase of simulation GaN PCSS device is designed by the same radial structure. The effect of trap energy level and density of traps on the breakdown voltage have been analyzed and the best simulation result is used for semi-insulating compensations. Also the effect of laser’s energy and wavelength, switch thickness and applied voltage on the switch resistance and photocurrent have been investigated. The changes are similar to the 4H-SiC PCSS. The material properties of semi insulating GaN and 4H-SiC PCSSs have been analyzed for breakdown, photocurrent profile such as recombination time in terms of their applications as a photoconductive switch at high bias conditions. GaN switch has higher breakdown voltage and show a better photocurrent profile compared with 4H-SiC switch. The peak photocurrent of GaN switch is higher than 4H-SiC switch and the recombination time is shorter in GaN PCSS. Afterward, simulation of a GaAs switch has been analyzed by using radial structure. However, in this case due to the GaAs lower energy gap breakdown voltage is lower than the two previous cases, but the results show a higher breakdown voltage compared with other GaAs PCSS structures.
  9. Keywords:
  10. Silicon Carbide ; High Power Laser ; Photoconductive Semiconductor Switch (PCSS) ; Semi Insulating Compensation ; Galliume Nitride Semiconductor ; Light Activated Switches

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