Abstract
The suitability of GaN PCSSs (photoconductive semiconductor switches) as high voltage switches (>50 kV) was studied using a variety of commercially available semi-insulating GaN wafers as the base material. Analysis revealed that the wafers’ physical properties were noticeably diverse, mainly depending on the producer. High Voltage PCSSs were fabricated in both vertical and lateral geometry with various contacts, ohmic (Ti/Al/Ni/Au or Ni/Au), with and without a conductive n-GaN or p-type layer grown by metal-organic chemical vapor deposition. Inductively coupled plasma (ICP) reactive ion etching (RIE) was used to form a mesa structure to reduce field enhancements allowing for a higher field to be applied before electrical breakdown. The length of the active region was also varied from a 3 mm gap spacing to a 600 µm gap spacing. The shorter gap spacing supports higher electric fields since the number of macro defects within the device’s active region is reduced. Such defects are common in hydride vapor phase epitaxy grown samples and are likely one of the chief causes for electrical breakdown at field levels below the bulk breakdown field of GaN. Finally, the switching behavior of PCSS devices was tested using a pulsed, high voltage testbed and triggered by an Nd:YAG laser. The best GaN PCSS fabricated using a 600 µm gap spacing, and a mesa structure demonstrated a breakdown field strength as high as ~260 kV/cm.
Highlights
PCSSs are a viable alternative to traditional vacuum or gas switches due to their high switching speed, reasonable lifetimes, and high electric field strength depending on the material
With proper fabrication to reduce the effect of field enhancements, Electronics 2021, 10, 1600 such SI GaN may be able to sustain the high fields necessary to operate in the lock-on such SI GaN may be able to sustain the high fields necessary to operate in the lock-on mode mode [7]
Bulk GaN PCSSs were fabricated with a variety of geometries to increase the average electric field that may be applied across the switch before electrical breakdown
Summary
PCSSs are a viable alternative to traditional vacuum or gas switches due to their high switching speed, reasonable lifetimes, and high electric field strength depending on the material. Such switches are capable of operating in two modes: (1) a linear “low-gain”. Fe, C, or Mn are used as dopants in SI-GaN to compensate for these shallow donors [4] Such SI-GaN has been proposed for a high breakdown field PCSS operating in the lock-in mode [5,6]. With proper fabrication to reduce the effect of field enhancements, Electronics 2021, 10, 1600 such SI GaN may be able to sustain the high fields necessary to operate in the lock-on such SI GaN may be able to sustain the high fields necessary to operate in the lock-on mode mode [7]
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