Insulated-Gate Photoconductive Switch Leakage Control
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Solution Overview
Problem
Traditional photoconductive semiconductor switches (PCSS) face issues with high dark-state leakage current and current lock-on problems due to nonlinear dark-state resistance and the need for high-voltage pulsed sources, which increase system cost and reduce portability, especially at high repetition rates.
Innovation Solution
A novel PCSS design featuring a semi-insulating substrate with specific doped layers and recesses forming a metal-insulator-semiconductor field effect transistor (MISFET) structure, which controls the space-charge region expansion and reduces leakage current, eliminating the need for high-voltage pulsed sources by ensuring the space-charge region expands into the semi-insulating substrate rather than the doped layer, thus improving dc withstand voltage and photocurrent peak.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PCSS uses semi-insulating substrate with deep-energy-level impurities to achieve high resistivity, then dark-state resistance is improved, but dark-state leakage current increases significantly with bias voltage
Solution Approach 1:
The patent changes the doping concentration parameters of the n-type and p-type layers to create optimal space-charge region characteristics. By carefully selecting doping concentrations (n-type: 10^15-10^18 cm^-3, p-type: 10^14-10^17 cm^-3) and layer thicknesses, the space-charge region expands into the semi-insulating substrate rather than the doped layers, achieving both high resistance and low leakage current
Solution Approach 2:
The patent creates a composite structure combining semi-insulating substrate with specifically doped n-type and p-type layers. This composite design allows the space-charge region to form in the semi-insulating region under reverse bias, utilizing the high resistivity of the semi-insulating material while the doped layers provide controlled electrical characteristics to minimize leakage
2Speed
If PCSS operates in high-gain mode with high bias voltage, then triggering sensitivity and rising edge speed are improved, but current lock-on occurs and device cannot turn off
Solution Approach 1:
The patent modifies the electrical parameters of the p-n junction by controlling doping concentrations and layer thicknesses. This creates a space-charge region that preferentially expands into the semi-insulating substrate under reverse bias, providing a natural voltage distribution that allows the device to exit high-gain mode and turn off properly after current conduction
Solution Approach 2:
The patent introduces the space-charge region as an intermediary mechanism between the doped layers and semi-insulating substrate. This space-charge region acts as a voltage-distributing element that mediates the electrical characteristics, enabling controlled transition from high-gain mode to off state by directing the electric field into the semi-insulating region
3Reliability
If high-voltage pulsed source is used to inhibit leakage current and force turn-off, then PCSS operation is improved, but system cost and complexity increase
Solution Approach 1:
The patent designs the PCSS to be self-regulating through its internal space-charge region characteristics. The device automatically controls leakage current and enables turn-off functionality through its inherent p-n junction physics and space-charge region behavior, eliminating the need for external high-voltage pulsed sources or complex control circuits
Solution Approach 2:
The patent extracts and eliminates the need for external high-voltage pulsed source components (such as Marx circuits) by incorporating the necessary functionality directly into the PCSS structure itself. The space-charge region design provides intrinsic leakage control and turn-off capability, removing complex external equipment and simplifying the overall system
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The novel PCSS design enhances dc withstand voltage and photocurrent pulse peak while reducing system costs and improving portability by eliminating the need for high-voltage pulsed sources, enabling high repetition rates and efficient operation.
Implementation Method 1
A photoconductive semiconductor switch (PCSS) triggered with an ultra-short pulsed laser
Implementation Method 2
whether there is avalanche multiplication of photon-generated carriers, namely, the linear operating mode and the high-gain operating mode
Data Source
AI summary
This present invention provides a novel photoconductive semiconductor switch (PCSS) comprising: a semi-insulating substrate, an anode formed on the upper surface of said semi-insulating substrate, a first n-type doped layer formed on the lower surface of said semi-insulating substrate, a p-type doped layer formed on said first n-type doped layer, a second n-type doped layer formed on said p-type doped layer, a cathode formed on said second n-type doped layer, several recesses facing towards said first n-type doped layer and vertically extending into a part of said first n-type doped layer, an insulating layer formed on said second n-type doped layer and on the walls and the bottoms of said recesses, a gate electrode consisting of two parts, one part of the which formed on said insulating layer on the walls and the bottoms of recesses, and the other part of the which formed on a part of the insulating layer on the second n-type doped layer for electrically connecting the part of the gate electrode on the recesses, wherein the cathode and the gate electrode are electrically isolated.