Carbon-Doped GaN Light Switch for Low-Resistance Photoconduction
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Solution Overview
Problem
Conventional light controlled semiconductor switches (LCSS) face challenges with high resistance and low photoresponsivity due to the use of indirect bandgap semiconductors like silicon carbide, which limits their performance in power switching and RF generation applications.
Innovation Solution
The development of a LCSS using gallium nitride (GaN) doped with carbon, which switches from a non-conductive off-state to a conductive on-state when excited by light, achieving low resistance and high photoresponsivity through the generation of free electrons in the conduction band, with specific resistances and blocking voltages optimized for power switching and RF applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If indirect bandgap semiconductor (silicon carbide) is used for LCSS, then the device can be fabricated for power switching applications, but the photoresponsivity is reduced and resistance increases
Solution Approach 1:
The patent changes the fundamental material parameter from indirect bandgap semiconductor (silicon carbide) to direct bandgap semiconductor (gallium nitride), which fundamentally alters the optical absorption characteristics and enables high photoresponsivity while maintaining low resistance through direct electron-hole pair generation in the conduction band
Solution Approach 2:
The patent uses composite material structure by doping gallium nitride with carbon to create GaN:C material system, which combines the advantages of direct bandgap for high photoresponsivity with carbon doping to control carrier concentration and minimize resistance, achieving both high reliability and low harmful factors
2Speed
If vanadium is used as extrinsic dopant in silicon carbide, then the minority carrier lifetime is reduced to less than 20 ns, but the resistance remains high due to reduced free electron carrier density
Solution Approach 1:
The patent changes the doping mechanism from transition metal doping (vanadium in SiC) which creates trap states and reduces carrier lifetime, to carbon doping in GaN which provides shallow donor levels and increases free electron carrier density, achieving both fast switching and low resistance simultaneously
Solution Approach 2:
The patent adopts a different doping strategy by copying the successful approach of carbon doping in GaN for high electron mobility transistors (HEMTs) and applying it to LCSS, where carbon provides n-type doping with shallow activation energy, maintaining high carrier density and low resistance while enabling fast switching through optical excitation
3Use of energy by moving object
If sub bandgap illumination is used in silicon carbide, then the LCSS can operate with lower energy photons, but the photoresponsivity is reduced due to indirect bandgap characteristics
Solution Approach 1:
The patent changes the bandgap type from indirect to direct, which fundamentally improves the optical absorption efficiency. This allows the use of near-bandgap or above-bandgap illumination in GaN:C, achieving both high photoresponsivity and energy efficiency, as direct bandgap materials can absorb photons with energies just above the bandgap with very high efficiency
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 GaN:C LCSS achieves low resistance in the on-state and high blocking voltage in the off-state, reducing gate driver noise and improving switching times, making it suitable for high-voltage operations without the need for high-voltage biasing of gate drivers.
Implementation Method 1
when light energy is sufficient to excite electrons into the conduction band of the LCSS semiconductor material, free electrons are generated in the semiconductor conduction band and electrical current flows through the LCSS
Implementation Method 2
a photoactive layer of gallium nitride (GaN) doped with carbon... when the light energy impinging on the semiconductor body is sufficient to excite electrons into the conduction band of the semiconductor body photoactive layer
Data Source
AI summary
A light controlled semiconductor switch (LCSS), method of making, and method of using are provided. In embodiments, a lateral LCSS includes: a semiconductor body including a photoactive layer of gallium nitride (GaN) doped with carbon; a first electrode in contact with a first surface of the semiconductor body; and a second electrode in contact with the first surface of the semiconductor body, the first and second electrodes defining an area through which light energy from at least one light source can impinge on the first surface, wherein the LCSS is configured to switch from a non-conductive off-state to a conductive on-state when the light energy impinging on the semiconductor body is sufficient to raise electrons within the photoactive layer into a conduction band of the photoactive layer.