GaN UV Sensor Intrinsic Amplification PPC Compensation
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Solution Overview
Problem
Existing GaN-based UV sensors face challenges with low sensitivity due to persistent photoconductivity (PPC) effects, high leakage current, and high cost, limiting their application in low-light conditions and requiring expensive substrates.
Innovation Solution
An AlGaN/GaN UV sensor with a low-resistance GaN layer and a high-resistance GaN layer, featuring a 2DEG conductive channel, where electrical refresh and heating are used to compensate for PPC effects, allowing for high responsivity and cost-effective fabrication on silicon substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GaN-based UV sensors are used to achieve solar blind detection, then UV sensitivity is improved, but persistent photoconductivity effects cause photocurrent drifts that limit practical sensing applications
Solution Approach 1:
The patent changes the operating parameters by applying periodic reverse bias pulses to the photodiode. This parameter change temporarily reverses the polarity across the junction, causing trapped charges to be released and recombination centers to be emptied, thereby resetting the persistent photoconductivity effects and stabilizing the photocurrent for subsequent measurements
Solution Approach 2:
The patent implements periodic reverse bias pulsing at specific frequencies and durations. This periodic action continuously resets the trapped charge populations in the GaN material, preventing the accumulation of persistent photoconductivity effects during continuous UV exposure and enabling stable long-term operation
2Measurement precision
If avalanche photodiodes are used to increase sensitivity, then UV detection capability is improved, but high leakage current before avalanche breakdown limits application
Solution Approach 1:
The patent applies reverse bias voltages that partially approach but do not exceed the avalanche breakdown voltage. This partial action provides sufficient electric field enhancement to improve carrier collection efficiency and sensitivity while avoiding the excessive leakage currents and device degradation that occur at full avalanche breakdown conditions
3Measurement precision
If phototransistors are used to achieve high photo current gains, then sensitivity is improved, but persistent photoconductivity requires heating that complicates technology and increases cost
Solution Approach 1:
The patent extracts and removes the complex heating system requirement by using electrical reverse bias pulsing instead of thermal heating. This extraction eliminates the need for separate heater components, low-mass membrane support structures, and associated control systems, thereby simplifying the device architecture and reducing costs while still achieving PPC suppression
4Measurement precision
If expensive substrates like sapphire or silicon carbide are used for UV sensor fabrication, then UV transparency is improved, but device cost increases significantly
Solution Approach 1:
The patent employs inexpensive silicon substrates instead of expensive sapphire or silicon carbide substrates. Although silicon is not naturally UV transparent, the thin-film GaN photodiode structure is designed to be sufficiently thin and highly absorbing that it achieves adequate UV detection performance on cost-effective silicon substrates, making the technology economically viable
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 solution achieves extra-high responsivity and overcomes PPC limitations, enabling faster operation and cost-effective production of UV sensors, with calculated responsivity of 10^8 A/W, suitable for various UV applications without the need for separate current amplifiers.
Implementation Method 1
A two-dimensional electron gas (2DEG) conductive channel exists at an upper surface of the high-resistance GaN layer
Implementation Method 2
An electrical current between the source contact and the drain contact is a function of UV light received by the GaN stack
Implementation Method 3
The phenomenon makes DC measurements, and hence practical sensing devices, difficult due to photocurrent drifts
Data Source
AI summary
A UV sensor includes a GaN stack including a low-resistance GaN layer formed over a nucleation layer, and a high-resistance GaN layer formed over the low-resistance GaN layer, wherein a 2DEG conductive channel exists at the upper surface of the high-resistance GaN layer. An AlGaN layer is formed over the upper surface of the high-resistance GaN layer. A source contact and a drain contact extend through the AlGaN layer and contact the upper surface of the high-resistance GaN layer (and are thereby electrically coupled to the 2DEG channel). A drain depletion region extends entirely from the upper surface of the high-resistance GaN layer to the low-resistance GaN layer under the drain contact. An electrical current between the source and drain contacts is a function of UV light received by the GaN stack. An electrode is connected to the low-resistance GaN layer to allow for electrical refresh of the UV sensor.