研究目的
To design and fabricate 4H-SiC UV avalanche photodiodes for single photon counting, propose a new method to determine the exact breakdown voltage, and study the influence of quenching circuit parameters on device performance.
研究成果
4H-SiC UV APDs with low dark current and high avalanche gain are successfully fabricated. A robust method for precise breakdown voltage determination is proposed, showing weak dependence on circuit parameters. The quenching resistance affects count rates, and self-quenching behavior due to the APD's series resistance is observed, indicating potential for optimized single photon detection.
研究不足
The study is limited to 4H-SiC APDs and passive quenching circuits; other materials or quenching methods are not explored. The method for breakdown voltage determination may have observational errors up to 0.1 V, and the influence of circuit parameters is only studied within specific ranges.
1：Experimental Design and Method Selection:
The study involves designing and fabricating 4H-SiC APDs with a positive beveled mesa structure and using a passive-quenching circuit to characterize single photon counting performance. A new method for determining breakdown voltage based on the initial emergence of photon count pulses is employed.
2：Sample Selection and Data Sources:
The APDs are fabricated using standard processing techniques on n-type 4H-SiC substrates with specific epitaxial layers. Data is collected from electrical and optical measurements under UV illumination from a 280 nm LED.
3：List of Experimental Equipment and Materials:
Equipment includes a dc voltage source, quenching resistor (R_L), sampling resistor (R_S), oscilloscope, digital counter, and a 280 nm LED. Materials involve 4H-SiC wafers, Ni/Ti/Al/Au and Ti/Au metal stacks for contacts, and SiO2 for passivation.
4：Experimental Procedures and Operational Workflow:
The APD is connected in series with the voltage source, R_L, and R_S. The bias voltage is ramped up to observe photon count pulses. Pulse waveforms are recorded with an oscilloscope, and count rates are measured with a digital counter. Parameters like R_L and R_S are varied to study their effects.
5：Data Analysis Methods:
Data analysis includes determining breakdown voltage from pulse emergence, measuring photon and dark count rates, and fitting I-V curves to calculate differential resistance using the equation dV/dI.
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