High-Performance Diamond Phototransistor with Gate Controllable Gain and Speed

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Devices

Background:

• Diamond-based photodetectors offer potential for UV detection due to their wide bandgap.
• Conventional two-terminal diamond photodetectors often lack sufficient gain and responsivity.
• Solar-blind photodetectors are crucial for applications requiring UV light detection while ignoring visible light.

Purpose of the Study:

• To fabricate and characterize a novel solar-blind phototransistor utilizing hydrogen-terminated diamond.
• To investigate the performance enhancements, particularly responsivity and photocurrent, attributed to the phototransistor's internal gain.
• To demonstrate the tunability of device performance, including photocurrent generation and decay time, via gate voltage adjustments.

Main Methods:

• Fabrication of a hydrogen-terminated diamond-based phototransistor.
• Characterization of device performance under 213 nm light illumination.
• Analysis of photoresponsivity, detectivity, and decay time as a function of gate voltage (V_G) and drain voltage (V_D).

Main Results:

• The fabricated phototransistor achieved high photoresponsivity (R) of 2.16 × 10^4 A/W and detectivity (D*) of 9.63 × 10^11 jones at V_G ≈ -1.5 V and V_D ≈ -5 V.
• Satisfactory performance with R = 146.7 A/W and D* = 6.19 × 10^10 jones was observed even at an ultralow operating voltage of -0.01 V.
• Photocurrent generation was tunable from photoconductive to optical gating effects with high optical gain by adjusting V_G.
• Decay time decreased from 1512.0 to 25.5 ms as V_G increased from 1.4 to 2.4 V, demonstrating effective tuning of device response.

Conclusions:

• The hydrogen-terminated diamond phototransistor demonstrates superior performance compared to conventional diamond photodetectors.
• The internal gain mechanism in the phototransistor significantly enhances responsivity and photocurrent.
• Gate voltage provides effective control over device performance, including responsivity, dark current, photocurrent-to-dark current ratio, and decay time, enabling versatile applications.