High-Responsivity GaN/InGaN Heterojunction Phototransistors

We report high-responsivity GaN/InGaN heterojunction phototransistors (HPTs) grown on sapphire substrates. Under the ultraviolet (UV) photon illumination from the front side of the wafer, an HPT shows broad photoresponse spectrum with the short-wavelength cutoff wavelength well beyond λ = 280 nm, and the UV-to-visible-band rejection ratio is >8×10<sup>3</sup>. The responsivity (R<sub>λ</sub>) of HPT is greater than 8 A/W at λ = 373 nm, and is greater than 3 A/W at λ = 280 nm as the device is biased at V<sub>CE</sub> = 10 V. As the HPT is biased at the near breakdown voltage (V<sub>CE</sub> 35 V), the responsivity performance was enhanced due to the carrier multiplication, resulting in R<sub>λ</sub> > 100 A/W at V<sub>CE</sub> = 40 V for P<sub>opt</sub> = 1.73 μW/cm<sup>2</sup> at λ = 373 nm. These results demonstrate that GaN/InGaN HPTs can achieve low light detection with a broadband photon response in the near-UV-to-deep-UV spectral ranges.

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