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 >8×103. The responsivity (Rλ) 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 VCE= 10 V. As the HPT is biased at the near breakdown voltage (VCE35 V), the responsivity performance was enhanced due to the carrier multiplication, resulting in Rλ> 100 A/W at VCE= 40 V for Popt= 1.73 μW/cm2at 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.