High-Responsivity GaN/InGaN Heterojunction Phototransistors

Abstract

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 $\lambda = 280$ nm, and the UV-to-visible-band rejection ratio is $> 8 \times 10^{3}$ . The responsivity ( $R_{\lambda }$ ) of HPT is greater than 8 A/W at $\lambda = 373$ nm, and is greater than 3 A/W at $\lambda = 280$ nm as the device is biased at $V_{\mathrm{ CE}}=10$ V. As the HPT is biased at the near breakdown voltage ( $V_{\mathrm{ CE}}> 35$ V), the responsivity performance was enhanced due to the carrier multiplication, resulting in $R_{\lambda }> 100$ A/W at $V_{\mathrm{ CE}}= 40$ V for $P_{\mathrm{ opt}}=1.73~\mu \text{W}$ /cm2 at $\lambda = 373$ 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.