GaN p-i-n ultraviolet photodetectors grown on homogenous GaN bulk substrates

Abstract

Gallium nitride p-i-n ultraviolet (UV) photodetectors (PDs) were fabricated on homogenous bulk substrates. The PDs exhibit high performances at room temperature: 1) The dark current density is as low as 2.11 × 10−9 A/cm2 and the detection rate is as high as 4.71 × 1014 cm⋅Hz1/2⋅W−1; 2) The UV/visible rejection ratio is about 3.1 × 103 and the highest responsivity is about 0.184 A/W; 3) The peak quantum efficiency is about 65.9 % and the average value in the deep UV region is still>40 %; 4) The turn-on and turn-off switching time constants are about 1.25 μs and 2.5 μs, respectively. Nevertheless, at 400 K the peak responsivity and quantum efficiency drop to 0.137 A/W and 50.59 %, respectively. An acceptor-like state model is proposed to explain the degradation, emphasizing that: 1) As the effective generation centers, they release the electron-hole pairs to the conductance and valence band edges, enhancing the photoelectric response in the long-wavelength region; 2) As the non-radiative recombination centers, they compete with the band-edge recombination, decreasing the responsivity and quantum efficiency. Finally, the noise characteristics are briefly discussed, which suggests a dominant Brown noise at reverse biases.