Ultrafast Uni-Traveling Carrier Photodiodes With GaAs0.5Sb0.5/In0.53 Ga0.47As Type-II Hybrid Absorbers for High-Power Operation at THz Frequencies

Abstract

We demonstrate a novel type of ultrafast photodiode (PD), which offers high-power performance in the THz regime. The incorporation of a type-II GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> (p)/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As (i) hybrid absorber in the InP-based uni-traveling carrier photodiode (UTC-PD) structure leads to an improvement in the responsivity, due to the narrowing of the bandgap and enhancement of the photo-absorption process at the type-II interface between the GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> and In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As absorption layers. Furthermore, the current blocking effect, which is usually one of the major factors limiting the output power of UTC-PDs, can be minimized due to the high-excess energy of the photo-generated electrons injected from the GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> layer to the InP-based collector layer. The flip-chip bonding packaged device with an active diameter of 3 μm shows a moderate responsivity (0.11 A/W) along with a record wide 3-dB optical-to-electrical bandwidth at 0.33 THz, among all those reported for long wavelength (1.3-1.55 μm) PDs. A 13-mA saturation current and a continuous wave output power as high as -3 dBm are successfully demonstrated at an operating frequency of 0.32 THz under an optical signal with a sinusoidal envelope and a ~63% modulation depth for PD excitation.