High-speed photodiodes for the mid-infrared spectral region 1.2–2.4 $\mu$m based on GaSb/GaInAsSb/GaAlAsSb heterostructures with a transmission band of 2–5 GHz
Abstract:
High-speed p-i-n photodiodes for the spectral range of 1.2–2.4 $\mu$m are fabricated for the first time based on a GaAs/GaInAsSb/GaAlAsSb heterostructure with separated sensitive-(50 $\mu$m in diameter) and contact mesas, which are connected by a bridge front contact. The use of an unconventional design for the contact mesa with a Si$_3$N$_4$ insulating sublayer 0.3 $\mu$m thick under the metal contact made it possible to lower both the intrinsic photodiode capacitance and the reverse dark currents. The photodiodes have a low intrinsic capacitance of 3–5 pF at zero bias and 0.8–1.5 pF at a reverse bias of 3.0 V. The photodiode operating speed, which is determined by the time of increasing the photoresponse pulse to a level of 0.1–0.9, is 50–100 ps. The transmission band of the photodiodes reaches 2–5 GHz. The photodiodes are characterized by low reverse dark currents $I_d$ = 200–1500 nA with a reverse bias of $U$ = -(0.5–3.0) V, a high current monochromatic sensitivity of $R_i$ = 1.10–1.15 A/W, and a detectability of $D^*(\lambda_{\mathrm{max}}$, 1000, 1) = 0.9 $\times$ 10$^{11}$ W$^{-1}$ cm Hz$^{1/2}$ at wavelengths of 2.0–2.2 $\mu$m.
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