High-Performance Near-IR Photodiodes: A Novel Chemistry-Based Approach to Ge and Ge–Sn Devices Integrated on Silicon

Abstract

Ge/Si heterostructure diodes based on n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> Si(100)/i-Ge/p-Ge and p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> Si(100)/i-Ge/n-Ge stacks and intrinsic region thickness of ~350 and ~900 nm, respectively, were fabricated using a specially developed synthesis protocol that allows unprecedented control of film microstructure, morphology, and purity at complementary metal-oxide-semiconductor compatible conditions. From a growth and doping perspective, a main advantage of our inherently low-temperature (390°C) soft-chemistry approach is that all high-energy processing steps are circumvented. Current-voltage measurements of circular mesas (60-250 μm in diameter) show dark current densities as low as 6 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at -1 V bias, which is clearly improved over devices fabricated under low thermal budgets using traditional Ge deposition techniques. Spectral photocurrent measurements indicate external quantum efficiencies between 30 and 60% of the maximum theoretical value at zero bias, and approaching full collection efficiency at high reverse biases. The above Ge devices are compared to analogous low-temperature-grown (350°C) Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.98</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.02</sub> diodes. The latter display much higher dark currents but also higher collection efficiencies close to 70% at zero bias. Moreover, the quantum efficiency of these Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.98</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.02</sub> diodes remains strong at wavelengths longer than 1550 nm out to 1750 nm due to the reduced band gap of the alloy relative to Ge.