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Heterojunction phototransistors (HPTs) are requested to have high electrical bandwidth (∼1GHz) performance for their application of high-speed digital fiber communication. In this letter, a method is disclosed to enhance the speed performance of Si∕SiGe-based HPTs, which can overcome the low quantum efficiency drawback (∼0.1A∕W) of Si-based high-speed photodetectors at the wavelength of 850nm due to its large internal gain. By use of the substrate terminal of HPT, the speed performance can be enhanced greatly with much less reduction in optical gain as compared to the traditional technique with base-terminal-bias. Under proper optical power excitation and the common ground of substrate and emitter terminals, we can achieve 1.8GHz fast-Fourier-transformed electrical bandwidth with 0.7A∕W responsivity simultaneously. The demonstrated device structure can serve as a key component in the short-reach fiber communication system.

A simple and complementary metal-oxide-semiconductor-compatible method for fabricating germanium (Ge) single-electron transistors (SETs) is proposed, in which the Ge quantum dots (QDs) are naturally formed by selective oxidation of Si0.95Ge0.05∕Si wires on a silicon-on-insulator substrate. Clear Coulomb-blockade oscillations, Coulomb staircase, and negative differential conductances were experimentally observed at room temperature. The tunneling currents through the Ge QDs were simulated by the Anderson model with two energy levels. Analysis of the current–voltage characteristics indicates that the single-electron addition energy of the Ge QD is about 125meV.

A complementary metal-oxide-semiconductor-compatible method is proposed to form atomic-scale germanium (Ge) quantum dots (

Room-temperature electroluminescence at 1.3 and 1.5 μm from Ge/Si quantum-dot light-emitting diodes is reported. The devices were fabricated in a mesa-type structure, with a silicon oxide layer on the top for surface/sidewall passivation. Different passivation processes were employed. We found that the integrated electroluminescence intensities were relatively less sensitive to temperature, persisting at nearly the same intensity up to RT. The fabricated device shows an internal quantum efficiency of about 0.015% at RT. The improved emission property is attributed to the reduced nonradiative recombination centers due to the surface passivation and thermal treatment.