RESUMO
The ability to detect single photons has led to the advancement of numerous research fields1-11. Although various types of single-photon detector have been developed12, because of two main factors-that is, (1) the need for operating at cryogenic temperature13,14 and (2) the incompatibility with complementary metal-oxide-semiconductor (CMOS) fabrication processes15,16-so far, to our knowledge, only Si-based single-photon avalanche diode (SPAD)17,18 has gained mainstream success and has been used in consumer electronics. With the growing demand to shift the operation wavelength from near-infrared to short-wavelength infrared (SWIR) for better safety and performance19-21, an alternative solution is required because Si has negligible optical absorption for wavelengths beyond 1 µm. Here we report a CMOS-compatible, high-performing germanium-silicon SPAD operated at room temperature, featuring a noise-equivalent power improvement over the previous Ge-based SPADs22-28 by 2-3.5 orders of magnitude. Key parameters such as dark count rate, single-photon detection probability at 1,310 nm, timing jitter, after-pulsing characteristic time and after-pulsing probability are, respectively, measured as 19 kHz µm-2, 12%, 188 ps, ~90 ns and <1%, with a low breakdown voltage of 10.26 V and a small excess bias of 0.75 V. Three-dimensional point-cloud images are captured with direct time-of-flight technique as proof of concept. This work paves the way towards using single-photon-sensitive SWIR sensors, imagers and photonic integrated circuits in everyday life.
RESUMO
A new simple method is proposed to extract the ambipolar diffusion length for two-dimensional (2D) electronic transport in thin film structures using a scanning photoluminescence microscopy (SPLM) setup. No spatially-resolved photoluminescence detection methods are required. By measuring the excitation-position-dependent PL intensity across the edge of a semiconductor, ambipolar diffusion length can be extracted from the SPLM profile through a simple analytic fitting function. Numerical simulation was first used to verify the fitting method. Then the fitting method was applied to extract the ambipolar diffusion length from the measured SPLM profile of a GaAs thin film structure. Carrier lifetime was obtained in an accompanying time-resolved photoluminescence measurement under the same excitation condition, and thus the ambipolar diffusion coefficient can be determined simultaneously. The new fitting method provides a simple way to evaluate carrier transport properties in 2D electronic transport structures such as thin films or quantum wells.
RESUMO
We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump-probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed.
RESUMO
The optical properties of GaAs nano-wires grown on shallow-trench-patterned Si(001) substrates were investigated by cathodoluminescence. The results showed that when the trench width ranges from 80 to 100 nm, the emission efficiency of GaAs can be enhanced and is stronger than that of a homogeneously grown epilayer. The suppression of non-radiative centers is attributed to the trapping of both threading dislocations and planar defects at the trench sidewalls. This approach demonstrates the feasibility of growing nano-scaled GaAs-based optoelectronic devices on Si substrates.
