Using a 820 nm-thick high-quality Ge_0.97Sn_0.03 alloy film grown on Si(001) by molecular beam epitaxy, GeSn p-i-n photodectectors have been fabricated. The detectors have relatively high responsivities, such as 0.52 A/W, 0.23 A/W, and 0.12 A/W at 1310 nm, 1540 nm, and 1640 nm, respectively, under a 1 V reverse bias. With a broad detection spectrum (800-1800 nm) covering the whole telecommunication windows and compatibility with conventional complementary metal-oxide-semiconductors (CMOS) technology, the GeSn devices are attractive for applications in both optical communications and optical interconnects.

A detailed analysis of the photoluminescence (PL) from Si nanocrystals (NCs) embedded in a silicon-rich ${\mathrm{SiO}}_2$ matrix is reported. The PL spectra consist of three Gaussian bands (peaks $A,B$, and $C$), originated from the quantum confinement effect of Si NCs, the interface state effect between a Si NC and a ${\mathrm{SiO}}_2$ matrix, and the localized state transitions of amorphous Si clusters, respectively. The size and the surface chemistry of Si NCs are two major factors affecting the transition of the dominant PL origin from the quantum confinement effect to the interface state recombination. The larger the size of Si NCs and the higher the interface state density (in particular, $\mathrm{Si}\mathrm{O}$ bonds), the more beneficial for the interface state recombination process to surpass the quantum confinement process, in good agreement with Qin’s prediction in Qin and Li [Phys. Rev. B 68, 85309 (2003)]. The realistic model of Si NCs embedded in a ${\mathrm{SiO}}_2$ matrix provides a firm theoretical support to explain the transition trend.

We reported an investigation of GeSn-based p-i-n photodetectors (PDs) with a Ge _0.92 Sn _0.08 active layer grown on n-type Si (100) substrate using molecular beam epitaxy (MBE). The GeSn photodetector achieved a wide spectrum detection whose cutoff wavelength can reach to 2.3 μm. The PDs exhibited a high performance near 2.0 μm with a responsivity of 93 mA/W and a dark current of 171 μA under a reverse bias of 1 V at room temperature. This work represented a promising technology to develop Si-based short-wave infrared (SWIR) photodetectors.

Herein, we evaluated an all-inorganic perovskite based MSM photodetector employing a bilayer composite film of mp-TiO₂ and CsPbBr₃ quantum dots as a photosensitizer.

In the current work, we fabricate an all-inorganic perovskite quantum dot-based photodetector with bifunctional linker molecules, which is highly superior to its counterpart without the linker. The ultrahigh on/off ratio of 10⁵ is two orders of magnitude higher than that of the device without the ligand treatment. Moreover, the responsivity increases from ∼2.2 A W⁻¹ to ∼24.5 A W⁻¹ and the detectivity from 3.5 × 10¹² Jones to 8.9 × 10¹³ Jones. To gain further insight into the effect of ligand-exchange by bifunctional linker molecules besides surface passivation, we divide the electron transfer process into two parts, the electron transfer from quantum dots (QDs) to the linker and from the linker to TiO₂. Injection of photoexcited electrons from colloidal CsPbBr₃ QDs into TiO₂ nanoparticles by bifunctional linker molecules is found to be much faster. Continuous-wave and time-resolved fluorescence spectra exhibit strong quenching for CsPbBr₃ QDs assembled by the linker or coupled to TiO₂ nanoparticles, which is consistent with electron transfer for QDs. From the results of the transient absorption measurement and fluorescence lifetime, the electron transfer time of QDs–TiO₂ linked by the bifunctional molecules is calculated to be within 40 ns, while that from QDs to TiO₂ particles directly is estimated to be ∼290 ns. This indicates that much faster electron injection occurs under the effect of the electron linker. In addition, the linker molecule modification can improve the adsorption of mp-TiO₂ to capture more QDs.