Y. H. Peng

The evolution of electroluminescence in Ge quantum-dot diodes with the fold number

The electroluminescence of the light-emitting diodes with five-, ten and 30-fold p-type Ge quantum dots grown on n+ Si substrates is studied. The enhanced integral electroluminescence intensity and blueshift of the 30-fold one at high temperature (>200K) act contrary to those in five- and ten-fold ones. It is attributed to the emission in the higher-fold quantum dots enabled by the injected electrons diffusing the farther at the higher temperature. Transmission electron microscopy shows that the size of the Ge quantum dots and the Si component in them, both increase with increasing the fold number. Due to the strain-induced intermixing at the high-fold quantum dots, those dots hence have large band gap and result in the intensity increment and blueshift at the high temperature.

Characterization and modeling of fast traps in thermal agglomerating germanium nanocrystal metal-oxide-semiconductor capacitor

In this paper, the germanium (Ge) nanocrystals (NCs) are synthesized by using the rapid-thermal annealing and are embedded into a three-layer (SiO2∕NCs–Ge∕SiO2) capacitor structure. The samples with∕without the postmetallization annealing (PMA) treatment are investigated to compare and study the PMA affections. The charge storage characteristics of our samples are investigated with the capacitance-voltage (C‐V) hystereses. The frequency independence of hysteresis windows is found and attributed to NCs as slow traps with a large characteristic time constant. The frequency-dependent C‐V and conductance-voltage (G‐V) experiments are further introduced to study the interface traps and the fast traps induced by the NC formation. In order to extract the related trap characteristics from the measured C‐V and G‐V, we propose to utilize the equivalent circuit and single-level trap model based on Shakley-Read-Hall theory. Three associated parameters including the areal trap density, trap conductance, and semiconduc...

A novel structure in Ge/Si epilayers grown at low temperature

Abstract We report the growth of Ge/Si strained layer at low temperature. A new growth mode is observed where ‘groove islands’ are formed beneath the Ge wetting layer. The new structure exhibits an Ge concentration dependent profile along the growth direction. This effect is tentatively attributed to the stress-driven intermixing of Ge/Si during the growth.

“Inverted hut” structure of Si–Ge nanocrystals studied by extended x-ray absorption fine structure method

Local structure around Ge in Si/Ge superlattices containing the “inverted hut” nanocrystals has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. In contrast to the usual nanometer-sized Ge “hut clusters” commonly grown on top of Si layers using the conventional Stranski–Krastanow self-organized growth mode, SiGe-alloy nanocrystals can be formed beneath the Ge wetting layer and grown into the Si layer in Si/Ge superlattices prepared in a low-temperature molecular beam epitaxy growth mode, and exhibit inverted hut nanocrystal structures regularly spaced along the Si/Ge interface. The EXAFS results obtained with varying Ge wetting layer thickness provide a direct evidence that intermixing of Ge and Si atoms takes place in a zone of about 1–3 monolayers on each side of the Si/Ge interface. The intermixing of constituent atoms allows a mechanism other than the usual formation of misfit dislocations to release the strain energy resulted from lattice mismatch between Si ...

Photogalvanic effects for interband transition in p-Si0.5Ge0.5∕Si multiple quantum wells

Circular photogalvanic effect (CPGE) and linear photogalvanic effect for interband transition have been observed simultaneously in Si0.5Ge0.5∕Si multiple quantum wells. The signature of the CPGE is evidenced by the change of its sign upon reversing the radiation helicity. It is found that the observed CPGE photocurrent is an order of magnitude greater than that obtained for intersubband transition. The dependences of the CPGE on the angle of incidence and the excitation intensities can be well interpreted based on its characteristics. The large signal of spin generation observed here at room temperature should be very useful for the realization of practical application of spintronics.

In-plane optical anisotropy in self-assembled Ge quantum dots induced by interfacial chemical bonds

In-plane optical anisotropy has been observed in self-assembled Ge quantum dots (QDs). It is found that the photoluminescence (PL) spectrum polarized along [110] exhibits different features compared to that corresponding to [11¯0]. Besides, the polarized PL spectrum is able to reveal a detailed fine structure much more pronounced than that in the unpolarized spectrum. It is shown that the observed optical anisotropy is a result of the inherent property of the type-II band alignment of Ge QDs embedded in Si matrix. The light emission arises from the recombination of electrons and holes across the interface, and it thus reflects the anisotropic nature of the interfacial chemical bonds.

Characteristics of Superlattice LED with a Si 0.8 Ge 0.2 or Si Capped Layer at Room Temperature

The comparison between the Si and Si0.8Ge0.2 capping layers shows that the conduction band offset of Si0.8Ge0.2 and Si can form a barrier for electrons, and that it can increase the quantity of carriers on conduction band. From the results of these experiments, the characteristics of carrier blockers formed by hetero structure can be applied in IV-IV optoelectronics devices to achieve higher optical power

Physical and Electrical Characteristics of Metal-Oxide-Semiconductor Capacitor Containing Germanium Nanocrystals

We present an extensive study about the formation of Ge nanocrystals by using two-step process deposition by a commercially UHVCVD system. We also investigate the growth duration effect on micro-Raman characterization in SiO2 matrix containing Ge-NCs. FTIR spectroscopy is employed to monitor the amount of various chemical bonds in SiO2 matrix embedded with Ge-NCs under various annealing temperatures. The C-V curves show the hysteresis indicating the charge storage. Furthermore, high temperature annealing effects are also presented and going to be discussed

Ge quantum dots sandwiched between two thick Si blocking layers to increase high detectivity

Summary from only given. Our Ge quantum dot IR photodetector (QDIP) shows a satisfactory detectivity. The responsivity is active in the 2 - 10 /spl mu/m under low biases and can be extended up to 20/spl mu/m under high biases.