Ge is an indirect bandgap semiconductor, which can be converted into a direct bandgap semiconductor by using the modification techniques. The carrier radiation recombination efficiency of modified Ge is high, which can be used in optical devices. The mobility of Ge semiconductor carriers is higher than that of Si semiconductor carriers, so Ge device can work fast and have good frequency characteristics in electronic device. In view of the application advantages of modified Ge semiconductors in both optical devices and electrical devices, it has been a potential material of monolithic optoelectronic integration. The Ge and GeSn as optoelectronic device materials have a great competitive advantage, but there is no mature Ge-based monolithic photoelectric integration. In order to realize Ge-based optical interconnection, the bandgap of luminous tube, detector and waveguide active layer material must satisfy the following sequence:Eg,waveguide Eg,luminoustube Eg,detector. Therefore, in order to achieve the same layer monolithic photoelectric integration, we must modulate the energy band structure of the active layer material of the device. Unfortunately, the literature in this area is lacking. The band structure is one of the theoretical foundations for the monolithic photoelectric integration of the modified Ge materials, but the work in this area is still inadequate. In this paper, this problem is investigated from three aspects. 1) Based on the generalized Hooke's law and the principle of deformation potential, a modified Ge bandgap type transformation model is established under different modification conditions, perfecting the theory of converting the indirect switching into direct band gap of Ge. 2) On the basis of establishing the strain tensor and deformation potential model, a modified Ge band E-k model is established, and the relevant conclusions can provide key parameters for LED and laser device simulation models. 3) Based on the theory of solid energy band, the bandgap width modulation scheme of the modified Ge under the uniaxial stress is proposed, which provides an important theoretical reference for realizing the Ge-based single-layer photoelectric integration. The results in this paper can provide an important theoretical basis for understanding the material physics of the modified Ge and designing the active layers of the light emitting devices in the Ge based optical interconnection.
A multi-wavelength bidirectional Brillouin-erbium fiber ring laser with switchable Brillouin frequency spacing (BFS) is proposed and experimentally demonstrated. In the presented Brillouin-erbium ring laser, including an optical amplifier and a highly nonlinear fiber, and without any optical isolator, due to Rayleigh scattering, stimulated Brillouin scattering, and cascaded four-wave mixing initiated successively by the Brillouin pump (BP) light, the odd- and even-order Stokes lines are generated and circulate in the opposite direction in the ring cavity. The BP light and Stokes-induced Rayleigh backscattering light also simultaneously circulate in the ring cavity. Only by adjusting BP power, the gain competition between Brillouin based Stokes and cavity modes’ oscillation can be controlled, the laser output can be conveniently switched between single BFS and odd- or even-order double BFS. In addition, under the certain BP power conditions, the proposed multi-wavelength Brillouin-erbium fiber laser also can realize switchable odd- or even-order Stokes generation and Stokes generation with single BFS, with an increasing wavelength number in turn, only by simply adjusting pump power of the erbium-doped fiber amplifier. Stability and wavelength tunability of the proposed multi-wavelength bidirectional Brillouin-erbium fiber ring laser are also investigated, respectively.
Based on the difference of thermal expansion coefficient between Si and Ge, low-intensity tensile stress can be introduced into Ge epitaxial layer on Si substrate. S-Ge/Si semiconductor (as known as low tensile strained Ge grown on Si substrate) has a higher carrier mobility when compared with unstrained-Ge or Si material, so that s-Ge/Si is appropriate for the production of high-speed circuit. At the same time, transformation from indirect bandgap semiconductor Ge into Pseudo-Direct bandgap semiconductor (which is also called PD-Ge) will be happen after s-Ge/Si is heavy doped, which makes LED produced of PD-Ge material perform a higher luminous efficiency because the radiative recombining probability of carriers in PD-Ge material is greatly improved compared with unstrained one. Taking the advantages referred of s-Ge/Si into account, s-Ge/Si has the potential to PD-Ge monolithic optoelectronic integration. Carrier mobility of the semiconductor is one of the key physical parameters during the design and simulation of PD-Ge monolithic optoelectronic integrated system. While as far as the authors are aware, carrier mobility model of s-Ge/Si is still rarely reported to date. In view of that all above, based on the E-k relation in both conduction band and valence band of s-Ge/Si material, the analytical models of physical parameters in energy band are established, and the models are verified by experiments. Then the s-Ge/Si carrier models are further established based on our band structure model, and the Monte Carlo method is used to verify our s-Ge/Si carrier mobility model. The quantificational results of our paper will help understand s-Ge/Si material physics and provide an important theoretical basis for the design of PD-Ge monolithic optoelectronic integration.
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