The Si metal-oxide-semiconductor structure can be used for light detection, and the dark current is significantly reduced
with the oxide layer. With the photo excitation, the generated carriers can be collected by electrodes as photo current. By
incorporating Ge, the metal-oxide-semiconductor photodetectors can increase the responsivity and extend the detection
wavelength. The interband transitions in the SiGe quantum dots enhance the 820 nm infrared absorption and extend the
detection range to 1550nm. The valence band offset between Si and SiGe forms discrete quantum states in the SiGe
layers. Hence, metal-oxide-semiconductor SiGe/Si quantum dot (well) infrared photodetectors can be used to detect midand
far- infrared using the intraband transitions. The Ge-on-insulator metal-oxide-semiconductor photodetectors can
further increase the detection speed by reducing parasitic capacitance. The large work function metal (Pt) is used for the
gate electrode to reduce the dark current. Moreover, the external mechanical strain can enhance the photo current with
slight degradation of dark current.
The radiative and nonradiative recombinations involved in efficient light-emitting metal-oxide-silicon tunneling diodes have been studied. The radiative recombination coefficient in the silicon light-emitting diode was previously found by us to be one order of magnitude greater than that of the bulk silicon. However, the nonradiative Shockley-Read-Hall recombination still dominates the carrier recombination processes near the Si/SiO2 interface. In the present work, we show by using the voltage-dependent photoluminescence that the position of the Fermi level near the Si/SiO2 interface significantly influences the nonradiative recombination rates. The nonradiative recombination states are shown to capture electrons much more effectively. This study suggests that significant reduction in nonradiative recombination is essential for efficient light emission from silicon.
We report the finding of photoluminescence (PL) and electroluminescence (EL) studies at silicon bandgap energy for the indium-tin-oxide (ITO)/SiO2/Si metal-oxide-semiconductor (MOS) tunneling diodes. The characteristics of temporal EL response, temperature dependence of EL and PL intensities, and voltage-dependent PL intensity, were used to investigate the radiative recombination and nonradiative Shockley-Read-Hall (SRH) recombination near the Si-SiO2 interface. The temporal EL response indicates that the radiative recombination coefficient in the light-emitting MOS tunneling diode is about ten times larger than that of the bulk silicon. However, the nonradiative SRH recombination is still the dominant carrier recombination process. The intensity of EL was found to be lesser sensitive with temperature than that of PL, which indicates that the nonradiadiative recombination is less thermally active and less efficient for EL. The voltage-dependent PL study shows that the PL intensity increases with the bias voltage. This observation is attributed to the variations of nonradiative SRH recombination rates due to the change of Fermi level with the bias voltage. This study shows that the nonradiative recombination near the Si-SiO2 interface strongly influences the luminescent efficiency.
We report room-temperature electroluminescence at Si bandgap energy from Metal-Oxide-Semiconductor (MOS) tunneling diodes. The ultrathin gate oxide with thickness 1 to approximately 3 nm was grown by rapid thermal oxidation (RTO) to allow significant current to tunnel through. The measured EL efficiency of the MOS tunneling diodes increases with the injection current and could be in the order of 10-5, which exceeds the limitation imposed by indirect bandgap nature of Si. We also study the temperature dependence of the electroluminescence and photoluminescence. The electroluminescence is much less dependent on temperature than photoluminescence from Si. The applied external field that results in the accumulation of majority carriers at Si/SiO2 interface in the case of electroluminescence could be the reason for such difference. The involved physics such as optical phonon, interface roughness, localized carriers, and exciton radiative recombination are used to explain the electroluminescence from silicon MOS tunneling diodes.
Silicon is the most important semiconductor material for electronics industry. However, its indirect bandgap makes it hardly emit light, so its applications in optoelectronics are limited. Many efforts had been devoted to converting silicon to light-emitting materials, including porous silicon-based devices, nanocrystalline Si, and so on. In this work, we report electroluminescence on silicon with simple metal-oxide-semiconductor (MOS) structure. The thin oxide is grown by well-controlled rapid thermal oxidation. With extremely thin oxide, significant tunneling current flows through the MOS structure as the metal is properly biased. The tunneled electrons could then occupy the upper energy levels more than the thermal-equilibrium situation. Then luminescence occurs when they have radiative transition to lower energy states. For low biased voltages, the emission occurs around 1150 nm, approximately corresponding to the Si bandgap energy. For large applied voltages, the emission shifts to longer wavelengths and becomes voltage- dependent. MOS structures fabricated on both p-type and n- type silicon exhibit electroluminescence. This is significant because the fabrication of those MOS structures is compatible with CMOS electronics. Therefore, the MOS EL devices provide a particular advantage over other types of luminescence on silicon. The details of the electroluminescence and its physical reason are reported and discussed.
Semiconductor surface gratings can find applications in various areas, including optical communications, display, storage, and sensing. The diffraction effects of a surface grating can be used for the operations of various devices. Although semiconductor surface gratings can be fabricated with etching techniques, such a process requires the preparation of a mask and is usually quite complicated. Recently, because of the development of high-power laser, direct writing of surface grating with laser has become an important alternative [1 ,2]. Basically, writing grating with laser is a process of exposing the sample to laser interference fringes. The photons at the bright lines of the fringes interact with the sample material to form periodical corrugations. Because we can control the period of the interference fringe through the interferometer setup and the depth of corrugation through the laser power level, fabrication of surface grating with laser is more flexible than other techniques. In this paper, we investigate the interaction mechanisms between laser photons and semiconductor in fabricating silicon surface gratings with 266 nm laser.