Emitting 1530 nm light on Silicon wafer is very useful because 1530nm is an important band in optical fiber communication. We explore a new way of light emission at 1530 nm. We demonstrate a simple and non-expensive process to form light-emitting layer. It can be deposited on silicon wafers. The properties of samples can be varied through controlling the composition. The emission efficiency can be further improved by introducing P2O5 and Yb2O3 nanoparticles into the solution. This emitting layer is able to show the signals only within several millimeters due to surface effect of nanoparticles, enabling the higher concentration of Er3+. The optical gain at 1530nm is measured using variable stripe length method. The gain coefficient can be as large as 18 cm-1.
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.
To extend the usage of silicon as light emitter in optoelectronics, two ways are exploited to overcome its indirect bangap obstacle. Metal-oxide-semiconductor structures with silicon dioxide (SiO2) nanoparticles as oxide layer exhibits electroluminescence with 1.5 x 10-4 external efficiency at Si bandgap energy. The enhancement in light emission is attributed to carrier concentration due to non-uniformity of oxide thickness. Another approach is to take advantage of direct bandgap materials. Chemically synthesized cadmium sulfide (CdS) nanoparticles are deposited on Si substrate and exhibits electroluminescence corresponding to different process treatment.
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.
The significance of surface states in nano-structures is studied using CdS nanoparticles. Spectral features like peak red-shift due to organic capping and influence of surface states have been observed. The pronounced enhancement of emission from surface states can be dominant with certain modiciation of CdS nanoparticles. Spectral behaviors of electroluminescence in different temperature are also studied.
The fabrication of CdS-nanoparticle light emitting diodes (LEDs) on Si and their properties at room temperature and variant temperatures are reported. Due to passivation of p- hydroxyl thiophenol group around nanoparticles, 86-meV spectral shift of free exciton transition at room temperature is observed. Controlled conditions for the preparation of CdS-nanoparticle LED such as heat treatment and/or with oxygen-rich environment are found to have significant influences on emission spectra. Radiative recombination of carriers trapped in oxygen-impurity level of 273 meV presents in samples prepared in oxygen-rich environment. Coalescence of nanoparticles into bulk form also occurs to contribute to increased magnitude of luminescence. Spectral behaviors of electroluminescence with varied temperature are studied.
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