Photoluminescence properties of size-controlled silicon nanocrystals at low temperatures

Abstract

This study attempts to clarify the origin of the temperature dependence of the photoluminescence ͑PL͒ spectra of silicon nanocrystals ͑Si-ncs͒ embedded in SiO 2 from 5 to 300 K. For this purpose, size-controlled Si-ncs with a narrow size distribution were fabricated, using the SiO/ SiO 2 multilayer structure. The PL intensity is strongly temperature dependent and presents a maximum at around 70 K, depending on the Si-nc size and on the excitation power. The origin of this maximum is first discussed thanks to PL dynamics study and power dependence study. The evolution of the PL energy with temperature is also discussed. In bulk semiconductors the temperature dependence of the gap is generally well represented by Varshni's law. Taking into account the quantum confinement energy, the PL energy of Si-ncs follows very well this law in the range 50-300 K. Below 50 K, a strong discrepancy to this law is observed characterized by a strong increase in the PL energy at low temperature, which is dependent on the Si-nc size distribution. This temperature dependence of the PL energy is correlated with a decrease in the radiative rate at low temperature and is explained by a preferential saturation effect of the bigger Si-ncs.

Luminescence of free-standing versus matrix-embedded oxide-passivated silicon nanocrystals: The role of matrix-induced strain

“…5(b) plots the temperature dependence of energy shift of PL maximum with regards to the lowest experimentally attainable temperatures for our measurements of FS samples along with the literature data on ME samples. 14,20 Clearly, the PL blueshift is significantly larger for FS SiNCs, of about 180 meV with respect to the ME value of 50 meV.…”

“…14 Last, the difference between ME-and FS-prepared SiNCs can be further tested using the measurements of temperature dependence of PL. Several experiments 14,20,45,46 have already reported on the temperature dependence of PL for ME samples. All of them concluded that the PL blueshift with decreasing temperature behaves very similarly to that of bulk Si, i.e., that PL blueshifts by about 50 meV when the temperature drops from 300 to 3 K, see Fig.…”

“…11,18 The etching or synthesis is then followed by slow oxidation in ambient conditions; the FS powder can also be deposited on a substrate or form a suspension/colloidal dispersion in liquid. ME oxide-capped SiNCs, on the other hand, can be prepared by the deposition of SiO x =SiO 2 superlattices 3,19,20 or Si-rich SiO 2 , 12,14,21,22 by the implantation of Si ions into SiO 2 matrix, 23 or by chemical synthesis in a polymer-based matrix. 24 After the deposition or implantation step, the samples are typically annealed (>1000 C), which results in the formation of SiNC, either as small inclusions inside an SiO 2 -based matrix or as densely packed thin films overgrown with SiO 2 .…”

Novel Photoluminescence from Porous SiGe/Si Multilayer Structure

“…3, results from the coefficient of the thermo-optic and thermal expansion and contraction effects of the cavity and the shrinkage of band gap [10,11]. As the temperature is increased from 10 K up to 300 K, the thermo-optic effect and the thermal expansion effect lead to the increase of the refractive index and the cavity length L, respectively.…”

Anomalous temperature dependence of photoluminescence in GeO x films and GeO x /SiO2 nano-heterostructures

“…exp = GeO x /SiO 2 multilayer heterostructures it is close to 0.4. The Berthelot temperature dependence can appear not only in experimental dependencies of PL intensity [11,[21][22][23][24], but also in experimental dependencies of conductivity of materials with low conductivity [20,25]. If there is possibility of electron tunneling between two point states (centers), the probability for tunneling should depend on temperature.…”