Optical characterization of crystalline silicon embedded in a‐Si matrix

Abstract

The photoluminescence of pure amorphous Si films and films with embedded Si quantum dots and large nano-crystallites is correlated with XRD and AFM measurements. Several PL bands in the IR spectral range with maxima at 0.90, 0.98, 1.18 and 1.39 eV have been revealed in studied samples. The 0.90-0.98 eV PL bands are attributed to band tail luminescence in Si nano-crystallites. Concurrently, the 1.18 and 1.39 eV PL bands are assigned to radiative transitions between quantum confined levels within Si quantum dots embedded into a-Si matrix. The bright visible and infrared (IR) PL of the nc-Si embedded into SiO x matrix was investigated and several models were proposed. These models include (i) the quantum confinement PL effect in small diameter (≤5 nm) Si quantum dots [2,3], (ii) radiative recombination via Si/SiO x surface states on Si nano-crystallites or via Si-based chemical species, and (iii) oxide defects at the Si/SiO x interface and/or in the SiO 2 layer [4][5][6][7][8]. In the quantum confinement model a strong dependence of the PL peak energy versus size of Si nano-crystallites is anticipated. However, in many cases size determination of Si nanocrystallites was not provided. Moreover, different dependencies of the PL peak positions on nc-Si sizes have been observed [9,10].Another PL model suggests the importance of the suboxide related defects at the Si / SiO x interface. The visible PL bands at 1.77, 2.05 and 2.30 eV were connected with oxide related defects at the interface or in the SiO x layer [11,12]. Substitution of the SiO 2 matrix by amorphous silicon (α-Si) may confirm the origin of visible PL bands and permit the investigation of the PL bands connected with quantum confined states in the nc-Si. Another motivation for using the amorphous Si versus SiO 2 as a matrix for nano-crystals is the possibility of the electric excitation of Si nano crystallite luminescence by electron/hole injection. This process has a low efficiency in the case of dielectric materials such as SiO 2 .This paper presents the results of photoluminescence and X-ray diffraction studies of amorphous Si films with embedded Si nano-or micro-crystallites. We combined PL spectroscopy with atomic force

Photoluminescence and structure investigations of Si nano-crystals in amorphous silicon matrix

“…These elementary PL bands could be attributed to amorphous silicon and Si NCs as well as to defects in the glass substrate. The comparative investigation of PL spectra of amorphous films and glass substrates confirmed that 1.75 eV PL band originates from the defects in glass substrate [11]. PL spectra measured at 300 K for second group of films prepared at 300°C substrate temperature and different filament temperatures are shown in Fig.…”

Photoluminescence of Si nanocrystallites in different types of matrices

“…It is shown earlier [9] that the size of Si nc in amorphous Si films increased from 2.5 up to 20 nm with the increase of Fig. 4(b)) and its spectral shift correlates with the temperature shrinkage of silicon band gap as well.…”

“…The gases flowed through the 0.75 mm diameter and 13 cm long coiled tungsten filament. The variation of substrate or filament temperatures allows obtaining amorphous Si films with Si nc sizes from the range 2.5 up to 20 nm, respectively [9].…”

“…The amorphous silicon films were grown by a hot wire-CVD technique in a high vacuum deposition system with a background pressure of $10 À4 Pa. All films were deposited on Corning 50 glass substrates at 10 Pa. A mixture of silane/hydrogen [SiH 4 ]/[H 2 ] gas sources with 10/30 flow ratio was used in the deposition process on heated substrates with temperatures 200°C [9]. As a result, deposited a-Si films contained a substantial concentration of hydrogen.…”

Correlation between the photoluminescence and different types of Si nano-clusters in amorphous silicon

“…Si NCs embedded in amorphous matrix. The matrix could be the silicon oxide [1,2], or silicon nitride [3], or amorphous silicon (a-Si) [4].…”