Study On Nanometer Structure And Iuminescence Dynamics Of Erbium-doped Thin Films Based On Silicon

Er-doped crystalline Si (c-Si) and thermally grown SiO₂/Si thin films were fabricated by metal vapor vacuum arc (MEVVA) ion source implanter. Er concentration profiles, chemical states, surface morphologies, microstructures and phases in these films have been investigated. For the first time, the formation of nanocrystalline Si (nc-Si) in Si-based thin films and Er³⁺-related photoluminescence around 1.54 μm and luminescence dynamics mechanics were also studied. Main results are as follows:1. Er concentration profiles, solubility, segregation and precipitation behaviors in Si-basedthin films were studied under various conditions of ion implantation and RTA. Erconcentration in these films is attained to the magnitude of ¹0²¹ cm^-3. Er peakconcentration in Si and SiO₂ is 9.78×10²¹ and 7.67×10²¹ cm^-3 respectively, which is thehighest values reported first time. With low ion dose (≤5×10¹⁶ Er/cm²) and weak flux (≤10 μA·cm^-2) segregation and precipitation were not found obviously in samples. Even at alow dose (5×10¹⁶ cm^-2), there was Er segregation in Er- implanted Si with strong flux (>10 μA·cm^-2). Er segregation and precipitation were formed during implantation with Erions dose (≥1×10¹⁷ cm^-2) and ion flux of 5 μA·cm^-2. Annealing processes is necessary toregrowth of substrate crystal lattice and optical activation of Er³⁺ ions as isolated ionluminescence center. The proportion of Si, SiO_x and SiO₂ varied according to theparameters of implantation and RTA. Excess Si concentration decreases with theincreasing of the thickness of SiO₂ layer, and increases with the increasing of Si dose.2. With the increasing of ion dose of Er-implanted c-Si, more Er segregates. It's surfacemorphology doesn't change until RTA at 900 ℃ for 15 s. Nc-Si nucleates at RTA of1000 ℃ , but growing rate is dominant. Nucleation becomes dominant after RTA of 1100℃, and nanometer needle structure of Si forms on the surface of Er-doped c-Si. Nc-Siembedded in SiO₂ is obtained through Si plus Er dual-implanted SiO₂ thin films. Thecrystallinity of Si nanocrystals is rather good after RTA, and the average diameter ofnanocrystal is estimated to be 4.8 nm. A large quantity of holes form when the annealingtemperature is too high. Nc-Si nucleates at defects during Si implantation with large ionflux or by the thermal peak effect. RTA of 1100 ℃ is better for Si nucleation. Ersegregation and Er silicides are observed when Er ion dose increases. Damages extendwhen Si ion dose increase, and the size of Si grows up to the magnitude of micron meter.3. Er3+-related photoluminescence spectra have been investigated at 77 K and room temperature (RT). PL quenches when ion dose of Er-doped c-Si exceeds lxlO17 cm'2, which can be efficiently avoided by decreasing ion beam current density. A better PL intensity and spectral shape can be obtained after RTA of 1000 °C for 15 s. RT PL isn't observed in Er-doped c-Si because of temperature quenching. With the increasing of the thickness of SiO2 film, PL intensity increases for Er-doped SiO2 thin films containing nc-Si. In order to achieve optimum PL intensity, the thickness of SiO2 film should be at least large than the projective range of Si and Er. The relation between annealing temperature and Er-related PL intensity is complicated, the largest PL yield can be achieved after RTA of 1100 °C for 15 s. Dependence of PL intensity on both Er and Si ion dose is similar. First PL intensity increases with the Er ion (or Si ion) dose increasing, then PL decreases after PL saturating at a certain ion dose. The threshold of Er ion dose is lxlO16 cm'2 and 5xlO16 cm'2 for 77 K and RT respectively, and The threshold of Si ion dose is 3xlO17 cm"2 and 5xlO17 cm"2 for 77 K and RT respectively. The discrepancy of the threshold at 77 K and RT demonstrates that nonradiative decay at RT differs from 77 K. Auger de-excitation is dominant at 77 K and energy back-transfer becomes prominent at RT. PL spectra at RT is obviously broader than that of 77 K due to thermal redistribution over the Stark levels. PL integrated intensity decreases by 65% -85 % upon going from 77 K to RT.4. Luminescewnce models in these two kinds of Si-based thin films have been presented according to the experimental results. Luminescence dynamics equation is also been established. Photocarriers mediated processes enable energy transferring from nc-Si (or c-Si) to the Er^ions and result in light emission of 1.54 urn in Er-doped c-Si. In Er-doped SiO2 films containing nc-Si, most of the electron-hole pairs tunnel into the SiO2 barrier, are absorbed, and then recombine radiatively in the Er ions. Only when the Er ions locates in the very close neighbor of nc-Si, such as the interface between the nc-Si and SiO2, Auger excitation process may happen. PL yields will reduce due to the Auger de-excitation and back-transfer process. The co-operative upconversion between two excited Er ions results in PL quenching when Er concentration is sufficiently high.