摘要
采用低压化学气相沉积 (LPCVD)方法 ,通过纯SiH4气体的表面热分解反应 ,在SiO2 表面上自组织生长了半球状Si纳米量子点 ,在室温条件下实验研究了其光致发光 (PL)特性 ,考察了PL效率与峰值能量随Si纳米量子点尺寸的变化关系。结果指出 ,当Si纳米量子点高度hc<5nm时 ,其PL效率基本保持不变。而当hc>5nm时 ,PL效率则急剧下降。同时 ,PL峰值能量随hc 的减少而增大 ,并与 (l/hc) 2 成正比依赖关系。如当hc 从 5 5nm减小至 0 8nm时 ,其峰值能量从 1 2 8eV增加到 1 4 3eV ,出现了约 0 15eV的谱峰蓝移。我们用量子限制效应
Hemispherical Si nanoquantum dots have been formed by self assembled growth on SiO 2/ c Si substrates using low pressure chemical vapor deposition (LPCVD). The n type Si(100) wafers were used as substrates in this study.After conventinal wet chemical cleaning steps,2 3nm thick SiO 2 was grown on Si(100) at 1000℃ in 2% O 2 diluted with N 2. Si nanocrystals were self assembled on the SiO 2 surface by LPCVD of SiH 4 in the temperature range of 560～590℃.The SiH 4 pressure was 0 27×10 2 Pa and the deposition time was 1min.We have experimentally studied the changes of PL efficiency and peak energy of Si nanodots with its heights h c. The results indicate that the PL efficiency remains unchanged when heights h e of Si dots are smaller than 5nm,while it dramatiaclly decreases as h c exceeds 5nm. The PL peak energy shifts from 1.28eV to 1 43eV when h c decreases from 5 5 to 0 8nm. We present a light emission mechanism, e.g., quantum confinement effect interface light emission center radiative recombination model. The model indicates that the photoluminescence is not caused by the band to band transition, but caused by the recombination through radiative centers exsisting in the Si/SiO 2 interface region. Namely, the radiative centers might indirectly play a role for the photoluminescence. Since localized states exist in the Si/SiO 2 interface region, which originate in silicon oxygen clusters act as radiative recombination centers. When electron hole pairs are genarated by laser excitation, they are trapped by the radiative localized states through thermalization process. Since the carrier thermalization to the radiative recombination, the centers in the nanodots are considered to be very slow and less sensitive to the dot size, the radiative recombination rate of photo excited carriers is almost constant for h c<5nm despite the enhancement of carrier transfer to the radiative recombination center by the quantum confinement effect.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2002年第3期261-264,共4页
Chinese Journal of Luminescence
