掺Er Si/Al_2O_3多层薄膜光致发光性质的研究

Photoluminescence Properties of Er-Doped Si/Al_2O_3 Multilayer Films

用脉冲激光沉积(PLD)的方法生长了掺Er Si(2nm)/Al2O3(1.5nm)多层薄膜,后期对其进行不同温度下的快速热退火(RTA)处理。在非Er离子(Er3+)共振激发476nm激光激发下,该薄膜得到来自于Er3+的室温特征光致发光(PL)谱,波峰波长为1.54μm,说明这种掺ErSi/Al2O3多层薄膜存在间接激发发光过程,退火得到的纳米Si在其中起到感光剂作用。分析了不同的退火温度对薄膜发光强度的影响,发现退火温度700℃时薄膜发光最强,其强度是同种方法制备的掺ErAl2O3薄膜的39倍。进一步结合不同退火温度下薄膜的喇曼散射谱分析发现,700℃退火的薄膜中Si虽然仍为非晶,但其中已出现数量较多的纳米Si团簇,它们是Er3+1.54μm发光的有效感光剂,增强了Er3+发光。而当温度高于700℃后,薄膜中纳米Si团簇已逐渐结晶,出现纳米Si晶粒,同时这种纳米Si晶粒尺寸随温度升高而变大、数量变少,带来的是作为感光剂的纳米Si数量的减少,导致Er3+薄膜发光强度减弱。因此在远低于纳米Si结晶所需的温度(一般需要高于900℃)下实现了掺ErSi/Al2O3多层薄膜中Er3+1.54μm的最优发光。

Er doped Si/Al2O3 multilayer films were grown by pulsed laser deposition(PLD)and post annealed by RTA.The room temperature Er-related PL spectra were observed under excitation of the Ar+ 476 nm laser which is not Er3+ resonant pumping.This means that in the films there are indirect excitations to Er3+ luminescence and the nanosilicons produced by RTA must be sensitisers.By analyzing the PL peak intensity at 1.54 μm as a function of annealing temperature,it is found that the film annealed at 700 ℃ gets the strongest photoluminescence which is 39 times higher than that of the Er doped Al2O3 reference film produced by the same method.Furthermore,the Raman scattering spectra shows that in the film annealed at 700 ℃ the silicon is still amorphous,but therein some Si nanoclusters which are effective sentitisers to Er3+ luminescence have already appear.Then,after the films are annealed at temperatures above 700 ℃,the Si-nanoclusters crystallize increasingly well and meanwhile the sizes of Si-nanocrystals become bigger and bigger leading to the number of effective sensitisers decrease.This phenomenon causes the decline of Er3+ PL intensity.It shows that the optimal annealing temperature is 700 ℃ which is far below the annealing temperature required for Er-doped samples containing Si-nanocrystal.