摘要
首次利用材料在超短脉冲激发下的瞬间高载流子密度特性研究了GaNxAs1-x/GaAs量子阱的光学特性.研究首次发现在高于量子阱的Mott迁移边(局域发光的高能端)存在一个非局域特性的新的发光峰.该峰具有与局域发光完全不同的光学性质.通过研究材料的不同温度和激发强度下的发光行为证实该新的发光峰是量子阱的本征能级发光.这一结果为目前人们在Ga(In)NAs材料体系中是否存在Ga(In)NAs合金态或者N是以杂质带的形式存在的争论提供了重要证据.在Ga(In)NAs以及InGaN等材料体系中都观察到PL发光峰随温度升高先红移,然后蓝移,再红移的所谓的“S”形变化.它的来源一直令人们疑惑不解.我们直接证明GaNxAs1-x材料中发光峰的“S”形变化是由于材料中的低能端的局域态随温度的淬灭以及相邻的局域态与非局域态之间在温度的作用下相互竞争的结果.这一结果为能量随温度的“S”形变化提供了最直接的实验证据.通过光荧光谱,时间分辨光谱研究了低N含量的GaNxAs1-x光学性质.首次发现在低N含量的GaNxAs1-x材料(N%<1%)中,在N的杂质态的高能端(低于GaAs带边)存在一个新的,其光学性质与N的杂质态完全不同的发光峰.实验证明该峰是GaNxAs1-x材料的合金态.这一结果说明在GaNxAs1-x中即便在N含量<0.1%时就已经形成了GaNxAs1-x的合金态.这个结果的重要意义在于它直接证明N在GaAs中能够形成GaNxAs1-x合金,而不是仅仅以N的杂质态存在.这为目前人们所争论的N在GaAs所起的作用,GaNxAs1-x光跃迁的来源,以及Ga(In)NAs的基本能带结构提供了直接的实验证据.最后利用选择激发在GaAs1-xSbx/GaAs量子阱中实验上第一次同时观察到空间直接(Type-I)跃迁和间接跃迁(Type-II).时间分辨荧光寿命谱进一步直接论证了GaAs1-xSbx/GaAs能带排列的Type-II特性.
Under short pulse laser excitation, it has been observed, for the first time, a new high-energy photoluminescence emission from GaNx As1-x/GaAs SQWs. This new emission has totally different optical properties compared with the localized exciton transition in GaNx As1-x, and is attributed to the recombination of delocalized excitons in QWs. At the same time, a competition process between localized and delocalized exciton emissions in GaNx As1-x/GaAs quantum wells is observed in the temperaturedependent PL spectra under the short pulse excitation. This competition process for the first time, reveals the physical origin of the temperature-induced S-shaped PL peak shift, which was often reported in the disordered alloy semiconductor system under continuous-wave excitation and puzzled people for a long time.We have also investigated a set of GaNxAs1-x, samples with small nitrogen composition（ x 〈 1% ）by PL, and time-resolved PL. After the PL dependence on temperature and excitation power and PL dynamics were measured,the new PL peak was identified as an intrinsic transition of alloy,rather than N-related bound states.This is the first observation in PL, showing that alloy state exists in GaNx As1-x materials even when N composition is smaller than 0.1%. Finally by selective excitation, both type-Ⅰ and type-Ⅱ transitions were observed simultaneously in GaAs1-x Sbx/GaAs SQWs for the first time.
出处
《中国科学院研究生院学报》
CAS
CSCD
2005年第5期645-655,共11页
Journal of the Graduate School of the Chinese Academy of Sciences
基金
supportedbythespecialfundsoftheMajorStateBasicResearchProject(G001CB3095,G20000683),theNationalNaturalScienceFoundationofChina(19974045,10274081,10334040)andtheNaturalScienceFoundationofJiangsu(BK2004403)
