亚稳态Ge_xSi_(1-x)/Si单量子阱的缺陷性质

Defect Properties of Metastable Ge_xSi_(1-x)/Si Single Quantum Wells

对于处在亚稳态生长区域内阱宽为15um锗组分x=0．25、0．33、0．40的单量子阱样品，及阱宽相同x=0．45、0．53的单量子阱样品，首先通过喇曼光谱测量了样品的应变弛豫程度，发现当锗组分增加到X≥0．45时，其应变开始逐渐弛豫，然后通过测量深能组瞬态谱（DLTS），研究应变弛豫程度不同的样品中形成的缺陷性质。在X=0.25、0.33、0．40样品中均可以观察到量子阱中载流子发射产生的DLTS峰，由它求得的能带们移值与理论预计值符合。对于X=0．45、0．53样品阱中载流子发射信号已被缺陷信号淹没，表明此时样品的缺陷浓度很大。相应的缺陷情况是：对于应变未弛豫的样品（X=0．25），DLTS测得的缺陷为一点缺陷；对于应变基本未弛豫的样品（X=0．33、0．40）DLTS测得的缺陷主要为一组界面缺陷；而应变部分弛豫的样品（X=0．45、0．53），DLTS测得的缺陷与前三种样品不同，样品的缺陷可能与形成的穿透位错有关。通过电化学腐蚀，可以确定这些缺陷均位于异质界面附近。

A series of GexSi1-x/Si single quantum well samples with x = 0. 25, 0. 33, 0. 40,0. 45 and 0. 53 are grown by the molecular beam epitaxy with 15 nm well thickness, which is smaller than hc, the critical thickness of psudomophical growth,for metastable samples with x=0. 25,0. 33 and 0. 40,a little larger than hcfor sample with x=0. 53. First,the degrees of strain relaxation of samples are measured by the Raman scattering spectra. When the Ge composition x is larger than0. 45,the strain begins to relax. To detect the interfacial defects in quantum wells, aspecial operating mode in deep level transient spectroscopy (DLTS ) isemployed. For the samples with x = 0. 25, 0. 33 and 0. 40, a majority carrier peakcorresponding to the confined carrier emissions from the quantum well can be seen.The activation energies derived from the peak temperatures agree well with thepredicted valence band offsets at the GexSi1-x/Si interfaces. In addition,a single level defect located in the quantum well or near its interface is found in the sample with x=0. 25,and a series of defects located at the heterointerfaces and distributed in an energy range above the midgap exist in the samples with x=0. 33 and x= 0. 40. For samples with x = 0. 45 and 0. 53, the situations are quite different, the DLTS peak corresponding to the well emission can no longer be seen. The majority carrier peaks in samples with x= 0. 45 and 0. 53 are believcd to be caused by the threading dislocations induced by the partial relaxation of misfit strains. By the electrochemical corrosion, it is found that all' defects of samples are located near the heterointerfaces of the samples.