空间有序的量子点超晶格的红外吸收

Infrared Absorption of Spatially Ordered Quantum Dot Superlattices

利用分子束外延技术,在高温下(540℃)生长了具有三维空间有序的自组织InGaAs/GaAs量子点超晶格结构,利用傅里叶变换红外光谱仪测量到了明显的垂直入射吸收峰,中心响应波长在11μm.作为对比,在低温下(480℃)生长了相同的结构,傅里叶变换红外光谱几乎没有测量到明显的垂直入射吸收峰.高分辨率X射线双晶衍射测量表明高温生长的量子点超晶格具有更好的晶体质量,原子力显微镜测量表明在高温540℃下生长的量子点具有明显的横向有序;而在低温480℃下生长的量子点并没有显示出横向有序.在进行垂直入射的吸收测量时,为了扣除量子点超晶格的周期结构带来的干涉效应,提出使用生长条件完全相同但量子点区没有掺杂的样品作为背景,提高了测量的准确性及分辨率.结果表明空间有序的量子点超晶格结构比空间无序的量子点超晶格更适宜作红外探测器结构.

A self-organized InGaAs/GaAs quantum dot superlattice structure with three dimensionally spatial ordering is grown at 540℃ by molecular beam epitaxy. A Fourier transform infrared （FTIR） spectroscopy measurement demonstrates a distinct intersubband transition absorption peak with the wavelength centered at 11μm under the normal incidence geometry. As a comparison,the FTIR measurement shows that the same structure grown at 480℃ does not have normal incidence intersubband transition absorption. High resolution X-ray diffraction measurements indicate that the quantum dot superlattice grown at high temperatures has a better crystalline quality than that grown at low temperatures. Atomic force microscopy measurements reveal that the quantum dots grown at 540℃ show clear lateral ordering,while those grown at 480℃ show a lack of lateral ordering. In order to remove the interference effect under the normal incidence geometry,the normal incidence absorption measurement is proposed,using the structure with the same growth condition but without doping the quantum dot layers. The accuracy and the resolution of the measurement under normal incidence geometry are therefore enhanced. Our results indicate that the quantum dot superlattice structure with spatial ordering is more suitable to be utilized in the infrared photodetector than the structure without spatial ordering.