MOCVD生长InAs/GaSbII类超晶格中界面形成动力学及其对超晶格性能的影响

The InAs/GaSb type-II superlattices(SLs) have the advantages of high quantum efficiency, low dark current and high operation temperature due to their special broken-gap type-II band alignment. So far, high-quality InAs/GaSb SL materials used for IR photodetectors have mostly been grown by MBE. However, the growth of InAs/GaSb SLs with high crystalline quality and good optical properties by MOCVD remains a great challenge, especially the formation mechanism of suitable interfaces has not been clarified. This proposed research is in the area of MOCVD growth of InAs/GaSb type-II SLs. The main focus of the proposed research is the MOCVD growth mechanism, especially the formation of controllable interfaces that can compensate the tensile strain between the SLs and the substrates. A novel type interfaces and a new way for the formation of such interfaces are suggested in this proposed research. The proposed research will be started from the initial state of the growth surface and the nucleation of the epitaxial layer. Then the formation mechanism of the SL interfaces will be studied.The properties of the MOCVD grown SL materials with the novel interfaces will be determined by Raman spectroscopy, Fourier-transform infrared absorption, photoluminescence spectroscopy, high-resolution TEM and XRD characterization, and optoelectronic measurements.The effects of the interfaces and the formation methods of the interfaces on the strain compensation, material quality and optical and electronic properties of the SLs will be investigated in details. Finally, a model of MOCVD growth kinetic processes of InAs/GaSb SL materials will be developed based on above investigation to provide basic physical ideas for MOCVD growth of the new IR detecting materials.

InAs/GaSb II类超晶格特殊的能带结构使基于该材料的红外探测器具有量子效率高、暗电流小、工作温度高等潜在优势，目前高质量的材料和高性能的器件大多依托于MBE技术，与之相比，MOCVD生长InAs/GaSb II类超晶格还存在许多机理上的问题，尤其是对界面形成动力学过程及其调控机理还没有深入理解，这是目前MOCVD生长II类超晶格的瓶颈。本项目提出一种新型的界面和形成方式，从外延表面初态入手，研究成核特点以及界面的形成机理，利用拉曼、FTIR光谱、高分辨TEM、XRD以及光电测试等手段研究界面的精细结构、超晶格的应变状态、材料的质量和光电性能，从而探索MOCVD外延中界面形成的可控性，阐明界面调控与超晶格材料中应变平衡以及材料光电性能之间的内在联系，由此设计界面结构，既能适应MOCVD生长特性，又能对超晶格实现应变补偿，最终建立II类超晶格MOCVD生长总体过程的物理模型。

InAs/GaSb及InAs/InAsSb超晶格材料通过层厚的调节可实现整个红外波段的响应，作为红外探测器具有量子效率高、暗电流小、工作温度等潜在优势，目前该类材料均采用MBE生长，MOCVD生长技术在产能方面具有明显优势，本项目在此背景下，开展了MOCVD生长锑化物超晶格的研究，利用多种结构测试等手段研究材料界面的精细结构、超晶格的应变状态，确定了利用As-Sb交换形成的As0.18Sb0.82混合界面，一方面可以满足MOCVD高温生长特征，另一方面可补偿超晶格外延层与衬底之间的残余应变，得到超晶格的质量接近MBE生长的同类材料。通过变温拉曼测试，首次给出了InAs/GaSb超晶格材料LO模、GaAs-like界面模的温度系数分别为-0.01674 cm^-1/K、-0.01552 cm^-1/K，对研究该超晶格材料的温度特性具有重要意义。. 研究了MOCVD生长的InAs/InAsSb超晶格的PL强度I与激发功率P的关系，从11K到200K均满足I~P^1.1～1.2的关系，即该材料直到200K发光都以激子复合为主，有可能成为高效率的发光器件；研究了超晶格带隙与温度的关系，根据Vashni经验公式拟合得到温度系数为0.3meV/K，小于CdHgTe的0.5meV/K，也就是说InAs/InAsSb超晶格帶隙随温度的变化更慢；观察到InAs/InAsSb超晶格低温载流子局域现象，局域能为5~6meV,通过适当的退火可降至2meV以下，一定程度上消除对载流子产生局域的缺陷中心，对提高该超晶格的光学性质具有科学意义。. 制作了中红外探测器，77K黑体响应率为1.2A/W，探测率大于10^9cmHz^1/2W^-1，表明MOCVD生长的锑化物材料可以作为红外探测器的有源区，针对锑化物的特征，进一步优化工艺流程，尤其是湿法刻蚀和钝化的条件，有望提高探测器的性能。