InAsP/InAsSb超晶格红外探测材料的MOCVD生长与特性研究

Infrared photodetectors based on InAs/GaSb superlattices can cover a broad range of infrared spectrum and their high degree of flexibility in bandgap engineering have also been demonstrated. However, further improvement in their quantum efficiency and dark current density is limited by the relatively low absorbance and the short carrier lifetime associated with the material. In this proposal, the “Ga-free” superlattices based on InAsP/InAsSb ternary alloys will be investigated for its MOCVD growth and its potential use as an efficient infrared absorber. High absorbance is suggested by preliminary calculations due to its near type-I band alignment, while longer carrier lifetime is expected for the absence of Ga-related point defect. Concerns about the segregation of Sb will be addressed by microscopic study and interface treatment to achieve absorber material of high quality; their absorbance and carrier transport properties will be compared under different alloy compositions and band alignments for optimal quantum efficiency; its theoretical advantages against InAs/GaSb will be finally validated by device characterizations. The success of this project shall enrich the portfolio of MOCVD-grown Sb-based infrared materials and attain our advantages in state-of-art infrared detection technologies.

InAs/GaSb超晶格红外探测器波长可调范围大、能带工程运用灵活、均匀性好，但其量子效率和暗电流水平受制于少子寿命短、吸收系数低等材料因素。本项目提出新型的“无Ga”InAsP/InAsSb三元合金超晶格材料，其载流子寿命不受Ga相关点缺陷影响，模拟显示工作波段可覆盖短波到长波红外，带边对齐可从Ⅰ型到Ⅱ型灵活调节，是一种潜在的少子寿命长、吸收系数高、光谱可调范围大的新型红外吸收材料。本项目拟利用MOCVD外延生长InAsP/InAsSb超晶格材料，利用微观手段分析锑元素的偏析，通过界面处理抑制其不利影响，实现合金超晶格的高质量生长；结合理论计算探索高吸收系数、高载流子输运特性所需的三元合金组分与带边对齐；最终通过器件指标对比，验证InAsP/InAsSb超晶格材料的理论优势。本项目的顺利展开将推进锑化物外延技术发展，丰富高性能红外探测材料的选择，开创具有自主知识产权的红外探测材料新体系。

InAs/GaSb二类超晶格被称为第三代红外探测材料，具有波长可调范围大、能带工程运用灵活、均匀性好等特点。但目前采用分子束外延（MBE）生长的InAs/GaSb超晶格的少子寿命较短，导致超晶格红外探测器的量子效率较低和暗电流水平高。本项目提出了无“Ga”的InAsP/InAsSb应力平衡的三元合金超晶格材料作为红外探测材料，其载流子寿命不受Ga相关点缺陷影响，模拟显示工作波段可覆盖短波到长波红外，带边对齐可从Ⅰ型到Ⅱ型灵活调节，是一种潜在的少子寿命长、吸收系数高、光谱可调范围大的新型红外吸收材料。本项目采用金属有机物化学气相沉积（MOCVD）在InAs衬底上生长了InGaAs/InAsSb超晶格以及InAsP/InAsSb超晶格材料和器件。首先采用经验紧束缚近似（ETBM）计算了InGaAs/InAsSb以及InAsP/InAsSb锑化物超晶格的带宽、带阶、波函数交叠等参数，设计了应力平衡超晶格的组分和厚度；然后采用一台Aixtron 2400 G3 MOCVD设备来在2寸的InAs衬底上生长超晶格，优化了生长温度、流量、V/III比等工艺参数。对于材料的测试发现，XRD可看见清晰的卫星峰，对于InGaAs/InAsSb超晶格，衬底峰和零级峰的峰位差异小于187弧秒，而对于InAsP/InAsSb超晶格仅为61 弧秒，基本上实现了应力平衡。AFM观察到平整表面，对于InGaAs/InAsSb超晶格的表面粗糙度小于0.2nm，且随着InGaAs层中Ga组分的增加，生长模式从台阶流模式转变到二维生长模式；对于InAsP/InAsSb超晶格，表面粗糙度仅为0.4nm。77K低温PL发现InGaAs/InAsSb超晶格的发光峰位在3.6~3.7µm左右，而光谱测量显示InAsP/InAsSb超晶格的截止波长在3µm左右。最后，我们在InAs衬底上生长了2微米厚的InAsP/InAsSb超晶格光电导型器件，吸收区材料为非掺弱n型，77K下测试响应率为20A/W，-0.1V偏压暗电流为2.5A/cm^2，探测率为超过1×10^10 cm√Hz/W。这些结构初步展示了MOCVD生长的InGaAs/InAsSb超晶格和InAsP/InAsSb超晶格作为中短波红外吸收材料的可行性。