【作者】 李华；

【导师】 张永刚； 李爱珍；

【作者基本信息】 中国科学院研究生院（上海微系统与信息技术研究所） ， 微电子学与固体电子学， 2007， 博士

【摘要】 本学位论文围绕量子级联激光器（QCL）的材料生长、特性和气态源分子束外延（GSMBE）技术为主线展开。本文针对量子级联激光器对InP基、GaAs基异质纳米结构材料的要求，对材料的气态源分子束外延生长、质量控制和特性进行了深入的研究和分析，达到有所发现、有所创新，指导器件结构和生长工艺优化，研制出器件质量的QCL材料。主要结果如下：1、用GSMBE技术生长了高质量的与InP和GaAs晶格匹配的Ⅲ-Ⅴ族基础材料，包括InP衬底上生长InP、InGaAs、InAlAs和在GaAs衬底上生长AlGaAs等。其中三元系外延材料的X射线衍射结果表明外延层的半峰宽仅略大于衬底半峰宽，达到了共格生长。由于作为QCL有源区阱层材料的InGaAs的质量对QCL的性能影响显著，研究了不同生长温度对InGaAs材料的结晶质量、电学和光学特性的影响，以及生长温度对InP材料的表面缺陷密度和电学性能的影响，获得了生长InP和QCL材料的优化条件。2、用X射线衍射方法研究了InP基InGaAs、InAlAs双轴应变体系。定量计算了材料的临界厚度与组分的关系。在X射线对称衍射的基础上，加入了非对称衍射方法，精确标定了应变材料的弛豫比例。发现随着InAs摩尔组分的变化，In_xGa_1-xAs、In_xAl_1-xAs两种材料外延层从完全应变到完全弛豫的组分区间比较小，x的变化范围都在0.1以内。所生长的压应变In_xGa_1-xAs（x＞0.53）材料的部分应变区间要大于张应变的In_xAl_1-xAs（x＜0.52）材料的部分应变区间。3、研究了InP基InGaAs、InAlAs和GaAs基A1GaAs材料的组分对Si掺杂行为的影响，发现InGaAs材料的掺杂浓度不受组分的影响，而后两种材料都有类似“V”形的掺杂谷，并且InAlAs材料还存在两个Si掺杂隙。揭示了两种含Al材料的掺杂谷都发生在直接-间接能带的转换点附近，表明能带转换对掺杂浓度有非常显著的影响，从能带理论和Hall测试两方面都做出了定性的解释。对InAlAs材料的变温霍尔研究表明，在掺杂谷附近它的施主离化能增加得很快，这也从实验上证实了能带类型转换点附近施主能级的异常变化。4、研究了2英寸InP基晶格匹配的InGaAs和InAlAs材料的组分均匀性，分析了生长条件和生长方法对均匀性的影响，获得了组分波动小于±0.1％的InGaAs、InAlAs材料，为QCL和其它器件结构的生长提供了大面积均匀性的保证。研究了GSMBE单原子层控制方法，设计了精确标定材料生长速率的实验，并分别应用于晶格匹配和应变补偿材料体系，所生长的QCL有源区结构实际厚度与设计厚度误差小于2％，表明这种标定方法非常可靠。5、研究了外延材料表面缺陷的起因和降低缺陷密度的途经。采用特殊温区结构的Ga和In束源炉以及科学地调控升降温过程，可使外延材料表面缺陷密度从10³／cm²降至10／cm²，为研制高质量激光器打下优良的材料品质基础。6、用GSMBE技术生长了一系列F-P腔和DFB量子级联激光器材料，研究了不同的注入区掺杂浓度及二元或三元系波导包覆层对QCL器件性能的影响。在亚洲首先研制出5～10gm范围内多模F-P腔QCL，实现了低温连续和室温脉冲激射。器件测试结果表明降低注入区的掺杂浓度有利于降低阈值电流密度，并且InP的波导包覆层比InAlAs有更好的散热性能。所生长的QCL结构在亚洲首先研制出7.4、7.6、7.7、8.4μm单模DVB-QCL，低温和室温阈值电流最低分别达到了574A／cm²（70K）和970A／cm²，最高连续工作温度达到了135K，并被成功地应用于探测N₂O气体。本论文对GSMBE技术、InP基和GaAs基基础材料以及QCL器件结构材料的生长优化和特性研究，为量子级联激光器材料与器件的研制提供了支持和可靠依据，并为后续的MBE方面的工作提供了有参考价值的信息。更多还原

【Abstract】 This dissertation mainly focused on the gas source molecular beam epitaxy （GSMBE） technology and the optimization growth of quantum cascade laser （QCL） materials. The growth conditions and properties of III-V group fundamental materials were also investigated as the high material quality required in QCL fabrication. The main results achieved in this work could be summarized as follows:1. High quality III-V group materials lattice-matched with InP and GaAs were grown by GSMBE, including InP, InGaAs, InAlAs on InP, and AlGaAs on GaAs. The best FWHM of XRD of the three kinds of ternaries is only wider than that of the substrates, indicating coherent growth and high single crystal qualities. Since the performance of QCLs is influenced remarkably by the quality of the InGaAs layers that act as quantum wells, the crystal qualities, electrical and optical properties of InGaAs were investigated with different growth temperatures. Likewise, the surface defect density and electrical properties dependent on growth temperature of InP layers were investigated. The results show that the best growth temperature for InP is 40℃lower than InGaAs, implying that the growth temperature has to be regulated during the GSMBE growth of QCL structures containing InP layers.2. The InP based In_xGa_1-xAs （x > 0.53） and In_xAl_1-xAs （x < 0.52） strained system were investigated by using XRD. The critical thickness versus material composition was evaluated. The relaxation ratio of strained layers was accurately calibrated by the integration of symmetric and asymmetric XRD. It was found that the composition intervals from the full strained layers to the full relaxed ones were quite narrow for both materials, and the span of x was less than 0.1.3. The Si incorporation behaviors in InP-based InGaAs, InAlAs and GaAs-based AlGaAs were investigated respectively for full composition ranges. The doping concentration of InGaAs layers were not affected by its composition, whereas, InAlAs and AlGaAs layers both exhibited a doping valley, locating at the direct-indirect bandgap crossover. At the both sides of InAlAs doping valley, there were other two doping gaps which showed high electrical resistance. The doping valley could be interpreted by both energy band theory and Hall effect measurement theory. The rise of donor ionization energy of Si-doped InAlAs was revealed near the doping valley by employing Hall effect measurement dependent on temperature, which gave us direct proof for the abnormal behavior of the donor energy at the crossover points.4. Composition uniformity of InGaAs and InAlAs lattice-matched layers grown on 2" InP substrates was studied. The composition fluctuation less than 0.1% was achieved for both materials, which guaranteed the uniformity for the growth of device structures. A monolayer control method was developed by using superlattice samples and XRD. This method was applied to calibrate the growth rate for both lattice-matched and strain-compensated QCL active cores. The thickness error between the real active core and the design is less than 2%.5. The origin of the surface defects of layers was studied. The defect density was reduced from 10³/cm² to 10/cm² by using the cells with special temperature zone for Ga and In, which laid an excellent material foundation for the development of high quality lasers.6. Several kinds of F-P and DFB QCL structures were grown by GSMBE, during which the device performance was investigated and compared for different injector doping concentration, as well as binary or ternary waveguide cladding. Several multi-mode F-P QCLs in the range of 5-10μm were realized for the first time in Asia. The devices could operate in CW mode at LT and pulsed mode at RT. It was shown that low threshold current density could be achieved by reducing the injector doping concentration, and the waveguide cladding of InP had better thermal properties than InAlAs. Single-mode DFB-QCLs with the wavelength of 7.4, 7.6, 7.7, 8.4μm were also fabricated for the first time in Asia. The threshold current densities at LT and RT were as low as 574A/cm² （70K） and 970A/cm² respectively. CW operation in both F-P and DFB QCLs was achieved at 135K. N₂O gas sensing has been demonstrated by using our own DFB-QCLs as light sources.更多还原