【作者】 胡小英；

【导师】 刘卫国；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 GaAs/AlGaAs量子阱红外探测器（Quantum Well Infrared Photodetectors，QWIP）是先进薄膜生长技术与微电子学相结合的新型红外探测器。具有材料均匀性好，生长制备工艺成熟，价格低，抗辐照性能好，及易于实现多色探测等优点。广泛用于生物医疗成像，空间资源检测，军事领域现代化高科技武器装备、地雷探测、红外制导系统、战场侦察、反坦克导弹热瞄镜等领域，已成为红外探测器的主流技术。但其较大的暗电流，较低的量子效率与过窄的频带宽成为其快速发展的瓶颈。本文以GaAs/AlGaAs QWIP单元探测器为应用背景，从相关器件结构优化设计入手，使用金属有机物化学气相沉积法（Metal Organic Chemical VaporDeposition，MOCVD）进行量子阱材料生长，设计QWIP样品性能参数自动测试系统，利用高分辨透射扫描电镜（High resolution transmissionelectron microscopy，HRTEM）对器件展开微观结构分析研究，采用室温光致荧光谱（Room TemperaturePhotoluminescence，RT-PL）对样品进行势垒与势阱PL谱测试，以对其微观能级结构进行剖析研究。旨在提高光电流，减小暗电流，建立器件微观结构与宏观表征的关系，为实现QWIP能级结构设计与材料生长工艺的优化奠定基础。论文主要研究内容，结论与成果如下：1、采用MOCVD生长30~50周期300μm×300μm台面，峰值响应波长8.5μmGaAs/Al0.3Ga0.7As量子阱样品数件，其电极压焊点面积大小与位置不同。对器件样品进行宏观光电特性测试，实验结果显示：样品暗电流，噪声，响应特性，伏安特性及探测率等呈现正负偏压的不对称性。结合样品的微观结构形貌，研究结果表明：样品界面位错穿过区域靠近AlGaAs层附近衬度区域的加宽，致使Al原子从AlGaAs层析出，导致穿透位错造成相位分离，这是引起量子阱光电性能变差的主要原因；材料生长工艺自身引起不同生长次序中GaAs与AlGaAs界面不对称性与掺杂元素的扩散，及GaAs薄膜中大量缺陷，其中包括有生长技术或掺杂带来的点缺陷及由衬底异质外延晶格失配引起的缓冲层缺陷等。这都是引起器件宏观特性曲线出现不对称的根本原因；样品器件位于台面的电极造成器件结区暗电流增加，表面及压焊点电极漏电也有一定影响。2、根据GaAs/AlGaAs QWIP的结构参数，建立了QWIP理想势阱模型。通过对QWIP样品解理后侧向剖面QW进行PL测试，结合势阱与势垒发光峰的位置，根据理想GaAs/AlGaAs势阱模型与量子阱能带理论进行数值拟合运算，获得QWIP样品的势垒组分、量子阱宽度等各项结构参数，并由此得到量子阱子带间跃迁能量，及其相应的峰值响应波长。实验结果显示：器件结构中势阱宽度偏离设计值1~2个原子层，势垒中Al组分偏离设计值1%~2%。虽然实际值相对于设计值有一定偏差，但该工作有利于防止偏离设计值的晶片流入器件制备工序，另一方面能够促使改进MOCVD生长工艺使其达到设计要求。3、建立QWIP荧光量子阱响应波长能带模型，确定QWIP峰值响应波长与势垒中Al组分关系，建立器件微观结构形貌与宏观光电特性关系。采用MOCVD制备Al摩尔含量为0.23，0.32实验样品。光谱测试结果显示：3#，4#样品峰值响应波长为8.36μm，7.58μm，与据薛定谔方程得到峰值波长9.672μm，7.928μm误差分别为15.6%，4.6%。研究结果表明：铝原子在GaAs与AlxGa1-xAs界面处扩散促使GaAs量子阱由标准方势阱变为余误差决定的形状，导致势阱降低，宽度增加，子能级分布变化，响应波长蓝移。说明光激发载流子正从束缚态到连续态向束缚态到准束缚态跃迁方式转变。HRTEM技术分析发现：位错引起GaAs与AlGaAs晶格不匹配及量子阱材料生长过程中对材料控制精度不够是造成3#样品误差过大主要原因。说明势垒中Al组分减小致使量子阱子带间距离逐渐缩小，导致峰值响应波长红移。RT-PL实验结果与理论计算相符合，说明势垒中Al组分可修饰QWIP光电特性。4、确定QWIP响应波长与GaAs势阱宽度关系。根据理想二维方势阱模型设计器件量子阱能级结构，采用MOCVD生长阱宽为4.5nm，5.5nm GaAs/Al0.3Ga0.7AsQWIP样品，利用傅里叶光谱仪对样品进行77K液氮温度光谱响应及势阱与势垒的PL测试。光谱实验结果显示：5#，6#样品峰值响应波长为8.39μm，7.69μm，与据理想二维方势阱模型获得8.924μm，8.051μm误差为6.36%，4.7%；同时响应光谱半高宽从27.3%上升至44.2%。而PL实验结果则显示：其与二维方势阱模型及薛定谔方程得到的结果一致。结合HRTEM研究样品微观结构形貌，结果说明：若加宽势阱，则光谱响应峰向高能方向漂移，及响应光谱半高宽上升。说明基态E1相对于势阱底而下降，导致子带间距增大，峰值波长蓝移，且在蓝移过程中发生半高宽增加的现象。而激发态E2逐渐从势阱口内向势阱口外移动，即光激发载流子跃迁形式从束缚态到连续态跃迁方式向束缚态到准束缚态跃迁方式的转变。5、样品HRTEM显示：Al原子从AlGaAs层析出将会引起微观领域光生电子与阱中热激发电子运动速度或方向发生变化，从而改变器件宏观光电特性；样品位错沿（100）面无法消除因插入GaAs层而导致GaAs与AlGaAs间晶格失配而起的应力应变，从而使得位错在接近量子阱区域发生微小的弯曲，进而影响器件的输出响应。更多还原

【Abstract】 The new-type GaAs/AlGaAs quantum well infrared photodetectors are combinedby the advanced film growth technology and micro-electronics. Because it has suchadvantages as even thickness, mature preparation technology, low cost, goodanti-irradiation properties, easy to implement multi-color detection and so on. Recentlyit has been main stream technology of infrared acquisition aid due to its wide use in thefollowing fields: biological and medical imaging, space resources determination, hightechnology and modern armaments in military arena, mines detection, infraredguidance-system, battlefield surveillance, thermal transmission microscopy ofanti-tank guided missiles and so on. However, its bigger dark current, lower quantumefficiency and narrower bandwidth have inhibited fast development.Optimized material growth and device microstructures are clearly needed to fullyexploit the potential of GaAs/AlGaAs QWIP based on single photon detectors. MetalOrganic Chemical Vapor Deposition (MOCVD) is used to grow the material, andautomatic testing system is designed for performance parameters of QWIP. HighResolution Transmission Electron Microscopy (HRTEM) is adopted to analyze samplemicrostructure, while Room Temperature Photoluminescence (RT-PL) is used to gainGaAs well and AlGaAs barrier PLs to study micrographic. Thus, the photocurrent canbe improved while dark current can be lower, and the relationship is establishedbetween microstructure and macro photoelectric performance, which will lay solidfoundations for energy structural design and optimized material growth of QWIP. Themain contents, conclusions and results in the dissertation are as follows:1. The30~50periods GaAs/Al0.3Ga0.7As QWIP samples with different pressurewelding area size and position, whose photosensitive surface is300μm×300μm andpeak wavelength is about8.5μm, are grown by MOCVD. Their photoelectriccharacteristics are tested and analyzed from experimental and theoretical research.The results indicated that dark current, noise, response, voltage-current characteristicand detection are asymmetry under forward and opposite voltage. Combined withmicrostructure of samples by HRTEM, the findings suggest: the thread dislocation nearAlGaAs is widened, which leads to Al atom detached from AlGaAs and causes phaseseparated. These are the fundamental reason that leads to photoelectric characteristicsworse. The asymmetry of interface between GaAs and AlGaAs caused by materialgrowth technology or doping elemental diffusion, moreover, massive defects in GaAsincluding point defects and buffer layer defects caused by crystal lattices mismatch in hetero epitaxial layers, which is fundamental reason that leads to asymmetry of devicemacro photoelectric characteristic curves. The electrode in photosensitive surface willincrease the dark current in junction, and so do surface and electrode leakage.2. The GaAs/AlGaAs QWIP desired potential well model is established accordingto structure parameters. The QWIP samples are cleavage and the peak wavelengths ofGaAs well and AlGaAs barrier PLs are gained. Thus, the structural parameters can beobtained by desired potential well model and the band theory, which includes Al content,well width, transition-energy between subbands, peak wavelength and so on. The resultsshow: the actual well width deviated from the designed one near to1~2atoms while theactual Al content deviated from the designed one near to1%~2%. The actual one hassome deviation from the designed one. But the work will help to keep chips withdeviation from preparing devices and improve MOCVD.3. The band model for peak wavelength of QWIP is built. The relationship betweenpeak wavelength of QWIP and Al content in AlGaAs and the one betweenmicrostructure and macro photoelectric characteristics are determined. Sample-deviceswith Al content0.23and0.32are grown by MOCVD. Results of spectrum test show:Peak wavelengths from test of3#and4#are8.36μm and7.58μm while the ones fromschroedinger equation are9.672μm and7.928μm, and the error between them is15.6%and4.6%respectively. Results indicates: All these display that diffusion of Al atom ininterface between GaAs and AlxGa1-xAs causes quantum-well (QW) changing fromnormal square model to the one determined by complementary error, which results inQW reduce, GaAs width increase, sub-band energy change, and peak wavelength blueshift, which illustrates optical excitation carriers are changing from bound-to-continuumto bound-to-quasi-bound model. It is found the reason leads to3#error much larger thatis crystal lattices mismatch caused by dislocation and worse control precision for thematerial by use of HRTEM. If Al content is reduced, the sub-band distance will shrinkand peak wavelength will be red shift. Results of RT-PL are compatible with theoreticalcalculations. Obviously, Al content can modify optoelectronic characteristics of QWIP.4. The relationship between peak wavelength of QWIP and well width of GaAs isestablished. GaAs/Al0.3Ga0.7As QWIPs with well width of4.5nm and5.0nm are grownby MOCVD based on two-dimensional perfect normal well model. The photoresponespectra of samples are tested by Fourier spectrometer in liquid nitrogen temperature(77K) while GaAs well and AlGaAs barrier PL ones are obtained bu RT-PL. Results ofspectral response indicate peak wavelengths from experiment of5#and6#are8.39μmand7.69μm while the ones from two-dimensional perfect normal well model are 8.924μm and8.051μm, and the error between them is6.36%and4.7%respectively. Atthe same time, full width at half maximum (FWHM) rises from27.3%to44.2%. Butresults of PL show: PL agrees with two-dimensional perfect normal well model andschroedinger equation. And micro-structure of samples is studied in detail byHRTEM. The above shows that if GaAs well is widened, peak spectral response willshift towards high energy and FWHM will go up. These make it clear that E1ofground state is falling relative to bottom of well, which leads to sub-band distance larger,peak wavelength blue shift in which FWHM is increasing. And E2of excited state ismoving from well inside to well outside, that’s optical excitation carriers are changingfrom bound-to-continuum to bound-to-quasi-bound model.5. After micro-structure of samples is studied in detail by HRTEM. The conclusioncan be obtained: Al atom detached from AlGaAs, which will lead to photoelectron andthermal excited electron in well speed and direction changed and alter macrographyphotoelectric characteristics of device. The thread dislocation along (100) can’t smooththe stress-strain caused by crystal lattice mismatch between GaAs and AlGaAs forintroducing into GaAs. And it will bend a little near the area of QW. Thus, this willaffect output response.更多还原