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Characterization of Structural Defects in Wide Band-Gap Compound Materials for Semiconductor and Opto-Electronic Applications.

机译：用于半导体和光电应用的宽带隙复合材料中结构缺陷的表征。

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摘要

Single crystals of binary and ternary compounds are touted to replace silicon for specialized applications in the semiconductor industry. However, the relative high density of structural defects in those crystals has hampered the performance of devices built on them. In order to enhance the performance of those devices, structurally perfect single crystals must be grown. The aim of this thesis is to investigate the interplay between crystal growth process and crystal quality as well as structural defect types and transport property. To this end, the thesis is divided into two parts.;The first part provides a general review of the theory of crystal growth (chapter I), an introduction to the materials being investigated (chapter II and III) and the characterization techniques being used (chapter IV).;• In chapter I, a brief description of the theory of crystal growth is provided with an eye towards the driving force behind crystal nucleation and growth along with the kinetic factors affecting crystal growth. The case of crystal growth of silicon carbide (SiC) by physical vapor transport (PVT) and chemical vapor deposition (CVD) is discussed. The Bridgman, travelling heater method (THM) and physical transport growth of cadmium zinc telluride (CZT) is also treated. In chapters II and III, we introduce the compound materials being investigated in this study. While a description of their crystal structure and properties is provided, the issues associated with their growth are discussed. In chapter IV, a description of the characterization techniques used in these studies is presented. These techniques are synchrotron X-ray topography (SXRT), transmission electron microscopy, transmission infrared microscopy (TIM), micro-Raman spectroscopy (muRS) and light microscopy. Extensive treatment of SXRT technique is also provided.;In the second part, the experimental results obtained in the course of these studies are presented and discussed. These results are divided into three subsections.;• The development of a new technique for the production of large and high quality silicon carbide single crystal boule is proposed. This technique herein referred to as Large Tapered Crystal (LTC) growth consists of two steps: growth of long SiC rod crystal by solvent-laser heated floating zone (Solvent-LHFZ) and lateral expansion of a seed by hot wall chemical vapor deposition (HWCVD). Solvent-LHFZ was successful as SiC rod crystals, replicating the polytype structure of the starting seed, were achieved at a growth rate varying from 4 to 100mum/hr. However, SXRT revealed the presence of an inhomogeneous strain in the grown crystal rod. This was further confirmed by SEM images, which showed the platelet-like morphology of the growth front with pockets in which iron (Fe)-rich material from the Fe solvent is trapped. It was furthermore observed that at high Fe to Si ratio (∼1.9), no growth was achieved. HWCVD enlargement was also successful as SiC boules, replicating the polytype structure of the starting seed, were achieved at growth rate of about 180mum/hr. The boules had a faceted hexagonal morphology with a strain-free surface marked by steps. Combination of SXRT, TEM and muRS revealed the presence of stacking disorder in the seed (3C, 4H and 15R-SiC) that replicated in the homoepitaxial layer. The formation of the observed stacking disorder is attributed to the low energy difference between stacking configurations on the growth surface as proposed by Takahashi and Ohtani.;• The influence of structural defect type and distribution on minority carrier lifetime in 4H-SiC epilayers was investigated. Structural defect type and distribution map was obtained using SXRT, whereas minority carrier lifetime map was obtained using muPCD. Decrease in carrier lifetime observed from muPCD map was associated with specific structural defects such as low angle grain boundaries (LAGBs), stacking faults (SFs), interfacial dislocations (IDs), half loop arrays (HLAs) as well as basal plane dislocations (BPDs) pinned at TSDs. While the effect of morphological defects was mitigated, combination of defects such as microcracks, overlapping triangular defects and BPD half loops were observed to reduce carrier lifetime. Furthermore, regions of high dislocation density were associated with low carrier lifetime.;• Finally, the effect of cadmium (Cd) overpressure on the quality of cadmium zinc telluride crystal ingots was investigated for two set of samples (set 1 and 2). Overall, high resistivity single crystals were achieved. Evaluation of the crystal quality by SXRT revealed that under certain Cd overpressures and growth conditions, the quality of the grown boule improved. Similarly, transmission infrared (IR) microscopy showed a correlation between the size/density and distribution of Te inclusions/precipitates and Cd overpressure. The size of Te inclusions was observed to decrease as a function of Cd overpressure as predicted from partial pressure data for stoichiometric melt. The best improvement in crystalline quality were observed for samples from set 1at a Cd reservoir of 785 °C and for set 2 samples for a Cd reservoir at 825 °C. This difference in Cd reservoir temperature for stoichiometric growth between set 1 and set 2 was attributed to other factors such as rate of cooling of Cd reservoir, rate of cooling of the crystal along with control of the melt interface. The summary of these results and the implication of this growth approach for producing high quality CZT single crystals are discussed.
机译：吹捧二元和三元化合物的单晶来代替硅，以用于半导体工业中的特殊应用。但是，那些晶体中相对较高的结构缺陷密度阻碍了构建在其上的器件的性能。为了增强这些器件的性能，必须生长出结构完美的单晶。本文的目的是研究晶体生长过程与晶体质量之间的相互作用，以及结构缺陷的类型和传输性能。为此，论文分为两个部分：第一部分对晶体生长理论（第一章）进行了综述，介绍了所研究的材料（第二章和第三章）以及所使用的表征技术。 （第四章）；•在第一章中，简要介绍了晶体生长理论，着眼于晶体成核和生长背后的驱动力以及影响晶体生长的动力学因素。讨论了通过物理气相传输（PVT）和化学气相沉积（CVD）进行碳化硅（SiC）晶体生长的情况。还处理了Bridgman，行进加热器法（THM）和碲化镉锌（CZT）的物理迁移生长。在第二章和第三章中，我们介绍了本研究中要研究的复合材料。虽然提供了其晶体结构和性能的描述，但讨论了与其生长相关的问题。第四章介绍了这些研究中使用的表征技术。这些技术是同步加速器X射线形貌（SXRT），透射电子显微镜，透射红外显微镜（TIM），显微拉曼光谱（muRS）和光学显微镜。第二部分介绍并讨论了在这些研究过程中获得的实验结果。这些结果分为三个小节。•提出了一种用于生产大型和高质量碳化硅单晶晶锭的新技术的开发。此技术在本文中称为大锥形晶体（LTC）生长，包括两个步骤：通过溶剂激光加热的浮区（Solvent-LHFZ）生长长SiC棒状晶体，以及通过热壁化学气相沉积（HWCVD）进行种子的横向膨胀）。溶剂-LHFZ是成功的，因为SiC棒状晶体以4至100mum / hr的生长速率复制了起始种子的多型结构。但是，SXRT显示在生长的晶体棒中存在不均匀的应变。 SEM图像进一步证实了这一点，该图像显示了带有囊袋的生长前沿的片状形态，在囊袋中捕获了来自Fe溶剂的富含铁（Fe）的材料。此外观察到，在高的铁硅比（〜1.9）下，没有获得生长。 HWCVD的扩大也很成功，因为SiC圆棒以约180mum / hr的生长速度复制了起始种子的多型结构。圆饼具有多面六边形的形态，无应变的表面标有台阶。 SXRT，TEM和muRS的组合揭示了在同质外延层中复制的种子（3C，4H和15R-SiC）中存在堆垛无序现象。 Takahashi和Ohtani提出，观察到的堆垛层错的形成是由于生长表面上的堆垛构型之间的能量差低。•研究了结构缺陷类型和分布对4H-SiC外延层中少数载流子寿命的影响。使用SXRT获得结构缺陷类型和分布图，而使用muPCD获得少数载流子寿命图。从muPCD图观察到的载流子寿命的减少与特定的结构缺陷有关，例如低角度晶界（LAGB），堆垛层错（SF），界面位错（ID），半环阵列（HLA）以及基底平面位错（BPD） ）固定在TSD上。虽然减轻了形态缺陷的影响，但观察到诸如微裂纹，重叠的三角形缺陷和BPD半环之类的缺陷组合会缩短载流子寿命。此外，高位错密度区域与低载流子寿命有关。•最后，对两组样品（第1组和第2组）研究了镉（Cd）超压对碲化镉锌锌晶锭质量的影响。总体而言，获得了高电阻率的单晶。通过SXRT对晶体质量的评估表明，在某些Cd超压和生长条件下，生长的晶锭的质量得到了改善。相似地，透射红外（IR）显微镜显示Te夹杂物/沉淀物的大小/密度和分布与Cd超压之间的相关性。如从化学计量的熔体的分压数据所预测的，观察到Te夹杂物的尺寸随着Cd超压的减小而减小。对于一组1的样品，在785°C的Cd储层中观察到晶体质量的最佳改善，对于一组2的Cd储藏在825°C的样品，其结晶质量得到最好的改善。组1和组2之间化学计量生长的Cd储层温度的差异归因于其他因素，例如Cd储层的冷却速率，晶体的冷却速率以及熔体界面的控制。讨论了这些结果的总结以及这种生长方法对生产高质量CZT单晶的意义。

著录项

  • 作者

    Goue, Ouloide Yannick.;

  • 作者单位

    State University of New York at Stony Brook.;

  • 授予单位 State University of New York at Stony Brook.;
  • 学科 Materials science.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 187 p.
  • 总页数 187
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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