The study of the structure and optical properties in quantum well and nanobelts of III-V semiconductor by using HR&EFTEM

• Main Authors: Jin-Sheng Tsai, 蔡錦盛
• Other Authors: Ji-Jung Kai
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/33817342017544509087

博士 === 國立清華大學 === 工程與系統科學系 === 93 === Recently, the III-V group semiconductors play a very important material in light emitting. These materials have great market potentials in the future. In this thesis, we study the microstructure of GaN/InGaN multiple-quantum-wells (MQWs)、GaN/AlN quantum well and GaP nano-belts using energy filter and high resolution transmission electron microscopy. Three topics in this thesis are investigated: (I) Correlation of optical properties and interfacial microstructure of InxGa1-xN/GaN MQWs; (II) Band Gap Mapping for GaN/AlN quantum well by Electron Spectroscopy Imaging (ESI) method; (III) Observation of vacancy ordering structure in GaP nanobelt. Most devices, such as Light Emitting Diode or Laser Diode, were made using quantum well as active layer. The advantages of quantum well structure are high coherent, low inject current, high quantum effect and optical gain. The first topic is the study of the correlation of optical properties and interfacial microstructure in InxGa1-xN/GaN multiple- quantum-wells (MQWs). The photoluminescence (PL) characteristics of MQWs can be correlated to a function of interfacial structures including the average alloy composition, width of well, interfacial roughness, compositional variation and piezoelectric strain in the MQWs. The correlation in InxGa1-xN/GaN MQWs was studied by PL spectrometry, and high-resolution transmission electron microscopy with nanoscaled composition analyses. Good agreement is obtained between the simulated PL spectra using structure-correlated parameters and the experimental ones measured by optical methods. Our result shows that intensity of photoluminescence is decreased as a result of increasing quantum well roughness and width after annealing, while annealing has a negligible effect on the full width at half maximum value of the PL peak. The electron energy loss spectrum (EELS) is a very useful analyzing tool, especially analyzing the composition and bonding in materials. For second topic, several techniques were developed to demonstrate the possibility to map the distribution of band gap energies for GaN/AlN quantum well structures using electron spectroscopy imaging (ESI). The phase correlation function was used to register different energy loss images among ESI series with accuracy of one pixel. The energy dispersion of ESI series was improved by a FFT interpolation method. An iterative multi-variable least square algorithm was derived to refine the fitting of the single scattering distribution (SSD) to an analytic form of the density of states (DOS) function ��(E)�f a(E-Eg)0.5. The inhomogeneity of the band energy of the quantum well can be revealed from the band energy map. A threshold filter method is applied to estimate the average value and standard deviation of the band-gap energy from barrier and well regions in the energy map. The average band-gap energy of AlN and GaN are determined to be 5.62 �b 0.35 eV and 3.87 �b 0.36 eV, respectively. The effect of delocalization on the accuracy of band energy determination is discussed. The 2�穊g accuracy of this analysis is comparable to half of the energy resolution of the ESI experiment. In recent years, the research of nano-size materials is attached importance. The properties of physics and chemical are different between bulk and nano-material. The defects play an important role for device. For third topic, III-V semiconductor GaP nano-belts were successfully synthesized with Fe2O3 catalyst on Si substrate by a simple evaporation process at high temperatures. The shape of these nano-belts is typically rectangular with width ranging from 50 to 500 nanometers and lengths can be up to several hundred micrometers. The thickness varies from 10 to 35 nm. A vacancies ordering structure were observed in GaP nano-belts. The ordering structure of vacancies were analyzed using high-resolution transmission electron microscopy, electron diffraction pattern and computer simulation. In [111] projection, the structure has a 120o super-structure, while in [211] projection it has super structure in and plane. This defected structure can be envisaged in terms of long period structure (LPS) with super-structure in (111) stacking plane.