李嗣涔臺灣大學：電機工程學研究所陳顯德Chen, Shen-DeShen-DeChen2007-11-262018-07-062007-11-262018-07-062005http://ntur.lib.ntu.edu.tw//handle/246246/53089經由原子力顯微境、掃描式與穿透式電子顯微境、光激放光頻譜的量測，砷化銦量子點的成長機制被深入的研究探討，也觀察到覆蓋在砷化銦量子點上的砷化銦鎵的相分離成長，砷化鎵成長在潤濕層上，砷化銦則被迫落在原有的量子點上，因而增加了量子點的高度，而使發光波長變長。包含了應力考量的等效量子井模型也被建立，用來計算量子點的內部能階，由其中得知絕大部分的應力來自上層的砷化鎵。以砷化鋁鎵或砷化鋁銦鎵作為阻擋層的量子點紅外線偵測器也已成功地研製並分析研究，此外，在砷化銦量子點上覆蓋一層二奈米的砷化鋁鎵更可以成功地研發出具有高效能、窄頻寬的多彩紅外線偵測器，並且找出其響應的物理機制。在這個紅外線偵測器的頻譜響應中，也觀察到負微分電導、響應隨溫度的變化以及可利用快速熱退火來調變的橫向電場模式響應的增強，它們分別以電子的谷間散射、遷移率隨溫度的變化和應變所導致的類似P軌域之第一激發態的能階分裂來解釋，快速熱退火則導致化學鍵的斷裂，因而改變應力。The growth mechanisms of the InAs QDs were investigated by using AFM, SEM, TEM and PL. Phase separation growth of InGaAs cap layer on InAs QDs was also observed. GaAs tends to fill up the valley between InAs QDs whereas InAs is forced to remain on the dots, which leads to longer emission wavelength. The effective quantum well model including strain was developed to calculate the energy levels inside the InAs QD and successfully interpreted the PL spectra. The stress mainly comes from the upper GaAs cap layer rather than the lower GaAs matrix. A QDIP with AlGaAs or InAlGaAs blocking layers was fabricated and analyzed. By introducing a 2 nm Al0.3Ga0.7As cap layer on 3 (2.2) ML InAs QDs, the high-performance narrow-bandwidth multicolor InAs/AlGaAs/GaAs QDIPs were successfully fabricated. The origins of the responses were explained. The negative differential conductance, temperature-dependent and TE-mode-enhanced responses were observed. The negative differential conductance is due to intervalley scatterings. The temperature-dependent response originates from the electronic mobility as a function of temperature. The enhanced TE-mode responses could be engineered by RTA and explained by the transition from the S-like ground state to the strain-induced splitting of P-like first excited states, and the RTA process changes the stress inside InAs QDs due to the bond breaking.Contents Chapter 1 Introduction 01 Chapter 2 Growth and Optical Properties of InAs Quantum Dots Prepared by Molecular Beam Epitaxy 4 2.1 Introduction 5 2.2 Experiments 5 2.2.1 The Growth of InAs Quantum Dots 5 2.2.2 The Measurements of PL, SEM, AFM and TEM 6 2.3 Results and Discussion 6 2.3.1 The Growth Mechanism of InAs QDs 6 2.3.2 The Effect of Stress on Vertically-aligned InAs QDs 16 2.3.3 Phase Separation Growth of InGaAs Cap Layer on InAs QDs 18 2.4 Summaries 33 Chapter 3 Study of Stress in InAs/(Al)GaAs Quantum Dots 35 3.1 Introduction 36 3.2 Experiments 37 3.2.1 The Preparation of InAs Quantum-Dot Samples 37 3.2.2 The Setup of Photoluminescence Measurements 39 3.3 Results 39 3.4 Theoretical Calculations and Discussion 41 3.5 Summaries 50 Chapter 4 Characteristics of InAs Quantum Dot Infrared Photodetectors with Blocking Layers 52 4.1 Introduction 53 4.2 QDIP with Asymmetric Blocking Layers 54 4.2.1 The Growth of Quantum Dot Infrared Photodetectors 54 4.2.2 Device Fabrication 54 4.2.3 I-V Characteristics Measurements 58 4.2.4 Relative Spectral Response Measurement 58 4.2.5 Calibration of Absolute Spectral Responsivity 61 4.2.6 Specific Detectivity 63 4.2.7 Results and Discussion 64 4.3 QDIP with Symmetric InAlGaAs Blocking Layers 72 4.3.1 Motivation 72 4.3.2 Sample Preparation 73 4.3.3 Results and Discussion 73 4.4 Summaries 83 Chapter 5 InAs/AlGaAs/GaAs Quantum Dot Infrared Photodetectors 85 5.1 Introduction 85 5.2 Experiments 87 5.2.1 The Growth of InAs/AlGaAs/GaAs QDIPs 87 5.2.2 Device Fabrication 89 5.2.3 The Measurements of Spectral Responses 90 5.3 The Multicolor InAs/AlGaAs/GaAs QDIP 92 5.3.1 Multicolor Spectrum and Extremely High Responsivity 92 5.3.2 Negative Differential Conductance 104 5.3.3 Temperature-Dependent Responses 106 5.4 The Polarization-Resolved Responsivities 114 5.4.1 3-ML InAs/AlGaAs/GaAs QDIP 114 5.4.2 2.2-ML InAs/AlGaAs/GaAs QDIP 117 5.5 Summaries 121 Chapter 6 Conclusions 124 Bibliography 129 Publication List 135 Figure Captions Fig. 2.1 The schematic device structure of the investigated samples. 7 Fig. 2.2 AFM images of (a) 1.5, (b) 2.2, (c) 3, (d) 4, (e)5 and (f) 6 ML InAs QDs. 9 Fig. 2.3 SEM images of (a) 1.5, (b) 2.2, (c) 3, (d) 4, (e)5 and (f) 6 ML InAs QDs. 10 Fig. 2.4 Cross-sectional TEM images of (a) 3 ML and (b) 5 ML InAs QDs. 14 Fig. 2.5 (a) PL spectra of different InAs coverage thicknesses, (b) PL peak energy and FWHM as a function of InAs coverage thickness. 15 Fig. 2.6 Schematics of InAs growth on GaAs. 17 Fig. 2.7 Device structures of samples A, B, C and D. 19 Fig. 2.8 PL spectra of samples A, B, C and D. 20 Fig. 2.9 Device structures of samples E, F, G and H. 22 Fig. 2.10 PL spectra of samples E, F, G and H. 23 Fig. 2.11 SEM images of (a) 3 ML InAs QDs, (b) 3 ML InAs QDs + 6 ML In0.33Ga0.67As, (c) 5 ML InAs QDs and (d) 5 ML InAs QDs+ 4 ML In0.5Ga0.5As. 25 Fig. 2.12 AFM images of (a) 3 ML InAs QDs, (b) 3 ML InAs QDs + 6 ML In0.33Ga0.67As, (c) 5 ML InAs QDs and (d) 5 ML InAs QDs+ 4 ML In0.5Ga0.5As. 26 Fig. 2.13 Schematics of AFM scanning. 28 Fig. 2.14 Illustrations of (a) 3 ML InAs QDs + 6 ML In0.33Ga0.67As growth and (b) 5 ML InAs QDs + 4 ML In0.5Ga0.5As growth. 31 Fig. 3.1 Sample structures for (a) AFM or SEM, (b) PL measurements. 38 Fig. 3.2 (a) AFM image of single QD, (b) cross-sectional view. 40 Fig. 3.3 PL spectra of samples A, B, C and D. 42 Fig. 3.4 (a) PL energy as a function of InAs bandgap, (b) PL energy as a function of well width with different strain conditions. 44 Fig. 3.5 Procedure of theoretical calculations. 48 Fig. 4.1 Device structure of the QDIP. 55 Fig. 4.2 Fabrication processes of a QDIP. 57 Fig. 4.3 Schematics of the measurement of 450 edge coupling. 59 Fig. 4.4 The setup of the response measurement. 60 Fig. 4.5 The setup of the blackbody radiation calibration for absolute responsivity. 62 Fig. 4.6 Dark current-voltage characteristics at different temperatures from 20 to 140 K, each step is 20 K. Bg represents the photocurrent measured at 20 K under 300 K background illumination. 65 Fig. 4.7 Activation energy as a function of the applied bias. 67 Fig. 4.8 Device band diagram of the asymmetric QDIP. 69 Fig. 4.9 Responsivities under (a) negative and (b) positive biases at 20 K. 70 Fig. 4.10 Peak responsivity as a function of applied voltage. 71 Fig. 4.11 Device structures of samples A, B and C. 74 Fig. 4.12 Dark I-V characteristics and the photocurrent measured from samples (a) A, (b) B and (c) C at 20 K under the illumination of 300 K background radiation. 76 Fig. 4.13 Activation energies of samples (a) A, (b) B and (c) C at different biases. 79 Fig. 4.14 Spectral responses of samples A, B and C at (a) -0.4 and (b) 0.4 V. 81 Fig. 4.15 Specific detectivities of samples A, B and C under different biases at 20 K. 82 Fig. 5.1 Device Structure of InAs/AlGaAs/GaAs QDIP. 88 Fig. 5.2 Schematics of the -edge-coupling measurement setup and the definitions of TE and TM modes. 91 Fig. 5.3 Spectral response of InAs/AlGaAs/GaAs QDIP under different biases and conventional InAs/GaAs QDIP in inset. 93 Fig. 5.4 (a) PL spectra with different laser powers, (b) the intensity ratio as a function of laser power. 94 Fig. 5.5 Schematics of AlGaAs cap layer on different-sized InAs QDs. 98 Fig. 5.6 (a) AFM image of single QD and (b) side-view along two directions. 100 Fig. 5.7 Band diagram of InAs QDs capped by 2 nm AlGaAs layer. 101 Fig. 5.8 Schematics of (a) recapture process in a conventional InAs/GaAs QDIP and (b) reflection of electron by the AlGaAs barrier in InAs/AlGaAs/GaAs QDIP. 105 Fig. 5.9 Spectral response of 2.2-ML InAs/AlGaAs/GaAs QDIP. 107 Fig. 5.10 Responsivities of the three peaks as a function of bias. 108 Fig. 5.11 Detectivities of the three peaks as a function of bias at different temperatures. 109 Fig. 5.12 Responsivities of the three peaks as a function of temperature at (a) -0.6 and (b) -1.6 volt. 110 Fig. 5.13 Temperature-dependent electronic mobility. 112 Fig. 5.14 Spectral response of 3 ML InAs/AlGaAs/GaAs QDIP measured at 20 K in terms of polarization (a) without and (b) with RTA. 115 Fig. 5.15 Spectral response of 2.2 ML InAs/AlGaAs/GaAs QDIP measured at 20 K in terms of polarization (a) without and (b) with RTA. 118 Fig. 5.16 Room temperature (~300 K) PL spectra of 2.2 ML InAs/AlGaAs/GaAs QDIPs without or with 30, 60, and 90 seconds RTA. 120 List of Tables Table 2.1 Statistical data of SEM and AFM measurements 11 Table 3.1 Parameters used in the theoretical calculations. 431984502 bytesapplication/pdfen-US量子點紅外線偵測器砷化銦quantum dotinfrared photodetectorInAsthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/53089/1/ntu-94-D89921008-1.pdf