臺灣博碩士論文加值系統

ㄧ個砷化銦量子點高度較小的量子點紅外線偵測器被發現具有不尋常的極化相關頻譜響應。由於高度較小，每一個量子點會承受較大垂直電場，此電場會讓垂直方向的電子能帶產生極大扭曲，使得在s極化光照射下，電子從基態躍遷到導電帶的機率增加，因此造成s極化光的頻譜響應變大。此外增加砷化鎵空間層厚度，可以減少量子點紅外線偵測器的暗電流，進而提高背景限制溫度。另外藉由將2.5 ML砷化銦量子點部份覆蓋砷化鎵後進行退火可以形成銦砷化鎵量子環結構。與2.5 ML砷化銦量子點比較，銦砷化鎵量子環的光激放光頻譜峰值會藍移。此現象是由於銦砷化鎵具有較大的能障及量子環高度較小所致。最後，採用銦砷化鎵量子環結構的紅外線偵測器被成功製作出來。此種量子環紅外線偵測器的特性亦被完整研究。

A quantum dot infrared photodetector (QDIP) with smaller dot height of InAs quantum dots (QDs) is found exhibiting unusual polarization dependence in spectral responses. Due to smaller dot height, every QD in this QDIP averagely shares larger vertical electric field, which creates very large band-bending on the vertical-confined electron band-diagram. Under this large band-bending, the transition probability of electrons from ground to conduction band under s-polarized light increases and this causes larger spectral response of s-polarized light. Besides, by increasing the GaAs spacer thickness, the dark current of QDIP can be reduced and thus improving background limited performance (BLIP) temperature. In addition, the InGaAs quantum rings (QRs) are formed by partially capping GaAs on 2.5 ML InAs QDs and then annealing. Compared with 2.5 ML InAs QD structure, PL peak blue-shift is observed for the QR structure. This phenomenon is attributed to a larger bandgap of the InGaAs material and a smaller QR rim height. Finally, infrared photodetectors employ InGaAs QR structure (QRIPs) are successfully fabricated, and their characteristics are completely investigated.

Contents

Chapter 1 Introduction 01
Chapter 2 The Fundamentals of Infrared Detectors and Experiments 4
2.1 Theory 4
2.1.1 Thermal Radiation 4
2.1.2 Infrared Detectors 5
2.1.3 Quantum Dot Infrared Photodetectors 8
2.2 Process Flow 11
2.2.1 Fabrication Process 11
2.2.2 H3PO4-H2O2-H2O Etching Solution 16
2.2.3 Lift-off Process 19
2.3 Measurement Systems 19
2.3.1 Current-Voltage Measurement 20
2.3.2 Introduction of FTIR 20
2.3.3 Relative Spectral Response 23
2.3.4 Absolute Responsivity 25
2.3.5 Specific Detectivity 28
Chapter 3 The Characteristics of Quantum Dot Infrared Photodetectors 30
3.1 The Effect of InAs QD Size on Polarization Dependence of QDIP 31
3.1.1 Sample Preparation 31
3.1.2 Atomic Force Microscope Measurement and Photoluminescence Measurement 31
3.1.3 Results and Discussion 37
3.2 The QDIP with Longer QD Migration Time and Thicker GaAs Spacer 44
3.2.1 Sample Preparation 44
3.2.2 Photoluminescence Measurement and Atomic Force Microscope Measurement 48
3.2.3 Results and Discussion 48
Chapter 4 The Characteristics of Quantum Ring Infrared Photodetectors 56
4.1 The Growth Mechanisms of QRs 57
4.2 The QRs Structures with Different InAs Thickness 57
4.2.1 Sample Preparation 57
4.2.2 Results and Discussion 59
4.3 The Characteristics of Quantum Ring Infrared Photodetector (QRIP) with 2.5 ML InAs QDs 62
4.3.1 Sample Preparation 62
4.3.2 Photoluminescence Measurement and Atomic Force Microscope Measurement 63
4.3.3 Results and Discussion 67
4.4 The Characteristics of QRIP with Different Growth Conditions 68
4.4.1 Sample Preparation 68
4.4.2 Photoluminescence Measurement and Atomic Force Microscope Measurement 73
4.4.3 Results and Discussion 73
Chapter 5 Conclusions 79
Bibliography 81








Figure Captions


Fig. 2.1 The Blackbody radiant existence under different temperatures. 6
Fig. 2.2 Schematic band diagrams of typeⅠand typeⅡ heterojunction device. 7
Fig. 2.3 Density of states in bulk material (3D), quantum well (2D), quantum wire (1D), and quantum dot (0D). 9
Fig. 2.4 The flow chart of device fabrication and testing. 11
Fig. 2.5 Device fabrication processes of infrared photodetector, (a) the first photoresist coating, (b) developing, (c) wet etching, (d) photoresist cleaning, (e) the second photoresist coating, (f) developing, (g) metal evaporation, (h) lift-off , and (i) 450 facet polishing 12
Fig. 2.6 Spectral response measurement of QDIP. 17
Fig. 2.7 The etching rates of different composition ratios in H3PO4-H2O2-H2O system.. 18
Fig. 2.8 The I-V measurement system. 21
Fig. 2.9 The principle of Michelson interferometer. 22
Fig. 2.10 The setup to measure relative spectral response. 24
Fig. 2.11 The setup to measure absolute spectral response. 27
Fig. 3.1 The device structure of (a) sample A and (b) sample B. 32
Fig. 3.2 The 500 nm × 500 nm AFM image of (a) sample A and (b) sample B. 34
Fig. 3.3 The 20 K PL spectrum of (a) sample A and (b) sample B. 36
Fig. 3.4 The 17 K spectral response of sample A with s / p-polarized lights at a bias of (a) 0.3 V (b) 0.4 V (c) 0.5 V (d) 0.7 V. 38
Fig. 3.5 The 17 K spectral response of sample B with s / p-polarized lights at a bias of (a) 0.3 V (b) -0.8 V (c) 1.3 V. 40
Fig. 3.6 Dark I-V characteristics and the photocurrent measured at 17 K under the illumination of 300 K background radiation of (a) sample A and (b) sample B. 43
Fig. 3.7 The relationship betweenΔEc , EF and Ea. 45
Fig. 3.8 The activation energy of (a) sample A and (b) sample B at different biases. 46
Fig. 3.9 The device structure of sample C. 47
Fig. 3.10 The 20 K PL spectrum of sample C. 49
Fig. 3.11 The 500 nm × 500 nm AFM image of sample C. 50
Fig. 3.12 The spectral response of sample C under different biases at 17 K. 52
Fig. 3.13 The transition mechanisms in sample C. 53
Fig. 3.14 (a) Dark I-V characteristics and the photocurrent measured at 17 K under the illumination of 300 K background radiation of sample C. (b) The dark I-V of samples A, B and C at 80 K. 55
Fig. 4.1 Possible scenario for the self-organized ring formation: (a) InAs dots are partly covered by a thin layer of GaAs. (b) during the annealing time, InAs diffuses away from its original location and forms a volcano-like structure on the surface (c). 58
Fig. 4.2 The schematic diagram of InGaAs QRs structure (sample D, E , F with different InAs thickness). 60
Fig. 4.3 The 500 nm × 500 nm AFM image of (a) samples D, (b) sample E and (c) sample F. 61
Fig. 4.4 The device structure of sample G. 64
Fig. 4.5 The 20 K PL spectrum of (a) InAs QD sample and (b) InGaAs QR sample. 65
Fig. 4.6 The 500 nm × 500 nm AFM image of InAs QD sample. 66
Fig. 4.7 The normalized 20 K spectral responses of sample G at 0.2 and 0.8 V, respectively. 69
Fig. 4.8 Dark I-V characteristics and the photocurrent measured at 20 K under the illumination of 300 K background radiation of sample G. 70
Fig. 4.9 The activation energy of sample G at different biases. 71
Fig. 4.10 The transition mechanisms in sample G. 72
Fig. 4.11 The device structure of sample H. 74
Fig. 4.12 (a) The 20 K PL spectrum and (b) 500 nm × 500 nm AFM image of sample H. 75
Fig. 4.13 The spectral response of sample H under different biases at 17 K. 77
Fig. 4.14 The transition mechanisms in sample H. 78










List of Tables


Table 2.1 Conditions and purposes of the cleaning solvent 14
Table 2.2 The photolithography conditions 14
Table 2.3 Evaporation condition 14
Table 3.1 Dot density, average height and average diameter of samples A and B 35
Table 3.2 The ratio of s- to p-polarization response for samples A and B at different biases 41

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