A study on the characteristics of silicon implanted with unfiltered plasma ions
- 주제(키워드) Ion implantation , unfiltered ion , Boron , Phosphorus , Hydrogen , emitter , solar cell
- 발행기관 고려대학교 대학원
- 지도교수 김동환
- 발행년도 2015
- 학위수여년월 2015. 2
- 학위구분 박사
- 학과 일반대학원 신소재공학과
- 세부전공 신소재공학전공
- 원문페이지 145 p
- 실제URI http://www.dcollection.net/handler/korea/000000058206
- 본문언어 영어
- 제출원본 000045827957
초록/요약
Formation of PN junction is one of the crucial processes for silicon solar cells. The PN junction in solar cell should (i) separate the charge carriers, (ii) have low recombination within the emitter bulk and its surface, (iii) provide the proper lateral conductivity and good Ohmic contacts to electrodes. Ion implantation has been introduced as a method of emitter tailoring to achieve high efficiency. Ion implantation has advantages such as (i) excellent control over surface dose, (ii) better control over the doping profile by separate the deposition and drive-in processes (iii) the possibility of patterned implantation and single-side junction and (iv) potential to make simpler process. While, the process cost of ion implantation is still higher than conventional diffusion process. Non-mass analyzed ion implanter is one fascination candidates to satisfy the continuing pressure on PV to lower the process cost and to fabricate high quality emitter. Unlike to the conventional ion implantation, a broad range of ion energies and other precursors can be possibly co-implanted at non-mass analyzed ion implantation. This causes the different characteristics of implanted junctions. To fabricated high performance PN junction, effect or behavior of unfiltered ions should be precisely predicted. In this research, the structural and electrical properties of silicon implanted with unfiltered ions were studied. First we observed that various fragments of B2H6 or PH3 sources were further implanted with boron or phosphorus ions. Since these fragments ions are heavier that the boron or phosphorus ions, high concentration of boron or phosphorus stopped near the surface because of the nuclear stopping. The high boron concentration near the surface, especially, involves the full amorphization which is favorable to junction formation. Large amount of hydrogen were observed after ion implantation using non-mass analyzed implanter. The hydrogen concentration profile exhibited multiple peaks. It is considered that various energy of hydrogen or hydrogen from different fragments ions of the B2H6 source were further implanted. Hydrogen related damage, H-platelets were observed, while most of the H-platelets were annealed out after the annealing process. On the contrary, extended boron defects were observed after annealing process because boron concentration over solubility limit formed boron interstitial clusters. Boron related damages were found near the projection range, therefore, nearer surface boron damages were observed at boron implanted with unfiltered ion. Dopant activation went faster over 850˚C for phosphorus ion implanted using non-mass analyzed implanter sample, because co-implanted hydrogen is lowering the total energy barrier when dopants diffuse from silicon interstitial sites to substitutional sites. Phosphorus emitter formed with unfiltered ions showed higher implied VOC and lower emitter saturation current at high temperature annealing. Junctions formed by unfiltered ions were applied to screen printed solar cell. The ion implanted emitter showed higher external quantum efficiency from 300nm to 450nm wavelength range and demonstrated 0.5%abs. higher efficiency than POCl3 diffused emitter. We consider that emitters fabricated with unfiltered ions have potential to high quality of PN junction and also have possibility of simple process for sophisticated high efficiency structures.
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ABSTRACT I
TABLE OF CONTENTS II
LIST OF FIGURES VI
LIST OF TABLES XI
1. Introduction 1
1.1 Motivation 1
1.2 Research Objective 8
1.3 References 9
2. PN junctions in semiconductors 10
2.1 Basic equation 10
2.2 The PN junction at equilibrium 13
2.3 The PN junction under illumination 15
3. Recombination 19
3.1 Radiative recombination 19
3.2 Auger recombination 21
3.3 Defect induced recombination at bulk 24
3.4 Defect induced recombination at surface 28
3.5 Emitter recombination 31
3.6 References 34
4. Experimental and analysis 36
4.1 Ion implantation 36
4.2 Structural and electrical property analysis 40
4.2.1 Transmission electron microscopy 40
4.2.2 X-ray diffraction 42
4.2.3 Quasi-steady state photoconductance 42
4.2.4 Secondary ion mass spectrometry 44
4.2.5 Four-point probe and Hall effect measurement 45
4.4 References 47
5 Phosphorus/Boron ion implanted silicon 48
5.1 Introduction 48
5.2 Lattice disorder and radiation damage 49
5.2.1 Atomic collision in silicon 49
5.2.2 Ion range and range calculation 52
5.2.3 Silicon recoil calculation and amorphization 56
5.2.4 Ion range and amorphization of hydrogen co-implantation on phosphorus / boron implanted silicon 64
5.3 Solid Phase epitaxial regrowth 76
5.3.1 Free energy change during solid phase epitaxial regrowth 76
5.3.2 Effect of orientation and impurity on solid phase epitaxial regrowth 77
5.4 Dopant activation. 82
5.4.1 Mechanism of dopant activation 82
5.4.2 Effect of hydrogen on dopant activation 82
5.5 Damages and defects after ion implantation and annealing 89
5.5.1 Ion implantation induced defects 89
5.5.2 Stress / strain analysis after annealing 91
5.5.3 Boron/ Hydrogen induced defects 96
5.6 References 103
6. Ion implanted silicon solar cell 108
6.1 Introduction 108
6.2 Solar spectrum and operation of solar cells 108
6.3 Loss of solar cells 114
6.3.1 Equivalent circuit 114
6.3.2 Short circuit current loss 117
6.3.3 Open circuit voltage loss 117
6.3.4 Fill factor loss 117
6.4 Properties of silicon solar cell 118
6.4.1 Sheet resistance, emitter saturation current and implied Voc 118
6.4.2 Performance of ion implanted silicon solar cell 124
6.5 References 127
7. Concluding remarks 128
