Optical Hyperdoping: Transforming Semiconductor Band Structure for Solar Energy Harvesting

Transcription

1 Optical Hyperdoping: Transforming Semiconductor Band Structure for Solar Energy Harvesting 3G Solar Technologies Multidisciplinary Workshop MRS Spring Meeting San Francisco, CA, 5 April 2010

2 Michael P. Brenner Michael Brenner Alan Aspuru-Guzik Alán Aspuru-Guzik Cynthia Friend Cynthia M. Friend Eric Mazur Eric Mazur

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4 Harvard NSF SOLAR team Aspuru group: Jacob Krich (PD) Justin Song (GS) Man Hong Yung (PD) Brenner group: Tobias Schneider (PD) Scott Norris (PD) Niall Mangan (GS) Friend group: Anne Co (PD) Stephen Jensen (GS) Mazur group: Meng-Ju Sher (GS) Yuting Lin (GS) Kasey Phillips (GS)

5 Introduction SF 6 Si irradiate with 100-fs 10 kj/m 2 pulses

6 Introduction black silicon

7 3 µm Introduction

8 Introduction absorptance (1 R int T int ) absorptance crystalline silicon wavelength (µm)

9 Introduction absorptance (1 R int T int ) black silicon absorptance crystalline silicon wavelength (µm)

10 Introduction

11 Introduction absorptance (1 R int T int ) absorptance multiple relections black silicon crystalline silicon wavelength (µm)

12 Introduction band structure changes: defects and/or impurities

13 Introduction optical hyperdoping puts 2% of sulfur in 200-nm surface layer

14 Introduction

15 Introduction open questions how do the impurities get incorporated? can we use optical hyperdoping for solar cells?

16 Outline goals optimizing dopant profile intermediate band

17 Goals interesting properties due to intermediate band CB impurity band VB

18 Goals generalize CB Si impurity band TiO 2 ZnO VB

19 Goals process CB Si impurity band TiO 2 ZnO properties VB structure

20 Goals process dopant incorporation modeling laser doping electrospray dopant delivery CB Si impurity band ZnO TiO 2 atomistic modeling XPS, STM, SIMS properties VB carrier life-time modeling band structure calculations T-dependent Hall IR spectroscopy structure

21 Goals Mathematics process dopant incorporation modeling laser doping electrospray dopant delivery CB Si impurity band ZnO TiO 2 atomistic modeling XPS, STM, SIMS properties VB carrier life-time modeling band structure calculations T-dependent Hall IR spectroscopy structure

22 Goals Chemistry process dopant incorporation modeling laser doping electrospray dopant delivery CB Si impurity band ZnO TiO 2 atomistic modeling XPS, STM, SIMS properties VB carrier life-time modeling band structure calculations T-dependent Hall IR spectroscopy structure

23 Goals Materials Science process dopant incorporation modeling laser doping electrospray dopant delivery CB Si impurity band ZnO TiO 2 atomistic modeling XPS, STM, SIMS properties VB carrier life-time modeling band structure calculations T-dependent Hall IR spectroscopy structure

24 Outline goals optimizing dopant profile intermediate band

25 Optimizing dopant profile Theoretical agenda explain enhanced doping optimize dopant profile for device design design process for optimal dopant profile

26 Optimizing dopant profile why does enhanced doping occur? Laser pulse Sulfur x Liquid Solid h(t) physical mechanisms: melting and resolidification of thin layer sulfur diffusion into liquid silicon incorporation into solid during resolidification

27 Optimizing dopant profile why does enhanced doping occur? Laser pulse Sulfur x Liquid Solid h(t) mathematical model: calculate dynamics of two fields temperature T(x,t) sulfur concentration c(x,t)

28 Optimizing dopant profile calculation step 1: temperature profile set up by laser

29 Optimizing dopant profile calculation step 1: temperature profile set up by laser Superheated!

30 Optimizing dopant profile calculation step 2: solid melts, solute incorporated

31 Optimizing dopant profile calculation step 2: solid melts, solute incorporated melting: heat diffusion energy balance

32 Optimizing dopant profile calculation step 2: solid melts, solute incorporated melting: heat diffusion energy balance incorporation: solute diffusion mass balance

33 Optimizing dopant profile calculation step 2: solid melts, solute incorporated melting: heat diffusion energy balance incorporation: solute diffusion mass balance

34 Optimizing dopant profile boundary condition critically affects dopant profile Laser pulse Sulfur x Liquid Solid h(t)

35 Optimizing dopant profile two scenarios

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38 Optimizing dopant profile two scenarios constant concentration constant sulfur flux

39 10 µm Optimizing dopant profile

40 10 µm Optimizing dopant profile

41 Optimizing dopant profile

42 Optimizing dopant profile

43 Optimizing dopant profile

44 Optimizing dopant profile

45 Optimizing dopant profile cross-sectional Transmission Electron Microscopy

46 M. Wall, F. Génin (LLNL) Optimizing dopant profile 1 µm

47 Optimizing dopant profile decouple ablation from melting

48 Optimizing dopant profile decouple ablation from melting

49 Optimizing dopant profile decouple ablation from melting undoped doped

50 Optimizing dopant profile decouple ablation from melting

51 Optimizing dopant profile secondary ion mass spectrometry 1.0 concentration (10 21 cm 3 ) depth (nm)

52 Optimizing dopant profile 1.0 concentration (10 21 cm 3 ) depth (nm)

53 Optimizing dopant profile appears to be closer to constant flux

54 Outline goals optimizing dopant profile intermediate band

55 Intermediate band what dopant states/bands cause IR absorption?

56 Intermediate band 1 part in 10 6 sulfur introduces donor states in gap CB ev ev ev 0.11 ev 0.09 ev 0.08 ev ev ev VB Janzén et al., Phys. Rev. B 29, 1907 (1984)

57 Intermediate band absorptance (1 R int T int ) wavelength (µm) 2 1 absorptance 0.5 crystalline Si energy (ev) 1.5

58 Intermediate band 10 6 sulfur doping wavelength (µm) 2 1 absorptance 0.5 sulfur impurity states Si band edge crystalline Si energy (ev) 1.5

59 Intermediate band laser-doped S:Si wavelength (µm) 2 1 laser-doped Si absorptance 0.5 sulfur impurity states Si band edge crystalline Si energy (ev) 1.5

60 Intermediate band laser-doped S:Si wavelength (µm) 2 1 laser-doped Si multiple relections absorptance 0.5 sulfur impurity states Si band edge crystalline Si energy (ev) 1.5

61 Intermediate band laser-doped S:Si wavelength (µm) 2 1 laser-doped Si absorptance 0.5 sulfur impurity band Si band edge crystalline Si energy (ev) 1.5

62 Intermediate band isolate surface layer for Hall measurements device layer buried oxide silicon substrate

63 Intermediate band isolate surface layer for Hall measurements device layer buried oxide silicon substrate

64 Intermediate band isolate surface layer for Hall measurements laser device doped layer region buried oxide silicon substrate

65 Intermediate band isolate surface layer for Hall measurements buried oxide silicon substrate

66 Intermediate band isolate surface layer for Hall measurements buried oxide silicon substrate

67 Intermediate band

68 Intermediate band Hall measurements 100 temperature (K) E d = 310 mev 10 n-doped cm N = cm 3 N/N room 1 p-doped 10 -cm 0.1 laser-doped /T (mk 1 )

69 Intermediate band transition to metallic behavior at high doping T (K) N s (cm 2 ) highly S doped Si Si substrate /T 1 (K 1 )

70 Intermediate band can we understand this intermediate band using atomistic modeling?

71 Intermediate band density of states

72 Intermediate band density of states unoccupied, localized: eats electrons occupied, localized: eats holes

73 Intermediate band recombination rate

74 What s next? change dopant/substrate combination

75 What s next? optimal dopant profile is flat 1.0 concentration (10 21 cm 3 ) depth (nm)

76 What s next? change incorporation process: electrospray pulse sequence design

77 Acknowledgments