Practical Quantum-Dot Lasers Monolithically Grown on Silicon for Silicon Photonics

Transcription

1 Department of Electronic and Electrical Engineering London Centre for Nanotechnology Practical Quantum-Dot Lasers Monolithically Grown on Silicon for Silicon Photonics Huiyun Liu

2 Outline Why lasers on the Si platform? The limitation of group-iv lasers III-V quantum well lasers on silicon Practical III-V quantum dot lasers on silicon from UCL Summary 2

3 1. Why laser on Si? Challenge for Data Centre 27% CAGR Source: Cisco Global Cloud Index, Si Photonics = Optical + Electronic Source: Intel Silicon Photonics Global data centre traffic is booming Traditional copper cabling is stifling datacentre evolution Silicon photonics can solve the slow data transfer problem 3

4 1. Why laser on Si? Challenge for Si microelectronics Challenges for CMOS at 32 nm and beyond: Lithography, Transistor, Interconnects, Chemical/Material issues; Commercially solution: multi-core chip with seriously problem of Cu interconnectors. Optical connector is the best solution for the connectors between the core in silicon chips and intra chip. 4

5 1. Why laser on Si? Challenge for Si photonics Various Waveguides 25G Modulator (NEC) 340G APD (Intel) What is missing in silicon photonics? Electronicallypumped silicon Lasers 8 channel WDM (IBM) -0.8dB Vertical Coupler(Helios)

6 Outline Why lasers on the Si platform? The limitation of group-iv lasers III-V quantum well lasers on silicon Practical III-V quantum dot lasers on silicon from UCL Summary 6

7 2. Group-IV lasers Challenges for Si photonics Although high-performance photonics components, such as modulators, detectors have been developed, SiGe system is not suitable for emitters because of their nature of indirect bandgap; A few groups, including Intel and MIT, have been working on Group-IV laser in last dew decades. D. Liang and J. Bowers, Nature Photon. 4, 511 (2010) 7

8 2. Group-IV lasers First cw silicon laser Raman laser It was reported by Intel; Silicon materials used in this laser; Optically pumped laser - it does not solve the problem; There is no electrically pumped silicon roman laser so far. H. Rong, R. Jone, A. Liu, O. Cohen, D. Hak, A. Fang, and M. Paniccla, Nature 433, (2005) 8

9 2. Group-IV lasers First electrically pumped Ge laser Phosphorous-doped Ge bulk used as active region; The lasing threshold is about 280 ka/cm 2 at 15 o C; The threshold is too high to have any practical applications. Power is too low. R. Camacho-Aguilera, Y. Cai, N. Patel, J. Bessette, M. Romagnoli, L. Kimerling, and J. Michel, Optics Express 20, (2012) 9

10 2. Group-IV lasers First GeSn laser GeSn could be direct bandgap with ~10% Sn; Low equilibrium Sn (<1%) in Ge; Larger mismatch between Ge and Sn (15%); Optically pumped devices at low temperature (<130K); More works on improving crystal quality are needed for future research activities. S. Wirths, R. Geiger, N. von den Driesch, G. Mussler, T. Stoica, S.Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J. M. Hartmann, H. Sigg, J. Faist, D. Buca and D. Grṳtzmacher, Nature Photon. 9, (2015) 10

11 Outline Why lasers on the Si platform? The limitation of group-iv lasers III-V quantum well lasers on silicon Practical III-V quantum dot lasers on silicon from UCL Summary 11

12 3. III-V QW laser on silicon Challenge for Si photonics: III-V on silicon III-V laser on Si is ideal solution. Direct epitaxial growth III-V has been working on for 30 years, and there were III-V QW lasers on Ge and Si with high threshold current density and short life time. Monolithic growth of III-V QWs on silicon was studied at 30 years ago. There significant challenge for epitaxial growth of QW laser. Wafer bonding technique has been well established in last 30 years, although there is still challenges. 12

13 3. III-V QW laser on silicon The Challenges for III-V growth on silicon Antiphase domains: III-V compound materials are composed of two different atomic sublattices. Sublattice shift may nucleate during epitaxial growth of III-V on Si and Ge. Sheets of wrong nearest neighbor bonds. This issue has been well solved. Threading dislocations: due to the lattice mismatch between III-V compounds and Si. This is still the main issue. Antiphase domain (APD) Threading dislocations (TD) 13

14 3. III-V QW laser on silicon Epitaxial Growth: Best GaAs/AlGaAs lasers grown on silicon The longest lifetime (> 200 hours) for GaAs/AlGaAs quantum well (QW) laser grown on silicon; Reasonable threshold current density; Still long way to go after 30 year studies worldwide. Z. I. Kazi, P. Thilakan, T. Egawa, M. Umeno, T. Jimbo, Japanese Journal of Applied Physics 40, pp ,

15 3. III-V QW laser on silicon Epitaxial Growth: GaSb-based lasers grown on silicon 2D array of misfit dislocations at the interface GaSb/Si Threshold current 900 A/cm 2 ; Lasing wavelength around ~ 2000 nm; cw operation 35 o C; No lifetime reported! J. R. Reboul, L. Cerutti, J. B. Rodriguez, P. Grech, and E. Tournie, Appl. Phys. Lett. 99, (2011) 15

16 3. III-V QW laser on silicon Wafer Bonding: InP-based 1.55-µm QW laser devices: Wafer bonding approach has been studied for more than 20 years; Output power is less than 10 mw; Operation up to 105 o C; Transceivers with 4 QW lasers were announced by Intel at last year; Wafer bonding is the most successful technique so far, although there are challenges in massive production and high yield for high density lasers on silicon chips. H. Chang, A. Fang, M. N. Sysak, H. Park, R. Jones, O. Cohen, O. Raday, M. Paniccia, and J. Bowers, Optics Express 15, (2007) 16

17 Outline Why lasers on the Si platform? The limitation of group-iv lasers III-V quantum well lasers on silicon Practical III-V quantum dot lasers on silicon from UCL Summary 17

18 4. III-V quantum-dot technology Why quantum dots semiconductor nanocrystal Narrow emission spectra δ- function DOS Large energy separation between ground and excited states. Difficult to thermally excite carriers out of GS leading to possible temperature independent lasing characteristics Active volume very small, very low threshold current is expected for QD lasers 18

19 4. III-V quantum-dot technology Quantum dot growth: Animation from QDLaser, Inc.

20 4. III-V quantum-dot technology III-V QD laser: Temperature-independent operation High slope-efficiency and temperature-insensitive operation with almost constant threshold-current and slope efficiency between - 40 and 100 o C. The realization of a 10 Gbit s 1 QD laser that can operate in environments of up to 100 o C nm InAs/GaAs QD laser diodes InP-based telecom laser diodes M. Sugawara and M. Usami, Nature Photon. 3, 30 (2009) 20

21 4. III-V quantum-dot technology III-V QD laser: BETTER solution for III-V/Si lasers Less sensitive to defects than quantum well (QW) lasers Stronger mechanical property to prevent the growth of defects during lasing operation, leading to much longer lifetime for QD laser diodes with higher defect density. Defects: threading dislocation QW QDs R. Beanland et al, J. Appl. Phys. 103, (2008) 21

22 4. III-V quantum-dot technology Defect reduction: Effects of defect filter layers InAlAs/GaAs strained superlattice High density (~ cm -2 ) of dislocations is generated at the GaAs/Si interface. InAlAs/GaAs SPLs is better DFL than InGaAs/GaAs SPLs. After the last set of InAlAs/GaAs SPL, the dislocation density has been remarkably reduced to ~ cm -2. Electronics Letters 50, (2014)

23 4. III-V quantum-dot technology 7-year studies on III-V quantum dot laser on silicon at UCL From 2011, the study has generated 20 papers in refereed journals (including 2 Nature Photonics and 2 ACS Photonics), two granted plus two filed patents filed at UCL, and 8 research grants (over 4.5 million for UCL MBE group). The first two papers on III-V quantum dots grown Ge (Nature Photon.) and silicon substrates (Optics Express) have been viewed by the leading journal in physical and engineering field. 23

24 4. III-V quantum-dot technology The best device after 7 year s work at UCL: Combining all the methods as: AlAs nucleation layer, InAlAs/GaAs dislocation filter layers, and in situ thermal annealing after strained superlattice layer. Nature Photon. 10, (2016)

25 4. III-V quantum-dot technology Device fabrication: The ridges were etched down to 100 nm below the active region for an improved carrier confinement. Ti/Pt/Au and InGe/Au were deposited on the p-gaas contacting layer and the exposed n-gaas buffer layer, respectively. As cleaved devices of 3.2 mm in length and 50 μm in wide were mounted and wire bonded on ceramic tiles to enable testing. No facet coating is applied. Nature Photon. 10, (2016)

26 4. III-V quantum-dot technology RT cw 1300-nm QD lasers Measured in continuous-wave mode; RT Lasing at 1315 nm with threshold current density of 62.2 A/cm 2, which corresponds to ~ 12.5 A/cm 2 (very close to best results for GaAs-based devices); Output power of 105 W at RT. First cw laser directly grown on silicon substrates with record threshold current density. Nature Photon. 10, (2016)

27 Output power / facet (mw) 4. III-V quantum-dot technology High temperature performance cw lasing up to 75 o C, limited by our current source; Plused lasing up to 120 o C; Characteristic temperature (T 0 ) is ~ 51 K between 20 and 60 o C, and ~ 35 K between 70 and 120 o C o C to 120 o C step 10 o C Ln (Jth) T0= 51K T0= 35K Temperature ( o C) Current Density (A/cm 2 ) Nature Photon. 10, (2016)

28 Threshold (ma) 4. III-V quantum-dot technology First practical laser monolithically grown on silicon: Ageing test performed at a fixed temperature of 26 o C; The output power was monitored cw drive current of 210 ma, 1.75 times the threshold current. And periodic LIV measurements also performed; 29.7% drop in power in 3100 hours with 26.4% drop in first 500 hours, and similar trend for the threshold current; An extrapolated mean time to failure (MTTF, defined by a doubling of the threshold) of over 100,158 hours was determined Fitting Curve Ith(t) = Ith(0)( t ) MTTF = (1/a) 1/m =100, Total ageing time (Hours) Nature Photon. 10, (2016)

29 4. III-V quantum-dot technology Recent results: Initial results on on-axis Si(100) substrates Opt. Express. 25, (2017).

30 4. III-V quantum-dot technology Recent results: cw operation of injection microdisk InAs/GaAs QD lasers grown on Si Opt. Letters 25, 3319 (2017)

31 4. III-V quantum-dot technology Recent results: First RT cw QD DFB laser array on silicon (unpublished).

32 Threshhold current density (A/cm 2 ) Summery The historical development of heterostructure lasers showing the record threshold current densities at the time of publication 10 5 Double Hetero Structure Quantum Well Miller et al. Quantum Dot Alferov et al. CW Alferov et al. Hayashi et al. Dupuis et al. Tsang Alferov et al. Chand et al. Egawa et al. (Si) Kazi et al. (Si, CW) Mi et al. (Si) Kirstaedter et al. Ledentsov et al. Liu et al. Ribbat, Selin Ribbat, Selin Lee et al. (SiGe, CW) Liu et al. (Ge, CW) Lee et al. (Si) Tang et al. (Si) Lee et al. (SiGe) Year 1. QD laser on GaAs; QD laser on Ge; QD laser on SiGe; u QD laser on Si. 2. CW indicates that the threshold current values were obtained from QD lasers under continuous-wave operation. The rest were obtained from QD lasers tested in pulse mode. J. Phys. D: Appl. Phys. 48 (2015)

33 Thank You UCL MBE Group