Direct growth of III-V quantum dot materials on silicon

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1 Direct growth of III-V quantum dot materials on silicon John Bowers, Alan Liu, Art Gossard Director, Institute for Energy Efficiency University of California, Santa Barbara Research supported by Josh Conway at DARPA MTO and Intel

2 III-V Laser Growth on Silicon 3 mm Silicon - ~$.2 cm mm InP - ~$4. cm - 2 (Photo courtesy of Dr. Jordan Lang, Yale) CMOS processing of photonics is already happening, yet high cost and small size of III- V wafers remains an issue. Goal: Grow III- V lasers on larger and cheaper silicon substrates without sacrificing laser performance for lower cost and higher throughput. [1] Bowers, John E., et al. "A Path to 3 mm Hybrid Silicon Photonic Integrated Circuits. OFC 214 2

3 III-V growth on 3 mm Silicon Wafers GaP on 3 mm Silicon using MOVPE GaAs on3 mm Silicon using MBE B. Kunert et al. 69 th Device Research Conference, Santa Barbara (211) Amy Liu, IQE Inc.

4 III-V Laser Growth on Silicon Polarity, lattice & thermal expansion mismatch between silicon and III-Vs result in high dislocation densities High thresholds (or no lasing), and poor reliability for QW lasers. Dangling bond/ threading dislocauon Bulk GaAs: a=.565 nm GaAs Silicon substrate Bulk Si: a=.543 nm Si substrate 4

5 Solution: Use Quantum Dots! SCH QW SCH Dislocations SCH QDs SCH In-plane band diagram: E c Dislocation trap states E v 5

6 Solution: Use Quantum Dots! 1991 Semiconductor Structure for Optoelectronic Components with Inclusions (Jean Gerard & Claude Weisbuch), U.S. Patent No. 5,75,742 3D confinement provided by quantum dots prevents carriers from migrating to dislocations. SCH QW SCH Dislocations SCH QDs SCH In-plane band diagram: E c Dislocation trap states E v 6

7 GRINSCH QDLs on Ge/Si Two graded index separate confinement heterostructure (GRINSCH) lasers were grown on GaAs-on-Ge-on-Si virtual substrates provided by IQE Inc. In one wafer, the QD barrier layers were p-doped with beryllium to improve T. 3 nm GaAs:Be 5 nm 4 % Al x Ga (1-x) As:Be 1.4 µm Al.4 Ga.6 As:Be 2 nm 2 4% Al x Ga (1-x) As:Be 3 nm Al.2 Ga.8 As:Be p/uid 37.5 nm GaAs 7x UID 5 nm GaAs 3 nm Al.2 Ga.8 As:Si 2 nm 4 2% Al x Ga (1-x) As:Si 1.4 µm Al.4 Ga.6 As:Si 5 nm 4% Al x Ga (1-x) As:Si 2 nm GaAs:Si 1 nm GaAs:UID 5 nm Ge:UID Si#(1)#6 o #[111]## GaAs Al.4 Ga.6 As 7x QDs Al.4 Ga.6 As GaAs 7

8 GRINSCH QDLs on Ge/Si TEM images of unprocessed laser material >1 8 cm -2 dislocation density in the QD active region Plan-view TEM of QD active region Cross-sectional view of the laser epi GaAs Al.4 Ga.6 As QDs Al.4 Ga.6 As GaAs 1 µm 1 µm Ge 8

9 GRINSCH QDLs on Ge/Si TEM images of unprocessed laser material >1 8 cm -2 dislocation density in the QD active region Plan view of QDs Cross-sectional view of QDs InAs QDs 5 nm 9

10 Device Fabrication Epi processed into ridge lasers 4-12 µm wide, 7-12 µm long cavities. Facets were polished, rear facet HR coated (~95%). 1

11 Low Thresholds Uniform threshold current densities across die/wafers. Low CW threshold (15 A/cm 2 ) Single Facet Power (mw) Voltage (V) Power (mw) x4 µm 2 undoped device Current (ma) Voltage (V) Counts Threshold Current (ma) µm 9 1 µm µm p doped undoped Ridge Width (µm) Threshold Current Density (A/cm 2 ) Liu, Alan Y., et al. "High performance continuous wave 1.3 µm quantum dot lasers on silicon." Applied Physics Letters 14.4 (214):

12 High Output Powers CW powers over 1 mw routinely achieved. Nearly 18 mw maximum CW single side output power at 2 o C from HR coated 113x1 µm 2 intrinsic active region (undoped) device. 33% differential efficiency and 18% WPE (at 15 ma) Single Side P max (mw) µm µm µm p doped undoped 1 2 Single Facet Power (mw) Voltage (V) Power (mw) 113x1 µm ma threshold Voltage (V) Drive current at P max (ma) Current (ma) 12

13 High Temperature Performance P-doping the active region improves thermal performance.[1] Continuous wave lasing up to 119 o C (dual state lasing at high currents/temperatures). Without p-doping Single Facet Power (mw) With p-doping 2 C 3 C 4 C 5 C 6 C 7 C 993x5 µm Current (ma) C 118 C 119 C 12 C [1] Alexander, Ryan R., et al. "Systematic study of the effects of modulation p-doping on 1.3-µm quantum-dot lasers." Quantum Electronics, IEEE Journal of (27):

14 Lifetimes of Previous GaAs based lasers on Silicon GaAs based lasers are very sensitive to defect density and susceptible to failure by recombination enhanced defect reactions (REDR) First GaAs lasers on silicon had lifetimes of ~1 seconds (RT, pulsed) (1987) Longest lifetime reported for GaAs based laser on Si (853 nm) is 8 hours (RT, CW) (2) [5] Groenert, Michael E., et al. "Improved room-temperature continuous wave GaAs/AlGaAs and InGaAs/GaAs/AlGaAs lasers fabricated on Si substrates via relaxed graded GeSi buffer layers." Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 21 (23):

15 Reliability Studies of QD lasers on Silicon Over 21 hours of continuous operation (testing stopped) >26x improvement over best reported lifetime for GaAs laser on Si: (21 hours at 3 o C, 2 ka cm -2 vs. 8 hours at RT, 1.3 ka cm -2 ) No catastrophic failures observed. Threshold"(mA)" 1" 8" 6" 4" 2" " Aged%threshold%and%output%power%at%3%C% Threshold"(mA)" Power"at"1"mA"(mW)" " " 5" 1" 15" 2" 25" Accumulated"aging"hours" 2" 15" 1" 5" Output"power"at"1"mA"(mW)" 15

16 Summary Quantum dot lasers perform better than quantum well lasers for epitaxial growth on Si. Quantum dot lasers epitaxially grown on silicon have the world record for any laser on silicon for High cw power (175 mw) High temperature cw lasing (119 C) But NOT for CW Lasing lifetime (21 hours) Technology is promising, but work remains to solve the degradation problem. 16