Quantum Well and Quantum Dot Intermixing for Optoelectronic Device - PowerPoint PPT Presentation

Quantum Well and Quantum Dot Intermixing for Optoelectronic Device Integration Chennupati Jagadish Australian National University Research School of Physical Sciences and Engineering, Canberra, ACT 0200 AUSTRALIA c.jagadish@ieee.org www.rsphysse.anu.edu.au/eme

Overview • Introduction • Methods of Intermixing • Quantum Wells • Ion Implantation Induced Interdiffusion GaAs/AlGaAs, InGaAs/AlGaAs, InP/InGaAs QWs • Lasers, Photodetectors • Impurity Free Interdiffusion GaAs/AlGaAs, InGaAs/AlGaAs, InGaAsN/GaAs QWs • Integrated Waveguide-Laser • Quantum Dots • Suppression of Interdiffusion • Implantation Induced Interdiffusion • Summary

Photonic I ntegrated Circuits / Optoelectronic I ntegrated Circuits • I ntegrated Circuits Show Superior Performance Over Discrete Devices • Multi-functional circuits, e.g. WDM sources • I ntegrated Transceivers • Low Cost, Packaging

Photonic I ntegrated Circuits Different Bandgaps on the same chip

WDM Source Optical output (to optical fibre) optical amplifier passive optical waveguides multi -wavelength laser diodes dielectric passivation implant isolation

Quantum Well Intermixing before after • Diffusion of In and Ga across interface creates graded region in the case of GaAs/InGaAs Quantum Wells • Changes Bandgap, refractive index, absorption Coefficient

Methods Widely Used for Quantum Well (Dot?) I ntermixing I mpurity I nduced Disordering, e.g. Zn, Si I mpurity Free I nterdiffusion, e.g. SiO 2 , SOG I on I mplantation I nduced I nterdiffusion Defects/ I mpurities introduced by these methods enhance atomic interdiffusion Goals: High Selectivity and Low Concentration of Residual Defects while achieving large band gap differences

Why I on I mplantation? Widely used in Microelectronics I ndustry Defect Concentration - I on Dose, I on Mass, I mplant Temperature, Dose Rate Defect Depth - I on Energy Selective I on I mplantation using Masks

Ion implantation induced quantum well intermixing Ion implantation Vacancy Point defects : Interstitial Intermixing

Schematic of 4 QW structure (40 keV Proton Defect Profile) QW1 =1.4 nm QW2=2.3 nm QW3=4.0 nm QW4=8.5 nm

10K Photoluminescence Spectra H.H. Tan et.al., Appl. Phys. Lett. 68, 2401 (1996).

Energy Shifts vs. Proton Dose 900 o C, 30 sec QW1 =1.4 nm QW2=2.3 nm QW3=4.0 nm QW4=8.5 nm H.H. Tan et.al., Appl. Phys. Lett. 68, 2401 (1996).

Thermal Stability of InP/InGaAs QWs with InP and InGaAs InGaAs/InP QW, InP cap 0.90 InGaAs/InP QW, InGaAs cap InGaAs 50nm 0.89 Peak Energy (eV) InP 250nm InP 200nm 0.88 InGaAs QW 0.87 InP buffer InP buffer 0.86 600 650 700 750 800 850 o C) Annealing Temperature (

Implantation Dose (20 keV P) and Temperature Dependence of Energy Shifts in InP/InGaAs QWs 700 o C, 60 sec 30 90 InGaAs capped 80 InP capped 25 o C 70 25 o C Energy Shift (meV) Energy Shift (meV) 25 20 o C 60 200 o C 200 50 15 40 10 30 20 5 10 0 0 12 13 14 12 13 14 10 10 10 10 10 10 -2 ) -2 ) Dose (cm Dose (cm C. Carmody, J. Appl. Phys. 93, 4468 (2003)

Damage Accumulation in InP and InGaAs InGaAs Cap InP Cap 3 3 3x10 3x10 random InGaAs cap unimplanted random InP cap 3 3 Normalised Yield Normalised Yield unimplanted 2x10 2x10 14 cm -2 implanted at 1 x 10 14 cm -2 implanted 1 x 10 o C room temperature and 200 at room temperature 3 3 1x10 1x10 14 cm -2 implanted at 200 o C 1 x 10 0 0 200 250 300 350 400 450 200 250 300 350 400 450 Channel Channel

Tuning the Emission Wavelength of GRINSCH Quantum Well Lasers GaAs/AlGaAs QW Lasers

Tuning the wavelength of QW lasers p-type contact Oxide isolation QW Substrate n-type contact un-implanted dose A dose B dose A < dose B λ 1 λ 2 λ 3 λ 1 > λ 2 > λ 3

GRI NSCH QW Laser and 220 keV Proton Defect Profile

Lasing Spectra and L-I Characteristics of GaAs/AlGaAs QW Lasers (900 o C, 60 sec) H.H. Tan and C. Jagadish, Appl. Phys. Lett. 71, 2680 (1997).

Multi-Step Implantation Scheme for Improved GaAs/AlGaAs QW Laser Performance

Tuning the Detection Wavelength of Quantum Well Infrared Photodetectors (QWIPs)

Quantum Well I nfrared Photodetectors

Quantum well intermixing before after λ ´ 1 λ 1 λ ´ 2

QWIP structure Grown by MBE 2 µ m GaAs cap (Si: 2 × 10 18 cm -3 ) 50 nm Al 0.3 Ga 0.7 As barrier 50 nm Al 0.3 Ga 0.7 As barrier × 48 4.5 nm GaAs (Si: 2 × 10 18 cm -3 ) 50 nm Al 0.3 Ga 0.7 As barrier 50 nm Al 0.3 Ga 0.7 As barrier 1.3 µ m GaAs (Si: 2 × 10 18 cm -3 ) 0.5 µ m AlAs buffer SI-Substrate

Defect distribution profile of 0.9 MeV Protons 2.0 Top QWs Bottom contact+substrate Displacement Density (a. u.) contact 1.5 1.0 0.5 0.0 0 2 4 6 8 10 12 14 Implantation Depth ( µ m)

Tuning the wavelength of QWIP Metal contact Top contact Multi-QWs Metal contact Bottom contact Substrate un-implanted dose A dose B λ 3 λ 2 λ 1 dose A < dose B λ 1 < λ 2 < λ 3

QWIP spectral response 1.2 950 o C, 30 sec un-implanted 1 × 10 16 cm -2 1.0 2 × 10 16 cm -2 M.B. Johnston et.al, Photoresponse (a. u.) 3 × 10 16 cm -2 0.8 Appl. Phys. Lett. 4 × 10 16 cm -2 75, 923 (1999). 0.6 L. Fu et al , Appl. Phys. Lett. 0.4 78, 10 (2001). 0.2 0.0 4 6 8 10 12 14 Wavelength ( µ m)

Responsivity 0.13 reference 0.12 L. Fu et al , Appl. Phys. 0.11 Lett. 78, 10 (2001). 0.10 1 × 10 16 cm -2 Responsivity (mA/W) 0.09 0.08 0.07 2 × 10 16 cm -2 0.06 0.05 0.04 0.03 0.02 3 × 10 16 cm -2 0.01 0.00 -3 -2 -1 0 1 2 3 Bias (V)

Responsivity One-step implant-anneal 0.14 reference sequence: 0.9 MeV 2 × 10 16 cm -2 / 1e16/RTA/1e16/RTA 0.12 950ºC 30 s 2e16/RTA 0.10 Two-step implant-anneal Response (mA/W) sequence: 0.08 0.9 MeV 1 × 10 16 cm -2 / 0.06 950ºC 30 s /0.9 MeV 1 × 10 16 cm -2 / 950ºC 0.04 30 s 0.02 0.00 -6 -4 -2 0 2 4 6 Bias (V) L. Fu et al , Infrared Phys. & Technol. 42, 171 (2001).

Relative spectral response 1.4 un-implanted reference one-step implant-annealed sample 1.2 two-step implant-annealed sample ∆λ / λ = 15.95% 1.0 L. Fu et al , Infrared Photoresponse (a. u.) Phys. & Technol. 0.8 ∆λ / λ = 17.43% 42, 171 (2001). 0.6 0.4 0.2 0.0 4 5 6 7 8 9 10 11 12 Wavelength ( µ m)

I mpurity Free Vacancy Disordering Dielectric Film (Silicon Dioxide) Ga Atom Ga Vacancy QW Silicon dioxide acts as a sink for Ga out-diffusion (i) Creation of Ga vacancies, (ii) Diffusion of Ga Vacancies

Why I mpurity Free Vacancy Disordering? Maintains Good Crystal Quality Low Concentration of Residual Defects Low Concentration of Electrically Active Defects Relatively Simple Technique and No Residual I mpurities in the Active Regions

Experimental conditions • Spin-on glass (un-doped and Ga-doped): 3000 rpm for 30 s, baking at 400°C for 15 min • SiO 2 : Plasma enhanced chemical vapour deposition (PECVD) • TiO 2 : E-beam evaporation • RTA: 700 ºC to 900ºC for 30 s • Low temperature photoluminescence

IFVD using doped spin-on layers GaAs/AlGaAs 2 QW structure un-doped SiO 2 QWs PL intensity (a. u) P-doped Substrate L. Fu et al., Appl. Phys. Lett. Ga-doped 7, 1171 (2002). L. Fu et. Al., Appl. Phys. Lett. 76, 837-839 (2000). 650 675 700 725 750 775 Wavelength (nm)

IFVD using doped spin-on layers InGaAs/AlGaAs structure un-doped L. Fu et. al., J. Appl. Phys. 92, 3579 (2002) PL Intensity (a. u.) P-doped Ga-doped 860 880 900 920 940 960 wavelength (nm)

I ntegration of a Waveguide and a Laser Diode Using I FVD

Lateral waveguiding P ++ GaAs contact layer active DQW active layer (gain) waveguide Ridge in the M. Buda et.al., gain part J. Electrochem. Soc. Ridge in the 150, G481 (2003). waveguide part 1.9 µ m 0.1 µ m L a =0.87 mm L p = 2.5 mm (laser diode) (waveguide)

Quantum Dot Photonic I ntegrated Circuits

Why Quantum Dots? Three Dimensional carrier confinement Leads to Atom Like Density of States Low Threshold Current Lasers High Quantum Efficiency High Thermal Stability (To) Lasers Lasers operating at 1.3 & 1.55 um on GaAs (VCSELs) Normal I ncidence Operation of QDI Ps

Self Assembled Growth of Quantum Dots Frank- van der Volmer-Weber Stranski-Krastanow Merwe Growth Growth Mode Growth Mode Mode Layer by Layer Direct I sland Growth Layer by Layer followed Growth Large lattice mismatch by I sland Nucleation Lattice matched Very High I nterfacial Dissimilar Lattice Systems, e.g. Energy, e.g Spacing, Low AlGaAs on GaAs GaN on Saphire I nterfacial Energy e.g. I nAs on GaAs

Quantum Dot Intermixing • Large surface area to volume ratio • Non-uniform composition profile • Large strain field around the dots

Growth details GaAs 5- 6ML 50% • Aixtron 200/4 MOCVD 300nm InGaAs reactor GaAs 300nm – rotation – IR lamps S-I GaAs Substrate • TMGa, TMIn, AsH 3 & PH 3 • Single layer In 0.5 Ga 0.5 As dots • Dot growth ~500-550°C • GaAs cap at 650°C Characterization • AFM and PL

Amount of Material 6.5ML 5.8ML 5ML 4ML • Increase material: – Density increases until saturation – Size decreases