PROMIS A Marie SkodowskaCurie Initial Training Network Postgraduate

PROMIS A Marie Skłodowska-Curie Initial Training Network Postgraduate Research on Dilute Metamorphic Nanostructures and Metamaterials in Semiconductor Photonics In. Sb Quantum Dots for High Efficiency mid-IR LEDs WP 4: Materials for Environment Applications E. Repiso, P. Carrington, A. R. J. Marshall, Q. Lu and A. Krier Cadiz PROMIS Workshop 18 -20 May 2016

Outline • Challenges in the Mid-infrared; 3. 3 and 4. 2 μm • Proposal: In. Sb Quantum Dots • MBE growth • PL and EL studies • Summary 2

Challenges in the Mid-infrared • Lattice matching of the active region • No Semi-insulating substrates CB • Inadequate electrical confinement; small band offset • Imbalance in the DOS • Leakage current; surface and bulk • Inter-valence band absorption • Auger - CHCC Eg 1 2 HH 1’ LH - CHSH • Shockley-Read-Hall; native defects or dislocations • Extraction efficiency (~1%) Δ 0 SO 3

Challenges in the Mid-infrared • Lattice matching of the active region • No Semi-insulating substrates CB • Inadequate electrical confinement; small band offset • Imbalance in the DOS 3’ 1 3 • Leakage current; surface and bulk • Inter-valence band absorption • Auger Eg 2 HH Δ 0 - CHCC LH - CHSH • Shockley-Read-Hall; native defects or dislocations • Extraction efficiency (~1%) SO 3

Approaches: Quantum Dots DH QW QD • δ-like density of states; more confinement. • Temperature insensitive. • Avoid lattice mismatch. • Have shown promising results at shorter wavelengths. 4

Approaches: In. Sb QDs in In. As III-V band line-ups X • Self organisation is possible due to large enough lattice mismatch, Da/a = 6. 5% Al. Sb • Compresive strain. -0. 41 • Type-II broken gap Band Line-up => Reduced Auger recombination => Higher emission efficiency at room temperature in e. V 0. 78 77 K Ga. Sb 0. 23 In. Sb -0. 17 -0. 03 0 In. As -0. 59 EC EV In. Sb a ~ 6. 1Å 910 me. V 415 me. V In. As Vurgaftman & Meyer, JAP(2001) 185 me. V DEC 680 me. V - + 6. 47Å + In. As Su-Huai Wei, Zunger A. , PRB (1995) EC EV 5

Stranski-Krastanov growth of In. Sb QDs • In and Sb are large atoms that behave as surfactants. In. Sb has a low bond energy – high surface mobility of atoms-. • Promote 2 D growth rather than 3 D. • Tendency to form large clusters of islands. • Low density of dots. In. Sb In. As Increasing strain In. Sb In. As 2 D Layer growth followed by 3 D island growth. Critical thickness = 1. 7 ML Veeco GENxplor 6

In. Sb submonolayer QDs In. Sb QDs within ultra-thin In. Sb layers (0. 5 -0. 9 ML) in In. As have been formed by exposing the growth surface to a Sb flux exploiting an efficient As-Sb exchange: Solov’ev 2005 (MBE) Sb Flux As rich surface In. As As – Sb exchange In. As 7

In. Sb submonolayer QDs In. Sb QDs within ultra-thin In. Sb layers (0. 5 -0. 9 ML) in In. As have been formed by exposing the growth surface to a Sb flux exploiting an efficient As-Sb exchange: Solov’ev 2005 (MBE) Sb Flux As rich surface In. As Dense array of In. Sb islands partly covering the surface In. As 7

Extra In. Sb insertions • To grow larger QDs at high growth temperatures – reduce Sb segregation, better quality material and to avoid long growth interruptions. • A In. Sb deposition in MEE mode is used following the Sb exchange. • In the insertions thicker than 1 ML, PL intensity drops drastically: growth of relaxed islands. Intensity (a. u. ) In. As Single Sb exchange + MEE 8

MBE growth and design of In. Sb/In. As QDs Samples for PL studies 17. 8 nm-In. As barriers In. Sb QDs (0. 8 ML) 9

Temperature dependent PL Temperature dependence: The characteristic temperature Tc = 109± 2 K 10

In. Sb QDs LEDs 0. 7 ML In. Sb QD, 10 Sheets / 17 nm barriers n-In. As n+ In. As Al. Ga. As. Sb electron blocking barrier (30 nm) p+In. As 0. 5 µm 0. 3 µm 0. 5 µm 11

Summary • Successful growth of high density (1· 1012/cm 2) In. Sb QDs in In. As with excellent crystalline quality and low defect density. • Bright PL up to room temperature with superior quenching compared to bulk In. As. • Room temperature LEDs with dominant radiative recombination, peak at 3. 8µm. • Demostrated the potential of type II In. Sb/In. As QDs for mid-infrared photonic devices. 12

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