N Nut Sritirawisarn

Formation of linear InAs quantum dot arrays on InGaAsP/InP (100) by self-organized anisotropic strain engineering and their optical properties

The formation of linear InAs quantum dot (QD) arrays based on self-organized anisotropic strain engineering of an InGaAsP∕InP (100) superlattice (SL) template in chemical beam epitaxy is demonstrated, and the optimized growth window is determined. InAs QD formation, thin InGaAsP capping, annealing, InGaAsP overgrowth, and stacking in SL template formation produce wirelike InAs structures along [001] due to anisotropic surface migration and lateral and vertical strain correlations. InAs QD ordering is governed by the corresponding lateral strain field modulation on the SL template surface. Careful optimization of InGaAsP cap layer thickness, annealing temperature, InAs amount and growth rate, and number of SL periods results in straight and well-separated InAs QD arrays. The InAs QD arrays exhibit excellent photoluminescence (PL) emission up to room temperature which is tuned into the 1.55μm telecommunications wavelength region through the insertion of ultrathin GaAs interlayers. Temperature dependent PL m...

Structure evolution of 3C-SiC on cubic and hexagonal substrates

We report on growth of 3C-SiC by sublimation process in vacuum with the aim to ultimately select conditions for single polytype growth of bulk crystals. The 3C polytype occurrence, growth mechanism and structure evolution have been in the focus of the study. To gain understanding of the initial formation of the cubic polytype, growth was performed on various substrates, such as 6H- and 4H-SiC (on-axis and vicinal), as well as freestanding 3C-SiC wafers. The growth configuration used allowed a high growth rate, e.g. up to 200 (m/h, respectively very thick layers. The grown material was studied by means of optical microscopy, AFM and HRTEM. 6H-SiC (0001) Si-face substrates may be a good choice if the 3C nucleation is well controlled, which can be achieved by selecting the initial temperature ramp up and substrate orientation. These growth conditions limit the number of nucleation centers and decrease the defective boundaries.

Initial Growth in 3C-SiC Sublimation Epitaxy on 6H-SiC

The effect of initial growth condition of 3C-SiC growth on the C-face of 6H-SiC has been studied in sublimation epitaxy. The initial temperature increase to initiate the sublimation has a strong effect on the polytype formation using on-axis substrates. Polytype inclusions of 6H-SiC in the 3C-SiC layers is found to be related to spiral growth. The micropipe dissociation process is discussed. At the slowest ramp-up of the temperature the 3C-SiC does not contain any inclusions. In 1 degree off-oriented substrates there were no 3C-SiC formation. In this case the different ramp-up conditions has an influence on the heights of the steps.

Lateral Ordering, Position, and Number Control of Self-Organized Quantum Dots: The Key to Future Functional Nanophotonic Devices

Lateral ordering, position, and number control of self-organized epitaxial semiconductor quantum dots (QDs) are demonstrated. Straight linear InAs QD arrays are formed by self- organized anisotropic strain engineering of an InGaAsP/InP (10 0) superlattice template in chemical beam epitaxy. The QD emission wavelength at room temperature is tuned into the important 1.55 mum telecom wavelength region through the insertion of ultrathin GaAs interlayers. Guided self-organized anisotropic strain engineering is demonstrated on shallow- and deep-patterned GaAs (3 1 1)B substrates by molecular beam epitaxy for the formation of complex InGaAs QD arrays. Lateral positioning and number control of InAs QDs, down to a single QD, are demonstrated on truncated InP (100) pyramids by selective-area metal-organic vapor phase epitaxy. Sharp emission around 1.55 mum is observed well above liquid nitrogen temperatures. The regrowth of a passive waveguide structure establishes submicrometer-scale active- passive integration. The demonstrated control over QD formation is the key to future functional nanophotonic devices and paves the way toward the ultimates of photonic-integrated circuits operating at the single and multiple electron and photon level with control of the quantum mechanical and electromagnetic interactions.

Wavelength controlled multilayer-stacked linear InAs quantum dot arrays on InGaAsP/InP(100) by self-organized anisotropic strain engineering : a self-ordered quantum dot crystal

Multilayer-stacked linear InAs quantum dot (QD) arrays are created on InAs/InGaAsP superlattice templates formed by self-organized anisotropic strain engineering on InP (100) substrates in chemical beam epitaxy. Stacking of the QD arrays with identical emission wavelength in the 1.55 μm region at room temperature is achieved through the insertion of ultrathin GaAs interlayers beneath the QDs with increasing interlayer thickness in successive layers. The increment in the GaAs interlayer thickness compensates the QD size/wavelength increase during strain correlated stacking. This is the demonstration of a three-dimensionally self-ordered QD crystal with fully controlled structural and optical properties.

InAs/InP Quantum Dots, Dashes, and Ordered Arrays

This paper reviews the growth and characterization of epitaxial self-assembled InAs/InP(100) quantum dots (QDs), quantum dashes (QDashes), and ordered QD arrays fabricated by the chemical-beam epitaxy (CBE). The buffer layer surface morphology of latticematched InGaAsP on InP(100) substrates is identified as the key parameter to determine either InAs QD or QDash formation. Growth conditions leading to the formation of QDashes are always accompanied by a rough buffer layer surface morphology, while well-shaped and symmetric QDs are reproducibly observed on smooth buffer layers. On such buffer layers the creation of laterally ordered linear InAs QD arrays based on self-organized anisotropic strain engineering of InAs/InGaAsP superlattice (SL) templates is achieved. InAs QD ordering is governed by local recognition of the lateral strain field modulation on the SL template which produces wirelike InAs structures along [001] due to anisotropic adatom surface migration and lateral/vertical strain correlation. Stacking in multilayers of linear InAs QD arrays with identical emission wavelength in the 1.55-mm region is realized upon insertion of ultrathin GaAs interlayers beneath the QDs with increasing thickness in successive layers, demonstrating a three-dimensionally self-ordered QD crystal with fully controlled structural and optical properties. # 2009 The Japan Society of Applied Physics

Ordered 1-D and 2-D InAs/InP quantum dot arrays at telecom wavelength

Lateral one-dimensional (1-D) and two-dimensional (2-D) InAs/InP quantum dot (QD) arrangements are created by the concept of self-organized anisotropic strain engineering of InAs/InGaAsP superlattice (SL) templates on InP (100) and (311)B substrates by chemical-beam epitaxy (CBE). The SL templates comprise several-periods of an InAs QD layer plus a thin cap layer, post-growth annealing, and a separation layer. QDs order on top of the templates due to local strain recognition. Distinct preferential In adatom surface migration during annealing and substrate miscut lead to linear QD arrays along [001] for InP (100) substrates and a periodic square lattice aligned ±45° off [-233] for InP (311)B substrates. Optimization of the growth parameters balances In desorption and leads to well-separated and highly uniform QD arrays. Importantly, strong photoluminescence (PL) of defect-free InAs QD arrays is observed with the wavelength tuned into the 1.55-μim telecom region at room temperature through the insertion of GaAs interlayer beneath the QDs. Finally, the concept of self-organized anisotropic strain engineering for QD ordering is extended for formation of more complex architectures by combining it with step-engineering on shallow- and deep-patterned substrates. On the sidewall areas, the steps generated by the artificial patterns play the major role in determination of the In adatom surface migration during annealing, altering the QD arrays direction away from [001] on stripe-patterned InP (100) substrates. On the contrary, the sidewalls on patterned InP (311)B are faceted, not affecting the orientation of the 2-D InAs QD arrays.

Role of Surface Morphology for INAS Quantum Dot or Dash Formation on INGAASP/INP (100)

We investigate the formation of self-assembled InAs quantum structures on lattice-matched InGaAsP on InP (100) substrates grown by chemical beam epitaxy. The surface morphology of the InGaAsP buffer layer plays a key role for the formation of InAs quantum dots (QDs) or dashes (QDashes). QDash formation is always accompanied by a rough buffer layer surface. Growth conditions such as higher growth temperature, larger As flux, and compressive buffer layer strain promote the formation of QDs. However, once, the buffer layer has a rough morphology, QDashes always form during InAs deposition. On the other hand, well-shaped and symmetric QDs are reproducibly formed on smooth InGaAsP buffer layers for the same InAs growth conditions. Hence, not the growth conditions during InAs deposition, but rather the surface morphology of the buffer layer determines the formation of QDs or QDashes, which both exhibit high optical quality.