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Three types of GaAsP metamorphic buffer layers, including linearly graded, step graded, and metamorphic superlattices, were compared for the purposes of virtual substrates for red laser diode heterostructures. Laser diodes were fabricated on GaAs substrates and relaxed GaAsP metamorphic superlattice virtual substrates. A laser diode structure with a tensile-strained quantum well on a standard miscut GaAs substrate achieved TM-polarized emission at a 638 nm wavelength with 45% peak power conversion efficiency (PCE) at a 880 mW continuous wave (CW) output power with T0 = 77 K and T1 = 266 K. An analogous laser diode structure with a compressively strained quantum well on the metamorphic superlattice emitted TE-polarized 639 nm light with 35.5% peak PCE at 880 mW CW with T0 = 90 K and T1 = 300 K.

Red laser diodes were fabricated on GaAs and GaAsP metamorphic-superlattice-substrates. The tensile strained QW on GaAs emitted 45% PCE, 638nm, TM-polarized light at 880mW CW. The compressively strained QW on the metamorphic structure emitted 639nm TE-polarized light with Tq=90K and Tj=300K.

Short-wavelength (λ∼3.6 μm) quantum-cascade-laser (QCL) designs, employing a metamorphic buffer layer (MBL) on a GaAs substrate, have been developed for strong carrier confinement to the active regions, as a result of implementing the deep well and tapered active-region concepts. The strain·thickness product values for the quantum wells and barriers comprising the QCL active regions (ARs) are kept basically the same as those employed for longer wavelength (λ∼4.8 μm) QCL AR structures grown on InP substrates. Strain-compensated superlattice (SL) structures, representative of the QCL AR, are grown by metalorganic vapor phase epitaxy (MOVPE) on an AlInGaAs compositionally step-graded MBL. Structural characterization of the SL structures underscores the importance of reducing the top-surface roughness of the underlying MBL. Intersubband absorption has been observed for doped SL structures grown on hydride-VPE-grown MBLs.

The hydride vapor phase epitaxy technique (HVPE) can deposit uniform materials at high growth rates, making it suitable for the formation of metamorphic buffer layers (MBLs). HVPE was used to form In x Ga 1− x As-based MBLs as substrates in the metalorganic vapor phase epitaxy (MOVPE) of superlattice (SL) structures. Samples were grown over a range of deposition temperatures and reactant flows and their effect on the ternary alloy composition and growth rate was determined. Over the compositional range of x InAs P InCl ). A compositionally step-graded MBL consisting of nine intermediate steps followed by a thick, constant composition layer of x InAs ∼0.23 was grown. The MBL was characterized by high-resolution x-ray diffraction (HRXRD) and reciprocal space mapping. The topmost layer was highly relaxed, exhibiting a residual strain of −0.0011±0.0002. Chemical-mechanical polishing (CMP) was used to reduce the surface cross hatching, affecting a decrease in rms roughness from 2.10 to 1.39 nm. A 20 period, In 0.33 Ga 0.67 As (3.1 nm)/Al 0.90 In 0.10 As (7.2 nm) strain-balanced superlattice (SL) structure was grown by MOVPE on the as-grown and CMP-prepared MBL and characterized by HRXRD. The diffraction pattern of the SL grown on the CMP-prepared MBL was significantly more intense with narrower x-ray diffraction peaks when compared with the SL on as-grown MBL.

Multi-junction III-V solar cells are based on a triple-junction design that employs a 1eV bottom junction grown on the GaAs substrate with a GaAs middle junction and a lattice-matched InGaP top junction. There are two possible approaches implementing the triple-junction design. The first approach is to utilize lattice-matched dilute nitride materials such as InGaAsN(Sb) and the second approach is to utilize lattice-mismatched InGaAs employing a metamorphic buffer layer (MBL). Both approaches have a potential to achieve high performance triple-junction solar cells. A record efficiency of 43.5% was achieved from multi-junction solar cells using the first approach [1] and the solar cells using the second approach yielded an efficiency of 41.1% [2]. We studied carrier dynamics and defects in bulk 1eV InGaAsNSb materials and InGaAs layers with MBL grown by MOVPE for multi-junction solar cells.

Bulk InGaAs layers with a 1eV band-gap grown on GaAs substrates are attractive for high efficiency multi-junction solar cells. However, a large amount of lattice mismatch between bulk InGaAs layer and GaAs substrate necessitates development of novel metamorphic buffer layers (MBL). A number of research groups have reported various MBLs for applications including HBTs, HEMTs, lasers, and solar cells. In this study, we report carrier dynamics and defects in MOVPE-grown bulk InGaAs layers (E g = ~ 1.0 - 1.1 eV at 300K) with two different types of MBLs including InGaAs and InGaPSb. We also report the effect of chemical-mechanical polishing (CMP) process on carrier lifetimes and the properties of the films subsequently grown on top of the MBL. We employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in InxGa1-xAs samples with and without the CMP process and a high resolution TEM to study defects in various structures.

A novel deep-well tapered-active quantum cascade laser design (λ∼3.6 μm) on a metamorphic buffer layer (MBL) virtual substrate is achieved. Strain-compensated superlattice structures, representative of the QCL active region, are grown on the MBL.

We have investigated the MOVPE growth of In x Ga 1−x As metamorphic buffer layer (MBL) structures with a focus on techniques to improve the surface morphology and determine the influence of morphology on subsequently grown single-junction device structures. To improve the surface roughness of the underlying MBL, Chemical-Mechanical Polishing (CMP) is employed and MOVPE regrowth of single-junction (SJ) solar cells on top of the polished surface is performed. AFM image analysis indicates the CMP process is effective in reducing the step-graded In x Ga 1−x As MBL surface roughness from ∼7–10 nm (as-grown) to 2.3 nm post CMP. A post-CMP ozone/HF treatment was found to be effective in removing silica residue remaining on the surface from the CMP process, allowing for the growth of films on top of the MBL surface subjected to CMP. Improved short circuit current density (J sc ) and external quantum efficiency (QE) were obtained from SJ (1eV) devices which employ the CMP process compared with those on as-grown MBLs.

Large-area, ultradense Ni nanopillar arrays were fabricated directly on bare n-GaAs substrates using diblock copolymer lithography and electrodeposition. The Ni nanopillar arrays are hexagonally arranged, exhibiting an average pillar diameter of ∼24 nm, and an areal density of ∼1011/cm2 over an entire surface area of 1 cm × 1 cm. These arrays represent large-scale, highly dense, sub-30 nm metal-nanopillar arrays made on III-V semiconductor substrates suitable as pattern masks. The fabrication method offers a simple and effective route to manufacturing large-area, highly dense, sub-30 nm metal nanostructures for III-V optoelectronic devices, in order to enhance their performance and functionalities.