D. T. Mathes

Photopumped red-emitting InP/In0.5Al0.3Ga0.2P self-assembled quantum dot heterostructure lasers grown by metalorganic chemical vapor deposition

We report the 300 K operation of optically pumped red-emitting lasers fabricated from InP self-assembled quantum dots embedded in In0.5Al0.3Ga0.2P layers on GaAs (100) substrates grown by metalorganic chemical vapor deposition. Quantum dots grown at 650 °C on In0.5Al0.3Ga0.2P layers have a high density on the order of 1010 cm−2 and the dominant size of individual quantum dots ranges from ∼5 to ∼10 nm for 7.5 monolayer “equivalent growth.” These InP/In0.5Al0.3Ga0.2P quantum dot heterostructures are characterized by atomic force microscopy, high-resolution transmission electron microscopy, and photoluminescence. Laser structures are prepared from wafers having two vertically stacked InP quantum dot active layers within a 100-nm-thick In0.5Al0.3Ga0.2P waveguide and upper and lower 600 nm InAlP cladding layers. We observe lasing at λ∼680 nm at room temperature in optically pumped samples.

High-density InP self-assembled quantum dots embedded in In0.5Al0.5P grown by metalorganic chemical vapor deposition

We describe the characteristics of high-density InP self-assembled quantum dots embedded in In0.5Al0.5P cladding layers grown at 650 °C on GaAs (100) substrates by metalorganic chemical vapor deposition. Quantum dots grown with different deposition times are characterized by atomic force microscopy, photoluminescence, and transmission electron microscopy. For certain growth conditions, we observe the formation of a high density of quantum dots on the order of 1010 cm−2. The quantum dot average height increases from ∼5 to ∼25 nm with deposition time, while the quantum dot density changes insignificantly. Photoluminescence (4 K) shows a gradual shift of emission spectral peak from 2.06 eV (for 7.5 ML) to 1.82 eV (for 22.5 ML), corresponding to changes in the dominant quantum dot size. Also, incoherent quantum dot formation is not observed for up to 15 ML growth.

Properties of InP self-assembled quantum dots embedded in In0.49(AlxGa1−x)0.51P for visible light emitting laser applications grown by metalorganic chemical vapor deposition

We have studied the properties of InP self-assembled quantum dots embedded in various In0.49(AlxGa1−x)0.51P matrix layers to optimize the growth condition of the quantum dots and structures for III-phosphide quantum-dot-based lasers operating in visible spectral regions. Self-assembled quantum dot-related structures are grown by low-pressure metalogranic chemical vapor deposition and characterized by atomic-force microscopy, high-resolution transmission-electron microscopy, and photoluminescence. High density (∼1010 cm−2) and conveniently sized (∼5×20 nm) quantum dots are produced by growth condition optimization. We find that the quantum-dot heterostructure with a In0.49(AlxGa1−x)0.51P matrix layer having the largest direct band gap produces the most efficient luminescence at room temperature. Laser structures are prepared using optimized growth conditions and matrix materials. Laser operation with lasing wavelengths λ=650–680 nm are demonstrated at 77 and 300 K by optical pumping.

A Study of Mixed Group-V Nitrides Grown by Gas-Source Molecular Beam Epitaxy Using a Nitrogen Radical Beam Source

We report a study of N incorporation in GaAs and InP by gas-source molecular beam epitaxy using a N radical beam source. For GaNAs grown at high temperatures, phase separation was observed, as evidenced from the formation of cubic GaN aside from GaNAs. By lowering the growth temperature, however, GaNAs alloys with N as high as 14.8% have been obtained without showing any phase separation. For InNP, no phase separation was observed in the temperature range studied (310 – 420 °C). Contrary to GaNAs, incorporating N in InP is very difficult, with only less than 1% N being achieved. Optical absorption measurement reveals strong red shift of bandgap energy with direct-bandgap absorption. However, no semimetallic region seems to exist for GaNAs and a composition-dependent bowing parameter has been observed.

Nanoscale structure and chemistry of Al0.49In0.51P thermal oxide

In this letter, the nanoscale structure and chemistry of the III–V thermal oxide formed from Al0.49In0.51P is described. Transmission electron microscopy studies have shown that the oxide is an amorphous compound, which occupies greater volume than the original unoxidized crystalline Al0.49In0.51P layer, and which contains O, Al, In, and P (i.e., none of the species are completely desorbed during the oxidation reaction). Electron energy loss spectroscopy and energy spectroscopic imaging have shown specifically that the oxidation products include Al2O3 and In2O3 and P, either as an oxide or in some other amorphous compound.

Self-Assembled Iii-Phospide Quantum Dots Grown by Metalorganic Chemical Vapor Deposition

We report InP self-assembled quantum dots embedded in In 0.51 Al 0.49 P grown by metalorganic chemical vapor deposition. Growth parameters are altered to study the InP quantum-dot growth characteristics under various growth conditions. Quantum-dot morphology is characterized using atomic-force microscopy. Also, photoluminescence studies of the light-emitting properties are performed. Direct-bandgap ternary In x Al I−x P ( x =˜0.7, ˜0.85) self-assembled quantum dots are also grown and compared with InP quantum dots.

Low-threshold room-temperature continuous-wave InP quantum dot coupled to InGaP quantum well heterorstructure lasers grown by metalorganic chemical vapor deposition

We have grown and characterized InP self-assembled quantum-dots embedded in In/sub 0.49/(Al/sub x/Ga/sub 1-x/)/sub 0.51/P. For In/sub 0.49/Al/sub 0.51/P/In/sub 0.49/(Al/sub x/Ga/sub 1-x/)/sub 0.51/P/In/sub 0.49/Ga/sub 0.51/P/InP QD+QW injection lasers, we have achieved and report CW lasing at 654 nm at 300K with greatly reduced threshold current densities.

InP self assembled quantum dot lasers grown on GaAs substrates by metalorganic chemical vapor deposition

Abstract : We describe the operation of lasers having active regions composed of InP self-assembled quantum dots embedded in In(0.5)Al(0.3)Ga(0.2)P grown on GaAs (100) substrates by MOCVD. InP quantum dots grown on In(0.5)Al(0.3)Ga(0.2)P have a high density on the order of about 1 - 2 x 10/sq cm with a dominant size of about 10-15 nm for 7.5 ML growth. (1) These In(0.5)Al(0.3)Ga(0.2)P/InP quantum dots have previously been characterized by atomic-force microscopy, high-resolution transmission electron microscopy and photoluminescence. (2) We report here the 300 K operation of optically pumped red-emitting quantum dots using both double quantum dots active regions and quantum-dot coupled with InGaP quantum-well active regions. Optically and electrically pumped 300 K lasers have been obtained using this active region design; these lasers show improved operation compared to the lasers having QD-based active region with threshold current densities as low as J(sub t/l) ^ 0.5 KA/sq cm.

The technology and applications of selective oxidation of AlGaAs

Wet oxidation of AlGaAs alloys, pioneered at the University of Illinois a decade ago, recently has been used to fabricate high performance vertical-cavity surface emitting lasers (VCSELs). The superior properties of oxide-confined VCSELs has stimulated interest in understanding the fundamentals of wet oxidation. We briefly review the technology of selective oxidation of III-V alloys, including the oxide microstructure and oxidation processing as well as describe its application to selectively oxidized VCSELs.