High efficiency single quantum well graded-index separate-confinement heterostructure lasers fabricated with MeV oxygen ion implantation

Single quantum well AlGaAs/GaAs graded-index separate-confinement heterostructure lasers have been fabricated using MeV oxygen ion implantation plus optimized subsequent thermal annealing. A high differential quantum efficiency of 85% has been obtained in a 360-µm-long and 10-µm-wide stripe geometry device. The results have also demonstrated that excellent electrical isolation (breakdown voltage of over 30 V) and low threshold currents (22 mA) can be obtained with MeV oxygen ion isolation. It is suggested that oxygen ion implantation induced selective carrier compensation and compositional disordering in the quantum well region as well as radiation-induced lattice disordering in AlxGa1–xAs/GaAs may be mostly responsible for the buried layer modification in this fabrication process

Submilliamp threshold InGaAs-GaAs strained layer quantum-well laser

Strained-layer InGaAs-GaAs single-quantum-well buried-heterostructure lasers were fabricated by a hybrid beam epitaxy and liquid-phase epitaxy technique. Very low threshold currents, 2.4 mA for an uncoated laser (L=425 μm) and 0.75 mA for a coated laser (R~0.9, L=198 μm), were obtained. A 3-dB modulation bandwidth of 7.6 GHz was demonstrated at low bias current (14 mA). Procedures for material preparation and device fabrication are introduced

Subpicosecond time-resolved Raman studies of field-induced transient transport in an InxGa1−xAs-based p-i-n semiconductor nanostructure

Electron transient transport in an InxGa1−xAs-based (x=0.53) p-i-nnanostructure under the application of an electric field has been studied by time-resolvedRaman spectroscopy on a subpicosecond time scale and at T=300K. The experimental results reveal the time evolution of the electron distribution function and electron drift velocity with subpicosecond time resolution. These experimental results are compared with those of both InP-based and GaAs-based p-i-nnanostructures and provide a consistent understanding and better insight of electron transient transport phenomena in semiconductors

Electric-field-induced heating and energy relaxation in GaN

Electric-field-induced heating is studied using noise measurements in n-type GaN grown on sapphire substrates. The measured electron temperature is found to be an order of magnitude higher than what is expected based on calculations of electron–phonon coupling via acoustic deformation potential scattering processes in GaN. The discrepancy may be explained by a large thermal boundary resistance between the GaN film and the sapphire substrate

Subpicosecond time-resolved Raman studies of LO phonons in GaN: Dependence on photoexcited carrier density

Subpicosecond time-resolved Raman spectroscopy has been used to measure the lifetime of the LO phonon mode in GaN for photoexcited electron-hole pair density ranging from1016to2×1019cm−3 . The lifetime has been found to decrease from 2.5ps , at low density, to0.35ps , at the highest density. The experimental findings should help resolve the recent controversy over the lifetime of LO phonon mode in GaN

Near-field optical spectroscopy and microscopy of self-assembled GaN∕AlN nanostructures

The spatial distribution and emission properties of small clusters of GaNquantum dots in an AlN matrix are studied using high-resolution electron and optical microscopy. High-resolution transmission electron microscopy reveals near vertical correlation among the GaNdots due to a sufficiently thin AlN spacer layer thickness, which allows strain induced stacking. Scanning electron and atomic force microscopy show lateral coupling due to a surface roughness of ∼50–60nm. Near-field photoluminescence in the illumination mode (both spatially and spectrally resolved) at 10K revealed emission from individual dots, which exhibits size distribution of GaNdots from localized sites in the stacked nanostructure. Strong spatial localization of the excitons is observed in GaNquantum dots formed at the tip of self-assembled hexagonal pyramid shapes with six [101¯1¯] facets

Properties of AlxGa1−xN layers grown by plasma-assisted molecular-beam epitaxy under Ga-rich conditions

AlxGa1−xN films were grown by plasma-assisted molecular-beam epitaxy on (0001)sapphire substrates under Ga-rich conditions. To control the AlxGa1−xN composition over the entire range, the Al and Ga arrival rates were fixed while the nitrogen arrival rate was varied. We have found that the Al fraction increased with decreasing N flow due to preferentially favorable bonding of Al and N over Ga and N. Consequently, the growth rate decreased as the Al mole fraction increased. A photoluminescence quantum efficiency at 15 K was markedly higher for the AlxGa1−xN layers grown under Ga-rich conditions (3%–48%) compared to the layers grown under N-rich conditions (1%–10%), indicating much reduced nonradiative recombination in samples grown under Ga-rich conditions

Gallium desorption kinetics on (0001) GaN surface during the growth of GaN by molecular-beam epitaxy

Gallium (Ga) surfacedesorption behavior was investigated using reflection high-energy electron diffraction during the GaNgrowth. It was found that the desorption of Ga atoms from the (0001) GaNsurfaces under different III-V ratio dependents on the coverage of adsorbed atoms. Doing so led to desorption energies of 2.76 eV for Ga droplets, 1.24–1.89 eV for Ga under Ga-rich growth conditions, and 0.82 eV – 0.94 eV for Ga under stoichiometric growth conditions. Moreover, the variation of the GaNsurface morphology under different III-V ratios on porous templates supports the conclusion that Ga desorption energy depends on the coverage, and the III/V ratio dominates the growth mode

Anisotropy of free-carrier absorption and diffusivity in m-plane GaN

Polarization-dependent free-carrier absorption (FCA) in bulk m-plane GaN at 1053 nm revealed approximately 6 times stronger hole-related absorption for E⊥c than for E||c probe polarization both at low and high carrier injection levels. In contrast, FCA at 527 nm was found isotropic at low injection levels due to electron resonant transitions between the upper and lower conduction bands, whereas the anisotropic impact of holes was present only at high injection levels by temporarily blocking electron transitions. Carrier transport was also found to be anisotropic under two-photon excitation, with a ratio of 1.17 for diffusivity perpendicular and parallel to the c-axis

High-spectral-resolution pulsed photoluminescence study of molecular-beam-epitaxy-grown GaAs/AlxGa1−xAs multi-quantum-well structures using a very-low-power tunable pulsed dye laser

Ultralow-power, high-resolution, pulsed-laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular-beam-epitaxial GaAs/AlxGa1−xAs multi-quantum-well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy-hole and light-hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques